NOAA TECHNICAL MEMORANDUM

NMFS-SEFSC-363

U.S. Atlantic and Gulf of Mexico

Marine Mammal Stock Assessments

By

Robert A. Blaylock, James W. Hain, Larry J. Hansen,

Debra L. Palka, and Gordon T. Waring

with contributions from

Kathryn Bisack, Mark Bravington, Simon Northridge,

Janeen Quintal, Belinda Rubenstein, and Amy Williams

U.S. Department of Commerce

National Oceanic and Atmospheric Administration

National Marine Fisheries Service

Southeast Fisheries Science Center

Miami, Florida 33149-1003

July 1995
NOAA TECHNICAL MEMORANDUM

NMFS-SEFSC-363 

U.S. Atlantic and Gulf of Mexico

Marine Mammal Stock Assessments

By

Robert A. Blaylock, James W. Hain, Larry J. Hansen,

Debra L. Palka, and Gordon T. Waring

with contributions from

Kathryn Bisack, Mark Bravington, Simon Northridge,

Janeen Quintal, Belinda Rubenstein, and Amy Williams

U.S. DEPARTMENT OF COMMERCE

Ronald H. Brown, Secretary

NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION

D. James Baker, Administrator

NATIONAL MARINE FISHERIES SERVICE

Rolland A. Schmitten, Assistant Administrator for Fisheries

July 1995

This Technical Memorandum series is used for documentation and timely communication of preliminary

results, interim reports, or similar special-purpose information. Although the memoranda are not subject to

complete formal review, editorial control, or detailed editing, they are expected to reflect sound professional

work.
NOTICE

The National Marine Fisheries Service (NMFS) does not approve, recommend, or endorse any

proprietary product or material mentioned in this publication. No reference shall be made to

NMFS, or to this publication furnished by NMFS, in any advertising or sales promotion which

would indicate or imply that NMFS approves, recommends, or endorses any proprietary product

or proprietary material mentioned herein, or which has as its purpose or intent to cause directly or

indirectly the advertised product to be used or purchased because of NMFS publication.

This report should be cited as follows:

Blaylock, R. A., J. W. Hain, L. J. Hansen, D. L. Palka, and G. T. Waring. 1995. U.S. Atlantic

and Gulf of Mexico marine mammal stock assessments. NOAA Tech. Mem. NMFS-SEFSC-363,

211 pp.

Authors’ affiliations: (RAB) National Marine Fisheries Service, Southeast Fisheries Science

Center, Miami Laboratory, 75 Virginia Beach Drive, Miami, FL 33149-1003; (LJH) National

Marine Fisheries Service, Southeast Fisheries Science Center, Charleston Laboratory, 217 Fort

Johnson Road, Charleston, SC 29412; and (DLP, JWH, and GTW) National Marine Fisheries

Service, Northeast Fisheries Science Center, 166 Water Street, Woods Hole, MA 02543.

Copies may be obtained by writing the authors or:

National Technical Information Service

5258 Port Royal Road

Springfield, VA 22161

Telephone: (703) 487-4650

FAX: (703) 321-8547

Rush Orders: (800) 336-4300
iii

TABLE OF CONTENTS

PREFACE .......................................................... vi

NORTH ATLANTIC RIGHT WHALE (Eubalaena glacialis):

Western North Atlantic Stock ....................................... 1

HUMPBACK WHALE (Megaptera novaeangliae):

Western North Atlantic Stock ....................................... 5

FIN WHALE (Balaenoptera physalus):

Western North Atlantic Stock ....................................... 9

SEI WHALE (Balaenoptera borealis):

Western North Atlantic Stock ...................................... 13

MINKE WHALE (Balaenoptera acutorostrata):

Canadian East Coast Stock ........................................ 16

BLUE WHALE (Balaenoptera musculus):

Western North Atlantic Stock ...................................... 21

SPERM WHALE (Physeter macrocephalus):

Western North Atlantic Stock ...................................... 23

DWARF SPERM WHALE (Kogia simus): 

Western North Atlantic Stock ...................................... 27

PYGMY SPERM WHALE (Kogia breviceps):

Western North Atlantic Stock ...................................... 29

KILLER WHALE (Orcinus orca):

Western North Atlantic Stock ...................................... 31

PYGMY KILLER WHALE (Feresa attenuata): 

Western North Atlantic Stock ...................................... 33

NORTHERN BOTTLENOSE WHALE (Hyperoodon ampullatus):

Western North Atlantic Stock ...................................... 35

CUVIER'S BEAKED WHALE (Ziphius cavirostris):

Western North Atlantic Stock ...................................... 37

TRUE'S BEAKED WHALE (Mesoplodon mirus):

Western North Atlantic Stock ...................................... 40

GERVAIS' BEAKED WHALE (Mesoplodon europaeus):

Western North Atlantic Stock ...................................... 44

BLAINVILLE'S BEAKED WHALE (Mesoplodon densirostris):

Western North Atlantic Stock ...................................... 48

SOWERBY'S BEAKED WHALE (Mesoplodon bidens):

Western North Atlantic Stock ...................................... 52

RISSO'S DOLPHIN (Grampus griseus):

Western North Atlantic Stock ...................................... 56

LONG-FINNED PILOT WHALE (Globicephala melas):

Western North Atlantic Stock ...................................... 60

SHORT-FINNED PILOT WHALE (Globicephala macrorhynchus): 

Western North Atlantic Stock ...................................... 66
iv

WHITE-SIDED DOLPHIN (Lagenorhynchus acutus):

Western North Atlantic Stock ...................................... 70

WHITE-BEAKED DOLPHIN (Lagenorhynchus albirostris):

Western North Atlantic Stock ...................................... 75

COMMON DOLPHIN (Delphinus delphis):

Western North Atlantic Stock ...................................... 77

ATLANTIC SPOTTED DOLPHIN (Stenella frontalis):

Western North Atlantic Stock ...................................... 82

PANTROPICAL SPOTTED DOLPHIN (Stenella attenuata):

Western North Atlantic Stock ...................................... 86

STRIPED DOLPHIN (Stenella coeruleoalba):

Western North Atlantic Stock ...................................... 90

SPINNER DOLPHIN (Stenella longirostris):

Western North Atlantic Stock ...................................... 94

BOTTLENOSE DOLPHIN (Tursiops truncatus):

Western North Atlantic Offshore Stock .............................. 96

BOTTLENOSE DOLPHIN (Tursiops truncatus):

Western North Atlantic Coastal Stock .............................. 100

HARBOR PORPOISE (Phocoena phocoena):

Gulf of Maine/Bay of Fundy Stock ................................. 106

HARBOR SEAL (Phoca vitulina):

Western North Atlantic Stock ..................................... 112

GRAY SEAL (Halichoerus grypus):

Western North Atlantic Stock ..................................... 116

HARP SEAL (Phoca groenlandica):

Western North Atlantic Stock ..................................... 119

HOODED SEAL (Cystophora cristata):

Western North Atlantic Stock ..................................... 122

SPERM WHALE (Physeter macrocephalus):

Northern Gulf of Mexico Stock ................................... 125

BRYDE'S WHALE (Balaenoptera edeni):

Northern Gulf of Mexico Stock ................................... 128

CUVIER'S BEAKED WHALE (Ziphius cavirostris):

Northern Gulf of Mexico Stock ................................... 131

BLAINVILLE’S BEAKED WHALE (Mesoplodon densirostris):

Northern Gulf of Mexico Stock ................................... 134

GERVAIS' BEAKED WHALE (Mesoplodon europaeus):

Northern Gulf of Mexico Stock ................................... 137

BOTTLENOSE DOLPHIN (Tursiops truncatus):

Gulf of Mexico Outer Continental Shelf Stock ........................ 140

BOTTLENOSE DOLPHIN (Tursiops truncatus):

Gulf of Mexico Continental Shelf Edge and Continental Slope Stock ....... 143

BOTTLENOSE DOLPHIN (Tursiops truncatus):

Western Gulf of Mexico Coastal Stock .............................. 146
v

BOTTLENOSE DOLPHIN (Tursiops truncatus):

Northern Gulf of Mexico Coastal Stock ............................. 150

BOTTLENOSE DOLPHIN (Tursiops truncatus):

Eastern Gulf of Mexico Coastal Stock .............................. 154

BOTTLENOSE DOLPHIN (Tursiops truncatus):

Gulf of Mexico Bay, Sound, and Estuarine Stocks ..................... 157

ATLANTIC SPOTTED DOLPHIN (Stenella frontalis):

Northern Gulf of Mexico Stock ................................... 163

PANTROPICAL SPOTTED DOLPHIN (Stenella attenuata):

Northern Gulf of Mexico Stock ................................... 166

STRIPED DOLPHIN (Stenella coeruleoalba):

Northern Gulf of Mexico Stock ................................... 169

SPINNER DOLPHIN (Stenella longirostris):

Northern Gulf of Mexico Stock ................................... 172

ROUGH-TOOTHED DOLPHIN (Steno bredanensis):

Northern Gulf of Mexico Stock ................................... 175

CLYMENE DOLPHIN (Stenella clymene):

Northern Gulf of Mexico Stock ................................... 178

FRASER'S DOLPHIN (Lagenodelphis hosei):

Northern Gulf of Mexico Stock ................................... 181

KILLER WHALE (Orcinus orca):

Northern Gulf of Mexico Stock ................................... 184

FALSE KILLER WHALE (Pseudorca crassidens):

Northern Gulf of Mexico Stock ................................... 187

PYGMY KILLER WHALE (Feresa attenuata):

Northern Gulf of Mexico Stock ................................... 190

DWARF SPERM WHALE (Kogia simus):

Northern Gulf of Mexico Stock ................................... 193

PYGMY SPERM WHALE (Kogia breviceps):

Northern Gulf of Mexico Stock ................................... 196

MELON-HEADED WHALE (Peponocephala electra):

Northern Gulf of Mexico Stock ................................... 199

RISSO'S DOLPHIN (Grampus griseus):

Northern Gulf of Mexico Stock ................................... 202

SHORT-FINNED PILOT WHALE (Globicephala macrorhynchus):

Northern Gulf of Mexico Stock ................................... 205

INDEX ........................................................... 208
vi

PREFACE

The National Marine Fisheries Service (NMFS) and the U.S. Fish and Wildlife Service (USFWS) were required to

produce stock assessment reports for all marine mammal stocks in waters within the U.S. Exclusive Economic Zone

under the 1994 amendments to the Marine Mammal Protection Act. This document contains the stock assessment

reports for the U.S. Atlantic and Gulf of Mexico marine mammal stocks under NMFS jurisdiction. Marine mammal

species which are under the management jurisdiction of the USFWS are not included in this report.

The Sea Sampling Investigations Unit at the Northeast Fisheries Science Center and the Oceanic Pelagic Resources

Division at the Southeast Fisheries Science Center Miami Laboratory provided marine mammal by-catch and fisheries

effort data. The Southeast U.S. Marine Mammal Stranding Network provided data on stranded marine mammals in

the NMFS Southeast Region and information on stranded marine mammals in the NMFS Northeast Region was

provided by the NMFS Northeast Regional Office. Amy Woodhead produced the cover illustration and Mary Nuñez

proof-read the final draft.

The authors wish to acknowledge the valuable contribution of the Atlantic Scientific Review Group which provided

the authors with constructive criticism of the draft assessment reports. Members of the Atlantic Scientific Review

Group who reviewed draft assessment reports are: Solange Brault, Joseph DeAlteris, James R. Gilbert, Michael J.

Harris, Robert D. Kenney, James G. Mead, Daniel K. Odell, Andrew J. Read, and Randall S. Wells. Their comments

greatly improved the quality of the reports. The authors also appreciate the thoughtful reviews and comments of the

Marine Mammal Commission, the Humane Society of the United States, and the NMFS Southeast and Northeast

Regional Offices. The exhaustive review and comments of Paul Wade of NMFS Office of Protected Resources greatly

improved the technical quality of the reports. Any omissions or errors are the sole responsibility of the authors. 

This is a working document and individual stock assessment reports will be updated as new information becomes

available and as changes to marine mammal stocks and fisheries occur; therefore, each stock assessment report is

intended to be a stand alone document. The authors solicit any new information or comments which would improve

future stock assessment reports.

This is Southeast Fisheries Science Center Contribution MIA-94/95-35.
1

NORTH ATLANTIC RIGHT WHALE (Eubalaena glacialis):

Western North Atlantic Stock

STOCK DEFINITION AND GEOGRAPHIC RANGE

Individuals of this population range from wintering and calving grounds in coastal waters of the southeastern

United States to summer feeding, nursery, and mating grounds in New England waters and northward to the Bay of

Fundy and the Scotian Shelf. Knowlton et al. (1992) recently reported several long-distance movements as far north

as Newfoundland, the Labrador Basin, and southeast of Greenland, suggesting an extended range for at least some

individuals and perhaps habitat areas not presently well described. Likewise, a calving and wintering ground has been

described for coastal waters of the southeastern U.S., but the range may be somewhat more extensive because sightings

have been reported from the Gulf of Mexico (Moore and Clark 1963; Schmidly et al. 1972) and 85% of the population

is unaccounted for during this season. 

Research results to date suggest five major habitats or congregation areas (southeastern United States coastal

waters, Great South Channel, Cape Cod Bay, Bay of Fundy, and Scotian Shelf) for western North Atlantic right whales.

However, movements within and between habitats and within regions may be more extensive than sometimes thought.

Results from a few successfully attached satellite telemetry tags suggest that sightings separated by perhaps two weeks

should not be assumed to indicate a stationary or resident animal. Instead, telemetry data have shown rather lengthy

and somewhat distant excursions (Mate et al. 1992). These findings cast new light on movements and habitat use, and

raise questions about the purpose or strategies for such excursions. 

New England waters are a primary feeding habitat for the right whale, which appears to feed primarily on

calanoid copepods in this area. Research suggests that right whales must locate and exploit extremely dense patches

of zooplankton to feed efficiently. These dense zooplankton patches are likely a primary characteristic of the spring,

summer, and fall right whale habitat (Kenney et al. 1986). The acceptable surface copepod resource is limited to

perhaps 3% of the region during the peak feeding season in Cape Cod and Massachusetts Bays (Mayo and Goldman,

in press). While feeding in the coastal waters off Massachusetts has been better studied, feeding by right whales has

been observed elsewhere over Georges Bank, in the Gulf of Maine, in the Bay of Fundy, and over the Scotian Shelf.

The characteristics of acceptable prey distribution in these areas is not well known. New England waters also serve

as a nursery for calves and, in some cases, for mating. 

Genetic analyses of tissue samples is providing insights to stock definition. Schaeff et al. (1993) have

suggested that western North Atlantic right whales probably represent a single breeding population that may be based

on three matrilines. They also suggest that, in addition to the Bay of Fundy, there exists an additional and undescribed

summer nursery area utilized by approximately one-third of the population. As described above, a related question is

where individuals other than calving females and a few juveniles overwinter. One or more major wintering and

summering grounds have yet to be described. 

POPULATION SIZE

Based on a census of individual whales identified using photo-identification techniques, the western North

Atlantic population size was estimated to be 295 individuals in 1992 (Knowlton et al. 1994). Because this was a nearly

complete census, it is assumed that this represents a minimum population size estimate. 

Historical Population Estimate

An estimate of pre-exploitation population size is not available. Basque whalers may have taken as many as

200 right whales a year at times during the 1500s in the Strait of Belle Isle region, and the stock of right whales may

have already been substantially reduced by the time whaling was begun by colonists in the Plymouth area in the 1600s

(Reeves and Mitchell 1987). A modest but persistent whaling effort along the eastern U.S lasted three centuries, and

the records include one report of 29 whales killed in Cape Cod Bay in a single day during January 1700. Based on

incomplete historical whaling data, these authors could only conclude that there were at least some hundreds of right

whales present in the western North Atlantic during the late 1600s. In a later study (Reeves et al. 1992), a series of

population trajectories using historical data and an estimated present population size of 350 were plotted. The results

suggest that there may have been at least 1,000 right whales in this population during the early to mid-1600s, with the
2

greatest population decline occurring in the early 1700s. The authors cautioned, however, that the record of removals

is incomplete, the results are preliminary, and refinements are required. 

Minimum Population Estimate

The western North Atlantic population size was estimated to be 295 individuals in 1992 (Knowlton et al.

1994), based on a census of individual whales identified using photo-identification techniques. A bias that might result

from including catalogued whales that had not been seen for an extended period of time and therefore might be dead,

was addressed by assuming that an individual whale not sighted for five years was dead (Knowlton et al. 1994). It is

assumed that the census of identified whales represents a minimum population size estimate.

Current Population Trend

The size of this population may have been as low as 50 or fewer animals at the turn of the century (Reeves

et al. 1992; Kenney 1992) versus an estimated 295 presently, suggesting that the stock is showing signs of slow

recovery. 

CURRENT AND MAXIMUM NET PRODUCTIVITY RATES

During 1980-1992, 145 calves were born to 65 identified cows. The number of calves born annually ranged

from five to 17, with a mean of 11.2 (SE = 0.90). There was no detectable trend in the number of calves produced per

year. The reproductively active female pool was static at approximately 51 individuals during 1987-1992. Mean

calving interval, based on 86 records, was 3.67 years. There was an indication that calving intervals may be increasing

over time, although the trend was not quite statistically significant (P = 0.083) (Knowlton et al. 1994).

The current annual population growth rate during 1986-1992 was estimated to be 2.5% (CV = 0.12) using

photo-identification techniques (Knowlton et al. 1994). A population increase rate of 3.8% was estimated from the

annual increase in aerial sighting rates in the Great South Channel, 1979-1989 (Kenney et al. 1995). The current

estimated population growth rate of the western North Atlantic stock is lower than that of the four stocks of southernhemisphere right whales for which data are available: western Australia, 12.7%; Argentina, 7.3%; east and west

Africa, 6.8% (Best 1993). 

The relatively low population size suggests that this stock is well below its optimum sustainable population

(OSP); therefore, the current population growth rate should reflect the maximum net reproductivity rate for this stock.

The current population growth rate reported by Knowlton et al. (1994) of 2.5% (CV = 0.12) was assumed to reflect

the maximum net reproductivity rate for this stock for purposes of this assessment.

POTENTIAL BIOLOGICAL REMOVAL

Potential biological removal (PBR) was specified as the product of minimum population size, one-half the

maximum productivity rate, and a "recovery" factor for endangered, depleted, threatened stocks, or stocks of unknown

status relative to OSP (Anon. 1994). The recovery factor was 0.10 because this species is listed as endangered under

the Endangered Species Act (ESA). PBR for the northern right whale is 0.4 whales. 

ANNUAL HUMAN-CAUSED MORTALITY AND SERIOUS INJURY

Approximately one-third of all right whale mortality is caused by human activities (Kraus 1990). Further,

the small population size and low annual reproductive rate suggest that human sources of mortality may have a greater

effect relative to population growth rates than for other whales. 

The principal factors believed to be retarding growth and, perhaps recovery of the population, are ship strikes

and net entanglement. Marks or scars from entanglement with fishing gear were reported from 57% of living right

whales, and 7% had major wounds probably due to collisions with ship propellers. Of the 25 mortalities recorded, five

(20%) could be attributed to ship collisions, and three (12%) were the result of entanglements. Young animals, ages

0-4 years, are apparently the most impacted portion of the population. In this age group, 20-30% of mortality is due

to ship strikes (Kraus 1990). 

For one area of concern, the coastal waters of the southeastern U.S., an awareness and mitigation program,

involving ten agencies and organizations, was begun in 1992, and has been upgraded and expanded annually. Other

areas may be included in the future. For waters of the northeastern U.S., a present concern, not yet completely defined,

is the possibility of habitat degradation in Massachusetts and Cape Cod bays due to a Boston sewage outfall now under

construction. Timetables for levels of treatment are under discussion. 
3

 Total estimated average annual fishery-related mortality and serious injury in fisheries monitored by NMFS

during 1989-1993 was 1.6 right whales annually (CV = 2.80). The average reported mortality and serious injury to

right whales due to ship strikes was one right whale per year during 1990-1994; therefore, estimated annual average

human-induced mortality and serious injury (including fishery and non-fishery related causes) was 2.6 right whales

per year. The total fishery-related mortality and serious injury for this stock is not less than 10% of the calculated PBR

and, therefore, cannot be considered to be insignificant and approaching zero mortality and serious injury rate. This

determination cannot be made for specific fisheries until the implementing regulations for Section 118 of the MMPA

have been reviewed by the public and finalized. 

Fishery Information

The estimated total number of hauls in the Atlantic large pelagic drift gillnet fishery increased from 714 in

1989 to 1144 in 1990; thereafter, with the introduction of quotas, effort was severely reduced. The estimated number

of hauls in 1991, 1992, and 1993 were 233, 243, and 232, respectively. Fifty-nine vessels participated in this fishery

between 1989 and 1993. Observer coverage, percent of sets observed, ranged from 8% in 1989, 6% in 1990, 20% in

1991, to 40% in 1992, and 42% in 1993. The greatest concentrations of effort were located along the southern edge

of Georges Bank and off Cape Hatteras. Examination of the species composition of the catch and locations of the

fishery throughout the year, suggested that the drift gillnet fishery be stratified into two strata, a southern or winter

stratum, and a northern or summer stratum. Estimates of the total by-catch, for each year, were obtained using the

aggregated catch rates, by strata (Northridge, in review). In July of 1993, a one and a half year old female was released

from a swordfish drift gillnet along the southern edge of Georges Bank. The wounding to the animal, including the

tail stock, suggested a high likelihood of reduced viability. Under the assumption that this animal eventually died, the

total estimated annual fishery-related mortalities (CV in parentheses) were 2.2 in 1989 (2.43), 3.4 in 1990 (2.37), 0.5

(1.49) in 1991, 0.4 in 1992 (1.44), and 1.3 in 1993 (0.63).

In this stock, 57% of living right whales bore evidence of entanglements with fishing gear. An entanglement

database maintained by NMFS Northeast Regional Office with records from 1975-1992 included 14 right whale

entanglements, including right whales in weirs, entangled in gillnets, and trailing line and buoys. Three right whales

entangled or trailing line were reported from waters in the Gulf of Maine and Bay of Fundy region in summer/fall 1994

(P. K. Hamilton, personal communication). In February 1994, two and perhaps three right whales in southeastern U.S.

coastal waters were reported injured in association with large-mesh gillnets (P. K Hamilton, personal communication).

An additional record (M. J. Harris, personal communication) reported a 9.1-10.6 m right whale entangled and released

south of Ft. Pierce, Florida in March 1982. Incidents of entanglements in groundfish gillnet gear, cod traps, and

herring weirs in waters of Atlantic Canada were summarized by Read (1994). In most instances, the right whales were

either released or escaped on their own, although several whales have been observed carrying net or line fragments.

Specific details of right whale entanglement in fishing gear are often lacking. When direct or indirect mortality occurs,

some carcasses come ashore and are subsequently examined, or are reported as "floaters" at sea; however, the number

of unreported and unexamined carcasses is unknown, but may be significant in the case of floaters. More information

is needed about fisheries interactions and where they occur. 

Other Mortality

Ship strikes are a major cause of mortality and injury to right whales (Kraus 1990). There have been five

known ship strikes, causing three injuries and two mortalities in coastal waters of the southeastern U.S. since the Kraus

(1990) summary report was published. There were also two mortalities likely due to ship collisions in the Bay of Fundy

area, 1992 and 1994, and two reported floaters off the mid-Atlantic, winter 93-94, possibly due to ship strikes (NMFS

unpublished data; P. K Hamilton, personal communication; Kenney and Kraus 1993). There have been four ship strike

mortalities, a fifth probable, and two more possible during 1990-1994, yielding a human-induced, non-fishery-related

mortality rate of between 0.8 and 1.4 right whales a year. As with entanglements, some injury or mortality due to ship

strikes, particularly in offshore waters, may go undetected. 

STATUS OF STOCK

The size of this stock is considered to be low relative to OSP and this species is listed as endangered under

the ESA. A Recovery Plan has been published and is in effect (NMFS 1991). The total level of human-caused
4

mortality and serious injury is unknown, but reported human-caused mortality and serious injury has exceeded two

right whales per year since 1990. This rate exceeds PBR and is significant because of the critically low population size

and the low population growth rate. This is a strategic stock because the North Atlantic right whale is an endangered

species.

REFERENCES

Anon. 1994. Report of the PBR (Potential Biological Removal) workshop. June 27-29, 1994. NOAA, NMFS

Southwest Fisheries Science Center, La Jolla, California, 13 pp. + Appendices. 

Best, P. B. 1993. Increase rates in severely depleted stocks of baleen whales. ICES J. Mar. Sci. 50: 169-186. 

Hain, J. (editor). 1992. The right whale in the western North Atlantic: A science and management workshop, 14-15

April 1992, Silver Spring, Maryland. Northeast Fisheries Science Center Reference Document No. 92-05,

NEFSC/NMFS Woods Hole, Massachusetts, 88 pp. 

Kenney, R. D., M. A. M. Hyman, R. E. Owen, G. P. Scott, and H. E. Winn. 1986. Estimation of prey densities

required by western North Atlantic right whales. Mar. Mam. Sci. 2(1): 1-13. 

Kenney, R. D. 1992. Western North Atlantic right whales: Abundance and trends from Great South Channel aerial

surveys. Pages 47-49 in J. Hain (editor), The right whale in the western North Atlantic: A science and

management workshop, 14-15 April 1992, Silver Spring, Maryland. Northeast Fisheries Science Center

Reference Document No. 92-05, NMFS, NEFSC, Woods Hole, Massachusetts, 88 pp. 

Kenney, R. D., H. E. Winn, and M. C. Macula. 1995. Cetaceans in the Great South channel, 1979-1989: right whale

(Eubalaena glacialis). Cont. Shelf Res. 15: 385-414. 

Kenney, R. D. and S. D. Kraus. 1993. Right whale mortality — a correction and an update. Mar. Mamm. Sci. 9:

445-446. 

Knowlton, A. R., J. Sigurjonsson, J. N. Ciano, and S. D. Kraus. 1992. Long-distance movements of North Atlantic

Right whales (Eubalaena glacialis). Mar. Mam. Sci. 8(4): 397-405. 

Knowlton, A. R., S. D. Kraus, and R. D. Kenney. 1994. Reproduction in North Atlantic right whales (Eubalaena

glacialis). Can. J. Zool. 72: 1297-1305. 

Kraus, S. D. 1990. Rates and potential causes of mortality in North Atlantic right whales (Eubalaena glacialis). Mar.

Mamm. Sci. 6(4): 278-291.

Kraus, S. D. and R. D. Kenney. 1991. Information on right whales (Eubalaena glacialis) in three proposed critical

habitats in United States waters in the western North Atlantic Ocean. Pub. No. PB91-194432, NTIS,

Springfield, Virginia, 65 pp. 

Mate, B. R., S. Nieukirk, R. Mescar, and T. Martin. 1992. Application of remote sensing methods for tracking large

cetaceans: North Atlantic right whales (Eubalaena glacialis). Final Report to the Minerals Management

Service, Contract No. 14-12-0001-30411, 167 pp. 

Mayo, C. A. and L. A. Goldman. In press. Food consumption and caloric intake of the right whale, Eubalaena

glacialis, in Cape Cod Bay. Can. J. Zool. 

Moore, J. C. and E. Clark. 1963. Discovery of right whales in the Gulf of Mexico. Science 141(3577): 269. 

NMFS. 1991. Recovery plan for the northern right whale (Eubalaena glacialis). Prepared by the Right Whale

Recovery Team for the National Marine Fisheries Service, Silver Spring, Maryland, 86 pp. 

Read, A. J. 1994. Interactions between cetaceans and gillnet and trap fisheries in the northwest Atlantic. Rep. Int.

Whal. Commn. Special Issue 15: 133-147. 

Reeves, R. R. and E. Mitchell. 1987. Shore whaling for right whales in the northeastern United States. Contract

Report No. NA85-WCC-06194, SEFSC/NMFS, Miami, FL, 108 pp. 

Reeves, R. R., J. M. Breiwick, and E. Mitchell. 1992. Pre-exploitation abundance of right whales off the eastern

United States. Pages 7-11 in The right whale in the western North Atlantic: A science and management

workshop, 14-15 April 1992, Silver Spring, Maryland. Northeast Fisheries Science Center Reference

Document No. 92-05. NEFSC/NMFS, Woods Hole, Massachusetts, 88 pp. 

Schaeff, C. M., S. D. Kraus, M. W. Brown, and B. N. White. 1993. Assessment of the population structure of the

western North Atlantic right whales (Eubalaena glacialis) based on sighting and mtDNA data. Can. J. Zool.

71: 339-345. 

Schmidly, D. J., C. O. Martin, and G. F. Collins. 1972. First occurrence of a black right whale (Balaena glacialis)

along the Texas coast. So west. Nat. 17(2): 214-215. 
5
6

HUMPBACK WHALE (Megaptera novaeangliae):

Western North Atlantic Stock

STOCK DEFINITION AND GEOGRAPHIC RANGE

During summer there are at least five geographically distinct humpback whale feeding aggregations occurring

between latitudes 42°N to 78°N. These feeding areas are (with approximate number of humpback whales in

parenthesis): Gulf of Maine (400); Gulf of St. Lawrence (200); Newfoundland and Labrador (2,500); western

Greenland (350); and the Iceland-Denmark strait (up to 2,000) (Katona and Beard 1990). The western North Atlantic

stock is considered to be include all humpback whales from these five feeding areas. 

Humpback whales from all of the western North Atlantic feeding areas migrate to the Caribbean in winter,

where courtship, breeding, and calving occur. The majority (85%) are found on Silver and Navidad Banks off the

north coast of the Dominican Republic. The remainder are scattered in Samana Bay (Dominican Republic), along the

northwest coast of Puerto Rico, through the Virgin Islands, and along the eastern Antilles chain south to Venezuela

(Katona and Beard 1990). Courtship groups on the wintering ground contain whales from different feeding

aggregations, so that humpbacks from the western North Atlantic probably interbreed (Katona et al. 1994). 

Apparently, not all humpback whales from this stock winter in the West Indies, as there are winter reports from

Bermuda, the Gulf of Maine, Newfoundland, Greenland, and Norway (Katona et al. 1994)

Clapham et al. (1992) reported a high degree of individual site fidelity, both within and between years, from

a long-term study of identified humpback whales in waters off Cape Cod. Some reproductive parameters which have

been estimated for humpback whales from this area are discussed below.

An increased number of sightings of young humpback whales in the vicinity of the Chesapeake and Delaware

Bays occurred in 1992 (Swingle et al. 1993). Wiley et al. (1995) reported 38 humpback whale stranding records which

occurred during 1985-1992 in the U.S. mid-Atlantic and southeastern states. Humpback whale strandings increased,

particularly along the Virginia and North Carolina coasts, and most stranded animals were sexually immature. They

concluded that these areas are becoming an increasingly important habitat for juvenile humpback whales and that

anthropogenic factors may negatively impact whales in this area. There have also been a number of wintertime

humpback sightings in coastal waters of the southeastern U.S. (NMFS unpublished data; New England Aquarium

unpublished data). Whether the increased sightings represent a distributional change, or are simply due to an increase

in sighting effort, is presently unknown. 

Feeding is the principal activity of humpback whales in New England waters and their distribution in New

England waters has been largely correlated to prey species and abundance, although behavior and bottom topography

are factors in foraging strategy (Payne et al. 1986, 1990). Humpback whales are believed to be largely piscivorous

when in these waters, feeding on herring (Clupea harengus), sand lance (Ammodytes dubius), and other small fishes.

Commercial depletion of herring and mackerel led to an increase in sand lance in the southwestern Gulf of Maine in

the mid 1970s with a concurrent decrease in humpback whale abundance in the northern Gulf of Maine. Humpback

whales were densest over the sandy shoals in the southwestern Gulf of Maine favored by the sand lance during much

of the late 1970s and early 1980s, and humpback distribution appeared to have shifted to this area (Payne et al. 1986).

An apparent reversal began in the mid 1980s, and herring and mackerel increased as sand lance again decreased

(Fogarty et al. 1991). Humpback whale abundance in the northern Gulf of Maine increased dramatically during 1992-

93 , along with a major influx of herring (T. Fernald, College of the Atlantic, personal communication). Humpback

whales were few in nearshore Massachusetts waters in the 1992-93 summer seasons and more abundant in the offshore

waters of Cultivator Shoal and Northeast Peak on Georges Bank, and Jeffreys Ledge — more traditional areas of

herring occurrence (D. K. Mattila, Center for Coastal Studies, personal communication). 

A major research initiative was begun in early 1992 — the Years of the North Atlantic Humpback (YONAH)

Project (Allen et al. 1993). This project is a large-scale, intensive, ocean-wide study of humpback whales throughout

their entire North Atlantic range conducted over three years. Photographs for individual identification and biopsy

samples for genetic analyses were collected from both summer feeding areas in the northeast and breeding grounds

in the West Indies. Data are now being analyzed to determine the current population status and genetic relationships

of humpback whales throughout their range.
7

POPULATION SIZE

A population size of 294 humpback whales (CV = 0.45) was estimated for the waters of the U.S. Atlantic

Exclusive Economic Zone, based on an inverse variance weighted pooling of CeTAP (1982) spring and summer data

and included a dive-time correction using a scale-up factor of 3.6. However, this estimate may not reflect the current

true population size because of the high degree of uncertainty (e.g., large coefficient of variation), the data are over a

decade old, and values were estimated just after cessation of extensive foreign fishing operations in the region. Katona

et al. (1994), using photo-identification techniques and Bailey's modification of the Chapman capture-recapture

method, estimated that the total humpback whale population in the North Atlantic Ocean west of Iceland during the

years 1979-1990 averaged 5,543 humpback whales (CV = 0.16). 

Minimum Population Estimate

The minimum population estimate is the lower limit of the two-tailed 60% confidence interval of the lognormal distributed abundance estimate of 5,543 whales (CV = 0.16) (Katona et al. 1994) and is 4,848 humpback

whales. This is equivalent to the 20th percentile of the log-normal distribution as specified by NMFS (Anon. 1994).

Current Population Trend

There are insufficient data with which to determine trends. Katona and Beard (1990) suggest an annual rate

of increase of 9%; however, the lower 95% confidence level was less than zero. The mean birth rate for identified

humpbacks in the southwestern Gulf of Maine during 1979-87 was 8% (CV = 0.25), with no significant inter-annual

differences, and the calving interval was 2.35 years (CV = 0.30) (Clapham and Mayo 1990; Clapham 1992). The

average age at attainment of sexual maturity for both males and females was five years (Clapham and Mayo 1990;

Clapham 1992). 

CURRENT AND MAXIMUM NET PRODUCTIVITY RATES

Katona and Beard (1990) suggested an annual rate of increase of 9% for the North Atlantic humpback whale;

however, the maximum net productivity rate was assumed to be 0.04 for purposes of this assessment because of the high

statistical uncertainty surrounding the estimated annual rate of increase. The value of 0.04 is based on theoretical

calculations showing that cetacean populations may not generally grow at rates much greater than 4% given the

constraints of their reproductive life history (Anon. 1994). 

POTENTIAL BIOLOGICAL REMOVAL

Potential biological removal (PBR) was specified as the product of minimum population size, one-half the

maximum productivity rate, and a "recovery" factor for endangered, depleted, threatened stocks, or stocks of unknown

status relative to optimum sustainable population (OSP) (Anon. 1994). The recovery factor was set at 0.10 because

this stock is listed as an endangered species under the Endangered Species Act (ESA). PBR for the western North

Atlantic humpback whale stock is 9.7 whales. 

ANNUAL HUMAN-CAUSED MORTALITY AND SERIOUS INJURY

There is an average of four to six entanglements of humpback whales a year in waters of the southern Gulf

of Maine and additional reports of ship-collision scars (D. L. DeKing, Center for Coastal Studies, Provincetown,

Massachusetts, personal communication). An entanglement database maintained by NMFS NE Regional Office

contained 64 records of entangled or injured humpbacks from 1975-1992. Humpbacks also become entangled offshore.

On 18 January 1993, a dead juvenile humpback was observed entangled in a swordfish drift-net along the 200 m

isobath northeast of Cape Hatteras. Entangled animals are often released, although some dead or injured animals likely

go unobserved and unreported. Occasionally, "floaters" are encountered at sea (NMFS unpublished data).

Of 20 dead humpback whales, principally in the mid-Atlantic, where decomposition state did not preclude

examination for human impacts, Wiley et al. (1995) reported that six (30%) had major injuries possibly attributable

to ship strikes, and five (25%) had injuries consistent with possible entanglement in fishing gear. One whale displayed

scars that may have been caused by both ship strike and entanglement. Thus, 60% of the whale carcasses which were

suitable for examination showed signs that anthropogenic factors may have contributed to, or been responsible for,

their death. 
8

Humpback whale entanglements occur in relatively high numbers in Canadian waters. Reports of collisions

with fixed fishing gear set for groundfish around Newfoundland averaged 365 annually from 1979 to 1987 (range 174-

813). An average of 50 humpback whale entanglements (range 26-66) were reported annually between 1979 and 1988

and 12 of 66 humpback whales that were entangled in 1988 died (Lien et al. 1988). 

Total average annual estimated fishery-related mortality and serious injury in fisheries monitored by NMFS

between 1989-1993 was 1.0 humpback whale (CV = 3.10). If Canadian entanglements and the possible mid-Atlantic

entanglement records reported above are considered, along with injuries that may lead to reduced viability and/or

eventual mortality of formerly entangled whales, this number will likely increase. The total fishery-related mortality

and serious injury for this stock is greater than 10% of the calculated PBR and cannot be considered insignificant and

approaching zero mortality and serious injury rate. This determination cannot be made for specific fisheries until the

implementing regulations for Section 118 of the MMPA have been reviewed by the public and finalized. 

Fishery Information

The estimated total number of hauls in the Atlantic large pelagic drift gillnet fishery increased from 714 in

1989 to 1144 in 1990; thereafter, with the introduction of quotas, effort was severely reduced. The estimated number

of hauls in 1991, 1992, and 1993 were 233, 243, and 232 respectively. Fifty-nine vessels participated in this fishery

between 1989 and 1993. Observer coverage, percent of sets observed, ranged from 8% in 1989, 6% in 1990, 20% in

1991, to 40% in 1992 and 42% in 1993. The greatest concentrations of effort were located along the southern edge

of Georges Bank and off Cape Hatteras. Examination of the species composition of the catch and locations of the

fishery throughout the year, suggested that the drift gillnet fishery be stratified into two strata, a southern or winter

stratum, and a northern or summer stratum. Estimates of the total by-catch, for each year, were obtained using the

aggregated catch rates, by strata (Northridge, in review). A single mortality was observed in January 1993 off Cape

Hatteras. Estimated annual mortality (CV in parentheses), extrapolated from fishery observer data, was 0.7 (7.0) in

1989, 1.7 (2.65) in 1990, 0.7 (2.00) in 1991, 0.4 (1.25) in 1992, and 1.5 in 1993 (0.45).

Other Mortality

 Between November 1987 and January 1988, 14 humpback whales died after consuming Atlantic mackerel

containing a dinoflagellate saxitoxin. The whales subsequently stranded in the vicinity of Cape Cod Bay and Nantucket

sound. During the first 6 months of 1990, seven dead juvenile (7.6 to 9.1 m long) humpback whales stranded between

North Carolina and New Jersey. The significance of these strandings is unknown, but is a cause for some concern. 

 

STATUS OF STOCK

The size of this stock is considered to be low relative to OSP and this species is listed as endangered under

the ESA. There are insufficient data to determine the population trends for humpback whales. The annual rate of

population increase was estimated at 9% (Katona and Beard 1990), but the lower 95% confidence level was less than

zero. The total level of human-caused mortality and serious injury is unknown, but current data indicate that it is

significant. This is a strategic stock because the humpback whale is listed as an endangered species under the ESA.

REFERENCES

Allen, J., P. Clapham, P. Hammond, S. Katona, F. Larsen, J. Lien, D. Mattila, N. O/ ien, P. Palsbo/l, J. Sigurjonsson,

and T. Smith. 1993. Years of the North Atlantic Humpback (YONAH): Progress Report. Rep. Int. Whal.

Commn. SC/45/NA6. 

Anon. 1994. Report of the PBR (Potential Biological Removal) workshop. June 27-29, 1994. NOAA, NMFS

Southwest Fisheries Science Center, La Jolla, California, 13 pp. + Appendices. 

CeTAP. 1982. A characterization of marine mammals and turtles in the mid- and north Atlantic areas of the U.S.

outer continental shelf. Cetacean and Turtle Assessment Program, University of Rhode Island. Final Report

#AA551-CT8-48 to the Bureau of Land Management, Washington, DC, 538 pp. 

Clapham, P. J. and C. A. Mayo. 1990. Reproduction of humpback whales (Megaptera novaeangliae) observed in the

Gulf of Maine. Rep. Int. Whal. Commn. Special Issue 12: 171-175. 

Clapham, P. J. 1992. Age at attainment of sexual maturity in humpback whales, Megaptera novaeangliae. Can. J.

Zool. 70: 1470-1472. 
9

Clapham, P. J., L. S. Baraff, C. A. Carlson, M. A. Christian, D. K. Mattila, C. A. Mayo, M. A. Murphy, and S.

Pittman. 1993. Seasonal occurrence and annual return of humpback whales, Megaptera novaeangliae, in

the southern Gulf of Maine. Can. J. Zool. 71: 440-443. 

Fogarty, M. J., E. B. Cohen, W. L. Michaels, and W. W. Morse. 1991.Predation and the regulation of sand lance

populations: An exploratory analysis. ICES Mar. Sci. Symp. 193: 120-124. 

Katona, S. K., and J. A. Beard. 1990. Population size, migrations, and feeding aggregations of the humpback whale

(Megaptera novaeangliae) in the western North Atlantic ocean. Rep. Int. Whal. Commn. Special Issue 12:

295-306. 

Katona, S. K., J. M. Allen, and P. Stevick. 1994. Maintaining the North Atlantic humpback whale catalog. Progress

report to the Northeast Fisheries Science Center, Contract No. 50EANF-1-00056, May 1994, 26 pp. 

Lien, J., W. Ledwell, and J. Naven. 1988. Incidental entrapment in inshore fishing gear during 1988: A preliminary

report to the Newfoundland and Labrador Department of Fisheries and Oceans, 15 pp. 

Northridge, S. In review. Estimation of cetacean mortality in the U.S. Atlantic swordfish and tuna driftnet and pair

trawl fisheries. Draft final report to the Northeast Fisheries Science Center, Contract No. 40ENNF500045,

18 pp. 

Payne, P. M., J. R. Nicholas, L. O'Brien, and K. D. Powers. 1986. The distribution of the humpback whale, Megaptera

novaeangliae, on Georges Bank and in the Gulf of Maine in relation to densities of the sand eel, Ammodytes

americanus. Fish. Bull., U.S. 84: 271-277. 

Payne, P. M., D. N. Wiley, S. B. Young, S. Pittman, P. J. Clapham, and J. W. Josssi. 1990. Recent fluctuations in

the abundance of baleen whales in the southern Gulf of Maine in relation to changes in selected prey. Fish.

Bull., U.S. 88(4): 687-696. 

Swingle, W. M., S. G. Barco, and T. D. Pitchford. 1993. Appearance of juvenile humpback whales feeding in the

nearshore waters of Virginia. Mar. Mamm. Sci. 9: 309-315. 

Wiley, D. N., R. A. Asmutis, T. D. Pitchford, and D. P. Gannon. 1995. Stranding and mortality of humpback whales,

Megaptera novaeangliae, in the mid-Atlantic and southeast United States, 1985-1992. Fish. Bull., U.S. 93:

196-205. 
10

Figure 1. Distribution of fin whale sightings from NEFSC

shipboard surveys during the summer in 1990-1994. Isobaths

are at 100 m and 1,000 m. 

FIN WHALE (Balaenoptera physalus):

Western North Atlantic Stock

STOCK DEFINITION AND GEOGRAPHIC RANGE

The Scientific Committee of the International

Whaling Commission (IWC) has proposed stock

boundaries for North Atlantic fin whales. Fin whales

off the eastern U.S., north to Nova Scotia and on to the

southeast coast of Newfoundland are believed to

constitute a single stock under the present IWC scheme

(Donovan 1991); however, the stock identity of North

Atlantic fin whales has received relatively little

attention. Whether the current stock boundaries define

biologically isolated units is uncertain, and

confirmation or revision awaits input from techniques

such as molecular genetics or telemetry. The existence

of a subpopulation structure was suggested by local

depletions that resulted from commercial over

harvesting (Mizroch et al. 1984). 

Fin whales are common in waters of the U.S.

Atlantic Exclusive Economic Zone (EEZ), principally

from Cape Hatteras northward (Fig. 1). Fin whales

accounted for 46% of the large whales and 24% of all

cetaceans sighted over the continental shelf during

aerial surveys (CeTAP) between Cape Hatteras and

Nova Scotia during 1978-82. While a great deal

remains unknown, the magnitude of the ecological role

of the fin whale is impressive. In this region fin whales

are the dominant cetacean species in all seasons, with

the largest standing stock, the largest food

requirements, and therefore the largest impact on the

ecosystem of any cetacean species (Hain et al. 1992).

 There is little doubt that New England waters constitute a major feeding grounds for the fin whale. There is

evidence of site fidelity by females, and perhaps some substock separation on the feeding range (Agler et al. 1993).

Seipt et al. (1990) reported that 49% of identified fin whales on Massachusetts Bay area feeding grounds were resighted

within years, and 45% were sighted between years. While recognizing localized as well as more extensive movements,

these authors suggested that fin whales on these grounds exhibited patterns of seasonal occurrence and annual return

that are in some respects similar to those shown for humpback whales. Information on life history and vital rates is

also available in data from the Canadian fishery, 1965-1971 (Mitchell 1974). In seven years, 3,528 fin whales were

taken at three whaling stations. The station at Blandford, Nova Scotia, took 1,402. 

Hain et al. (1992), based on an analysis of neonate stranding data, suggested that calving takes place during

approximately four months from October-January in latitudes of the U.S. mid-Atlantic region; however, it is unknown

where calving, mating, and wintering for most of the population occurs. Preliminary results from the Navy's IUSS

program (C. Clark, unpublished data) suggest a deep-ocean component to fin whale distribution. It is likely that fin

whales occurring in the U.S. Atlantic EEZ undergo migrations into Canadian waters, open-ocean areas, and perhaps

more equatorial regions. 

POPULATION SIZE

A population estimate based on an inverse variance weighted pooling of CeTAP (1982) spring and summer

data is 4,680 fin whales [coefficient of variation (CV) = 0.23] and includes a dive-time correction factor of 4.85. An

average for these two seasons was chosen because the greatest proportion of the population off the northeast U.S. coast
11

appears to be in the CeTAP study area in these seasons. However, this estimate is highly uncertain because the data

are a decade old, and values were estimated just after cessation of extensive foreign fishing operations in the region.

More recent abundance estimates, based on aerial surveys in August-October 1991, a shipboard survey during

June-July 1991, and shipboard surveys conducted during the summer in 1991 and 1992, are available. In each case,

the estimates are for a portion of the northeastern U.S. Atlantic EEZ during one or two seasons. 

An aerial survey in the CeTAP study area, which included an interplatform experiment between a Twin Otter

and an AT-11, was conducted from August-October 1991. The survey repeated many of the CeTAP-defined survey

blocks and added several continental slope survey blocks; however, due to weather and logistical constraints, several

survey blocks south and east of Georges Bank were not surveyed. The data were analyzed using DISTANCE (Buckland

et al. 1993; Laake et al. 1993) and confidence intervals were calculated using the bootstrap log-normal method. The

resulting abundance estimates were 529 fin whales (CV = 0.19) and 194 fin whales (CV = 0.18), respectively, for the

AT-11 and Twin Otter. Data were not pooled because the interplatform calibration analysis has not been conducted.

These estimates are not comparable to the CeTAP estimates, because the 1991 data are from a single survey, AugustOctober and the CeTAP estimates were based on data pooled over several years of seasonal surveys. 

The abundance estimate from the June-July 1991 shipboard survey along the southern and northeast margin

of Georges Bank, approximately between the 200 and 2,000 m isobaths, was 35 fin whales (CV = 0.56). 

For the summer 1991-92 shipboard surveys, a weighted-average abundance for the northern Gulf of Mainelower Bay of Fundy region is 2,700 fin whales (CV = 0.59), where each annual estimate is weighted by the inverse of

its variance (NMFS unpublished data). The data used were obtained from two shipboard line transect sighting surveys

designed to estimate abundance of harbor porpoises (Palka, in press). Two independent teams of observers on the same

ship surveyed using the naked eye in non-closing mode. The abundance estimate includes an estimate of g(0),

probability of detection, for both teams combined, of 0.52 (CV = 0.19). [Using each team's data separately produces

a g(0) value of 0.32 (CV = 0.26)]. The g(0)-corrected abundance estimate was calculated using the product interval

analytical method (Palka, in press). Variability was estimated using bootstrap resampling techniques. Several

qualifications are appropriate. First, the study area was stratified by water depth and expected density of harbor

porpoises. This stratification scheme could cause uncertainties in a fin whale abundance estimate because offshore

waters in the central northern Gulf of Maine, which may be part of the fin whale habitat but not part of the harbor

porpoise habitat, were surveyed at a low intensity. To produce the fin whale abundance estimate, it was assumed that

observed densities of fin whales in the surveyed offshore waters were similar to densities in the unsurveyed offshore

waters. This is not unreasonable. Second, this estimate has not explicitly accounted for dive times and ship

avoidance; both factors are expected to influence the abundance estimate for this species. 

Minimum Population Estimate

The minimum population estimate is based on the 1991-92 shipboard survey abundance estimate of 2,700

whales (CV = 0.59) (NMFS unpublished data). The minimum population estimate is the lower limit of the two-tailed

60% confidence interval of the log-normal distributed abundance estimate, which is equivalent to the 20th percentile

of the log-normal distribution as specified by NMFS (Anon. 1994), and was 1,704 fin whales.

Current Population Trend

There are insufficient data to determine the population trends for this species. Even at a conservatively

estimated rate of increase, however, the numbers of fin whales may have increased substantially in recent years (Hain

et al. 1992). 

CURRENT AND MAXIMUM NET PRODUCTIVITY RATES

Current and maximum net productivity rates are not known for this stock. The maximum net productivity

rate was assumed to be 0.04 for purposes of this assessment. This value is based on theoretical calculations showing

that cetacean populations may not grow at rates much greater than 4% given the constraints of their reproductive life

history (Anon. 1994). Based on photographically identified fin whales, Agler et al. (1993) estimated that the gross

annual reproduction rate was at 8%, with a mean calving interval of 2.7 years. 
12

POTENTIAL BIOLOGICAL REMOVAL

Potential biological removal (PBR) was specified as the product of minimum population size, one-half the

maximum productivity rate, and a "recovery" factor for endangered, depleted, threatened stocks, or stocks of unknown

status relative to optimum sustainable population (OSP) (Anon. 1994). The recovery factor was set at 0.10 because

the fin whale is listed as endangered under the Endangered Species Act (ESA). PBR for this stock is 3.4 whales. 

ANNUAL HUMAN-CAUSED MORTALITY AND SERIOUS INJURY

The number of fin whales taken at three whaling stations in Canada from 1965-71 totaled 3,528 whales

(Mitchell 1974). Reports of non-directed takes of fin whales are fewer over the last two decades than for other

endangered large whales such as right and humpback whales.

There was no reported fishery-related mortality or serious injury to fin whales in fisheries observed by NMFS

during 1989-1993. The total fishery-related mortality and serious injury for this stock is less than 10% of the

calculated PBR and can be considered insignificant and approaching zero mortality and serious injury rate. This

determination cannot be made for specific fisheries until the implementing regulations for Section 118 of the MMPA

have been reviewed by the public and finalized. 

Fishery Information

No fishery-related mortality or serious injury of fin whales was reported in the Sea Sampling by-catch

database; therefore, no detailed fishery information is presented here. 

Fin whales were reported as entangled on nine occasions in an entanglement database maintained by NMFS

NE Regional Office including records from 1975-1992. Two of the nine were dead and the fate of others is unknown.

Five of the entanglement records were of whales entangled in or trailing line of an unspecified source and three records

were of entanglement with lobster-pot gear and line.

Because of the large role of fin whales in their ecosystem (Hain et al. 1992), there is likely a link between the

abundance of fin whales and the fishery resources. Foreign fishing activities in the 1960s and 70s may have been more

important ecologically to the fin whale, as compared to direct interactions, since these activities over-exploited several

fish stocks (i.e., herring, mackerel, etc.) that are known fin whale prey. On the other hand, Sissenwine et al. (1984)

speculated that fin whales contributed to the demise of the already overfished Georges Bank herring stock in the midand late 1970s. 

Ship Strikes

 There are nine records of ship collisions, boat strikes, and propeller scars between 1980-1994 in the

Smithsonian Institution's Marine Mammal database. This is a small number of individuals relative to the size of the

population.

STATUS OF STOCK

 The status of this stock relative to OSP is unknown, but the species is listed as endangered under the ESA.

There are insufficient data to determine the population trends for fin whales. The total level of human-caused mortality

and serious injury is unknown, but it is believed to be insignificant. Any fishery-related mortality would be illegal

because there is no recovery plan currently in place. This is a strategic stock because the fin whale is listed as an

endangered species under the ESA.

REFERENCES

Agler, B. A., R. L. Schooley, S. E. Frohock, S. K. Katona, and I. E. Seipt. 1993. Reproduction of photographically

identified fin whales, Balaenoptera physalus, from the Gulf of Maine. J. Mamm. 74(3): 577-587. 

Anon. 1994. Report of the PBR (Potential Biological Removal) workshop. June 27-29, 1994. NOAA, NMFS

Southwest Fisheries Science Center, La Jolla, California, 13 pp. + Appendices. 

Best, P. B. 1993. Increase rates in severely depleted stocks of baleen whales. ICES Jour. Mar. Sci. 50: 169-186. 

Buckland, S. T., D. R. Andersen, K. P. Burnham, and J. L. Laake. 1993. Distance sampling: Estimating abundance

of biological populations. Chapman and Hall, New York, 446 pp. 

Donovan, G. P. 1991. A review of IWC stock boundaries. Rep. Int. Whal. Commn. Special Issue 13: 39-68. 
13

Hain, J. H. W., M. J. Ratnaswamy, R. D. Kenney, and H. E. Winn. 1992. The fin whale, Balaenoptera physalus, in

waters of the northeastern United States continental shelf. Rep. Int. Whal. Commn. 42: 653-669. 

Laake, J. L., S. T. Buckland, D. R. Anderson, and K. P. Burnham. DISTANCE user’s guide, V2.0. Colorado

Cooperative Fish & Wildlife Research Unit, Colorado State University, Ft. Collins, Colorado, 72 pp. 

Mizroch, A. A., D. W. Rice, and J. M. Breiwick. 1984. The fin whale, Balaenoptera physalus. Mar. Fisheries

Rev. 46: 20-24.

Mitchell, E. 1974. Present status of Northwest Atlantic fin and other whale stocks. Pages 109-169, in W. E. Schevill

(editor), The whale problem: A status report. Harvard University Press, Cambridge, Massachusetts, 419 pp.

Palka, D. In press. Abundance estimate of the Gulf of Maine harbor porpoise. Rep. Int. Whal. Commn. Special Issue

16. 

Seipt, I. E., P. J. Clapham, C. A. Mayo, and M. P. Hawvermale. 1990. Population characteristics of individually

identified fin whales, Balaenoptera physalus, in Massachusetts Bay. Fish. Bull., U.S. 88(2): 271-278

Sissenwine, M. P., W. J. Overholtz, and S. H. Clark. 1984. In search of density dependence. Pages 119-137 in

Proceedings of the workshop on biological interactions among marine mammals and commercial fisheries

in the southeastern Bering Sea. Alaska Sea Grant Report 84-1, Alaska Sea Grant College Program,

University of Alaska, Fairbanks, Alaska. 
14

SEI WHALE (Balaenoptera borealis):

Western North Atlantic Stock

STOCK DEFINITION AND GEOGRAPHIC RANGE

Indications are that, at least during the feeding season, the sei whale population is centered in northerly

waters, perhaps on the Scotian Shelf (Mitchell and Chapman 1977). The southern portion of the species' range during

spring and summer includes the northern portions of the U.S. Atlantic Exclusive Economic Zone (EEZ) — the Gulf

of Maine and Georges Bank. The period of greatest abundance there is in spring with sightings concentrated along

the eastern margin of Georges Bank and into the Northeast Channel area, and along the southwestern edge of Georges

Bank in the area of Hydrographer Canyon (CeTAP 1982). The sei whale is generally found in the deeper waters

characteristic of the continental shelf edge region (Hain et al. 1985). Mitchell (1975) similarly reported that sei whales

off Nova Scotia were often distributed closer to the 2,000 m depth contour than were fin whales. 

This general offshore pattern of sei whale distribution is disrupted during episodic incursions into more

shallow and inshore waters. The sei whale, like the right whale, is largely planktivorous — feeding primarily on

euphausiids and copepods. In years of reduced predation on copepods by other predators, and thus greater abundance

of this prey source, sei whales are reported in more inshore locations, such as the Great South Channel and Stellwagen

Bank areas (Kenney, personal communication; Payne et al. 1990). An influx of sei whales into the southern Gulf of

Maine occurred in the summer of 1986 (Schilling et al. 1992). 

Based on analysis of records from the Blandford, Nova Scotia, whaling station, where 825 sei whales were

taken between 1965 and 1972, Mitchell (1975) described two "runs" of sei whales, in June-July and in SeptemberOctober. He speculated that the sei whale population migrates from south of Cape Cod and along the coast of eastern

Canada in June and July, and returns on a southward migration again in September and October; however, such a

migration remains unverified.

Mitchell and Chapman (1977) reviewed the sparse evidence on stock identity of northwest Atlantic sei whales,

and suggested two stocks — a Nova Scotia stock and a Labrador Sea stock. The Nova Scotian stock includes the

continental shelf waters of the northeastern U.S., and extends northeastward to south of Newfoundland. The Scientific

Committee of the IWC, while adopting these general boundaries, noted that the stock identity of sei whales (and indeed

all North Atlantic whales) was a major research problem (Donovan 1991). In the absence of evidence to the contrary,

the proposed IWC stock definition is provisionally adopted. 

POPULATION SIZE

Mitchell and Chapman (1977), based on tag-recapture data, estimated the Nova Scotia, Canada, stock to

contain between 1,393 and 2,248 sei whales. Based on census data, they estimated a minimum Nova Scotian

population of 870 sei whales. 

The total number of sei whales in the U.S. Atlantic EEZ is unknown. Seasonal abundance estimates are

available from an aerial survey program conducted in the continental shelf and shelf edge waters between Cape

Hatteras, North Carolina, and Nova Scotia from 1978 to 1982 (CeTAP 1982). A spring population estimate of 253

(CV = 0.63) was based on CeTAP (1982) data. This estimate is not corrected for submerged animals that may have

gone unsighted by the aerial surveys. Spring data were used since it was the only seasonal estimate provided in CeTAP

(1982). This estimate may not reflect the current true population because of the fact that data are a decade old and

because of low survey effort in areas and seasons that are likely to be significant for sei whales. No sei whales were

sighted during an August-October 1991 aerial survey in the CeTAP study area (NMFS unpublished data); therefore,

there are no current estimates of sei whale abundance. 

Minimum Population Estimate

A current minimum population size cannot be estimated because there are no current abundance estimates

(within the last 10 years). 

Current Population Trend

There are insufficient data to determine the population trends for this species. 
15

CURRENT AND MAXIMUM NET PRODUCTIVITY RATES

Current and maximum net productivity rates are not known for this stock. The maximum net productivity

rate was assumed to be 0.04 for purposes of this assessment. This value is based on theoretical calculations showing

that cetacean populations may not grow at rates much greater than 4% given the constraints of their reproductive life

history (Anon. 1994). 

POTENTIAL BIOLOGICAL REMOVAL

Potential biological removal (PBR) was specified as the product of minimum population size, one-half the

maximum productivity rate, and a "recovery" factor for endangered, depleted, threatened stocks, or stocks of unknown

status relative to optimum sustainable population (OSP) (Anon. 1994). No PBR can be calculated because minimum

population size is unknown.

ANNUAL HUMAN-CAUSED MORTALITY AND SERIOUS INJURY

There are few if any data on fishery interactions or human impacts. There are no reports of mortality,

entanglement, or injury in the NEFSC or NE Regional Office databases; however, there is a report of a ship strike.

The New England Aquarium documented a sei whale carcass hung on the bow of a container ship as it docked in

Boston on November 17, 1994. The crew estimated that the whale had been hung on the bow for approximately four

days prior to the ship’s arriving in port. There was no reported fishery-related mortality or serious injury to fin whales

in fisheries observed by NMFS during 1989-1993. The total fishery-related mortality and serious injury for this stock

is unknown, but can be considered insignificant and approaching zero mortality and serious injury rate. This

determination cannot be made for specific fisheries until the implementing regulations for Section 118 of the MMPA

have been reviewed by the public and finalized. 

Fishery Information

There have been no reported entanglements or other interactions between sei whales and commercial fishing

activities; therefore there are no descriptions of fisheries.

STATUS OF STOCK

The status of this stock relative to OSP is unknown, but the species is listed as endangered under the ESA.

There are insufficient data to determine the population trends for sei whales. The total level of human-caused mortality

and serious injury is unknown, but it is believed to be insignificant. Any fishery-related mortality would be unlawful

because there is no recovery plan currently in place. This is a strategic stock because the sei whale is listed as an

endangered species under the ESA.

REFERENCES

Anon. 1994. Report of the PBR (Potential Biological Removal) workshop. June 27-29, 1994. NOAA, NMFS

Southwest Fisheries Science Center, La Jolla, California, 13 pp. + Appendices. 

CeTAP. 1982. A characterization of marine mammals and turtles in the mid- and north Atlantic areas of the U.S.

outer continental shelf. Cetacean and Turtle Assessment Program, University of Rhode Island. Final Report

#AA551-CT8-48 to the Bureau of Land Management, Washington, DC, 538 pp. 

Donovan, G. P. 1991. A review of IWC stock boundaries. Rep. Int. Whal. Commn. Special Issue 13: 39-68. 

Hain, J. H. W., M. A. M. Hyman, R. D. Kenney, and H. E. Winn. 1985. The role of cetaceans in the shelf-edge region

of the northeastern United States. Mar. Fish. Rev. 47(1): 13-17. 

Mitchell, E. 1975. Preliminary report on Nova Scotia fishery for sei whales (Balaenoptera borealis). Rep. Int. Whal.

Commn. 25: 218-225. 

Mitchell, E. and D. G. Chapman. 1977. Preliminary assessment of stocks of northwest Atlantic sei whales

(Balaenoptera borealis). Rep. Int. Whal. Commn. Special Issue 1: 117-120.

Payne, P. M., D. N. Wiley, S. B. Young, S. Pittman, P. J. Clapham, and J. W. Jossi. 1990. Recent fluctuations in the

abundance of baleen whales in the southern Gulf of Maine in relation to changes in selected prey. Fish. Bull.,

U.S. 88: 687-696. 
16

Schilling, M. R., I. Seipt, M. T. Weinrich, S. E. Frohock, A. E. Kuhlberg, and P. J. Clapham. 1992. Behavior of

individually identified sei whales, Balaenoptera borealis, during an episodic influx into the southern Gulf

of Maine in 1986. Fish. Bull., U.S. 90(4): 749-755. 
17

Figure 1. Distribution of minke whale sightings from NEFSC

shipboard surveys during the summer in 1990-1994. Isobaths

are at 100 m and 1,000 m. 

MINKE WHALE (Balaenoptera acutorostrata):

Canadian East Coast Stock

STOCK DEFINITION AND GEOGRAPHIC RANGE

Minke whales have a cosmopolitan distribution

in polar, temperate and tropical waters. In the North

Atlantic there are four recognized populations —

Canadian east coast, west Greenland, central North

Atlantic, and northeastern North Atlantic (Donovan

1991). These four population divisions were defined by

examining segregation by sex and length, catch

distributions, sightings, marking data and pre-existing

ICES boundaries; however, there is very little data from

the Canadian east coast population. 

Minke whales off the eastern coast of the

United States are considered to be part of the Canadian

east coast population, which inhabits the area from the

eastern half of the Davis Strait out to 45EW and south

to the Gulf of Mexico. The relationship between this

and the other three populations is uncertain. 

The minke whale is the third most abundant

large whale in the U.S. Atlantic Exclusive Economic

Zone (EEZ). It is common and widely distributed

(CeTAP 1982); however, because of its smaller size,

more rapid movements, and less observable behavior,

there is more uncertainty about abundance, distribution,

and behavior than for other large cetaceans. There

appears to be a strong seasonal component to minke

whale distribution. Spring and summer are times of

relatively widespread and common occurrence, and they

are most abundant in New England waters during this time. The number of minke whales and the area occupied by

them is reduced in the fall. In winter, the species appears to be largely absent from the area. Like most other baleen

whales, the minke whale generally occupies the continental shelf proper, rather than the continental shelf edge region.

Records summarized by Mitchell (1991) hint at a possible winter distribution in the West Indies and in mid-ocean

south and east of Bermuda. As with several other cetacean species, the possibility of a deep-ocean component to

distribution exists but remains unconfirmed. 

POPULATION SIZE

The total number of minke whales in the Canadian East Coast population is unknown. However, three

estimates exist for portions of the habitat — a 1978-1982 estimate (CeTAP 1982), a shipboard survey estimate from

the summers of 1991 and 1992, and a shipboard estimate, from June-July 1993. 

Seasonal abundance estimates are available from an aerial survey program conducted in the continental shelf

and continental shelf edge waters between Cape Hatteras, North Carolina, and Nova Scotia from 1978 to 1982 (CeTAP

1982). A spring population estimate of 320 minke whales was based on CeTAP (1982) data [coefficient of variation

(CV) = 0.23]. This estimate may not reflect the actual population size because a dive-time correction was not included,

the data are a decade old, and survey effort was low in certain seasons and areas (e.g., the fall season on eastern and

southeastern Georges Bank). 

Minke whale abundance in the northern Gulf of Maine-lower Bay of Fundy region during the summers of

1991 and 1992 was estimated to be 2,650 minke whales (CV = 0.31). This is a weighted-average abundance estimate

where each annual estimate is weighted by the inverse of its variance (NMFS unpublished data). The data used in
18

estimating minke whale abundance were obtained from two shipboard line transect sighting surveys designed to

estimate abundance of harbor porpoises (Palka, in press). Two independent teams of observers on the same ship

surveyed using the naked eye in non-closing mode. The abundance estimate includes an estimate of g(0), probability

of detection, for both teams of 0.60 (CV = 0.12) [using each team's data separately produced a g(0) value of 0.31 (CV

= 0.22)]. The g(0)-corrected abundance estimate was calculated using the product interval analytical method (Palka,

in press). Variability was estimated using bootstrap resampling techniques. 

The 1991-1993 estimates suggest that minke whale abundance may be an order of magnitude greater than was

estimated by CeTAP in 1982; however, two qualifications to the estimate must be made. The study area was stratified

by water depth and expected density of harbor porpoises, although the observed distribution of minke whales suggests

that the stratification scheme was appropriate for minke whales. Secondly, this estimate has not accounted for dive

times and ship avoidance. Both of these behavioral factors could significantly influence the abundance estimate, but

if they were taken into account this would probably not result in a lower abundance estimate. 

An abundance estimate was also derived in a limited portion of the stock range using data collected during

a June-July 1993 NEFSC shipboard line transect survey conducted between the 200 and 2,000 m isobaths from the

southern edge of Georges Bank, across the entrance to the Northeast Channel, and to the southwestern edge of the

Scotian Shelf. The estimate for this area is 330 whales (CV = 0.66). 

There are no estimates of abundance for this species in Canadian waters, which lie farther north or east of the

above two surveys. 

Minimum Population Estimate

The minimum population estimate is the lower limit of the two-tailed 60% confidence interval of the lognormal distributed abundance average estimate of 2,650 whales based on the 1991-1992 surveys (CV = 0.31) (NMFS

unpublished data), which is equivalent to the 20th percentile of the log-normal distribution as specified by NMFS

(Anon. 1994), and was 2,053 minke whales. The 1991-1992 survey was used because it covered a larger proportion

of the known habitat than that covered during the 1993 survey. The Gulf of Maine and Georges Bank abundance

estimates were not combined because the June-July 1993 Georges Bank survey was conducted at a place through which

minke whales migrate to spend the summer in the Gulf of Maine (the time and place of the 1991-1992 surveys). 

Current Population Trend

There are insufficient data to determine the population trends for this species. 

CURRENT AND MAXIMUM NET PRODUCTIVITY RATES

Current and maximum net productivity rates are not known for this stock. The maximum net productivity

rate was assumed to be 0.04 for purposes of this assessment. This value is based on theoretical calculations showing

that cetacean populations may not generally grow at rates much greater than 4% given the constraints of their

reproductive life history (Anon. 1994). 

Some biological parameters that could be used to estimate this rate are as follows. Females mature when 6-8

years old; pregnancy rates are approximately 0.86 to 0.93; thus, the calving interval is between 1 and 2 years. Calves

are probably born during October to March, after 10 to 11 months gestation. Nursing lasts for less than 6 months.

Maximum ages are not known, but for Southern Hemisphere minke whales the maximum age appears to be about 50

years (Katona et al. 1993; IWC 1991). 

POTENTIAL BIOLOGICAL REMOVAL

Potential biological removal (PBR) was specified as the product of minimum population size, one-half the

maximum productivity rate, and a "recovery" factor for endangered, depleted, threatened stocks, or stocks of unknown

status relative to optimum sustainable population (OSP) (Anon. 1994). The recovery factor was set at 0.50 because

of the stock's status relative to its OSP level is unknown. PBR for this stock is 21 whales. 

ANNUAL HUMAN-CAUSED MORTALITY AND INJURY

In U.S. waters, an entanglement database maintained by NE Regional Office for 1975-1992 includes 36

records of minke whales. The gear includes unspecified fishing net, unspecified cable or line, fish trap, weirs, seines,

gillnets, and lobster gear. In a review of cetaceans and fishery interactions, Read (1994) reported that a minke whale
19

was found dead in a Rhode Island fish trap in 1976, and that a minke whale was trapped and released alive in a herring

weir off northern Maine in 1990. One minke whale was reported caught in a bluefin tuna purse seine off Stellwagen

Bank in 1991 and released uninjured (D. Beach, NMFS NE Regional Office, personal communication).

The only two records of minke whales in the NEFSC Sea Sampling database were from July 1991, south of

Penobscot Bay, Maine, and October 1992, off the coast of New Hampshire near Jeffreys Ledge, in the Gulf of Maine

sink gillnet fishery. One was dead, one was released alive. A minke whale was caught and released in the Japanese

tuna longline fishery in 3,000 m of water, south of Lydonia Canyon on Georges Bank, in September 1986 (Waring et.

al 1990). An immature female minke whale, entangled with line around the tail stock, came ashore on the

Jacksonville, Florida, jetty on 31 January 1990, and on 15 March 1992, a juvenile female minke whale with propeller

scars was found floating east of the St. Johns channel entrance (R. Bonde, USFWS, Gainesville, FL, personal

communication).

 Information about minke whale interactions with fishing gear is not well quantified or recorded in most parts

of Canada. The following were reported in Read (1994). Six minke whales were reported entangled in gillnets in

Newfoundland and Labrador during 1989. One of these animals escaped towing gear, the rest died. Five minke whales

were entrapped and died in Newfoundland cod traps during 1989. During 1980 and 1990, 15 of 17 minke whales were

released alive from herring weirs in the Bay of Fundy. In 1990, ten minke whales were trapped in the Bay of Fundy

weirs, but all were released alive. Salmon gillnets in Canada have taken a few minke whales. In Newfoundland in

1979, one minke whale died in a salmon net. Between 1979 and 1990, it was estimated that 15% of the minke whale

takes were in salmon gillnets. 

Minke whales have been and are still being hunted in the North Atlantic. From the Canadian East Coast

population, documented whaling occurred from 1948 to 1972 with a total kill of 1,103 animals (IWC 1992). Animals

from all other North Atlantic populations are presently still being harvested at low levels, at less than 300 animals per

population. 

Because minke whales inhabit coastal waters during much of the year, they may be affected by pollution. For

example, the levels of polychlorinated biphenyls in blubber from minke whales in the St. Lawrence estuary in Canada

were high (Gaskin 1985). 

Indirect impacts on prey species are also possible. Fish in the diet of minke whales include herring, capelin,

cod, pollock, salmon, mackerel and sand lance. All of these species, except sand lance, are commercially harvested;

and cod and pollock are considered as fully exploited or overexploited (NMFS 1993). Consequentially, the abundance

and distribution of minke whales may be affected by the commercial fishing of the above fish and squid species. 

Accurate estimates of human-caused mortality are not available because it is likely that many entanglements,

injuries, and mortalities go unobserved and/or unrecorded, and existing data are fragmentary. Total annual estimated

average fishery-related mortality and serious injury to this stock in the Atlantic in fisheries observed by NMFS during

1990-1993 was 2.5 minke whales (CV = 1.92). The total fishery-related mortality and serious injury for this stock is

greater than 10% of the calculated PBR and, therefore, cannot be considered to be insignificant and approaching zero

mortality and serious injury rate. This determination cannot be made for specific fisheries until the implementing

regulations for Section 118 of the MMPA have been reviewed by the public and finalized. 

Fishery Information

Prior to 1977, there was no documentation of marine mammal by-catch in distant-water fleet (DWF) activities

off the northeast coast of the U.S. With implementation of the Magnuson Fisheries Conservation and Management

Act in that year an observer program was established which has recorded fishery data and information of incidental

by-catch of marine mammals. In 1982, there were 112 different foreign vessels; 16%, or 18, were Japanese tuna

longline vessels operating along the U.S. east coast. This was the first year that the Northeast Regional Observer

Program assumed responsibility for observer coverage of the longline vessels. Between 1983 and 1988, the number

of Japanese longline vessels operating within the EEZ each year were 3, 5, 7, 6, 8, and 8, respectively. Observer

coverage was 100%. No mortalities were observed, but one animal was released alive in September 1986 (Waring et

al. 1990). 

There are approximately 349 vessels (full and part time) in the New England multispecies sink gillnet fishery

(Walden, in review). Observer coverage in trips has been 1%, 6%, 7.5%, and 5% for years 1990 to 1993. The fishery

has been observed in the Gulf of Maine and in Southern New England. One mortality was observed in this fishery in

1991. Estimated fishery-related mortality and serious injury attributable to this fishery was ten minke whales (CV =
20

0.96) in 1991 (Northridge, in review). Annual estimated average fishery-related mortality and serious injury to this

stock in the Atlantic during 1990-1993 attributable to the sink gillnet fishery was 2.5 minke whales (CV = 1.92). 

The Canadian groundfish gillnet fishery is important and widespread. Many fisherman hold groundfish

gillnet licenses but the number of active fisherman are unknown. In 1989, approximately 6,800 licenses were issued

to fishermen along the southern coast of Labrador, and northeast and southern coast of Newfoundland. In the Gulf

of St. Lawrence, there were about 3,900 licenses issued in 1989, while in the Bay of Fundy and southwestern Nova

Scotia 659 licenses were issued. 

There were 3,121 cod traps operating in Newfoundland and Labrador during 1979. That number was

estimated to have grown to about 7,500 in 1980. The cod trap fishery in Newfoundland closed in 1993 due to the

depleted groundfish resources. 

The Atlantic Canadian and Greenland salmon gillnet fishery is seasonal, with the peak from June to

September, depending on the location. In southern and eastern Newfoundland, and Labrador during 1989, there were

2,196 gear units used, where each gear unit consist of a net 91 m long. There is no effort data available for the

Greenland fishery. However the fishery was stopped in 1993 as a result of an agreement between the fishermen and

North Atlantic Salmon Fund (Read 1994). There was no reported fishery-related mortality or serious injury to minke

whales in this fishery.

In U.S. and Canadian waters the herring weir fishery occurs from May to September each year along the

southwestern shore of the Bay of Fundy, and scattered along the western Nova Scotia and northern Maine coasts. In

1990 there were 180 active weirs in western Bay of Fundy, and 56 active weirs in Maine (Read 1994). There was no

reported fishery-related mortality or serious injury to minke whales in this fishery in U.S. Atlantic EEZ waters.

Ship Strikes

 Minke whales inhabit coastal waters during much of the year and are subject to collision with vessels. In

one record in the NE Regional Office marine mammal stranding database, on 7 July 1974, the necropsy suggested a

vessel collision. 

STATUS OF STOCK

The status of minke whales relative to OSP in the U.S. Atlantic EEZ is unknown. The minke whale is not

listed as endangered under the Endangered Species Act (ESA). In Canada, the Cetacean Protection Regulations of

1982, promulgated under the standing Fisheries Act, prohibit the catching or harassment of all species of cetaceans,

including the minke whale. The level of human-caused mortality and serious injury is not likely to be high relative

to stock size because while fishery interactions do occur, most minke whales escape or are released unharmed. This

is not a strategic stock because estimated fishery-related mortality and serious injury does not exceed PBR and the

minke whale is not listed as a threatened or endangered species under the ESA. 

REFERENCES

Anon. 1994. Report of the PBR (Potential Biological Removal) workshop. June 27-29, 1994. NOAA, NMFS

Southwest Fisheries Science Center, La Jolla, California, 13 pp. + Appendices. 

CeTAP. 1982. A characterization of marine mammals and turtles in the mid- and north Atlantic areas of the U.S.

outer continental shelf. Cetacean and Turtle Assessment Program, University of Rhode Island. Final Report,

Contract AA51-C78-48, Bureau of Land Management, Washington, DC, 538 pp. 

Donovan, G. P. 1991. A review of IWC stock boundaries. Rep. Int. Whal. Commn. Special Issue 13: 39-68. 

IWC [International Whaling Commission]. 1991. Appendix 11. Biological parameters of North Atlantic minke

whales in Annex F Report of the sub-committee on North Atlantic Minke whales. Rep. Int. Whal. Commn.

41: 160.

IWC [International Whaling Commission]. 1992. Annex K. Report of the working group on North Atlantic Minke

trials. Rep. Int. Whal. Commn. 42: 246-251. 

Gaskin, D. E. 1985. The ecology of whales and dolphins. Heinemann Educational Books, Inc. Portsmouth, NH. 

Katona, S. K., V. Rough, and D. T. Richardson. 1993. A field guide to whales, porpoises, and seals from Cape Cod

to Newfoundland. Smithsonian Institution Press. Washington. 316 pp. 
21

Mitchell, E. D. 1991. Winter records of the Minke whale (Balaenoptera acutorostrata Lacepede 1804) in the

southern North Atlantic. Rep. Int. Whal. Commn. 41: 455-457. 

NMFS [National Marine Fisheries Service]. 1993. Status of fishery resources off the northeastern United States for

1993. NOAA Tech. Mem. NMFS-F/NEC 101. 

Northridge, S. In review. Estimation of cetacean mortality in the U.S. Atlantic swordfish and tuna driftnet and pair

trawl fisheries. Draft final report to the Northeast Fisheries Science Center, Contract No. 40ENNF500045,

18 pp. 

Palka, D. In press. Abundance estimate of the Gulf of Maine harbor porpoise. Rep. Int. Whal. Commn. Special Issue

16.

Read, A. J. 1994. Interactions between cetaceans and gillnet and trap fisheries in the northwest Atlantic. Rep. Int.

Whal. Commn. Special Issue 15: 133-147. 

Waring, G. T., P. Gerrior, P. M. Payne, B. Parry, and J. R. Nicolas. 1990. Incidental take of marine mammals in

foreign fishery activities off the northeast United States, 1977-88. Fish. Bull., U.S. 88(2): 347-360.

Walden, J. In review. Results of the Gulf of Maine gillnet survey 1989-92. NOAA, NMFS, NEFSC [Northeast

Fisheries Science Center] Ref. Doc., Woods Hole, Massachusetts.
22

BLUE WHALE (Balaenoptera musculus):

Western North Atlantic Stock

STOCK DEFINITION AND GEOGRAPHIC RANGE

The distribution of the blue whale, Balaenoptera musculus, in the western North Atlantic generally extends

from the Arctic to at least mid-latitudes. Blue whales are most frequently sighted in the waters off eastern Canada,

with the majority of recent records from the Gulf of St. Lawrence (Sears et al. 1987). The species was hunted around

Newfoundland in the first half of the 20th century (Sergeant 1966). The present Canadian distribution, broadly

described, is spring, summer, and fall in the Gulf of St. Lawrence, especially along the north shore from the St.

Lawrence River estuary to the Strait of Belle Isle and off eastern Nova Scotia. The species occurs in winter off southern

Newfoundland and also in summer in Davis Strait (Mansfield 1985). 

The blue whale is best considered as an occasional visitor in U.S. Atlantic Exclusive Economic Zone (EEZ)

waters, which may be the current southern limit of its range (CeTAP 1982; Wenzel et al. 1988). All of the five

sightings described in the foregoing two references were in August. Yochem and Leatherwood (1985) summarized

records that suggested an occurrence of this species south to Florida and the Gulf of Mexico, although the actual

southern limit of the species’ range is unknown. 

The blue whale may be nomadic and open-ocean in habitat. In one example, an individual was tracked from

near Newfoundland to south of Bermuda (Gagnon and Clark 1993). 

POPULATION SIZE

Little is known except for the Gulf of St. Lawrence area. Here, 308 individuals have been catalogued (Sears

et al. 1987). Mitchell (1974) estimated that the blue whale population in the western North Atlantic may number only

in the low hundreds. R. Sears (personal communication) suggests that no present evidence exists to refute this

estimate. 

Minimum Population Estimate

The 308 recognizable individuals from the Gulf of St. Lawrence area which were catalogued by Sears et al.

(1987) is considered to be a minimum population estimate. 

Current Population Trend

There are insufficient data to determine the population trends for this species. Off west and southwest Iceland,

an increasing trend of 4.9% a year was reported for the period 1969-1988 (Sigurjonsson and Gunnlaugsson 1990). 

CURRENT AND MAXIMUM NET PRODUCTIVITY RATES

Current and maximum net productivity rates are not known for this stock. The maximum net productivity

rate was assumed to be 0.04 for purposes of this assessment. This value is based on theoretical calculations showing

that cetacean populations may not generally grow at rates much greater than 4% given the constraints of their

reproductive life history (Anon. 1994). 

POTENTIAL BIOLOGICAL REMOVAL

Potential biological removal (PBR) was specified as the product of minimum population size, one-half the

maximum productivity rate, and a "recovery" factor for endangered, depleted, threatened stocks, or stocks of unknown

status relative to optimum sustainable population (OSP) (Anon. 1994). The recovery factor was set at 0.10 because

the species is listed as endangered under the Endangered Species Act (ESA). PBR for this stock is 0.6 blue whales.

ANNUAL HUMAN-CAUSED MORTALITY AND SERIOUS INJURY

There are no records of fishery-related mortality or serious injury to blue whales in the U.S. Atlantic EEZ.

Total fishery-related mortality and serious injury for this stock is considered insignificant and approaching zero

mortality and serious injury rate. This determination cannot be made for specific fisheries until the implementing

regulations for Section 118 of the MMPA have been reviewed by the public and finalized. 
23

Fishery Information

No fishery information is presented because there are no observed fishery-related mortalities or serious injury.

STATUS OF STOCK

The status of this stock relative to OSP is unknown, but the species is listed as endangered under the ESA.

 There are insufficient data to determine population trends for blue whales. The total level of human-caused mortality

and serious injury is unknown, but it is believed to be insignificant. Any fishery-related mortality would be unlawful

because there is no recovery plan currently in place. This is a strategic stock because the blue whale is listed as an

endangered species under the ESA.

REFERENCES

Anon. 1994. Report of the PBR (Potential Biological Removal) workshop. June 27-29, 1994. NOAA, NMFS

Southwest Fisheries Science Center, La Jolla, California, 13 pp. + Appendices. 

CeTAP. 1982. A characterization of marine mammals and turtles in the mid- and north Atlantic areas of the U.S.

outer continental shelf. Cetacean and Turtle Assessment Program, University of Rhode Island. Final Report

#AA551-CT8-48 to the Bureau of Land Management, Washington, DC, 538 pp. 

Gagnon, G. J. and C. W. Clark. 1993. The use of U.S. Navy IUSS passive sonar to monitor the movement of blue

whales. Abstract, Tenth Biennial Conference on the Biology of Marine Mammals, Galveston, TX, 11-15

November 1993. 

Mansfield, A. W. 1985. Status of the blue whale, Balaenoptera musculus, in Canada. Canadian Field Naturalist

99(3): 417-420.

Mitchell, E. 1974. Present status of northwest Atlantic fin and other whale stocks. Pages 108-169 in W. E. Schevill

(editor), The whale problem: A status report. Harvard University Press, Cambridge, Massachusetts, 419 pp.

Sears, R., F. Wenzel, and J. M. Williamson. 1987. The blue whale: a catalog of individuals from the western North

Atlantic (Gulf of St. Lawrence). Mingan Island Cetacean Study, St. Lambert, Quebec, Canada, 27 pp. 

Sergeant, D. E. 1966. Populations of large whale species in the western North Atlantic with special reference to the

fin whale. Fish. Res. Board. Canada Circular No. 9, 30 pp. 

Sigurjonsson, J. and T. Gunnlaugsson. 1990. Recent trends in abundance of blue (Balaenoptera musculus) and

humpback whales (Megaptera novaeangliae) off west and southwest Iceland, with a note on occurrence of

other cetacean species. Rep. Int. Whal. Commn. 40: 537-551. 

Wenzel, F., D. K. Mattila, and P. J. Clapham. 1988. Balaenoptera musculus in the Gulf of Maine. Mar. Mam. Sci.

4(2): 172-175. 

Yochem, P. K. and S. Leatherwood. 1985. Blue whale. Pages 193-240 in S. H. Ridgeway and R. Harrison (editors),

Handbook of Marine Mammals, Vol. 3: The Sirenians and Baleen Whales, Academic Press, New York. 
24

Figure 1. Distribution of sperm whale sightings from NEFSC

shipboard surveys during the summer in 1990-1994. Isobaths

are at 100 m and 1,000 m. 

SPERM WHALE (Physeter macrocephalus):

Western North Atlantic Stock

STOCK DEFINITION AND GEOGRAPHIC RANGE

The sperm whale is reported during all four

seasons along the continental shelf edge in the

northeastern U.S. Atlantic coast Exclusive Economic

Zone (EEZ) (CeTAP 1982). These data as well as

observations in the literature suggest that the

distribution of the sperm whale continues well beyond

the continental shelf edge, over the continental slope,

and into mid-ocean regions (Fig. 1). Waring et al.

(1993) suggest that this offshore distribution is more

commonly associated with the Gulf Stream edge and

other features. In the shoreward direction, Hain and

Kenney (unpublished data) report an occurrence on the

continental shelf from August through November

inshore of the 100m depth contour south of New

England and on the southern Scotian Shelf. 

There appears to be a distinct seasonal cycle.

In winter, sperm whales are concentrated east and

northeast of Cape Hatteras. In spring, the center of

distribution shifts northward to east of the Delmarva

peninsula, and is widespread throughout the central

portion of the mid-Atlantic bight and the southern

portion of Georges Bank. In summer, the distribution

is similar but now also includes the area east and north

of Georges Bank and into the Northeast Channel region,

as well as the continental shelf south of New England.

In the fall, sperm whale occurrence south of New

England on the continental shelf is at its highest level, and there remains a continental shelf edge occurrence in the

mid-Atlantic bight. 

The sperm whales that occur in the eastern U.S. EEZ likely represent only a fraction of the total stock, perhaps

at a lateral periphery of the entire range. The nature of linkages of this habitat with those to the south, north, and

offshore is unknown. Historical whaling records compiled by Schmidly (1981) suggest an offshore distribution off the

southeast U.S., over the Blake Plateau, and offshore in the deep ocean. In the southeast Caribbean, both large and

small adults, as well as calves and juveniles of different sizes are reported (Watkins et al. 1985). 

Geographic distribution of sperm whales may be linked to their social structure and their low reproductive

rate and both of these factors have management implications. Several basic groupings or social units are generally

recognized — nursery schools, harem or mixed schools, juvenile or immature schools, bachelor schools, bull schools

or pairs, and solitary bulls (Best 1979). These groupings have a distinct geographical distribution, with females and

juveniles generally based in tropical and subtropical waters, and males more wide-ranging and occurring in higher

latitudes. The basic social unit of the sperm whale appears to be the mixed school of adult females plus their calves

and some juveniles of both sexes, normally numbering 20-40 animals in all. There is evidence that some social bonds

persist for many years. Sperm whales have a very low reproductive rate, probably the lowest recorded for any marine

mammal to date. The gestation period is estimated at 14-16 months, with a 5-year reproductive cycle.

POPULATION SIZE

The total numbers of sperm whales off the U.S. or Canadian Atlantic coast are unknown, though several

estimates from selected regions of the habitat do exist. Seasonal abundance estimates are available from an aerial
25

survey program conducted in continental shelf and continental shelf edge waters between Cape Hatteras, North

Carolina, and Nova Scotia from 1978 to 1982 (CeTAP 1982). An estimate based on an inverse variance weighted

pooling of CeTAP (1982) spring and summer data is 219 (CV = 0.36). An average for these two seasons was chosen

because the greatest proportion of the population off the northeast U.S. coast appears to be in the CeTAP study area

in these seasons. The data were analyzed using DISTANCE (Buckland et al. 1993; Laake et al. 1993), where the

confidence interval was calculated using the bootstrap log normal method. This estimate was not corrected for g(0),

the probability of detecting an animal group on the trackline. 

Abundance estimates were also derived using data collected during an autumn 1991 line transect aerial survey

in the CeTAP study area (NMFS unpublished data), which included an interplatform experiment between a Twin Otter

and an AT-11), and from four fine-scale shipboard line transect surveys (August 1990, June-July 1991, June-July 1993,

and August 1994) conducted in continental shelf edge and deeper oceanic waters (NMFS unpublished data). For both

the aerial and shipboard surveys, sightings were almost exclusively in the continental shelf edge and continental slope

areas. The 1991 aerial survey repeated many of the CeTAP-defined survey blocks, and added several continental slope

survey blocks. Due to weather and logistical constraints, several survey blocks south and east of Georges Bank were

not surveyed. Abundance estimates from this 1991 aerial survey were 337 (CV = 0.50) and 705 (CV = 0.66) for the

AT-11 and NOAA Twin Otter, respectively. Data were not pooled, because the interplatform calibration analysis has

not been conducted. Furthermore, these estimates are not fully comparable to the CeTAP estimates, because the 1991

data are from a single survey, August to October, while the CeTAP estimates were based on data pooled over several

years of seasonal surveys. 

An abundance estimate from the August 1990 shipboard survey, conducted principally along the Gulf Stream

north wall between Cape Hatteras and Georges Bank, is 338 (CV = 0.31). The 1991 shipboard survey estimate, based

principally on sighting effort conducted between the 200 and 2,000 meter isobaths from Cape Hatteras to Georges Bank

is 736 (CV = 0.36). The estimate for the 1993 survey, conducted principally between the 200 and 2,000 meter isobaths

from the southern edge of Georges Bank, across the Northeast Channel to the southeastern edge of the Scotian Shelf

is 116 (CV = 0.40). The 1994 estimate, based on survey effort within a Gulf Stream warm-core ring located in

continental slope waters southeast of Georges Bank is 623 (CV = 0.52). 

Because the estimates presented here were not dive-time corrected, they are likely downwardly biased and an

underestimate of actual abundance. Given that the average dive-time of sperm whales is 45 min (W. A. Watkins,

personal communication), the bias may be substantial. 

 Although the stratification schemes used in the 1990-1994 surveys did not always sample the same areas or

encompass the entire sperm whale habitat, they did focus on segments of known or suspected high-use habitats off the

northeastern U.S. coast. The collective 1990-94 data suggest that, seasonally, at least several hundred sperm whales

are occupying these waters, with perhaps greater abundances in the mid Atlantic region. This is consistent with the

earlier CeTAP data from a decade previous. Sperm whale abundance may increase offshore, particularly in association

with Gulf Stream and warm-core ring features; however, at present there is no reliable estimate of total sperm whale

abundance in the western North Atlantic. 

Minimum Population Estimate

 The minimum population estimate was based on the AT-11 aerial survey population estimate in autumn 1991

of 337 sperm whales (CV = 0.50). This estimate was selected because the AT-11 survey provided the most complete

coverage of continental shelf edge and continental slope waters off the northeast U.S. coast. The minimum population

estimate is the lower limit of the two-tailed 60% confidence interval of the log-normal distributed abundance estimate,

which is equivalent to the 20th percentile of the log-normal distribution as specified by NMFS (Anon. 1994), and was

226 sperm whales.

Current Population Trend

There are insufficient data to determine the population trends for this species. 

CURRENT AND MAXIMUM NET PRODUCTIVITY RATES

While more is probably known about sperm whale life history in other areas, some life history and vital rates

information is available for the northwest Atlantic. Some of the life history parameters which have been estimated

include: calving interval is 3-4 years, lactation period is 24 months, gestation period is 14.5-16.5 months, births occur
26

mainly in July to November, length at birth is 405 cm, length at sexual maturity 11.0-12.0 m for males, and 8.3-9.2

m for females, mean age at sexual maturity is 19 years for males and 9 years for females, and mean age at physical

maturity is 45 years for males and 30 years for females (Best 1974; Lockyer 1981). 

Current and maximum net productivity rates for this stock are not known. The maximum net productivity

rate was assumed to be 0.04 for purposes of this assessment. This value is based on theoretical calculations showing

that cetacean populations may not generally grow at rates much greater than 4% given the constraints of their

reproductive life history (Anon. 1994). 

POTENTIAL BIOLOGICAL REMOVAL

Potential biological removal (PBR) was specified as the product of minimum population size, one-half the

maximum productivity rate, and a "recovery" factor for endangered, depleted, threatened stocks, or stocks of unknown

status relative to optimum sustainable population (OSP) (Anon. 1994). The recovery factor is 0.10 because this species

is listed as endangered under the Endangered Species Act (ESA). PBR for this stock is 0.5 sperm whales. 

ANNUAL HUMAN-CAUSED MORTALITY

Four hundred twenty-four sperm whales were taken in the Newfoundland-Labrador area between 1904-1972

and 109 sperm whales were taken near Nova Scotia in 1964-1972 (Mitchell and Kozicki 1984) in a Canadian fishery.

There was also a well-documented sperm whale fishery based on the west coast of Iceland. Other sperm whale catches

occurred near West Greenland, the Azores, Madeira, Spain, Spanish Morocco, Norway (coastal and pelagic), Faroes,

and British coastal. Whether the northwest Atlantic population is discrete from those fished elsewhere in the

northwestern or northeastern Atlantic is currently unresolved. There exists one tag return of a male tagged off Browns

Bank (Nova Scotia) in 1966 and returned from Spain in 1973. At present, because of their general offshore

distribution, sperm whales are less likely to be impacted by humans and those impacts that do occur are less likely to

be recorded. There has been no complete analysis and reporting of existing data on this topic for the western North

Atlantic. Only a single record exists in the present NEFSC by-catch database. In July 1990, a sperm whale was

entangled and subsequently released (injured) from a swordfish drift net near the continental shelf edge on southern

Georges Bank. 

Total annual estimated average fishery-related mortality and serious injury to this stock in the U.S. Atlantic

EEZ during 1989-1993 was 1.6 sperm whales (CV = 2.72). There is no information on incidental mortality in

fisheries in Canadian waters. Total fishery-related mortality and serious injury for this stock is greater than 10% of

the calculated PBR, based on limited survey data, and cannot be considered insignificant and approaching zero

mortality and serious injury rate. This determination cannot be made for specific fisheries until the implementing

regulations for Section 118 of the MMPA have been reviewed by the public and finalized. 

Fishery Information

The estimated total number of hauls in the Atlantic large pelagic drift gillnet fishery increased from 714 in

1989 to 1144 in 1990; thereafter, with the introduction of quotas, effort was severely reduced. The estimated number

of hauls in 1991, 1992, and 1993 were 233, 243, and 232 respectively. Fifty-nine vessels participated in this fishery

between 1989 and 1993. Observer coverage, percent of sets observed, ranged from 8% in 1989, 6% in 1990, 20% in

1991, to 40% in 1992 and 42% in 1993. The greatest concentrations of effort were located along the southern edge

of Georges Bank and off Cape Hatteras. Examination of the species composition of the catch and locations of the

fishery throughout the year, suggested that the drift gillnet fishery be stratified into two strata, a southern or winter

stratum, and a northern or summer stratum. One sperm whale was entangled in this fishery and released showing signs

of serious injury. Annual fishery-related mortality and serious injury was estimated using the aggregated catch rates,

by strata (Northridge, in review). Estimated annual fishery-related mortality and serious injury (CV in parentheses)

was 2.2 sperm whales in 1989 (2.43), 4.4 in 1990 (1.77), 0.5 in 1991 (1.49), 0.4 (1.44) in 1992, and 0.3 (1.37) in 1993.

STATUS OF STOCK

The status of this stock relative to OSP is unknown, but the species is listed as endangered under the ESA.

There are insufficient data to determine population trends. The current stock abundance estimate was based upon a

small portion of the known stock range within the U.S. EEZ. This is believed to be an underestimate and estimates

of stock size based on surveys of the entire range are expected to result in a higher calculated PBR. This is a strategic
27

stock because the species is listed as endangered under the ESA and estimated annual fishery-related mortality and

serious injury exceeds PBR

REFERENCES

Anon. 1994. Report of the PBR (Potential Biological Removal) workshop. June 27-29, 1994. NOAA, NMFS

Southwest Fisheries Science Center, La Jolla, California, 13 pp. + Appendices. 

Best, P. B. 1974. Biology of the sperm whale. Pages 53-81 in W. E. Schevill (editor), The whale problem: A status

report. Harvard University Press, Cambridge, Massachusetts, 419 pp. 

Best, P. B. 1979. Social organization in sperm whales, Physeter macrocephalus. Pages 227-289 in H. E. Winn and

B. L. Olla (editors), Behavior of marine animals, Vol. 3: Cetaceans. Plenum Press, New York. 

Buckland, S. T., D. R. Andersen, K. P. Burnham, and J. L. Laake. 1993. Distance sampling: Estimating abundance

of biological populations. Chapman and Hall, New York, 442 pp. 

CeTAP. 1982. A characterization of marine mammals and turtles in the mid- and north Atlantic areas of the U.S.

outer continental shelf. Cetacean and Turtle Assessment Program, University of Rhode Island. Final Report

#AA551-CT8-48 to the Bureau of Land Management, Washington, DC, 538 pp. 

Hain, J. H. W., M. A. M. Hyman, R. D. Kenney, and H. E. Winn. 1985. The role of cetaceans in the shelf-edge region

of the northeastern United States. Mar. Fish. Rev. 47(1): 13-17. 

Laake, J. L., S. T. Buckland, D. R. Anderson, and K. P. Burnham. DISTANCE user’s guide, V2.0. Colorado

Cooperative Fish & Wildlife Research Unit, Colorado State University, Ft. Collins, Colorado, 72 pp. 

Lockyer, C. 1981. Estimates of growth and energy budget for the sperm whale. Pages 491-504 in Mammals in the

seas, III. FAO Fish. Ser. No. 5. FAO, Rome, 504 pp. 

Mitchell, E. and V. M. Kozicki. 1984. Reproductive condition of male sperm whales, Physeter macrocephalus, taken

off Nova Scotia. Rep. Int. Whal. Commn. (Special Issue 6): 243-252. 

Northridge, S. In review. Estimation of cetacean mortality in the U.S. Atlantic swordfish and tuna driftnet and pair

trawl fisheries. Draft final report to the Northeast Fisheries Science Center, Contract No. 40ENNF500045,

18 pp. 

Schmidly, D. J. 1981. Marine mammals of the southeastern United States and the Gulf of Mexico. Department of

the Interior, U.S. Fish and Wildlife Service Publication FWS/OBS-80/41, Washington, DC, 166 pp. 

Waring, G. T., C. P. Fairfield, C. M. Ruhsam, and M. Sano. 1993. Sperm whales associated with Gulf Stream

features off the north-eastern USA shelf. Fish. Oceanogr. 2(2): 101-105

Watkins, W. A., K. E. Moore, and P. Tyack. 1985. Sperm whale acoustic behavior in the southeast Caribbean.

Cetology 49: 1-15. 
28

DWARF SPERM WHALE (Kogia simus): 

Western North Atlantic Stock

STOCK DEFINITION AND GEOGRAPHIC RANGE

The dwarf sperm whale (Kogia simus) and the pygmy sperm whale (K. breviceps) appear to be distributed

worldwide in temperate to tropical waters (Caldwell and Caldwell 1994). Sightings of these animals in the northern

Gulf of Mexico occur primarily along the continental shelf edge and over the deeper waters off the continental shelf

(Mullin et al. 1991; NMFS unpublished data). Pygmy sperm whales and dwarf sperm whales are difficult to

distinguish and sightings of either species are often categorized as Kogia spp. There is no information on stock

differentiation for the Atlantic population. 

POPULATION SIZE

Estimates of abundance were derived through the application of distance sampling analysis (Buckland et al.

1993) and the computer program DISTANCE (Laake et al. 1993) to sighting data collected during a 1992 winter,

visual sampling, line-transect vessel survey of the U.S. Atlantic Exclusive Economic Zone (EEZ) waters between

Miami, Florida, and Cape Hatteras, North Carolina. Abundance was estimated for both species combined because the

majority of sightings were not identified to species, and both species are known to occur in the area. The estimated

abundance of dwarf sperm whales and pygmy sperm whales combined for the 1992 surveys was 420 animals

(coefficient of variation, CV = 0.60) (Hansen et al. 1994). Dwarf sperm whale abundance cannot be estimated due to

uncertainty of species identification of sightings. 

Minimum Population Estimate

A minimum population size could not be estimated because of the uncertainty in species identification. 

Current Population Trend

No information was available evaluate trends in population size. 

CURRENT AND MAXIMUM NET PRODUCTIVITY RATES

Current and maximum net productivity rates are not known for this stock. 

POTENTIAL BIOLOGICAL REMOVAL

Potential biological removal level (PBR) was not calculated because the minimum population size cannot be

estimated. 

ANNUAL HUMAN-CAUSED MORTALITY AND SERIOUS INJURY

The level of past or current, direct, human-caused mortality of dwarf sperm whales in the U.S. Atlantic EEZ

is unknown. Available information indicates there is likely little, if any, fisheries interaction with dwarf sperm whales

in the U.S. Atlantic EEZ. It is not known whether total fishery-related mortality and serious injury for this stock is

less than 10% of PBR and can therefore be considered insignificant and approaching zero mortality and serious injury

rate, because PBR cannot be calculated. This determination cannot be made for specific fisheries until the

implementing regulations for Section 118 of the MMPA have been reviewed by the public and finalized. 

Fisheries Information

Current data sources include the Northeast Fisheries Science Center (NEFSC) Weigh Out Data Program and

Sea Sampling Observer Program initiated in 1989. In 1986, NMFS established a mandatory logbook system for large

pelagic fisheries. In late 1992 and in 1993 the SEFSC provided observer coverage of pelagic longline vessels fishing

off the Grand Banks (Tail of the Banks) and provides observer coverage of vessels fishing south of Cape Hatteras.

By-catch has been observed by NMFS Sea Samplers in the swordfish/tuna/shark drift gillnet fishery, but no

mortalities have been documented in the Atlantic swordfish/tuna/shark longline, Atlantic swordfish/tuna/shark pair

trawl, New England multispecies sink gillnet and Gulf of Maine groundfish trawl fisheries. 
29

 Fifty-nine different vessels participated in this fishery at one time or another between 1989 and 1993.

Observer coverage, expressed as percent of sets observed, ranged from 8% in 1989, 6% in 1990, 20% in 1991, to 40%

in 1992, and 42% in 1993. Effort was concentrated along the southern edge of Georges Bank and off Cape Hatteras.

Examination of the species composition of the catch and locations of the fishery throughout the year, suggested that

the drift gillnet fishery be stratified into two strata, a southern or winter stratum, and a northern or summer stratum.

There were no reports of mortality or serious injury to dwarf sperm whales attributable to this fishery.

There were no reports of incidental mortality or injury of dwarf sperm whales associated with the U.S. longline

swordfish/tuna fishery which has been monitored at approximately 5% coverage by NMFS observers since 1992.

However, other fisheries which operate in areas frequented by dwarf sperm whales were not monitored by observers.

There were no documented strandings of dwarf sperm whales along the U.S. Atlantic coast during 1987-

present which were classified as likely caused by fishery interactions. Stranding data probably underestimate the extent

of fishery-related mortality and serious injury because not all of the marine mammals which die or are seriously injured

may wash ashore, nor will all of those that do wash ashore necessarily show signs of entanglement or other fisheryinteraction. Finally, the level of technical expertise among stranding network personnel varies widely as does the

ability to recognize signs of fishery interaction.

Other Mortality

 At least 19 dwarf sperm whale strandings have been documented along the U.S. Atlantic coast between Cape

Hatteras, North Carolina, and Miami, Florida, during 1987-1994. Three of the stranded animals had plastic, or a

plastic bag or bags in their stomachs, and one of these three had possible propeller cuts on or near the flukes. 

STATUS OF STOCK

The status of this stock relative to OSP is unknown. This species is not listed as endangered or threatened

under the Endangered Species Act. There is insufficient information with which to assess population trends. Upon

the advice of the Atlantic Scientific Review Group this stock has been designated a strategic stock because PBR cannot

been determined and there is an unknown amount of possible human-caused mortality from the ingestion of marine

debris such as plastic bags and from possible boat strikes. 

REFERENCES

Buckland, S. T., D. R. Anderson, K. P. Burnham and J. L. Laake. 1993. Distance Sampling: estimating abundance

of biological populations. Chapman & Hall, London, 446 pp. 

Caldwell, D. K. and M. C. Caldwell 1989. Pygmy sperm whale Kogia breviceps (de Blainville, 1838): dwarf sperm

whale Kogia simus Owen, 1866. Pages 235-260 in S. H. Ridgway and R. Harrison, Handbook of marine

mammals, Vol. 4: river dolphins and the larger toothed whales. Academic Press, San Diego. 

Hansen, L. J., K. D. Mullin and C. L. Roden. 1994. Preliminary estimates of cetacean abundance in the northern Gulf

of Mexico from vessel surveys. Southeast Fisheries Science Center, Miami Laboratory, Contribution No. MIA93/94-58.

Laake, J. L., S. T. Buckland, D. R. Anderson, and K. P. Burnham. DISTANCE user’s guide, V2.0. Colorado

Cooperative Fish & Wildlife Research Unit, Colorado State University, Ft. Collins, Colorado, 72 pp. 

Mullin, K., W. Hoggard, C. Roden, R. Lohoefener, C. Rogers and B. Taggart. 1991. Cetaceans on the upper

continental slope in the north-central Gulf of Mexico. OCS Study/MMS 91-0027. U.S. Dept. of the Interior,

Minerals Management Service, Gulf of Mexico OCS Regional Office, New Orleans, Louisiana, 108 pp.
30

PYGMY SPERM WHALE (Kogia breviceps):

Western North Atlantic Stock

STOCK DEFINITION AND GEOGRAPHIC RANGE

The dwarf sperm whale (Kogia breviceps) and the pygmy sperm whale (K. simus) appear to be distributed

worldwide in temperate to tropical waters (Caldwell and Caldwell 1994). Sightings of these animals in the northern

Gulf of Mexico occur primarily along the continental shelf edge and over the deeper waters off the continental shelf

(Mullin et al. 1991; Southeast Fisheries Science Center unpublished data). Pygmy sperm whales and dwarf sperm

whales are difficult to distinguish and sightings of either species are often categorized as Kogia spp. There is no

information on stock differentiation for the Atlantic population. 

POPULATION SIZE

Estimates of abundance were derived through the application of distance sampling analysis (Buckland et al.

1993) and the computer program DISTANCE (Laake et al. 1993) to sighting data collected during a 1992 winter,

visual sampling, line-transect vessel survey of the U.S. Atlantic Exclusive Economic Zone (EEZ) waters between

Miami, Florida, and Cape Hatteras, North Carolina. Abundance was estimated for both species combined because the

majority of sightings were not identified to species, and both species are known to occur in the area. The estimated

abundance of dwarf sperm whales and pygmy sperm whales combined for the 1992 surveys was 420 animals

(coefficient of variation, CV = 0.60) (Hansen et al. 1994). Pygmy sperm whale abundance cannot be estimated due

to uncertainty of species identification of sightings. 

Minimum Population Estimate

A minimum population size could not be estimated because of the uncertainty in species identification. 

Current Population Trend

No information was available to evaluate trends in population size. 

CURRENT AND MAXIMUM NET PRODUCTIVITY RATES

Current and maximum net productivity rates are not known for this stock. 

POTENTIAL BIOLOGICAL REMOVAL

Potential biological removal level (PBR) was not calculated because the minimum population estimate cannot

be calculated. 

ANNUAL HUMAN-CAUSED MORTALITY AND SERIOUS INJURY

The level of past or current, direct, human-caused mortality of pygmy sperm whales in the U.S. Atlantic EEZ

is unknown. Available information indicates there is likely little, if any, fisheries interaction with pygmy sperm whales

in the U.S. Atlantic EEZ. 

There were no documented strandings of pygmy sperm whales along the U.S. Atlantic coast during 1987-

present which were classified as likely caused by fishery interactions. Stranding data probably underestimate the extent

of fishery-related mortality and serious injury because not all of the marine mammals which die or are seriously injured

may wash ashore, nor will all of those that do wash ashore necessarily show signs of entanglement or other fisheryinteraction. Finally, the level of technical expertise among stranding network personnel varies widely as does the

ability to recognize signs of fishery interaction.

It is not known whether total fishery-related mortality and serious injury for this stock is less than 10% of PBR

and can therefore be considered insignificant and approaching zero mortality and serious injury rate, because PBR

cannot be calculated. This determination cannot be made for specific fisheries until the implementing regulations for

Section 118 of the MMPA have been reviewed by the public and finalized. 
31

Fisheries Information

Current data sources include the Northeast Fisheries Science Center (NEFSC) Weighout Data Program and

Sea Sampling Observer Program initiated in 1989. In 1986, NMFS established a mandatory logbook system for large

pelagic fisheries. In late 1992 and in 1993, the SEFSC provided observer coverage of pelagic longline vessels fishing

off the Grand Banks (Tail of the Banks) and provides observer coverage of vessels fishing south of Cape Hatteras. 

By-catch has been observed by NMFS Sea Samplers in the swordfish/tuna/shark drift gillnet fishery, but no

mortalities have been documented in the Atlantic swordfish/tuna/shark longline, Atlantic swordfish/tuna/shark pair

trawl, New England multispecies sink gillnet and Gulf of Maine groundfish trawl fisheries. 

The estimated total number of hauls in the Atlantic large pelagic drift gillnet fishery increased from 714 in

1989 to 1,144 in 1990; thereafter, with the introduction of quotas, effort was severely reduced. The estimated number

of hauls in 1991, 1992, and 1993 were 233, 243, and 232 respectively. Fifty-nine different vessels participated in this

fishery at one time or another between 1989 and 1993. Observer coverage, expressed as percent of sets observed,

ranged from 8% in 1989, 6% in 1990, 20% in 1991, to 40% in 1992, and 42% in 1993. Effort was concentrated along

the southern edge of Georges Bank and off Cape Hatteras. Examination of the species composition of the catch and

locations of the fishery throughout the year, suggested that the drift gillnet fishery be stratified into two strata, a

southern or winter stratum, and a northern or summer stratum. There were no reports of fishery-related mortality or

serious injury to pygmy sperm whales attributable to this fishery.

There were no reports of incidental mortality or injury of pygmy sperm whales associated with the U.S.

swordfish/tuna longline fishery which has been monitored at approximately 5% coverage by NMFS observers since

1992. However, other fisheries which operate in areas frequented by pygmy sperm whales were not monitored by

observers. 

Other Mortality

At least 142 pygmy sperm whale strandings were documented along the U.S. Atlantic coast between Cape

Hatteras, North Carolina, and Miami, Florida, during 1987-1994. Two of the stranded animals had plastic, or a plastic

bag or bags in their stomachs, and one additional animal had possible propeller cuts on it's flukes. 

STATUS OF STOCK

The status of this stock relative to OSP is unknown. This species is not listed as endangered or threatened

under the Endangered Species Act. There is insufficient information with which to assess population trends. Upon

the advice of the Atlantic Scientific Review Group this stock has been designated a strategic stock because PBR cannot

been determined and there is an unknown amount of possible human-caused mortality from the ingestion of marine

debris such as plastic bags and from possible boat strikes. 

REFERENCES

Buckland, S. T., D. R. Anderson, K. P. Burnham and J. L. Laake. 1993. Distance Sampling: estimating abundance

of biological populations. Chapman & Hall, London, 446 pp. 

Caldwell, D. K. and M. C. Caldwell 1989. Pygmy sperm whale Kogia breviceps (de Blainville, 1838): dwarf sperm

whale Kogia simus Owen, 1866. Pages 235-260 in S. H. Ridgway and R. Harrison, Handbook of marine

mammals, Vol. 4: river dolphins and the larger toothed whales. Academic Press, San Diego. 

Hansen, L. J., K. D. Mullin and C. L. Roden. 1994. Preliminary estimates of cetacean abundance in the northern Gulf

of Mexico from vessel surveys. Southeast Fisheries Science Center, Miami Laboratory, Contribution No. MIA93/94-58.

Laake, J. L., S. T. Buckland, D. R. Anderson, and K. P. Burnham. DISTANCE user’s guide, V2.0. Colorado

Cooperative Fish & Wildlife Research Unit, Colorado State University, Ft. Collins, Colorado, 72 pp. 

Mullin, K., W. Hoggard, C. Roden, R. Lohoefener, C. Rogers and B. Taggart. 1991. Cetaceans on the upper

continental slope in the north-central Gulf of Mexico. OCS Study/MMS 91-0027. U.S. Dept. of the Interior,

Minerals Management Service, Gulf of Mexico OCS Regional Office, New Orleans, Louisiana, 108 pp. 
32

KILLER WHALE (Orcinus orca):

Western North Atlantic Stock

STOCK DEFINITION AND GEOGRAPHIC RANGE

Killer whales are characterized as uncommon or rare in waters of the U.S. Atlantic Exclusive Economic Zone

(EEZ) (Katona et al. 1988). The 12 killer whale sightings constituted 0.1% of the 11,156 cetacean sightings in the

1978-81 CeTAP surveys (CeTAP 1982). The same is true for eastern Canadian waters, where the species has been

described as relatively uncommon and numerically few (Mitchell and Reeves 1988). Their distribution, however,

extends from the Arctic ice-edge to the West Indies. They are normally found in small groups, although 40 animals

were reported from the southern Gulf of Maine in September 1979, and 29 animals in Massachusetts Bay in August

1986 (Katona et al. 1988). In the U.S. Atlantic EEZ, while their occurrence is unpredictable, they do occur in fishing

areas, perhaps coincident with tuna, in warm seasons (Katona et al. 1988; NMFS unpublished data). In an extensive

analysis of historical whaling records, Reeves and Mitchell (1988) plotted the distribution of killer whales in offshore

and mid-ocean areas. Their results suggest that the offshore areas need to be considered in present-day distribution,

movements, and stock relationships. 

Stock definition is unknown. Results from other areas (e.g., the Pacific Northwest and Norway) suggest that

social structure and territoriality may be important. 

POPULATION SIZE

The total number of killer whales off the eastern U.S. coast is unknown. 

Minimum Population Estimate

Present data are insufficient to calculate a minimum population estimate. 

Current Population Trend

There are insufficient data to determine the population trends for this species. 

CURRENT AND MAXIMUM NET PRODUCTIVITY RATES

Current and maximum net productivity rates are not known for this stock. The maximum net productivity

rate was assumed to be 0.04 for purposes of this assessment. This value is based on theoretical calculations showing

that cetacean populations may not generally grow at rates much greater than 4% given the constraints of their

reproductive life history (Anon. 1994). 

POTENTIAL BIOLOGICAL REMOVAL

No PBR can be estimated for this species at this time, because the minimum population size cannot be

determined. 

ANNUAL HUMAN-CAUSED MORTALITY

In 1994, one killer whale was caught in the Gulf of Maine sink gillnet fishery but released alive. No takes

were documented in a review of Canadian gillnet and trap fisheries (Read 1994). 

Fishery Information

In 1992, there were approximately 349 vessels (full and part time) in the New England multispecies gillnet

fishery (Walden, in review). Observer coverage in trips had been 1%, 6%, 7.5%, and 5% for the years 1990 to 1993.

The fishery has been observed in the Gulf of Maine and in southern New England. Though the data have not been

analyzed, the fishery in 1994 (the only year with by-catch) is probably similar to that in the past. 

Because there are no observed mortalities or serious injury between 1990 and 1993, the total fishery-related

mortality and serious injury for this stock is considered insignificant and approaching zero mortality and serious injury

rate. This determination cannot be made for specific fisheries until the implementing regulations for Section 118 of

the MMPA have been reviewed by the public and finalized. 
33

STATUS OF STOCK

The status of killer whales relative to OSP in U.S. Atlantic coast waters is unknown. The species is not listed

as threatened or endangered under the Endangered Species Act. In Canada, the Cetacean Protection Regulations of

1982, promulgated under the standing Fisheries Act, prohibit the catching or harassment of all cetacean species. There

are insufficient data to determine the population trends for this species. This is not a strategic stock because, although

PBR could not be calculated, there is no evidence of human-induced mortality. 

REFERENCES

Anon. 1994. Report of the PBR (Potential Biological Removal) workshop. June 27-29, 1994. NOAA, NMFS

Southwest Fisheries Science Center, La Jolla, CA, 13 pp. + Appendices. 

CeTAP. 1982. A characterization of marine mammals and turtles in the mid- and north Atlantic areas of the U.S.

outer continental shelf. Cetacean and Turtle Assessment Program, University of Rhode Island. Final Report

#AA551-CT8-48 to the Bureau of Land Management, Washington, DC, 538 pp. 

Katona, S. K., J. A. Beard, P. E. Girton, and F. Wenzel. 1988. Killer whales (Orcinus orca) from the Bay of Fundy

to the Equator, including the Gulf of Mexico. Rit. Fiskideild. 9: 205-224. 

Mitchell, E. and R. R. Reeves. 1988. Records of killer whales in the western North Atlantic, with emphasis on eastern

Canadian waters. Rit. Fiskideild. 9: 161-193. 

Read, A. J. 1994. Interactions between cetaceans and gillnet and trap fisheries in the Northwest Atlantic. Rep. Int.

Whal. Commn. Special Issue 15: 133-147.

Reeves, R. R. and E. Mitchell. 1988. Killer whale sightings and takes by American pelagic whalers in the North

Atlantic. Rit. Fiskideild. 9: 7-23

Walden, J. In review. Results of the Gulf of Maine gillnet survey 1989-92. NOAA, NMFS, NEFSC [Northeast

Fisheries Science Center] Ref. Doc., Woods Hole, Massachusetts. 
34

PYGMY KILLER WHALE (Feresa attenuata): 

Western North Atlantic Stock

STOCK DEFINITION AND GEOGRAPHIC RANGE

The pygmy killer whale is distributed worldwide in tropical and subtropical waters (Ross and

Leatherwood 1994). Sightings of these animals in the northern Gulf of Mexico occur primarily over the deeper

waters off the continental shelf (NMFS unpublished data). There is no information on stock differentiation for the

Atlantic population. 

POPULATION SIZE

A single sighting of this species was made during a 1992 winter, visual sampling, line-transect vessel

survey of the U.S. Atlantic Exclusive Economic Zone (EEZ) from Miami, Florida, to Cape Hatteras, North

Carolina (Hansen et al. 1994). This sighting, of a herd of six animals, was not made during visual sampling effort;

therefore, the sighting could not be used to estimate abundance of pygmy killer whales, but it does confirm the

presence of this species in the U.S. Atlantic EEZ. 

Minimum Population Estimate

The minimum population estimate based on the count of animals in the single sighting, was six pygmy

killer whales (Hansen et al. 1994). 

Current Population Trend

No information was available to evaluate trends in population size. 

CURRENT AND MAXIMUM NET PRODUCTIVITY RATES

Current and maximum net productivity rates are not known for this stock; therefore, the default maximum

net productivity rate of 0.04 (Anon. 1994) was used for purposes of this assessment. 

POTENTIAL BIOLOGICAL REMOVAL

Potential biological removal level (PBR) was specified as the product of the minimum population size, one

half the maximum net productivity rate, and a recovery factor for endangered, threatened, or depleted stocks, or

stocks of unknown status relative to optimum sustainable population (OSP) (Anon. 1994). The recovery factor was

set at 0.50 because the status of the stock relative to OSP is unknown. The resulting PBR for this stock is 0.1

pygmy killer whale. 

ANNUAL HUMAN-CAUSED MORTALITY AND SERIOUS INJURY

The level of past or current, direct, human-caused mortality of pygmy killer whales in the U.S. Atlantic

EEZ is unknown; however, there has historically been some take of this species in small cetacean fisheries in the

Caribbean (Caldwell and Caldwell 1971). Available information indicates there likely is little, if any, fisheries

interaction with pygmy killer whales in the U.S. Atlantic EEZ. There have been no logbook reports of fisheryrelated mortality or serious injury and no fishery-related mortality or serious injury has been observed.

There have been no documented strandings of pygmy killer whales in the along the U.S. Atlantic coast

during 1987-present which have been classified as likely caused by fishery interactions or other human-related

causes. Stranding data probably underestimate the extent of fishery-related mortality and serious injury because

not all of the dolphins which die or are seriously injured in fishery interactions wash ashore, nor will all of those

that do wash ashore necessarily show signs of entanglement or other fishery-interaction. Finally, the level of

technical expertise among stranding network personnel varies widely as does the ability to recognize signs of

fishery interaction. 

The total known fishery-related mortality and serious injury for this stock is less than 10% of the

calculated PBR and, therefore, can be considered insignificant and approaching zero mortality and serious injury

rate. This determination cannot be made for specific fisheries until the implementing regulations for Section 118

of the MMPA have been reviewed by the public and finalized. 
35

Fisheries Information

Current data sources include the Northeast Fisheries Science Center (NEFSC) Weighout Data Program

and Sea Sampling Observer Program initiated in 1989. In 1986, NMFS established a mandatory logbook system

for large pelagic fisheries. In late 1992 and in 1993, the SEFSC provided observer coverage of pelagic longline

vessels fishing off the Grand Banks (Tail of the Banks) and provides observer coverage of vessels fishing south of

Cape Hatteras. 

By-catch has been observed by NMFS Sea Samplers in the swordfish/tuna/shark drift gillnet fishery, but

no mortalities have been documented in the Atlantic swordfish/tuna/shark longline, Atlantic swordfish/tuna/shark

pair trawl, New England multispecies sink gillnet and Gulf of Maine groundfish trawl fisheries. 

The estimated total number of hauls in the Atlantic large pelagic drift gillnet fishery increased from 714

in 1989 to 1,144 in 1990; thereafter, with the introduction of quotas, effort was severely reduced. The estimated

number of hauls in 1991, 1992, and 1993 were 233, 243, and 232 respectively. Fifty-nine different vessels

participated in this fishery at one time or another between 1989 and 1993. Observer coverage, expressed as

percent of sets observed, ranged from 8% in 1989, 6% in 1990, 20% in 1991, to 40% in 1992, and 42% in 1993. 

Effort was concentrated along the southern edge of Georges Bank and off Cape Hatteras. Examination of the

species composition of the catch and locations of the fishery throughout the year, suggested that the drift gillnet

fishery be stratified into two strata, a southern or winter stratum, and a northern or summer stratum. There were

no reports of fishery-related mortality or serious injury to pygmy killer whales attributable to this fishery.

There have been no reports of incidental mortality or injury of pygmy killer whales associated with the

U.S. longline swordfish/tuna fishery which has been monitored at approximately 5% coverage by NMFS observers

since 1992; however, there may be other fisheries which operate in areas frequented by pygmy killer whales which

are not monitored by NMFS observers.

Other Mortality

 This stock may be subjected to human-induced mortality caused by habitat degradation (e.g., industrial

and agricultural pollution) and indirect effects of fisheries on prey. There have been, however, no studies to date

which have determined the amount, if any, of indirect human-induced mortality resulting from habitat degradation

or competition for prey. 

STATUS OF STOCK

The status of pygmy killer whales relative to OSP in U.S. Atlantic coast waters is unknown. The species

is not listed as threatened or endangered under the Endangered Species Act. There are insufficient data to

determine the population trends for this species. This is not a strategic stock because there is no known fisheryrelated mortality or serious injury.

REFERENCES

Anon. 1994. Report of the PBR (Potential Biological Removal) workshop. June 27-29, 1994. NOAA, NMFS

Southwest Fisheries Science Center, La Jolla, California, 13 pp. + Appendices. 

Caldwell, D. K. and M. C. Caldwell. 1971. The pygmy killer whale, Feresa attenuata, in the western Atlantic,

with a summary of world records. J. Mamm. 52:206-209. 

Hansen, L. J., K. D. Mullin and C. L. Roden. 1994. Preliminary estimates of cetacean abundance in the northern

Gulf of Mexico from vessel surveys, and of selected cetacean species in the U.S. Atlantic Exclusive

Economic Zone from vessel surveys from vessel surveys. Southeast Fisheries Science Center, Miami

Laboratory, Contribution No. MIA-93/94-58 

Ross, G. J. B. and S. Leatherwood. 1994. Pygmy killer whale Feresa attenuata (Gray, 1874). Pages 387-404 in S.

H. Ridgway and R. Harrison (editors), Handbook of marine mammals, Vol. 5: The first book of dolphins. 

Academic Press, San Diego, 418 pp. 
36

NORTHERN BOTTLENOSE WHALE (Hyperoodon ampullatus):

Western North Atlantic Stock

STOCK DEFINITION AND GEOGRAPHIC RANGE

Northern bottlenose whales are characterized as extremely uncommon or rare in waters of the U.S. Atlantic

Exclusive Economic Zone. The two sightings of three individuals constituted less than 0.1% of the 11,156 cetacean

sightings in the 1978-82 CeTAP surveys. Both sightings were in the spring, along the 2,000 m isobath (CeTAP 1982).

Northern bottlenose whales are distributed in the North Atlantic from Nova Scotia to about 70E in the Davis

Strait, along the east coast of Greenland to 77E and from England to the west coast of Spitzbergen. It is largely a deepwater species and is very seldom found in waters less than 2,000 m deep (reviewed by Mead 1989). 

There are two main centers of bottlenose whale distribution in the western north Atlantic, one in the area

called "The Gully" just north of Sable Island, Nova Scotia, and the other in Davis Strait off northern Labrador. Studies

at the entrance to the Gully from 1988-1991 identified 208 individuals and estimated the local population size at a few

hundred individuals (Faucher et al. 1991). Mitchell and Kozicki (1975) documented stranding records in the Bay

of Fundy and as far south as Rhode Island. Stock definition is unknown. 

POPULATION SIZE

The total number of northern bottlenose whales off the eastern U.S. coast is unknown. 

Minimum Population Estimate

Present data are insufficient to calculate a minimum population estimate. 

Current Population Trend

There are insufficient data to determine the population trends for this species. 

CURRENT AND MAXIMUM NET PRODUCTIVITY RATES

Current and maximum net productivity rates are not known for this stock. The maximum net productivity

rate was assumed to be 0.04 for purposes of this assessment. This value is based on theoretical calculations showing

that cetacean populations may not generally grow at rates much greater than 4% given the constraints of their

reproductive life history (Anon. 1994). 

POTENTIAL BIOLOGICAL REMOVAL

No PBR can be estimated for this species at this time, because the minimum population size cannot be

determined. 

ANNUAL HUMAN-CAUSED MORTALITY

No mortalities have been reported in U.S. waters. A fishery for northern bottlenose whales existed in

Canadian waters during both the 1800s and 1900s. Its development was due to the discovery that bottlenose whales

contained spermaceti. A Norwegian fishery expanded from east to west (Labrador and Newfoundland) in several

episodes. The fishery peaked in 1965. Decreasing catches led to the cessation of the fishery in the 1970s, and provided

evidence that the population was depleted. A small fishery operated by Canadian whalers from Nova Scotia operated

in the Gully, and took 87 animals from 1962-1967 (Mead 1989; Mitchell 1977). 

Fishery Information

Because there are no observed mortalities or serious injury, no fishery information is presented. The total

fishery-related mortality and serious injury for this stock is considered insignificant and approaching zero mortality

and serious injury rate. This determination cannot be made for specific fisheries until the implementing regulations

for Section 118 of the MMPA have been reviewed by the public and finalized. 
37

STATUS OF STOCK

The status of northern bottlenose whales relative to OSP in U.S. Atlantic coast waters is unknown; however,

a depletion in Canadian waters in the 1970s may have impacted U.S. distribution and may be relevant to current status

in U.S. waters. The species is not listed as threatened or endangered under the Endangered Species Act. In Canada,

the Cetacean Protection Regulations of 1982, promulgated under the standing Fisheries Act, prohibit the catching or

harassment of all cetacean species. There are insufficient data to determine the population trends for this species. This

is not a strategic stock because there are no recent records of fishery-related mortality or serious injury. 

REFERENCES

Anon. 1994. Report of the PBR (Potential Biological Removal) workshop. June 27-29, 1994. NOAA, NMFS

Southwest Fisheries Science Center, La Jolla, California, 13 pp. + Appendices. 

CeTAP. 1982. A characterization of marine mammals and turtles in the mid- and north Atlantic areas of the U.S.

outer continental shelf. Cetacean and Turtle Assessment Program, University of Rhode Island. Final Report

#AA551-CT8-48 to the Bureau of Land Management, Washington, DC, 538 pp. 

Faucher, A. and H. Whitehead. 1991. Population biology, social structure, and movements of northern bottlenose

whales (Hyperoodon ampullatus) in the Gully, Nova Scotia. Paper presented at Ninth Biennial conference

on the Biology of Marine Mammals, 5-9 December 1991, Chicago, Illinois.

Mead, J. G. 1989. Bottlenose whales. Pages 321-348 in S. H. Ridgway and R. Harrison (editors), Handbook of

marine mammals, Volume 4: River dolphins and the larger toothed whales,. Academic Press, New York. 

Mitchell, E. D. 1977. Evidence that the northern bottlenose whale is depleted. Rep. Int. Whal. Commn. 27: 195-203.

Mitchell, E. D. and V. M. Kozicki. 1975. Autumn stranding of a northern bottlenose whale (Hyperoodon ampullatus)

in the Bay of Fundy. J. Fish. Res. Bd. Can. 32: 1019-1040.
38

Figure 1. Distribution of beaked whale sightings from NEFSC

shipboard surveys during the summer in 1990-1994. Isobaths

are at 100 m and 1,000 m. 

CUVIER'S BEAKED WHALE (Ziphius cavirostris):

Western North Atlantic Stock

STOCK DEFINITION AND GEOGRAPHIC RANGE

The distribution of Cuvier's beaked whales is

poorly known, and is based mainly on stranding records

(Leatherwood et al. 1976). Strandings have been

reported from Nova Scotia along the eastern U.S. coast

south to Florida, around the Gulf of Mexico, and within

the Caribbean (Leatherwood et al. 1976; CeTAP 1982;

Heyning 1989; Houston 1990). Stock structure in the

western North Atlantic is unknown. 

Cuvier's beaked whale sightings have occurred

principally along the continental shelf edge in the midAtlantic region off the northeast U.S. coast (CeTAP

1982; NMFS unpublished data). Most sightings were in

late spring or summer. Based on sighting data, this

species is a rare inhabitant of waters off the northeast

U.S. coast (CeTAP 1982). 

POPULATION SIZE

The total number of Cuvier's beaked whales off

the eastern U.S. coast is unknown. Seasonal abundance

estimates reported in CeTAP (1982) are based on

"probable" sightings; therefore, population size could

not be estimated. 

Minimum Population Estimate

Present data are insufficient to calculate a

minimum population estimate. 

Current Population Trend

There are insufficient data to determine the population trends for this species. 

CURRENT AND MAXIMUM NET PRODUCTIVITY RATES

Current and maximum net productivity rates are not known for this stock. The maximum net productivity

rate was assumed to be 0.04 for purposes of this assessment. This value is based on theoretical calculations showing

that cetacean populations may not generally grow at rates much greater than 4% given the constraints of their

reproductive life history (Anon. 1994). 

Some of the life history parameters which have been estimated include: length at birth is 2 to 3 m, length at

sexual maturity 6.1 m for females, and 5.5 m for males, maximum age for females were 30 growth layer groups

(GLG's) and for males was 36 GLG's, which may be annual layers (Mitchell 1975; Mead 1984; Houston 1990). 

POTENTIAL BIOLOGICAL REMOVAL

No PBR can be estimated for this species at this time, because the minimum population size cannot be

determined. 

ANNUAL HUMAN-CAUSED MORTALITY AND SERIOUS INJURY

Beaked whales (many unidentified as to species) have been killed in the pelagic drift gillnet fishery off the

U.S. Atlantic coast. While there are no reported takes in other continental shelf edge fisheries (i.e., pelagic pair trawl,
39

longline), observer coverage in these fisheries is low and because beaked whales occupy this habitat, unreported takes

may have occurred. 

 Total fishery-related mortality and serious injury cannot be estimated separately for each beaked whale

species because of the uncertainty in species identification by fishery observers. The Atlantic Scientific Review Group

advised adopting the risk-averse strategy of assuming that any beaked whale stock which occurred in the U.S. Atlantic

Exclusive Economic Zone (EEZ) might have been subject to the observed fishery-related mortality and serious injury.

Twenty-two fishery-related beaked whale mortalities were observed between 1989 and 1993. The 1989-1993 total

average estimated annual fishery-related mortality of beaked whales in the U.S. EEZ was 34 (CV = 0.69). Although

PBR cannot be determined, the total fishery-related mortality and serious injury for this stock is not considered to be

insignificant and approaching zero mortality and serious injury rate. This determination cannot be made for specific

fisheries until the implementing regulations for Section 118 of the MMPA have been reviewed by the public and

finalized. 

Fisheries Information

There is no historical information available that documents incidental mortality in either U.S. or Canadian

Atlantic coast fisheries. 

Current data sources include the Northeast Fisheries Science Center (NEFSC) Weigh Out Data Program and

Sea Sampling Observer Program initiated in 1989. In 1986, NMFS established a mandatory logbook system for large

pelagic fisheries. These logbooks are maintained at Southeast Fisheries Science Center (SEFSC). In late 1992 and

in 1993 the SEFSC provided observer coverage of pelagic longline vessels fishing off the Grand Banks (Tail of the

Banks) and currently provides observer coverage of vessels fishing south of Cape Hatteras. Total fishery-related

mortality and serious injury cannot be estimated separately for each beaked whale species because of the uncertainty

in species identification by fishery observers. The Atlantic Scientific Review Group advised adopting the risk-averse

strategy of assuming that any beaked whale stock which occurred in the U.S. Atlantic EEZ might have been subject

to the observed fishery-related mortality and serious injury.

By-catch has been observed by NMFS Sea Samplers in the swordfish/tuna/shark drift gillnet fishery, but no

mortalities have been documented in the Atlantic swordfish/tuna/shark longline, Atlantic swordfish/tuna/shark pair

trawl, New England multispecies sink gillnet, or New England groundfish trawl observed fisheries. 

The estimated total number of hauls in the Atlantic large pelagic drift gillnet fishery increased from 714 in

1989 to 1,144 in 1990; thereafter, with the introduction of quotas, effort was severely reduced. The estimated number

of hauls in 1991, 1992, and 1993 were 233, 243, and 232 respectively. Fifty-nine different vessels participated in this

fishery at one time or another between 1989 and 1993. Observer coverage, expressed as percent of sets observed,

ranged from 8% in 1989, 6% in 1990, 20% in 1991, to 40% in 1992, and 42% in 1993. Effort was concentrated along

the southern edge of Georges Bank and off Cape Hatteras. Examination of the species composition of the catch and

locations of the fishery throughout the year, suggested that the drift gillnet fishery be stratified into two strata, a

southern or winter stratum, and a northern or summer stratum. Estimates of the total by-catch, for each year, were

obtained using the aggregated (pooled 1989-1993) catch rates, by strata (Northridge, in review). By-catch of beaked

whales has only occurred from Georges Canyon to Hydrographer Canyon along the continental shelf break and

continental slope during July to October. Twenty-two fishery-related beaked whale mortalities were observed between

1989 and 1993. The estimated annual fishery-related mortality (CV in parentheses) was 60 in 1989 (0.49), 76 in 1990

(0.56), 13 in 1991 (0.57), 9.7 in 1992 (0.53), and 12 in 1993 (0.32).

STATUS OF STOCK

The status of Cuvier's beaked whale relative to OSP in U.S. Atlantic coast waters is unknown. This species

is not listed as threatened or endangered under the Endangered Species Act. In Canada, the Cetacean Protection

Regulations of 1982, promulgated under the Standing Fisheries Act, prohibit the catching or harassment of all cetacean

species. There are insufficient data to determine population trends and the level of human-caused mortality and serious

injury is unknown because of uncertainty regarding species identification in observed fisheries. If one were to assume

that the incidental fisheries mortality of the four Mesoplodon spp. and Z. cavirostris was random with respect to species

(i.e., in proportion to their relative abundance), then the minimum population estimate for all of those stocks would

need to sum to at least 3,400 in order for an annual mortality of 34 animals not to exceed the PBR of any one of these

species. Because an assumption of unselective incidental fishing mortality is probably overly optimistic and represents
40

a best case situation, it is likely that a combined minimum population estimate of substantially greater than 3,400

would be necessary for an annual mortality of 34 to not exceed the PBR of any one of these five stocks. The largest

recent abundance estimate available for beaked whales in the western North Atlantic was 612 (CV = 0.73), which

would result in a minimum population estimate of 353 beaked whales; however, this estimate does not include a

correction factor for submerged animals which may be substantial. This is a strategic stock because of uncertainty

regarding stock size and evidence of fishery-related mortality and serious injury. 

 

REFERENCES

Anon. 1994. Report of the PBR (Potential Biological Removal) workshop. June 27-29, 1994. NOAA, NMFS

Southwest Fisheries Science Center, La Jolla, California, 13 pp. + Appendices. 

CeTAP. 1982. A characterization of marine mammals and turtles in the mid- and north Atlantic areas of the U.S.

outer continental shelf. Cetacean and Turtle Assessment Program, University of Rhode Island. Final Report

#AA551-CT8-48 to the Bureau of Land Management, Washington, DC, 538 pp. 

Heyning, J. E. 1989. Cuvier's beaked whale, Ziphius cavirostris G. Cuvier, 1823. Pages 289-308 in S. H. Ridgway

and R. Harrison (editors), Handbook of Marine Mammals, Vol. 4: River dolphins and larger toothed whales.

Academic Press, London, 442 pp. 

Houston, J. 1990. Status of Cuvier's Beaked Whale, Ziphius cavirostris, in Canada. Can. Fld. Nat. 105(2): 215-218.

Leatherwood, S., D. K. Caldwell and H. E. Winn. 1976. Whales, dolphins, and porpoises of the western North

Atlantic. A guide to their identification. U.S. Dept. of Commerce, NOAA Tech. Rep. NMFS Circ. 396, 176

pp. 

Mead, J. G. 1984. Survey of reproductive data for the beaked whales (Ziphiidae). Rep. Int. Whal. Commn. (Special

Issue 6): 91-96. 

Mitchell, E. D. (editor). 1975. Review of the biology and fisheries for smaller cetaceans. Report of the meeting on

smaller cetaceans. Int. Whal. Commn. J. Fish. Res. Bd. Can. 32(7): 875-1240.

Northridge, S. In review. Estimation of cetacean mortality in the U.S. Atlantic swordfish and tuna driftnet and pair

trawl fisheries. Draft final report to the Northeast Fisheries Science Center, Contract No. 40ENNF500045,

18 pp. 

Read, A. J. 1994. Interactions between cetaceans and gillnet and trap fisheries in the Northwest Atlantic. Rep. Int.

Whal. Commn. Special Issue 15: 133-147.
41

Figure 1. Distribution of beaked whale sightings from NEFSC

shipboard surveys during the summer in 1990-1994. Isobaths

are at 100 m and 1,000 m. 

TRUE'S BEAKED WHALE (Mesoplodon mirus):

Western North Atlantic Stock

STOCK DEFINITION AND GEOGRAPHIC RANGE

Within the genus Mesoplodon, there are four

species of beaked whales in the northwest Atlantic. These

include True's beaked whale, Mesoplodon mirus;

Gervais' beaked whale, M. europaeus; Blainville's

beaked whale, M. densirostris; and Sowerby's beaked

whale, M. bidens. These species are difficult to identify

to the species level at sea; therefore, much of the

available characterization for beaked whales is to genus

level only. 

The distribution of Mesoplodon spp. in the

northwest Atlantic is known principally from stranding

records (Mead 1989). Off the northeast U.S. coast,

beaked whale (Mesoplodon spp.) sightings have

occurred principally along the southern edge of Georges

Bank (CeTAP, 1982; NMFS unpublished data). Most

sightings were in late spring and summer. In addition,

beaked whales were also sighted in Gulf Stream features

during NEFSC 1990-1994 surveys (NMFS unpublished

data). 

True's beaked whale is a temperate-water

species that has been reported from Cape Breton Island,

Nova Scotia, to the Bahamas (Leatherwood et al. 1976,

Mead 1989). It is considered rare in Canadian waters

(Houston 1989). 

POPULATION SIZE

Population size can presently be described only for undifferentiated Mesoplodon spp. The total number of

beaked whales (Mesoplodon spp.) along the eastern U.S. or Canadian coasts is unknown, though several estimates from

select regions of the habitat do exist. Seasonal abundance estimates are available from an aerial line transect survey

program conducted in the continental shelf waters between Cape Hatteras, North Carolina, and Nova Scotia from 1978

to 1982 (CeTAP 1982), just after cessation of extensive foreign fishing operations in this region. An abundance

estimate based on CeTAP summer data is 120 (CV = 0.71). This estimate was not corrected for g(0), the probability

of detecting an animal group on the trackline. 

Abundance estimates were also derived using data collected during an autumn 1991 aerial survey in the

CeTAP study area (NMFS unpublished data), which included an interplatform experiment between a Twin Otter and

an AT-11), and from several fine-scale ship line transect surveys (August 1990, June-July 1991, June-July 1993, and

August 1994) conducted in continental shelf edge and deeper oceanic waters (NMFS unpublished data). The data were

analyzed using DISTANCE (Buckland et al. 1993; Laake et al. 1993) where the CV was estimated using the bootstrap

lognormal method. For the aerial and shipboard surveys, sightings were almost exclusively in the continental shelf

edge and continental slope water areas. Abundance estimates from the 1991 aerial survey were 612 (CV = 0.73) and

370 (CV = 0.65), respectively, for the AT-11 and Twin Otter. Data were not pooled, because the interplatform

calibration analysis has not been conducted. Furthermore, these estimates are not fully comparable to the CeTAP

estimates, because the 1991 data are from a single survey, August to October, while the CeTAP estimates were based

on data pooled over several years of seasonal surveys. 

An abundance estimate from the August 1990 shipboard survey, conducted principally along the Gulf Stream

north wall between Cape Hatteras and Georges Bank, was 442 (CV = 0.51). The 1991 survey estimate, based
42

principally on sighting effort conducted between the 200 and 2,000 meter isobaths from Cape Hatteras to Georges Bank

is 262 beaked whales (CV = 0.99). The estimate for the 1993 survey, conducted principally between the 200 and 2,000

meter isobaths from the southern edge of Georges Bank, across the Northeast Channel to the southwestern edge of the

Scotian Shelf was 330 beaked whales (CV = 0.66). The 1994 estimate, based on survey effort within a Gulf Stream

warm-core ring located in continental slope waters southeast of Georges Bank was 99 beaked whales (CV = 0.64).

Because the number of beaked whale sightings in each survey were extremely low (3 to 10), and their sightability and

behavior preclude pooling with other cetaceans, the abundance estimates are based on small sample sizes. Therefore,

the above abundance estimates should be viewed with caution. 

Although the 1990-1994 surveys did not sample exactly the same areas or encompass the entire beaked whale

habitat, they did focus on segments of known or suspected high-use habitats off the northeastern U.S. coast. The

collective 1990-94 data suggest that, seasonally, at least several hundred beaked whales are occupying these waters,

highest levels of abundance in the Georges Bank region. This is consistent with the earlier CeTAP results. Recent

results suggest that beaked whale abundance may be highest in association with Gulf Stream and warm-core ring

features. However, at present there are no estimates of total abundance for beaked whales in the western North

Atlantic. 

Because the estimates presented here were not dive-time corrected, they are likely negatively biased and

probably underestimate actual abundance. Given that Mesoplodon spp. prefers deep-water habitats (Mead 1989) the

bias may be substantial. 

Minimum Population Estimate

Present data are insufficient to calculate a minimum population estimate. 

Current Population Trend

There are insufficient data to determine the population trends for this species. 

CURRENT AND MAXIMUM NET PRODUCTIVITY RATES

Current and maximum net productivity rates are not known for this stock. The maximum net productivity

rate was assumed to be 0.04 for purposes of this assessment. This value is based on theoretical calculations showing

that cetacean populations may not generally grow at rates much greater than 4% given the constraints of their

reproductive life history (Anon. 1994). 

POTENTIAL BIOLOGICAL REMOVAL

No PBR can be estimated for this species at this time, because the minimum population size cannot be

determined. 

ANNUAL HUMAN-CAUSED MORTALITY AND SERIOUS INJURY

Beaked whales (many unidentified as to species) have been killed in the pelagic drift gillnet fishery off the

U.S. Atlantic coast. While there are no reported takes in other continental shelf edge fisheries (i.e., pelagic pair trawl,

longline), observer coverage in these fisheries is low and because beaked whales occupy this habitat, unreported takes

may have occurred. 

 Total fishery-related mortality and serious injury cannot be estimated separately for each beaked whale

species because of the uncertainty in species identification by fishery observers. The Atlantic Scientific Review Group

advised adopting the risk-averse strategy of assuming that any beaked whale stock which occurred in the U.S. Atlantic

Exclusive Economic Zone (EEZ) might have been subject to the observed fishery-related mortality and serious injury.

Twenty-two fishery-related beaked whale mortalities were observed between 1989 and 1993. The 1989-1993 total

average estimated annual fishery-related mortality of beaked whales in the U.S. EEZ was 34 (CV = 0.69). Although

PBR cannot be determined, the total fishery-related mortality and serious injury for this stock is not considered to be

insignificant and approaching zero mortality and serious injury rate. This determination cannot be made for specific

fisheries until the implementing regulations for Section 118 of the MMPA have been reviewed by the public and

finalized. 
43

Fisheries Information

There is no historical information available that documents incidental mortality in either U.S. or Canadian

Atlantic coast fisheries (Read 1994). 

Current data sources include the Northeast Fisheries Science Center (NEFSC) Weigh Out Data Program and

Sea Sampling Observer Program initiated in 1989. In 1986, NMFS established a mandatory logbook system for large

pelagic fisheries. These logbooks are maintained at Southeast Fisheries Science Center (SEFSC). In late 1992 and

in 1993 the SEFSC provided observer coverage of pelagic longline vessels fishing off the Grand Banks (Tail of the

Banks) and currently provides observer coverage of vessels fishing south of Cape Hatteras. Total fishery-related

mortality and serious injury cannot be estimated separately for each beaked whale species because of the uncertainty

in species identification by fishery observers. The Atlantic Scientific Review Group advised adopting the risk-averse

strategy of assuming that any beaked whale stock which occurred in the U.S. Atlantic EEZ might have been subject

to the observed fishery-related mortality and serious injury.

By-catch has been observed by NMFS Sea Samplers in the swordfish/tuna/shark drift gillnet fishery, but no

mortalities have been documented in the Atlantic swordfish/tuna/shark longline, Atlantic swordfish/tuna/shark pair

trawl, New England multispecies sink gillnet, or New England groundfish trawl observed fisheries. 

The estimated total number of hauls in the Atlantic large pelagic drift gillnet fishery increased from 714 in

1989 to 1,144 in 1990; thereafter, with the introduction of quotas, effort was severely reduced. The estimated number

of hauls in 1991, 1992, and 1993 were 233, 243, and 232 respectively. Fifty-nine different vessels participated in this

fishery at one time or another between 1989 and 1993. Observer coverage, expressed as percent of sets observed,

ranged from 8% in 1989, 6% in 1990, 20% in 1991, to 40% in 1992, and 42% in 1993. Effort was concentrated along

the southern edge of Georges Bank and off Cape Hatteras. Examination of the species composition of the catch and

locations of the fishery throughout the year, suggested that the drift gillnet fishery be stratified into two strata, a

southern or winter stratum, and a northern or summer stratum. Estimates of the total by-catch, for each year, were

obtained using the aggregated (pooled 1989-1993) catch rates, by strata (Northridge, in review). By-catch of beaked

whales has only occurred from Georges Canyon to Hydrographer Canyon along the continental shelf break and

continental slope during July to October. Twenty-two fishery-related beaked whale mortalities were observed between

1989 and 1993. The estimated annual fishery-related mortality (CV in parentheses) was 60 in 1989 (0.49), 76 in 1990

(0.56), 13 in 1991 (0.57), 9.7 in 1992 (0.53), and 12 in 1993 (0.32). The 1989-1993 average estimated annual fisheryrelated mortality of beaked whales was 34 (CV = 0.69).

STATUS OF STOCK

The status of True's beaked whale relative to OSP in U.S. Atlantic coast waters is unknown. This species is

not listed as threatened or endangered under the Endangered Species Act. In Canada, the Cetacean Protection

Regulations of 1982, promulgated under the Standing Fisheries Act, prohibit the catching or harassment of all cetacean

species. There are insufficient data to determine population trends and the level of human-caused mortality and serious

injury is unknown because of uncertainty regarding species identification in observed fisheries. If one were to assume

that the incidental fisheries mortality of the four Mesoplodon spp. and Z. cavirostris was random with respect to species

(i.e., in proportion to their relative abundance), then the minimum population estimate for all of those stocks would

need to sum to at least 3,400 in order for an annual mortality of 34 animals not to exceed the PBR of any one of these

species. Because an assumption of unselective incidental fishing mortality is probably overly optimistic and represents

a best case situation, it is likely that a combined minimum population estimate of substantially greater than 3,400

would be necessary for an annual mortality of 34 to not exceed the PBR of any one of these five stocks. The largest

recent abundance estimate available for beaked whales in the western North Atlantic was 612 (CV = 0.73), which

would result in a minimum population estimate of 353 beaked whales; however, this estimate does not include a

correction factor for submerged animals which may be substantial. This is a strategic stock because of uncertainty

regarding stock size and evidence of fishery-related mortality and serious injury. 

REFERENCES
44

Anon. 1994. Report of the PBR (Potential Biological Removal) workshop. June 27-29, 1994. NOAA, NMFS

Southwest Fisheries Science Center, La Jolla, California, 13 pp. + Appendices. 

Buckland, S. T., D. R. Andersen, K. P. Burnham, and J. L. Laake. 1993. Distance sampling: Estimating abundance

of biological populations. Chapman and Hall, New York, 446 pp. 

CeTAP. 1982. A characterization of marine mammals and turtles in the mid- and north Atlantic areas of the U.S.

outer continental shelf. Cetacean and Turtle Assessment Program, University of Rhode Island. Final Report

#AA551-CT8-48 to the Bureau of Land Management, Washington, DC, 538 pp. 

Houston, J. 1989. Status of True's Beaked Whale, Mesoplodon mirus, in Canada. Can. Fld. Nat. 104(1): 135-137.

Laake, J. L., S. T. Buckland, D. R. Anderson, and K. P. Burnham. DISTANCE user’s guide, V2.0. Colorado

Cooperative Fish & Wildlife Research Unit, Colorado State University, Ft. Collins, Colorado, 72 pp. 

Leatherwood, S., D. K. Caldwell and H. E. Winn. 1976. Whales, dolphins, and porpoises of the western North

Atlantic. A guide to their identification. U.S. Dept. of Commerce, NOAA Tech. Rep. NMFS Circ. 396, 176

pp. 

Mead, J. G. 1989. Beaked whales of the genus Mesoplodon. Pages 349-430 in S. H., Ridgway and R. Harrison

(editors), Handbook of marine mammals, Vol. 4: River Dolphins and toothed whales. Academic press, San

Diego, 442 pp. 

Northridge, S. In review. Estimation of cetacean mortality in the U.S. Atlantic swordfish and tuna driftnet and pair

trawl fisheries. Draft final report to the Northeast Fisheries Science Center, Contract No. 40ENNF500045,

18 pp. 

Read, A. J. 1994. Interactions between cetaceans and gillnet and trap fisheries in the Northwest Atlantic. Rep. Int.

Whal. Commn. Special Issue 15: 133-147.
45

Figure 1. Distribution of beaked whale sightings from NEFSC

shipboard surveys during the summer in 1990-1994. Isobaths

are at 100 m and 1,000 m. 

GERVAIS' BEAKED WHALE (Mesoplodon europaeus):

Western North Atlantic Stock

STOCK DEFINITION AND GEOGRAPHIC RANGE

Within the genus Mesoplodon, there are four

species of beaked whales in the northwest Atlantic.

These include Gervais' beaked whale, Mesoplodon

europaeus; True's beaked whale, M. mirus; Blainville's

beaked whale, M. densirostris; and Sowerby's beaked

whale, M. bidens. These species are difficult to identify

to the species level at sea; therefore, much of the

available characterization for beaked whales is to genus

level only. 

The distribution of Mesoplodon spp. in the

northwest Atlantic is known principally from stranding

records (Mead 1989). Off the northeast U.S. coast,

beaked whale (Mesoplodon spp.) sightings have

occurred principally along the southern edge of Georges

Bank (CeTAP 1982; NMFS unpublished data). Most

sightings were in late spring and summer. In addition,

beaked whales were also sighted in Gulf Stream features

during NEFSC 1990-1994 surveys (NMFS unpublished

data). 

Gervais's beaked whales are believed to be

principally oceanic, and strandings have been reported

from the mid-Atlantic Bight to Florida, into the

Caribbean and the Gulf of Mexico (Leatherwood et al.

1976; Mead 1989). This is the commonest species of

Mesoplodon stranded along the U.S. Atlantic coast.

The northernmost stranding was off New York (Mead

1989). 

POPULATION SIZE

Population size can presently be described only for undifferentiated Mesoplodon spp. The total number of

beaked whales (Mesoplodon spp.) along the eastern U.S. or Canadian coasts are unknown, though several estimates

from select regions of the habitat do exist. Seasonal abundance estimates are available from an aerial line transect

survey program conducted in the continental shelf waters between Cape Hatteras, North Carolina, and Nova Scotia

from 1978 to 1982 (CeTAP 1982), just after cessation of extensive foreign fishing operations in this region. An

abundance estimate based on CeTAP summer data is 120 (CV = 0.71). This estimate was not corrected for g(0), the

probability of detecting an animal group on the trackline. 

Abundance estimates were also derived using data collected during an autumn 1991 aerial line transect survey

in the CeTAP study area (NMFS unpublished data), which included an interplatform experiment between a Twin Otter

and an AT-11), and from several fine-scale ship line transect surveys (August 1990, June-July 1991, June-July 1993,

and August 1994) conducted in continental shelf edge and deeper oceanic waters (NMFS unpublished data). For the

aerial and shipboard surveys, sightings were almost exclusively in the continental shelf edge and continental slope

water areas. The data were analyzed using DISTANCE (Buckland et al. 1993; Laake et al. 1993) where the CV was

estimated using the bootstrap lognormal method. Abundance estimates from the 1991 aerial survey were 612 (CV =

0.73) and 370 (CV = 0.65), respectively, for the AT-11 and Twin Otter. Data were not pooled, because the

interplatform calibration analysis has not been conducted. Furthermore, these estimates are not fully comparable to

the CeTAP estimates, because the 1991 data are from a single survey, August to October, while the CeTAP estimates

were based on data pooled over several years of seasonal surveys. 
46

An abundance estimate from the August 1990 survey, conducted principally along the Gulf Stream north wall

between Cape Hatteras and Georges Bank, was 442 (CV = 0.51). The 1991 survey estimate, based principally on

sighting effort conducted between the 200 and 2,000 meter isobaths from Cape Hatteras to Georges Bank was 262

beaked whales (CV = 0.99). The estimate for the 1993 survey, conducted principally between the 200 and 2,000 meter

isobaths from the southern edge of Georges Bank, across the Northeast Channel to the southwestern edge of the Scotian

Shelf was 330 beaked whales (CV = 0.66). The 1994 estimate, based on survey effort within a Gulf Stream warm-core

ring located in continental slope waters southeast of Georges Bank was 99 beaked whales (CV = 0.64). Because the

number of beaked whale sightings in each survey were extremely low (3 to 10), and their sightability and behavior

preclude pooling with other cetaceans, the estimates of abundance are based on small sample sizes. Therefore, the

above abundance estimates should be viewed with caution. 

Although the 1990-1994 surveys did not sample exactly the same areas or encompass the entire beaked whale

habitat, they did focus on segments of known or suspected high-use habitats off the northeastern U.S. coast. The

collective 1990-94 data suggest that, seasonally, at least several hundred beaked whales are occupying these waters,

with highest levels of abundance in the Georges Bank region. This is consistent with the earlier CeTAP results.

Recent results suggest that beaked whale abundance may be highest in association with Gulf Stream and warm-core

ring features. However, at present there are no estimates of total abundance for beaked whales in the western North

Atlantic. 

Because the estimates presented here were not dive-time corrected, they are likely negatively biased and

probably underestimate actual abundance. Given that Mesoplodon spp. prefers deep-water habitats (Mead 1989) the

bias may be substantial. 

Minimum Population Estimate

Present data are insufficient to calculate a minimum population estimate. 

Current Population Trend

There are insufficient data to determine the population trends for this species. 

CURRENT AND MAXIMUM NET PRODUCTIVITY RATES

Current and maximum net productivity rates are not known for this stock. The maximum net productivity

rate was assumed to be 0.04 for purposes of this assessment. This value is based on theoretical calculations showing

that cetacean populations may not generally grow at rates much greater than 4% given the constraints of their

reproductive life history (Anon. 1994). 

POTENTIAL BIOLOGICAL REMOVAL

No PBR can be estimated for this species at this time, because the minimum population size cannot be

determined. 

ANNUAL HUMAN-CAUSED MORTALITY AND SERIOUS INJURY

Beaked whales (many unidentified as to species) have been killed in the pelagic drift gillnet fishery off the

U.S. Atlantic coast. While there are no reported takes in other continental shelf edge fisheries (i.e., pelagic pair trawl,

longline), observer coverage in these fisheries is low and because beaked whales occupy this habitat, unreported takes

may have occurred. 

 Total fishery-related mortality and serious injury cannot be estimated separately for each beaked whale

species because of the uncertainty in species identification by fishery observers. The Atlantic Scientific Review Group

advised adopting the risk-averse strategy of assuming that any beaked whale stock which occurred in the U.S. Atlantic

Exclusive Economic Zone (EEZ) might have been subject to the observed fishery-related mortality and serious injury.

Twenty-two fishery-related beaked whale mortalities were observed between 1989 and 1993. The 1989-1993 total

average estimated annual fishery-related mortality of beaked whales in the U.S. EEZ was 34 (CV = 0.69). Although

PBR cannot be determined, the total fishery-related mortality and serious injury for this stock is not considered to be

insignificant and approaching zero mortality and serious injury rate. This determination cannot be made for specific

fisheries until the implementing regulations for Section 118 of the MMPA have been reviewed by the public and

finalized. 
47

Fisheries Information

There is no historical information available that documents incidental mortality in either U.S. or Canadian

Atlantic coast fisheries (Read, 1994). 

Current data sources include the Northeast Fisheries Science Center (NEFSC) Weigh Out Data Program and

Sea Sampling Observer Program initiated in 1989. In 1986, NMFS established a mandatory logbook system for large

pelagic fisheries. These logbooks are maintained at Southeast Fisheries Science Center (SEFSC). In late 1992 and

in 1993 the SEFSC provided observer coverage of pelagic longline vessels fishing off the Grand Banks (Tail of the

Banks) and currently provides observer coverage of vessels fishing south of Cape Hatteras. Total fishery-related

mortality and serious injury cannot be estimated separately for each beaked whale species because of the uncertainty

in species identification by fishery observers. The Atlantic Scientific Review Group advised adopting the risk-averse

strategy of assuming that any beaked whale stock which occurred in the U.S. Atlantic EEZ might have been subject

to the observed fishery-related mortality and serious injury.

By-catch has been observed by NMFS Sea Samplers in the swordfish/tuna/shark drift gillnet fishery, but no

mortalities have been documented in the Atlantic swordfish/tuna/shark longline, Atlantic swordfish/tuna/shark pair

trawl, New England multispecies sink gillnet, or New England groundfish trawl observed fisheries. 

The estimated total number of hauls in the Atlantic large pelagic drift gillnet fishery increased from 714 in

1989 to 1,144 in 1990; thereafter, with the introduction of quotas, effort was severely reduced. The estimated number

of hauls in 1991, 1992, and 1993 were 233, 243, and 232 respectively. Fifty-nine different vessels participated in this

fishery at one time or another between 1989 and 1993. Observer coverage, expressed as percent of sets observed,

ranged from 8% in 1989, 6% in 1990, 20% in 1991, to 40% in 1992, and 42% in 1993. Effort was concentrated along

the southern edge of Georges Bank and off Cape Hatteras. Examination of the species composition of the catch and

locations of the fishery throughout the year, suggested that the drift gillnet fishery be stratified into two strata, a

southern or winter stratum, and a northern or summer stratum. Estimates of the total by-catch, for each year, were

obtained using the aggregated (pooled 1989-1993) catch rates, by strata (Northridge, in review). By-catch of beaked

whales has only occurred from Georges Canyon to Hydrographer Canyon along the continental shelf break and

continental slope during July to October. Twenty-two fishery-related beaked whale mortalities were observed between

1989 and 1993. The estimated annual fishery-related mortality (CV in parentheses) was 60 in 1989 (0.49), 76 in 1990

(0.56), 13 in 1991 (0.57), 9.7 in 1992 (0.53), and 12 in 1993 (0.32).

STATUS OF STOCK

The status of Gervais’ beaked whale relative to OSP in U.S. Atlantic coast waters is unknown. This species

is not listed as threatened or endangered under the Endangered Species Act. In Canada, the Cetacean Protection

Regulations of 1982, promulgated under the Standing Fisheries Act, prohibit the catching or harassment of all cetacean

species. There are insufficient data to determine population trends and the level of human-caused mortality and serious

injury is unknown because of uncertainty regarding species identification in observed fisheries. If one were to assume

that the incidental fisheries mortality of the four Mesoplodon spp. and Z. cavirostris was random with respect to species

(i.e., in proportion to their relative abundance), then the minimum population estimate for all of those stocks would

need to sum to at least 3,400 in order for an annual mortality of 34 animals not to exceed the PBR of any one of these

species. Because an assumption of unselective incidental fishing mortality is probably overly optimistic and represents

a best case situation, it is likely that a combined minimum population estimate of substantially greater than 3,400

would be necessary for an annual mortality of 34 to not exceed the PBR of any one of these five stocks. The largest

recent abundance estimate available for beaked whales in the western North Atlantic was 612 (CV = 0.73), which

would result in a minimum population estimate of 353 beaked whales; however, this estimate does not include a

correction factor for submerged animals which may be substantial. This is a strategic stock because of uncertainty

regarding stock size and evidence of fishery-related mortality and serious injury. 

REFERENCES

Anon. 1994. Report of the PBR (Potential Biological Removal) workshop. June 27-29, 1994. NOAA, NMFS

Southwest Fisheries Science Center, La Jolla, California, 13 pp. + Appendices. 
48

Buckland, S. T., D. R. Andersen, K. P. Burnham, and J. L. Laake. 1993. Distance sampling: Estimating abundance

of biological populations. Chapman and Hall, New York, 446 pp. 

CeTAP. 1982. A characterization of marine mammals and turtles in the mid- and north Atlantic areas of the U.S.

outer continental shelf. Cetacean and Turtle Assessment Program, University of Rhode Island. Final Report

#AA551-CT8-48 to the Bureau of Land Management, Washington, DC, 538 pp. 

Laake, J. L., S. T. Buckland, D. R. Anderson, and K. P. Burnham. DISTANCE user’s guide, V2.0. Colorado

Cooperative Fish & Wildlife Research Unit, Colorado State University, Ft. Collins, Colorado, 72 pp. 

Leatherwood, S., D. K. Caldwell and H. E. Winn. 1976. Whales, dolphins, and porpoises of the western North

Atlantic. A guide to their identification. U.S. Dept. of Commerce, NOAA Tech. Rep. NMFS Circ. 396, 176

pp. 

Mead, J. G. 1989. Beaked whales of the genus Mesoplodon. Pages 349-430 in S. H. Ridgeway and R. Harrison

(editors), Handbook of marine mammals, Vol. 4: River dolphins and the larger toothed whales. Academic

Press, San Diego, 442 pp. 

Northridge, S. In review. Estimation of cetacean mortality in the U.S. Atlantic swordfish and tuna driftnet and pair

trawl fisheries. Draft final report to the Northeast Fisheries Science Center, Contract No. 40ENNF500045,

18 pp. 

1994. Interactions between cetaceans and gillnet and trap fisheries in the Northwest Atlantic. Rep. Int. Whal.

Commn. Special Issue 15: 133-147.
49

Figure 1. Distribution of beaked whale sightings from NEFSC

shipboard surveys during the summer in 1990-1994. Isobaths

are at 100 m and 1,000 m. 

BLAINVILLE'S BEAKED WHALE (Mesoplodon densirostris):

Western North Atlantic Stock

STOCK DEFINITION AND GEOGRAPHIC RANGE

Within the genus Mesoplodon, there are four

species of beaked whales in the northwest Atlantic.

These include: Blainville's beaked whale, Mesoplodon

densirostris; True's beaked whale, M. mirus; Gervais'

beaked whale, M. europaeus; and Sowerby's beaked

whale, M. bidens. These species are difficult to identify

to the species level at sea; therefore, much of the

available characterization for beaked whales is to genus

level only. 

The distribution of Mesoplodon spp. in the

northwest Atlantic is known principally from stranding

records (Mead 1989). Off the northeast U.S. coast,

beaked whale (Mesoplodon spp.) sightings have

occurred principally along the southern edge of Georges

Bank (including cow/calf pairs) (CeTAP 1982; Nicolas

et al. 1993; NMFS unpublished data). Most sightings

were in late spring and summer. In addition, beaked

whales were also sighted in Gulf Stream features during

NEFSC 1990-1994 surveys (NMFS unpublished data).

Blainville's beaked whales have been reported

from southwestern Nova Scotia to Florida, and are

believed to be widely but sparsely distributed in tropical

to warm-temperate waters (Leatherwood et al. 1976;

Mead 1989). There are two records of standings in

Nova Scotia which probably represent strays from the

Gulf Stream (Mead 1989). They are considered rare in

Canadian waters (Houston 1989). 

POPULATION SIZE

Population size can presently be described only for undifferentiated Mesoplodon spp. The total number of

beaked whales (Mesoplodon spp.) along the eastern U.S. or Canadian coasts is unknown, though several estimates from

select regions of the habitat do exist. Seasonal abundance estimates are available from an aerial line transect survey

program conducted in the continental shelf waters between Cape Hatteras, North Carolina, and Nova Scotia from 1978

to 1982 (CeTAP 1982), just after cessation of extensive foreign fishing operations in this region. An abundance

estimate based on CeTAP summer data is 120 (CV = 0.71). This estimate was not corrected for g(0), the probability

of detecting an animal group on the trackline. 

Abundance estimates were also derived using data collected during an autumn 1991 aerial survey in the

CeTAP study area (NMFS unpublished data), which included an interplatform experiment between a Twin Otter and

an AT-11), and from several fine-scale ship line transect surveys (August 1990, June-July 1991, June-July 1993, and

August 1994) conducted in continental shelf edge and deeper oceanic waters (NMFS unpublished data). For the aerial

and shipboard surveys, sightings were almost exclusively in the continental shelf edge and continental slope water

areas. The data were analyzed using DISTANCE (Buckland et al. 1993; Laake et al. 1993) where the CV was

estimated using the bootstrap lognormal method. Abundance estimates from the 1991 aerial survey were 612 (CV =

0.73) and 370 (CV = 0.65), respectively, for the AT-11 and Twin Otter. Data were not pooled, because the

interplatform calibration analysis has not been conducted. Furthermore, these estimates are not fully comparable to
50

the CeTAP estimates, because the 1991 data are from a single survey, August to October, while the CeTAP estimates

were based on data pooled over several years of seasonal surveys. 

An abundance estimate from the August 1990 shipboard survey, conducted principally along the Gulf Stream

north wall between Cape Hatteras and Georges Bank, was 442 (CV = 0.51). The 1991 survey estimate, based

principally on sighting effort conducted between the 200 and 2,000 meter isobaths from Cape Hatteras to Georges Bank

was 262 beaked whales (CV = 0.99). The estimate for the 1993 survey, conducted principally between the 200 and

2,000 meter isobaths from the southern edge of Georges Bank, across the Northeast Channel to the southwestern edge

of the Scotian Shelf was 330 beaked whales (CV = 0.66). The 1994 estimate, based on survey effort within a Gulf

Stream warm-core ring located in continental slope waters southeast of Georges Bank was 99 beaked whales (CV =

0.64). Because the number of beaked whale sightings in each survey were extremely low (3 to 10), and their

sightability and behavior preclude pooling with other cetaceans, the estimates of abundance are based on small sample

sizes. Therefore, the above abundance estimates should be viewed with caution. 

Although the 1990-1994 surveys did not sample exactly the same areas or encompass the entire beaked whale

habitat, they did focus on segments of known or suspected high-use habitats off the northeastern U.S. coast. The

collective 1990-94 data suggest that, seasonally, at least several hundred beaked whales are occupying these waters,

with highest levels of abundance in the Georges Bank region. This is consistent with the earlier CeTAP results.

Recent results suggest that beaked whale abundance may be highest in association with Gulf Stream and warm-core

ring features. However, at present there are no estimates of total abundance for beaked whales in the western North

Atlantic. 

Because the estimates presented here were not dive-time corrected, they are likely negatively biased and

probably underestimate actual abundance. Given that Mesoplodon spp. prefers deep-water habitats (Mead 1989) the

bias may be substantial. 

Minimum Population Estimate

Present data are insufficient to calculate a minimum population estimate. 

Current Population Trend

There are insufficient data to determine the population trends for this species. 

CURRENT AND MAXIMUM NET PRODUCTIVITY RATES

Current and maximum net productivity rates are not known for this stock. The maximum net productivity

rate was assumed to be 0.04 for purposes of this assessment. This value is based on theoretical calculations showing

that cetacean populations may not generally grow at rates much greater than 4% given the constraints of their

reproductive life history (Anon. 1994). 

POTENTIAL BIOLOGICAL REMOVAL

No PBR can be estimated for this species at this time, because the minimum population size cannot be

determined. 

ANNUAL HUMAN-CAUSED MORTALITY AND SERIOUS INJURY

Beaked whales (many unidentified as to species) have been killed in the pelagic drift gillnet fishery off the

U.S. Atlantic coast. While there are no reported takes in other continental shelf edge fisheries (i.e., pelagic pair trawl,

longline), observer coverage in these fisheries is low and because beaked whales occupy this habitat, unreported takes

may have occurred. 

 Total fishery-related mortality and serious injury cannot be estimated separately for each beaked whale

species because of the uncertainty in species identification by fishery observers. The Atlantic Scientific Review Group

advised adopting the risk-averse strategy of assuming that any beaked whale stock which occurred in the U.S. Atlantic

Exclusive Economic Zone (EEZ) might have been subject to the observed fishery-related mortality and serious injury.

Twenty-two fishery-related beaked whale mortalities were observed between 1989 and 1993. The 1989-1993 total

average estimated annual fishery-related mortality of beaked whales in the U.S. EEZ was 34 (CV = 0.69). Although

PBR cannot be determined, the total fishery-related mortality and serious injury for this stock is not considered to be

insignificant and approaching zero mortality and serious injury rate. This determination cannot be made for specific
51

fisheries until the implementing regulations for Section 118 of the MMPA have been reviewed by the public and

finalized. 

Fisheries Information

There is no historical information available that documents incidental mortality in either U.S. or Canadian

Atlantic coast fisheries (Read 1994). 

Current data sources include the Northeast Fisheries Science Center (NEFSC) Weigh Out Data Program and

Sea Sampling Observer Program initiated in 1989. In 1986, NMFS established a mandatory logbook system for large

pelagic fisheries. These logbooks are maintained at Southeast Fisheries Science Center (SEFSC). In late 1992 and

in 1993 the SEFSC provided observer coverage of pelagic longline vessels fishing off the Grand Banks (Tail of the

Banks) and currently provides observer coverage of vessels fishing south of Cape Hatteras. Total fishery-related

mortality and serious injury cannot be estimated separately for each beaked whale species because of the uncertainty

in species identification by fishery observers. The Atlantic Scientific Review Group advised adopting the risk-averse

strategy of assuming that any beaked whale stock which occurred in the U.S. Atlantic EEZ might have been subject

to the observed fishery-related mortality and serious injury.

By-catch has been observed by NMFS Sea Samplers in the swordfish/tuna/shark drift gillnet fishery, but no

mortalities have been documented in the Atlantic swordfish/tuna/shark longline, Atlantic swordfish/tuna/shark pair

trawl, New England multispecies sink gillnet, or New England groundfish trawl observed fisheries. 

The estimated total number of hauls in the Atlantic large pelagic drift gillnet fishery increased from 714 in

1989 to 1,144 in 1990; thereafter, with the introduction of quotas, effort was severely reduced. The estimated number

of hauls in 1991, 1992, and 1993 were 233, 243, and 232 respectively. Fifty-nine different vessels participated in this

fishery at one time or another between 1989 and 1993. Observer coverage, expressed as percent of sets observed,

ranged from 8% in 1989, 6% in 1990, 20% in 1991, to 40% in 1992, and 42% in 1993. Effort was concentrated along

the southern edge of Georges Bank and off Cape Hatteras. Examination of the species composition of the catch and

locations of the fishery throughout the year, suggested that the drift gillnet fishery be stratified into two strata, a

southern or winter stratum, and a northern or summer stratum. Estimates of the total by-catch, for each year, were

obtained using the aggregated (pooled 1989-1993) catch rates, by strata (Northridge, in review). By-catch of beaked

whales has only occurred from Georges Canyon to Hydrographer Canyon along the continental shelf break and

continental slope during July to October. Twenty-two fishery-related beaked whale mortalities were observed between

1989 and 1993. The estimated annual fishery-related mortality (CV in parentheses) was 60 in 1989 (0.49), 76 in 1990

(0.56), 13 in 1991 (0.57), 9.7 in 1992 (0.53), and 12 in 1993 (0.32).

STATUS OF STOCK

The status of Blainville's beaked whale relative to OSP in U.S. Atlantic coast waters is unknown. This species

is not listed as threatened or endangered under the Endangered Species Act. In Canada, the Cetacean Protection

Regulations of 1982, promulgated under the Standing Fisheries Act, prohibit the catching or harassment of all cetacean

species. There are insufficient data to determine population trends and the level of human-caused mortality and serious

injury is unknown because of uncertainty regarding species identification in observed fisheries. If one were to assume

that the incidental fisheries mortality of the four Mesoplodon spp. and Z. cavirostris was random with respect to species

(i.e., in proportion to their relative abundance), then the minimum population estimate for all of those stocks would

need to sum to at least 3,400 in order for an annual mortality of 34 animals not to exceed the PBR of any one of these

species. Because an assumption of unselective incidental fishing mortality is probably overly optimistic and represents

a best case situation, it is likely that a combined minimum population estimate of substantially greater than 3,400

would be necessary for an annual mortality of 34 to not exceed the PBR of any one of these five stocks. The largest

recent abundance estimate available for beaked whales in the western North Atlantic was 612 (CV = 0.73), which

would result in a minimum population estimate of 353 beaked whales; however, this estimate does not include a

correction factor for submerged animals which may be substantial. This is a strategic stock because of uncertainty

regarding stock size and evidence of fishery-related mortality and serious injury. 

REFERENCES

Anon. 1994. Report of the PBR (Potential Biological Removal) workshop. June 27-29, 1994. NOAA, NMFS

Southwest Fisheries Science Center, La Jolla, California, 13 pp. + Appendices. 
52

Buckland, S. T., D. R. Andersen, K. P. Burnham, and J. L. Laake. 1993. Distance sampling: Estimating abundance

of biological populations. Chapman and Hall, New York, 446 pp. 

CeTAP. 1982. A characterization of marine mammals and turtles in the mid- and north Atlantic areas of the U.S.

outer continental shelf. Cetacean and Turtle Assessment Program, University of Rhode Island. Final Report

#AA551-CT8-48 to the Bureau of Land Management, Washington, DC, 538 pp. 

Houston, J. 1989. Status of Blainville's Beaked Whale, Mesoplodon densirostris, in Canada. Can. Fld. Nat. 104(1):

117-120.

Laake, J. L., S. T. Buckland, D. R. Anderson, and K. P. Burnham. DISTANCE user’s guide, V2.0. Colorado

Cooperative Fish & Wildlife Research Unit, Colorado State University, Ft. Collins, Colorado, 72 pp. 

Leatherwood, S., D. K. Caldwell and H. E. Winn. 1976. Whales, dolphins, and porpoises of the western North

Atlantic. A guide to their identification. U.S. Dept. of Commerce, NOAA Tech. Rep. NMFS Circ. 396, 176

pp. 

Mead, J. G. 1989. Beaked whales of the genus Mesoplodon. Pages 349-430 in S. H. Ridgeway and R. Harrison

(editors), Handbook of marine mammals, Vol. 4: River dolphins and the larger toothed whales. Academic

Press, San Diego, 442 pp. 

Nicolas, J., A. Williams, G. Repucci. 1993. Observations of beaked whales (Mesoplodon spp.) in the western North

Atlantic Ocean. Proceedings of the Tenth Biennial Conference on the Biology of Marine Mammals, Nov. 11-

15, 1993, Galveston, TX (Abstract). 

Northridge, S. In review. Estimation of cetacean mortality in the U.S. Atlantic swordfish and tuna driftnet and pair

trawl fisheries. Draft final report to the Northeast Fisheries Science Center, Contract No. 40ENNF500045,

18 pp. 

Read, A. J. 1994. Interactions between cetaceans and gillnet and trap fisheries in the Northwest Atlantic. Rep. Int.

Whal. Commn. Special Issue 15: 133-147. 
53

Figure 1. Distribution of beaked whale sightings from NEFSC

shipboard surveys during the summer in 1990-1994. Isobaths

are at 100 m and 1,000 m. 

SOWERBY'S BEAKED WHALE (Mesoplodon bidens):

Western North Atlantic Stock

STOCK DEFINITION AND GEOGRAPHIC RANGE

Within the genus Mesoplodon, there are four

species of beaked whales in the northwest Atlantic.

These include: Sowerby's beaked whale, Mesoplodon

bidens; True's beaked whale, M. mirus; Gervais' beaked

whale, M. europaeus; and Blainville's beaked whale,

M. densirostris. These species are difficult to identify

to the species level at sea; therefore, much of the

available characterization for beaked whales is to genus

level only. 

The distribution of Mesoplodon spp. in the

northwest Atlantic is known principally from stranding

records (Mead 1989; Lien et al. 1990). Off the

northeast U.S. coast, beaked whale (Mesoplodon spp.)

sightings have occurred principally along the southern

edge of Georges Bank (including cow/calf pairs)

(CeTAP 1982; Nicolas et al. 1993; NMFS unpublished

data). Most sightings were in late spring and summer.

In addition, beaked whales were also sighted in Gulf

Stream features during NEFSC 1990-1994 surveys

(NMFS unpublished data). 

Sowerby's beaked whales have been reported

from New England waters north to the ice pack, and

individuals are seen along the Newfoundland coast in

summer (Leatherwood et al. 1976; Mead 1989).

Furthermore, a single stranding occurred off the

Florida west coast (Mead 1989). This species is

considered rare in Canadian waters (Lien et al. 1990).

POPULATION SIZE

Population size can presently be described only for undifferentiated Mesoplodon spp. The total number of

beaked whales (Mesoplodon spp.) along the eastern U.S. or Canadian coasts is unknown, though several estimates from

select regions of the habitat do exist. Seasonal abundance estimates are available from an aerial line transect survey

program conducted in the continental shelf waters between Cape Hatteras, North Carolina, and Nova Scotia from 1978

to 1982 (CeTAP 1982), just after cessation of extensive foreign fishing operations in this region. An abundance

estimate based on CeTAP summer data is 120 (CV = 0.71). This estimate was not corrected for g(0), the probability

of detecting an animal group on the trackline. 

Abundance estimates were also derived using data collected during the autumn 1991 aerial survey in the

CeTAP study area (NMFS unpublished data), which included an interplatform experiment between a Twin Otter and

an AT-11, and from several fine-scale ship line transect surveys (August 1990, June-July 1991, June-July 1993, and

August 1994) conducted in continental shelf edge and deeper oceanic waters (NMFS unpublished data). For the aerial

and shipboard surveys, sightings were almost exclusively in the continental shelf edge and continental slope water

areas. The data were analyzed using DISTANCE (Buckland et al. 1993; Laake et al. 1993) where the CV was

estimated using the bootstrap lognormal method. Abundance estimates from the 1991 aerial survey were 612 (CV =

0.73) and 370 (CV = 0.65), respectively, for the AT-11 and Twin Otter. Data were not pooled, because the

interplatform calibration analysis has not been conducted. Furthermore, these estimates are not fully comparable to

the CeTAP estimates, because the 1991 data are from a single survey, August to October, while the CeTAP estimates

were based on data pooled over several years of seasonal surveys. 
54

An abundance estimate from the August 1990 shipboard survey, conducted principally along the Gulf Stream

north wall between Cape Hatteras and Georges Bank, was 442 (CV = 0.51). The 1991 survey estimate, based

principally on sighting effort conducted between the 200 and 2,000 meter isobaths from Cape Hatteras to Georges Bank

was 262 beaked whales (CV = 0.99). The estimate for the 1993 survey, conducted principally between the 200 and

2,000 meter isobaths from the southern edge of Georges Bank, across the Northeast Channel to the southwestern edge

of the Scotian Shelf was 330 beaked whales (CV = 0.66). The 1994 estimate, based on survey effort within a Gulf

Stream warm-core ring located in continental slope waters southeast of Georges Bank was 99 beaked whales (CV =

0.64). Because the number of beaked whale sightings in each survey were extremely low (3 to 10), and their

sightability and behavior preclude pooling with other cetaceans, the estimates of abundance are based on small sample

sizes. Therefore, the above abundance estimates should be viewed with caution. 

Although the 1990-1994 surveys did not sample exactly the same areas or encompass the entire beaked whale

habitat, they did focus on segments of known or suspected high-use habitats off the northeastern U.S. coast. The

collective 1990-94 data suggest that, seasonally, at least several hundred beaked whales are occupying these waters,

with highest levels of abundance in the Georges Bank region. This is consistent with the earlier CeTAP results.

Recent results suggest that beaked whale abundance may be highest in association with Gulf Stream and warm-core

ring features. However, at present there are no estimates of total abundance for beaked whales in the western North

Atlantic. 

Because the estimates presented here were not dive-time corrected, they are likely negatively biased and

probably underestimate actual abundance. Given that Mesoplodon spp. prefers deep-water habitats (Mead 1989) the

bias may be substantial. 

Minimum Population Estimate

Present data are insufficient to calculate a minimum population estimate for this stock. 

Current Population Trend

There are insufficient data to determine the population trends for this species. 

CURRENT AND MAXIMUM NET PRODUCTIVITY RATES

Current and maximum net productivity rates are not known for this stock. The maximum net productivity

rate was assumed to be 0.04 for purposes of this assessment. This value is based on theoretical calculations showing

that cetacean populations may not generally grow at rates much greater than 4% given the constraints of their

reproductive life history (Anon. 1994). 

POTENTIAL BIOLOGICAL REMOVAL

No PBR can be estimated for this species at this time, because the minimum population size cannot be

determined. 

ANNUAL HUMAN-CAUSED MORTALITY AND SERIOUS INJURY

Beaked whales (many unidentified as to species) have been killed in the pelagic drift gillnet fishery off the

U.S. Atlantic coast. While there are no reported takes in other continental shelf edge fisheries (i.e., pelagic pair trawl,

longline), observer coverage in these fisheries is low and because beaked whales occupy this habitat, unreported takes

may have occurred. 

 Total fishery-related mortality and serious injury cannot be estimated separately for each beaked whale

species because of the uncertainty in species identification by fishery observers. The Atlantic Scientific Review Group

advised adopting the risk-averse strategy of assuming that any beaked whale stock which occurred in the U.S. Atlantic

Exclusive Economic Zone (EEZ) might have been subject to the observed fishery-related mortality and serious injury.

Twenty-two fishery-related beaked whale mortalities were observed between 1989 and 1993. The 1989-1993 total

average estimated annual fishery-related mortality of beaked whales in the U.S. EEZ was 34 (CV = 0.69). Although

PBR cannot be determined, the total fishery-related mortality and serious injury for this stock is not considered to be

insignificant and approaching zero mortality and serious injury rate. This determination cannot be made for specific

fisheries until the implementing regulations for Section 118 of the MMPA have been reviewed by the public and

finalized. 
55

Fisheries Information

There is no historical information available that documents incidental mortality in either U.S. or Canadian

Atlantic coast fisheries (Read 1994). 

Current data sources include the Northeast Fisheries Science Center (NEFSC) Weigh Out Data Program and

Sea Sampling Observer Program initiated in 1989. In 1986, NMFS established a mandatory logbook system for large

pelagic fisheries. These logbooks are maintained at Southeast Fisheries Science Center (SEFSC). In late 1992 and

in 1993 the SEFSC provided observer coverage of pelagic longline vessels fishing off the Grand Banks (Tail of the

Banks) and currently provides observer coverage of vessels fishing south of Cape Hatteras. Total fishery-related

mortality and serious injury cannot be estimated separately for each beaked whale species because of the uncertainty

in species identification by fishery observers. The Atlantic Scientific Review Group advised adopting the risk-averse

strategy of assuming that any beaked whale stock which occurred in the U.S. Atlantic EEZ might have been subject

to the observed fishery-related mortality and serious injury.

By-catch has been observed by NMFS Sea Samplers in the swordfish/tuna/shark drift gillnet fishery, but no

mortalities have been documented in the Atlantic swordfish/tuna/shark longline, Atlantic swordfish/tuna/shark pair

trawl, New England multispecies sink gillnet, or New England groundfish trawl observed fisheries. 

The estimated total number of hauls in the Atlantic large pelagic drift gillnet fishery increased from 714 in

1989 to 1,144 in 1990; thereafter, with the introduction of quotas, effort was severely reduced. The estimated number

of hauls in 1991, 1992, and 1993 were 233, 243, and 232 respectively. Fifty-nine different vessels participated in this

fishery at one time or another between 1989 and 1993. Observer coverage, expressed as percent of sets observed,

ranged from 8% in 1989, 6% in 1990, 20% in 1991, to 40% in 1992, and 42% in 1993. Effort was concentrated along

the southern edge of Georges Bank and off Cape Hatteras. Examination of the species composition of the catch and

locations of the fishery throughout the year, suggested that the drift gillnet fishery be stratified into two strata, a

southern or winter stratum, and a northern or summer stratum. Estimates of the total by-catch, for each year, were

obtained using the aggregated (pooled 1989-1993) catch rates, by strata (Northridge, in review). By-catch of beaked

whales has only occurred from Georges Canyon to Hydrographer Canyon along the continental shelf break and

continental slope during July to October. Twenty-two fishery-related beaked whale mortalities were observed between

1989 and 1993. The estimated annual fishery-related mortality (CV in parentheses) was 60 in 1989 (0.49), 76 in 1990

(0.56), 13 in 1991 (0.57), 9.7 in 1992 (0.53), and 12 in 1993 (0.32).

STATUS OF STOCK

The status of Sowerby's beaked whale relative to OSP in U.S. Atlantic coast waters is unknown. This species

is not listed as threatened or endangered under the Endangered Species Act. In Canada, the Cetacean Protection

Regulations of 1982, promulgated under the Standing Fisheries Act, prohibit the catching or harassment of all cetacean

species. There are insufficient data to determine population trends and the level of human-caused mortality and serious

injury is unknown because of uncertainty regarding species identification in observed fisheries. If one were to assume

that the incidental fisheries mortality of the four Mesoplodon spp. and Z. cavirostris was random with respect to species

(i.e., in proportion to their relative abundance), then the minimum population estimate for all of those stocks would

need to sum to at least 3,400 in order for an annual mortality of 34 animals not to exceed the PBR of any one of these

species. Because an assumption of unselective incidental fishing mortality is probably overly optimistic and represents

a best case situation, it is likely that a combined minimum population estimate of substantially greater than 3,400

would be necessary for an annual mortality of 34 to not exceed the PBR of any one of these five stocks. The largest

recent abundance estimate available for beaked whales in the western North Atlantic was 612 (CV = 0.73), which

would result in a minimum population estimate of 353 beaked whales; however, this estimate does not include a

correction factor for submerged animals which may be substantial. This is a strategic stock because of uncertainty

regarding stock size and evidence of fishery-related mortality and serious injury. 

REFERENCES

Anon. 1994. Report of the PBR (Potential Biological Removal) workshop. June 27-29, 1994. NOAA, NMFS

Southwest Fisheries Science Center, La Jolla, California, 13 pp. + Appendices. 
56

Buckland, S. T., D. R. Andersen, K. P. Burnham, and J. L. Laake. 1993. Distance sampling: Estimating abundance

of biological populations. Chapman and Hall, New York, 446 pp. 

CeTAP. 1982. A characterization of marine mammals and turtles in the mid- and north Atlantic areas of the U.S.

outer continental shelf. Cetacean and Turtle Assessment Program, University of Rhode Island. Final Report

#AA551-CT8-48 to the Bureau of Land Management, Washington, DC, 538 pp. 

Laake, J. L., S. T. Buckland, D. R. Anderson, and K. P. Burnham. DISTANCE user’s guide, V2.0. Colorado

Cooperative Fish & Wildlife Research Unit, Colorado State University, Ft. Collins, Colorado, 72 pp. 

Leatherwood, S., D. K. Caldwell and H. E. Winn. 1976. Whales, dolphins, and porpoises of the western North

Atlantic. A guide to their identification. U.S. Dept. of Commerce, NOAA Tech. Rep. NMFS Circ. 396, 176

pp. 

Lien J., F. Barry, K. Breeck, and U. Zuschlag. 1990. Status of Sowerby's Beaked Whale, Mesoplodon bidens, in

Canada. Can. Fld. Nat. 104(1): 125-130.

Mead, J. G. 1989. Beaked whales of the genus Mesoplodon. Pages 349-430 in S. H. Ridgway and R. Harrison

(editors), Handbook of Marine Mammals, Vol. 4: River dolphins and the larger toothed whales. Academic

Press, London. 

Nicolas, J., A. Williams, G. Repucci. 1993. Observations of beaked whales (Mesoplodon spp.) in the western North

Atlantic Ocean. Proceedings of the Tenth Biennial Conference on the Biology of Marine Mammals, Nov. 11-

15, 1993, Galveston, TX (Abstract). 

Northridge, S. In review. Estimation of cetacean mortality in the U.S. Atlantic swordfish and tuna driftnet and pair

trawl fisheries. Draft final report to the Northeast Fisheries Science Center, Contract No. 40ENNF500045,

18 pp. 

Read, A. J. 1994. Interactions between cetaceans and gillnet and trap fisheries in the Northwest Atlantic. Rep. Int.

Whal. Commn. Special Issue 15: 133-147.
57

Figure 1. Distribution of Risso’s dolphin sightings from

NEFSC shipboard surveys during the summer in 1990-1994. 

Isobaths are at 100 m and 1,000 m. 

RISSO'S DOLPHIN (Grampus griseus):

Western North Atlantic Stock

STOCK DEFINITION AND GEOGRAPHIC RANGE

Risso's dolphin is distributed worldwide in tropical and temperate seas. Risso's dolphins generally have an

oceanic range, and occur along the Atlantic coast of North America from Florida to eastern Newfoundland

(Leatherwood et al. 1976; Baird and Stacey 1990). Off the northeast U.S. coast, Risso's dolphin is distributed along

the continental shelf edge from Cape Hatteras northward to Georges Bank during the spring, summer, and autumn

(CeTAP 1982; Payne et al. 1984). In winter, the range begins at the mid-Atlantic bight and extends further into

oceanic waters (Payne et al. 1984). In general, the population generally occupies the mid-Atlantic continental shelf

edge year round, and is rarely seen in the Gulf of Maine (Payne et al. 1984). During 1990, 1991, and 1993

spring/summer surveys conducted in continental shelf edge and deeper oceanic waters, sightings of Risso's dolphins

were associated with strong bathymetric features, Gulf Stream warm-core rings, and the Gulf Stream north wall

(Waring et al. 1992; Waring 1993). There is no information on stock differentiation of Risso's dolphin in the western

North Atlantic. 

POPULATION SIZE

The total number of Risso's dolphins off the

eastern U.S. and Canadian Atlantic coast is unknown,

although several estimates from selected regions do

exist. Seasonal abundance estimates are available from

an aerial survey program conducted in continental shelf

and continental shelf edge waters between Cape

Hatteras, North Carolina, and Nova Scotia from 1978

to 1982 (CeTAP 1982). An estimate based on a

weighted (variance) pooling of CeTAP (1982) spring

and summer data is 4,980 (CV = 0.34). An average for

these two seasons was chosen because the greatest

proportion of the population off the northeast U.S. coast

appears to be in the CeTAP study area in these seasons.

This estimate was not corrected for g(0), the probability

of detecting an animal group on the trackline. 

Abundance estimates were also derived using

data collected during an autumn 1991 aerial survey in

the CeTAP study area (NMFS unpublished data), which

included an interplatform experiment between a Twin

Otter and an AT-11), and from two fine-scale ship

surveys (June-July 1991 and June-July 1993) conducted

in continental shelf edge and deeper oceanic waters

(NMFS unpublished data). For the aerial and

shipboard surveys, sightings were almost exclusively in

the continental shelf edge and continental slope water

areas. 

Abundance estimates from the 1991 aerial

survey were 16,818 (CV = 0.52) and 6,496 (CV = 0.74), respectively, for the AT-11 and Twin Otter. Data were not

pooled, because the areas covered by the two survey platforms were not comparable. Furthermore, these estimates are

not fully comparable to the CeTAP estimates, because the 1991 data are from a single survey, August to October, while

the CeTAP estimates were based on data pooled over several years of seasonal surveys. 

Estimates have been prepared for two of the shipboard surveys in which Risso's dolphins were sighted. An

estimate from the 1991 survey, based principally on sighting effort conducted between the 200 and 2,000 meter isobaths
58

from Cape Hatteras to Georges Bank is 5,353 Risso’s dolphins (CV = 0.68). The estimate for the 1993 survey,

conducted principally between the 200 and 2,000 meter isobaths from the southern edge of Georges Bank, across the

Northeast Channel to the southwestern edge of the Scotian Shelf is 212 Risso’s dolphins (CV = 0.62). The few Risso's

dolphin sightings made during August 1990 and 1994 were widely scattered, and therefore were not used to obtain

abundance estimates. It should be noted, however, that nearly all of the sightings in these two years were in deeper

oceanic waters (Waring 1993; NMFS unpublished data). Although the 1991 and 1993 surveys did not sample exactly

the same areas or encompass the entire Risso's dolphin habitat, they did focus on segments of known or suspected highuse habitats off the northeastern U.S. coast. The collective data suggest that at least several thousand Risso's dolphins

occupy these waters seasonally; however, survey coverage to date was not judged adequate to provide a definitive

estimate of Risso's dolphin abundance in the western North Atlantic. 

Present population trends of Risso's dolphins in Canadian waters are unknown due to the scarcity of reported

sightings and lack of distribution surveys. 

Minimum Population Estimate

 The minimum population estimate was based on the AT-11 aerial survey abundance estimate in autumn

1991, of 16,818 Risso’s dolphins (CV = 0.52) (NMFS unpublished data). The AT-11 estimate was selected because

that survey provided the most complete coverage of continental shelf edge and continental slope waters off the northeast

U.S. coast. The minimum population estimate is the lower limit of the two-tailed 60% confidence interval of the lognormal distributed abundance estimate, which is equivalent to the 20th percentile of the log-normal distribution as

specified by NMFS (Anon. 1994), and was 11,140 Risso's dolphins.

Current Population Trend

There are insufficient data to determine the population trends for this species. 

CURRENT AND MAXIMUM NET PRODUCTIVITY RATES

Current and maximum net productivity rates are not known for this stock. The maximum net productivity

rate was assumed to be 0.04 for purposes of this assessment. This value is based on theoretical calculations showing

that cetacean populations may not generally grow at rates much greater than 4% given the constraints of their

reproductive life history (Reilly and Barlow 1986). 

POTENTIAL BIOLOGICAL REMOVAL

Potential biological removal (PBR) was specified as the product of minimum population size, one-half the

maximum productivity rate, and a "recovery" factor for endangered, depleted, threatened stocks, or stocks of unknown

status relative to optimum sustainable population (OSP) (Anon. 1994). The recovery factor was set at 0.50 because

of the stock's status relative to its OSP level is unknown. PBR for this stock is 111 Risso's dolphins. 

ANNUAL HUMAN-CAUSED MORTALITY

Foreign fishery observers documented the incidental take of a small number of Risso's dolphins in foreign

squid (three animals) and tuna longline (one animal) fisheries (Waring et al. 1990). Between 1989 and 1993, 36

mortalities were observed in the large pelagic drift gillnet fishery, one mortality in the pelagic pair trawl fishery, and

one in the pelagic longline fishery (NMFS unpublished data, see below). No mortalities were documented for the New

England multispecies sink gillnet and groundfish trawl fisheries and no takes were documented in a review of

Canadian gillnet and trap fisheries (Read 1994).

Total average annual total fishery-related mortality is 68 Risso’s dolphins (CV = 0.53). Total fishery-related

mortality and serious injury for this stock is not less than 10% of the calculated PBR and, therefore, cannot be

considered to be insignificant and approaching zero mortality and serious injury rate. This determination cannot be

made for specific fisheries until the implementing regulations for Section 118 of the MMPA have been reviewed by

the public and finalized. 

Fisheries Information

Prior to 1977, there was no documentation of marine mammal by-catch in distant-water fleet (DWF) activities

off the northeast coast of the U.S. With implementation of the Magnuson Fisheries Conservation and Management
59

Act (MFCMA) in that year, an observer program was established which has recorded fishery data and information of

incidental by-catch of marine mammals. DWF effort in the U.S. Atlantic Exclusive Economic Zone (EEZ) under

MFCMA has been directed primarily towards Atlantic mackerel and squid. From 1977 through 1982, an average of

120 different foreign vessels per year (range 102-161) operated within the U.S. Atlantic EEZ. In 1982, there were 112

different foreign vessels; 16%, or 18, were Japanese tuna longline vessels operating along the U.S. east coast. This

was the first year that the Northeast Regional Observer Program assumed responsibility for observer coverage of the

longline vessels. Between 1983 and 1991, the numbers of foreign vessels operating within U.S. Atlantic EEZ each year

were 67, 52, 62, 33, 27, 26, 14, 13, and 9, respectively. Between 1983 and 1988, the numbers of DWF vessels included

3, 5, 7, 6, 8, and 8, respectively, Japanese longline vessels. Observer coverage on DWF vessels was 25-35% during

1977-82, and increased to 58%, 86%, 95%, and 98%, respectively, in 1983-86. From 1987-91, 100% observer

coverage was maintained. Foreign fishing operations for squid and mackerel ceased at the end of the 1986 and 1991

fishing seasons, respectively. NMFS foreign-fishery observers have reported four deaths of Risso's dolphins incidental

to squid and mackerel fishing activities in the continental shelf and continental slope waters between March 1977 and

December 1991 (Waring et al. 1990; NMFS unpublished data). Three animals were taken by squid trawlers and a

single animal was killed in longline fishing operations. 

 Data on incidental takes in U.S. fisheries are available from several sources. In 1986, NMFS established a

mandatory logbook system for large pelagic fisheries. Data files are maintained at the Southeast Fisheries Science

Center (SEFSC). The Northeast Fisheries Science Center (NEFSC) Sea Sampling Observer Program was initiated in

1989, and since that year several fisheries have been covered by the program. In late 1992 and in 1993, the SEFSC

provided observer coverage of pelagic longline vessels fishing off the Grand Banks (Tail of the Banks) and provides

observer coverage of vessels fishing south of Cape Hatteras. 

The estimated total number of hauls in the Atlantic large pelagic drift gillnet fishery increased from 714 in

1989 to 1,144 in 1990; thereafter, with the introduction of quotas, effort was severely reduced. The estimated number

of hauls in 1991, 1992, and 1993 were 233, 243, and 232 respectively. Fifty-nine different vessels participated in this

fishery at one time or another between 1989 and 1993. Observer coverage, expressed as percent of sets observed,

ranged from 8% in 1989, 6% in 1990, 20% in 1991, to 40% in 1992, and 42% in 1993. Effort was concentrated along

the southern edge of Georges Bank and off Cape Hatteras. Examination of the species composition of the catch and

locations of the fishery throughout the year, suggested that the drift gillnet fishery be stratified into two strata, a

southern or winter stratum, and a northern or summer stratum. Estimates of the total by-catch, for each year, were

obtained using the aggregated (pooled 1989-1993) catch rates, by strata (Northridge, in review). Thirty seven Risso's

dolphin mortalities were observed between 1989 and 1993. One animal was entangled and released alive. By-catch

occurred during July, September and October along continental shelf edge canyons off the southern New England coast.

Estimated annual mortality and serious injury (CV in parentheses) attributable to the drift gillnet fishery was 87 in

1989 (0.52), 144 in 1990 (0.46), 21 in 1991 (0.55), 31 in 1992 (0.27), and 14 in 1993 (0.42); average annual mortality

and serious injury during 1989-1993 was 59 (0.61).

During the period 1989 to 1993, effort in the Atlantic swordfish/tuna/shark pair trawl fishery has increased,

from zero hauls in 1989 and 1990, to an estimated 171 hauls in 1991 and then to an estimated 989 and 1087 hauls in

1992 and 1993 respectively. The fishery operated from August to November in 1991, from June to November in 1992,

and from June to October in 1993. Sea sampling began in October of 1992 where 101 sets (10% of the total) were

sampled. In 1993, 201 hauls (18% of the total) were sampled. Nineteen vessels have operated in this fishery. The

fishery extends from 35oN to 41oN, and from 69EW to 72EW. Approximately 50% of the total effort was in a one

degree square at 39oN, 72oW, around Hudson Canyon. Examination of the locations and species composition of the

by-catch, showed little seasonal change for the 6 months of operation and did not warrant any seasonal or areal

stratification of this fishery (Northridge, in review). One mortality was observed in 1992. Estimated annual mortality

and serious injury (CV in parentheses) to Risso’s dolphins in the Atlantic swordfish/tuna/shark pair trawl fishery was

0.6 in 1991 (1.0), 4.3 in 1992 (0.76) and 3.2 in 1993 (1.0); average annual mortality and serious injury during 1991-

1993 was 2.7 (0.98). 

Pelagic swordfish, tunas, and billfish are the targets of the U.S. longline fishery in the U.S. Atlantic and Gulf

of Mexico EEZ (SEFSC unpublished logbook data). Total longline effort for the Atlantic pelagic fishery (including

the Caribbean), based on mandatory logbook reporting, was 11,279 sets in 1991, 10,605 sets in 1992, and 11,538 in

1993 (Cramer 1994). The fishery has been observed from January to March off Cape Hatteras, in May and June in the

entire Mid-Atlantic, and in July through December in the Mid-Atlantic Bight and off Nova Scotia. This fishery has
60

been monitored with about 5% observer coverage, in terms of trips observed, since 1992. One Risso’s dolphin mortality

was observed in 1993, producing an estimated total longline fishery-related mortality of 13 Risso’s dolphins (CV =

0.19) for 1993, and a 1992-1993 estimated annual average of 6.5 (CV = 0.27). 

STATUS OF STOCK

The status of Risso's dolphins relative to OSP in the U.S. Atlantic EEZ is unknown. The species is not listed

as threatened or endangered under the Endangered Species Act. In Canada, the Cetacean Protection Regulations of

1982, promulgated under the Standing Fisheries Act, prohibit the catching or harassment of all cetacean species. There

are insufficient data to determine the population trends for this species. The 1990-93 average annual fishery-related

mortality did not exceed PBR; therefore, this is not a strategic stock. 

REFERENCES

Anon. 1994. Report of the PBR (Potential Biological Removal) workshop. June 27-29, 1994. NOAA, NMFS

Southwest Fisheries Science Center, La Jolla, California, 13 pp. + Appendices. 

Baird, R. W. and P. J. Stacey. 1990. Status of Risso's dolphin, Grampus griseus, in Canada. Can. Fld. Nat. 105:233-

242. 

CeTAP. 1982. A characterization of marine mammals and turtles in the mid- and north Atlantic areas of the U.S.

outer continental shelf. Cetacean and Turtle Assessment Program, University of Rhode Island. Final Report

#AA551-CT8-48 to the Bureau of Land Management, Washington, DC, 538 pp. 

Leatherwood, S., D. K. Caldwell and H. E. Winn. 1976. Whales, dolphins, and porpoises of the western North

Atlantic. A guide to their identification. U.S. Dept. of Commerce, NOAA Tech. Rep. NMFS Circ. 396, 176

pp. 

Payne, P. M., L. A. Selzer and A. R. Knowlton. 1984. Distribution and density of cetaceans, marine turtles, and

seabirds in the shelf waters of the northeastern United States, June 1980-December 1983, based on shipboard

observations. NOAA/NMFS Contract No. NA-81-FA-C-00023. 

Read, A. J. 1994. Interactions between cetaceans and gillnet and trap fisheries in the northwest Atlantic. Rep. Int.

Whal. Commn. Special Issue 15: 133-147. 

Reilly, S. B. and J. Barlow. 1986. Rates of increase in dolphin population size. Fish. Bull., U.S. 84(3): 527-533. 

Waring, G. T., P. Gerrior, P. M. Payne, B. L. Parry and J. R. Nicolas. 1990. Incidental take of marine mammals in

foreign fishery activities off the northeast United States, 1977-1988, Fish. Bull., U.S., 88:347-360.

Waring, G. T., C. P. Fairfield, C. M. Ruhsam and M. Sano. 1992. Cetaceans associated with Gulf Stream features

off the northeastern USA shelf. ICES Marine Mammals Comm. CM 1992/N:12, 29 pp. 

Waring, G. T. 1993. Spatial patterns of six cetaceans along a linear habitat. Proceedings of the Tenth Biennial

Conference on the Biology of Marine Mammals, Nov. 11-15, 1993, Galveston, TX (Abstract). 
61

Figure 1. Distribution of pilot whale sightings from NEFSC

shipboard surveys during the summer in 1990-1994. Isobaths

are at 100 m and 1,000 m. 

LONG-FINNED PILOT WHALE (Globicephala melas):

Western North Atlantic Stock

STOCK DEFINITION AND GEOGRAPHIC RANGE

There are two species of pilot whales in the Western Atlantic — the Atlantic or long-finned pilot whale,

Globicephala melas, and the short-finned pilot whale, G. macrorhynchus. These species are difficult to identify to the

species level at sea; therefore, some of the descriptive material below refers to Globicephala spp., and is identified as

such. The species boundary is considered to be in the New Jersey to Cape Hatteras area. Sightings north of this area

are likely G. melas. 

Pilot whales (Globicephala spp.) are distributed principally along the continental shelf edge in the winter and

early spring off the northeast U.S. coast, (CeTAP 1982; Payne and Heinemann 1993). In late spring, pilot whales

move onto Georges Bank and into the Gulf of Maine and more northern waters, and remain in these areas through late

autumn (CeTAP 1982; Payne and Heinemann 1993). In general, pilot whales generally occupy areas of high relief

or submerged banks. They are also associated with the Gulf Stream north wall and thermal fronts along the continental

shelf edge. 

The long-finned pilot whale is distributed from North Carolina to Iceland and possibly the Baltic Sea

(Sergeant 1962; Leatherwood et al. 1979; Abend 1993). The stock structure of the North Atlantic population is

currently unknown (Anon., 1993); however, several recently initiated genetic studies and proposed North Atlantic

sighting surveys will likely provide information required to delineate stock boundaries. 

POPULATION SIZE

The total number of long-finned pilot whales

off the eastern U.S. and Canadian Atlantic coast is

unknown, but several estimates from selected regions do

exist. Mitchell (1974) used cumulative catch data from

the 1951-61 drive fishery off Newfoundland to estimate

the initial population size (ca. 50,000 animals). Mercer

(1975), used population models to estimate a population

in the same region of between 43,000-96,000 longfinned pilot whales, with a range of 50,000-60,000

being considered the best estimate. 

Seasonal abundance estimates are available

from an aerial survey program conducted in the

continental shelf waters between Cape Hatteras, North

Carolina, and Nova Scotia from 1978 to 1982 (CeTAP

1982). Because pilot whales are difficult to identify at

sea, seasonal abundance estimates were reported at the

generic level. An estimate based on variance-weighted

pooling of CeTAP (1982) spring, summer, and autumn

data is 11,120 long-finned pilot whales (CV = 0.29).

An average for these three seasons was chosen because

the greatest proportion of the population off the

northeast U.S. coast appears to be in the CeTAP study

area in these seasons. This estimate was not corrected

for g(0), the probability of detecting an animal group on

the trackline. 

Abundance estimates were also derived using

data collected during an autumn 1991 aerial survey in the CeTAP study area (Northeast Fisheries Science Center

NMFS unpublished data), which included an interplatform experiment between a Twin Otter and an AT-11), and from

three fine-scale ship surveys (August 1990, June-July 1991, and June-July 1993) conducted in continental shelf edge
62

and deeper oceanic waters (NMFS unpublished data). Sightings were made along the continental shelf edge, in the

western Gulf of Maine, and on the northwestern edge of Georges Bank during the 1991 aerial survey. Abundance

estimates for Globicephala spp. were 5,377 (CV = 0.53) and 3,668 (CV = 0.28) for the AT-11 and NOAA Twin Otter

, respectively. Data were not pooled, because the interplatform calibration analysis has not been conducted. These

estimates are not fully comparable to the CeTAP estimates, because the 1991 data are from a single survey conducted

during August-October, while the CeTAP estimates were based on data pooled over several years of seasonal surveys.

The three shipboard surveys covered relatively small portions of the northeastern U.S. Exclusive Economic

Zone (EEZ) and pilot whale sightings during these surveys are shown in Figure 1. The abundance estimate from the

August 1990 survey, conducted principally along the Gulf Stream north wall between Cape Hatteras and Georges Bank,

is 1,043 long-finned pilot whales (CV = 0.78). The 1991 survey estimate, based principally on sighting effort

conducted between the 200 and 2,000 meter isobaths from Cape Hatteras to Georges Bank is 896 (CV = 0.68). The

estimate for the 1993 survey, conducted principally between the 200 and 2,000 meter isobaths from the southern edge

of Georges Bank, across the Northeast Channel to the southwestern edge of the Scotian Shelf is 668 long-finned pilot

whales (CV = 0.55). 

Although the 1990-1993 surveys did not sample the same areas or encompass the entire pilot whale habitat,

they did focus on segments of known or suspected high-use habitats off the northeastern U.S. coast. The collective

1990-93 data suggest that, seasonally, at least several thousand pilot whales are occupying these waters; however,

survey coverage to date is not judged adequate to provide a definitive estimate of pilot whale abundance in the western

North Atlantic. 

Minimum Population Estimate

 The minimum population estimate was based on the AT-11 aerial survey abundance estimate in 1991 of

5,377 long-finned pilot whales (CV = 0.53) (NMFS unpublished data). The AT-11 estimate was selected because that

survey provided the most complete coverage of continental shelf edge and continental slope waters off the northeast

U.S. coast. The minimum population estimate is the lower limit of the two-tailed 60% confidence interval of the lognormal distributed abundance estimate, which is equivalent to the 20th percentile of the log-normal distribution as

specified by NMFS (Anon. 1994) and was 3,537 long-finned pilot whales. 

Current Population Trend

There are insufficient data to determine the population trends for this species. 

CURRENT AND MAXIMUM NET PRODUCTIVITY RATES

Current and maximum net productivity rates are not known for this stock. The maximum net productivity

rate was assumed to be 0.04 for purposes of this assessment. This value is based on theoretical calculations showing

that cetacean populations may not generally grow at rates much greater than 4% given the constraints of their

reproductive life history (Anon. 1994). 

Some of the life history parameters which have been estimated from animals taken in the Newfoundland drive

fishery include: calving interval 3.3 years; lactation period about 21-22 months; gestation period 12 months; births

mainly from June to November. Length at birth is 177 cm; mean length at sexual maturity, 490 cm, males; and 356

cm, females; age at sexual maturity is 12 years for males and 6 years for females, and mean adult length is 557 cm for

males and 448 cm for females; and maximum age was 40 for males, and 50 for females (Sergeant 1962; Kasuya et al.

1988). Analysis of data recently collected from animals taken in the Faroe Islands drive fishery produced higher values

for all parameters (Bloch et al. 1993; Desportes et al. 1993; Martin and Rothery 1993). These differences are likely

related, at least in part, to larger sample sizes and newer analytical techniques. 

POTENTIAL BIOLOGICAL REMOVAL

Potential biological removal (PBR) was specified as the product of minimum population size, one-half the

maximum productivity rate, and a "recovery" factor for endangered, depleted, threatened stocks, or stocks of unknown

status relative to optimum sustainable population (OSP) (Anon. 1994). The recovery factor was set at 0.40 because

of the high variance associated with the estimate of total annual fishery-related mortality and serious injury for

Globicephala spp. PBR for this stock is 28 long-finned pilot whales. 
63

ANNUAL HUMAN-CAUSED MORTALITY

Pilot whales also have a propensity to mass strand throughout their range, but the role of human activity in

these events is unknown. Between two and 120 pilot whales have stranded annually either individually or in groups

in the NMFS Northeast Region (Anon. 1993) since 1980. 

Foreign fishery observers documented 436 pilot whale mortalities in Atlantic mackerel and squid fisheries

(Waring et al. 1990; Waring,1995). Between 1989 and 1993, forty two mortalities were observed in the large pelagic

drift-gillnet fishery, five in the pelagic pair trawl fishery, and one each in the pelagic longline and groundfish trawl

fisheries (NMFS unpublished data; see below). Although only one mortality has been observed in the U.S. large

pelagic longline fishery, 24 pilot whales were released alive, two injured, after becoming entangled or hooked in this

gear. Pilot whales are frequently observed to feed on hooked fish, particularly big-eye tuna (NMFS unpublished data).

One mortality was observed in New England groundfish trawl fisheries. There were no takes in the New England

multispecies sink gillnet fishery. An unknown number of pilot whales have also been taken in Newfoundland and

Labrador, and Bay of Fundy, groundfish gillnets, Atlantic Canada and Greenland salmon gillnets, and Atlantic Canada

cod traps (Read 1994).

Total fishery-related mortality and serious injury cannot be estimated separately for the two species of pilot

whales in the U.S. Atlantic EEZ because of the uncertainty in species identification by fishery observers. The Atlantic

Scientific Review Group advised adopting the risk-averse strategy of assuming that either species might have been

subject to the observed fishery-related mortality and serious injury. Total estimated annual fishery-related mortality

of pilot whales from NMFS-observed fisheries was the sum of integer-rounded annual mortality estimates across the

pelagic longline, drift gillnet, and groundfish trawl fisheries and was 109 pilot whales, Globicephala spp. (CV = 0.90).

Total fishery-related mortality and serious injury of pilot whales is not less than 10% of the calculated PBR

for this stock and, therefore, cannot be considered to be insignificant and approaching zero mortality and serious injury

rate. This determination cannot be made for specific fisheries until the implementing regulations for Section 118 of

the MMPA have been reviewed by the public and finalized. 

Fisheries Information

Prior to 1977, there was no documentation of marine mammal by-catch in distant-water fleet (DWF) activities

off the northeast coast of the U.S. A fishery observer program, which has collected fishery data and information on

incidental by-catch of marine mammals, was established in 1977 with the implementation of the Magnuson Fisheries

Conservation and Management Act (MFCMA). DWF effort in the Atlantic coast EEZ under MFCMA has been

directed primarily towards Atlantic mackerel and squid. An average of 120 different foreign vessels per year (range

102-161) operated within the Atlantic coast EEZ during 1977 through 1982. In 1982, there were 112 different foreign

vessels; 18 (16%) were Japanese tuna longline vessels operating along the U.S. Atlantic coast. This was the first year

that the Northeast Regional Observer Program assumed responsibility for observer coverage of the longline vessels.

The number of foreign vessels operating within the U.S. Atlantic EEZ each year between 1983 and 1991 averaged 33

and ranged from nine to 67. The number of Japanese longline vessels included among the DWF vessels averaged six

and ranged from three to eight between 1983 and 1988. MFCMA observer coverage on DWF vessels was 25-35%

during 1977-82, increased to 58%, 86%, 95%, and 98%, respectively, during 1983-86, and 100% observer coverage

was maintained from 1987-91. Foreign fishing operations for squid ceased at the end of the 1986 fishing season and,

for mackerel, at the end of the 1991 fishing season. 

During 1977-1991, observers in this program recorded 436 pilot whale mortalities in foreign-fishing activities

(Waring et al. 1990; Waring 1995). A total of 391 (90%) were taken in the mackerel fishery, and 41 (9%) occurred

during Loligo and Illex squid-fishing operations. This total includes 48 documented takes by U.S. vessels involved

in joint venture fishing operations in which U.S. captains transfer their catches to foreign processing vessels. Due to

temporal fishing restrictions, the by-catch occurred during winter/spring (December to May) in continental shelf and

continental shelf edge waters (Fairfield et al. 1993; Waring, 1995); however, the majority of the takes occurred in late

spring along the 100 m isobath. Two animals were also caught in both the hake fishery and tuna longline fisheries

(Waring et al. 1990). 

The Atlantic Canadian and Greenland salmon gillnet fishery is seasonal, with the peak from June to

September, depending on location. In southern and eastern Newfoundland, and Labrador during 1989, 2,196 nets 91

m long were used. There are no effort data available for the Greenland fishery; however, the fishery was terminated

in 1993 under an agreement between Canada and North Atlantic Salmon Fund (Read 1994). 
64

The groundfish gillnet fishery is widespread and important. Many fisherman hold groundfish gillnet licenses

but the number of active fishermen is unknown. In 1989, approximately 6,800 licenses were issued to fishermen along

the southern coast of Labrador, and northeast and southern coast of Newfoundland. In the Gulf of St. Lawrence, there

were about 3,900 licenses issued in 1989, while in the Bay of Fundy and southwestern Nova Scotia 659 licenses were

issued. 

There were 3,121 cod traps operating in Newfoundland and Labrador during 1979, and about 7,500 in 1980

(Read 1994). This fishery was closed at the end of 1993 due to collapse of Canadian groundfish resources. 

The distribution of long-finned pilot whale, a northern species, overlaps with that of the short-finned pilot

whale, a predominantly southern species, between 35E30'N to 38E00'N (Leatherwood et al. 1976). Although longfinned pilot whales are most likely taken in the waters north of Delaware Bay, many of the pilot whale takes are not

identified to species and by-catch does occur in the overlap area. In this summary, therefore, long-finned pilot whales

(Globicephala melas) and unidentified pilot whales (Globicephala spp.) are considered together. 

Data on current incidental takes in U.S. fisheries are available from several sources. In 1986, NMFS

established a mandatory logbook system for large pelagic fisheries. Data files are maintained at the Southeast Fisheries

Science Center (SEFSC). The Northeast Fisheries Science Center (NEFSC) Sea Sampling Observer Program was

initiated in 1989, and since that year several fisheries have been covered by the program. In late 1992 and in 1993,

the SEFSC provided observer coverage of pelagic longline vessels fishing off the Grand Banks (Tail of the Banks) and

provides observer coverage of vessels fishing south of Cape Hatteras. 

The estimated total number of hauls in the Atlantic large pelagic drift gillnet fishery increased from 714 in

1989 to 1,144 in 1990; thereafter, with the introduction of quotas, effort was severely reduced. The estimated number

of hauls in 1991, 1992, and 1993 were 233, 243, and 232 respectively. Fifty-nine different vessels participated in this

fishery at one time or another between 1989 and 1993. Observer coverage, expressed as percent of sets observed,

ranged from 8% in 1989, 6% in 1990, 20% in 1991, to 40% in 1992, and 42% in 1993. Effort was concentrated along

the southern edge of Georges Bank and off Cape Hatteras. Examination of the species composition of the catch and

locations of the fishery throughout the year, suggested that the drift gillnet fishery be stratified into two strata, a

southern or winter stratum, and a northern or summer stratum. Estimates of the total by-catch, for each year, were

obtained using the aggregated (pooled 1989-1993) catch rates, by strata (Northridge, in review). Forty-two pilot whale

(Globicephala spp.) mortalities were observed between 1989 and 1993. Six animals were released alive but one was

injured. The annual fishery-related mortality (CV in parentheses) was 77 in 1989 (1.1), 132 in 1990 (0.59), 30 in 1991

(0.76), 33 in 1992 (0.29), and 31 in 1993 (0.34); average annual mortality between 1989-1993 was 61 pilot whales

(0.87). Because animals released alive may have subsequently died due to injuries received during entanglement, pilot

whales that were released were included in the mortality estimates. Pilot whales were taken along the continental shelf

edge, northeast of Cape Hatteras in January and February. Takes were recorded at the continental shelf edge east of

Cape Charles, Virginia, in June. Pilot whales were taken from Hydrographer Canyon along the Great South Channel

to Georges Bank from July-November. Takes occurred at the Oceanographer Canyon continental shelf break and along

the continental shelf northeast of Cape Hatteras in October-November.

 Effort in the Atlantic swordfish/tuna/shark pair trawl fishery has increased during the period 1989 to 1993,

from zero hauls in 1989 and 1990, to an estimated 171 hauls in 1991, and then to an estimated 989 and 1087 hauls

in 1992 and 1993, respectively. The fishery operated from August-November in 1991, from June-November in 1992,

and from June-October in 1993. Sea sampling began in October 1992, and 101 sets (10% of the total) were sampled

in that season, 201 hauls (18% of the total) were sampled in 1993. Nineteen vessels have operated in this fishery. The

fishery extends from 35oN to 41oN, and from 69EW to 72EW. Approximately 50% of the total effort was within a one

degree square at 39oN, 72oW, around Hudson Canyon. Examination of the locations and species composition of the

by-catch, showed little seasonal change for the six months of operation and did not warrant any seasonal or areal

stratification of this fishery (Northridge, in review). Five pilot whale (Globicephala spp.) mortalities were reported

from logbook entries in 1993, but no fishery-related mortality or serious injury was reported by observers. 

Pelagic swordfish, tunas, and billfish are the targets of the U.S. longline fishery in the U.S. Atlantic and Gulf

of Mexico EEZ (SEFSC unpublished logbook data). Interactions between the longline swordfish/tuna fishery and pilot

whales have been reported; however, a vessel may fish in more than one statistical reporting area and it is not possible

to separate estimates of fishing effort other than to subtract Gulf of Mexico effort from Atlantic fishing effort, which

includes the Caribbean Sea. This fishery has been monitored with about 5% observer coverage, in terms of trips

observed, since 1992. Total longline effort for the Atlantic pelagic fishery (including the Caribbean), based on
65

mandatory logbook reporting, was 11,279 sets in 1991, 10,605 sets in 1992, and 11,538 in 1993 (Cramer 1994). The

fishery has been observed from January to March off Cape Hatteras, in May and June in the entire Mid-Atlantic, and

in July through December in the Mid-Atlantic Bight and off Nova Scotia. Twenty four animals were released alive,

but two were injured. One mortality was observed between 1990 and 1993. January-March by-catch was concentrated

on the continental shelf edge northeast of Cape Hatteras. By-catch was recorded in this area during April-June, and

takes also occurred north of Hydrographer Canyon off the continental shelf in water over 1,000 fathoms during AprilJune. During the July-September period, takes occurred on the continental shelf edge east of Cape Charles, Virginia,

and on Block Canyon slope in over 1,000 fathoms of water. October-December by-catch occurred along the 20 to 50

fathom contour lines between Barnegatt Bay and Cape Hatteras. Estimated take was based on a generalized linear

model (Poisson error assumption) fit to the available observed incidental take and self-reported incidental take and

effort data for the fishery (SEFSC unpublished data). The estimated fishery-related mortality to pilot whales in the

U.S. Atlantic attributable to this fishery occurred in 1992 and was 22 (CV = 0.23); average annual mortality between

1992-1993 was eleven pilot whales (0.33). 

Vessels in the New England groundfish multispecies trawl fishery, a Category III fishery under the MMPA,

were observed in order to meet fishery management needs, rather than marine mammal management needs. An

average of 970 (CV = 0.04) vessels (full and part time) participated annually in the fishery during 1989-1993. The

fishery is active in New England in all seasons. One mortality was documented between 1989 and 1993. Also, one

animal was released alive. The estimated fishery-related mortality in 1990 was 184 (CV = 0.99); average annual

fishery-related mortality during 1989-1993 was 37 pilot whales (2.21).

The mid-Atlantic mackerel and squid trawl fisheries were combined into the Atlantic mid-water trawl fishery

in the revised proposed list of fisheries in 1995. The fishery occurs along the U.S. mid-Atlantic continental shelf

region between New Brunswick, Canada, and Cape Hatteras year around. The mackerel trawl fishery was classified

as a Category II fishery since 1990 and the squid fishery was originally classified as a Category II fishery in 1990, but

was reclassified as a Category III fishery in 1992. The combined fishery has been proposed for classification as a

Category II fishery. Three fishery-related mortality of pilot whales were reported in logbook reports from the mackerel

trawl fishery between 1990-1992.

Other Mortality

A potential human-caused source of mortality is from polychlorinated biphenyls (PCBs) and DDT, moderate

levels of which have been found in pilot whale blubber (Taruski 1975; Muir et al. 1988). The effect of the observed

levels of such contaminants is unknown. 

STATUS OF STOCK

The status of long-finned pilot whales relative to OSP in U.S. Atlantic coast waters is unknown, but stock

abundance may have been affected by reduction in foreign fishing, curtailment of the Newfoundland drive fishery for

pilot whales in 1971, and increased abundance of herring, mackerel, and squid stocks. There are insufficient data to

determine the population trends for this species. The species is not listed under the Endangered Species Act. In

Canada, the Cetacean Protection Regulations of 1982, promulgated under the Standing Fisheries Act, prohibit the

catching or harassment of all cetacean species. The total level of human-caused mortality and serious injury is believed

to be significant based on current data. This is a strategic stock because the 1989-93 estimated average annual fisheryrelated mortality to pilot whales, Globicephala spp., exceeds PBR. 

REFERENCES

Abend, A. 1993. Long-finned pilot whale distribution and diet as determined from stable carbon and nitrogen ratio

isotope tracers. M.S. Thesis, University of Massachusetts, Amherst. 

Anon. 1994. Report of the PBR (Potential Biological Removal) workshop. June 27-29, 1994. NOAA, NMFS

Southwest Fisheries Science Center, La Jolla, California, 13 pp. + Appendices. 

Anon. 1993. Status of fishery resources off the northeastern United States for 1993. NOAA Tech. Mem. NMFSF/NEC-101, 140 pp. 

Bloch, D., M. Zachariassen and P. Zachariassen. 1993. Some external characters of the long-finned pilot whale off

Faroe Island and a comparison with the short-finned pilot whale. Rep. Int. Whal. Commn. Special Issue

14:117-135. 
66

CeTAP. 1982. A characterization of marine mammals and turtles in the mid- and north Atlantic areas of the U.S.

outer continental shelf. Cetacean and Turtle Assessment Program, University of Rhode Island. Final Report,

Contract AA51-C78-48, Bureau of Land Management, Washington, DC. 538 pp. 

Desportes, G., M. Saboureau and A. Lacroix. 1993. Reproductive maturity and seasonality of male pilot long-finned

whales off the Faroe Islands. Rep. Int. Whal. Commn. Special Issue 14: 233-262. 

Fairfield, C. P., G. T. Waring and M. H. Sano. 1993. Pilot whales incidentally taken during the distant water fleet

Atlantic mackerel fishery in the mid-Atlantic Bight, 1984-88. Rep. Int. Whal. Commn. Special Issue 14: 107-

116. 

Kasuya, T., D. E. Sergeant and K. Tanaka. 1988. Re-examination of life history parameters of long-finned pilot

whales in the Newfoundland waters. Sci. Rep. Whales Res. Inst. No. 39: 103-119. 

Leatherwood, S., D. K. Caldwell and H. E. Winn. 1976. Whales, dolphins, and porpoises of the western North

Atlantic. A guide to their identification. U.S. Dept. of Commerce, NOAA Tech. Rep. NMFS Circ. 396, 176

pp. 

Martin, A. R. and P. Rothery. 1993. Reproductive parameters of female long-finned pilot whales (Globicephala

melas) around the Faroe Islands. Rep. Int. Whal. Commn. Special Issue 14: 263-304. 

Mercer, M. C. 1975. Modified Leslie-DeLury population models of the long-finned pilot whale (Globicephala

melaena) and annual production of the short-finned squid (Illex illecebrosus) based upon their interactions

at Newfoundland. J. Fish. Res. Bd. Can. 32(7): 1145-54. 

Mitchell, E. 1975. Present status of northwest Atlantic fin and other whale stocks. Pages 108-169 in W. E. Schevill

(editor), The whale problem: A status report. Harvard University Press, Cambridge, Massachusetts, 419 pp.

Muir, D. C. G., R. Wagermann, N. P. Grift, R. J. Norstrom, M. Simon, and J. Lien. 1988. Organochlorine chemical

and heavy metal contaminants in white-beaked dolphins (Lagenorhynchus albirostris) and pilot whales

(Globicephala melaena) from the coast of Newfoundland. Canada. Arch. Environ. Contam. Toxicol. 17: 613-

29. 

Payne, P. M. and D. W. Heinemann. 1993. The distribution of pilot whales (Globicephala spp.) in shelf/shelf edge

and slope waters of the northeastern United States, 1978-1988. Rep. Int. Whal. Commn. Special Issue 14:

51-68. 

Sergeant D. E. 1962. The biology of the pilot or pothead whale (Globicephala melaena (Traill) in Newfoundland

waters. Bull. Fish. Res. Bd. Can. 132: 1-84. 

Taruski, A. G., C. E. Olney, and H. E. Winn. 1975. Chlorinated hydrocarbons in cetaceans. J. Fish. Res. Bd. Can.

32(11): 2205-9. 

Waring, G. T., P. Gerrior, P. M. Payne, B. L. Parry and J. R. Nicolas. 1990. Incidental take of marine mammals in

foreign fishery activities off the northeast United States, 1977-1988. Fish. Bull., U.S. 88(2): 347-360.

Waring, G. T. 1995. Fishery and ecological interactions for selected cetaceans off the northeast USA. Ph.D.

dissertation, University of Massachusetts, Amherst, 260 pp. 
67

Cape Hatteras

Cape Canaveral

Figure 1. Sightings of short-finned pilot whales

(filled circles) and unidentified pilot whales

(unfilled circles) during NOAA Ship Oregon II

marine mammal survey cruise in winter 1992.

SHORT-FINNED PILOT WHALE (Globicephala macrorhynchus): 

Western North Atlantic Stock

STOCK DEFINITION AND GEOGRAPHIC RANGE

There are two species of pilot whales in the Western Atlantic: the Atlantic or long-finned pilot whale,

Globicephala melas, and the short-finned pilot whale, G. macrorhynchus. These species are difficult to identify to

the species level at sea; therefore, some of the descriptive material below refers to Globicephala spp. and is

identified as such. The species boundary is considered to be in the New Jersey to Cape Hatteras area. Sightings

north of this area are likely G. melas. 

The short-finned pilot whale is distributed worldwide in tropical to warm temperate waters (Leatherwood

and Reeves 1983). The northern extent of the range of this species within the U.S. Atlantic Exclusive Economic

Zone (EEZ) is generally thought to be Cape Hatteras, North Carolina (Leatherwood and Reeves 1983). Sightings

of these animals in U.S. Atlantic EEZ occur primarily within the Gulf Stream [Southeast Fisheries Science Center

(SEFSC) unpublished data], and primarily along the

continental shelf and continental slope in the northern Gulf of

Mexico (Mullin et al. 1991; SEFSC unpublished data). There

is no information on stock differentiation for the Atlantic

population. 

POPULATION SIZE

Estimates of abundance were derived through the

application of distance sampling analysis (Buckland et al.

1993) and the computer program DISTANCE (Laake et al.

1993) to sighting data collected during a 1992 winter, visual

sampling, line-transect vessel survey of the U.S. Atlantic EEZ

waters between Miami, Florida, and Cape Hatteras, North

Carolina. The estimated abundance of short-finned pilot

whales for the 1992 survey was 749 (coefficient of variation,

CV = 0.64) (Hansen et al. 1994). 

Minimum Population Estimate

The minimum population estimate is the lower limit

of the two-tailed 60% confidence interval of the log-normal

distributed abundance estimate, which is equivalent to the 20th

percentile of the log-normal distributed average abundance

estimate (Hansen et al. 1994) as specified by NMFS (Anon.

1994). The minimum population estimate was based on the

1992 survey abundance estimate of 749 short-finned pilot

whales (CV = 0.64) (Hansen et al. 1994) and was 457. 

Current Population Trend

There are insufficient data to determine the

population trends for this species. 

CURRENT AND MAXIMUM NET PRODUCTIVITY RATES

Current and maximum net productivity rates are not known for this stock; therefore, the default maximum

net productivity rate of 0.04 (Anon. 1994) was used for purposes of this assessment. 

POTENTIAL BIOLOGICAL REMOVAL

Potential biological removal level (PBR) was specified as the product of the minimum population size, one

half the maximum net productivity rate, and a recovery factor for endangered, threatened, or depleted stocks, or
68

stocks of unknown status relative to optimum sustainable population (OSP) (Anon. 1994). The recovery factor was

set at 0.40 because of the high variance associated with the estimate of total annual fishery-related mortality and

serious injury for Globicephala spp. PBR for this stock is 3.7 short-finned pilot whales. 

ANNUAL HUMAN-CAUSED MORTALITY AND SERIOUS INJURY

The level of past or current, direct, human-caused mortality of short-finned pilot whales in the U.S.

Atlantic EEZ is unknown. The short-finned pilot whale has been taken in the U.S. longline swordfish/tuna fishery

in Atlantic waters off the southeastern U.S. (Lee et al. 1994; SEFSC unpublished data). Pilot whales have been

taken in fisheries operating in the deeper, offshore waters off the northeastern U.S. waters north of the presumed

range of this stock. The pilot whales taken in these fisheries may have been the long-finned pilot whale, G. melas

(Waring 1990); however, total fishery-related mortality and serious injury cannot be estimated separately for the

two species of pilot whales because of the uncertainty in species identification by fishery observers. 

There were 101 short-finned pilot whale strandings documented during 1987-1993 along the U.S. Atlantic

coast between Cape Hatteras, North Carolina, and Miami, Florida; two of these were classified as likely caused by

fishery interactions. 

Total fishery-related mortality and serious injury cannot be estimated separately for the two species of

pilot whales in the U.S. Atlantic EEZ because of the uncertainty in species identification by fishery observers. The

Atlantic Scientific Review Group advised adopting the risk-averse strategy of assuming that either species might

have been subject to the observed fishery-related mortality and serious injury. Total estimated annual fisheryrelated mortality of pilot whales from NMFS-observed fisheries was the sum of the integer-rounded annual

mortality estimates across the pelagic longline, drift gillnet, and groundfish trawl fisheries and was 109 pilot

whales, Globicephala spp. (CV = 0.90).

Total fishery-related mortality and serious injury of pilot whales is not less than 10% of the calculated

PBR for this stock and, therefore, cannot be considered to be insignificant and approaching zero mortality and

serious injury rate. This determination cannot be made for specific fisheries until the implementing regulations for

Section 118 of the MMPA have been reviewed by the public and finalized. 

Fisheries Information

Data on current incidental takes in U.S. fisheries are available from several sources. In 1986, NMFS

established a mandatory logbook system for large pelagic fisheries. Data files are maintained at the Southeast

Fisheries Science Center (SEFSC). The Northeast Fisheries Science Center (NEFSC) Sea Sampling Observer

Program was initiated in 1989, and since that year several fisheries have been covered by the program. In late

1992 and in 1993, the SEFSC provided observer coverage of pelagic longline vessels fishing off the Grand Banks

(Tail of the Banks) and provides observer coverage of vessels fishing south of Cape Hatteras. 

The estimated total number of hauls in the Atlantic large pelagic drift gillnet fishery increased from 714

in 1989 to 1,144 in 1990; thereafter, with the introduction of quotas, effort was severely reduced. The estimated

number of hauls in 1991, 1992, and 1993 were 233, 243, and 232 respectively. Fifty-nine different vessels

participated in this fishery at one time or another between 1989 and 1993. Observer coverage, expressed as

percent of sets observed, ranged from 8% in 1989, 6% in 1990, 20% in 1991, to 40% in 1992, and 42% in 1993. 

Effort was concentrated along the southern edge of Georges Bank and off Cape Hatteras. Examination of the

species composition of the catch and locations of the fishery throughout the year, suggested that the drift gillnet

fishery be stratified into two strata, a southern or winter stratum, and a northern or summer stratum. Estimates of

the total by-catch, for each year, were obtained using the aggregated (pooled 1989-1993) catch rates, by strata

(Northridge, in review). Forty-two pilot whale (Globicephala spp.) mortalities were observed between 1989 and

1993. Six animals were released alive but one was injured. The annual fishery-related mortality (CV in

parentheses) was 77 in 1989 (1.1), 132 in 1990 (0.59), 30 in 1991 (0.76), 33 in 1992 (0.29), and 31 in 1993 (0.34);

average annual mortality between 1989-1993 was 61 pilot whales (0.87). Because animals released alive may have

subsequently died due to injuries received during entanglement, pilot whales that were released were included in

the mortality estimates. Pilot whales were taken along the continental shelf edge, northeast of Cape Hatteras in

January and February. Takes were recorded at the continental shelf edge east of Cape Charles, Virginia, in June. 

Pilot whales were taken from Hydrographer Canyon along the Great South Channel to Georges Bank from July-
69

November. Takes occurred at the Oceanographer Canyon continental shelf break and along the continental shelf

northeast of Cape Hatteras in October-November. 

Pelagic swordfish, tunas, and billfish are the targets of the U.S. longline fishery in the U.S. Atlantic and

Gulf of Mexico EEZ (SEFSC unpublished logbook data). Interactions between the longline swordfish/tuna fishery

and pilot whales have been reported; however, a vessel may fish in more than one statistical reporting area and it is

not possible to separate estimates of fishing effort other than to subtract Gulf of Mexico effort from Atlantic fishing

effort, which includes the Caribbean Sea. This fishery has been monitored with about 5% observer coverage, in

terms of trips observed, since 1992. Total longline effort for the Atlantic pelagic fishery (including the Caribbean),

based on mandatory logbook reporting, was 11,279 sets in 1991, 10,605 sets in 1992, and 11,538 in 1993 (Cramer

1994). The fishery has been observed from January to March off Cape Hatteras, in May and June in the entire

Mid-Atlantic, and in July through December in the Mid-Atlantic Bight and off Nova Scotia. Twenty four animals

were released alive, but two were injured. One mortality was observed between 1990 and 1993. January-March

by-catch was concentrated on the continental shelf edge northeast of Cape Hatteras. By-catch was recorded in this

area during April-June, and takes also occurred north of Hydrographer Canyon off the continental shelf in water

over 1,000 fathoms during April-June. During the July-September period, takes occurred on the continental shelf

edge east of Cape Charles, Virginia, and on Block Canyon slope in over 1,000 fathoms of water. OctoberDecember by-catch occurred along the 20 to 50 fathom contour lines between Barnegatt Bay and Cape Hatteras.

Estimated take was based on a generalized linear model (Poisson error assumption) fit to the available observed

incidental take and self-reported incidental take and effort data for the fishery (SEFSC unpublished data). The

estimated fishery-related mortality to pilot whales in the U.S. Atlantic attributable to this fishery occurred in 1992

and was 22 (CV = 0.23); average annual mortality between 1992-1993 was eleven pilot whales (0.33). 

Vessels in the New England groundfish multispecies trawl fishery, a Category III fishery under the

MMPA, were observed in order to meet fishery management needs, rather than marine mammal management

needs. An average of 970 (CV = 0.04) vessels (full and part time) participated annually in the fishery during

1989-1993. The fishery is active in New England in all seasons. One mortality was documented between 1989

and 1993. Also, one animal was released alive. The estimated fishery-related mortality in 1990 was 184 (CV =

0.99); average annual fishery-related mortality during 1989-1993 was 37 pilot whales (2.21).

The mid-Atlantic mackerel and squid trawl fisheries were combined into the Atlantic mid-water trawl

fishery in the revised proposed list of fisheries in 1995. The fishery occurs along the U.S. mid-Atlantic continental

shelf region between New Brunswick, Canada, and Cape Hatteras year around. The mackerel trawl fishery was

classified as a Category II fishery since 1990 and the squid fishery was originally classified as a Category II fishery

in 1990, but was reclassified as a Category III fishery in 1992. The combined fishery has been proposed for

classification as a Category II fishery. Three fishery-related mortality of pilot whales were reported in logbook

reports from the mackerel trawl fishery between 1990-1992.

STATUS OF STOCK

The status of the short-finned pilot whale relative to OSP in U.S. Atlantic coast waters is unknown. There

are insufficient data to determine the population trends for this stock. They are not listed under the Endangered

Species Act. This is a strategic stock because the 1989-93 estimated average annual fishery-related mortality to

pilot whales, Globicephala spp., exceeds PBR for this stock. 

REFERENCES

Anon. 1994. Report of the PBR (Potential Biological Removal) workshop. June 27-29, 1994. NOAA, NMFS

Southwest Fisheries Science Center, La Jolla, California, 13 pp. + Appendices.

Buckland, S. T., D. R. Anderson, K. P. Burnham and J. L. Laake. 1993. Distance Sampling: estimating

abundance of biological populations. Chapman & Hall, London, 446 pp. 

Hansen, L. J., K. D. Mullin and C. L. Roden. 1994. Preliminary estimates of cetacean abundance in the northern

Gulf of Mexico from vessel surveys, and of selected cetacean species in the U.S. Atlantic Exclusive

Economic Zone from vessel surveys from vessel surveys. Southeast Fisheries Science Center, Miami

Laboratory, Contribution No. MIA-93/94-58.

Laake, J. L., S. T. Buckland, D. R. Anderson, and K. P. Burnham. DISTANCE user’s guide, V2.0. Colorado

Cooperative Fish & Wildlife Research Unit, Colorado State University, Ft. Collins, Colorado, 72 pp. 
70

Leatherwood, S. and R. R. Reeves. 1983. The Sierra Club handbook of whales and dolphins. Sierra Club Books,

San Francisco, 302 pp. 

Lee, D. W., C. J. Brown, A. J. Catalano, J. R. Grubich, T. W. Greig, R. J. Miller and M. T. Judge. 1994. SEFSC

pelagic longline observer program data summary for 1992-1993. NOAA Tech. Mem. NMFS-SEFSC-347.

19 pp. 

Mullin, K., W. Hoggard, C. Roden, R. Lohoefener, C. Rogers and B. Taggart. 1991. Cetaceans on the upper

continental slope in the north-central Gulf of Mexico. OCS Study/MMS 91-0027. U.S. Dept. of the

Interior, Minerals Management Service, Gulf of Mexico OCS Regional Office, New Orleans, Louisiana,

108 pp. 
71

Figure 1. Distribution of white-sided dolphin sightings from

NEFSC shipboard surveys during the summer in 1990-1994. 

Isobaths are at 100 m and 1,000 m. 

WHITE-SIDED DOLPHIN (Lagenorhynchus acutus):

Western North Atlantic Stock

STOCK DEFINITION AND GEOGRAPHIC RANGE

White-sided dolphins are found in temperate and sub-polar waters of the North Atlantic, primarily on

continental shelf waters to the 100 m depth contour. The species occurs from central west Greenland to the

Chesapeake Bay (about 37EN) and perhaps as far east as 55o W (Evans 1987). There is no information concerning

stock structure within this range. 

White-sided dolphins are most common in continental shelf waters from Hudson Canyon (approximately

39EN) north through Georges Bank, in the Gulf of Maine to the lower Bay of Fundy. Low numbers of white-sided

dolphins occur from Chesapeake Bay to Jeffreys Ledge (off New Hampshire) during winter and early spring (January

to April). From May through June, large aggregations are found from Georges Bank to the southwest Gulf of Maine,

while some animals have been seen from the southern Grand Banks, along Newfoundland and into the Labrador Sea.

From July to December, the distribution of sightings extends from Georges Bank to the lower Bay of Fundy (Payne and

Heinemann 1990) and along Nova Scotia all the way along the coasts to the Labrador Sea and west Greenland (Gaskin

1992). 

Before the 1960's, white-sided dolphins in U.S. waters were usually found offshore on the continental slope.

There has been an apparent increase in the number of white-sided dolphins seen on the continental shelf from the

1960's to the present. This shift may be due to an increase in sand lance in continental shelf waters of the Gulf of

Maine (Katona et al. 1993). With declining sand lance abundance (NMFS unpublished data), occurrence of whitesided dolphins in continental shelf waters may similarly decrease. 

POPULATION SIZE

The total number of white-sided dolphins along

the eastern U.S. and Canadian Atlantic coast is unknown,

although two estimates from select regions do exist.

Seasonal abundance estimates are available from an aerial

survey line transect program conducted in continental

shelf and continental shelf edge waters between Cape

Hatteras, North Carolina, and Nova Scotia from 1978 to

1982 (CeTAP 1982), just after the cessation of extensive

foreign fishing operations in this region. A population

estimate based on an inverse variance weighted pooling of

CeTAP spring, summer, and autumn data is 28,600

[coefficient of variation (CV) = 0.21]. An average for

these three seasons was chosen because the greatest

proportion of the population off the northeast U.S. coast

appears to be in the CeTAP study area during these

seasons. This estimate was not corrected for g(0), the

probability of detecting an animal group on the trackline.

Shipboard line transect surveys in 1991, 1992,

and 1993 have provided more recent abundance estimates

and white-sided dolphin sightings during these surveys

are shown in Figure 1. A weighted-average abundance

for the northern Gulf of Maine/lower Bay of Fundy region

during the summers of 1991 and 1992 is 20,400 (CV =

0.63), where each annual estimate is weighted by the

inverse of its variance (NMFS unpublished data). Two

independent teams on the same ship surveyed using the

naked eye in non-closing mode. This estimate includes an
72

estimate of g(0) for both teams of 0.62 (CV = 0.90). (The average g(0) for each team separately is 0.35 (CV = 0.46)).

In addition, the estimate takes in account of size bias (bias caused by large groups of dolphins being detected with

higher probability than small groups). The g(0)-corrected abundance estimate was calculated using the product interval

analytical method (Palka, in press) with size-biased corrected estimates of density for the two separate teams. The sizebiased density estimates were derived using the computer program DISTANCE version 2.0 (Buckland et al. 1993;

Laake et al. 1993). The variance was estimated by bootstrapping the size-biased team density estimates. 

The data used were obtained from two shipboard line transect sighting surveys designed to estimate abundance

of harbor porpoises (Palka, in press). The study area was stratified by water depth and expected density of harbor

porpoises. This stratification scheme could cause uncertainties in a white-sided dolphin abundance estimate because

white-sided dolphin habitat in the north-central Gulf of Maine was surveyed at a low intensity. White-sided dolphin

abundance was estimated under the reasonable assumption that observed densities of white-sided dolphins in the

surveyed offshore waters were similar to densities in the unsurveyed offshore waters. 

An abundance estimate was also derived using data collected during a June-July 1993 fine-scale ship survey

conducted principally between the 200 and 2,000 m isobaths from the southern edge of Georges Bank, across the

Northeast Channel to the southwestern edge of the Scotian Shelf (NMFS unpublished data). The survey was conducted

by one team searching through high-powered binoculars. The data were analyzed using DISTANCE (Buckland et al.

1993; Laake et al. 1993), where the confidence was estimated using the bootstrap log normal method, and group-size

bias was considered. The abundance estimate for white-sided dolphins in this limited portion of their range was 729

(CV = 0.47). 

There are no published abundance estimates for this species in Canadian waters which lie farther north or east

of the above surveys (Gaskin 1992). 

Minimum Population Estimate

The minimum population estimate was based on the 1991-92 shipboard survey abundance estimate of 20,400

white-sided dolphins (CV = 0.63) (NMFS unpublished data). The minimum population estimate is the lower limit of

the two-tailed 60% confidence interval of the log-normal distributed abundance estimate, which is equivalent to the

20th percentile of the log-normal distribution as specified by NMFS (Anon. 1994), and was 12,538 white-sided

dolphins.

Current Population Trend

There are insufficient data to determine the population trends for this species. 

CURRENT AND MAXIMUM NET PRODUCTIVITY RATES

Current and maximum net productivity rates are not known for this stock. Some of the life history parameters

which have been estimated include: calving interval is 2-3 years; lactation period is 18 months; gestation period is 10-

12 months and births occur from May to early August, mainly in June and July. Length at birth is 110 cm, length at

sexual maturity is 230-240 cm for males, and 201-222 cm for females, age at sexual maturity is 8-9 years for males

and 6-8 years for females, and the mean adult length is 250 cm for males and 224 cm for females (Evans 1987).

Maximum reported age for males is 22 years and for females, 27 years (Sergeant et al. 1980). 

The maximum net productivity rate was assumed to be 0.04 for purposes of this assessment. This value is

based on theoretical calculations showing that cetacean populations may not generally grow at rates much greater than

4% given the constraints of their reproductive life history (Reilly and Barlow 1986). 

POTENTIAL BIOLOGICAL REMOVAL

Potential biological removal (PBR) was specified as the product of minimum population size, one-half the

maximum productivity rate, and a "recovery" factor for endangered, depleted, threatened stocks, or stocks of unknown

status relative to optimum sustainable population (OSP) (Anon. 1994). The recovery factor was set at 0.50 because

of the stock's status relative to its OSP level is unknown. PBR for this stock is 125 white-sided dolphins. 

ANNUAL HUMAN-CAUSED MORTALITY AND SERIOUS INJURY

Incidental takes of white-sided dolphins have been recorded in the Gulf of Maine and Bay of Fundy groundfish

gillnet fisheries (Gilbert and Wynne 1987; Gaskin 1992). In the mid 1980's, during a University of Maine study,
73

gillnet fishermen retained six carcasses for biological studies. NMFS foreign fishery observers have reported 44 takes

of Atlantic white-sided dolphins incidental to fishing activities in the continental shelf and continental slope waters

between March 1977 and December 1991 (Waring et al. 1990; NMFS unpublished data). Of these animals, 96% were

taken in the Atlantic mackerel fishery. This total includes nine documented takes by U.S. vessels involved in jointventure fishing operations in which U.S. captains transfer their catches to foreign processing vessels. Recently, whitesided dolphins have been caught in the pelagic drift gillnet fishery, and the New England trawl and sink gillnet

fisheries. No mortalities were documented in the Atlantic swordfish/tuna/shark longline and Atlantic

swordfish/tuna/shark pair trawl fisheries. 

There is little information available which quantifies fishery interactions involving white-sided dolphins in

Canadian waters. Two white-sided dolphins were reported caught in groundfish gillnets set in the Bay of Fundy during

1985 to 1989, and nine were taken in West Greenland between 1964 and 1966 in salmon drift nets (Gaskin 1992).

Several (number not specified) were also taken in Newfoundland and Labrador groundfish gillnets in the 1960's. A

few were taken in an experimental drift gillnet fishery for salmon off West Greenland which took place from 1965 to

1982 (Read 1994). More recent information on Canadian white-sided dolphin takes were not available. 

Estimated average annual fishery-related mortality and serious injury to the western North Atlantic whitesided dolphin stock during 1989-1993 was 127 dolphins (CV = 0.52). Total fishery-related mortality and serious injury

for this stock is not less than 10% of the calculated PBR and, therefore, cannot be considered to be insignificant and

approaching zero mortality and serious injury rate. This determination cannot be made for specific fisheries until the

implementing regulations for Section 118 of the MMPA have been reviewed by the public and finalized. 

Fisheries Information

Prior to 1977, there was no documentation of marine mammal by-catch in distant-water fleet (DWF) activities

off the northeast coast of the U.S. With implementation of the Magnuson Fisheries Conservation and Management

Act (MFCMA) in that year, an observer program was established which has recorded fishery data and information of

incidental by-catch of marine mammals. DWF effort in the U.S. Atlantic Exclusive Economic Zone (EEZ) under

MFCMA has been directed primarily towards Atlantic mackerel and squid. From 1977 through 1982, an average of

120 different foreign vessels per year (range 102-161) operated within the Atlantic coast EEZ. In 1982, there were

112 different foreign vessels; 16%, or 18, were Japanese tuna longline vessels operating along the U.S. east coast. This

was the first year that the Northeast Regional Observer Program assumed responsibility for observer coverage of the

longline vessels. Between 1983 and 1991, the numbers of foreign vessels operating within the Atlantic coast EEZ each

year were 67, 52, 62, 33, 27, 26, 14, 13, and 9, respectively. Between 1983 and 1988, the numbers of DWF vessels

included 3, 5, 7, 6, 8, and 8, respectively, Japanese longline vessels. Observer coverage on DWF vessels was 25-35%

during 1977-82, and increased to 58%, 86%, 95%, and 98%, respectively, in 1983-86; 100% observer coverage was

maintained during 1987-91. Foreign fishing operations for squid ceased at the end of the 1986 fishing season and for

mackerel at the end of the 1991 season.

The estimated total number of hauls in the Atlantic large pelagic drift gillnet fishery increased from 714 in

1989 to 1,144 in 1990; thereafter, with the introduction of quotas, effort was severely reduced. The estimated number

of hauls in 1991, 1992, and 1993 were 233, 243, and 232 respectively. Fifty-nine different vessels participated in this

fishery at one time or another between 1989 and 1993. Observer coverage, expressed as percent of sets observed,

ranged from 8% in 1989, 6% in 1990, 20% in 1991, to 40% in 1992, and 42% in 1993. Effort was concentrated along

the southern edge of Georges Bank and off Cape Hatteras. Examination of the species composition of the catch and

locations of the fishery throughout the year, suggested that the drift gillnet fishery be stratified into two strata, a

southern or winter stratum, and a northern or summer stratum. Estimates of the total by-catch, for each year, were

obtained using the aggregated (pooled 1989-1993) catch rates, by strata (Northridge, in review). Estimated annual

fishery-related mortality and serious injury (CV in parentheses) was 4.4 in 1989 (1.80), 6.8 in 1990 (1.50), 0.9 in 1991

(2.00), 0.8 in 1992 (1.30), and 2.7 in 1993 (0.32); estimated average annual mortality and serious injury during related

to this fishery during 1989-1993 was 3.1 white-sided dolphins (1.88). 

Vessels in the New England groundfish multispecies trawl fishery, a Category III fishery under the MMPA,

were observed in order to meet fishery management needs, rather than marine mammal management needs. An

average of 970 (CV = 0.04) vessels (full and part time) participated annually in the fishery during 1989-1993. The

fishery is active in New England in all seasons. One mortality was documented between 1989 and 1993. The
74

estimated fishery-related mortality in 1992 was 110 (CV = 1.00) and average annual estimate fishery-related mortality

during 1989-1993 was 22 white-sided dolphins ( CV = 2.24). 

The mid-Atlantic mackerel and squid trawl fisheries were combined into the Atlantic mid-water trawl fishery

in the revised proposed list of fisheries in 1995. The fishery occurs along the U.S. mid-Atlantic continental shelf

region between New Brunswick, Canada, and Cape Hatteras year around. The mackerel trawl fishery was classified

as a Category II fishery since 1990 and the squid fishery was originally classified as a Category II fishery in 1990, but

was reclassified as a Category III fishery in 1992. The combined fishery has been proposed for classification as a

Category II fishery. One fishery-related mortality of a white-sided dolphin was reported in logbook reports from the

mackerel trawl fishery between 1990-1992.

There are approximately 349 vessels (full and part time) in the New England multispecies sink gillnet fishery

(Walden, in review). Observer coverage in trips has been 1%, 6%, 7.5%, and 5% for years 1990 to 1993. The fishery

has been observed in the Gulf of Maine and in Southern New England. There have been 73 mortalities observed in

this fishery between 1990 and 1993. One animal was released alive and not injured. Estimated annual fishery-related

mortalities (CV in parentheses) were 49 in 1991 (0.46), 154 in 1992 (0.35), and 205 in 1993 (0.31); average annual

estimated fishery-related mortality during 1991-1993 was 102 white-sided dolphins (0.42). In January to March, the

by-catch occurred in Massachusetts Bay, south of Cape Ann and west of Stellwagen Bank. From April to June, bycatch locations became more dispersed, from Casco Bay to Cape Ann, along the 30 fathom contour out to Jeffreys

Ledge, with one take location near Cultivator Shoal and one in southern New England near Block Island. In July

through September, incidental takes occurred from Frenchman's Bay to Massachusetts Bay. In inshore waters, the

takes were aggregated while offshore takes were more dispersed. In October through December, takes were confined

from Cape Elizabeth out to Jeffreys Ledge and south to Nantucket Sound. 

Other Mortality

Polychlorinated biphenyls (PCBs) and DDT, which have been found in moderate levels in the blubber (Gaskin

1985) are potential sources of human-caused mortality; however, the effect of the observed levels of pollutants is not

known. 

Mass strandings involving up to a hundred or more animals at one time are common for this species. From

1968 to 1993, 348 Atlantic white-sided dolphins are known to have stranded on the New England coast (Hain and

Waring, in preparation). The causes of these strandings are not known. Because such strandings have been known

since antiquity, it could be presumed that recent strandings are a normal condition (Gaskin 1992). It is unknown

whether human causes, such as fishery interactions and pollution, have increased the number of strandings. Stranding

data probably underestimate the extent of fishery-related mortality and serious injury because not all of the marine

mammals which die or are seriously injured may wash ashore, nor will all of those that do wash ashore necessarily

show signs of entanglement or other fishery-interaction. Finally, the level of technical expertise among stranding

network personnel varies widely as does the ability to recognize signs of fishery interaction.

STATUS OF STOCK

The status of white-sided dolphins relative to OSP in the U.S. Atlantic EEZ is unknown. The species is not

listed as threatened or endangered under the Endangered Species Act. In Canada, the Cetacean Protection Regulations

of 1982, promulgated under the Standing Fisheries Act, prohibit the catching or harassment of all cetacean species.

There are insufficient data to determine the population trends for this species. This is a strategic stock because average

annual fishery-related mortality exceeds PBR. 

REFERENCES

Anon. 1994. Report of the PBR (Potential Biological Removal) workshop. June 27-29, 1994. NOAA, NMFS

Southwest Fisheries Science Center, La Jolla, California, 13 pp. + Appendices. 

Buckland, S. T., D. R. Anderson, K. P. Burnham, and J. L. Laake. 1993. Distance Sampling: Estimating abundance

of biological populations. Chapman & Hall, New York, 446 pp. 

CeTAP. 1982. A characterization of marine mammals and turtles in the mid- and north Atlantic areas of the U.S.

outer continental shelf. Cetacean and Turtle Assessment Program, University of Rhode Island. Final Report,

Contract AA51-C78-48, Bureau of Land Management, Washington, DC, 538 pp. 
75

Evans, P. G. H. 1987. The natural history of whales and dolphins. Facts on File Publications, New York, 343 pp. 

Gaskin, D. E. 1985. The ecology of whales and dolphins. Heinemann Educational Books: London. 459 pp. 

Gaskin, D. E. 1992. Status of Atlantic white-sided dolphin, Lagenorhynchus acutus, in Canada. Can. Fld. Nat. 106:

64-72. 

Gilbert, J. R. and K. M. Wynne. 1987. Marine mammal interactions with New England gillnet fisheries. Final

Report, Contract No. NA-84-EAC-00070, National Marine Fisheries Service, Northeast Fisheries Science

Center, Woods Hole, Massachusetts, 12 pp. 

Hain, J. H. W. and G. T. Waring. In preparation. Marine mammals in New England shelf waters. In R. W. Langton

and J. B. Pearce (editors), Selected living resources, habitat conditions, and human perturbations of the Gulf

of Maine: Environmental and ecological considerations for fishery managements. NOAA Tech. Mem.,

Northeast Fisheries Science Center, Woods Hole, Massachusetts. 

Katona, S. K., V. Rough, and D. T. Richardson. 1993. A field guide to whales, porpoises, and seals from Cape Cod

to Newfoundland. Smithsonian Institution Press, Washington, DC, 316 pp. 

Laake, J. L., S. T. Buckland, D. R. Anderson, and K. P. Burnham. DISTANCE user’s guide, V2.0. Colorado

Cooperative Fish & Wildlife Research Unit, Colorado State University, Ft. Collins, Colorado, 72 pp. 

Palka, D. In press. Abundance estimate of the Gulf of Maine harbor porpoise. Rep. Int. Whal. Commn. Special Issue

16. 

Payne, M. and D. W. Heinemann. 1990. A distributional assessment of cetaceans in the shelf and shelf edge waters

of the northeastern United States based on aerial and shipboard surveys, 1978-1988. Report to National

Marine Fisheries Science Center, Woods Hole, Massachusetts. 

Read, A. J. 1994. Interactions between cetaceans and gillnet and trap fisheries in the northwest Atlantic. Rep. Int.

Whal. Commn. Special Issue 15: 133-147. 

Reilly, S. B. and J. Barlow. 1986. Rates of increase in dolphin population size. Fish. Bull., U.S. 84(3): 527-533. 

Sergeant, D. E., D. J. St. Aubin, and J. R. Geraci. 1980. Life history and northwest Atlantic status of the Atlantic

white-sided dolphin, Lagenorhynchus acutus. Cetology No. 37: 1-12. 

Walden, J. In review. Results of the Gulf of Maine gillnet survey 1989-92. NOAA, NMFS, NEFSC [Northeast

Fisheries Science Center] Ref. Doc., Woods Hole, Massachusetts. 

Waring, G. T., P. Gerrior, P. M. Payne, B. L. Parry, and J. R. Nicolas. 1990. Incidental take of marine mammals in

foreign fishery activities off the northeast United States, 1977-1988. Fish. Bull., U.S. 88(2): 347-360.
76

WHITE-BEAKED DOLPHIN (Lagenorhynchus albirostris):

Western North Atlantic Stock

STOCK DEFINITION AND GEOGRAPHIC RANGE

White-beaked dolphins are the more northerly of the two species of Lagenorhynchus in the Northwest Atlantic

(Leatherwood et al. 1976). The species is found from southern New England, north to western and southern Greenland

and Davis Straits (Leatherwood et al. 1976, CeTAP 1982). Stock structure is unknown. 

In waters off the northeastern U.S. coast, white-beaked dolphin sightings have been concentrated in the

western Gulf of Maine and around Cape Cod (CeTAP 1982). The limited distribution of this northern species in U.S.

waters has been attributed to opportunistic feeding (CeTAP 1982); however, white-beaked dolphins may have been

more common in the Gulf of Maine before the 1960s. It has been hypothesized to have exchanged habitat with whitesided dolphins, which were once more common offshore (Katona et al. 1993). 

POPULATION SIZE

The total number of white-beaked dolphins in U.S. and Canadian Atlantic waters is unknown. Seasonal

abundance estimates are available from an aerial line transect survey program conducted in the continental shelf and

continental shelf edge waters between Cape Hatteras, North Carolina and Nova Scotia from 1978 to 1982 (CeTAP

1982). A population estimate of 573 white-beaked dolphins [coefficient of variation (CV) = 0.69] in waters off Cape

Cod was based on CeTAP (1982) spring sightings. White-beaked dolphins were not encountered during an AugustOctober 1991 aerial survey in the CeTAP study area, nor were white-beaked dolphins sighted during several fine-scale

ship-based surveys conducted in August 1990, June-July 1991,August-September 1991, June-July 1993, AugustSeptember 1993, and August 1994, conducted in the Gulf of Maine and over U.S. Atlantic continental shelf edge and

deeper oceanic waters (NMFS unpublished data). 

A population estimate for Canadian waters of 5,500 white-beaked dolphins was based on a aerial survey off

eastern Newfoundland and southeastern Labrador (Alling and Whitehead 1987). A ship-based survey of a small

segment of the Labrador Shelf in August 1982 provided an estimate of 3,486 white-beaked dolphins [95% confidence

interval (CI) = 2,001-4,971] (Alling and Whitehead 1987). A CV was not given, but, assuming a symmetric CI, it

would be 0.22.

 There are no abundance estimates for this species in waters between the Gulf of Maine and the

Newfoundland/Labrador region. 

Minimum Population Estimate

Present data are insufficient to calculate a minimum population estimate in U.S. Exclusive Economic Zone

(EEZ) waters. 

Current Population Trend

There are insufficient data to determine the population trends for this species. 

CURRENT AND MAXIMUM NET PRODUCTIVITY RATES

Current and maximum net productivity rates are not known for this stock. The maximum net productivity

rate was assumed to be 0.04 for purposes of this assessment. This value is based on theoretical calculations showing

that cetacean populations may not generally grow at rates much greater than 4% given the constraints of their

reproductive life history (Reilly and Barlow 1986). 

POTENTIAL BIOLOGICAL REMOVAL

No PBR can be estimated for this species at this time, because the minimum population size cannot be

determined. 
77

ANNUAL HUMAN-CAUSED MORTALITY AND SERIOUS INJURY

White-beaked dolphins have been killed in the Canadian groundfish gillnet fisheries off Newfoundland and

Labrador and in the Gulf of St. Lawrence (Alling and Whitehead 1987; Read, in press); however, the total number of

animals killed is not known. 

There are no documented reports of fishery-related mortality or serious injury to this stock in the U.S. EEZ;

therefore, total fishery-related mortality and serious injury for this stock is considered insignificant and approaching

zero mortality and serious injury rate. This determination cannot be made for specific fisheries until the implementing

regulations for Section 118 of the MMPA have been reviewed by the public and finalized. 

Fisheries Information

Because of the absence of observed fishery-related mortality and serious injury to this stock in the U.S. EEZ,

no U.S. fishery information is provided. 

The Canadian Atlantic groundfish gillnet fishery is important and widespread. Many fisherman hold

groundfish gillnet licenses but the number of active fishermen is unknown. In 1989, approximately 6,800 licenses were

issued to fishermen along the southern coast of Labrador, and northeast and southern coast of Newfoundland. About

3,900 licenses were issued in 1989 in the Gulf of St. Lawrence and 659 licenses were issued in the Bay of Fundy and

southwestern Nova Scotia. 

Other Mortality

White-beaked dolphins were, and still may be, hunted for food by residents in northern and southern Labrador

(Alling and Whitehead 1987). These authors, based on interview data, estimated that 366 white-beaked dolphins were

killed each year. 

STATUS OF STOCK

The status of white-beaked dolphins, relative to OSP, in U.S. Atlantic coast waters is unknown. They are not

listed as threatened or endangered under the Endangered Species Act. In Canada, the Cetacean Protection Regulations

of 1982, promulgated under the Standing Fisheries Act, prohibit the catching or harassment of all cetacean species.

There are insufficient data to determine the population trends for this species. This stock has a marginal occurrence

in U.S. waters; therefore, this stock is not a strategic stock. 

REFERENCES

Alling, A. K. and H. P. Whitehead. 1987. A preliminary study of the status of white-beaked dolphins, Lagenorhynchus

albirostris, and other small cetaceans off the coast of Labrador. Can. Fld. Nat. 101(2): 131-135. 

CeTAP. 1982. A characterization of marine mammals and turtles in the mid- and north Atlantic areas of the U.S.

outer continental shelf. Cetacean and Turtle Assessment Program, University of Rhode Island. Final Report

#AA551-CT8-48 to the Bureau of Land Management, Washington, DC, 538 pp. 

Katona, S. K., V. Rough, and D. T. Richardson. 1993. A field guide to whales, porpoises, and seals from Cape Cod

to Newfoundland. Washington, D. C. : Smithsonian Institution Press. 316 pp. 

Leatherwood, S., D. K. Caldwell and H. E. Winn. 1976. Whales, dolphins, and porpoises of the western North

Atlantic. A guide to their identification. U.S. Dept. of Commerce, NOAA Tech. Rep. NMFS Circ. 396, 176

pp. 

Northridge, S. In review. Estimation of cetacean mortality in the U.S. Atlantic swordfish and tuna driftnet and pair

trawl fisheries. Draft final report to the Northeast Fisheries Science Center, Contract No. 40ENNF500045,

18 pp. 

Read, A. J. 1994. Interactions between cetaceans and gillnet and trap fisheries in the northwest Atlantic. Rep. Int.

Whal. Commn. Special Issue 15: 133-147. 

Reilly, S. B. and J. Barlow. 1986. Rates of increase in dolphin population size. Fish. Bull., U.S. 84(3): 527-533. 
78

Figure 1. Distribution of common dolphin sightings from

NEFSC shipboard surveys during the summer in 1990-1994. 

Isobaths are at 100 m and 1,000 m. 

COMMON DOLPHIN (Delphinus delphis):

Western North Atlantic Stock

STOCK DEFINITION AND GEOGRAPHIC RANGE

The common dolphin may be one of the most widely distributed species of cetaceans, as it is found world-wide

in temperate, tropical, and subtropical seas. In the North Atlantic, common dolphins appears to be present along the

coast over the continental shelf along the 200-300 m isobaths or over prominent underwater topography from 50E N

to 40ES latitude (Evans 1994). The species is less common south of Cape Hatteras, although schools have been

reported as far south as eastern Florida (Gaskin 1992). At least some of the reported sightings of common dolphins

in the Gulf of Mexico may have been Stenella clymene, which has a color pattern similar to that of common dolphins

(Evans 1994). Information regarding common dolphin stock structure in the western North Atlantic does not exist.

However, a high variance in skull morphometric measurements suggests the existence of more than a single stock (J.

G. Mead, personal communication). 

Common dolphins are distributed in broad bands along the continental slope (100 to 2,000 meters), and are

associated with other Gulf Stream features in waters off the northeastern U.S. coast (CeTAP 1982; Selzer and Payne

1988; Waring et al 1992). They are widespread from Cape Hatteras northeast to Georges Bank (35o to 42o North

latitude) in outer continental shelf waters from mid-January to May (Hain et al. 1981; CeTAP 1982; Payne et al. 1984).

Common dolphins move northward onto Georges Bank and the Scotian Shelf from mid-summer to autumn. Selzer

and Payne (1988) reported very large aggregations (greater than 3,000 animals) on Georges Bank in autumn. Common

dolphins are rarely found in the Gulf of Maine, where temperature and salinity regimes are lower than on the

continental slope of the Georges Bank/mid-Atlantic region (Selzer and Payne 1988). Migration onto the Scotian Shelf

and continental shelf off Newfoundland occurs during summer and autumn when water temperatures exceed 11EC

(Sergeant et al. 1970). 

POPULATION SIZE

The total number of common dolphins off the

eastern U.S. and Canadian Atlantic coast is unknown,

although several estimates from selected regions do

exist. Seasonal abundance estimates are available from

an aerial line transect survey program conducted in

continental shelf and continental shelf edge waters

between Cape Hatteras, North Carolina, and Nova

Scotia from 1978 to 1982 (CeTAP 1982). R. Kenney

(personal communication) provided abundance

estimates that accounted for survey effort in two

continental slope survey blocks and uncertainties

resulting from sightings of unidentified small dolphins.

An estimate based on an inverse variance weighted

pooling of revised CeTAP (1982) spring and summer

data is 29,610 (CV = 0.39). An average for these two

seasons was chosen because the greatest proportion of

the population off the northeast U.S. coast appears to be

in the CeTAP study area in these seasons. This

estimate was not corrected for g(0), the probability of

detecting an animal group on the trackline. 

More recent abundance estimates were derived

using data collected during two fine-scale ship line

transect surveys (June-July 1991 and June-July 1993)

conducted in continental shelf edge and deeper oceanic

waters (Northeast Fisheries Science Center NMFS
79

unpublished data). Common dolphin sightings during these surveys are shown in Figure 1. The data were analyzed

using DISTANCE (Buckland et al. 1993; Laake et al. 1993) where confidence intervals were calculated using the

bootstrap lognormal method. An abundance estimate from the 1991 survey, based principally on sighting effort

conducted between the 200 and 2,000 meter isobaths from Cape Hatteras to Georges Bank was 4,984 common dolphins

(CV = 0.55). The estimate for the 1993 survey, conducted principally between the 200 and 2,000 meter isobaths from

the southern edge of Georges Bank, across the Northeast Channel to the southwestern edge of the Scotian Shelf was

1,645 common dolphins (CV = 0.47). 

Although the 1991 and 1993 surveys did not sample the same areas or encompass the entire common dolphin

habitat (e. g., little effort in mid-continental shelf waters), they did focus on segments of known or suspected high-use

habitats off the northeastern U.S. coast. The 1991 and 1993 data suggest that, seasonally, at least several thousand

common dolphins are occupying continental shelf edge waters, with perhaps highest abundance in the Georges Bank

region. This is consistent with the earlier CeTAP data from a decade previous. Survey coverage to date is not adequate

to provide a definitive estimate of common dolphin abundance for the western North Atlantic and because the estimates

presented here were not corrected for school size bias and g(0), they probably underestimate actual abundance. 

Minimum Population Estimate

 The minimum population estimate was based on the 1991 shipboard survey abundance estimate of 4,984

common dolphins (CV = 0.55) (NMFS unpublished data). This estimate was selected because it provided the most

complete coverage of common dolphin habitat off the northeast U.S. coast. The minimum population estimate is the

lower limit of the two-tailed 60% confidence interval of the log-normal distributed abundance estimate, which is

equivalent to the 20th percentile of the log-normal distribution as specified by NMFS (Anon. 1994), and was 3,233

common dolphins.

Current Population Trend

There are insufficient data to determine the population trends for this species. 

CURRENT AND MAXIMUM NET PRODUCTIVITY RATES

Current and maximum net productivity rates are not known for this stock. The maximum net productivity

rate was assumed to be 0.04 for purposes of this assessment. This value is based on theoretical calculations showing

that cetacean populations may not generally grow at rates much greater than 4% given the constraints of their

reproductive life history (Reilly and Barlow 1986). 

POTENTIAL BIOLOGICAL REMOVAL

Potential biological removal (PBR) was specified as the product of minimum population size, one-half the

maximum productivity rate, and a "recovery" factor for endangered, depleted, threatened stocks, or stocks of unknown

status relative to optimum sustainable population (OSP) (Anon. 1994). The recovery factor was set at 0.50 because

of the stock's status relative to its OSP level is unknown. PBR for this stock is 32 common dolphins. 

ANNUAL HUMAN-CAUSED MORTALITY AND SERIOUS INJURY

During the period 1977-1986, observers recorded 123 mortalities in foreign Loligo squid-fishing activities

(Waring et al. 1990). In 1985 and 1986, Italian vessels took 56 and 54 animals, respectively, which accounts for 89%

(n = 110) of the total takes in foreign Loligo squid-fishing operations. No mortalities were reported in foreign Illex

squid fishing operations. Because of spatial/temporal fishing restrictions, most of the by-catch occurred along the

continental shelf edge (100 m) isobath during winter (December to February). 

From 1977-1991, observers recorded 110 mortalities in foreign mackerel-fishing operations (Waring et al.

1990; NMFS unpublished data). This total includes one documented take by a U.S. vessel involved in joint-venture

fishing operations in which U.S. captains transfer their catches to foreign processing vessels. The by-catch occurred

during winter/spring (December to May). 

Incidental mortality has also been observed in the pelagic drift gillnet and pair trawl fisheries (see below) off

the U.S. Atlantic coast. No mortalities were documented in the Atlantic swordfish/tuna/shark longline, New England

multispecies sink gillnet, and groundfish trawl observed fisheries. An unknown number of common dolphins have
80

been taken in an experimental salmon drift-gillnet fishery off Greenland (Read 1994). In general, there is little known

regarding historical or current common dolphin by-catch in Canadian fisheries.

Estimated average annual mortality and serious injury for all of the NMFS-observed fisheries is 449 common

dolphins per year (CV = 0.47). The total fishery-related mortality and serious injury for this stock is not less than 10%

of the calculated PBR and, therefore, cannot be considered to be insignificant and approaching zero mortality and

serious injury rate. This determination cannot be made for specific fisheries until the implementing regulations for

Section 118 of the MMPA have been reviewed by the public and finalized. 

Fisheries Information

Prior to 1977, there was no documentation of marine mammal by-catch in distant-water fleet (DWF) activities

off the northeast coast of the U.S. With implementation of the Magnuson Fisheries Conservation and Management

Act (MFCMA), an observer program was established which has recorded fishery data and information of incidental

by-catch of marine mammals. DWF effort in the Atlantic coast Exclusive Economic Zone (EEZ) under MFCMA has

been directed primarily towards Atlantic mackerel and squid. From 1977 through 1982, an average of 120 different

foreign vessels per year (range 102-161) operated within the Atlantic coast EEZ. In 1982, there were 112 different

foreign vessels; 16%, or 18, were Japanese tuna longline vessels operating along the U.S. east coast. This was the first

year that the Northeast Regional Observer Program assumed responsibility for observer coverage of the longline

vessels. Between 1983 and 1991, the numbers of foreign vessels operating within the Atlantic coast EEZ each year

were 67, 52, 62, 33, 27, 26, 14, 13, and 9, respectively. Between 1983 and 1988, the numbers of DWF vessels included

3, 5, 7, 6, 8, and 8, respectively, Japanese longline vessels. Observer coverage on DWF vessels was 25-35% during

1977-82, and increased to 58%, 86%, 95%, and 98%, respectively, in 1983-86. From 1987-91, 100% observer

coverage was maintained. Foreign fishing operations for squid and mackerel ceased at the end of the 1986 and 1991

fishing seasons, respectively. 

The Canadian and Greenland salmon gillnet fishery is seasonal, with the peak from June to September,

depending on location. In southern and eastern Newfoundland, and Labrador during 1989, 2,196 nets 91 m long were

used. The fishery was terminated in 1993 (Read 1994). 

 Data on current incidental takes in U.S. fisheries are available from several sources. In 1986, NMFS

established a mandatory logbook system for large pelagic fisheries. Data files are maintained at the Southeast Fisheries

Science Center (SEFSC). The Northeast Fisheries Science Center (NEFSC) Sea Sampling Observer Program was

initiated in 1989, and since that year several fisheries have been covered by the program. In late 1992 and in 1993, the

SEFSC provided observer coverage of pelagic longline vessels fishing off the Grand Banks (Tail of the Banks) and

provides observer coverage of vessels fishing south of Cape Hatteras. 

Pelagic swordfish, tunas, and billfish are the targets of the longline fishery operating in the U.S. Atlantic and

Gulf of Mexico. This fishery has been monitored with about 5% observer coverage, in terms of trips observed, since

1992. Total longline effort for the Atlantic pelagic fishery (including the Caribbean), based on mandatory logbook

reporting, was 11,279 sets in 1991, 10,605 sets in 1992, and 11,538 in 1993 (Cramer 1994). There was no reported

fishery-related mortality or serious injury to this stock attributable to this fishery. 

The estimated total number of hauls in the Atlantic large pelagic drift gillnet fishery increased from 714 in

1989 to 1,144 in 1990; thereafter, with the introduction of quotas, effort was severely reduced. The estimated number

of hauls in 1991, 1992, and 1993 were 233, 243, and 232 respectively. Fifty-nine different vessels participated in this

fishery at one time or another between 1989 and 1993. Observer coverage, expressed as percent of sets observed,

ranged from 8% in 1989, 6% in 1990, 20% in 1991, to 40% in 1992, and 42% in 1993. Effort was concentrated along

the southern edge of Georges Bank and off Cape Hatteras. Examination of the species composition of the catch and

locations of the fishery throughout the year, suggested that the drift gillnet fishery be stratified into two strata, a

southern or winter stratum, and a northern or summer stratum. Estimates of the total by-catch, for each year, were

obtained using the aggregated (pooled 1989-1993) catch rates, by strata (Northridge, in review). Three hundred and

seven common dolphin mortalities were observed between 1989 and 1993 in this fishery. Mortalities were observed

in all seasons and areas. Five animals were released alive, but four were injured. Estimated annual mortality and

serious injury attributable to this fishery (CV in parentheses) was 540 in 1989 (0.55), 893 in 1990 (0.40), 223 in 1991

(0.36), 227 in 1992 (0.20), and 238 in 1993 (0.16); average annual estimated fishery-related mortality during 1989-

1993 attributable to this fishery was 424 common dolphins (0.50).
81

During the period 1989 to 1993, effort in the Atlantic swordfish/tuna/shark pair trawl fishery increased from

zero hauls in 1989 and 1990, to an estimated 171 hauls in 1991 and then to an estimated 989 and 1,087 hauls in 1992

and 1993, respectively. The fishery operated from August to November in 1991, from June to November in 1992, and

from June to October in 1993. Sea sampling began in October of 1992 where 101 sets (10% of the total) were sampled.

In 1993, 201 hauls (18% of the total) were sampled. Nineteen vessels have operated in this fishery. The fishery

operates in the area between 35EN to 41EN and 69EW to 72EW. Approximately 50% of the total effort was within a

one degree square at 39EN, 72EW, around Hudson Canyon. Examination of the locations and species composition of

the by-catch, showed little seasonal change for the six months of operation and did not warrant any seasonal or areal

stratification of this fishery. Nine mortalities were observed between 1991 and 1993. The estimated annual fisheryrelated mortality and serious injury attributable to this fishery (CV in parentheses) was 5.6 in 1991 (0.53), 32 in 1992

(0.48), and 35 in 1993 (0.43). Average annual estimate fishery-related mortality attributable to this fishery during

1991-1993 was 24 common dolphins (CV = 0.52). 

STATUS OF STOCK

The status of common dolphins, relative to OSP, in the U.S. Atlantic EEZ is unknown. The species is not

listed as threatened or endangered under the Endangered Species Act. In Canada, the Cetacean Protection Regulations

of 1982, promulgated under the Standing Fisheries Act, prohibit the catching or harassment of all cetacean species.

There are insufficient data to determine the population trends for this species. This is a strategic stock because average

annual fishery-related mortality and serious injury exceeds PBR. 

REFERENCES

Anon. 1994. Report of the PBR (Potential Biological Removal) workshop. June 27-29, 1994. NOAA, NMFS

Southwest Fisheries Science Center, La Jolla, California, 13 pp. + Appendices. 

Buckland, S. T., D. R. Andersen, K. P. Burnham, and J. L. Laake. 1993. Distance Sampling: Estimating abundance

of biological populations. Chapman and Hall, New York, 446 pp. 

CeTAP. 1982. A characterization of marine mammals and turtles in the mid- and north Atlantic areas of the U.S.

outer continental shelf. Cetacean and Turtle Assessment Program, University of Rhode Island. Final Report,

Contract AA51-C78-48, Bureau of Land Management, Washington, DC, 538 pp. 

Evans, W. E. 1994. Common dolphin, white-bellied porpoise. Pages 191-224 in S. H. Ridgway and R. Harrison

(editors), Handbook of marine mammals, Volume 5: The first book of dolphins. Academic Press, San Diego

. Gaskin, D. E. 1992. Status of common dolphin, Delphinus delphis, in Canada. Can. Fld. Nat. 106: 55-63. 

Hain, J. H. W., R. K. Edel, H. E. Hays, S. K. Katona, and J. D. Roanowicz. 1981. General distribution of cetaceans

in the continental shelf waters of the northeastern U.S. Pages II1-II277 in CeTAP (Cetacean and Turtle

Assessment program), A characterization of marine mammals and turtles in the mid- and north Atlantic areas

of the U.S. outer continental shelf, Annual Report for 1979. Contract No. AA551-CT8-48, U.S. Dept. of

Interior, Bureau of Land Management, Washington, DC. 

Laake, J. L., S. T. Buckland, D. R. Anderson, and K. P. Burnham. DISTANCE user’s guide, V2.0. Colorado

Cooperative Fish & Wildlife Research Unit, Colorado State University, Ft. Collins, Colorado, 72 pp. 

Leatherwood, S., D. K. Caldwell, and H. E. Winn. 1976. Whales, dolphins, and porpoises of the western North

Atlantic. A guide to their identification. U.S. Dept. of Commerce, NOAA Tech. Rep. NMFS Circ. 396, 176

pp. 

Northridge, S. In review. Estimation of cetacean mortality in the U.S. Atlantic swordfish and tuna driftnet and pair

trawl fisheries. Draft final report to the Northeast Fisheries Science Center, Contract No. 40ENNF500045,

18 pp. 

Payne, P. M., L. A. Selzer, and A. R. Knowlton. 1984. Distribution and density of cetaceans, marine turtles, and

seabirds in the shelf waters of the northeastern United States, June 1980-December 1983, based on shipboard

observations. NOAA/NMFS Contract No. NA-81-FA-C-00023. 

Read, A. J. 1994. Interactions between cetaceans and gillnet and trap fisheries in the northwest Atlantic. Rep. Int.

Whal. Commn. Special Issue 15: 133-147. 

Reilly, S. B. and J. Barlow. 1986. Rates of increase in dolphin population size. Fish. Bull., U.S. 84(3): 527-533. 
82

Selzer, L. A. and P. M. Payne. 1988. The distribution of white-sided (Lagenorhynchus acutus) and common dolphins

(Delphinus delphis) vs. environmental features of the continental shelf of the northeastern United States. Mar.

Mamm. Sci. 4(2): 141-153. 

Sergeant, D. E., A. W. Mansfield and B. Beck. 1970. Inshore records of cetacea for eastern Canada, 1949-68. J. Fish.

Res. Bd. Can. 27: 1903-1915. 

Waring, G. T., P. Gerrior, P. M. Payne, B. L. Parry and J. R. Nicolas. 1990. Incidental take of marine mammals in

foreign fishery activities off the northeast United States, 1977-1988. Fish. Bull., U.S. 88(2): 347-360.

Waring, G. T., C. P. Fairfield, C. M. Ruhsam and M. Sano. 1992. Cetaceans associated with Gulf Stream features

off the northeastern USA shelf. ICES Marine Mammals Comm. CM 1992/N: 12, 29 pp.
83

Figure 1. Distribution of spotted dolphin sightings from

NEFSC shipboard surveys during the summer in 1990-1994.

Isobaths are at 100 m and 1,000 m. 

ATLANTIC SPOTTED DOLPHIN (Stenella frontalis):

Western North Atlantic Stock

STOCK DEFINITION AND GEOGRAPHIC RANGE

There are two species of spotted dolphin in the Western Atlantic — the Atlantic spotted dolphin, Stenella

frontalis, formerly S. plagiodon (Perrin et al. 1987), and the pantropical spotted dolphin, S. attenuata. These species

are difficult to differentiate at sea. 

Atlantic spotted dolphins are distributed in tropical and warm temperate waters of the western North Atlantic

(Leatherwood et al. 1976). Their distribution is from southern New England, south through the Gulf of Mexico and

the Caribbean to Venezuela (Leatherwood et al. 1976; Perrin et al. 1987). The large, heavily spotted form of the

Atlantic spotted dolphin along the southeastern and Gulf coasts of the United States inhabits the continental shelf,

usually being found inside or near the 200 m isobath (within 250-350 km of the coast) but sometimes coming into very

shallow water adjacent to the beach. Off the northeast U.S. coast, spotted dolphins are widely distributed on the

continental shelf, along the continental shelf edge, and offshore over the deep ocean south of 40o N (CeTAP 1982).

Atlantic spotted dolphins regularly occur in the inshore waters south of Chesapeake Bay and near the continental shelf

edge and continental slope waters north of this region (Payne et al. 1984). Sightings have also been made along the

north wall of the Gulf Stream and warm-core ring features (Waring et al. 1992). Stock structure in the western North

Atlantic is unknown. 

POPULATION SIZE

The total number of spotted dolphins off the

eastern U.S. coast is unknown. Seasonal abundance

estimates for a portion of the known range are available

from an aerial line transect survey program conducted in

the continental shelf and continental shelf edge waters

between Cape Hatteras, North Carolina and Nova Scotia

from 1978 to 1982 (CeTAP 1982). R. Kenney (personal

communication) provided abundance estimates for both

species of spotted dolphins combined that accounted for

survey effort in two continental slope survey blocks and

uncertainties resulting from sightings of unidentified

small dolphins. An estimate based on inverse varianceweighted pooling of the revised CeTAP (1982) spring

and summer data is 6,107 spotted dolphins (CV = 0.27).

An average for these two seasons was chosen because the

greatest proportion of the population off the northeast

U.S. coast appears to be in the CeTAP study area in these

seasons. This estimate was not corrected for g(0), the

probability of detecting dolphins on the trackline.

Furthermore, this survey did not cover important spotted

dolphin habitat in the continental shelf between Cape

Hatteras and Florida, and Atlantic deep oceanic waters.

Spotted dolphin sighting data were collected

during the autumn 1991 aerial line transect survey in the

CeTAP study area and from several fine-scale ship line

transect surveys (August 1990, June-July 1991 and JuneJuly 1993) conducted in continental shelf edge and deeper oceanic waters (NMFS unpublished data). Spotted dolphin

sightings during these surveys are shown in Figure 1. These data were too limited for use in estimating abundance

because these surveys did not adequately sample spotted dolphin high-use habitats off the northeastern U.S. coast.
84

Minimum Population Estimate

The minimum population estimate for both species of spotted dolphins combined was based on the CeTAP

(1982) abundance estimate which was 6,107 spotted dolphins (CV = 0.27). The minimum population estimate is the

lower limit of the two-tailed 60% confidence interval of the log-normal distributed abundance estimate and was 4,885

spotted dolphins. This is equivalent to the 20th percentile of the log-normal distribution as specified by NMFS (Anon.

1994). 

Current Population Trend

There are insufficient data to determine the population trends for this species. 

CURRENT AND MAXIMUM NET PRODUCTIVITY RATES

Current and maximum net productivity rates are not known for this stock. The maximum net productivity

rate was assumed to be 0.04 for purposes of this assessment. This value is based on theoretical calculations showing

that cetacean populations may not generally grow at rates much greater than 4% given the constraints of their

reproductive life history (Reilly and Barlow 1986). 

POTENTIAL BIOLOGICAL REMOVAL

Potential biological removal (PBR) was specified as the product of minimum population size, one-half the

maximum productivity rate, and a "recovery" factor for endangered, depleted, threatened stocks, or stocks of unknown

status relative to optimum sustainable population (OSP) (Anon. 1994). The recovery factor was set at 0.16 because

of the stock's status relative to OSP is unknown and the minimum population estimate is 11 years older than the latest

fishery-related mortality estimate. PBR for both species of spotted dolphins combined would be sixteen; however, it

is inappropriate to calculate a PBR for the Atlantic spotted dolphin (S. Frontalis) stock because it was impossible to

separately identify the two species.

ANNUAL HUMAN-CAUSED MORTALITY AND SERIOUS INJURY

No spotted dolphin mortalities were observed in 1977-1991 foreign fishing activities. Nineteen mortalities

have been documented between 1989 and 1993 (see below) in the pelagic drift gillnet fishery. Six whole animal

carcasses that were sent to the Smithsonian were identified as Pantropical spotted dolphins (Stenella attenuata). The

remaining 13 animals were not identified to species. No mortalities were documented in the Atlantic

swordfish/tuna/shark pair trawl, New England multispecies sink gillnet, and groundfish trawl fisheries; and no takes

have been documented in a review of Canadian gillnet and trap fisheries (Read 1994). 

Total annual estimated average fishery-related mortality and serious injury to both species of spotted dolphins

combined in the Atlantic by both fisheries is 31 spotted dolphins (CV = 1.13). Total fishery-related mortality and

serious injury for this stock is not less than 10% of the calculated PBR and, therefore, cannot be considered to be

insignificant and approaching zero mortality and serious injury rate. This determination cannot be made for specific

fisheries until the implementing regulations for Section 118 of the MMPA have been reviewed by the public and

finalized. 

Fisheries Information

Data on current incidental takes in U.S. fisheries are available from several sources. In 1986, NMFS

established a mandatory logbook system for large pelagic fisheries. Data files are maintained at the Southeast Fisheries

Science Center (SEFSC). The Northeast Fisheries Science Center (NEFSC) Sea Sampling Observer Program was

initiated in 1989 and since that year several fisheries have been covered by the program. In late 1992 and in 1993, the

SEFSC provided observer coverage of pelagic longline vessels fishing off the Grand Banks (Tail of the Banks) and

provides observer coverage of vessels fishing south of Cape Hatteras. Total fishery-related mortality and serious injury

cannot be estimated separately for the two species of spotted dolphins in the U.S. Atlantic Exclusive Economic Zone

(EEZ) because of the uncertainty in species identification by fishery observers. The Atlantic Scientific Review Group

advised adopting the risk-averse strategy of assuming that either species might have been subject to the observed

fishery-related mortality and serious injury.

Pelagic swordfish, tunas, and billfish are the targets of the U.S. longline fishery in the U.S. Atlantic and Gulf

of Mexico EEZ (SEFSC unpublished logbook data). Interactions between the longline swordfish/tuna fishery and
85

spotted dolphins have been reported; however, a vessel may fish in more than one statistical reporting area and it is

not possible to separate estimates of fishing effort other than to subtract Gulf of Mexico effort from Atlantic fishing

effort, which includes the Caribbean Sea. This fishery has been monitored with about 5% observer coverage, in terms

of trips observed, since 1992. Total longline effort for the Atlantic pelagic fishery (including the Caribbean), based

on mandatory logbook reporting, was 11,279 sets in 1991, 10,605 sets in 1992, and 11,538 in 1993 (Cramer 1994).

Estimated take was based on a generalized linear model (Poisson error assumption) fit to the available observed

incidental take and self-reported incidental take and effort data for the fishery (SEFSC unpublished data). Annual

estimates of mortality and serious injury were based on observed takes across the entire Atlantic longline

swordfish/tuna fishery (including the Gulf of Mexico). All observed takes were used because the species occurs

throughout area of the fishery, but observed takes were infrequent in any given region of the fishery. There was no

mortality or serious injury reported in 1992 and estimated fishery-related mortality and serious injury to spotted

dolphins (both species) in the Atlantic longline swordfish/tuna fishery in 1993 was 16 (CV = 0.19); average annual

mortality and serious injury attributable to this fishery in 1992-1993 was 8.0 spotted dolphins (CV = 0.27).

The estimated total number of hauls in the Atlantic large pelagic drift gillnet fishery increased from 714 in

1989 to 1,144 in 1990; thereafter, with the introduction of quotas, effort was severely reduced. The estimated number

of hauls in 1991, 1992, and 1993 were 233, 243, and 232 respectively. Fifty-nine different vessels participated in this

fishery at one time or another between 1989 and 1993. Observer coverage, expressed as percent of sets observed,

ranged from 8% in 1989, 6% in 1990, 20% in 1991, to 40% in 1992, and 42% in 1993. Effort was concentrated along

the southern edge of Georges Bank and off Cape Hatteras. Examination of the species composition of the catch and

locations of the fishery throughout the year, suggested that the drift gillnet fishery be stratified into two strata, a

southern or winter stratum, and a northern or summer stratum. Estimates of the total by-catch, for each year, were

obtained using the aggregated (pooled 1989-1993) catch rates, by strata (Northridge, in review). Nineteen spotted

dolphin mortalities were observed in the drift gillnet fishery between 1989 and 1993 and occurred northeast of Cape

Hatteras within the 183 m isobath in February-April, and near Lydonia Canyon in October. Estimated annual mortality

and serious injury attributable to this fishery (CV in parentheses) was 23 in 1989 (2.14), 51 in 1990 (1.12), 11 in 1991

(1.21), 20 in 1992 (0.35), and 8.4 in 1993 (0.79). 

STATUS OF STOCK

The status of Atlantic spotted dolphins, relative to OSP in the U.S. Atlantic EEZ is unknown. The species

is not listed as threatened or endangered under the Endangered Species Act. In Canada, the Cetacean Protection

Regulations of 1982, promulgated under the Standing Fisheries Act, prohibit the catching or harassment of all cetacean

species. There are insufficient data to determine the population trends for this species. This is a strategic stock because

the average annual fishery-related mortality and serious injury of spotted dolphins would exceed PBR for this stock

(if it could be calculated) even if the minimum population estimate for spotted dolphins were exclusively S. Frontalis.

REFERENCES

Anon. 1994. Report of the PBR (Potential Biological Removal) workshop. June 27-29, 1994. NOAA, NMFS

Southwest Fisheries Science Center, La Jolla, California, 13 pp. + Appendices. 

CeTAP. 1982. A characterization of marine mammals and turtles in the mid- and north Atlantic areas of the U.S.

outer continental shelf. Cetacean and Turtle Assessment Program, University of Rhode Island. Final Report,

Contract AA51-C78-48, Bureau of Land Management, Washington, DC, 538 pp. 

Leatherwood, S., D. K. Caldwell and H. E. Winn. 1976. Whales, dolphins, and porpoises of the western North

Atlantic. A guide to their identification. U.S. Dept. of Commerce, NOAA Tech. Rep. NMFS Circ. 396, 176

pp. 

Northridge, S. In review. Estimation of cetacean mortality in the U.S. Atlantic swordfish and tuna driftnet and pair

trawl fisheries. Draft final report to the Northeast Fisheries Science Center, Contract No. 40ENNF500045,

18 pp. 

Payne, P. M., L. A. Selzer and A. R. Knowlton. 1984. Distribution and density of cetaceans, marine turtles, and

seabirds in the shelf waters of the northeastern United States, June 1980-December 1983, based on shipboard

observations. NOAA/NMFS Contract No. NA-81-FA-C-00023. 

Perrin, W. F.,E. D. Mitchell, J. G. Mead, D. K. Caldwell, M. C. Caldwell, P. J. H. van Bree, and W. H. Dawbin. 1987.

Revision of the spotted dolphins, Stenella spp. Mar. Mamm. Sci. 3(2): 99-170.
86

Perrin, W. F., D. K. Caldwell, and M. C. Caldwell. 1994. Atlantic spotted dolphin. Pages 173-190 in S. H. Ridgway

and R. Harrison (editors), Handbook of marine mammals, Volume 5: The first book of dolphins. Academic

Press, San Diego, 418 pp. 

Read, A. J. 1994. Interactions between cetaceans and gillnet and trap fisheries in the northwest Atlantic. Rep. Int.

Whal. Commn. Special Issue 15: 133-147. 

Reilly, S. B. and J. Barlow. 1986. Rates of increase in dolphin population size. Fish. Bull., U.S. 84(3): 527-533. 

Waring, G. T., C. P. Fairfield, C. M. Ruhsam and M. Sano. 1992. Cetaceans associated with Gulf Stream features

off the northeastern USA shelf. ICES Marine Mammals Comm. CM 1992/N:12, 29 pp. 
87

Figure 1. Distribution of spotted dolphin sightings from

NEFSC shipboard surveys during the summer in 1990-1994.

Isobaths are at 100 m and 1,000 m. 

PANTROPICAL SPOTTED DOLPHIN (Stenella attenuata):

Western North Atlantic Stock

STOCK DEFINITION AND GEOGRAPHIC RANGE

There are two species of spotted dolphin in the Western Atlantic — the Atlantic spotted dolphin, Stenella

frontalis, formerly S. plagiodon (Perrin et al. 1987), and the pantropical spotted dolphin, S. attenuata. These species

are difficult to differentiate at sea. 

The pantropical spotted dolphin is distributed worldwide in tropical and some sub-tropical oceans (Perrin et

al. 1987; Perrin and Hohn 1994). Sightings of this species in the northern Gulf of Mexico occur over the deeper

waters, and rarely over the continental shelf or continental shelf edge (Mullin et al. 1991; Southeast Fisheries Science

Center, SEFSC, unpublished data). Pantropical spotted dolphins were seen in all seasons during recent seasonal aerial

surveys of the northern Gulf of Mexico, and during recent winter aerial surveys offshore of the southeastern U.S.

Atlantic coast (SEFSC unpublished data). Some of the Pacific populations have been divided into different geographic

stocks based on morphological characteristics (Perrin et al. 1987; Perrin and Hohn 1994); however, there is no

information on stock differentiation in the Atlantic population. 

POPULATION SIZE

The total number of spotted dolphins off the

eastern U.S. coast is unknown. Seasonal abundance

estimates are available from an aerial line transect

survey program conducted in the continental shelf and

continental shelf edge waters between Cape Hatteras,

North Carolina and Nova Scotia from 1978 to 1982

(CeTAP 1982). R. Kenney (personal communication)

provided abundance estimates for both species of

spotted dolphins combined that accounted for survey

effort in two continental slope survey blocks and

uncertainties resulting from sightings of unidentified

small dolphins. An estimate based on inverse varianceweighted pooling of the revised CeTAP (1982) spring

and summer data is 6,107spotted dolphins (CV =

0.27). An average for these two seasons was chosen

because the greatest proportion of the population off the

northeast U.S. coast appears to be in the CeTAP study

area in these seasons. This estimate was not corrected

for g(0), the probability of detecting dolphins on the

trackline. Furthermore, this survey did not cover

important spotted dolphin habitat in the continental

shelf between Cape Hatteras and Florida, or in oceanic

waters.

Spotted dolphin sighting data were collected

during the autumn 1991 aerial line transect survey in

the CeTAP study area and from several fine-scale ship

line transect surveys (August 1990, June-July 1991 and

June-July 1993) conducted in continental shelf edge and deeper oceanic waters (NMFS unpublished data). Spotted

dolphin sightings during these surveys are shown in Figure 1. These data were too limited for use in estimating

abundance because these surveys did not adequately sample spotted dolphin high-use habitats off the northeastern U.S.

coast.
88

Minimum Population Estimate

The minimum population estimate for both species of spotted dolphins combined was based on the CeTAP

(1982) abundance estimate which was 6,107 spotted dolphins (CV = 0.27). The minimum population estimate is the

lower limit of the two-tailed 60% confidence interval of the log-normal distributed abundance estimate and was 4,885

spotted dolphins. This is equivalent to the 20th percentile of the log-normal distribution as specified by NMFS (Anon.

1994). 

Current Population Trend

There are insufficient data to determine the population trends for this species. 

CURRENT AND MAXIMUM NET PRODUCTIVITY RATES

Current and maximum net productivity rates are not known for this stock. The maximum net productivity

rate was assumed to be 0.04 for purposes of this assessment. This value is based on theoretical calculations showing

that cetacean populations may not generally grow at rates much greater than 4% given the constraints of their

reproductive life history (Reilly and Barlow 1986). 

POTENTIAL BIOLOGICAL REMOVAL

Potential biological removal (PBR) was specified as the product of minimum population size, one-half the

maximum productivity rate, and a "recovery" factor for endangered, depleted, threatened stocks, or stocks of unknown

status relative to optimum sustainable population (OSP) (Anon. 1994). The recovery factor was set at 0.16 because

of the stock's status relative to OSP is unknown and the minimum population estimate is 11 years older than the latest

fishery-related mortality estimate. PBR for both species of spotted dolphins combined would be sixteen; however, it

is inappropriate to calculate a PBR for the pantropical spotted dolphin (S. attenuata) stock because it was impossible

to separately identify the two species.

ANNUAL HUMAN-CAUSED MORTALITY AND SERIOUS INJURY

No spotted dolphin mortalities were observed in 1977-1991 foreign fishing activities. Nineteen mortalities

have been documented between 1989 and 1993 (see below) in the pelagic drift gillnet fishery. Six whole animal

carcasses that were sent to the Smithsonian were identified as pantropical spotted dolphins (S. attenuata). The

remaining 13 animals were not identified to species. No mortalities were documented in the Atlantic

swordfish/tuna/shark pair trawl, New England multispecies sink gillnet, and groundfish trawl fisheries; and no takes

have been documented in a review of Canadian gillnet and trap fisheries (Read 1994). 

Total annual estimated average fishery-related mortality and serious injury to both species of spotted dolphins

combined in the Atlantic by both fisheries is 31 spotted dolphins (CV = 1.13). Total fishery-related mortality and

serious injury for this stock is not less than 10% of the calculated PBR and, therefore, cannot be considered to be

insignificant and approaching zero mortality and serious injury rate. This determination cannot be made for specific

fisheries until the implementing regulations for Section 118 of the MMPA have been reviewed by the public and

finalized. 

Fisheries Information

Data on current incidental takes in U.S. fisheries are available from several sources. In 1986, NMFS

established a mandatory logbook system for large pelagic fisheries. Data files are maintained at the Southeast Fisheries

Science Center (SEFSC). The Northeast Fisheries Science Center (NEFSC) Sea Sampling Observer Program was

initiated in 1989 and since that year several fisheries have been covered by the program. In late 1992 and in 1993, the

SEFSC provided observer coverage of pelagic longline vessels fishing off the Grand Banks (Tail of the Banks) and

provides observer coverage of vessels fishing south of Cape Hatteras. Total fishery-related mortality and serious injury

cannot be estimated separately for the two species of spotted dolphins in the U.S. Atlantic Exclusive Economic Zone

(EEZ) because of the uncertainty in species identification by fishery observers. The Atlantic Scientific Review Group

advised adopting the risk-averse strategy of assuming that either species might have been subject to the observed

fishery-related mortality and serious injury.

Pelagic swordfish, tunas, and billfish are the targets of the U.S. longline fishery in the U.S. Atlantic and Gulf

of Mexico EEZ (SEFSC unpublished logbook data). Interactions between the longline swordfish/tuna fishery and
89

spotted dolphins have been reported; however, a vessel may fish in more than one statistical reporting area and it is

not possible to separate estimates of fishing effort other than to subtract Gulf of Mexico effort from Atlantic fishing

effort, which includes the Caribbean Sea. This fishery has been monitored with about 5% observer coverage, in terms

of trips observed, since 1992. Total longline effort for the Atlantic pelagic fishery (including the Caribbean), based

on mandatory logbook reporting, was 11,279 sets in 1991, 10,605 sets in 1992, and 11,538 in 1993 (Cramer 1994).

Estimated take was based on a generalized linear model (Poisson error assumption) fit to the available observed

incidental take and self-reported incidental take and effort data for the fishery (SEFSC unpublished data). Annual

estimates of mortality and serious injury were based on observed takes across the entire Atlantic longline

swordfish/tuna fishery (including the Gulf of Mexico). All observed takes were used because the species occurs

generally throughout area of the fishery, but observed takes were infrequent in any given region of the fishery. There

was no mortality or serious injury reported in 1992 and estimated fishery-related mortality and serious injury to spotted

dolphins (both species) in the Atlantic longline swordfish/tuna fishery in 1993 was 16 (CV = 0.19); average annual

mortality and serious injury attributable to this fishery in 1992-1993 was 8.0 spotted dolphins (CV = 0.27).

The estimated total number of hauls in the Atlantic large pelagic drift gillnet fishery increased from 714 in

1989 to 1,144 in 1990; thereafter, with the introduction of quotas, effort was severely reduced. The estimated number

of hauls in 1991, 1992, and 1993 were 233, 243, and 232 respectively. Fifty-nine different vessels participated in this

fishery at one time or another between 1989 and 1993. Observer coverage, expressed as percent of sets observed,

ranged from 8% in 1989, 6% in 1990, 20% in 1991, to 40% in 1992, and 42% in 1993. Effort was concentrated along

the southern edge of Georges Bank and off Cape Hatteras. Examination of the species composition of the catch and

locations of the fishery throughout the year, suggested that the drift gillnet fishery be stratified into two strata, a

southern or winter stratum, and a northern or summer stratum. Estimates of the total by-catch were obtained for each

year using the aggregated (pooled 1989-1993) catch rates, by strata (Northridge, in review). Nineteen spotted dolphin

mortalities were observed in the drift gillnet fishery between 1989 and 1993 and occurred northeast of Cape Hatteras

within the 183 m isobath in February-April, and near Lydonia Canyon in October. Estimated annual mortality and

serious injury of spotted dolphins (both species) attributable to this fishery (CV in parentheses) was 23 in 1989 (2.14),

51 in 1990 (1.12), 11 in 1991 (1.21), 20 in 1992 (0.35), and 8.4 in 1993 (0.79). 

STATUS OF STOCK

The status of pantropical spotted dolphins, relative to OSP in the U.S. Atlantic EEZ is unknown. The species

is not listed as threatened or endangered under the Endangered Species Act. In Canada, the Cetacean Protection

Regulations of 1982, promulgated under the Standing Fisheries Act, prohibit the catching or harassment of all cetacean

species. There are insufficient data to determine the population trends for this species. This is a strategic stock because

the average annual fishery-related mortality and serious injury of spotted dolphins would exceed PBR for this stock

(if it could be calculated) even if the minimum population estimate for spotted dolphins were exclusively S. attenuata.

REFERENCES

Anon. 1994. Report of the PBR (Potential Biological Removal) workshop. June 27-29, 1994. NOAA, NMFS

Southwest Fisheries Science Center, La Jolla, California, 13 pp. + Appendices. 

CeTAP. 1982. A characterization of marine mammals and turtles in the mid- and north Atlantic areas of the U.S.

outer continental shelf. Cetacean and Turtle Assessment Program, University of Rhode Island. Final Report,

Contract AA51-C78-48, Bureau of Land Management, Washington, DC, 538 pp. 

Cramer, J. 1994. Large pelagic logbook newsletter - 1993. NOAA Tech. Mem. NMFS-SEFSC-352, 19 pp. 

Mullin, K., W. Hoggard, C. Roden, R. Lohoefener, C. Rogers and B. Taggart. 1991. Cetaceans on the upper

continental slope in the north-central Gulf of Mexico. OCS Study/MMS 91-0027. U.S. Dept. of the Interior,

Minerals Management Service, Gulf of Mexico OCS Regional Office, New Orleans, Louisiana, 108 pp. 

Northridge, S. In review. Estimation of cetacean mortality in the U.S. Atlantic swordfish and tuna driftnet and pair

trawl fisheries. Draft final report to the Northeast Fisheries Science Center, Contract No. 40ENNF500045,

18 pp. 

Perrin, W. F.,E. D. Mitchell, J. G. Mead, D. K. Caldwell, M. C. Caldwell, P. J. H. van Bree, and W. H. Dawbin. 1987.

Revision of the spotted dolphins, Stenella spp. Mar. Mamm. Sci. 3(2): 99-170.
90

Perrin, W. F., D. K. Caldwell, and M. C. Caldwell. 1994. Atlantic spotted dolphin. Pages 173-190 in S. H. Ridgway

and R. Harrison (editors), Handbook of marine mammals, Volume 5: The first book of dolphins. Academic

Press, San Diego, 418 pp. 

Perrin, W. F. and A. A. Hohn. 1994. Pantropical spotted dolphin Stenella attenuata. Pages 71-98 in S. H. Ridgway

and R. Harrison (editors), Handbook of marine mammals, Vol. 5: The first book of dolphins. Academic

Press, San Diego, 418 pp. 

Read, A. J. 1994. Interactions between cetaceans and gillnet and trap fisheries in the northwest Atlantic. Rep. Int.

Whal. Commn. Special Issue 15: 133-147. 

Reilly, S. B. and J. Barlow. 1986. Rates of increase in dolphin population size. Fish. Bull., U.S. 84(3): 527-533. 
91

Figure 1. Distribution of striped dolphin sightings from

NEFSC shipboard surveys during the summer in 1990-1994.

Isobaths are at 100 m and 1,000 m. 

STRIPED DOLPHIN (Stenella coeruleoalba):

Western North Atlantic Stock

STOCK DEFINITION AND GEOGRAPHIC RANGE

The striped dolphin, Stenella coeruleoalba, is distributed worldwide in temperate and tropical seas of the

world. Striped dolphins are found in the western North Atlantic from Nova Scotia south to at least Jamaica and in the

Gulf of Mexico. In general, striped dolphins appear to prefer continental slope waters offshore to the Gulf Stream

(Leatherwood et al. 1976; Perrin et al. 1994; Schmidly 1981). There is no information concerning striped dolphin

stock structure in the western North Atlantic. 

In waters off the northeastern U.S. coast, striped dolphins are distributed along the continental shelf edge from

Cape Hatteras to the southern margin of Georges Bank, and also occur offshore over the continental slope and rise in

the mid-Atlantic region (CeTAP 1982). Continental shelf edge sightings in this program were generally centered along

the 1,000 m depth contour in all seasons (CeTAP 1982). During 1990 and 1991 cetacean habitat-use surveys, striped

dolphins were associated with the Gulf Stream north wall and warm-core ring features (Waring et al. 1992). 

POPULATION SIZE

The total number of striped dolphins in the

U.S. Exclusive Economic Zone (EEZ) is unknown.

Seasonal abundance estimates are available from an

aerial line transect survey program conducted in the

continental shelf and continental shelf edge waters

between Cape Hatteras, North Carolina and Nova Scotia

from 1978 to 1982 (CeTAP 1982). R. Kenney (personal

communication) provided abundance estimates that

accounted for survey effort in two continental slope

survey blocks and uncertainties resulting from sighting

of unidentified small dolphins. An estimate based on an

inverse variance weighted pooling of revised CeTAP

(1982) spring and summer data is 36,780 (CV = 0.27).

An average for these two seasons was chosen because

the greatest proportion of the population off the

northeast U.S. coast appears to be in the CeTAP study

area in these seasons. This estimate was not corrected

for g(0), the probability of detecting an animal group

on the trackline. 

Abundance estimates were also derived using

data collected during an autumn 1991 aerial line

transect survey in the CeTAP study area (NMFS

unpublished data), which included an interplatform

experiment between a Twin Otter and an AT-11).

Sightings were almost exclusively in the continental

shelf edge waters. The data were analyzed using

DISTANCE (Buckland et al. 1993; Laake et al. 1993) where confidence intervals were calculated using the bootstrap

lognormal method. Abundance estimates, based on a low number of sightings, from this survey were 13,157 (CV =

0.45) and 25,939 (CV = 0.36), respectively, for the AT-11 and NOAA Twin Otter. Data were not pooled, because the

interplatform calibration analysis has not been conducted. These estimates are not comparable to the CeTAP estimates,

because the 1991 data are from a single survey conducted during August-October, while the CeTAP estimates were

based on data pooled over several years of seasonal surveys.

Striped dolphin sighting data were also collected during three fine-scale ship line transect surveys (August

1990, June-July 1991, and June-July 1993) conducted in continental shelf edge and deeper oceanic waters (NMFS
92

unpublished data) and striped dolphin sightings during these surveys are shown in Figure 1. These data were too

limited for use in estimating abundance because these surveys did not adequately sample striped dolphin high-use

habitats off the northeastern U.S. coast. 

Minimum Population Estimate

The minimum population estimate was based on the AT-11 aerial survey abundance estimate of 13,157 striped

dolphins (CV = 0.45) (NMFS unpublished data) in 1991. This estimate was used because that survey provided the

most complete coverage of continental shelf edge and continental slope waters off the northeast U.S. coast. The

minimum population estimate is the lower limit of the two-tailed 60% confidence interval of the log-normal distributed

abundance estimate, which is equivalent to the 20th percentile of the log-normal distribution as specified by NMFS

(Anon. 1994), and was 9,165 striped dolphins. 

Current Population Trend

There are insufficient data to determine the population trends for this species. 

CURRENT AND MAXIMUM NET PRODUCTIVITY RATES

Current and maximum net productivity rates are not known for this stock. The maximum net productivity

rate was assumed to be 0.04 for purposes of this assessment. This value is based on theoretical calculations showing

that cetacean populations may not generally grow at rates much greater than 4% given the constraints of their

reproductive life history (Reilly and Barlow 1986). 

POTENTIAL BIOLOGICAL REMOVAL

Potential biological removal (PBR) was specified as the product of minimum population size, one-half the

maximum productivity rate, and a "recovery" factor for endangered, depleted, threatened stocks, or stocks of unknown

status relative to optimum sustainable population (OSP) (Anon. 1994). The recovery factor was 0.40 because of the

high variance (CV = 1.30) associated with the estimated total annual fishery-related mortality and serious injury for

striped dolphins. PBR for this stock is 73 striped dolphins. 

ANNUAL HUMAN-CAUSED MORTALITY AND SERIOUS INJURY

No mortalities were observed in 1977-1991 foreign fishing activities off the northeast U.S. coast. Nineteen

mortalities were documented between 1989 and 1993 (see below) in the pelagic drift-gillnet fishery, and two mortalities

were documented in 1991 in the New England groundfish trawl fishery. No mortalities were documented in the

Atlantic swordfish/tuna/shark longline, Atlantic swordfish/tuna/shark pair trawl and New England multispecies sink

gillnet fisheries. Also, no takes have been documented in a review of Canadian gillnet and trap fisheries (Read 1994).

 Total estimated average annual fishery-related mortality and serious injury to this stock in the Atlantic during

1989-1993 was 63 striped dolphins annually (CV = 1.30). The total fishery-related mortality and serious injury for

this stock is not less than 10% of the calculated PBR and cannot be considered to be insignificant and approaching zero

mortality and serious injury rate. This determination cannot be made for specific fisheries until the implementing

regulations for Section 118 of the MMPA have been reviewed by the public and finalized. 

Fisheries Information

 Data on current incidental takes in U.S. fisheries are available from several sources. In 1986, NMFS

established a mandatory logbook system for large pelagic fisheries. Data files are maintained at the Southeast Fisheries

Science Center (SEFSC). The Northeast Fisheries Science Center (NEFSC) Sea Sampling Observer Program was

initiated in 1989, and since that year several fisheries have been covered by the program. In late 1992 and in 1993, the

SEFSC provided observer coverage of pelagic longline vessels fishing off the Grand Banks (Tail of the Banks) and

provides observer coverage of vessels fishing south of Cape Hatteras. 

Pelagic swordfish, tunas, and billfish are the targets of the U.S. longline fishery in the U.S. Atlantic and Gulf

of Mexico EEZ (SEFSC unpublished logbook data). Interactions between the longline swordfish/tuna fishery and

striped dolphins have been reported; however, a vessel may fish in more than one statistical reporting area and it is

not possible to separate estimates of fishing effort other than to subtract Gulf of Mexico effort from Atlantic fishing

effort, which includes the Caribbean Sea. This fishery has been monitored with about 5% observer coverage, in terms
93

of trips observed, since 1992. Total longline effort for the Atlantic pelagic fishery (including the Caribbean), based

on mandatory logbook reporting, was 11,279 sets in 1991, 10,605 sets in 1992, and 11,538 sets in 1993 (Cramer 1994).

 There were no reported human-caused mortality or serious injury to this stock by this fishery. 

The estimated total number of hauls in the Atlantic large pelagic drift gillnet fishery increased from 714 in

1989 to 1,144 in 1990; thereafter, with the introduction of quotas, effort was severely reduced. The estimated number

of hauls in 1991, 1992, and 1993 were 233, 243, and 232 respectively. Fifty-nine different vessels participated in this

fishery at one time or another between 1989 and 1993. Observer coverage, expressed as percent of sets observed,

ranged from 8% in 1989, 6% in 1990, 20% in 1991, to 40% in 1992, and 42% in 1993. Effort was concentrated along

the southern edge of Georges Bank and off Cape Hatteras. Examination of the species composition of the catch and

locations of the fishery throughout the year, suggested that the drift gillnet fishery be stratified into two strata, a

southern or winter stratum, and a northern or summer stratum. Estimates of the total by-catch, for each year, were

obtained using the aggregated (pooled 1989-1993) catch rates, by strata (Northridge, in review). Nineteen striped

dolphin mortalities were observed in this fishery between 1989 and 1993 and occurred east of Cape Hatteras in January

and February, and along the southern margin of Georges Bank in summer and autumn. Estimated annual mortality

and serious injury (CV in parentheses) attributable to this fishery was 39 striped dolphins in 1989 (0.84), 57 in 1990

(0.73), ten in 1991 (0.87), 7.7 in 1992 (0.65), and 21 in 1993 (0.20). The 1989-1993 average annual mortality and

serious injury to striped dolphins in the Atlantic large pelagic drift gillnet fishery was 27 dolphins (0.90).

Vessels in the New England groundfish multispecies trawl fishery, a Category III fishery under the MMPA,

were observed in order to meet fishery management needs, rather than marine mammal management needs. An

average of 970 (CV = 0.04) vessels (full and part time) participated annually in the fishery during 1989-1993. The

fishery is active in New England waters in all seasons. The only reported fishery-related mortalities (two) occurred

in 1991. Total estimated mortality and serious injury attributable to this fishery in 1991 was 181 (CV = 0.97); average

annual mortality and serious injury during 1989-1993 was 36 striped dolphins (CV = 2.17). 

STATUS OF STOCK

The status of striped dolphins, relative to OSP, in the U.S. Atlantic EEZ is unknown. The species is not listed

as threatened or endangered under the Endangered Species Act. In Canada, the Cetacean Protection Regulations of

1982, promulgated under the Standing Fisheries Act, prohibit the catching or harassment of all cetacean species. There

are insufficient data to determine the population trends for this species. Average annual fishery-related mortality and

serious injury does not exceed the PBR; therefore, this is not a strategic stock. 

REFERENCES

Anon. 1994. Report of the PBR (Potential Biological Removal) workshop. June 27-29, 1994. NOAA, NMFS

Southwest Fisheries Science Center, La Jolla, California, 13 pp. + Appendices. 

Buckland, S. T., D. R. Andersen, K. P. Burnham, and J. L. Laake. 1993. Distance sampling: Estimating abundance

of biological populations. Chapman and Hall, New York, 446 pp. 

CeTAP. 1982. A characterization of marine mammals and turtles in the mid- and north Atlantic areas of the U.S.

outer continental shelf. Cetacean and Turtle Assessment Program, University of Rhode Island. Final Report,

Contract AA51-C78-48, Bureau of Land Management, Washington, DC, 538 pp. 

Laake, J. L., S. T. Buckland, D. R. Anderson, and K. P. Burnham. DISTANCE user’s guide, V2.0. Colorado

Cooperative Fish & Wildlife Research Unit, Colorado State University, Ft. Collins, Colorado, 72 pp. 

Leatherwood, S., D. K. Caldwell and H. E. Winn. 1976. Whales, dolphins, and porpoises of the western North

Atlantic. A guide to their identification. U.S. Dept. of Commerce, NOAA Tech. Rep. NMFS Circ. 396, 176

pp. 

Northridge, S. In review. Estimation of cetacean mortality in the U.S. Atlantic swordfish and tuna driftnet and pair

trawl fisheries. Draft final report to the Northeast Fisheries Science Center, Contract No. 40ENNF500045,

18 pp. 

Perrin, W. F., C. E. Wilson, and F. I. Archer II. 1994. Pages 129-159 in S. H. Ridgway and R. Harrison (editors),

Handbook of marine mammals, Volume 5: The first book of dolphins, Academic Press, San Diego. 

Read, A. J. 1994. Interactions between cetaceans and gillnet and trap fisheries in the northwest Atlantic. Rep. Int.

Whal. Commn. Special Issue 15: 133-147. 

Reilly, S. B. and J. Barlow. 1986. Rates of increase in dolphin population size. Fish. Bull., U.S. 84(3): 527-533. 
94

Schmidly, D. J. 1981. Marine mammals of the southeastern United States coast and the Gulf of Mexico. Pub. No.

FWS/OBS-80/41, U.S. Fish and Wildlife Service, Office of Biological Services, Washington, DC, 163 pp. 

Waring, G. T., C. P. Fairfield, C. M. Ruhsam and M. Sano. 1992. Cetaceans associated with Gulf Stream features

off the northeastern USA shelf. ICES Marine Mammals Comm. CM 1992/N:12, 29 pp. 
95

SPINNER DOLPHIN (Stenella longirostris):

Western North Atlantic Stock

STOCK DEFINITION AND GEOGRAPHIC RANGE

Spinner dolphins are distributed in oceanic and coastal tropical waters (Leatherwood et al. 1976). This is

presumably an offshore, deep-water species (Schmidly 1981; Perrin and Gilpatrick 1994), and its distribution in the

Atlantic is very poorly known. In the western North Atlantic, these dolphins occur in deep water along most of the

U.S. coast south to the West Indies and Venezuela, including the Gulf of Mexico. Spinner dolphin sightings have

occurred exclusively in deeper (>2,000 m) oceanic waters (CeTAP 1982; Waring et al. 1992) off the northeast U.S.

coast. Stranding records exist from North Carolina, South Carolina, and Florida in the Atlantic and in Texas and

Florida in the Gulf of Mexico. The North Carolina strandings represent the northernmost documented distribution

of this species in the Atlantic. Stock structure in the western North Atlantic is unknown. 

POPULATION SIZE

The number of spinner dolphins inhabiting the U.S. Atlantic Exclusive Economic Zone (EEZ) is unknown

and seasonal abundance estimates are not available for this species since it was rarely seen in the CeTAP (1982) study

area. 

Minimum Population Estimate

Present data are insufficient to calculate a minimum population estimate. 

Current Population Trend

There are insufficient data to determine the population trends for this species. 

CURRENT AND MAXIMUM NET PRODUCTIVITY RATES

Current and maximum net productivity rates are not known for this stock. The maximum net productivity

rate was assumed to be 0.04 for purposes of this assessment. This value is based on theoretical calculations showing

that cetacean populations may not generally grow at rates much greater than 4% given the constraints of their

reproductive life history (Reilly and Barlow 1986). 

POTENTIAL BIOLOGICAL REMOVAL

No PBR can be estimated for this species at this time, because the minimum population size cannot be

determined. 

ANNUAL HUMAN-CAUSED MORTALITY AND SERIOUS INJURY

One mortality has been observed in the large pelagic drift-gillnet fishery. No takes were documented in a

review of Canadian gillnet and trap fisheries (Read 1994). 

 Total average annual estimated average fishery-related mortality and serious injury to this stock in the

Atlantic during 1989-1993 was 1.0 spinner dolphin (CV = 3. 07). PBR cannot be calculated for this stock, but there

is fishery-related mortality and serious injury; therefore, total fishery-related mortality and serious injury cannot be

considered insignificant and approaching zero mortality and serious injury rate. This determination cannot be made

for specific fisheries until the implementing regulations for Section 118 of the MMPA have been reviewed by the public

and finalized. 

Fisheries Information

 Data on current incidental takes in U.S. fisheries are available from several sources. In 1986, NMFS

established a mandatory logbook system for large pelagic fisheries and the data are maintained at the Southeast

Fisheries Science Center (SEFSC). The Northeast Fisheries Science Center (NEFSC) Sea Sampling Observer Program

was initiated in 1989, and since that year several fisheries have been covered by the program. In late 1992 and in 1993,
96

the SEFSC provided observer coverage of pelagic longline vessels fishing off the Grand Banks (Tail of the Banks) and

provides observer coverage of vessels fishing south of Cape Hatteras. 

Pelagic swordfish, tunas, and billfish are the targets of the longline fishery operating in the U.S. Atlantic and

Gulf of Mexico. Effort for the western North Atlantic pelagic longline fishery totaled approximately 5.3 million hooks

set by 281 vessels in 1993 (Cramer 1994). This fishery has been monitored with about 5% observer coverage, in terms

of trips observed, since 1992. There was no reported fishery-related mortality or serious injury to this stock attributable

to the pelagic longline fishery.

The estimated total number of hauls in the Atlantic large pelagic drift gillnet fishery increased from 714 in

1989 to 1,144 in 1990; thereafter, with the introduction of quotas, effort was severely reduced. The estimated number

of hauls in 1991, 1992, and 1993 were 233, 243, and 232 respectively. Fifty-nine different vessels participated in this

fishery at one time or another between 1989 and 1993. Observer coverage, expressed as percent of sets observed,

ranged from 8% in 1989, 6% in 1990, 20% in 1991, to 40% in 1992, and 42% in 1993. Effort was concentrated along

the southern edge of Georges Bank and off Cape Hatteras. Examination of the species composition of the catch and

locations of the fishery throughout the year, suggested that the drift gillnet fishery be stratified into two strata, a

southern or winter stratum, and a northern or summer stratum. Estimates of the total by-catch, for each year, were

obtained using the aggregated (pooled 1989-1993) catch rates, by strata (Northridge, in review). One spinner dolphin

mortality was observed between 1989 and 1993 and occurred east of Cape Hatteras in March 1993. Estimated annual

fishery-related mortality and serious injury attributable to this fishery (CV in parentheses) was 0.7 in 1989 (7. 00), 1.7

in 1990 (2.65), 0.7 in 1991 (2.00), 1.4 in 1992 (0.61), and 0.5 in 1993 (0.89).

STATUS OF STOCK

The status of spinner dolphins relative to OSP in the U.S. Atlantic EEZ is unknown. The species is not listed

as threatened or endangered under the Endangered Species Act. In Canada, the Cetacean Protection Regulations of

1982, promulgated under the Standing Fisheries Act, prohibit the catching or harassment of all cetacean species. There

are insufficient data to determine the population trends for this species. Population size and PBR cannot be estimated,

but fishery-related mortality is very low; therefore, this stock is not a strategic stock. 

REFERENCES

CeTAP. 1982. A characterization of marine mammals and turtles in the mid- and north Atlantic areas of the U.S.

outer continental shelf. Cetacean and Turtle Assessment Program, University of Rhode Island. Final Report,

Contract AA51-C78-48, Bureau of Land Management, Washington, DC, 538 pp. 

Perrin, W. F. and J. W. Gilpatrick, Jr. 1994. Spinner dolphin. Pages 99-128 in S. H. Ridgway and R. Harrison

(editors), Handbook of marine mammals, Volume 5: The first book of dolphins. Academic Press, San Diego,

418 pp. 

Read, A. J. 1994. Interactions between cetaceans and gillnet and trap fisheries in the northwest Atlantic. Rep. Int.

Whal. Commn. Special Issue 15: 133-147. 

Reilly, S. B. and J. Barlow. 1986. Rates of increase in dolphin population size. Fish. Bull., U.S. 84(3): 527-533. 

Schmidly, D. J. 1981. Marine mammals of the southeastern United States coast and the Gulf of Mexico. Pub. No.

FWS/OBS-80/41, U.S. Fish and Wildlife Service, Office of Biological Services, Washington, DC, 163 pp. 

Waring, G. T., C. P. Fairfield, C. M. Ruhsam and M. Sano. 1992. Cetaceans associated with Gulf Stream features

off the northeastern USA shelf. ICES Marine Mammals Comm. CM 1992/N:12, 29 pp. 
97

Figure 1. Distribution of bottlenose dolphin sightings from

NEFSC shipboard surveys during the summer in 1990-1994.

Isobaths are at 100 m and 1,000 m. 

BOTTLENOSE DOLPHIN (Tursiops truncatus):

Western North Atlantic Offshore Stock

STOCK DEFINITION AND GEOGRAPHIC RANGE

There are two hematologically and morphologically distinct bottlenose dolphin ecotypes (Duffield et al. 1983;

Duffield 1986) which correspond to a shallow, warm water ecotype and a deep, cold water ecotype; both ecotypes have

been shown to inhabit waters in the western North Atlantic Ocean (Hersh and Duffield 1990). 

Bottlenose dolphins which had stranded alive in the western North Atlantic in areas with direct access to deep

oceanic waters had hemoglobin profiles which matched that of the deep, cold water ecotype (Hersh and Duffield 1990).

Hersh and Duffield (1990) also described morphological differences between the deep, cold water ecotype dolphins and

dolphins with hematological profiles matching the shallow, warm water ecotype which had stranded in the

Indian/Banana River in Florida. Based on the

distribution of sightings during ship-based surveys

(Fig. 1) and survey personnel observations (NMFS

unpublished data), the western North Atlantic offshore

stock is believed to consist of bottlenose dolphins

corresponding to the hematologically and

morphologically distinct deep, cold water ecotype.

Extensive aerial surveys in 1979-1981

indicated that the stock extended along the entire

continental shelf break from Georges Bank to Cape

Hatteras during spring and summer (CeTAP 1982;

Kenney 1990). The distribution of sightings

contracted towards the south in the fall and the central

portion of the survey area was almost devoid of

sightings in the winter, although there were still

sightings as far north as the southern edge of Georges

Bank. The offshore stock is concentrated along the

continental shelf break in waters of depths > 25 m and

extends beyond the continental shelf into continental

slope waters in lower concentration (Fig. 1) (Kenney

1990). No distribution or abundance data are

available from Canadian waters. Dolphins with

characteristics of the offshore type have been stranded

as far south as the Florida Keys, but there are no

abundance or distribution estimates available for this

stock in U.S. Exclusive Economic Zone (EEZ) waters

south of Cape Hatteras. 

POPULATION SIZE

The total number of bottlenose dolphins off the Atlantic U.S. coast is unknown. Historical seasonal abundance

estimates are available from an aerial survey program conducted in the continental shelf waters between Cape Hatteras,

North Carolina, and Nova Scotia from 1978 to 1982 (CeTAP 1982). The peak average estimated abundance of the

offshore stock occurred in the fall and was estimated to be 7,696 with coefficient of variation (CV) = 0.58. 

Recent abundance was estimated using data collected during an autumn 1991 aerial line transect survey in

the CeTAP study area (NMFS unpublished data), which included an interplatform experiment between a Twin Otter

and an AT-11 aircraft, and from three fine-scale ship surveys (August 1990, June-July 1991, and June-July 1993)

conducted in continental shelf edge and deeper oceanic waters (NMFS unpublished data). 

The three shipboard surveys covered relatively small portions of the northeastern U.S. EEZ. The abundance

estimate from the August 1990 survey, conducted principally along the Gulf Stream north wall between Cape Hatteras

and Georges Bank, was 2,903 bottlenose dolphins (CV = 0.66). The 1991 survey estimate, based principally on
98

sighting effort conducted between the 200 and 2,000 meter isobaths from Cape Hatteras to Georges Bank was 5,990

bottlenose dolphins (CV = 0.39). The estimate for the 1993 survey, conducted principally between the 200 and 2,000

meter isobaths from the southern edge of Georges Bank, across the Northeast Channel to the southwestern edge of the

Scotian Shelf was 716 bottlenose dolphins (CV = 0.44). Although the 1990-1993 surveys did not sample the same

areas or encompass the entire bottlenose dolphin habitat, they did focus on segments of known or suspected high-use

habitats off the northeastern U.S. coast. The collective 1990-93 data suggest that, seasonally, at least several thousand

bottlenose dolphins are occupying these waters; however, survey coverage to date is not judged adequate to provide a

definitive estimate of bottlenose dolphin abundance in the western North Atlantic because of the limited scope of the

shipboard surveys. 

The 1991 aerial survey sightings during both the AT-11 and Twin Otter surveys were almost exclusively in

the continental shelf edge waters. Data from both survey platforms was used in estimating stock size because the

independent abundance estimates were not significantly different and coverage of continental shelf edge waters by both

platforms was similar. The sighting data were analyzed using standard line transect perpendicular sighting distance

analysis methods (Buckland et al. 1993) and the computer program DISTANCE (Laake et al. 1993). Bottlenose

dolphin abundance was not significantly different between survey platforms and was estimated at 12,760 dolphins (CV

= 0.84) from the AT-11 aircraft and 12,090 dolphins (CV = 0.38) from the Twin Otter aircraft. The inverse varianceweighted mean of these independent abundance estimates was used in calculating the minimum population estimate

and was 12,194 bottlenose dolphins (CV = 0.35) (NMFS unpublished data).

Minimum Population Estimate

The minimum population estimate is the lower limit of the two-tailed 60% confidence interval of the lognormal distributed mean abundance estimate of 12,194 bottlenose dolphins (CV = 0.35) from the 1991 aerial surveys

(NMFS unpublished data). This is equivalent to the 20th percentile of the log-normal distribution as specified by

NMFS (Anon. 1994). The minimum population estimate is 9,195 bottlenose dolphins. 

Current Population Trend

The data are insufficient to determine population trends. The recent aerial survey estimates are not

comparable to the CeTAP estimates because the recent data are from a single survey conducted during August-October

while the CeTAP estimates were based on data pooled over several years of seasonal surveys. 

CURRENT AND MAXIMUM NET PRODUCTIVITY RATES

Current and maximum net productivity rates are not known for this stock. The maximum net productivity

rate was assumed to be 0.04 for purposes of this assessment. This value is based on theoretical calculations showing

that cetacean populations may not generally grow at rates much greater than 4% given the constraints of their

reproductive life history (Reilly and Barlow 1986). 

POTENTIAL BIOLOGICAL REMOVAL

Potential biological removal (PBR) has been specified as the product of minimum population size, one-half

the maximum productivity rate, and a "recovery" factor for endangered, depleted, threatened stocks, or stocks of

unknown status relative to optimum sustainable population size (OSP). In accordance with the guidelines for

estimating PBR, the recovery factor was 0.50 because of the stock's unknown status relative to OSP and because the

coefficient of variation of the estimated fishery-related mortality and serious injury was less than 0.30. PBR for the

mid-Atlantic offshore bottlenose dolphin stock is 92 dolphins. 

ANNUAL HUMAN-CAUSED MORTALITY AND SERIOUS INJURY

There are no available estimates of human-caused mortality or serious injury except for estimates extrapolated

from data obtained through NMFS fishery observer programs. 

 Estimated average annual fishery-related mortality or serious injury to this stock is 128 offshore bottlenose

dolphins (CV = 0.39). This level is not less than 10% of the calculated PBR and, therefore, cannot be considered to

be insignificant and approaching zero mortality and serious injury rate. This determination cannot be made for specific

fisheries until the implementing regulations for Section 118 of the MMPA have been reviewed by the public and

finalized. 
99

Fishery Information

There was no documentation of marine mammal mortality or serious injury in distant-water fleet (DWF)

activities off the northeast coast of the U.S. prior to 1977. A fisheries observer program which has recorded fishery

data and information on incidental by-catch of marine mammals was established with implementation of the Magnuson

Fisheries Conservation and Management Act (MFCMA) in 1977. DWF effort in the U.S. Atlantic EEZ under

MFCMA was directed primarily towards Atlantic mackerel and squid. An average of 120 different foreign vessels per

year (range 102-161) operated within the Atlantic coast EEZ from 1977 through 1982. In 1982, the first year that the

NMFS Northeast Regional Observer Program assumed responsibility for observer coverage of the longline vessels, there

were 112 different foreign vessels, eighteen (16%) of which were Japanese tuna longline vessels operating along the

U.S. east coast. Between 1983 and 1991, the number of foreign fishing vessels operating within the U.S. Atlantic EEZ

each year declined from 67 to nine. Between 1983 and 1988, the numbers of DWF vessels included 3, 5, 7, 6, 8, and

8, respectively, Japanese longline vessels. Observer coverage on DWF vessels was 25-35% during 1977-82, and

increased to 58%, 86%, 95%, and 98%, respectively, in 1983-86. From 1987-91, 100% observer coverage was

maintained. Foreign fishing operations for squid ceased at the end of the 1986 fishing season and for mackerel at the

end of the 1991 season. Observers in this program recorded nine bottlenose dolphin mortalities in foreign-fishing

activities during 1977-1988 (Waring et al. 1990). Seven takes occurred in the mackerel fishery, and one bottlenose

dolphin each was caught in both the squid and hake trawl fisheries. 

Data on current incidental takes in U.S. fisheries are available from several sources. In 1986, NMFS

established a mandatory logbook system for large pelagic fisheries. Data files are maintained at the Southeast Fisheries

Science Center (SEFSC). The Northeast Fisheries Science Center (NEFSC) Sea Sampling Observer Program was

initiated in 1989, and since that year several fisheries have been covered by the program. 

In late 1992 and in 1993, the SEFSC provided observer coverage of pelagic longline vessels fishing off the

Grand Banks (Tail of the Banks). SEFSC also provides observer coverage of vessels fishing south of Cape Hatteras.

The Atlantic longline fisheries target primarily swordfish and yellowfin tuna from the Grand Banks south into the

Caribbean and the Gulf of Mexico. There have been no reported lethal takes of this stock by the longline fishery

recently, but one bottlenose dolphin was taken and released alive by the fishery during 1993 in offshore waters outside

of the U.S. EEZ (NMFS unpublished data). 

The estimated total number of hauls in the Atlantic large pelagic drift gillnet fishery increased from 714 in

1989 to 1,144 in 1990; thereafter, with the introduction of quotas, effort was severely reduced. The estimated number

of hauls in 1991, 1992, and 1993 were 233, 243, and 232 respectively. Fifty-nine different vessels participated in this

fishery at one time or another between 1989 and 1993. Observer coverage, expressed as percent of sets observed,

ranged from 8% in 1989, 6% in 1990, 20% in 1991, to 40% in 1992, and 42% in 1993. Effort was concentrated along

the southern edge of Georges Bank and off Cape Hatteras. Examination of the species composition of the catch and

locations of the fishery throughout the year, suggested that the drift gillnet fishery be stratified into two strata, a

southern or winter stratum, and a northern or summer stratum. Estimates of the total by-catch, for each year, were

obtained using the aggregated (pooled 1989-1993) catch rates, by strata (Northridge, in review). Thirty-nine bottlenose

dolphin mortalities have been observed between 1989 and 1993. Estimated bottlenose dolphin kills (CV in

parentheses) extrapolated for each year were 72 in 1989 (0.59), 115 in 1990 (0.42), 26 in 1991 (0.44), 28 in 1992

(0.21), and 22 in 1993 (0.25). Mean annual estimated fishery-related mortality for this fishery in 1989-1993 was 53

bottlenose dolphins (CV = 0.56). 

Atlantic swordfish/tuna/shark pair trawl fishery effort has increased from none in 1989 and 1990, to an

estimated 171 hauls in 1991, and then to an estimated 989 and 1,087 hauls in 1992 and 1993, respectively. The fishery

operated in August-November in 1991, June-November in 1992, and June-October in 1993. Sea sampling began in

October of 1992 when 101 hauls (10% of the total) were sampled. In 1993, 201 hauls (18%) were sampled. Nineteen

vessels have operated in this fishery. The fishery extends from 35EN to 41EN, and from 69EW to 72EW.

Approximately 50% of the total effort was within a one degree square at 39EN, 72EW, around Hudson Canyon. Fishery

locations and species composition of the by-catch showed little seasonal change during the six months of operation and

did not warrant stratification of observer effort. Twenty-one bottlenose dolphin mortalities were observed between 1991

and 1993. Estimated annual fishery-related mortality (CV in parentheses) was 13 dolphins in 1991 (0.53), 73 in 1992

(0.49), and 85 in 1993 (0.41). The estimated mean annual bottlenose dolphin mortality attributable to this fishery is

57 (CV = 0.51). 
100

Vessels in the New England groundfish multispecies trawl fishery, a Category III fishery under the MMPA,

were observed in order to meet fishery management needs, rather than marine mammal management needs. An

average of 970 (CV = 0.04) vessels (full and part time) participated annually in the fishery during 1989-1993. The

fishery is active in New England waters in all seasons. One bottlenose dolphin mortality was documented in 1991 and

the total estimated mortality in this fishery in 1991 was 91 (CV = 0.97). The average fishery-related mortality

attributable to this fishery between 1989-1993 was 18 bottlenose dolphins (CV = 2.17). 

The mid-Atlantic mackerel and squid trawl fisheries were combined into the Atlantic mid-water trawl fishery

in the revised proposed list of fisheries in 1995. The fishery occurs along the U.S. mid-Atlantic continental shelf

region between New Brunswick, Canada, and Cape Hatteras year around. The mackerel trawl fishery was classified

as a Category II fishery since 1990 and the squid fishery was originally classified as a Category II fishery in 1990, but

was reclassified as a Category III fishery in 1992. The combined fishery has been proposed for classification as a

Category II fishery. Although there were reports of bottlenose dolphin mortalities in the foreign fishery during 1977-

1988, there were no fishery-related mortalities of bottlenose dolphins reported in logbook reports from the mackerel

trawl fishery between 1990-1992.

Other Mortality

There are no other known sources of human-caused mortality affecting this stock. 

STATUS OF STOCK

The status of this stock relative to OSP is unknown. The western north Atlantic offshore bottlenose dolphin

is not listed as threatened or endangered under the Endangered Species Act. In Canada, the Cetacean Protection

Regulations of 1982, promulgated under the Standing Fisheries Act, prohibit the catching or harassment of all cetacean

species. There are insufficient data to determine the population trends for this species. This stock is a strategic stock

because estimated annual fishery-related mortality and serious injury exceeds PBR. 

REFERENCES

Anon. 1994. Report of the PBR (Potential Biological Removal) workshop. June 27-29, 1994. NOAA, NMFS

Southwest Fisheries Science Center, La Jolla, California, 13 pp. + Appendices. 

Buckland, S. T., D. R. Andersen, K. P. Burnham, and J. L. Laake. 1993. Distance sampling: Estimating abundance

of biological populations. Chapman and Hall, New York, 446 pp. 

CeTAP (Cetacean and Turtle Assessment Program). 1982. "A Characterization of Marine Mammals and Turtles in

the Mid- and North Atlantic Areas of the U.S. Outer Continental Shelf, Final Report", Contract AA551-CT8-

48, U.S. NTIS PB83-215855, Bureau of Land Management, Washington, DC, 576 pp. 

Duffield, D. A. 1986. Investigation of genetic variability in stocks of the bottlenose dolphin (Tursiops truncatus).

Final report to the NMFS/SEFC, Contract No. NA83-GA-00036, 53 pp. 

Duffield, D. A., Ridgway, S. H., and Cornell, L. H. 1983. Hematology distinguishes coastal and offshore forms of

dolphins (Tursiops). Can. J. Zool. 61: 930-933. 

Hersh, S. L. and D. A. Duffield. 1990. Distinction between northwest Atlantic offshore and coastal bottlenose

dolphins based on hemoglobin profile and morphometry. Pages 129-139 in S. Leatherwood and R. R. Reeves

(editors), The bottlenose dolphin, Academic Press, San Diego, 653 pp.

Laake, J. L., S. T. Buckland, D. R. Anderson, and K. P. Burnham. DISTANCE user’s guide, V2.0. Colorado

Cooperative Fish & Wildlife Research Unit, Colorado State University, Ft. Collins, Colorado, 72 pp. 

Kenney, R. D. 1990. Bottlenose dolphins off the northeastern United States. Pages 369-386 in S. Leatherwood and

R. R. Reeves (editors), The bottlenose dolphin, Academic Press, San Diego, 653 pp. 

Northridge, S. In review. Estimation of cetacean mortality in the U.S. Atlantic swordfish and tuna driftnet and pair

trawl fisheries. Draft final report to the Northeast Fisheries Science Center, Contract No. 40ENNF500045.

18 pp. 

NMFS. 1991. Proposed regime to govern the interactions between marine mammals and commercial fishing

operations after October 1, 1993. Draft Environmental Impact Statement. June 1991. 

Reilly, S. B. and J. Barlow. 1986. Rates of increase in dolphin population size. Fish. Bull., U.S. 84(3): 527-533. 

Waring, G. T., P. Gerrior, P. M. Payne, B. L. Parry and J. R. Nicolas. 1990. Incidental take of marine mammals in

foreign fishery activities off the northeast United States, 1977-1988. Fish. Bull., U.S. 88(2): 347-360.
101

Figure 1. Sightings of bottlenose dolphins during aerial

surveys to the 25 m isobath north of Cape Hatteras during

summer 1994, 9 km past the eastern Gulf Stream wall

south of Cape Hatteras during winter 1991, and three

coastal surveys within one km of shore from New Jersey to

mid-Florida during the summer in 1994.

BOTTLENOSE DOLPHIN (Tursiops truncatus):

Western North Atlantic Coastal Stock

STOCK DEFINITION AND GEOGRAPHIC RANGE

There are two hematologically and morphologically distinct bottlenose dolphin ecotypes (Duffield et al. 1983;

Duffield 1986) which correspond to a shallow, warm water ecotype and a deep, cold water ecotype; both ecotypes have

been shown to inhabit waters in the western North Atlantic Ocean (Hersh and Duffield 1990). Bottlenose dolphins

which had stranded alive in the western North Atlantic in areas with direct access to deep oceanic waters had

hemoglobin profiles matching that of the deep, cold water ecotype (Hersh and Duffield 1990). Hersh and Duffield

(1990) also described morphological differences between the deep, cold water ecotype dolphins and dolphins with

hematological profiles matching the shallow, warm water ecotype which had stranded in the Indian/Banana River in

Florida. Because of their occurrence in shallow, relatively warm waters along the U.S. Atlantic coast and because their

morphological characteristics are similar to the shallow, warm water ecotype described by Hersh and Duffield (1990),

the Atlantic coastal bottlenose dolphin stock is believed to consist of this ecotype. There are currently insufficient data

to allow separation of locally resident bottlenose dolphins (such as those from the Indian/Banana River) from the

coastal stock in the western North Atlantic.

The structure of the coastal bottlenose dolphin

stock in the western North Atlantic is uncertain, but what

is known about it suggests that the structure is complex. A

portion of the coastal stock migrates north of Cape

Hatteras, North Carolina, to New Jersey during the summer

(Scott et al. 1988). It has been suggested that this stock is

restricted to waters < 25 m in depth within the northern

portion of its range (Kenney 1990) because of an apparent

disjunct distribution of bottlenose dolphins centered on the

25 m isobath which was observed during surveys of the

region (CeTAP 1980). The lowest density of bottlenose

dolphins was observed over the continental shelf, with

higher densities along the coast and near the continental

shelf edge. The coastal stock is believed to reside south of

Cape Hatteras in the late winter (Mead 1975; Kenney

1990); however, the depth distribution of the stock south of

Cape Hatteras is uncertain and the coastal and offshore

stocks may overlap there. There was no apparent

longitudinal discontinuity in bottlenose dolphin herd

sightings during aerial surveys south of Cape Hatteras in

the winter (Blaylock and Hoggard 1994).

Scott et al. (1988) hypothesized a single coastal

migratory stock ranging seasonally from as far north as

Long Island, NY, to as far south as central Florida, citing

stranding patterns during a high mortality event in 1987-88

and observed density patterns along the U.S. Atlantic coast.

Figure 1 illustrates the distribution of 584 bottlenose

dolphin herd sightings during aerial surveys from shore to

approximately 9 km past the Gulf Stream edge south of

Cape Hatteras in the winter in 1992 (Blaylock and Hoggard

1994), from shore seaward to the 25 m isobath during the

summer north of Cape Hatteras in 1994 (Blaylock 1995),

and within one km of the shore from New Jersey to midFlorida during three coastal surveys conducted during the

summer in 1994 (Blaylock 1995). The proportion of the
102

sightings illustrated which might be of bottlenose dolphins from other than the coastal stock is unknown; however, it

is reasonable to assume that the coastal surveys within one km of shore minimized inclusion of the offshore stock. 

A working hypothesis for the coastal bottlenose dolphin stock structure postulates that there are local, resident

stocks in certain embayments and that transient stocks migrate seasonally into and out of these embayments (Scott et

al. 1988). In the Indian-Banana River, 28 of 36 marked bottlenose dolphins either resided in or returned to the river

system for a period of at least ten years (Odell and Asper 1990). Eight of the marked dolphins were never positively

resighted. None of the marked dolphins were reported from outside the river system; however, search outside of the

river system was limited. If the working hypothesis is correct, exchange between resident and transient components

of the coastal stock could be sufficient to mask any genetic indicators of stock distinction, even though the stock

components might be sufficiently distinct to respond differently to population pressures. 

POPULATION SIZE

 Mitchell (1975) estimated that the coastal bottlenose dolphin population which was exploited by a shorebased net fishery until 1925 (Mead 1975) was at least 13,748 bottlenose dolphins in the 1800s. Recent estimates of

bottlenose dolphin abundance in the U.S. Atlantic coastal area were made from two types of aerial surveys. The first

type was aerial survey using standard line transect sampling with perpendicular distance data analysis (Buckland et

al. 1993) and the computer program DISTANCE (Laake et al. 1993). The alternate survey method consisted of a

simple count of all bottlenose dolphins seen from aerial surveys within one km of shore.

An aerial line-transect survey conducted during February-March 1991 in the coastal area south of Cape

Hatteras. Sampling transects extended orthogonally from shore out to approximately 9 km past the western wall of

the Gulf Stream into waters as deep as 140 m, and the area surveyed extended from Cape Hatteras to mid-Florida

(Blaylock and Hoggard 1994). Systematic transects were placed randomly with respect to bottlenose dolphin

distribution and approximately 3.3% of the total survey area of approximately 89,900 km2 was visually searched.

Survey transects, area, and dates were chosen utilizing the known winter distribution of the stocks in order to sample

the entire coastal population; however, the offshore stock may represent some unknown proportion of the resulting

population size estimates. Preliminary estimates of abundance were derived through the application of distance

sampling analysis (Buckland et al. 1993) and the computer program DISTANCE (Laake et al. 1993) to the

perpendicular distance sighting data. Bottlenose dolphin abundance was estimated to be 12,435 dolphins with

coefficient of variation (CV) = 0.18 and the log-normal 95% confidence interval was 9,684-15,967 (Blaylock and

Hoggard 1994). 

Perpendicular sighting distance analysis (Buckland et al. 1983) of line transect data from an aerial survey

throughout the northern portion of the range in July 1994, from Cape Hatteras to Sandy Hook, New Jersey, and from

shore to the 25 m isobath, resulted in an abundance estimate of 25,841 bottlenose dolphins (CV = 0.40) (Blaylock

1995) within the approximately 25,600 km2 area. These data were collected during a pilot study for designing future

surveys and are considered to be preliminary in nature.

Either of the aerial line transect surveys and the resulting abundance estimates may have included dolphins

from the offshore stock. It is not currently possible to distinguish the two bottlenose dolphin ecotypes during visual

aerial surveys and the distribution of the two ecotypes in U.S. Atlantic EEZ waters is uncertain. Additional research

is needed to interpret the significance of the line transect survey results.

 An aerial survey of the coastal waters within a one km strip along the shore from Sandy Hook to

approximately Vero Beach, Florida, was also conducted during July 1994 (Blaylock 1995). Dolphins from the offshore

stock are believed unlikely to occur in this area. Observers counted all bottlenose dolphins seen within the one km strip

alongshore from Cape Hatteras to Sandy Hook (northern area) and within the one km strip alongshore south of Cape

Hatteras to approximately Vero Beach (southern area). The average of three counts of bottlenose dolphins in the

northern area was 927 dolphins (range = 303-1,667) and the average of three counts of bottlenose dolphins in the

southern area was 630 dolphins (range = 497-815). The sum of the highest counts in both areas was 2,482 dolphins.

Minimum Population Estimate

Reasonable assurance of a minimum population estimate was not provided by line transect surveys because

the proportion of dolphins from the offshore stock which might have been observed is unknown. The minimum

population size was therefore taken as the highest count of bottlenose dolphins within the one km strip from shore

between Sandy Hook and Vero Beach obtained during the July 1994 survey. The maximum count within one km of
103

shore between Sandy Hook and Cape Hatteras was 1,667 bottlenose dolphins and it was 815 bottlenose dolphins within

one km of shore between Cape Hatteras and Vero Beach. The resulting minimum population size estimate for the

western North Atlantic coastal bottlenose dolphin stock is 2,482 dolphins. 

Current Population Trend

 Kenney (1990) reported an estimated 400-700 bottlenose dolphins from the inshore strata of aerial surveys

conducted along the U.S. Atlantic coast north of Cape Hatteras in the summer during 1979-1981. These estimates

resulted from line transect analyses; thus, they cannot be used in comparison with the direct count data collected in

1994 to assess population trends. 

There was no significant difference in bottlenose dolphin abundance estimated from aerial line transect

surveys conducted south of Cape Hatteras in the winter of 1983 and the winter of 1991 using comparable survey

designs (NMFS unpublished data; Blaylock and Hoggard 1994) in spite of the 1987-88 mortality incident during which

it was estimated that the coastal migratory population may have been reduced by up to 53% (Scott et al. 1988). 

CURRENT AND MAXIMUM NET PRODUCTIVITY RATES

Current and maximum net productivity rates are not known for this stock. The maximum net productivity

rate was assumed to be 0.04 for purposes of this assessment. This value is based on theoretical calculations showing

that cetacean populations may not generally grow at rates much greater than 4% given the constraints of their

reproductive life history (Reilly and Barlow 1986). 

POTENTIAL BIOLOGICAL REMOVAL

Potential biological removal (PBR) has been specified as the product of the minimum population size, one-half

the maximum productivity rate, and a "recovery" factor for endangered, depleted, threatened stocks, or stocks of

unknown status relative to optimum sustainable population size (OSP) (Anon. 1994). The recovery factor was set at

0.50 because of the stock is listed as depleted under the Marine Mammal Protection Act. PBR for the U.S. Atlantic

coastal bottlenose dolphin stock is 25 dolphins. 

ANNUAL HUMAN-CAUSED MORTALITY AND SERIOUS INJURY

Four bottlenose dolphins were reported by the Northeast Region Stranding network to have shown signs of

entanglement with fishing gear in Virginia in 1992 (K. Thounhurst, NMFS, personal communication, 1994). One of

these was associated with pound net gear. In 1993, eight bottlenose dolphins in Virginia and one in Maryland were

reported as entangled in fishing gear, but the gear type was not reported (NMFS unpublished data). Signs of

interaction with fisheries (entanglement, net marks, missing appendages) were present in 22% of the bottlenose dolphin

strandings investigated in North Carolina in 1993 (NMFS unpublished data). 

The percentage of total mortality represented by stranded dolphins is unknown, but 20 bottlenose dolphin

mortalities which showed signs of fishery interaction were reported in the Atlantic states of the NMFS Southeast

Region in 1993 (NMFS unpublished data). A total of 29 bottlenose dolphins from the U.S. Atlantic coastal stock in

the combined 1993 stranding records from both of the NMFS regions were reported to have shown indications of some

sort of fishery interaction (NMFS unpublished data). It is unclear whether the interactions contributed to the

mortalities or occurred post-mortem. Examination of marine mammal stranding records from the NMFS Southeast

Region collected during 1988-1993 showed that an average of 21 (CV = 0.30) stranded bottlenose dolphins from the

area including North Carolina to the Florida Keys were discovered annually showing signs of human interaction

ranging from net marks and entanglement to gunshot wounds and boat propeller strikes (Southeast U.S. Marine

Mammal Stranding Network unpublished data). 

Stranding data probably underestimate the extent of fishery-related mortality and serious injury because not

all of the dolphins which die or are seriously injured may wash ashore, nor will all of those that do wash ashore

necessarily show signs of entanglement or other fishery-interaction. Another factor complicating the estimation of

fishery-related mortality and serious injury to this stock using stranding data is the fact that an unknown proportion

of stranded dolphins are from the offshore stock. Finally, the level of technical expertise among stranding network

personnel varies widely as does the ability to recognize signs of fishery interaction.

The total fishery-related mortality and serious injury for this stock is not less than 10% of the calculated PBR

and, therefore, cannot be considered to be insignificant and approaching zero mortality and serious injury rate. This
104

Gear Type Effort

Haul seines 222

Purse seines 11,962

Otter trawls, bottom 22,550

Otter trawls, midwater 70

Gillnets, anchored or staked 22,252

Gillnets, drift and runaround 11,792

Table I. Roughly estimated average annual fishing

effort (number deployed) by gear type for U.S.

Atlantic coastal fisheries from New Jersey to Key

West, Florida, in 1992-1993, having the potential

for causing serious injury or mortality to

bottlenose dolphins (NMFS unpublished data). 

determination cannot be made for specific fisheries until the implementing regulations for Section 118 of the MMPA

have been reviewed by the public and finalized. 

Fishery Information

Menhaden purse seiners have reported an annual incidental take of one to five bottlenose dolphins (NMFS

1991, pp. 5-73). Observer data are not available. The Atlantic menhaden purse seine fishery targets the Atlantic

menhaden, Brevortia tyrannus, in Atlantic coastal waters approximately 3-18 m in depth. Twenty-two vessels operate

off northern Florida to New England from April-January (NMFS 1991, pp. 5-73). 

Coastal gillnets operate in different seasons targeting different species in different states throughout the range

of this stock. Most nets are staked close to shore, but some are allowed to drift, and nets range in length from 91 m

to 914 m. A gillnet fishery for American shad, Alosa sapidissima, operates seasonally from Connecticut to Georgia,

with nets being moved from coastal ocean waters into fresh water with the shad spawning migration (Read 1994).

There has been no direct observation by NMFS of this particular fishery, which is conducted in state waters, but it is

considered likely that a few bottlenose dolphins are taken in this fishery each year (Read 1994). The North Carolina

sink gillnet fishery operates in October-May targeting weakfish, croaker, spot, bluefish, and dogfish. Another gillnet

fishery along the North Carolina Outer Banks targets bluefish in January-March. Similar mixed-species gillnet

fisheries, under state jurisdiction, operate seasonally along the coast from Florida to New Jersey, with the exclusion

of Georgia. There are no estimates of bottlenose dolphin mortality or serious injury available for these fisheries. A

rough estimate of the average total annual coastal gillnet fishing effort is given in Table I.

Observer coverage of the U.S. Atlantic coastal gillnet fishery was initiated by the NEFSC Sea Sampling

program in July, 1993; and from July to December 1993, 20 trips were observed. From January to April 1994, 71 trips

were observed. This fishery, which extends from North Carolina to New York, is actually a combination of small

vessel fisheries that target a variety of fish species, some of which operate right off the beach. The number of vessels

in this fishery is unknown, because records are held by both

state and federal agencies, and have not, as of yet, been

centralized and standardized. Percent coverage by the

program is unknown, but it is believed to be very low. No

bottlenose dolphins were taken in the observed trips.

The shrimp trawl fishery operates from North

Carolina through northern Florida virtually year around,

moving seasonally up and down the coast. Estimated total

fishing effort is given in Table I. One bottlenose dolphin was

recovered dead from a shrimp trawl in Georgia in 1995

(Southeast U.S. Marine Mammal Stranding Network

unpublished data), but no bottlenose dolphin mortality or

serious injury has been previously reported to NMFS. 

A haul seine fishery operates along northern North

Carolina beaches during the spring and fall targeting mullet,

spot, sea trout, and bluefish. There has been no by-catch of

marine mammals reported to NMFS. 

Other Mortality

The nearshore habitat occupied by this stock is adjacent to areas of high human population and in the northern

portion of its range is highly industrialized. The blubber of stranded dolphins examined during the 1987-88 mortality

event contained anthropogenic contaminants in levels among the highest recorded for a cetacean (Geraci 1989). There

are no estimates of indirect human-caused mortality resulting from pollution or habitat degradation, but a recent

assessment of the health of live-captured bottlenose dolphins from Matagorda Bay, Texas, associated high levels of

certain chlorinated hydrocarbons with low health assessment scores (Reif et al., in preparation). 

STATUS OF STOCK

This stock is considered to be depleted relative to OSP and it is listed as depleted under the Marine Mammal

Protection Act (MMPA). There are data suggesting that the population was at an historically high level immediately
105

prior to the 1987-88 mortality event (Keinath and Musick 1988); however, the 1987-88 anomalous mortality event was

estimated to have decreased the population by as much as 53% (Scott et al. 1988). A comparison of historical and

recent winter aerial survey data in the area south of Cape Hatteras found no statistically significant difference between

population size estimates (Student's t-test, P > 0.10), but these estimates may have included an unknown proportion

of the offshore stock Population trends cannot be determined due to insufficient data. 

There are no observer data directly linking serious injury and mortality to fisheries, but the total number of

bottlenose dolphins assumed from this stock which stranded showing signs of fishery or human-related mortality

exceeded PBR in 1993. 

The species is not listed as threatened or endangered under the Endangered Species Act, but because this stock

is listed as depleted under the MMPA it is a strategic stock. 

REFERENCES

Anon. 1994. Report of the PBR (Potential Biological Removal) workshop. June 27-29, 1994. NOAA, NMFS

Southwest Fisheries Science Center, La Jolla, California, 13 pp. + Appendices. 

Blaylock, R. A. 1995. A pilot study to estimate abundance of the U.S. Atlantic coastal migratory bottlenose dolphin

stock. NOAA Tech. Mem. NMFS-SEFSC-362, 9 pp.

Blaylock, R. A. and W. Hoggard. 1994. Preliminary estimates of bottlenose dolphin abundance in southern U.S.

Atlantic and Gulf of Mexico continental shelf waters. NOAA Tech. Mem. NMFS-SEFSC-356, 10 pp. 

Buckland, S. T., D. R. Anderson, K. P. Burnham, and J. L. Laake. 1993. Distance sampling: Estimating abundance

of biological populations. Chapman & Hall, London, 446 pp. 

CeTAP (Cetacean and Turtle Assessment Program). 1982. "A Characterization of Marine Mammals and Turtles in

the Mid- and North Atlantic Areas of the U.S. Outer Continental Shelf, Final Report", Contract AA551-CT8-

48, U.S. NTIS PB83-215855, Bureau of Land Management, Washington, DC, 576 pp. 

Duffield, D. A. 1986. Investigation of genetic variability in stocks of the bottlenose dolphin (Tursiops truncatus).

Final report to the NMFS/SEFC, Contract No. NA83-GA-00036, 53 pp. 

Duffield, D. A., Ridgway, S. H., and Cornell, L. H. 1983. Hematology distinguishes coastal and offshore forms of

dolphins (Tursiops). Can. J. Zool. 61: 930-933. 

Geraci, J. R. 1989. Clinical investigation of the 1987-88 mass mortality of bottlenose dolphins along the U.S. central

and south Atlantic coast. Final Report to National Marine Fisheries Service, U.S. Navy, Office of Naval

Research, and Marine Mammal Commission, 63 pp. 

Hersh, S. L. and D. A. Duffield. 1990. Distinction between northwest Atlantic offshore and coastal bottlenose

dolphins based on hemoglobin profile and morphometry. Pages 129-139 in S. Leatherwood and R. R. Reeves

(editors), The bottlenose dolphin, Academic Press, San Diego, 653 pp. 

Keinath, J. A. and J. A. Musick. 1988. Population trends of the bottlenose dolphin (Tursiops truncatus) in Virginia.

Final Contract Report, Contract No. 40-GENF-800564, Southeast Fisheries Science Center, Miami, FL, 36

pp. 

Kenney, R. D. 1990. Bottlenose dolphins off the northeastern United States. Pages 369-386 in S. Leatherwood and

R. R. Reeves (editors), The bottlenose dolphin, Academic Press, San Diego, 653 pp. 

Laake, J. L., S. T. Buckland, D. R. Anderson, and K. P. Burnham. DISTANCE user’s guide, V2.0. Colorado

Cooperative Fish & Wildlife Research Unit, Colorado State University, Ft. Collins, Colorado, 72 pp.

Mead, J. G. 1975. Preliminary report on the former net fisheries for Tursiops truncatus in the western North Atlantic.

J. Fish. Res. Bd. Can. 32(7): 1155-1162. 

Mitchell, E. 1975. Porpoise, dolphin and small whale fisheries of the world. Status and problems. Int. Union

Conserv. Natur. Resour. Monogr. 3: 1-129. 

NMFS. 1991. Proposed regime to govern the interactions between marine mammals and commercial fishing

operations after October 1, 1993. Draft Environmental Impact Statement, June 1991. 

Odell, D. K. and E. D. Asper. 1990. Distribution and movements of freeze-branded bottlenose dolphins in the Indian

and Banana Rivers, Florida. Pages 515-540 in S. Leatherwood and R. R. Reeves (editors), The bottlenose

dolphin, Academic Press, San Diego, 653 pp. 

Read, A. J. 1994. Interactions between cetaceans and gillnet and trap fisheries in the northwest Atlantic. Rep. Int.

Whal. Commn. Special Issue 15: 133-147. 
106

Reif, J. S., L. J. Hansen, S. Galloway, G. Mitchum, T. L. Schmitt. In preparation. The relationship between

chlorinated hydrocarbon contaminants and selected health parameters in bottlenose dolphins (Tursiops

truncatus) from Matagorda Bay, Texas, 1992. Colorado State University, Fort Collins, and NMFS, Southeast

Fisheries Science Center, Miami, Florida. 

Reilly, S. B. and J. Barlow. 1986. Rates of increase in dolphin population size. Fish. Bull., U.S. 84(3): 527-533. 

Scott, G. P., D. M. Burn, and L. J. Hansen. 1988. The dolphin dieoff: long term effects and recovery of the

population. Proceedings: Oceans '88, IEEE Cat. No. 88-CH2585-8,Vol. 3: 819-823. 
107

Figure 1. Distribution of harbor porpoise sightings from

NEFSC shipboard surveys during the summer in 1991-1992.

Isobaths are at 100 m and 1,000 m. 

HARBOR PORPOISE (Phocoena phocoena):

Gulf of Maine/Bay of Fundy Stock

STOCK DEFINITION AND GEOGRAPHIC RANGE

This stock is found in U.S. and Canadian Atlantic waters. During the summer (July to September), harbor

porpoises are concentrated in the northern Gulf of Maine and southern Bay of Fundy region, generally in waters less

than 150 m deep (Gaskin 1977; Kraus et al. 1983; Palka 1994a). During fall (October-December) and spring (AprilJune), harbor porpoises are widely dispersed from North Carolina to Maine, and harbor porpoise density is much lower

than during the summer. No specific migratory routes to the northern Gulf of Maine/lower Bay of Fundy region have

been documented. Harbor porpoises are seen from near the coastline into the middle of the Gulf of Maine (>200 m

deep) in both spring and fall. There is little information about the distribution of harbor porpoise during winter

(December to March), although numerous strandings have occurred on beaches from North Carolina to New York.

There are two stranding records from Florida (Smithsonian strandings data base). 

Gaskin (1984, 1992) proposed that there were four separate populations in the western North Atlantic, these

being the Gulf of Maine/Bay of Fundy, Gulf of St. Lawrence, Newfoundland and Greenland populations. Presently

there is insufficient evidence to accept or reject this hypothesis. Results of a workshop held in February, 1994 were

inconclusive with respect to population structure of harbor porpoises in the western North Atlantic, although it was

agreed upon that animals found in the Gulf of Maine and Bay of Fundy are from the same stock (Palka 1994b).

Research is currently being conducted to re-analyze existing genetic data and analyze new samples in order to resolve

the larger scale stock structure question. This report follows Gaskin's hypothesis on harbor porpoise stock structure

in the western North Atlantic; Gulf of Maine and Bay of Fundy harbor porpoises are recognized as a single

management stock separate from harbor porpoise populations in the Gulf of St. Lawrence, Newfoundland, and

Greenland. 

POPULATION SIZE

Two line-transect sighting surveys were

conducted — one in 1991, the other in 1992 — to

estimate the absolute population size of the harbor

porpoises aggregated in the Gulf of Maine/Bay of

Fundy region during the summer. The study area was

stratified by water depth and expected density of

harbor porpoises. Harbor porpoise sightings are

shown in Figure 1. 

The shipboard sighting survey procedure to

estimate abundance corrected for g(0) used two

independent teams that searched using the naked eye

in non-closing mode. Abundance, corrected for g(0),

was estimated using the direct-duplicate method

(Palka, in press) and variability was estimated using

bootstrap re-sampling methods. The abundance

estimates were 37,500 harbor porpoises in 1991

[coefficient of variation (CV) = 0.29, 95% confidence

interval (CI) = 26,700-86,400] and 67,500 harbor

porpoises in 1992 (CV = 0.23, 95% CI = 32,900-

104,600). The inverse variance weighted-average

estimate (Smith et al. 1993) of harbor porpoise

abundance was 47,200 harbor porpoises (CV = 0.19,

95% CI = 39,500-70,600). Possible reasons for the

inter-annual abundance and distribution differences

include inter-annual changes in water temperature and

availability of primary prey species (Palka 1994a).
108

Potential biases that have not been explicitly accounted for in the present abundance estimates are ship avoidance, time

of submergence, and potential recounting of animals. Preliminary analyses indicate that ship avoidance, though

present to some degree, did not substantially affect the abundance estimate (NEFSC 1992). 

Minimum Population Estimate 

The minimum population estimate is the lower limit of the two-tailed 60% confidence interval of the lognormal distributed abundance estimate of 47,200 harbor porpoises (CV = 0.19) (Palka, in press). This is equivalent

to the 20th percentile of the log-normal distribution as specified by NMFS (Anon. 1994). The minimum population

estimate is 40,297 harbor porpoises. 

Current Population Trend

There are insufficient data to determine the population trends for this species. Previous abundance estimates

for harbor porpoises in the Gulf of Maine/Bay of Fundy are available from earlier studies, (e. g. 4,000 animals, Gaskin

1977, and 15,800 animals, Kraus et al. 1983). These estimates cannot be used in a trends analysis because they were

for selected small regions within the entire known summer range and, in some cases, did not incorporate any estimate

of g(0) (NEFSC 1992). 

CURRENT AND MAXIMUM NET PRODUCTIVITY RATES

Although current population growth rates of western North Atlantic harbor porpoises have not been estimated

due to lack of data, several attempts have been made to estimate potential population growth rates. Barlow and Boveng

(1991), who used a re-scaled human life table, estimated the upper bound of the annual potential growth rate to be

9.4%. Woodley and Read (1991) used a re-scaled Himalayan tahr life table to estimate the likely annual growth rate

to be 4%. In an attempt to estimate the potential population growth rate which incorporated many of the uncertainties

in survivorship and reproduction, Caswell et al. (1994) used a Monte Carlo method to calculate a distribution of growth

rates, which indicated that the potential growth rate is unlikely to be greater than 10% per year. The median of this

distribution is approximately 4%, but, it is not known whether this is the best estimate (Palka 1994b). Therefore, the

maximum net productivity rate was assumed to be 0.04 for purposes of this assessment. This value is based on

theoretical calculations showing that cetacean populations may not generally grow at rates much greater than 4% given

the constraints of their reproductive life history (Anon. 1994). 

POTENTIAL BIOLOGICAL REMOVAL

Potential biological removal (PBR) was specified as the product of minimum population size, one-half the

maximum productivity rate, and a "recovery" factor for endangered, depleted, threatened stocks, or stocks of unknown

status relative to optimum sustainable population (OSP) (Anon. 1994). The recovery factor was set at 0.50 because

of the stock's status relative to its OSP level is unknown. PBR for this stock is 403 harbor porpoises. 

ANNUAL HUMAN-CAUSED MORTALITY

Total annual estimated average fishery-related mortality and serious injury to this stock in the Atlantic during

1989-1993 was 1,876 harbor porpoises (CV = 0.32). This is probably an underestimate because it does not include

fishery-related mortality and serious injury in Canadian fisheries, nor does it include mortality associated with the U.S.

Atlantic coastal gillnet fishery. Average annual fishery-related mortality and serious injury may actually be more on

the order of 2,100-2,350 harbor porpoises per year. Total annual fishery-related mortality and serious injury for this

stock is not less than 10% of the calculated PBR and, therefore, cannot be considered to be insignificant and

approaching zero mortality and serious injury rate. This determination cannot be made for specific fisheries until the

implementing regulations for Section 118 of the MMPA have been reviewed by the public and finalized. 

Fishery Information

The Canadian gillnet fishery occurs mostly in the western portion of the Bay of Fundy during the summer and

early autumn months, when the density of harbor porpoises is highest there. This fishery has been well-documented,

with 19 gillnetters active in 1986, 28 active in 1987, and 21 in 1988 (Polacheck 1989). Canadian total harbor porpoise

by-catch in this fishery was thought to be low, based on casual observations and discussions with fishermen. The 1986
109

estimated harbor porpoise by-catch was 94-116 and estimated by-catch was 130 harbor porpoises in 1989 (O'Boyle and

Zwanenburg 1994). 

An observer program implemented in the Canadian Bay of Fundy sink gillnet fishery during the summer of

1993 provided total by-catch estimates of between 222-424 harbor porpoises (O'Boyle and Zwanenburg 1994). No

measure of variability was estimated. This program was expanded in 1994 and the 1994 by-catch was estimated to be

between 80-120 harbor porpoises (DFO 1995). 

Some harbor porpoises are caught in Canadian and U.S. weirs in a fishery which occurs from May to

September each year. Weirs are found along the southwestern shore of the Bay of Fundy, and scattered along the

western Nova Scotia and northern Maine coasts. There were 180 active weirs in the western Bay of Fundy and 56

active weirs in Maine in 1990 (Read 1994). Smith et al. (1983) estimated that approximately 70 harbor porpoises

become trapped annually and, on average, 27 harbor porpoises die annually in Bay of Fundy weirs; the rest are

released alive. At least 43 harbor porpoises were trapped in Bay of Fundy weirs in 1990, but the number killed is

unknown. In 1993, after a cooperative program between fishermen and Canadian biologists began, over 100 harbor

porpoises were released alive and an unknown number died (Read 1994). 

There is evidence that harbor porpoises were harvested by natives in Maine and Canada before the 1960's,

and the meat was used for human consumption, oil, and fish bait (NEFSC 1992). The extent of these past harvests is

unknown, though it is believed to be small. Up until the early 1980s, small kills by native hunters (Passamaquoddy

Indians) were reported. However, in recent years it is believed to have nearly stopped (Polacheck 1989). 

A sampling program was conducted to collect information concerning marine mammal by-catch in the New

England groundfish gillnet fishery in 1984. Approximately 10% of the vessels fishing in Maine, New Hampshire, and

Massachusetts were sampled. Among the eleven gillnetters who received permits and logbooks, 30 harbor porpoises

were reported caught. It was estimated, using rough estimates of fishing effort, that a maximum of 600 harbor

porpoises were killed annually in this fishery (Gilbert and Wynne 1985, 1987). 

Data on incidental takes in U.S. fisheries are available from several sources. In 1986, NMFS established a

mandatory logbook system for large pelagic fisheries. The Northeast Fisheries Science Center (NEFSC) Sea Sampling

Observer Program was initiated in 1989, and since that year several fisheries have been covered by the program. In

late 1992 and in 1993, the SEFSC provided observer coverage of pelagic longline vessels fishing off the Grand Banks

(Tail of the Banks) and provides observer coverage of vessels fishing south of Cape Hatteras. 

By-catch has been observed by NMFS Sea Samplers in the New England multispecies gillnet, Atlantic

swordfish/tuna/shark gillnet, and New England groundfish trawl fisheries; but no mortalities were documented in the

Atlantic swordfish/tuna/shark longline, and Atlantic swordfish/tuna/shark pair trawl fisheries. 

There were approximately 349 full and part-time vessels in the New England multispecies sink gillnet fishery,

which covers the Gulf of Maine and southern New England, in 1993. An additional 187 vessels were reported to

occasionally fish in the Gulf of Maine with gillnets for bait or personal use; however, these vessels were not covered

by the observer program (Walden, in review) and their fishing effort was not used in estimating mortality. Observer

coverage in terms of trips has been 1%, 6%, 7. 5%, and 5% for years 1990 to 1993, respectively. There were 220

harbor porpoise mortalities related to this fishery observed between 1990 and 1993 and one was released alive

uninjured. Annual estimates of harbor porpoise by-catch in the New England multispecies sink gillnet fishery reflect

seasonal distribution of the species and of fishing effort. Estimated annual by-catch (CV in parentheses) from this

fishery during 1990-1993 was 2,900 in 1990 (0.32), 2,000 in 1991 (0.35), 1,200 in 1992 (0.21), and 1,400 in 1993

(0.18) (Bravington and Bisack, in review; CUD 1994); average estimated harbor porpoise mortality and serious injury

in the New England multispecies sink gillnet fishery during 1989-1993 was 1,875 (0.32). These estimates include a

correction factor for the under-recorded number of by-caught animals that occurred during unobserved hauls on trips

with observers on the boat, when applicable. Need for such a correction became evident following re-analysis of data

from the sea sampling program indicating that for some years by-catch rates from unobserved hauls were lower than

that for observed hauls. Further analytical details are given in Palka (1994b) and CUD (1994). These revised by-catch

estimates replace those published earlier (Smith et al. 1993). These estimates are still negatively biased because they

do not include porpoises that fell out of the net while still underwater. This bias cannot be quantified at this time. Bycatch in the northern Gulf of Maine occurs primarily from June to September; while in the southern Gulf of Maine bycatch occurs from January to May and September to December. 

There is no evidence of differential mortality in U.S. or Canadian gillnet fisheries by age or sex, although there

is substantial inter-annual variation in the age and sex composition of the by-catch (Read and Hohn, in review). 
110

Pinger experiments, using acoustic alarms attached to some observed gillnets, were conducted in the Gulf of

Maine in 1992, 1993, and 1994. All trips were observed for all vessels involved in these experiments, whether or not

the nets had alarms attached. There were 12, 33, and 29 harbor porpoise mortalities observed during 1992, 1993, and

1994, respectively, from these trips. These mortalities were included estimating annual mortality.

Observer coverage of the U.S. Atlantic coastal gillnet fishery was initiated by the NEFSC Sea Sampling

program in July, 1993; and from July to December 1993, 20 trips were observed. From January to April 1994, 71 trips

were observed. This fishery, which extends from North Carolina to New York, is actually a combination of small

vessel fisheries that target a variety of fish species, some of which operate right off the beach. The number of vessels

in this fishery is unknown, because records which are held by both state and federal agencies have not been centralized

and standardized. Percent coverage by the program is unknown, but it is believed to be very low. No harbor porpoises

were taken in these observed trips. This result was not unexpected for July through December because there is little

evidence that harbor porpoises are in the this area during this time frame; however, this is not the case for January to

April. The absence of observed takes in early 1994 may reflect low observer coverage or its distribution since, harbor

porpoise strandings seem to be very localized with respect to time and area, and localities also change from year to

year. Polacheck et al. (in press) reported one incidental take in shad nets in the York River, Virginia. In general,

strandings along U.S. Atlantic beaches suggest that harbor porpoises are taken in the Virginia shad fishery and other

coastal gillnet fisheries (Read 1994). 

Vessels in the New England groundfish multispecies trawl fishery, a Category III fishery under the MMPA,

were observed in order to meet fishery management needs, rather than marine mammal management needs. An

average of 970 (CV = 0.04) vessels (full and part time) participated annually in the fishery during 1989-1993. This

fishery is active in New England waters in all seasons. One harbor porpoise mortality was observed in this fishery

between 1989 and 1993. This take occurred in February, 1992 east of Barnegatt Inlet, New York at the continental

shelf break. The animal was clearly dead prior to being taken by the trawl, because it was severely decomposed and

the tow duration of 3.3 hours was insufficient to allow extensive decomposition; therefore, there is no estimated bycatch for this fishery. The estimated total number of hauls in the Atlantic large pelagic drift gillnet fishery

increased from 714 in 1989 to 1,144 in 1990; thereafter, with the introduction of quotas, effort was severely reduced.

Fifty-nine different vessels participated in this fishery at one time or another between 1989 and 1993. The estimated

number of hauls in 1991, 1992, and 1993 were 233, 243, and 232, respectively. Observer coverage, expressed as

percent of sets observed, ranged from 8% in 1989, 6% in 1990, 20% in 1991, to 40% in 1992, and 42% in 1993. Effort

was concentrated along the southern edge of Georges Bank and off Cape Hatteras. Examination of the species

composition of the catch and locations of the fishery throughout the year suggested that the drift gillnet fishery be

stratified into two strata, a southern or winter stratum, and a northern or summer stratum. Estimates of the total bycatch, for each year, were obtained using the aggregated (pooled 1989-1993) catch rates, by strata (Northridge, in

review). One harbor porpoise mortality was observed between 1989 and 1993. This by-catch was notable because it

occurred in continental shelf edge waters adjacent to Cape Hatteras. Estimated annual fishery-related mortality (CV

in parentheses) attributable to this fishery was 0.7 in 1989 (7. 00), 1.7 in 1990 2.65), 0.7 in 1991 (2.00), 0.4 in 1992,

and 1.5 in 1993 (0.45); average estimated harbor porpoise mortality and serious injury in the Atlantic large pelagic

drift gillnet fishery during 1989-1993 was 1.0 (3.06). 

Other Mortality

Sixty-four harbor porpoise strandings were reported from Maine to North Carolina between January and June,

1993. Fifty of those harbor porpoises were reported stranded in the U.S. Atlantic region from New York to North

Carolina between February and May. Many of the carcasses recovered in this area during this time period had cuts

and body damage suggestive of net marking (Haley and Read 1993). Five out of eight carcasses and fifteen heads from

the strandings that were examined showed signs of human interactions (net markings on skin and missing flippers or

flukes). Decomposition of the remaining animals prevented determination of the cause of death. Earlier reports of

harbor porpoise entangled in gillnets in Chesapeake Bay and along the New Jersey coast and reports of apparent

mutilation of harbor porpoise carcasses, raised concern that the 1993 strandings were related to a coastal net fishery,

such as the American shad coastal gillnet fishery (Haley and Read 1993). Between January and May 1994, 35 harbor

porpoises were found stranded along the beaches from North Carolina to New York (A. J. Read, personal

communication).
111

Stranding data probably underestimate the extent of fishery-related mortality and serious injury because not

all of the marine mammals which die or are seriously injured may wash ashore, nor will all of those that do wash

ashore necessarily show signs of entanglement or other fishery-interaction. Finally, the level of technical expertise

among stranding network personnel varies widely as does the ability to recognize signs of fishery interaction.

Other potential human-induced factors that may be affecting this harbor porpoise population include high

levels of contaminants in their tissues and increased ship activity. Of particular concern are high levels of

polychlorinated biphenyls (PCBs) and other lipophilic organochlorines in their tissues (Gaskin et al. 1983). No obvious

pathology has been noted in more than 300 necropsies of harbor porpoises incidentally captured in gillnets in the Bay

of Fundy (A. J. Read, unpublished data), but it is not known whether these contaminants have other effects. It has been

suggested that increased shipping activity in several coastal bays has caused the disappearance of harbor porpoises in

those coastal bays (NEFSC 1992). 

STATUS OF STOCK

The National Marine Fisheries Service has proposed listing the Gulf of Maine harbor porpoise as threatened

under the Endangered Species Act (NMFS 1993). In Canada, the Cetacean Protection Regulations of 1982,

promulgated under the standing Fisheries Act, prohibit the catching or harassment of all species of cetaceans, including

the harbor porpoise. There are insufficient data to determine the population trends for this species. Total annual

fishery-related mortality and serious injury exceeds PBR and this is a strategic stock.

REFERENCES

Anon. 1994. Report of the PBR (Potential Biological Removal) workshop. June 27-29, 1994. NOAA, NMFS

Southwest Fisheries Science Center, La Jolla, California, 13 pp. + Appendices. 

Barlow, J. and P. Boveng. 1991. Modeling age-specific mortality for marine mammal populations. Mar. Mam. Sci.

7:50-65. 

Bravington, M. V. and K. D. Bisack. In review. Estimates of harbor porpoise by-catch in the Gulf of Maine

sink gillnet fishery, 1990-1993. Submitted to Fish. Bull., U.S. 

Caswell, H., S. Brault, A. Read, T. Smith, and J. Barlow. 1994. Rate of increase of harbor porpoise populations:

Estimation and uncertainty. Working paper No. 10B presented at the NMFS Harbor Porpoise Workshop -

February 1994. NOAA, NMFS, NEFSC, Woods Hole, Massachusetts. 

CUD [Conservation and Utilization Division]. 1994. Estimating harbor porpoise by-catch in the Gulf of Maine sink

gillnet fishery, NOAA, NMFS, NEFSC Ref. Doc. 94-24, Woods Hole, Massachusetts. 

DFO [Canadian Department of Fisheries and Oceans]. 1995. Harbour porpoise by-catch in the Bay of Fundy gillnet

fishery. Project Summary; Industry Services and Native Fisheries. No. 48, February, 1995. 4 pp.

Gaskin, D. E. 1977. Harbour porpoise, Phocoena phocoena (L.), in the western approaches to the Bay of Fundy 1969-

75. Rep. Int. Whal. Comm 27: 487-492. 

Gaskin, D. E., R. Frank, and M. Holdrinet. 1983. Polychlorinated biphenyls in harbor porpoises, Phocoena phocoena

(L.), from the Bay of Fundy, Canada and adjacent waters, with some information on chlordane and

hexachlorobenzene levels. Archives of Environmental contamination and Toxicology 12: 211-219. 

Gaskin, D. E. 1984. The harbor porpoise Phocoena phocoena (L.): Regional populations, status, and information on

direct and indirect catches. Rep. Int. Whal. Comm 34: 569-586. 

Gaskin, D. E. 1992. The status of the harbour porpoise. Can. Fld. Nat. 106: 36-54. 

Gilbert, J. R. and K. M. Wynne. 1985. Harbor seal populations and fisheries interactions with marine mammals in

New England, 1984. Fourth Annual Report, Contract NA-80-FA-C-00029, Northeast Fisheries Center,

Woods Hole, MA, 15 pp. 

Gilbert, J. R. and K. M. Wynne. 1987. Harbor seal populations and fisheries interactions with marine mammals in

New England. Final Report Contract NA-EA-C-0070, Northeast Fisheries Center, Woods Hole,

Massachusetts. 15 pp. 

Haley, N. J. and A. J. Read. 1993. Summary of the workshop on harbor porpoise mortalities and human interaction.

NOAA Tech. Mem. NMFS-F/NER 5. 
112

Kraus, S. D., J. H. Prescott, and G. S. Stone. 1983. Harbour porpoise, Phocoena phocoena, in the U.S. coastal waters

of the Gulf of Maine: A survey to determine seasonal distribution and abundance. Report to the Director,

National Marine Fisheries Service, Northeast Region, Woods Hole, Massachusetts, 15 pp. 

NEFSC [Northeast Fisheries Science Center]. 1992. Harbor porpoise in eastern North America: Status and research

needs. Results of a scientific workshop held May 5-8, 1992 at the Northeast Fisheries Science Center, Woods

Hole, MA. NOAA, NMFS, NEFSC Ref. Doc. 92-06, Woods Hole, Massachusetts. 

NMFS [National Marine Fisheries Service]. 1993. Proposed listing of Gulf of Maine population of harbor porpoises

as threatened under the Endangered Species Act. Federal Register 58: 3108-3120, January 07, 1993. 

Northridge, S. In review. Estimation of cetacean mortality in the U.S. Atlantic swordfish and tuna driftnet and pair

trawl fisheries. Draft final report to the Northeast Fisheries Science Center, Contract No. 40ENNF500045,

18 pp. 

O'Boyle, R. N. and K. C. T. Zwanenburg (editors). Report of the Scotia-Fundy regional advisory process (RAP).

Canadian Manuscript Report of Fisheries and Aquatic Sciences No. 2252. 

Palka, D. 1994a. Correlations between sighting rates of harbor porpoises and environmental factors using sighting

survey data collected in 1992 and 1993. Working paper No. 17 presented at the NMFS Harbor Porpoise

Workshop - February 1994, NOAA, NMFS, NEFSC, Woods Hole, Massachusetts. 

Palka, D. (editor). 1994b. Results of a Scientific workshop to evaluate the status of harbor porpoises (Phocoena

phocoena) in the western North Atlantic. NOAA, NMFS, NEFSC [Northeast Fisheries Science Center] Ref.

Doc. 94-09, Woods Hole, Massachusetts. 

Palka, D. In press. Abundance estimate of the Gulf of Maine harbor porpoise. Rep. Int. Whal. Commn. Special Issue

16. 

Polacheck, T. 1989. Harbor porpoises and the gillnet fishery. Oceanus 32(1): 63-70.

Polacheck, T., F. W. Wenzel, and G. Early. In press. Rep. Int. Whal. Commn. Special Issue 16. 

Read, A. J. 1994. Interactions between cetaceans and gillnet and trap fisheries in the northwest Atlantic. Rep. Int.

Whal. Commn. Special Issue 15: 133-147. 

Read, A. J. and A. A. Hohn. In press. Life in the fast lane: The life history of harbour porpoises from the Gulf of

Maine. Mar. Mamm. Sci. 

Smith, G. J. D., A. J. Read, and D. E. Gaskin. 1983. Incidental catch of harbor porpoises, Phocoena phocoena (L.),

in herring weirs in Charlotte County, New Brunswick, Canada. Fish. Bull., U.S. 81(3): 660-2. 

Smith, T., D. Palka, and K. Bisack. 1993. Biological Significance of by-catch of harbor porpoise in the Gulf of Maine

demersal gillnet fishery. NOAA, NMFS, NEFSC [Northeast Fisheries Science Center] Ref. Doc. 93-23,

Woods Hole, Massachusetts. 

Walden, J. In review. Results of the Gulf of Maine gillnet survey 1989-92. NOAA, NMFS, NEFSC [Northeast

Fisheries Science Center] Ref. Doc., Woods Hole, Massachusetts. 

Woodley, T. H. and A. J. Read. 1991. Potential rates of increase of a harbor porpoise (Phocoena phocoena)

population subjected to incidental mortality in commercial fisheries. Can. J. Fish. Aquat. 48:2429-35. 
113

HARBOR SEAL (Phoca vitulina):

Western North Atlantic Stock

STOCK DEFINITION AND GEOGRAPHIC RANGE

The harbor seal is found in the western North Atlantic, from the eastern Canadian Arctic and Greenland south

to southern New England and New York, and occasionally to the Carolinas (Boulva and McLaren 1979; Katona et al.

1993). Although the stock structure of the western North Atlantic population is unknown, it is thought that harbor

seals found along the eastern U.S. and Canadian coasts represent one population (P. M. Payne, personal

communication, 1989). 

Harbor seals are year-round inhabitants of the coastal waters of eastern Canada and Maine (Katona et al.

1993), and occur seasonally along the southern New England and New York coasts from September through late May

(Schneider and Payne 1983). Scattered sightings and strandings have been recorded as far south as Georgia (NMFS

unpublished data). A general southward movement from the Bay of Fundy to southern New England waters occurs

in autumn and early winter (Rosenfeld et al. 1988; Whitman and Payne 1990). A northward movement from southern

New England to Maine and eastern Canada occurs prior to the pupping season, which takes place from mid-May

through June along the Maine Coast (Wilson 1978; Whitman and Payne 1990). No pupping areas have been identified

in southern New England (Payne and Schneider 1984). The overall geographic range throughout coastal New England

has not changed significantly during the last century (Payne and Selzer 1989). 

The majority of animals moving into southern New England waters are juveniles. Whitman and Payne (1990)

suggest that the age-related dispersal may reflect the higher energy requirements of younger animals. 

POPULATION SIZE

Since passage of the MMPA in 1972, the number of seals along the New England coast has increased nearly

five-fold. Summer aerial survey haul-out counts along the Maine Coast totaled 28,810 animals (Kenney and Gilbert

1994). This number is considered to be a minimum abundance estimate because it is uncorrected for animals in the

water or outside the survey area. Increased abundance of seals in the northeast region has also been documented during

aerial and boat surveys of overwintering haul-out sites in southern New England and eastern Long Island (Payne and

Selzer 1989; V. Rough, personal communication). Canadian scientists counted 3,600 harbor seals during an August

1992 aerial survey in the Bay of Fundy (Stobo and Fowler 1994), but noted that the survey was not designed to obtain

a population estimate. 

Minimum Population Estimate

A minimum population estimate is 28,810 seals, based on uncorrected total counts along the Maine coast in

1993. 

Current Population Trend

Based on 1981, 1982, 1986, and 1993 surveys conducted along the Maine coast, Kenney and Gilbert (1994)

estimated a 8.7% annual rate of increase in Maine coastal waters. Possible factors contributing to this increase include

MMPA protection and increased prey. There are no indications that population growth has slowed or that it is at or

near its potential maximum level. The rapid increase observed during the past two decades may reflect past reduction

of the population by historical bounty hunting, possibly to a very low level. 

CURRENT AND MAXIMUM NET PRODUCTIVITY RATES

Current and maximum net productivity rates are not known for this stock. The maximum net productivity

rate was assumed to be 0.12 for purposes of this assessment (Anon. 1994). 

POTENTIAL BIOLOGICAL REMOVAL

Potential biological removal (PBR) was specified as the product of minimum population size, one-half the

maximum productivity rate, and a "recovery" factor for endangered, depleted, threatened stocks, or stocks of unknown

status relative to optimum sustainable population (OSP) (Anon. 1994). The recovery factor was set at 1.0 because the

stock size is known to be increasing. PBR for this stock is 1,729 harbor seals. 
114

ANNUAL HUMAN-CAUSED MORTALITY

Harbor seals, were bounty hunted in New England waters until the late 1960's. This hunt may have caused

the demise of this stock in U.S. waters (Katona et al. 1993). 

Researchers and fishery observers have documented incidental mortality in several fisheries, particularly

within the Gulf of Maine (see below). An unknown level of mortality also occurs in the mariculture industry (i.e.,

salmon farming), and by deliberate shooting (NMFS unpublished data). 

An unknown number of harbor seals have been taken in Newfoundland and Labrador, Gulf of St. Lawrence

and Bay of Fundy groundfish gillnets, Atlantic Canada and Greenland salmon gillnets, Atlantic Canada cod traps, and

in Bay of Fundy herring weirs (Read 1994). Furthermore, some of these mortalities (e.g., seals trapped in herring

weirs) are the result of direct shooting. The Canadian government has recently implemented a pilot program that

permits mariculture operators to use acoustic deterrents or shoot problem seals. The success of this program will be

evaluated in April 1995 (J. Conway, Can. Dept. Fish. & Oceans, personal communication). 

Average annual estimated fishery-related mortality and serious injury to this stock in the U.S. Exclusive

Economic Zone (EEZ) during 1990-1993, based on observed fishery interactions, was 476 harbor seals (CV = 0.46).

Total fishery-related mortality and serious injury for this stock is not less than 10% of the calculated PBR and,

therefore, cannot be considered to be insignificant and approaching zero mortality and serious injury rate. This

determination cannot be made for specific fisheries until the implementing regulations for Section 118 of the MMPA

have been reviewed by the public and finalized. 

Fisheries Information

Incidental takes of harbor seals have been recorded in groundfish gillnet, herring purse seine, halibut tub

trawl, and lobster fisheries (Gilbert and Wynne, 1985 and 1987). A study conducted by the University of Maine

reported a combined average of 22 seals entangled annually by 17 groundfish gillnetters off the coast of Maine (Gilbert

and Wynne 1987). All seals were young of the year and were caught from late June through August, and in early

October. Interviews with a limited number of mackerel gillnetters indicated only one harbor seal entanglement and

a negligible loss of fish to seals. Net damage and fish robbing were not reported to be a major economic concern to

gillnetters interviewed (Gilbert and Wynne 1987). 

Herring purse seiners have reported accidentally entrapping seals off the mid-coast of Maine, but indicated

that the seals were rarely drowned before the seine was emptied (Gilbert and Wynne 1985). Capture of seals by halibut

tub trawls are rare. One vessel captain indicted that he took one or two seals a year. These seals were all hooked

through the skin and released alive, indicating they were snagged as they followed baited hooks. Infrequent reports

suggest seals may rob bait off longlines, although this loss is considered negligible (Gilbert and Wynne 1985). 

Incidental takes in lobster traps in inshore waters off Maine are reportedly rare. Captures of approximately

two seal pups per port per year were recorded by mid-coastal lobstermen off Maine (Gilbert and Wynne 1985). Seals

have been reported to rob bait from inshore lobster traps, especially in the spring, when fresh bait is used. These

incidents may involve only a few individual animals. Lobstermen claim that seals consume shedding lobsters. 

The Atlantic Canadian and Greenland salmon gillnet fishery is seasonal, with the peak from June to

September, depending on location. In southern and eastern Newfoundland, and Labrador during 1989, 2,196 nets 91

m long were used. There is no effort data available for the Greenland fishery. However, the fishery was terminated

in 1993 under an agreement between Canada and North Atlantic Salmon Fund (Read 1994). 

The Canadian Atlantic groundfish gillnet fishery is important and widespread. Many fisherman hold

groundfish gillnet licenses but the number of active fishermen is unknown. In 1989, approximately 6,800 licenses were

issued to fishermen along the southern coasts of Labrador, and northeast and southern coast of Newfoundland. In the

Gulf of St. Lawrence, there were about 3,900 licenses issued in 1989, while in the Bay of Fundy and southwestern Nova

Scotia 659 licenses were issued. 

There were 3,121 cod traps operating in Newfoundland and Labrador during 1979, and about 7,500 in 1980

(Read 1994). This fishery was closed at the end of 1993 due to collapse of Canadian groundfish resources. 

Herring weirs are also distributed throughout the Bay of Fundy; it has been reported that 180 weirs were

operating in the Bay of Fundy in 1990 (Read 1994). 
115

 Data on current incidental takes in U.S. fisheries are available from several sources. In 1986, NMFS

established a mandatory logbook system for large pelagic fisheries. Data files are maintained at the Southeast Fisheries

Science Center (SEFSC). The Northeast Fisheries Science Center (NEFSC) Sea Sampling Observer Program was

initiated in 1989, and since that year several fisheries have been covered by the program. In late 1992 and in 1993, the

SEFSC provided observer coverage of pelagic longline vessels fishing off the Grand Banks (Tail of the Banks) and

provides observer coverage of vessels fishing south of Cape Hatteras. 

There are approximately 349 vessels (full and part time) in the New England multispecies sink gillnet fishery

(Walden, in review). Observer coverage in terms of trips has been 1%, 6%, 7. 5%, and 5% for 1990 to 1993,

respectively. The fishery has been observed in the Gulf of Maine and in Southern New England. There were 71 harbor

seal mortalities, excluding three animals taken in the 1994 pinger experiment (NMFS unpublished data), observed in

the New England multispecies sink gillnet fishery between 1990 and 1993. The estimated annual mortalities (CV in

parentheses) in this fishery were 602 in 1990 (0.68), 231 in 1991 (0.22), 373 in 1992 (0.23), and 698 in 1993 (0.19).

Average annual estimated fishery-related mortality and serious injury to this stock attributable to this fishery during

1990-1993 was 476 harbor seals (CV = 0.46). The stratification design used is the same as that for harbor porpoise

(Bravington and Bisack, in review). The by-catch occurred in Massachusetts Bay, south of Cape Ann and west of

Stellwagen Bank during January-March. By-catch locations became more dispersed during April-June from Casco

Bay to Cape Ann, along the 30 fathom contour out to Jeffreys Ledge, with one take location near Cultivator Shoal and

one off southern New England near Block Island. Incidental takes occurred from Frenchman's Bay to Massachusetts

Bay during July-September. In inshore waters, the takes were aggregated while offshore takes were more dispersed.

Incidental takes were confined from Cape Elizabeth out to Jeffreys Ledge and south to Nantucket Sound during

October-December.

Other Mortality

Small numbers of harbor seals regularly strand during the winter period in southern New England and midAtlantic regions (NMFS unpublished data). Sources of mortality include human interactions (boat strikes and fishing

gear), storms, abandonment by the mother, and disease (Katona et al. 1993; NMFS unpublished data). In 1980, more

than 350 seals were found dead in the Cape Cod area from an influenza outbreak (Geraci et al. 1981).

 Stranding data probably underestimate the extent of fishery-related mortality and serious injury because not

all of the marine mammals which die or are seriously injured may wash ashore, nor will all of those that do wash

ashore necessarily show signs of entanglement or other fishery-interaction. Finally, the level of technical expertise

among stranding network personnel varies widely as does the ability to recognize signs of fishery interaction.

STATUS OF STOCK

The status of harbor seals, relative to OSP, in the U.S. EEZ is unknown, but the population is increasing. The

species is not listed as threatened or endangered under the Endangered Species Act. In Canada seals are protected from

harassment and unauthorized killing under current Marine Mammal Regulations. Kenney and Gilbert (1994)

estimated a 8.7% annual rate of increase of this stock in Maine coastal waters based on 1981, 1982, 1986, and 1993

surveys conducted along the Maine coast. The population is increasing despite the known fishery-related mortality.

This is not a strategic stock because fishery-related mortality and serious injury does not exceed PBR.

REFERENCES

Anon. 1994. Report of the PBR (Potential Biological Removal) workshop. June 27-29, 1994. NOAA, NMFS

Southwest Fisheries Science Center, La Jolla, California, 13 pp. + Appendices. 

Boulva, J. and I. A. McLaren. 1979. Biology of the harbor seal, Phoca vitulina, in eastern Canada. Bull. Fish. Res.

Bd. Can. 200:1-24. 

Bravington, M. V. and K. D. Bisack. In review. Estimates of harbor porpoise by-catch in the Gulf of Maine sink

gillnet fishery, 1990-93. Submitted to Fish. Bull. 

Geraci, R., D. J. St. Aubin and I. K. Barker. 1981. Mass mortality of harbor seals: pneumonia associated with

influenza A virus. Science 215: 1129-1131. 

Gilbert, J. R. and K. M. Wynne. 1985. Harbor seal populations and fisheries interactions with marine mammals in

New England, 1984. Interim Rep., NOAA NA-84-EAC-00070, NMFS, NEFSC., Woods Hole, MA, 15 pp.
116

Gilbert, J. R. and K. M. Wynne. 1987. Marine mammal interactions with New England gillnet fisheries. Final Report

Contract No. NA-84-EAC-00070, NOAA, NMFS, NEFSC, Woods Hole, MA, 12 pp. 

Katona, S. K., V. Rough, and D. T. Richardson. 1993. A field guide to whales, porpoises, and seals from Cape Cod

to Newfoundland. Smithsonian Institution Press: Washington, DC, 316 pp. 

Kenney, M. K. and J. R. Gilbert. 1994. Increase in harbor and gray seal populations in Maine. Dept. of Commerce,

NOAA-NMFS Contract Rep. 50-EANF-2-00064, 19 pp. 

Payne, P. M. and L. A. Selzer. 1989. The distribution, abundance and selected prey of the harbor seal, Phoca vitulina

concolor, in southern New England. Mar. Mamm. Sci. 5(2): 173-192. 

Payne. P. M. and D. C. Schneider. 1984. Yearly changes in abundance of harbor seals, Phoca vitulina, at a winter

haul-out site in Massachusetts. Fish. Bull., U.S. 82: 440-442. 

Read, A. J. 1994. Interactions between cetaceans and gillnet and trap fisheries in the northwest Atlantic. Rep. Int.

Whal. Commn. Special Issue 15: 133-147. 

Rosenfeld, M., M. George, and J. M. Terhune. 1988. Evidence of autumnal harbour seal, Phoca vitulina, movement

from Canada to the United States. Can. Field-Nat. 102(3): 527-529. 

Schneider, D. C. and P. M. Payne. 1983. Factors affecting haul-out of harbor seals at a site in southeastern

Massachusetts. J. Mamm. 64(3): 518-520.

Stobo, W.T. and G.M. Fowler. 1994. Aerial surveys of seals in the Bay of Fundy and off southwest Nova Scotia. Can.

Tech. Rep. Fish. Aquat. Sci. 1943:57pp.

Walden, J. In review. Results of the Gulf of Maine gillnet survey 1989-92. NOAA, NMFS, NEFSC [Northeast

Fisheries Science Center] Ref. Doc., Woods Hole, Massachusetts. 

Whitman, A. A. and P. M. Payne. 1990. Age of harbour seals, Phoca vitulina concolor, wintering in southern New

England. Can. Field-Nat. 104(4): 579-582. 

Wilson, S. C. 1978. Social organization and behavior of harbor seals, Phoca concolor, in Maine. Final Report to

Marine Mammal Commission, Contract MM6ACO13, GPO-PB-280-188. 
117

GRAY SEAL (Halichoerus grypus):

Western North Atlantic Stock

STOCK DEFINITION AND GEOGRAPHIC RANGE

There is one gray seal stock in the western North Atlantic; it ranges from New England to Labrador and is

centered in the Gulf of St. Lawrence (Katona et al. 1993; Davies 1957). This stock is separated by both geography and

differences in the breeding season from the eastern Atlantic stock (Bonner 1981). The western Atlantic stock is

distributed and breeds principally in eastern Canadian waters; however, small numbers of animals and pupping have

been observed on several isolated islands along the Maine coast and in Nantucket-Vineyard Sound, Massachusetts

(Katona et al. 1993; Rough 1995; J. R. Gilbert, personal communication). 

POPULATION SIZE

A winter breeding colony on Muskeget Island, west of Nantucket Island, may provide some measure of gray

seal population trends and expansion in distribution. Sightings in New England increased during the 1980s as the gray

seal population and range expanded in eastern Canada. Five pups were born at Muskeget in 1988. The number of

pups increased to 12 in 1992, 30 in 1993, and 59 in 1994. Maximum counts obtained during the spring molt did not

exceed 13 in any year during the 1970s, but rose to 61 in 1984, 192 in 1988, 503 in 1992, and 1,549 in 1993. Aerial

surveys in April and May of 1994 recorded a peak count of 2,035 gray seals for Muskeget Island (Nantucket) and

Monomoy (Cape Cod) combined (Rough 1995). 

Estimates of the total western Atlantic gray seal population are not available. Pup production on Sable Island,

Nova Scotia, has been about 13 percent per year since 1962 (Mohn and Bowen 1994). The 1986 population estimate

for individuals that are one year old and older was between 100,000 and 130,000 animals (Stobo and Zwanenburg

1990). The 1993 estimate (Sable Island and Gulf of St. Lawrence stocks) is 143,000 animals (Mohn and Bowen 1994).

The population in waters off Maine has increased from about 30 in the early 1980's to between 500-1,000 animals in

1993 (J. R. Gilbert, personal communication, 1994).

Minimum Population Estimate

The minimum population estimate, based on uncorrected total counts (see above), is 2,035 gray seals. 

Current Population Trend

Gray seal abundance is likely increasing in the U.S. Atlantic Exclusive Economic Zone (EEZ), but the actual

trend is unknown. The population has been increasing for several decades in Canadian waters. Approximately 57%

of the western North Atlantic population is from the Sable Island stock. 

CURRENT AND MAXIMUM NET PRODUCTIVITY RATES

Current and maximum net productivity rates are not known for this stock. Pup production on Sable Island

is about 13% annually (Mohn and Bowen 1994), slightly above the theoretical "default" maximum net productivity

rate for pinnipeds (0.12) used in this assessment. 

POTENTIAL BIOLOGICAL REMOVAL

Potential biological removal (PBR) was specified as the product of minimum population size, one-half the

maximum productivity rate, and a "recovery" factor for endangered, depleted, threatened stocks, or stocks of unknown

status relative to optimum sustainable population (OSP) (Anon. 1994). The recovery factor was set at 1.0 for pinniped

stocks that are increasing at about 90% of maximum potential rate. PBR for this stock is 122 gray seals. 

ANNUAL HUMAN-CAUSED MORTALITY AND SERIOUS INJURY

Gray seals, like harbor seals, were hunted for bounty in New England waters until the late 1960's. This hunt

may have severely depleted this stock in U.S. waters (Rough 1995). 

Researchers and fishery observers have documented incidental mortality in several fisheries in recent years,

particularly within the Gulf of Maine. There were three records of incidental catch of gray seals in the 1989-1993
118

Northeast Fisheries Science Center (NEFSC) Sea Sampling database. All occurred in 1993 (February, March, and

May) in the sink gillnet fishery. Two records were from the Gulf of Maine, and the third, in May, was from SE of

Block Island. In addition, V. Rough (personal communication) has documented several animals with netting around

their necks in the Cape Cod/Nantucket area. An unknown level of mortality also occurs in the mariculture industry

(i.e., salmon farming) and by deliberate shooting (NMFS unpublished data). There are 79 records of stranded gray

seals in the Northeast Marine Mammal Stranding Network database for 1989-1993.

 Stranding data probably underestimate the extent of fishery-related mortality and serious injury because not

all of the marine mammals which die or are seriously injured may wash ashore, nor will all of those that do wash

ashore necessarily show signs of entanglement or other fishery-interaction. Finally, the level of technical expertise

among stranding network personnel varies widely as does the ability to recognize signs of fishery interaction.

 An unknown number of gray seals have been taken in Newfoundland and Labrador, Gulf of St. Lawrence,

and Bay of Fundy groundfish gillnets, Atlantic Canada and Greenland salmon gillnets, Atlantic Canada cod traps, and

in Bay of Fundy herring weirs (Read 1994). In addition to incidental catches, some mortalities (e.g., seals trapped in

herring weirs) were the result of direct shooting, and there were culls of about 1,700 animals annually during the 1970's

and early 1980's on Sable Island (Anon. 1986). 

Because of fishermen's concerns regarding gray seal predation on economically important fish stocks and

transmission of the cod worm, Canada now has an open season (March-December) on gray seals (J. Conway, personal

communication). The number of gray seals shot each year is unknown. 

 Estimated average annual fishery-related mortality and serious injury to this stock in the U.S. Atlantic EEZ

during 1990-1993 was 4.5 gray seals (CV = 2.00). The total fishery-related mortality and serious injury for this stock

is less than 10% of the calculated PBR and, therefore, can be considered to be insignificant and approaching zero

mortality and serious injury rate. This determination cannot be made for specific fisheries until the implementing

regulations for Section 118 of the MMPA have been reviewed by the public and finalized. 

Fishery Information

The Atlantic Canadian and Greenland salmon gillnet fishery is seasonal, with the peak from June to

September, depending on location. In southern and eastern Newfoundland, and Labrador during 1989, 2,196 nets 91

m long were used. There is no effort data available for the Greenland fishery. However, the fishery was terminated

in 1993 under an agreement between Canada and North Atlantic Salmon Fund (Read 1994). 

The Canadian Atlantic groundfish gillnet fishery is important and widespread. Many fisherman hold

groundfish gillnet licenses but the number of active fishermen is unknown. In 1989, approximately 6,800 licenses were

issued to fishermen along the southern coast of Labrador, and northeast and southern coasts of Newfoundland. There

were about 3,900 licenses issued in the Gulf of St. Lawrence in 1989, while 659 licenses were issued in the Bay of

Fundy and southwestern Nova Scotia. 

There were 3,121 cod traps operating in Newfoundland and Labrador during 1979, and about 7,500 in 1980

(Read 1994). This fishery was closed at the end of 1993 due to collapse of Canadian groundfish resources. 

Herring weirs are also distributed throughout the Bay of Fundy; it has been reported that 180 weirs were

operating in the Bay of Fundy in 1990 (Read 1994). 

Data on current incidental takes in U.S. fisheries are available from several sources. In 1986, NMFS

established a mandatory logbook system for large pelagic fisheries. Data files are maintained at the Southeast Fisheries

Science Center (SEFSC). The NEFSC Sea Sampling Observer Program was initiated in 1989, and since that year

several fisheries have been covered by the program. In late 1992 and in 1993, the SEFSC provided observer coverage

of pelagic longline vessels fishing off the Grand Banks (Tail of the Banks) and provides observer coverage of vessels

fishing south of Cape Hatteras. 

There are approximately 349 vessels (full and part time) in the New England multispecies sink gillnet fishery

(Walden, in review). Observer coverage in trips has been 1%, 6%, 7. 5%, and 5% for years 1990 to 1993. The fishery

has been observed in the Gulf of Maine and in Southern New England. Three mortalities were observed in this fishery

in 1993, in winter off the Massachusetts coast. The estimated mortality in 1993 was 18 gray seals (CV = 1.00).

Estimated average annual fishery-related mortality and serious injury to this stock during 1990-1993 attributable to

this fishery was 4.5 gray seals (CV = 2.00).
119

STATUS OF STOCK

The status of the gray seal population, relative to OSP, in U.S. and Canadian Atlantic coast waters is

unknown. The species is not listed as threatened or endangered under the Endangered Species Act. Recent data

indicate that this population is increasing. In New England waters, both the number of pupping sites and pup

production is increasing. In Canada they are protected from harassment and intentional killing under the Marine

Mammal Regulations, although some aquaculture operators have been authorized to shoot nuisance animals. The

estimated annual level of human-caused mortality and serious injury in the U.S. Atlantic EEZ does not exceed PBR

and this is not a strategic stock. 

REFERENCES

Anon. 1994. Report of the PBR (Potential Biological Removal) workshop. June 27-29, 1994. NOAA, NMFS

Southwest Fisheries Science Center, La Jolla, California, 13 pp. + Appendices. 

Anon. 1986. Seals and sealing in Canada. Rep. of the Royal Commission on Seals and Sealing, Vol. 1, 65 pp.

Available from Canadian Government Publishing Centre, Ottawa, Canada.

Bonner, W. N. 1981. Grey seal Halichoerus grypus Fabricus, 1791. Pages 111-144 in S. H. Ridgeway and R. J.

Harrison (editors), Handbook of Marine Mammals, Vol. 2: Seals. Academic Press, London, 359 pp. 

Davies, J. L. 1957. The geography of the gray seal. J. Mamm. 38: 297-310.

Katona, S. K., V. Rough, and D. T. Richardson. 1993. A field guide to whales, porpoises, and seals from Cape Cod

to Newfoundland. Smithsonian Institution Press, Washington, DC. 316 pp. 

Mohn, R. and W. D. Bowen. 1994. A model of grey seal predation on 4VsW cod and its effects on the dynamics and

potential yield of cod. DFO Atlantic Fisheries Res. Doc. 94/64. 

Read, A. J. 1994. Interactions between cetaceans and gillnet and trap fisheries in the northwest Atlantic. Rep. Int.

Whal. Commn. Special Issue 15: 133-147. 

Rough, V. 1995. Gray seals in Nantucket Sound, Massachusetts, winter and spring, 1994. Final report to Marine

Mammal Commission, Contract T10155615, 28 pp. NTIS Pub. PB95-191391.

Stobo, W. T. and K. C. T. Zwanenburg. 1990. Grey seal (Halichoerus grypus) pup production on Sable Island and

estimates of recent production in the northwest Atlantic. Pages 171-184 in W. D. Bowen (editor), Population

biology of sealworm (Pseudoterranova decipiens) in relation to its intermediate and seal hosts. Can. Bull.

Fish. and Aq. Sci. 222. 

Walden, J. (In review). Results of the Gulf of Maine gillnet survey 1989-92. NOAA, NMFS, NEFSC, Woods Hole,

Massachusetts. NEFSC [Northeast Fisheries Science Center] Ref. Doc. 95. 
120

HARP SEAL (Phoca groenlandica):

Western North Atlantic Stock

STOCK DEFINITION AND GEOGRAPHIC RANGE

The harp seal occurs throughout much of the North Atlantic and Arctic Oceans (Ronald and Healey 1981;

Lavigne and Kovacs 1988); however, in recent years numbers of sightings and strandings have been increasing off the

east coast of the United States from Maine to New Jersey (Katona et al. 1993). These appearances usually occur in

January-May, when the western North Atlantic stock of harp seals is at its most southern point of migration. The

worlds' harp seal population is divided into three separate stocks, each identified with a specific breeding site (Bonner

1990; Lavigne and Kovacs 1988). The largest stock is located in the western North Atlantic off eastern Canada and

is divided into two breeding herds which breed on the pack ice. The Front herd breeds off the coast of Newfoundland

and Labrador and the Gulf herd breeds near the Magdalen Islands in the middle of the Gulf of St. Lawrence (Lavigne

and Kovacs 1988). The second stock breeds in the White Sea off the coast of the Soviet Union and the third stock

breeds on the West Ice off of eastern Greenland (Lavigne and Kovacs 1988). 

Harp seals are highly migratory. Breeding occurs at different times between mid-February and April for each

stock. Adults then assemble north of their whelping patches to undergo the annual moult. The migration then

continues north to summer feeding grounds. In late September, after a summer of feeding, nearly all adults and some

of the immature animals swim southward ahead of the advancing ice enroute to winter breeding and pupping grounds.

The extreme southern limit of the harp seal's habitat extends into the U.S. Atlantic Exclusive Economic Zone

(EEZ) during winter and spring. The Northeast Marine Mammal Stranding Network reported an annual average of

eight harp seals stranded during 1989-92. Strandings increased to between 45-50 per year in 1993-94 and, in addition

to Massachusetts, carcasses were recovered in Connecticut, New York, and New Jersey (Rubinstein 1994). The

increased number of strandings may indicate a possible shift in distribution or expansion southward into U.S. waters;

if so, fishery interactions may increase. 

POPULATION SIZE

The total population size of harp seals is unknown; however, seasonal abundance estimates are available which

used a variety of methods including aerial surveys, and mark-recapture. Generally, these methods include surveying

the whelping concentrations and mathematically modeling pup production. Harp seal pup production in the 1950s was

estimated at 645,000 (Sergeant 1975), decreasing to 225,000 by 1970 (Sergeant 1975). Estimates began to increase

at this time and have continued to rise, reaching 478,000 in 1979 (Bowen and Sergeant 1985) and 577,900 in 1990

(Stenson et al. 1993). Roff and Bowen (1983) developed an estimation model to provide a more precise estimate of

total population. This technique incorporates recent pregnancy rates and estimates of age-specific hunting mortality

(CAFSAC 1992). Total population can be determined by multiplying pup production by a factor between 5.35 and

5.38, giving a total of approximately three million harp seals in 1990. Shelton et al. (1992) applied a harp seal

estimation model to the 1990 pup production and obtained an estimate of 3.1 million (range 2.7-3.5 million; Stenson

1993). 

Minimum population estimate

Present data are insufficient to calculate this value for U.S. waters. It is estimated there are at least 2.7 million

harp seals in Canada. 

Current population trend

The population appears to be increasing in U.S. waters, judging from the increased number of stranded harp

seals, but the magnitude of the suspected increase is unknown. In Canada, the average annual growth rate has been

estimated to be about 7% (Stenson 1993). 

CURRENT AND MAXIMUM NET PRODUCTIVITY RATES

The most appropriate data are based on Canadian studies. Recent studies indicate that pup production has

increased but the rate of population increase cannot be quantified at this time (Stenson 1993). 
121

POTENTIAL BIOLOGICAL REMOVAL

No PBR can be estimated for this species at this time, because the minimum population size in U.S. waters

cannot be determined. 

ANNUAL HUMAN-CAUSED MORTALITY AND SERIOUS INJURY

There are no records of harp seals in the NEFSC 1989-1993 Sea Sampling by-catch database; however, 40-50

seals which identified by observers as harbor seals in spring 1994 may have, in fact, been harp seals. Biological and

photographic data from takes are under review. 

An unknown number of harp seals have been taken in Newfoundland and Labrador groundfish gillnets (Read

1994). Harp seals are being taken in Canadian lumpfish and groundfish gillnets, and trawls, but estimates of total

removals have not been calculated to date (Anon. 1994). Harp seals have been commercially hunted since the mid1800's in the Canadian Atlantic (Stenson 1993). A total allowable catch (TAC) of 200,000 harp seals was set for the

large vessel hunt in 1971. The TAC varied until 1982 when it was set at the current level of 186,000 seals (Stenson

1993). Catches ranged from 53,000 to 95,000 between 1988-1992 (Stenson 1993). 

The total fishery-related mortality and serious injury for this stock is believed to be very low relative to the

population size in Canadian waters and can be considered insignificant and approaching zero mortality and serious

injury rate. This determination cannot be made for specific fisheries until the implementing regulations for Section

118 of the MMPA have been reviewed by the public and finalized. 

Fishery Information

The Atlantic Canadian and Greenland salmon gillnet fishery is seasonal, with the peak from June to

September, depending on location. During 1989, 2,196 nets 91 m in length were used in southern and eastern

Newfoundland, and Labrador. There are no effort data available for the Greenland fishery and the fishery was

terminated in 1993 under an agreement between Canada and North Atlantic Salmon Fund (Read 1994). 

The Canadian Atlantic groundfish gillnet fishery is important and widespread. Many fisherman hold

groundfish gillnet licenses but the number of active fishermen is unknown. In 1989, approximately 6,800 licenses were

issued to fishermen along the southern coast of Labrador and the northeast and southern coasts of Newfoundland. In

the Gulf of St. Lawrence, there were about 3,900 licenses issued in 1989, while in the Bay of Fundy and southwestern

Nova Scotia 659 licenses were issued. 

There were 3,121 cod traps operating in Newfoundland and Labrador during 1979, and about 7,500 in 1980

(Read 1994). This fishery was closed at the end of 1993 due to collapse of Canadian groundfish resources. 

STATUS OF STOCK

The status of the harp seal stock, relative to OSP, in the U.S. EEZ is unknown, but the population appears to

be increasing in Canadian waters. The species is not listed as threatened or endangered under the Endangered Species

Act. In Canada they are protected from harassment and intentional killing is controlled under the Marine Mammal

Regulations. The level of human-caused mortality and serious injury in the U.S. Atlantic EEZ is unknown, but

believed to be very low relative to the total stock size; therefore, this is not a strategic stock. 

REFERENCES

Anon. 1994. Report of the Joint ICES/NAFO Working Group on Harp and Hooded Seals, Copenhagen, 15-21

September 1993. ICES C. M. 1994/Assess, 45 pp. 

Bonner, W. N. 1990. The natural history of seals. Fact on File, New York, 196 pp. 

Bowen, W. D. and D. E. Sergeant. 1985. A Mark-recapture estimate of 1983 Harp seal Pup Production in the

Northwest Atlantic. NAFO SCR. Doc. 85/I/1. 

CAFSAC. 1992. Update on population estimates of Harp seal in the Northwest Atlantic. Canadian Atlantic Fisheries

Scientific Advisory Committee, CAFSAC Adv. Doc. 92/8

Lavigne, D. M. and K. M. Kovacs. 1988. Harps and Hoods Ice Breeding Seals of the Northwest Atlantic. University

of Waterloo Press, Waterloo, Ontario, Canada, 174 pp. 

Read, A. J. 1994. Interactions between cetaceans and gillnet and trap fisheries in the northwest Atlantic. Rep. Int.

Whal. Commn. Special Issue 15: 133-147. 
122
123

Roff, D. A. and W. D. Bowen. 1983. Population dynamics and management of the Northwest Atlantic harp seal.

Can. J. Fish. Aquat. Sci. 40: 919-932. 

Ronald, K. and P. J. Healey. 1981. Harp Seal. Pages 55-87 in S. H. Ridgway and R. J. Harrison (editors), Handbook

of marine mammals, Vol. 2: Seals. Academic Press, New York, 359 pp. 

Rubinstein, B. 1994. An apparent shift in distribution of ice seals, Phoca groenlandica, Cystophora cristata, and

Phoca hispida, toward the east coast of the United States. M.A. Thesis, Boston University, Boston, MA, 45

pp. 

Sergeant, D. E. 1975. Estimating numbers of Harp seals. Rapp. P. -v. Reun. Cons. Int. Explor. Mer. 169: 274-280.

Shelton, P. A., N. G. Caddigan and G. B. Stenson. 1992. Model estimates of harp seal population trajectories in the

Northwest Atlantic. CAFSAC Res. Doc. 92/89, 23 pp. 

Stenson, G. B. 1993. The status of pinnipeds in the Newfoundland region. NAFO SCR Doc. 93/34. 

Stenson, G. B., R. A. Myers, M. O. Hammill, I-H Ni, W. G. Warren, and M. S. Kingsley. 1993. Pup Production of

Harp Seals, Phoca groenlandica, in the Northwest Atlantic. Can. J. Fish. Aquat. Sci. 50: 2429-2439.
124

HOODED SEAL (Cystophora cristata):

Western North Atlantic Stock

STOCK DEFINITION AND GEOGRAPHIC RANGE

The hooded seal occurs throughout much of the North Atlantic and Arctic Oceans (King 1983) preferring

deeper water and occurring farther offshore than harp seals (Lavigne and Kovacs 1988). Hooded seals tend to wander

far out of their range and have been seen as far south as Puerto Rico, with increased occurrences from Maine to Florida.

These appearances usually occur between January and May. Although it is not known which stock these seals come

from, it is known that during this time frame, the Northwest Atlantic stock of hooded seals are at their most southern

point of migration in the Gulf of St. Lawrence. The worlds' hooded seal population is divided into three separate

stocks, each identified with a specific breeding site (Lavigne and Kovacs 1988). One stock, which whelps off the coast

of eastern Canada, is divided into two breeding herds which breed on the pack ice. The Front herd breeds off the coast

of Newfoundland and Labrador and the Gulf herd breeds in the Gulf of St. Lawrence. The second stock breeds on the

White Ice off eastern Greenland and the third stock occurs in the Davis Strait.

Hooded seals are a highly migratory species. Breeding occurs at the same time for each stock in February.

Adults from all stocks then assemble in the Denmark Strait to moult between June and August (King 1983), and

following this, the seals disperse widely. Some move south and west around the southern tip of Greenland, and then

north along the west coast of Greenland. Others move to the east and north between Greenland and Svalbard during

late summer and early fall (Lavigne and Kovacs 1988). Little else is known about the activities of hooded seals during

the rest of the year until they assemble again in February for breeding. 

Hooded seals are rarely found in the U.S. Atlantic Exclusive Economic Zone. Small numbers of hooded seals

at the extreme southern limit of their range occur in the winter and spring seasons. The Northeast Marine Mammal

Stranding Network reports an average of seven hooded seals stranded annually from 1989-92. In 1993-94, strandings

increased to between 19-24 a year and carcasses were recovered from Massachusetts, Connecticut, and New York

(Rubinstein 1994). The increased number of strandings may indicate a possible shift in distribution or range expansion

southward into U.S. waters; if so, fishery interactions may increase. 

POPULATION SIZE

The number of hooded seals in the western North Atlantic is unknown. Seasonal abundance estimates are

available based on a variety of methods including aerial surveys. These methods often include surveying the whelping

concentrations and mathematically modeling the pup production. Hooded seal pup production between 1966 and 1971

was estimated between 27,000 and 41,000 annually (Benjaminsen and Oritsland 1975). Estimated pup production

dropped to 26,000 hooded seal pups in 1978 (Winters 1978). Pup production estimates began to increase after 1978,

reaching 62,000 by 1984 (Hay et al. 1985), and rose to 82,000 in 1990 (Hammill et al. 1992). No recent population

estimate is available, but assuming a ratio of pups to total population of 1:5, pup production in the Gulf and Front herds

would represent a total population of approximately 400,000-450,000 hooded seals (Stenson 1993). It appears that the

number of hooded seals is increasing.

 

Minimum population estimate

Present data are insufficient to calculate this value for U.S. waters. It is estimated that there are approximately

400,000 hooded seals in Canadian waters. 

Current population trend

The population appears to be increasing in U.S. Atlantic EEZ, judging from stranding records, although the

actual magnitude of this increase is unknown. The Canadian population appears to be increasing but, because different

methods have been used over time to estimate population size, the magnitude of this increase has not been quantified.
125

CURRENT AND MAXIMUM NET PRODUCTIVITY RATES

The most appropriate data are based on Canadian studies. Pup production in Canada may be increasing slowly

(5% per annum), but due to the wide confidence intervals and lack of understanding regarding stock dynamics, it is

possible that pup production is stable or declining (Stenson 1993). 

POTENTIAL BIOLOGICAL REMOVAL

No PBR can be estimated for this species at this time, because the minimum population size in U.S. waters

cannot be determined. 

ANNUAL HUMAN-CAUSED MORTALITY AND SERIOUS INJURY

There are no records of fishery-related mortality to hooded seals in the NEFSC 1989-1993 Sea Sampling

database. 

An unknown number of hooded seals have been taken in Newfoundland and Labrador groundfish gillnets

(Read 1994). The following summary on the hooded seal fishery is taken from (Stenson 1993). In Atlantic Canada,

hooded seals have been commercially hunted at the Front since the late 1800's. In 1974 total allowable catch (TAC)

was set at 15,000, and reduced to 12,000 in 1983 and to 2,340 in 1984. In 1991 the TAC was increased to 15,000.

A TAC of 8,000 was set for 1992 and 1993. From 1974 through 1982, the average catch was 12,800 animals, mainly

pups. Since 1983 catches ranged from 33 in 1986 to 6,321 in 1991, with a mean catch of 1,116 between 1983 and

1992. 

Hunting in the Gulf of St. Lawrence has been prohibited since 1964. No commercial hunting of hooded seals

is permitted in the Davis Strait. 

The total fishery-related mortality and serious injury for this stock is very low relative to the population size,

especially in Canadian waters. This mortality can be considered insignificant and approaching zero mortality and

serious injury rate. This determination cannot be made for specific fisheries until the implementing regulations for

Section 118 of the MMPA have been reviewed by the public and finalized. 

Fishery Information

No hooded seals have been taken incidentally in U.S. waters. 

The Canadian Atlantic groundfish gillnet fishery is important and widespread. Many fisherman hold

groundfish gillnet licenses but the number of active fishermen is unknown. In 1989, approximately 6,800 licenses were

issued to fishermen along the southern coast of Labrador and the northeast and southern coasts of Newfoundland.

There were about 3,900 licenses issued in 1989 in the Gulf of St. Lawrence, while in the Bay of Fundy and

southwestern Nova Scotia 659 licenses were issued. 

There were 3,121 cod traps operating in Newfoundland and Labrador during 1979, and about 7,500 in 1980

(Read 1994). This fishery was closed at the end of 1993 due to collapse of Canadian groundfish resources. 

Hooded seals are being taken in Canadian lumpfish and groundfish gillnets and trawls; however, estimates

of total removals have not been calculated to date (Anon. 1994). 

STATUS OF STOCK

The status of hooded seals relative to OSP is unknown. They are not listed as threatened or endangered under

the Endangered Species Act. In Canada they are protected from harassment and intentional killing is controlled under

the Marine Mammal Regulations. This is not a strategic stock because the level of human-caused mortality and serious

injury is believed to be very low relative to overall stock size.

REFERENCES

Anon. 1994. Report of the Joint ICES/NAFO Working Group on Harp and Hooded Seals, Copenhagen, 15-21

September 1993. ICES C. M. 1994/Assess, 45 pp. 

Benjaminsen, T., and T. Oritsland. 1975. The survival of year-classes and estimates of production and sustainable

yield of northwest Atlantic harp seals. Int. Comm. Northwest Atl. Fish. Res. Doc. 75/121. 

Hammill, M. O., G. B. Stenson, and R. A. Myers. 1992. Hooded seal (Cystophora cristata) pup production in the

Gulf of St. Lawrence. Can. J. Fish. Aquat. Sci. 49: 2546-2550.
126

Hay, K., G. B. Stenson, D. Wakeham, and R. A. Myers. 1985. Estimation of pup production of hooded seals

(Cystophora cristata) at Newfoundland during March 1985. Con. Atl. Fish. Sci. Adv. Comm. 85/96. 

King, J. E. 1983. Seals of the World. Cornell University Press, Ithaca, NY, 240 pp. 

Lavigne, D. M. and K. M. Kovacs. 1988. Harps and Hoods Ice Breeding Seals of the Northwest Atlantic. University

of Waterloo Press, Waterloo, Ontario, Canada, 174 pp. 

Read, A. J. 1994. Interactions between cetaceans and gillnet and trap fisheries in the northwest Atlantic. Rep. Int.

Whal. Commn. Special Issue 15: 133-147. 

Rubinstein, B. 1994. An apparent shift in distribution of ice seals, Phoca groenlandica, Cystophora cristata, and

Phoca hispida, toward the east coast of the United States. M.A. Thesis, Boston University, Boston, MA, 45

pp. 

Stenson, G. B. 1993. The status of pinnipeds in the Newfoundland region. NAFO SCR Doc. 93/34. 

Winters, G. H. 1978. Production, mortality, and sustainable yield of northwest Atlantic harp seals (Pagophilus

groenlandicus). J. Fish. Res. Bd. Can. 35: 1249-1261. 
127

Figure 1. Distribution of sperm whale sightings during NOAA Ship Oregon II marine

mammal surveys during 1991-1994. The straight lines show transects during two ship

surveys and are examples of typical ship survey transects. Isobaths are in 183 m (100

fm) intervals. 

SPERM WHALE (Physeter macrocephalus):

Northern Gulf of Mexico Stock

STOCK DEFINITION AND GEOGRAPHIC RANGE

Sperm whales are found throughout the world's oceans in deep waters from between about 60E N and 60E S

latitudes (Leatherwood and Reeves 1983; Rice 1989). There has been speculation, based on year round occurrence of

strandings, opportunistic sightings, and whaling catches, that sperm whales in the Gulf of Mexico may constitute a

distinct stock (Schmidly 1981), but there is no information on stock differentiation. Seasonal aerial surveys confirm

that sperm whales are present in the northern Gulf of Mexico in all seasons, but sightings are more common during

the summer months (Mullin et al. 1991; Davis et al., in preparation).

POPULATION SIZE

Estimates of abundance were derived through the application of distance sampling analysis (Buckland et al.

1993) and the computer program DISTANCE (Laake et al. 1993) to sighting data collected during 1991-1994 springsummer, visual sampling, line-transect vessel surveys of the northern Gulf of Mexico (Hansen et al. 1995) (Fig. 1),

which includes data collected as part of the GulfCet program (Davis et al., in preparation). These surveys were

conducted throughout the area from approximately the 200 m isobath along the U.S. coast to the seaward extent of the

U.S. Exclusive Economic Zone.

The seasonal GulfCet aerial

surveys included only a small

portion of the stock range and

these data were not used for

abundance estimation .

Estimated abundance of sperm

whales by survey year

[coefficient of variation (CV) in

parentheses] was 143 in 1991

(0.58), 931 in 1992 (0.48), 229

in 1993 (0.52), and 771 in 1994

(0.42) (Hansen et al. 1995).

Survey effort-weighted estimated

average abundance of sperm

whales for all surveys combined

was 530 (CV = 0.31) (Hansen et

al. 1995).

Minimum Population Estimate

The minimum population estimate is the lower limit of the two-tailed 60% confidence interval of the lognormal distributed abundance estimate, which is equivalent to the 20th percentile of the log-normal distributed

abundance estimate as specified by NMFS (Anon. 1994). The minimum population estimate was calculated from the

1991-1994 average abundance estimate of 530 sperm whales (CV = 0.31) (Hansen et al. 1995) and is 411 sperm

whales. 

Current Population Trend

No trend was discernable in the average annual abundance estimates. All of the log-normal 95% confidence

intervals of the annual estimates overlap, indicating that the estimates were not significantly different at that level. The

variation in abundance estimates may represent inter-annual variation in distribution, rather than a change in

abundance. 

CURRENT AND MAXIMUM NET PRODUCTIVITY RATES
128

Current and maximum net productivity rates are not known for this stock; therefore, the default maximum

net productivity rate of 0.04 (Anon. 1994) was used for purposes of this assessment. 

POTENTIAL BIOLOGICAL REMOVAL

Potential biological removal level (PBR) was specified as the product of the minimum population size, one

half the maximum net productivity rate, and a recovery factor for endangered, threatened, or depleted stocks, or stocks

of unknown status relative to optimum sustainable population (OSP) (Anon. 1994). The recovery factor was 0.10

because sperm whales are an endangered species. The resulting PBR for this stock is 0.8 sperm whales. 

ANNUAL HUMAN-CAUSED MORTALITY AND SERIOUS INJURY

A commercial fishery for sperm whales operated in the Gulf of Mexico during the late 1700's to the early

1900's, but the exact number of whales taken is not known (Townsend 1935). 

The level of current, direct, human-caused mortality and serious injury of sperm whales in the northern Gulf

of Mexico is unknown, but available information indicates there likely is little, if any, fisheries interaction with sperm

whales in the northern Gulf of Mexico. 

There were no documented strandings of sperm whales in the northern Gulf of Mexico during 1987-1994

which were classified as likely caused by fishery interactions or other human-related causes. Stranding data probably

underestimate the extent of fishery-related mortality and serious injury because not all of the marine mammals which

die or are seriously injured may wash ashore, nor will all of those that do wash ashore necessarily show signs of

entanglement or other fishery-interaction. Finally, the level of technical expertise among stranding network personnel

varies widely as does the ability to recognize signs of fishery interaction. 

The total known fishery-related mortality and serious injury for this stock is less than 10% of the calculated

PBR and, therefore, can be considered insignificant and approaching zero mortality and serious injury rate. This

determination cannot be made for specific fisheries until the implementing regulations for Section 118 of the MMPA

have been reviewed by the public and finalized. 

Fisheries Information

Pelagic swordfish, tunas, and billfish are the targets of the longline fishery operating in the U.S. Gulf of

Mexico. Total longline effort for the Gulf of Mexico pelagic fishery, including OCS edge, continental slope, and

Mexican territorial waters, based on mandatory logbook reporting, was 4,400 sets in 1991, 4,850 sets in 1992, and

3,260 sets in 1993 (Cramer 1994). This fishery has been monitored with about 5% observer coverage, in terms of trips

observed, since 1992. There were no reports of mortality or serious injury to sperm whales by this fishery. 

Pair trawl fishing gear has the potential to capture marine mammals, but there have been no reports of

mortality or serious injury to marine mammals in the Gulf of Mexico. This fishery has not been observed by NMFS

observers, and there are no other data available as to the extent of this fishery in the Gulf of Mexico. It is assumed that

it is very limited in scope and duration. 

Other Mortality

A total of nine sperm whale strandings were documented in the northern Gulf of Mexico during 1987-1994.

One of the whales had deep, parallel cuts posterior to the dorsal ridge that were believed to be caused by the propeller

of a large vessel. This trauma was assumed to be the proximate cause of this stranding. 

 Stranding data probably underestimate the extent of fishery-related mortality and serious injury because not

all of the marine mammals which die or are seriously injured may wash ashore, nor will all of those that do wash

ashore necessarily show signs of entanglement or other fishery-interaction. Finally, the level of technical expertise

among stranding network personnel varies widely as does the ability to recognize signs of fishery interaction.

 

STATUS OF STOCK

Stock size is considered to be low relative to OSP and the species is therefore listed as endangered under the

Endangered Species Act (ESA). There are insufficient data to determine population trends. The total level of humancaused mortality and serious injury is unknown, but it is believed to be insignificant; however, because this species is
129

listed as endangered and there is presently no recovery plan in place, any fishery-related mortality would be unlawful.

This is a strategic stock because the sperm whale is listed as an endangered species under the ESA.

REFERENCES

Anon. 1994. Report of the PBR (Potential Biological Removal) workshop. June 27-29, 1994. NOAA, NMFS

Southwest Fisheries Science Center, La Jolla, California, 13 pp. + Appendices. 

Buckland, S. T., D. R. Anderson, K. P. Burnham and J. L. Laake. 1993. Distance Sampling: estimating abundance

of biological populations. Chapman & Hall, London, 446 pp. 

Cramer, J. 1994. Large pelagic logbook newsletter - 1993. NOAA Tech. Mem. NMFS-SEFSC-352, 19 pp. 

Davis, R., G. Scott, B. Würsig, W. Evans, G. Fargion, L. Hansen, K. Mullin, N. May, T. Leming, B. Mate, J. Norris,

and T. Jefferson. In preparation. Distribution and abundance of marine mammals in the north-central and

western Gulf of Mexico: Final Report. OCS Study #MMS 94-0003. Texas Institute of Oceanography and the

National Marine Fisheries Service. U.S. Dept. of the Interior, Minerals Mgmt. Service, Gulf of Mexico OCS

Region, New Orleans, Louisiana. 

Hansen, L. J., K. D. Mullin and C. L. Roden. 1995. Estimates of cetacean abundance in the northern Gulf of Mexico

from vessel surveys. Southeast Fisheries Science Center, Miami Laboratory, Contribution No. MIA-94/95-25,

9 pp. + tables and figures.

Laake, J. L., S. T. Buckland, D. R. Anderson, and K. P. Burnham. DISTANCE user’s guide, V2.0. Colorado

Cooperative Fish & Wildlife Research Unit, Colorado State University, Ft. Collins, Colorado, 72 pp. 

Leatherwood, S. and R. R. Reeves. 1983. The Sierra Club handbook of whales and dolphins. Sierra Club Books, San

Francisco, 302 pp. 

Mullin, K., W. Hoggard, C. Roden, R. Lohoefener, C. Rogers and B. Taggart. 1991. Cetaceans on the upper

continental slope in the north-central Gulf of Mexico. OCS Study/MMS 91-0027. U.S. Dept. of the Interior,

Minerals Management Service, Gulf of Mexico OCS Regional Office, New Orleans, Louisiana, 108 pp. 

Rice, D. W. 1989. Sperm whale, Physeter macrocephalus Linnaeus, 1758. Pages 177-233 in S. H. Ridgway and R.

Harrison (editors), Handbook of marine mammals, Vol. 4: river dolphins and the larger toothed whales.

Academic Press, London, 442 pp. 

Schmidly, D. J. 1981. Marine mammals of the southeastern United States and the Gulf of Mexico. U.S. Fish and

Wildlife Service, Office of Biological Services, Washington, DC, FWS/OBS-80/41, 165 pp. 

Townsend, C. H. 1935. The distribution of certain whales as shown by logbook records of American whale ships.

Zoologica 19: 1-50.
130

Figure 1. Distribution of Bryde’s whale sightings (filled circles) and unidentified

balaenopterid whales (unfilled circles) during NOAA Ship Oregon II marine mammal

surveys during 1991-1994. The straight lines show transects during two ship surveys

and are examples of typical ship survey transects. Isobaths are in 183 m (100 fm)

intervals. 

BRYDE'S WHALE (Balaenoptera edeni):

Northern Gulf of Mexico Stock

STOCK DEFINITION AND GEOGRAPHIC RANGE

Bryde's whales are considered the tropical and sub-tropical baleen whale of the world's oceans. In the western

Atlantic, Bryde's whales are reported from off the southeastern United States and the southern West Indies to Cabo

Frio, Brazil (Leatherwood and Reeves 1983). It is postulated that the Bryde's whales found in the Gulf of Mexico may

represent a resident stock (Schmidly 1981; Leatherwood and Reeves 1983), but there is no information on stock

differentiation. Most sightings of Bryde's whales have occurred during the spring-summer months (Hansen et al. 1995;

Davis et al., in preparation), but strandings have occurred throughout the year (Jefferson et al. 1992). 

POPULATION SIZE

Estimates of abundance were derived through the application of distance sampling analysis (Buckland et al.

1993) and the computer program DISTANCE (Laake et al. 1993) to sighting data collected during 1991-1994 springsummer, visual sampling, line-transect vessel surveys of the northern Gulf of Mexico (Hansen et al. 1995) (Fig. 1),

which includes data collected as part of the GulfCet program (Davis et al., in preparation). These surveys were

conducted throughout the area from approximately the 200 m isobath along the U.S. coast to the seaward extent of the

U.S. Exclusive Economic Zone.

The seasonal GulfCet aerial

surveys included only a small

portion of the stock range and

these data were not used for

abundance estimation. The

estimated abundance of Bryde’s

whales by survey year was 218 in

1991 (coefficient of variation,

CV = 1.01) and zero in 1992,

1993, and 1994 (Hansen et al.

1995). Survey effort-weighted

estimated average abundance of

Bryde's whales for all surveys

combined was 35 (CV = 1.10)

(Hansen et al. 1995) and was

based on only three sightings, all

of which occurred in 1991. 

Minimum Population Estimate

 The minimum population estimate is the lower limit of the two-tailed 60% confidence interval of the lognormal distributed abundance estimate, which is equivalent to the 20th percentile of the log-normal distributed

abundance estimate as specified by NMFS (Anon. 1994). The minimum population estimate was based on the 1991-

1994 average estimated abundance of Bryde's whales which was 35 (CV = 1.10) (Hansen et al. 1995) and is 17 Bryde’s

whales. 

Current Population Trend

The abundance estimates decreased to zero for survey years 1992-1994 because Bryde's whales were not

sighted during vessel surveys those years. This could be due to chance rather than to a decrease in population size and

the result of a relatively small population size and low sampling intensity or it could be due to inter-annual variation

in distribution. 
131

CURRENT AND MAXIMUM NET PRODUCTIVITY RATES

Current and maximum net productivity rates are not known for this stock; therefore, the default maximum

net productivity rate of 0.04 (Anon. 1994) was used for purposes of this assessment. 

POTENTIAL BIOLOGICAL REMOVAL

Potential biological removal level (PBR) was specified as the product of the minimum population size, one

half the maximum net productivity rate, and a recovery factor for endangered, threatened, or depleted stocks, or stocks

of unknown status relative to optimum sustainable population (OSP) (Anon. 1994). The recovery factor was set at 0.50

because the status of the stock relative to OSP is unknown. The resulting PBR for this stock is 0.2 Bryde’s whales. 

ANNUAL HUMAN-CAUSED MORTALITY AND SERIOUS INJURY

The level of past or current, direct, human-caused mortality of Bryde's whales in the northern Gulf of Mexico

is unknown, but available information indicates there is little fisheries interaction with Bryde's whales in the northern

Gulf of Mexico. There was one report of a Bryde’s whale entangled in line, but the line was removed and the animal

released alive. 

There were no documented strandings of Bryde’s whales in the northern Gulf of Mexico during 1987-1994

which were classified as likely caused by fishery interactions or other human-related causes. Stranding data probably

underestimate the extent of fishery-related mortality and serious injury because not all of the marine mammals which

die or are seriously injured may wash ashore, nor will all of those that do wash ashore necessarily show signs of

entanglement or other fishery-interaction. Finally, the level of technical expertise among stranding network personnel

varies widely as does the ability to recognize signs of fishery interaction. 

The total known fishery-related mortality and serious injury for this stock is less than 10% of the calculated

PBR and, therefore, can be considered insignificant and approaching zero mortality and serious injury rate. This

determination cannot be made for specific fisheries until the implementing regulations for Section 118 of the MMPA

have been reviewed by the public and finalized. 

Fisheries Information

Pelagic swordfish, tunas, and billfish are the targets of the longline fishery operating in the U.S. Gulf of

Mexico. Total longline effort for the Gulf of Mexico pelagic fishery, including OCS edge, continental slope, and

Mexican territorial waters, based on mandatory logbook reporting, was 4,400 sets in 1991, 4,850 sets in 1992, and

3,260 sets in 1993 (Cramer 1994). This fishery has been monitored with about 5% observer coverage, in terms of trips

observed, since 1992. There were no reports of mortality or serious injury to Bryde’s whales by this fishery. 

Pair trawl fishing gear has the potential to capture marine mammals, but there have been no reports of

mortality or serious injury to marine mammals in the Gulf of Mexico. This fishery has not been observed by NMFS

observers, and there are no other data available as to the extent of this fishery in the Gulf of Mexico. It is assumed that

it is very limited in scope and duration. 

Other Mortality

No human-caused mortality has been reported for this stock. 

STATUS OF STOCK

The status of this stock relative to OSP is unknown and there are insufficient data to determine population

trends. This species is not listed under the Endangered Species Act. The total level of human-caused mortality and

serious injury is unknown, but it is believed to be insignificant; therefore, this is not a strategic stock.

REFERENCES

Anon. 1994. Report of the PBR (Potential Biological Removal) workshop. June 27-29, 1994. NOAA, NMFS

Southwest Fisheries Science Center, La Jolla, California, 13 pp. + Appendices. 

Buckland, S. T., D. R. Anderson, K. P. Burnham and J. L. Laake. 1993. Distance Sampling: estimating abundance

of biological populations. Chapman & Hall, London, 446 pp. 

Cramer, J. 1994. Large pelagic logbook newsletter - 1993. NOAA Tech. Mem. NMFS-SEFSC-352, 19 pp. 
132

Davis, R., G. Scott, B. Würsig, W. Evans, G. Fargion, L. Hansen, K. Mullin, N. May, T. Leming, B. Mate, J. Norris

and T. Jefferson. In preparation. Distribution and abundance of marine mammals in the north-central and

western Gulf of Mexico: Final Report. OCS Study #MMS 94-0003. Texas Institute of Oceanography and the

National Marine Fisheries Service. U.S. Dept. of the Interior, Minerals Mgmt. Service, Gulf of Mexico OCS

Region, New Orleans, Louisiana. 

Hansen, L. J., K. D. Mullin and C. L. Roden. 1995. Estimates of cetacean abundance in the northern Gulf of Mexico

from vessel surveys. Southeast Fisheries Science Center, Miami Laboratory, Contribution No. MIA-94/95-25,

9 pp. + tables and figures.

Jefferson, T. A., S. Leatherwood, L. K. M. Shoda and R. L. Pitman. 1992. Marine mammals of the Gulf of Mexico:

a field guide for aerial and shipboard observers. Texas A&M University Printing Center, College Station,

Texas, 92 pp.

Laake, J. L., S. T. Buckland, D. R. Anderson, and K. P. Burnham. DISTANCE user’s guide, V2.0. Colorado

Cooperative Fish & Wildlife Research Unit, Colorado State University, Ft. Collins, Colorado, 72 pp. 

Leatherwood, S. and R. R. Reeves. 1983. The Sierra Club handbook of whales and dolphins. Sierra Club Books, San

Francisco, 302 pp. 

Schmidly, D. J. 1981. Marine mammals of the southeastern United States and the Gulf of Mexico. U.S. Fish and

Wildlife Service, Office of Biological Services, Washington, DC, FWS/OBS-80/41, 165 pp. 
133

Figure 1. Distribution of Curvier’s beaked whale sightings (filled circles) and

unidentified beaked whale sightings (unfilled circles) during NOAA Ship Oregon II

marine mammal surveys during 1991-1994. The straight lines show transects during

two surveys and are examples of typical ship survey transects. Isobaths are in 183 m

(100 fm) intervals. 

CUVIER'S BEAKED WHALE (Ziphius cavirostris):

Northern Gulf of Mexico Stock

STOCK DEFINITION AND GEOGRAPHIC RANGE

Cuvier's beaked whales are distributed throughout the world's oceans except for the polar regions

(Leatherwood and Reeves 1983; Heyning 1989). Strandings have occurred in all months along the United States east

coast (Schmidly 1981) and have been documented throughout the year in the Gulf of Mexico. Strandings of Cuvier's

beaked whales along the west coast of North America, based on skull characteristics, are thought to represent members

of a panmictic population (Mitchell 1968), but there is no information on stock differentiation in the Gulf of Mexico

and nearby waters. 

Beaked whales were seen in all seasons during recent seasonal GulfCet aerial surveys of the northern Gulf

of Mexico (Davis et al., in preparation). Some of the aerial survey sightings may have included Curvier’s beaked

whale, but identification of beaked whale species from aerial surveys is problematic.

POPULATION SIZE

Estimates of abundance were derived through the application of distance sampling analysis (Buckland et al.

1993) and the computer program DISTANCE (Laake et al. 1993) to sighting data collected during 1991-1994 springsummer, visual sampling, line-transect vessel surveys of the northern Gulf of Mexico (Hansen et al. 1995) (Fig. 1),

which includes data collected as part of the GulfCet program (Davis et al., in preparation). These surveys were

conducted throughout the area from approximately the 200 m isobath along the U.S. coast to the seaward extent of the

U.S. Exclusive Economic Zone. The seasonal GulfCet aerial surveys included only a small portion of the stock range

and these data were not used for

abundance estimation. The

estimated abundance [coefficient

of variation (CV) i n

parentheses] by survey year was

zero in 1991and 1992, 70 in

1993 (0.63), and 38 in 1994

(0.80) (Hansen et al. 1995).

Survey effort-weighted estimated

average abundance average

abundance of Cuvier's beaked

whales was 30 (CV = 0.50)

(Hansen et al. 1995). The

estimated abundance of

Curvier’s beaked whales is

probably low because only

sightings of beaked whales

which could be positively

identified to species were used. 

Minimum Population Estimate

The minimum population estimate was based on average estimated abundance of Cuvier's beaked whales for

all surveys combined which was 30 whales (CV = 0.50) (Hansen et al. 1995). The minimum population estimate is

the lower limit of the two-tailed 60% confidence interval of the log-normal distributed abundance estimate, which is

equivalent to the 20th percentile of the log-normal distributed abundance estimate as specified by NMFS (Anon. 1994).

The minimum population estimate is 20 Cuvier's beaked whales. 

Current Population Trend

The abundance estimates were zero in 1991 and 1992, and then increased for 1993 and 1994. Cuvier's beaked

whales were not sighted during the 1991 and 1992 vessel surveys. This could be due to chance given the small
134

estimated population size and sampling intensity or inter-annual variation in distribution, rather than a change in

population size. 

CURRENT AND MAXIMUM NET PRODUCTIVITY RATES

Current and maximum net productivity rates are not known for this stock; therefore, the default maximum

net productivity rate of 0.04 (Anon. 1994) was used for purposes of this assessment. 

POTENTIAL BIOLOGICAL REMOVAL

Potential biological removal level (PBR) was specified as the product of the minimum population size, one

half the maximum net productivity rate, and a recovery factor for endangered, threatened, or depleted stocks, or stocks

of unknown status relative to optimum sustainable population (OSP) (Anon. 1994). The recovery factor was set at 0.50

because the status of the stock relative to OSP is unknown. PBR for this stock is 0.2 Cuvier's beaked whales. 

ANNUAL HUMAN-CAUSED MORTALITY AND SERIOUS INJURY

Cuvier's beaked whales were taken occasionally in a small, directed fishery for cetaceans that operated out

of the Lesser Antilles (Caldwell and Caldwell 1971). 

The actual level of past or current, direct, human-caused mortality of Cuvier's beaked whales in the northern

Gulf of Mexico is unknown, but there have been no reports of fishery-related mortality or serious injury to beaked

whales by U.S. fisheries in the Gulf of Mexico. Available information indicates there likely is little, if any, fisheries

interaction with Cuvier's beaked whales in the northern Gulf of Mexico. 

There were no documented strandings of Cuvier's beaked whales in the northern Gulf of Mexico during 1987-

1994 which were classified as likely caused by fishery interactions or other human-related causes. Stranding data

probably underestimate the extent of fishery-related mortality and serious injury because not all of the marine mammals

which die or are seriously injured may wash ashore, nor will all of those that do wash ashore necessarily show signs

of entanglement or other fishery-interaction. Finally, the level of technical expertise among stranding network

personnel varies widely as does the ability to recognize signs of fishery interaction. 

Total fishery-related mortality and serious injury for this stock is less than 10% of the calculated PBR and,

therefore, can be considered insignificant and approaching zero mortality and serious injury rate. This determination

cannot be made for specific fisheries until the implementing regulations for Section 118 of the MMPA have been

reviewed by the public and finalized. 

Fisheries Information

Pelagic swordfish, tunas, and billfish are the targets of the longline fishery operating in the U.S. Gulf of

Mexico. Total longline effort for the Gulf of Mexico pelagic fishery, including OCS edge, continental slope, and

Mexican territorial waters, based on mandatory logbook reporting, was 4,400 sets in 1991, 4,850 sets in 1992, and

3,260 sets in 1993 (Cramer 1994). This fishery has been monitored with about 5% observer coverage, in terms of trips

observed, since 1992. There were no reports of mortality or serious injury to Cuvier's or any beaked whales by this

fishery. 

Pair trawl fishing gear has the potential to capture marine mammals, but there have been no reports of

mortality or serious injury to marine mammals in the Gulf of Mexico. This fishery has not been observed by NMFS

observers, and there are no other data available as to the extent of this fishery in the Gulf of Mexico. It is assumed that

it is very limited in scope and duration. 

STATUS OF STOCK

The status of this stock relative to OSP is unknown and there are insufficient data to determine population

trends. This species is not listed under the Endangered Species Act. The total level of human-caused mortality and

serious injury is unknown, but it is believed to be insignificant; therefore, this is not a strategic stock. 

REFERENCES

Anon. 1994. Report of the PBR (Potential Biological Removal) workshop. June 27-29, 1994. NOAA, NMFS

Southwest Fisheries Science Center, La Jolla, California, 13 pp. + Appendices. 
135

Buckland, S. T., D. R. Anderson, K. P. Burnham and J. L. Laake. 1993. Distance Sampling: estimating abundance

of biological populations. Chapman & Hall, London, 446 pp. 

Caldwell, D. K. and M. C. Caldwell. 1971. Beaked whales, Ziphius cavirostris, in the Bahamas. Florida Academy of

Science Quarterly Journal. 34: 157-160.

Cramer, J. 1994. Large pelagic logbook newsletter - 1993. NOAA Tech. Mem. NMFS-SEFSC-352, 19 pp. 

Davis, R., G. Scott, B. Würsig, W. Evans, G. Fargion, L. Hansen, K. Mullin, N. May, T. Leming, B. Mate, J. Norris

and T. Jefferson. In preparation. Distribution and abundance of marine mammals in the north-central and

western Gulf of Mexico: Final Report. OCS Study #MMS 94-0003. Texas Institute of Oceanography and the

National Marine Fisheries Service. U.S. Dept. of the Interior, Minerals Mgmt. Service, Gulf of Mexico OCS

Region, New Orleans, Louisiana. 

Hansen, L. J., K. D. Mullin and C. L. Roden. 1995. Estimates of cetacean abundance in the northern Gulf of Mexico

from vessel surveys. Southeast Fisheries Science Center, Miami Laboratory, Contribution No. MIA-94/95-25,

9 pp. + tables and figures.

Heyning, J. E. 1989. Cuvier's beaked whale Ziphius cavirostris G. Cuvier, 1923. Pages 289-308 in S. H. Ridgway and

R. Harrison (editors), Handbook of marine mammals, Vol. 4: River dolphins and the larger toothed whales,

Academic Press, London, 442 pp. 

Jefferson, T. A., S. Leatherwood, L. K. M. Shoda and R. L. Pitman. 1992. Marine mammals of the Gulf of Mexico:

a field guide for aerial and shipboard observers. Texas A&M University Printing Center, College Station,

92 pp. 

Laake, J. L., S. T. Buckland, D. R. Anderson, and K. P. Burnham. DISTANCE user’s guide, V2.0. Colorado

Cooperative Fish & Wildlife Research Unit, Colorado State University, Ft. Collins, Colorado, 72 pp. 

Leatherwood, S. and R. R. Reeves. 1983. The Sierra Club handbook of whales and dolphins. Sierra Club Books, San

Francisco, 302 pp. 

Schmidly, D. J. 1981. Marine mammals of the southeastern United States and the Gulf of Mexico. U.S. Fish and

Wildlife Service, Office of Biological Services, Washington, DC, FWS/OBS-80/41, 165 pp. 
136

Figure 1. Distribution of beaked whale sightings during NOAA Ship Oregon II marine

mammal surveys during 1991-1994. The straight lines show transects during two

surveys and are examples of typical survey transects. Isobaths are in 183 m (100 fm)

intervals. 

BLAINVILLE’S BEAKED WHALE (Mesoplodon densirostris):

Northern Gulf of Mexico Stock

STOCK DEFINITION AND GEOGRAPHIC RANGE

Only three species of Mesoplodon are known, from strandings and/or sightings, to occur in the Gulf of Mexico

(Jefferson et al. 1992; Hansen et al. 1995). These are Blainville's beaked whale (M. densirostris), Gervais' beaked

whale (M. europaeus), and Sowerby's beaked whale (M. bidens). The occurrence of Sowerby’s beaked whale in the Gulf

of Mexico is considered extralimital because there is only one known stranding of this species in the Gulf of Mexico

(Bonde and O’Shea 1989) and because it normally occurs in northern temperate waters of the North Atlantic (Mead

1989).

Identification of Mesoplodon species at sea is problematic; therefore, nearly all sightings of these species are

identified as beaked whales and may include sightings of Ziphius cavirostris that were not identified as such. Beaked

whales were seen in all seasons during recent seasonal GulfCet aerial surveys of the northern Gulf of Mexico (Davis

et al., in preparation). 

Blainville’s beaked whales appear to be widely but sparsely distributed in warm temperate and tropical waters

of the world’s oceans (Leatherwood et al. 1976; Leatherwood and Reeves 1983). Strandings have occurred along the

northwestern Atlantic coast from Florida to Nova Scotia (Schmidly 1981), and there have been two documented

strandings of this species in the northern Gulf of Mexico and one sighting (Jefferson et al. 1992; Hansen et al. 1995).

There is no information on stock differentiation. 

POPULATION SIZE

Estimates of abundance of beaked whales were derived through the application of distance sampling analysis

(Buckland et al. 1993) and the computer program DISTANCE (Laake et al. 1993) to sighting data collected during

1991-1994 spring-summer, visual sampling, line-transect vessel surveys of the northern Gulf of Mexico (Hansen et

al. 1995) (Fig. 1), which includes data collected as part of the GulfCet program (Davis et al., in preparation). These

surveys were conducted throughout the area from approximately the 200 m isobath along the U.S. coast to the seaward

extent of the U.S. Exclusive Economic Zone. The seasonal GulfCet aerial surveys included only a small portion of the

stock range and these data were not used for abundance estimation. Survey effort-weighted estimated average

abundance of beaked whales not

identified to species for all

surveys combined was 117

(coefficient of variation, CV =

0.38) (Hansen et al. 1995).

Estimated beaked whale

abundance (CV in parentheses)

by survey year was 129 in 1991

(0.78),18 in 1992 (1.27), 53 in

1993 (0.78), and 287 in 1994

(0.48) (Hansen et al. 1995). 

These estimates may also include

an unknown number of Cuvier’s

beaked whales (Ziphius

cavirostris) and abundance of

Blainville’s beaked whale cannot

be estimated due to uncertainty of

species identification at sea.

Minimum Population Estimate

A minimum population estimate was not calculated because of uncertainty of species identification of

sightings. 
137

Current Population Trend

The abundance estimates of beaked whales for 1991-1993 were lower than 1994, but there was considerable

overlap of the log-normal 95% confidence intervals, which indicates the estimates were not significantly different at

that level. Any differences in abundance estimates could be due to chance given the small estimated population size

and sampling intensity or a change in distribution, rather than a change in population size. 

CURRENT AND MAXIMUM NET PRODUCTIVITY RATES

Current and maximum net productivity rates are not known for this stock; therefore, the default maximum

net productivity rate of 0.04 (Anon. 1994) was used for purposes of this assessment. 

POTENTIAL BIOLOGICAL REMOVAL

Potential biological removal level (PBR) was not calculated because the minimum population size cannot be

calculated. 

ANNUAL HUMAN-CAUSED MORTALITY AND SERIOUS INJURY

The level of past or current, direct, human-caused mortality of beaked whales in the northern Gulf of Mexico

is unknown, but there have been no documented reports of fishery-related mortality or serious injury to beaked whales

by U.S. fisheries in the Gulf of Mexico. Available information indicates there likely is little, if any, fisheries interaction

with beaked whales in the northern Gulf of Mexico. 

There were no documented strandings of beaked whales in the northern Gulf of Mexico during 1987-1994

which were classified as likely caused by fishery interactions or other human-related causes. Stranding data probably

underestimate the extent of fishery-related mortality and serious injury because not all of the marine mammals which

die or are seriously injured may wash ashore, nor will all of those that do wash ashore necessarily show signs of

entanglement or other fishery-interaction. Finally, the level of technical expertise among stranding network personnel

varies widely as does the ability to recognize signs of fishery interaction. 

Although PBR cannot be calculated, the total known fishery-related mortality and serious injury for this stock

is zero and, therefore, can be considered insignificant and approaching zero mortality and serious injury rate. This

determination cannot be made for specific fisheries until the implementing regulations for Section 118 of the MMPA

have been reviewed by the public and finalized. 

Fisheries Information

Pelagic swordfish, tunas, and billfish are the targets of the longline fishery operating in the U.S. Gulf of

Mexico. Total longline effort for the Gulf of Mexico pelagic fishery, including OCS edge, continental slope, and

Mexican territorial waters, based on mandatory logbook reporting, was 4,400 sets in 1991, 4,850 sets in 1992, and

3,260 sets in 1993 (Cramer 1994). This fishery has been monitored with about 5% observer coverage, in terms of trips

observed, since 1992. 

Pair trawl fishing gear has the potential to capture marine mammals, but there have been no reports of

mortality or serious injury to marine mammals in the Gulf of Mexico. This fishery has not been observed by NMFS

observers, and there are no other data available as to the extent of this fishery in the Gulf of Mexico. It is assumed that

it is very limited in scope and duration. 

STATUS OF STOCK

The status of this stock relative to OSP is unknown and there are insufficient data to determine population

trends. This species is not listed under the Endangered Species Act. The total level of human-caused mortality and

serious injury is unknown, but it is believed to be insignificant; therefore, this is not a strategic stock. 

REFERENCES

Anon. 1994. Report of the PBR (Potential Biological Removal) workshop. June 27-29, 1994. NOAA, NMFS

Southwest Fisheries Science Center, La Jolla, California, 13 pp. + Appendices. 

Bonde, R. K. and T. J. O’Shea. 1989. Sowerby’s beaked whale (Mesoplodon bidens) in the Gulf of Mexico. J.

Mammal. 70: 447-449. 
138

Buckland, S. T., D. R. Anderson, K. P. Burnham and J. L. Laake. 1993. Distance Sampling: estimating abundance

of biological populations. Chapman & Hall, London, 446 pp. 

Cramer, J. 1994. Large pelagic logbook newsletter - 1993. NOAA Tech. Mem. NMFS-SEFSC-352, 19 pp. 

Davis, R., G. Scott, B. Würsig, W. Evans, G. Fargion, L. Hansen, K. Mullin, N. May, T. Leming, B. Mate, J. Norris

and T. Jefferson. In preparation. Distribution and abundance of marine mammals in the north-central and

western Gulf of Mexico: Final Report. OCS Study #MMS 94-0003. Texas Institute of Oceanography and the

National Marine Fisheries Service. U.S. Dept. of the Interior, Minerals Mgmt. Service, Gulf of Mexico OCS

Region, New Orleans, Louisiana. 

Hansen, L. J., K. D. Mullin and C. L. Roden. 1995. Estimates of cetacean abundance in the northern Gulf of Mexico

from vessel surveys. Southeast Fisheries Science Center, Miami Laboratory, Contribution No. MIA-94/95-25,

9 pp. + tables and figures.

Jefferson, T. A., S. Leatherwood, L. K. M. Shoda and R. L. Pitman. 1992. Marine mammals of the Gulf of Mexico:

a field guide for aerial and shipboard observers. Texas A&M University Printing Center, College Station, TX.

92 pp. 

Laake, J. L., S. T. Buckland, D. R. Anderson, and K. P. Burnham. DISTANCE user’s guide, V2.0. Colorado

Cooperative Fish & Wildlife Research Unit, Colorado State University, Ft. Collins, Colorado, 72 pp. 

Leatherwood, S., D. K. Caldwell and H. E. Winn. 1976. Whales, dolphins, and porpoises of the western North

Atlantic. NOAA Tech. Rep. NMFS CIRC-396, 176 pp. 

Leatherwood, S. and R. R. Reeves. 1983. The Sierra Club handbook of whales and dolphins. Sierra Club Books, San

Francisco, 302 pp. 

Mead, J. G. 1989. Beaked whales of the genus Mesoplodon. Pages 349-430 in S. H. Ridgway and R. Harrison

(editors), Handbook of marine mammals, Vol. 4: River dolphins and the larger toothed whales. Academic

Press, London, 442 pp. 
139

Figure 1. Distribution of beaked whale sightings during NOAA Ship Oregon II marine

mammal surveys during 1991-1994. The straight lines show transects during two

surveys and are examples of typical survey transects. Isobaths are in 183 m (100 fm)

intervals. 

GERVAIS' BEAKED WHALE (Mesoplodon europaeus):

Northern Gulf of Mexico Stock

STOCK DEFINITION AND GEOGRAPHIC RANGE

Only three species of Mesoplodon are known, from strandings and/or sightings, to have occurred in the Gulf

of Mexico (Jefferson et al. 1992; Hansen et al. 1995). These are Blainville's beaked whale (M. densirostris), Gervais'

beaked whale (M. europaeus), and Sowerby's beaked whale (M. bidens). The occurrence of Sowerby’s beaked whale

in the Gulf of Mexico is considered extralimital because there is only one known stranding of this species in the Gulf

of Mexico (Bonde and O’Shea 1989), and because it normally occurs in northern temperate waters of the North

Atlantic (Mead 1989). Identification of Mesoplodon species at sea is problematic. Therefore, nearly all sightings of

these species are identified as beaked whales and may include sightings of Ziphius cavirostris which were not

identified as such. Beaked whales were seen in all seasons during recent seasonal GulfCet aerial surveys of the

northern Gulf of Mexico (Davis et al., in preparation). 

Strandings of Gervais' beaked whales have occurred along the northwestern Atlantic coast from Florida to

New York (Mead 1989), and there have been at least ten documented strandings of this species in the Gulf of Mexico

(Jefferson et al. 1992). There is no information on stock differentiation. 

POPULATION SIZE

Estimates of abundance of beaked whales were derived through the application of distance sampling analysis

(Buckland et al. 1993) and the computer program DISTANCE (Laake et al. 1993) to sighting data collected during

1991-1994 spring-summer, visual sampling, line-transect vessel surveys of the northern Gulf of Mexico (Hansen et

al. 1995) (Fig. 1), which includes data collected as part of the GulfCet program (Davis et al., in preparation). These

surveys were conducted throughout the area from approximately the 200 m isobath along the U.S. coast to the seaward

extent of the U.S. Exclusive Economic Zone. The seasonal GulfCet aerial surveys included only a small portion of the

stock range and these data were not used for abundance estimation. Survey effort-weighted estimated average

abundance of beaked whales not

identified to species for all

surveys combined was 117

(coefficient of variation, CV =

0.38) (Hansen et al. 1995).

Estimated beaked whale

abundance (CV in parentheses)

by survey year was 129 in 1991

(0.78),18 in 1992 (1.27), 53 in

1993 (0.78), and 287 in 1994

(0.48) (Hansen et al. 1995). 

These estimates may also include

an unknown number of Cuvier’s

beaked whales (Ziphius

cavirostris) and abundance of

Gervais’ beaked whale cannot be

estimated due to uncertainty of

species identification at sea.

Minimum Population Estimate

A minimum population estimate could not be not calculated because of uncertainty of species identification

of sightings. 

Current Population Trend
140

The abundance estimates of beaked whales for 1991-1993 were lower than 1994, but there was considerable

overlap of the log-normal 95% confidence intervals, which indicates the estimates were not significantly different at

that level. Any differences in abundance estimates could be due to chance given the small estimated population size

and sampling intensity or a change in distribution, rather than a change in population size. 

CURRENT AND MAXIMUM NET PRODUCTIVITY RATES

Current and maximum net productivity rates are not known for this stock; therefore, the default maximum

net productivity rate of 0.04 (Anon. 1994) was used for purposes of this assessment. 

POTENTIAL BIOLOGICAL REMOVAL

Potential biological removal level (PBR) was not calculated because the minimum population size cannot be

calculated. 

ANNUAL HUMAN-CAUSED MORTALITY AND SERIOUS INJURY

The level of past or current, direct, human-caused mortality of beaked whales in the northern Gulf of Mexico

is unknown, but there have been no documented reports of fishery-related mortality or serious injury to beaked whales

by U.S. fisheries in the Gulf of Mexico. Available information indicates there likely is little, if any, fisheries interaction

with beaked whales in the northern Gulf of Mexico. 

There were no documented strandings of beaked whales in the northern Gulf of Mexico during 1987-1994

which were classified as likely caused by fishery interactions or other human-related causes. Stranding data probably

underestimate the extent of fishery-related mortality and serious injury because not all of the marine mammals which

die or are seriously injured may wash ashore, nor will all of those that do wash ashore necessarily show signs of

entanglement or other fishery-interaction. Finally, the level of technical expertise among stranding network personnel

varies widely as does the ability to recognize signs of fishery interaction. 

Although PBR cannot be calculated, the total known fishery-related mortality and serious injury for this stock

is zero and, therefore, can be considered insignificant and approaching zero mortality and serious injury rate. This

determination cannot be made for specific fisheries until the implementing regulations for Section 118 of the MMPA

have been reviewed by the public and finalized. 

Fisheries Information

 Pelagic swordfish, tunas, and billfish are the targets of the longline fishery operating in the U.S. Gulf of

Mexico. Total longline effort for the Gulf of Mexico pelagic fishery, including OCS edge, continental slope, and

Mexican territorial waters, based on mandatory logbook reporting, was 4,400 sets in 1991, 4,850 sets in 1992, and

3,260 sets in 1993 (Cramer 1994). This fishery has been monitored with about 5% observer coverage, in terms of trips

observed, since 1992. 

Pair trawl fishing gear has the potential to capture marine mammals, but there have been no reports of

mortality or serious injury to marine mammals in the Gulf of Mexico. This fishery has not been observed by NMFS

observers, and there are no other data available as to the extent of this fishery in the Gulf of Mexico. It is assumed that

it is very limited in scope and duration. 

STATUS OF STOCK

 The status of this stock relative to OSP is unknown and there are insufficient data to determine population

trends. This species is not listed under the Endangered Species Act. The total level of human-caused mortality and

serious injury is unknown, but it is believed to be insignificant; therefore, this is not a strategic stock. 

REFERENCES

Anon. 1994. Report of the PBR (Potential Biological Removal) workshop. June 27-29, 1994. NOAA, NMFS

Southwest Fisheries Science Center, La Jolla, California, 13 pp. + Appendices. 

Bonde, R. K. and T. J. O’Shea. 1989. Sowerby’s beaked whale (Mesoplodon bidens) in the Gulf of Mexico. J.

Mammal. 70: 447-449. 

Buckland, S. T., D. R. Anderson, K. P. Burnham and J. L. Laake. 1993. Distance Sampling: estimating abundance

of biological populations. Chapman & Hall, London, 446 pp. 
141

Cramer, J. 1994. Large pelagic logbook newsletter - 1993. NOAA Tech. Mem. NMFS-SEFSC-352, 19 pp. 

Davis, R., G. Scott, B. Würsig, W. Evans, G. Fargion, L. Hansen, K. Mullin, N. May, T. Leming, B. Mate, J. Norris

and T. Jefferson. In preparation. Distribution and abundance of marine mammals in the north-central and

western Gulf of Mexico: Final Report. OCS Study #MMS 94-0003. Texas Institute of Oceanography and the

National Marine Fisheries Service. U.S. Dept. of the Interior, Minerals Mgmt. Service, Gulf of Mexico OCS

Region, New Orleans, Louisiana. 

Hansen, L. J., K. D. Mullin and C. L. Roden. 1995. Estimates of cetacean abundance in the northern Gulf of Mexico

from vessel surveys. Southeast Fisheries Science Center, Miami Laboratory, Contribution No. MIA-94/95-25,

9 pp. + tables and figures.

Jefferson, T. A., S. Leatherwood, L. K. M. Shoda and R. L. Pitman. 1992. Marine mammals of the Gulf of Mexico:

a field guide for aerial and shipboard observers. Texas A&M University Printing Center, College Station, 92

pp. 

Laake, J. L., S. T. Buckland, D. R. Anderson, and K. P. Burnham. DISTANCE user’s guide, V2.0. Colorado

Cooperative Fish & Wildlife Research Unit, Colorado State University, Ft. Collins, Colorado, 72 pp. 

Mead, J. G. 1989. Beaked whales of the genus Mesoplodon. Pages 349-430 in S. H. Ridgway and R. Harrison

(editors), Handbook of marine mammals, Vol. 4: River dolphins and the larger toothed whales. Academic

Press, London, 442 pp. 
142

Figure 1. Sightings of U.S. Gulf of Mexico outer continental shelf (OCS) bottlenose

dolphin stock during GOMEX regional aerial surveys (filled circles). Bottlenose

dolphin sightings along the OCS edge and continental slope during NOAA Ship Oregon

II surveys (unfilled circles), shown for comparison, are believed to be a separate stock. 

 The straight lines show transects during two ship surveys and are examples of typical

ship survey transects. Isobaths are in 183 m (100 fm) intervals. 

BOTTLENOSE DOLPHIN (Tursiops truncatus):

Gulf of Mexico Outer Continental Shelf Stock

STOCK DEFINITION AND GEOGRAPHIC RANGE

The Gulf of Mexico Outer Continental Shelf (OCS) bottlenose dolphin stock is assumed to consist of the

shallow, warm water bottlenose dolphin ecotype hypothesized by Hersh and Duffield (1990) inhabiting waters over the

U.S. OCS in the northern Gulf of Mexico from approximately 9 km seaward of the 18 m isobath to approximately 9

km seaward of the 183 m isobath and from the U.S.-Mexican border to the Florida Keys. The stock range may extend

into Mexican and Cuban territorial waters; however, there are no available estimates of either abundance or mortality

from those countries. As a working hypothesis, the bottlenose dolphins inhabiting the 0-18 m depth stratum are

believed to constitute coastal stocks in the western, northern, and eastern U.S. Gulf of Mexico separate from the OCS

stock; however, the OCS stock may overlap with coastal stocks in some areas and may be genetically indistinguishable

from those stocks. The OCS stock may be combined with some or all of the coastal stocks when additional data become

available. 

In addition, the aerial surveys from which the current abundance estimates were derived overlapped the outer

continental shelf edge which is believed to be inhabited by the OCS edge and continental slope stock (Fig. 1). This

stock is believed to consist of the deep, cold water ecotype described by Hersh and Duffield for the Atlantic (1990).

It is not currently possible to differentiate the two ecotypes visually during aerial surveys.

POPULATION SIZE

Preliminary estimates of abundance were derived using distance sampling analysis (Buckland et al. 1993) and

the computer program DISTANCE (Laake et al. 1993) with sighting data collected during Gulf of Mexico regional

aerial line-transect surveys in September-October 1992 and 1993 (Blaylock and Hoggard 1994) and 1994 (NMFS

unpublished data). Transects providing systematic coverage of the area and assumed to be randomly placed with

respect to bottlenose dolphin distribution extended orthogonally from approximately 9 km past the 18 m isobath to

approximately 9 km past the 183

m isobath. Approximately 3.3%

of the total area was visually

sampled. Preliminary analyses

provided a bottlenose dolphin

abundance estimate of 50,247

dolphins with coefficient of

variation (CV) = 0.18. The

survey area overlapped with a

portion of the area occupied by

the OCS edge and continental

slope stock which was assumed to

occur in waters over the OCS

edge and beyond to the seaward

limits of the U.S. Exclusive

Economic Zone. This would tend

to inflate the abundance estimate,

but it is not currently possible to

estimate the amount of potential

bias.

Minimum Population Estimate

The minimum population estimate was based on the abundance estimate of 50,247 dolphins (CV = 0.18). 

The minimum population estimate is the lower limit of the two-tailed 60% confidence interval of the log-normal

distributed abundance estimate, which is equivalent to the 20th percentile of the log-normal distribution as specified

by NMFS (Anon. 1994). The minimum population estimate is 43,233 bottlenose dolphins. 
143

Current Population Trend

The data are insufficient to determine population trends. Aerial surveys conducted during autumn 1983 and

1985 by the Southeast Fisheries Science Center (SEFSC) produced an abundance estimate of 31,519 bottlenose

dolphins (CV = 0.08) for this stock (Scott et al. 1989). This population thus appears to have increased from earlier

estimated levels; however, a valid statistical comparison of the historical and present estimated population sizes is not

presently possible because of the preliminary nature of the recent population size estimate and the possible biases

caused by overlap of the survey area with the OCS edge and continental slope stock. 

CURRENT AND MAXIMUM NET PRODUCTIVITY RATES

Current and maximum net productivity rates are not known for this stock. The maximum net productivity

rate was assumed to be 0.04 for purposes of this assessment. This value is based on theoretical calculations showing

that cetacean populations may not generally grow at rates much greater than 4% given the constraints of their

reproductive life history (Reilly and Barlow 1986). 

POTENTIAL BIOLOGICAL REMOVAL

Potential biological removal (PBR) was specified as the product of minimum population size, one-half the

maximum productivity rate, and a "recovery" factor for endangered, depleted, threatened stocks, or stocks of unknown

status relative to optimum sustainable population (OSP) (Anon. 1994). The recovery factor was set at 0.50 because

of the stock's status relative to its OSP level is unknown. PBR for this stock is 432 bottlenose dolphins. 

ANNUAL HUMAN-CAUSED MORTALITY AND SERIOUS INJURY

There are no observed cases of human-caused mortality and serious injury in this stock; however, based on

an observed non-lethal take in U.S. Atlantic waters in 1993 in the pelagic longline fishery, this stock may be subject

to incidental take resulting in serious injury or mortality. Fishery interactions have been reported to occur between

bottlenose dolphins and the longline swordfish/tuna fishery in the Gulf of Mexico (SEFSC unpublished logbook data)

and annual fishery-related mortality and serious injury to bottlenose dolphins is estimated to be 2.8 per year (CV =

0.74) during 1992-1993. This could include bottlenose dolphins from the outer continental shelf edge and continental

slope stock.

 Total fishery-related mortality and serious injury for this stock is less than 10% of the calculated PBR and,

therefore, can be considered to be insignificant and approaching zero mortality and serious injury rate. This

determination cannot be made for specific fisheries until the implementing regulations for Section 118 of the MMPA

have been reviewed by the public and finalized. 

Fishery Information

Annual fishing effort for the shrimp trawl fishery in the U.S. Gulf of Mexico OCS during 1988-1993 averaged

approximately 2.58 million hours of tows (CV = 0.07) (NMFS unpublished data). This fishery was monitored by

NMFS observers in 1992 and 1993, but less than 1% of the fishing effort was observed (NMFS unpublished data).

There have been no reports of incidental mortality or injury associated with the shrimp trawl fishery in this area. 

Pelagic swordfish, tunas, and billfish are the targets of the longline fishery operating in the U.S. Gulf of

Mexico. Total longline effort for the Gulf of Mexico pelagic fishery, including OCS edge, continental slope, and

Mexican territorial waters, based on mandatory logbook reporting, was 4,400 sets in 1991, 4,850 sets in 1992, and

3,260 sets in 1993 (Cramer 1994). This fishery has been monitored with about 5% observer coverage, in terms of trips

observed, since 1992. Estimated take was based on a generalized linear model (Poisson error assumption) fit to the

available observed incidental take and self-reported incidental take and effort data for the fishery. The following

estimates were based on observed takes across the Atlantic longline swordfish/tuna fishery (which includes the Gulf

of Mexico). All observed takes were used because the species occurs generally throughout the area of the fishery, but

observed takes were infrequent in any given region of the fishery. There were no lethal takes of bottlenose dolphins

observed or reported in 1992 and 1993, and only one non-lethal take was reported in 1993, which is assumed to have

caused serious injury. The estimated level of fishery-related mortality and serious injury for the entire fishery,

including waters outside of the Gulf of Mexico, in 1993 was 16 bottlenose dolphins (CV = 0.19). No take was observed

in the Gulf of Mexico, but interactions between bottlenose dolphins and this fishery in the Gulf of Mexico have been

reported under the Marine Mammal Protection Act Interim Exemption Program (NMFS 1993).
144

Given the fact that fishery interactions have been reported to occur between bottlenose dolphins and the

longline swordfish/tuna fishery in the Gulf of Mexico, a probable level of fishery-related mortality and serious injury

rate can be estimated. Under the assumption that the probability of an incidental take is proportional to fishing effort

(number of sets), the estimated level of incidental mortality and serious injury partitioned to include only the Gulf of

Mexico stock would be 5.5 bottlenose dolphins in 1993 (CV = 0.19). Average annual fishery-related mortality and

serious injury during 1992-1993 would be 2.8 bottlenose dolphins (CV= 0.74). This estimate could include dolphins

from the OCS edge and continental slope stock.

Pair trawl fishing gear has the potential to capture marine mammals, but there have been no reports of

mortality or serious injury to marine mammals in the Gulf of Mexico. This fishery has not been observed by NMFS

observers, and there are no other data available as to the extent of this fishery in the Gulf of Mexico. It is assumed that

it is very limited in scope and duration in the Gulf of Mexico. 

A trawl fishery for butterfish was monitored by NMFS observers for a short period in the 1980's with no

records of incidental take of marine mammals (Burn and Scott 1988; NMFS unpublished data), although an

experimental set by NMFS resulted in the death of two bottlenose dolphins (Burn and Scott 1988). There are no other

data available. 

Other Human-Related Mortality or Serious Injury

The use of explosives to remove oil rigs in the portions of the OCS in the western Gulf of Mexico has the

potential to cause serious injury or mortality to marine mammals. These activities have been closely monitored by

NMFS observers since 1987 (Gitschlag and Hale, in press) and Gitschlag and Herczeg (in press) described the

monitoring activities that occurred in 1992. There have been no reports of either serious injury or mortality to

bottlenose dolphins (NMFS unpublished data). 

STATUS OF STOCK

The status of this stock relative to OSP is not known and the population trend cannot be determined due to

insufficient data. This species is not listed as threatened or endangered under the Endangered Species Act. This is

not a strategic stock because fishery-related mortality and serious injury does not exceed PBR. 

REFERENCES

Anon. 1994. Report of the PBR (Potential Biological Removal) workshop. June 27-29, 1994. NOAA, NMFS

Southwest Fisheries Science Center, La Jolla, California, 13 pp. + Appendices. 

Blaylock, R. A. and W. Hoggard. 1994. Preliminary estimates of bottlenose dolphin abundance in southern U.S.

Atlantic and Gulf of Mexico continental shelf waters. NOAA Tech. Mem. NMFS-SEFSC-356, 10 pp. 

Buckland, S. T., D. R. Anderson, K. P. Burnham, and J. L. Laake. 1993. Distance sampling: Estimating abundance

of biological populations. Chapman & Hall, London, 446 pp. 

Burn, D. And G. P. Scott. 1988. Synopsis of available information on marine mammal-fisheries interactions in the

southeastern United States: preliminary report. NMFS/SEFC, Miami Laboratory, Coastal resources Division,

Contribution ML-CRG-87/88-26, 37 pp. 

Gitschlag, G. R. and J. K. Hale. In press. Susceptibility of sea turtles to underwater explosives at offshore energy

structure removals. Submitted to N. E. Gulf Science. 

Gitschlag, G. R. and B. A. Herczeg. In press. Sea turtle observations at explosive removals of energy structures.

Submitted to Mar. Fish. Rev. 

Hersh, S. L. and D. A. Duffield. 1990. Distinction between northwest Atlantic offshore and coastal bottlenose

dolphins based on hemoglobin profile and morphometry. Pages 129-139 in S. Leatherwood and R. R. Reeves

(editors), The bottlenose dolphin, Academic Press, San Diego, 653 pp. 

Laake, J. L., S. T. Buckland, D. R. Anderson, and K. P. Burnham. DISTANCE user’s guide, V2.0. Colorado

Cooperative Fish & Wildlife Research Unit, Colorado State University, Ft. Collins, Colorado, 72 pp. 

Northridge, S. In review. Estimation of cetacean mortality in the U.S. Atlantic swordfish and tuna driftnet and pair

trawl fisheries. Draft final report to the Northeast Fisheries Science Center, Contract No. 40ENNF500045.

18 pp. 

Reilly, S. B. and J. Barlow. 1986. Rates of increase in dolphin population size. Fish. Bull., U.S. 84(3): 527-533. 
145

Figure 1. Distribution of sightings of bottlenose dolphins during NOAA Ship Oregon

II marine mammal surveys in the Gulf of Mexico outer continental shelf (OCS) edge and

continental slope waters (filled circles). Sightings of the OCS bottlenose dolphin stock

made during GOMEX regional aerial surveys (unfilled circles) are shown for

comparison. The bottlenose dolphin on the OCS are believed to be a separate stock. 

The straight lines show transects during two ship surveys and are examples of typical

ship survey transects. Isobaths are in 183 m (100 fm) intervals.

BOTTLENOSE DOLPHIN (Tursiops truncatus):

Gulf of Mexico Continental Shelf Edge and Continental Slope Stock

STOCK DEFINITION AND GEOGRAPHIC RANGE

This bottlenose dolphin stock is defined as the stock which occupies the outer edge of the U.S. Gulf of Mexico

Outer Continental Shelf (OCS) and waters over the continental slope within the U.S. Exclusive Economic Zone (EEZ),

from the latitude and longitude of the U.S. EEZ off the U.S.-Mexico border to the latitude of the U.S. EEZ south of

Key West, Florida. Close observation by experienced NMFS observers from shipboard surveys conducted throughout

much of its range (Fig. 1) indicates that most of the dolphins sighted during ship-based surveys over the continental

shelf edge and continental slope were the relatively large and robust dolphins assumed to be of the deep water ecotype

hypothesized by Hersh and Duffield (1990). These dolphins were reported to be larger and darker in color than

bottlenose dolphins seen over the continental shelf closer to shore (NMFS unpublished data). This stock’s range may

extend into Mexican and Cuban waters; however, there are no estimates available for bottlenose dolphin abundance

or mortality from those countries.

POPULATION SIZE

Preliminary estimates of abundance were derived using distance sampling analysis (Buckland et al. 1993) and

the computer program DISTANCE (Laake et al. 1993) with sighting data collected during shipboard line-transect

surveys conducted during the spring of 1992-1994 (Fig. 1). These surveys were conducted throughout the area from

approximately the 200 m isobath along the U.S. coast to the seaward extent of the U.S. Exclusive Economic Zone. The

seasonal GulfCet aerial surveys included only a small portion of the stock range and these data were not used for

abundance estimation. Average

bottlenose dolphin abundance

over six surveys was estimated

at 5,618 dolphins with

coefficient of variation (CV) =

0.26. In this analysis, it was

assumed that all of the

bottlenose dolphins sighted

during the ship-based surveys

were of this stock. The survey

area overlapped in some areas

with the OCS stock which was

assumed to occur from

approximately 9 km seaward of

the 18 m isobath to

approximately 9 km seaward of

the 183 m isobath; however, the

amount of overlap is considered

insignificant and its effect on

the abundance estimate is not

known. 

Minimum Population Estimate

The minimum population estimate was based on the average bottlenose dolphin abundance estimate of 5,618

bottlenose dolphins (CV = 0.26). The minimum population estimate is the lower limit of the two-tailed 60%

confidence interval of the log-normal distributed abundance estimate, which is equivalent to the 20th percentile of the

log-normal distribution as specified by NMFS (Anon. 1994). The minimum population estimate is 4,530 bottlenose

dolphins. 

Current Population Trend
146

The data are insufficient to determine population trends. 

CURRENT AND MAXIMUM NET PRODUCTIVITY RATES

Current and maximum net productivity rates for this stock are unknown. The maximum net productivity rate

for purposes of this assessment, was assumed to be 0.04. This value is based on theoretical calculations showing that

cetacean populations may not generally grow at rates much greater than 4% given the constraints of their reproductive

life history (Reilly and Barlow, 1986). 

POTENTIAL BIOLOGICAL REMOVAL

Potential biological removal (PBR) has been specified as the product of minimum population size, one-half

the maximum productivity rate, and a "recovery" factor for endangered, depleted, threatened stocks, or stocks of

unknown status relative to optimum sustainable population (OSP). The recovery factor was 0.50 because of the stock's

unknown status relative to OSP. PBR for this stock is 45 bottlenose dolphins. 

ANNUAL HUMAN-CAUSED MORTALITY AND SERIOUS INJURY

There are no observed cases of human-caused mortality and serious injury in this stock; however, based on

an observed non-lethal take in U.S. Atlantic waters in 1993 in the pelagic longline fishery, this stock may be subject

to incidental take resulting in serious injury or mortality. Fishery interactions have been reported to occur between

bottlenose dolphins and the longline swordfish/tuna fishery in the Gulf of Mexico [Southeast Fisheries Science Center

(SEFSC) unpublished logbook data] and annual fishery-related mortality and serious injury to bottlenose dolphins is

estimated to be 2.8 per year (CV = 0.74) during 1992-1993. This estimate could include bottlenose dolphins from the

OCS stock.

The total fishery-related mortality and serious injury for this stock is less than 10% of the calculated PBR and,

therefore, can be considered to be insignificant and approaching zero mortality and serious injury rate. This

determination cannot be made for specific fisheries until the implementing regulations for Section 118 of the MMPA

have been reviewed by the public and finalized. 

Fishery Interaction

Pelagic swordfish, tunas, and billfish are the targets of the longline fishery operating in the U.S. Gulf of

Mexico. Total longline effort for the Gulf of Mexico pelagic fishery, including OCS edge, continental slope, and

Mexican territorial waters, based on mandatory logbook reporting, was 4,400 sets in 1991, 4,850 sets in 1992, and

3,260 sets in 1993 (Cramer 1994). This fishery has been monitored with about 5% observer coverage, in terms of trips

observed, since 1992. Estimated take was based on a generalized linear model (Poisson error assumption) fit to the

available observed incidental take and self-reported incidental take and effort data for the fishery. The following

estimates were based on observed takes across the Atlantic longline swordfish/tuna fishery (which includes the Gulf

of Mexico). All observed takes were used because the species occurs generally throughout the area of the fishery, but

observed takes were infrequent in any given region of the fishery. There were no lethal takes of bottlenose dolphins

observed or reported in 1992 and 1993, and only one non-lethal take was reported in 1993, which is assumed to have

caused serious injury. The estimated level of fishery-related mortality and serious injury for the entire fishery,

including waters outside of the Gulf of Mexico, in 1993 was 16 bottlenose dolphins (CV = 0.19). No take was observed

in the Gulf of Mexico, but there are logbook reports of interactions between bottlenose dolphins and this fishery

(SEFSC unpublished logbook data).

Given the fact that fishery interactions have been reported to occur between bottlenose dolphins and the

longline swordfish/tuna fishery in the Gulf of Mexico, a probable level of fishery-related mortality and serious injury

rate can be estimated. Under the assumption that the probability of an incidental take is proportional to fishing effort

(number of sets), the estimated level of incidental mortality and serious injury partitioned to include only the Gulf of

Mexico stock would be 5.5 bottlenose dolphins in 1993 (CV = 0.19). Average annual fishery-related mortality and

serious injury during 1992-1993 would be 2.8 bottlenose dolphins (CV= 0.74). This estimate could include dolphins

from the OCS stock. 

Pair trawl fishing gear has the potential to capture marine mammals, but there have been no reports of

mortality or serious injury to marine mammals in the Gulf of Mexico. This fishery has not been observed by NMFS
147

observers, and there are no other data available as to the extent of this fishery in the Gulf of Mexico. It is assumed that

it is very limited in scope and duration. 

A trawl fishery for butterfish was monitored by NMFS observers for a short period in the 1980's with no

records of incidental take of marine mammals (Burn and Scott 1988; NMFS unpublished data), although an

experimental NMFS set resulted in the death of two bottlenose dolphins (Burn and Scott 1988). There are no other

data available. 

Other Mortality

No direct or indirect human-caused mortality has been reported for this stock. 

STATUS OF STOCK

The status of this stock relative to OSP is not known and the population trend cannot be determined due to

insufficient data. This species is not listed as threatened or endangered under the Endangered Species Act. This is

not a strategic stock because fishery-related mortality or serious injury does not exceed PBR. 

REFERENCES

Anon. 1994. Report of the PBR (Potential Biological Removal) workshop. June 27-29, 1994. NOAA, NMFS

Southwest Fisheries Science Center, La Jolla, California, 13 pp. + Appendices. 

Buckland, S. T., D. R. Anderson, K. P. Burnham, and J. L. Laake. 1993. Distance sampling: Estimating abundance

of biological populations. Chapman & Hall, London, 446 pp. 

Burn, D. And G. P. Scott. 1988. Synopsis of available information on marine mammal-fisheries interactions in the

southeastern United States: preliminary report. NMFS/SEFC, Miami Laboratory, Coastal resources Division,

Contribution ML-CRG-87/88-26, 37 pp. 

Cramer, J. 1994. Large pelagic logbook newsletter - 1993. NOAA Tech. Mem. NMFS-SEFSC-352, 19 pp. 

Hersh, S. L. and D. A. Duffield. 1990. Distinction between northwest Atlantic offshore and coastal bottlenose

dolphins based on hemoglobin profile and morphometry. Pages 129-139 in S. Leatherwood and R. R. Reeves

(editors), The bottlenose dolphin, Academic Press, San Diego, 653 pp. 

Laake, J. L., S. T. Buckland, D. R. Anderson, and K. P. Burnham. DISTANCE user’s guide, V2.0. Colorado

Cooperative Fish & Wildlife Research Unit, Colorado State University, Ft. Collins, Colorado, 72 pp. 

Northridge, S. In review. Estimation of cetacean mortality in the U.S. Atlantic swordfish and tuna driftnet and pair

trawl fisheries. Draft final report to the Northeast Fisheries Science Center, Contract No. 40ENNF500045.

18 pp. 

Reilly, S. B. and J. Barlow. 1986. Rates of increase in dolphin population size. Fish. Bull., U.S. 84(3): 527-533. 
148

Figure 1. Sightings of coastal bottlenose dolphins during GOMEX aerial surveys of

the Gulf of Mexico in 1992-1994. Western Gulf of Mexico coastal bottlenose dolphin

stock is shown with filled circles. Isobaths are in 183 m (100 fm) intervals.

BOTTLENOSE DOLPHIN (Tursiops truncatus):

Western Gulf of Mexico Coastal Stock

STOCK DEFINITION AND GEOGRAPHIC RANGE

The western Gulf of Mexico coastal bottlenose dolphin stock has been defined for management purposes as

the bottlenose dolphins inhabiting the nearshore coastal waters in the U.S. Gulf of Mexico from the Texas border to

the Mississippi River mouth, from shore or presumed bay boundaries to 9.3 km seaward of the 18.3 m isobath (Fig.

1). As a working hypothesis, it is assumed that the dolphins occupying habitats with dissimilar climactic, coastal, and

oceanographic characteristics might be restricted in their movements between habitats and, thus, constitute separate

stocks. The western coastal

area is characterized by an arid

to temperate climate, sand

beaches, and low fresh water

input. The northern coastal

stock area which is

characterized by a temperate

climate, barrier islands, sand

beaches, coastal marshes and

marsh islands, and has a

relatively high level of fresh

water input from rivers and

streams. The eastern coastal

stock area is temperate to

subtropical in climate, is

bordered by a mixture of coastal

marshes, sand beaches, marsh

and mangrove islands, and has an intermediate level of freshwater input.

The stock occurs trans-boundary with Mexico; however, there is no information available for abundance

estimation, nor for estimating fishery-related mortality in Mexican waters. The ratio of DDE to DDT was

extraordinarily high in tissues of one bottlenose dolphin stranded on the Texas coast (Varanasi et al. 1992), suggesting

recent exposure to DDT which is still in use in Mexico. 

The Mississippi River outflow may constitute an effective ecological barrier to stock migration at the eastern

boundary. This assumption has not been tested and interbreeding may, in fact, occur between this and the northern

coastal stock at this boundary; therefore, the definition of this stock may be revised and the stock may be incorporated

with the northern coastal stock when more data become available. There are data which suggest that there is

considerable longshore movement by some members of the western coastal stock (NMFS unpublished data), but the

extent of this movement is unknown. 

Some of this stock may co-occur with the resident bay, sound, and estuarine stocks, and breeding may occur

among these stocks. For instance, two bottlenose dolphins previously seen in the South Padre Island area in Texas

were seen in Matagorda Bay, 285 km north, in May 1992 and May 1993 (Lynn 1995). These sightings suggest that

some bay stocks dolphins occasionally traverse the coastal stock area. 

Portions of this stock may co-occur with the U.S. Gulf of Mexico outer continental shelf (OCS) stock. The

seaward boundary for this stock corresponds to aerial survey strata (NMFS unpublished data) and thus, represents a

management boundary rather than an ecological boundary. Anecdotal evidence suggests that both the coastal and OCS

stocks consist of the shallow, warm water ecotype described by Hersh and Duffield (1990). Data are not currently

available to determine genetically if the two stocks should be separated or, if so, where; and interbreeding may occur

at the boundary interface. 

POPULATION SIZE

Preliminary abundance estimates were derived using distance sampling analysis (Buckland et al. 1993) and

the computer program DISTANCE (Laake et al. 1993) with sighting data collected during aerial line-transect surveys
149

in September-October 1992 (Blaylock and Hoggard 1994). Sampling transects extended orthogonally from shore out

to approximately 9 km past the 18 m isobath. The 1992 coastal survey area extended from the U.S. -Mexican border

to the Mississippi River mouth. Systematic transects were placed randomly with respect to bottlenose dolphin

distribution and provided approximately 5% visual coverage of the survey area. Bottlenose dolphin abundance was

estimated to be 3,499 dolphins (CV = 0.21) (Blaylock and Hoggard 1994). 

Minimum Population Estimate

The minimum population estimate was based on the1992 abundance estimate of 3,499 bottlenose dolphins

(CV = 0.21) (Blaylock and Hoggard 1994). The minimum population estimate is the lower limit of the two-tailed 60%

confidence interval of the log-normal distributed abundance estimate, which is equivalent to the 20th percentile of the

log-normal distribution as specified by NMFS (Anon. 1994). The minimum population estimate is 2,938 bottlenose

dolphins. 

Current Population Trend

 Aerial surveys of this area conducted by NMFS in autumn 1983 resulted in an estimated bottlenose dolphin

abundance of 4,718 (CV = 0.10). The data are not sufficient to conduct a statistical trend analysis, but the current

population size estimate is significantly lower than the 1983 estimate (Student's t-test, P < 0.001) and suggests a

decline in stock abundance. 

This stock was subject to higher than usual mortality levels in 1990, 1992, and 1993-94, and the incidence

of bottlenose dolphin strandings along the Texas coast in those years was significantly higher than the 1984-94 mean

stranding rate (Southeast U.S. Marine Mammal Stranding Network unpublished data). Some of these mortalities may

have been related to accumulation of anthropogenic hydrocarbon contaminants. A recent study indicated an inverse

relationship between hydrocarbon contaminant levels and certain bacterial and viral antigen titers in bottlenose

dolphins from Matagorda Bay, Texas (Reif et al., in preparation). 

CURRENT AND MAXIMUM NET PRODUCTIVITY RATES

Current and maximum net productivity rates are not known for this stock. The maximum net productivity

rate was assumed to be 0.04 for purposes of this assessment. This value is based on theoretical calculations showing

that cetacean populations may not generally grow at rates much greater than 4% given the constraints of their

reproductive life history (Reilly and Barlow 1986). 

POTENTIAL BIOLOGICAL REMOVAL

Potential biological removal (PBR) has been specified as the product of minimum population size, one-half

the maximum productivity rate, and a "recovery" factor for endangered, depleted, threatened stocks, or stocks of

unknown status relative to optimum sustainable population size (OSP). The recovery factor was set at 0.50 because

of the stock's unknown status relative to optimum sustainable population levels, because of an undetermined level of

fishery-related mortality, and because of the recent occurrence of three anomalous mortality events. PBR for this stock

is 29 dolphins. 

ANNUAL HUMAN-CAUSED MORTALITY AND SERIOUS INJURY

The level of direct human-caused mortality in this stock is unknown. An annual mean of 13 (CV = 0.46)

bottlenose dolphins stranded on the Texas coast during the period 1988-1993, showing signs of fishery interactions

such as net entanglement, mutilation, gunshot wounds, etc. (Southeast U.S. Marine Mammal Stranding Network

unpublished data). This was 10.3% of the total bottlenose dolphin strandings reported for this area. 

 There are a number of difficulties associated with the interpretation of stranding data. It is possible that some

or all of the stranded dolphins may have been from a bay, sound or estuarine stock; however, the proportion of the

stranded dolphins belonging to another stock cannot be determined because of the difficulty of determining from where

the stranded carcass originated. Stranding data probably underestimate the extent of fishery-related mortality and

serious injury because not all of the dolphins which die or are seriously injured in fishery interactions wash ashore, nor

will all of those that do wash ashore necessarily show signs of entanglement or other fishery-interaction. Finally, the

level of technical expertise among stranding network personnel varies widely as does the ability to recognize signs of

fishery interaction.
150

The total fishery-related mortality and serious injury for this stock is not less than 10% of the calculated PBR

and, therefore, cannot be considered to be insignificant and approaching zero mortality and serious injury rate. This

determination cannot be made for specific fisheries until the implementing regulations for Section 118 of the MMPA

have been reviewed by the public and finalized. 

Fisheries Information

Annual fishing effort for the shrimp trawl fishery in the western Gulf of Mexico coastal stock area during

1988-1993 averaged approximately 0.35 million hours of tows (CV = 0.16) (NMFS unpublished data). This fishery

was monitored by NMFS observers in 1992 and 1993, but less than 1% of the fishing effort was observed (NMFS

unpublished data). There have been no reports of incidental mortality or injury in the western Gulf of Mexico coastal

bottlenose dolphin stock associated with the shrimp trawl fishery in this area. 

 The menhaden purse seine fishery targets the Atlantic menhaden, Brevortia tyrannus, in Gulf of Mexico

coastal waters approximately 3-18 m in depth (NMFS 1991). Seventy-five menhaden vessels operate within 1.6 km

of shore from Apalachicola, Florida to Freeport, Texas, from April-October. Lethal takes of bottlenose dolphins

reported by the menhaden fishery during the period 1982-1988 ranged between 0-4 dolphins annually (NMFS

unpublished data). 

Gillnets are not used in Texas, and gillnets over 46 m3 in area will not be allowed in Florida past July 1995,

but fixed and runaround gillnets are currently in use in Louisiana, Mississippi, and Alabama. These fisheries, for the

most part, operate year around. They are state-controlled and licensed, and vary widely in intensity and target species.

No marine mammal mortalities associated with gillnet fisheries have been reported in these states, but stranding data

suggest that gillnet and marine mammal interaction does occur, causing mortality and serious injury. 

The fishery for blue crabs operates in estuarine areas throughout the Gulf coast employing traps attached to

a buoy with rope. Bottlenose dolphins have been reported stranded in Mississippi with polypropylene rope around their

flukes indicating the possibility of entanglement with crab pot lines (NMFS 1991); however, this fishery has not been

monitored by observers. 

Two bottlenose dolphins were entangled and died in a scientific research net fishery for sea turtles in Sabine

Pass in 1993 (A. Landry, Texas A&M University, report to Texas Marine Mammal Stranding Network, August 1993).

The nets used in this Endangered Species Act (ESA) permitted research activity were two 4.9 m deep x 91.5 m in

length stationary entanglement nets adjacent to each other. They were fished in shallow water (0.9-2.5 m depth),

monitored continuously throughout the day, and removed at night. 

Other Mortality

The coast adjacent to the nearshore habitat occupied by this stock varies from agricultural to industrial and,

in some places, such as Galveston Island, is dense in human population. Concentrations of chlorinated hydrocarbons

and metals were relatively low in most of the bottlenose dolphins examined in conjunction with an anomalous mortality

event in Texas bays in 1990; however, some had concentrations at levels of possible toxicological concern (Varanasi

et al. 1992). Agricultural runoff following periods of high rainfall in 1992 was implicated in a high level of bottlenose

dolphin mortalities in Matagorda Bay, which is adjacent to the western coastal stock area (NMFS unpublished data).

A recent study of hydrocarbon contaminant levels was conducted in conjunction with a health assessment

study of 35 live-captured bottlenose dolphins in Matagorda Bay which adjoins the coastal stock area. Alpha-HCB,

p,p,DDE, and PCB concentrations were inversely related to the magnitude of the serum antibody titer to Erysipelas

spp. and Staphylococcus spp. bacteria (Reif et al., in preparation.). A similar and more pronounced trend was seen

in relationship to the pseudorabies virus; however, since pseudorabies virus is not known to infect bottlenose dolphins,

the significance of this finding is not clear. Concentrations of contaminants were higher in dolphins having evidence

of exposure to the cetacean morbillivirus. The reason for the difference in the relationship between antibody titers to

bacteria and pseudorabies and antibody titers to cetacean morbillivirus is not understood. 

STATUS OF STOCK

The status of this stock relative to OSP is unknown. A population trend analysis is not available due to

insufficient information. This species is not listed as threatened or endangered under the ESA. The occurrence of

three anomalous mortality events among bottlenose dolphins along the Texas coast since 1990 (NMFS unpublished
151

data) is cause for concern and the available evidence suggests that bottlenose dolphin stocks in the northern and

western portion of the U.S. Gulf of Mexico may have experienced a morbillivirus epidemic in 1993 (Lipscomb 1993);

however, the effects of these events on stock abundance has yet to be determined. This is not a strategic stock because

the known level of fishery-related mortality or serious injury does not exceed PBR. 

REFERENCES

Anon. 1994. Report of the PBR (Potential Biological Removal) workshop. June 27-29, 1994. NOAA, NMFS

Southwest Fisheries Science Center, La Jolla, California, 13 pp. + Appendices. 

Blaylock R. A. and W. Hoggard. 1994. Preliminary estimates of bottlenose dolphin abundance in southern U.S.

Atlantic and Gulf of Mexico continental shelf waters. NOAA Tech. Mem. NMFS-SEFSC-356, 10 pp. 

Buckland, S. T., D. R. Anderson, K. P. Burnham, and J. L. Laake. 1993. Distance sampling: Estimating abundance

of biological populations. Chapman & Hall, London, 446 pp. 

Hersh, S. L. and D. A. Duffield. 1990. Distinction between northwest Atlantic offshore and coastal bottlenose

dolphins based on hemoglobin profile and morphometry. Pages 129-139 in S. Leatherwood and R. R. Reeves

(editors), The bottlenose dolphin, Academic Press, San Diego, 653 pp. 

Laake, J. L., S. T. Buckland, D. R. Anderson, and K. P. Burnham. DISTANCE user’s guide, V2.0. Colorado

Cooperative Fish & Wildlife Research Unit, Colorado State University, Ft. Collins, Colorado, 72 pp. 

Lipscomb, T. P. 1993. Some answers to questions about morbillivirus. Pages 4-5 in R. A. Blaylock, B. Mase, and

D. K. Odell (editors), Strandings - Newsletter of the Southeast U.S. Marine Mammal Stranding Network, Vol.

2 No. 3, Southeast Fisheries Science Center, Miami Laboratory, Miami, Florida, 8 pp. 

NMFS. 1991. Proposed regime to govern the interactions between marine mammals and commercial fishing

operations after October 1, 1993. Draft Environmental Impact Statement. June 1991. 

Reif, J. S., L. J. Hansen, S. Galloway, G. Mitchum, T. L. Schmitt. In preparation. The relationship between

chlorinated hydrocarbon contaminants and selected health parameters in bottlenose dolphins (Tursiops

truncatus) from Matagorda Bay, Texas, 1992. Colorado State University, Fort Collins, and NMFS, Southeast

Fisheries Science Center, Miami, Florida. 

Reilly, S. B. and J. Barlow. 1986. Rates of increase in dolphin population size. Fish. Bull., U.S. 84(3): 527-533. 

Varanasi, U., K. L. Tilbury, D. W. Brown, M. M. Krahn, C. A. Wigren, R. C. Clark, and S-L. Chan. 1992. Pages

56-86 in L. J. Hansen (editor), Report on investigation of 1990 Gulf of Mexico bottlenose dolphin strandings,

Southeast Fisheries Science Center Contribution MIA-92/93-21, 219 pp. 
152

Figure 1. Sightings of coastal bottlenose dolphins during GOMEX aerial surveys of

the Gulf of Mexico in 1992-1994. Northern Gulf of Mexico coastal bottlenose dolphin

stock is shown with filled circles. Isobaths are in 183 m (100 fm) intervals.

BOTTLENOSE DOLPHIN (Tursiops truncatus):

Northern Gulf of Mexico Coastal Stock

STOCK DEFINITION AND GEOGRAPHIC RANGE

The northern Gulf of Mexico coastal bottlenose dolphin stock has been defined for management purposes as

those bottlenose dolphins occupying the nearshore coastal waters in the U.S. Gulf of Mexico from the Mississippi River

mouth to approximately 84o W longitude, from shore, barrier islands, or presumed bay boundaries to 9.3 km seaward

of the 18.3 m isobath (Fig. 1). As a working hypothesis, it is assumed that the dolphins occupying habitats with

dissimilar climactic, coastal, and oceanographic characteristics might be restricted in their movements between habitats

and, thus, constitute separate stocks. The northern coastal stock area is characterized by a temperate climate, barrier

islands, sand beaches, coastal

marshes and marsh islands, and

has a relatively high level of

fresh water input from rivers

and streams. It is bordered on

the east by an extensive area of

coastal marsh and marsh islands

typical of Florida’s Apalachee

Bay. The western coastal area

is characterized by an arid to

temperate climate, sand beaches,

and low fresh water input. The

eastern coastal stock area is

temperate to subtropical in

climate, is bordered by a mixture

of coastal marshes, sand

beaches, marsh and mangrove

islands, and has an intermediate

level of freshwater input.

The definition of this stock may be changed and it may be incorporated with other Gulf of Mexico stocks when

more data become available. Seasonal changes in bottlenose dolphin abundance in Mississippi Sound (NMFS

unpublished data) suggests that there is interchange with at least that portion of the Gulf of Mexico bay and sound

stocks; however, its extent and significance is not presently known. Portions of this stock may co-occur with the U.S.

Gulf of Mexico outer continental shelf (OCS) stock. The seaward boundary for this stock corresponds to aerial survey

strata (NMFS unpublished data) and thus, represents a management boundary rather than an ecological boundary.

Anecdotal evidence suggests that both the coastal and OCS stocks consist of the shallow, warm water ecotype described

by Hersh and Duffield (1990). Data are not currently available to determine genetically if the stocks should be

separated or, if so, where; and interbreeding may occur at the boundary interface. 

POPULATION SIZE

Preliminary estimates of abundance were derived using distance sampling analysis (Buckland et al.1993) and

the computer program DISTANCE (Laake et al. 1993) with sighting data collected during aerial line-transect surveys

in September-October 1993 (Blaylock and Hoggard 1994). Systematic sampling transects, placed randomly with

respect to the bottlenose dolphin distribution, extended orthogonally from shore out to approximately 9 km past the

18 m isobath. The area surveyed extended from the Mississippi River mouth to approximately 84o W Longitude, and

approximately 5% of the total area was visually searched. Bottlenose dolphin abundance was estimated to be 4,191

dolphins with coefficient of variation (CV) = 0.21 (Blaylock and Hoggard 1994). 
153

Minimum Population Estimate

The minimum population estimate was based on the 1993 abundance estimate of 4,191 dolphins (CV = 0.21)

(Blaylock and Hoggard 1994). The minimum population estimate is the lower limit of the two-tailed 60% confidence

interval of the log-normal distributed abundance estimate, which is equivalent to the 20th percentile of the log-normal

distribution as specified by NMFS (Anon. 1994). The minimum population estimate is 3,518 bottlenose dolphins. 

Current Population Trend

 Aerial surveys of this area conducted partly in autumn 1983 and partly in autumn 1985, by NMFS resulted

in an estimated bottlenose dolphin abundance of 1,319 (CV = 0.10). The data are not sufficient to conduct a statistical

trend analysis, but the current population size estimate is significantly higher than the 1983-85 estimate (Student's ttest, P < 0.005). 

CURRENT AND MAXIMUM NET PRODUCTIVITY RATES

Current and maximum net productivity rates for this stock are unknown. The maximum net productivity rate

was assumed to be 0.04 for purposes of this assessment. This value is based on theoretical calculations showing that

cetacean populations may not generally grow at rates much greater than 4% given the constraints of their reproductive

life history (Reilly and Barlow 1986). 

POTENTIAL BIOLOGICAL REMOVAL

Potential biological removal (PBR) has been specified as the product of minimum population size, one-half

the maximum productivity rate, and a "recovery" factor for endangered, depleted, threatened stocks, or stocks of

unknown status relative to optimum sustainable population size (OSP). The recovery factor was set at 0.50 because

of the stock's unknown status relative to optimum sustainable population levels, because the stock apparently sustains

some unknown level of fishery-related mortality, and because of the unknown effects of the 1993 mortality event. PBR

for this stock is 35 dolphins. 

ANNUAL HUMAN-CAUSED MORTALITY AND SERIOUS INJURY

The level of direct human-caused mortality in this stock is unknown. An annual average of ten bottlenose

dolphins (CV = 0.41) stranded on the coast of Louisiana, Mississippi, or Alabama during the period 1988-1993,

showing signs of fishery interactions such as net entanglement, mutilation, gunshot wounds, etc. (Southeast U.S.

Marine Mammal Stranding Network unpublished data). This was 8.2% of the total bottlenose dolphin strandings

reported for this area. There are a number of difficulties associated with the interpretation of stranding data. It

is possible that some or all of the stranded dolphins may have been from a bay, sound or estuarine stock; however, the

proportion of the stranded dolphins belonging to another stock cannot be determined because of the difficulty of

determining from where the stranded carcass originated. Stranding data probably underestimate the extent of fisheryrelated mortality and serious injury because not all of the dolphins which die or are seriously injured in fishery

interactions wash ashore, nor will all of those that do wash ashore necessarily show signs of entanglement or other

fishery-interaction. Finally, the level of technical expertise among stranding network personnel varies widely as does

the ability to recognize signs of fishery interaction.

The total fishery-related mortality and serious injury for this stock is unknown, but considering the evidence

from stranding data, it may not be less than 10% of the calculated PBR and, therefore, cannot be considered to be

insignificant and approaching zero mortality and serious injury rate. This determination cannot be made for specific

fisheries until the implementing regulations for Section 118 of the MMPA have been reviewed by the public and

finalized. 

Fisheries Information

Annual fishing effort for the shrimp trawl fishery in the northern Gulf of Mexico coastal stock area during

1988-1993 averaged approximately 2.17 million hours of tows (CV = 0.13) (NMFS unpublished data). This fishery

was monitored by NMFS observers in 1992 and 1993, but less than 1% of the fishing effort was observed (NMFS

unpublished data). There have been no reports of incidental mortality or injury in the northern Gulf of Mexico coastal

bottlenose dolphin stock associated with the shrimp trawl fishery in this area. 
154

 The menhaden purse seine fishery targets the Atlantic menhaden, Brevortia tyrannus, in Gulf of Mexico

coastal waters approximately 3-18 m in depth (NMFS 1991). Seventy-five menhaden vessels operate within 1.6 km

of shore from Apalachicola, Florida to Freeport, Texas, from April-October. Lethal takes of bottlenose dolphins

reported by the menhaden fishery during the period 1982-1988 ranged between 0-4 dolphins annually (NMFS

unpublished data). 

Other clupeid purse seiners opportunistically target Spanish sardine, thread herring, ladyfish, cigarfish, and

blue runners. Single boat purse seiners, fishing for sardines and herrings, operate in coastal waters between the

Mississippi River delta and Pascagoula, Mississippi and in the Florida panhandle between Pensacola and Apalachicola.

It is estimated that ten vessels participate in this fishery between May-October. There are no estimates of dolphin

mortality associated with this fishery. 

Gillnets are not used in Texas, and gillnets over 46 m3 in area will not be allowed in Florida past July 1995,

but fixed and runaround gillnets are currently in use in Louisiana, Mississippi, and Alabama. These fisheries, for the

most part, operate year around. They are state-controlled and licensed, and vary widely in intensity and target species.

No marine mammal mortalities associated with gillnet fisheries have been reported in these states, but stranding data

suggest that gillnet and marine mammal interaction does occur, causing mortality and serious injury. 

The fishery for blue crabs operates in estuarine areas throughout the Gulf coast employing traps attached to

a buoy with rope. Bottlenose dolphins have been reported stranded in Mississippi with polypropylene rope around their

flukes indicating the possibility of entanglement with crab pot lines (NMFS 1991); however, this fishery has not been

monitored by observers. 

Other Mortality

The nearshore habitat occupied by this stock is adjacent to areas of high human population. Two stranded

dolphins from the northern Gulf coastal area (one from Mississippi and one from Alabama) had the highest levels of

DDT derivatives of any of the bottlenose dolphin liver samples analyzed in conjunction with the 1990 mortality

investigation conducted by NMFS (Varanasi et al. 1992). The significance of these findings are unclear, but there is

some evidence that increased exposure to anthropogenic compounds may reduce immune function in bottlenose

dolphins. A recent study found the magnitude of the serum antibody titer to Erysipelas spp. and Staphylococcus spp.

bacteria in bottlenose dolphins was inversely related to á-HCB, p,p,DDE, and PCB's concentrations (Reif et al., in

preparation). 

This stock was subject to a high incidence of mortality in 1993, which was suspected to have been the result

of a morbillivirus epidemic. The effect of this mortality event on the stock cannot be determined, in part, because the

mortality may have also affected the bay, sound and estuarine stock and the stock identity of the stranded animals could

not be determined. The increase in mortalities began in the Florida panhandle area and moved westward during that

period (NMFS unpublished data). Concentrations of contaminants were found to be higher in dolphins having

evidence of exposure to the cetacean morbillivirus (Reif et al., in preparation). The reason for the relationship between

cetacean morbillivirus antibody titers and high contaminant levels is not understood and the effect of the epidemic on

this stock has not been determined. 

STATUS OF STOCK

The status of this stock relative to OSP is not known and population trends cannot be determined due to

insufficient data. This species is not listed as threatened or endangered under the Endangered Species Act. This is

not a strategic stock because the known level of fishery-related mortality or serious injury does not exceed PBR. 

REFERENCES

Anon. 1994. Report of the PBR (Potential Biological Removal) workshop. June 27-29, 1994. NOAA, NMFS

Southwest Fisheries Science Center, La Jolla, California, 13 pp. + Appendices. 

Blaylock, R. A. and W. Hoggard. 1994. Preliminary estimates of bottlenose dolphin abundance in southern U.S.

Atlantic and Gulf of Mexico continental shelf waters. NOAA Tech. Mem. NMFS-SEFSC-356, 10 pp. 

Buckland, S. T., D. R. Anderson, K. P. Burnham, and J. L. Laake. 1993. Distance sampling: Estimating abundance

of biological populations. Chapman & Hall, London, 446 pp. 
155

Hersh, S. L. and D. A. Duffield. 1990. Distinction between northwest Atlantic offshore and coastal bottlenose

dolphins based on hemoglobin profile and morphometry. Pages 129-139 in S. Leatherwood and R. R. Reeves

(editors), The bottlenose dolphin, Academic Press, San Diego, 653 pp. 

Laake, J. L., S. T. Buckland, D. R. Anderson, and K. P. Burnham. DISTANCE user’s guide, V2.0. Colorado

Cooperative Fish & Wildlife Research Unit, Colorado State University, Ft. Collins, Colorado, 72 pp. 

Lipscomb, T. P. 1993. Some answers to questions about morbillivirus. Pages 4-5 in R. A. Blaylock, B. Mase, and

D. K. Odell (editors), Strandings - Newsletter of the Southeast U.S. Marine Mammal Stranding Network, Vol.

2 No. 3, Southeast Fisheries Science Center, Miami Laboratory, Miami, Florida, 8 pp. 

NMFS. 1991. Proposed regime to govern the interactions between marine mammals and commercial fishing

operations after October 1, 1993. Draft Environmental Impact Statement. June 1991. 

Reif, J. S., L. J. Hansen, S. Galloway, G. Mitchum, T. L. Schmitt. In preparation. The relationship between

chlorinated hydrocarbon contaminants and selected health parameters in bottlenose dolphins (Tursiops

truncatus) from Matagorda Bay, Texas, 1992. Colorado State University, Fort Collins, and NMFS, Southeast

Fisheries Science Center, Miami, Florida. 

Reilly, S. B. and J. Barlow. 1986. Rates of increase in dolphin population size. Fish. Bull., U.S. 84(3): 527-533. 
156

Figure 1. Sightings of coastal bottlenose dolphins during GOMEX aerial surveys of

the Gulf of Mexico in 1992-1994. Eastern Gulf of Mexico coastal bottlenose dolphin

stock is shown with filled circles. Isobaths are in 183 m (100 fm) intervals.

BOTTLENOSE DOLPHIN (Tursiops truncatus):

Eastern Gulf of Mexico Coastal Stock

STOCK DEFINITION AND GEOGRAPHIC RANGE

 The eastern Gulf of Mexico coastal bottlenose dolphin stock has been defined for management purposes as

the bottlenose dolphins occupying the area which extends from approximately 84o W Longitude to Key West, Florida,

from shore, barrier islands, or presumed bay boundaries to 9.3 km seaward of the 18.3 m isobath (Fig. 1). As a

working hypothesis, it is assumed that the dolphins occupying habitats with dissimilar climactic, coastal, and

oceanographic characteristics might be restricted in their movements between habitats and, thus, constitute separate

stocks. The eastern coastal stock area is temperate to subtropical in climate, is bordered by a mixture of coastal

marshes, sand beaches, marsh

and mangrove islands, and has

an intermediate level of

freshwater input. It is bordered

on the north by an extensive area

of coastal marsh and marsh

islands typical of Florida’s

Apalachee Bay. The western

coastal area is characterized by

an arid to temperate climate,

sand beaches, and low fresh

water input. The northern

coastal stock area is

characterized by a temperate

climate, barrier islands, sand

beaches, coastal marshes and

marsh islands, and has a

relatively high level of fresh

water input from rivers and streams.

Portions of this stock may co-occur with the U.S. Gulf of Mexico outer continental shelf (OCS) stock. The

seaward boundary for this stock corresponds to aerial survey strata (NMFS unpublished data) and thus, represents a

management boundary rather than an ecological boundary. Anecdotal evidence suggests that both the coastal and OCS

stocks consist of the shallow, warm water ecotype described by Hersh and Duffield (1990). Data are not currently

available to determine genetically if the two stocks should be separated or, if so, where; and interbreeding may occur

at the boundary interface. 

POPULATION SIZE

Preliminary estimates of abundance were derived using distance sampling analysis (Buckland et al. 1993)

and the computer program DISTANCE (Laake et al. 1993) with sighting data collected during aerial line-transect

surveys conducted during autumn 1994 (NMFS unpublished data). Systematic sampling transects, placed randomly

with respect to the bottlenose dolphin distribution, extended orthogonally from shore out to approximately 9 km past

the 18 m isobath. Approximately 5% of the total survey area was visually searched. Bottlenose dolphin abundance

was estimated to be 9,912 dolphins with coefficient of variation (CV) = 0.12. 

Minimum Population Estimate

The minimum population estimate was based on the 1994 abundance estimate of 9,912 (CV = 0.12) (NMFS

unpublished data). The minimum population estimate is the lower limit of the two-tailed 60% confidence interval of

the log-normal distributed abundance estimate, which is equivalent to the 20th percentile of the log-normal distribution

as specified by NMFS (Anon. 1994). The minimum population estimate is 8,963 bottlenose dolphins. 
157

Current Population Trend

Aerial surveys of this area conducted by NMFS in autumn 1985, resulted in an estimated bottlenose dolphin

abundance of 4,711 (CV = 0.05). The data are not sufficient to conduct a statistical trend analysis, but the current

population size estimate is significantly higher than the 1985 estimate (Student's t-test, P < 0.0005). 

CURRENT AND MAXIMUM NET PRODUCTIVITY RATES

Current and maximum net productivity rates are not known for this stock. The maximum net productivity

rate was assumed to be 0.04 for purposes of this assessment. This value is based on theoretical calculations showing

that cetacean populations may not generally grow at rates much greater than 4% given the constraints of their

reproductive life history (Reilly and Barlow 1986). 

POTENTIAL BIOLOGICAL REMOVAL

Potential biological removal (PBR) has been specified as the product of minimum population size, one-half

the maximum productivity rate, and a "recovery" factor for endangered, depleted, threatened stocks, or stocks of

unknown status relative to optimum sustainable population size (OSP). The recovery factor was set at 0.50 because

of the stock's unknown status relative to OSP. PBR for this stock is 90 dolphins. 

ANNUAL HUMAN-CAUSED MORTALITY AND SERIOUS INJURY

The level of direct human-caused mortality in this stock is unknown. An annual mean of eight bottlenose

dolphins (CV = 0.41) stranded on the Florida Gulf coast during the period 1988-1993, showing signs of fishery

interactions such as net entanglement, mutilation, gunshot wounds, etc. (Southeast U.S. Marine Mammal Stranding

Network unpublished data). This was 8.9% of the total bottlenose dolphin strandings reported for this area. Morgan

and Patton (1990) reported that 12.9% of 116 cetaceans examined by Mote Marine Laboratory's marine mammal

stranding response program on the west coast of Florida between 1984 and 1990 exhibited evidence of human-caused

mortality or serious injury. 

 There are a number of difficulties associated with the interpretation of stranding data. It is possible that some

or all of the stranded dolphins may have been from a bay, sound or estuarine stock; however, the proportion of the

stranded dolphins belonging to another stock cannot be determined because of the difficulty of determining from where

the stranded carcass originated. Stranding data probably underestimate the extent of fishery-related mortality and

serious injury because not all of the dolphins which die or are seriously injured in fishery interactions wash ashore, nor

will all of those that do wash ashore necessarily show signs of entanglement or other fishery-interaction. Finally, the

level of technical expertise among stranding network personnel varies widely as does the ability to recognize signs of

fishery interaction.

The total known fishery-related mortality and serious injury for this stock is less than 10% of the calculated

PBR and, therefore, can be considered to be insignificant and approaching zero mortality and serious injury rate. This

determination cannot be made for specific fisheries until the implementing regulations for Section 118 of the MMPA

have been reviewed by the public and finalized. 

Fisheries Information

Annual fishing effort for the shrimp trawl fishery in the eastern Gulf of Mexico coastal stock area during

1988-1993 averaged approximately 0.102 million hours of tows (CV = 0.30) (NMFS unpublished data). This fishery

was monitored by NMFS observers in 1992 and 1993, but less than 1% of the fishing effort was observed (NMFS

unpublished data). There was one report in 1992 of an incidental mortality in the eastern Gulf of Mexico coastal

bottlenose dolphin stock which was associated with the shrimp trawl fishery in this area. 

Gillnets are not used in Texas, and gillnets over 46 m3 in area will not be allowed in Florida past July 1995,

but fixed and runaround gillnets are currently in use in Louisiana, Mississippi, and Alabama. These fisheries, for the

most part, operate year around. They are state-controlled and licensed, and vary widely in intensity and target species.

No marine mammal mortalities associated with gillnet fisheries have been reported in these states, but stranding data

suggest that gillnet and marine mammal interaction does occur, causing mortality and serious injury. A coastal gillnet

fishery for menhaden was reported to have taken one bottlenose dolphin in 1991 (NMFS unpublished data). There are

no effort data available for this fishery. 
158

The menhaden purse seine fishery targets the Atlantic menhaden, Brevortia tyrannus, in Gulf of Mexico

coastal waters approximately 3-18 m in depth (NMFS 1991). Seventy-five menhaden vessels operate within 1.6 km

of shore from Apalachicola, Florida to Freeport, Texas, from April-October. Lethal takes of bottlenose dolphins

reported by the menhaden fishery during the period 1982-1988 ranged between 0-4 dolphins annually (NMFS

unpublished data). 

Other clupeid purse seiners opportunistically target Spanish sardine, thread herring, ladyfish, cigarfish, and

blue runners. There are no effort data available for this fishery and there are no estimates of dolphin mortality

associated with this fishery. 

A fishery for blue crabs operates in estuarine areas throughout the Gulf coast employing traps attached to a

buoy with rope. Bottlenose dolphins have been reported stranded in other coastal locations in the Gulf of Mexico with

polypropylene rope around their flukes indicating the possibility of entanglement with crab pot lines (NMFS 1991);

however, this fishery has not been monitored by observers. 

Other Mortality

The nearshore habitat occupied by this stock is adjacent to areas of high human population and in some areas

of Florida, such as the Tampa Bay area, is highly industrialized. PCB concentrations in three stranded dolphins

sampled from this stock ranged from 16-46 Fg/g wet weight. Concentrations of á-HCB, p,p,DDE, and PCB's were

inversely related to the magnitude of the serum antibody titer to Erysipelas spp. and Staphylococcus spp. bacteria in

a study of bottlenose dolphins in Texas (Reif et al., in preparation). A similar and more pronounced trend was seen

in relationship to the pseudorabies virus; however, since pseudorabies virus is not known to infect bottlenose dolphins,

the significance of this finding is not clear. Concentrations of contaminants were higher in dolphins having evidence

of exposure to the cetacean morbillivirus. The reason for the difference in the relationship between antibody titers to

bacteria and pseudorabies and antibody titers to cetacean morbillivirus is not understood. 

STATUS OF STOCK

The status of this stock relative to OSP is not known and population trends cannot be determined due to

insufficient data. This species is not listed as threatened or endangered under the Endangered Species Act. This is

not a strategic stock because the known level of fishery-related mortality or serious injury does not exceed PBR. 

REFERENCES

Anon. 1994. Report of the PBR (Potential Biological Removal) workshop. June 27-29, 1994. NOAA, NMFS

Southwest Fisheries Science Center, La Jolla, California, 13 pp. + Appendices. 

Buckland, S. T., D. R. Anderson, K. P. Burnham, and J. L. Laake. 1993. Distance sampling: Estimating abundance

of biological populations. Chapman & Hall, London, 446 pp. 

Laake, J. L., S. T. Buckland, D. R. Anderson, and K. P. Burnham. DISTANCE user’s guide, V2.0. Colorado

Cooperative Fish & Wildlife Research Unit, Colorado State University, Ft. Collins, Colorado, 72 pp. 

Morgan, M. A. and G. W. Patton. 199 0. Human dolphin interactions on the west coast of Florida: Documentation

from MML's marine mammal response program. MML Technical Report #191, 9 pp. 

NMFS. 1991. Proposed regime to govern the interactions between marine mammals and commercial fishing

operations after October 1, 1993. Draft Environmental Impact Statement. June 1991. 

Reilly, S. B. and J. Barlow. 1986. Rates of increase in dolphin population size. Fish. Bull., U.S. 84(3): 527-533. 
159

BOTTLENOSE DOLPHIN (Tursiops truncatus):

Gulf of Mexico Bay, Sound, and Estuarine Stocks

STOCK DEFINITION AND GEOGRAPHIC RANGE

Studies relying on identification of individual dolphins (Scott et al. 1990; Wells 1986a) suggest that bottlenose

dolphins inhabiting many of the bays, sounds, and other estuaries adjacent to the Gulf of Mexico form discrete

communities. Although breeding may occur between adjacent communities, the geographic nature of these areas

suggests that each community exists as a functioning unit of its ecosystem and, under the Marine Mammal Protection

Act, must be maintained as such. Therefore, each of those areas forming a contiguous, enclosed or semi-enclosed body

of water is considered to contain a distinct bottlenose dolphin stock and will be reported as such within this report.

However, because there are insufficient data currently available with which to evaluate fisheries within each area, a

separate stock assessment report will not be prepared for each local stock at this time. 

Mark-recapture studies using photo-identification of individual dolphins in the vicinity of Sarasota and Tampa

Bays in Florida showed that individual dolphins remained in a given area year around (Scott et al. 1990). Wells

(1986a) described three distinct dolphin "communities" in the area in and around Sarasota Bay. One community was

formed by dolphins residing in the Gulf of Mexico coastal waters, another consisted of the dolphins in the deep water

areas of Passage Key Inlet and Tampa Bay (adjacent to Sarasota Bay), and a third community resided in the shallow

waters of Sarasota Bay. Electrophoretic isozyme analysis showed significant differences between dolphins of the

shallow water Sarasota community and the Tampa Bay community, and from dolphins from Charlotte Harbor, to the

south; however, there was a high degree of genetic heterozygosity indicating that the Sarasota community was not

genetically isolated (Duffield and Wells 1986). Wells (1986b) suggested that the Sarasota community is likely one of

a number of communities which comprise a population, the limits of which are unknown. He suggested that the

continuous distribution of bottlenose dolphins around the Gulf of Mexico coast theoretically allows genetic exchange

between adjacent communities; however, he also noted that the females of the highly-structured Sarasota community

form a stable, discrete, long-term breeding unit with strong geographical fidelity (Wells 1986b). Depletion of a

bottlenose dolphin community within a restricted geographical area could have a deleterious effect on its ability to

recover. Conservative management practice dictates that such a community be treated as a stock for managing

interactions with fisheries. 

Recent photo-identification and radio-tracking studies confirmed that some individuals remained in the same

general areas within Matagorda Bay, Texas, throughout the year (Lynn 1995); thus, the situation there may be similar

to that of the Florida west coast. Movement by resident bottlenose dolphins in Texas through passes linking bays with

the Gulf of Mexico appears to be relatively limited (Shane 1977; Gruber 1981; McHugh 1989; Lynn 1995), but it

apparently does occur and these stocks may not be reproductively isolated from the coastal stocks. Two bottlenose

dolphins previously seen in the South Padre Island, Texas, coastal area were seen in Matagorda Bay, 285 km north,

in May 1992 and May 1993 (Lynn 1995). Preliminary analyses of MtDNA using polymerase chain reaction procedures

suggested that Matagorda Bay dolphins appear to be a localized population (NMFS unpublished data). Over 1,000

individual bottlenose dolphins have been identified in bay and coastal waters near the northeast end of Galveston

Island, Texas ( Bräger et al. 1994; Bräger 1992, 1993; Henningsen 1991), but most of these were sighted only once

and approximately 200 individuals were reported to use the area over the long term (Bräger et al. 1994). 

Much less is known about the movements of resident bottlenose dolphins in estuaries of the northern Gulf of

Mexico. There are observed seasonal differences in bottlenose dolphin abundance in Mississippi Sound that suggest

seasonal migration (NMFS unpublished data); however, the spatial migration patterns are not currently known. It

appears probable that some exchange occurs between the Mississippi Sound stock and the coastal stock in this area.

Additional information may result in the future combining of these stocks in this area. 

POPULATION SIZE

Population size (Table I) for all of the stocks except Sarasota Bay, Florida, was estimated from preliminary

analyses of line-transect data collected during aerial surveys conducted in September-October 1992 in Texas and

Louisiana, in September-October 1993 in Louisiana, Mississippi, Alabama, and the Florida panhandle (Blaylock and

Hoggard 1994), and aerial surveys of the west coast of Florida in September-November 1994 (NMFS unpublished data).

Standard line transect perpendicular sighting distance analytical methods were used (Buckland et al. 1993) and the
160

Blocks Gulf of Mexico Estuary NBEST CV NMIN PBR Year Reference

B51 Laguna Madre 80 1.57 31 0.3 1992 Blaylock and Hoggard 1994

B52 Nueces Bay, Corpus Christi Bay 58 0.61 36 0.4 " "

B50 Compano Bay, Aransas Bay, San Antonio Bay, Redfish

Bay, Espirito Santo Bay 

55 0.82 30 0.3 " "

B54 Matagorda Bay, Tres Palacios Bay, Lavaca Bay 61 0.45 42 0.4 " "

B55 West Bay 29 1.10 14 0.1 " "

B56 Galveston Bay, East Bay, Trinity Bay 152 0.43 107 1.1 " "

B57 Sabine Lake 0 — 0 0.0 " "

B58 Calcasieu Lake 0 — 0 0.0 " "

B59 Vermillion Bay, West Cote Blanche Bay, Atchafalaya Bay 0 1 — 0 0.0 " "

B60 TerreBonne Bay, Timbalier Bay 100 0.53 66 0.7 1993 "

B61 Barataria Bay 219 0.55 142 1.4 " "

B30 Mississippi River Delta 0

 1 — 0 0.0 " "

B02-05,29,31 Bay Boudreau, Mississippi Sound 1,401 0.13 1,256 13 " "

B06 Mobile Bay, Bonsecour Bay 122 0.34 92 0.9 " "

B07 Perdido Bay 0

 1 — 0 0.0 " "

B08 Pensacola Bay, East Bay 33 0.80 18 0.2 " "

B09 Choctawhatchee Bay 242 0.31 188 1.9 " "

B10 St. Andrew Bay 124 0.57 79 0.8 " "

B11 St. Joseph Bay 0 — 0 0.0 " "

B12-13 St. Vincent Sound, Apalachicola Bay, St. Georges Sound 387 0.34 293 2.9 " "

B14-15 Apalachee Bay 491 0.39 358 3.6 " "

B16 Waccasassa Bay, Withlacoochee Bay, Crystal Bay 100 0.85 54 0.5 1994 "

B17 St. John's Sound, Clearwater Harbor 37 1.06 18 0.2 " "

B32-34 Tampa Bay 559 0.24 458 4.6 " "

B20 Sarasota Bay 97 na 397 1.0 1992 Wells 1992

B35 Little Sarasota Bay 2

 2 0.24 2 0.0 1985 Scott et al. 1989

B21 Lemon Bay 0

 1 — 0 0.0 1994 Blaylock and Hoggard 1994

B22-23 Pine Sound, Charlotte Harbor, Gasparilla Sound 209 0.38 153 1.5 " "

B36 Caloosahatchee River 0 1,2 — 0 0.0 1985 Scott et al. 1989

B24 Estero Bay 104 0.67 62 0.6 1994 Blaylock and Hoggard 1994

B25 Chokoloskee Bay, Ten Thousand Islands, Gullivan Bay 208 0.46 144 1.4 " "

B27 Whitewater Bay 242 0.37 179 1.8 " "

B28 Florida Keys (Bahia Honda Key to Key West) 29 1.00 14 0.1 " "

Table I. Bottlenose dolphin abundance (NBEST), coefficient of variation (CV), minimum population estimate (NMIN), and Potential

Biological Removal (PBR) in U.S. Gulf of Mexico bays, sounds, and other estuaries. Blocks refer to aerial survey blocks illustrated

in Fig. 1.

 Notes: 1Bottlenose dolphins not sighted during earlier surveys (Scott et al. 1989). 2Block not surveyed during surveys reported in

Blaylock and Hoggard (1994). 3No CV because NBEST was a direct count of known individuals. 

computer program DISTANCE (Laake et al. 1993). Stock size in Sarasota Bay, Florida, was obtained through direct

count of known individuals (Wells 1992). 

Minimum Population Estimate

The minimum population estimate (Table I) is the lower limit of the two-tailed 60% confidence interval of

the log-normal distributed abundance estimate, which is equivalent to the 20th percentile of the log-normal distribution

specified by NMFS (Anon. 1994). The minimum population estimate was calculated for each block from the estimated

population size and its associated coefficient of variation. Where the population size resulted from a direct count of

known individuals, the minimum population size was identical to the estimated population size. 

Current Population Trend

The data are insufficient to determine population trends. Three anomalous mortality events have occurred

among portions of this stock between 1990 and 1994; however, it is not possible to accurately partition the mortalities

between the bay and coastal stocks, thus the impact of these mortality events on these stocks is not known. 

CURRENT AND MAXIMUM NET PRODUCTIVITY RATES
161

Figure 1. U.S. Gulf of Mexico bays and sounds. Each of the alpha-numerically designated blocks corresponds to one of

the NMFS Southeast Fisheries Science Center logistical aerial surveys areas listed in Table I. The bottlenose dolphins

inhabiting each bay and sound are considered to comprise a unique stock for purposes of this assessment. 

Current and maximum net productivity rates are not known for this stock. The maximum net productivity

rate was assumed to be 0.04 for purposes of this assessment. This value is based on theoretical calculations showing

that cetacean populations may not generally grow at rates much greater than 4% given the constraints of their

reproductive life history (Reilly and Barlow 1986). 

POTENTIAL BIOLOGICAL REMOVAL

PBR has been specified as the product of minimum population size, one-half the maximum productivity rate,

and a "recovery" factor for endangered, depleted, threatened stocks, or stocks of unknown status relative to optimum

sustainable population size (OSP). The recovery factor was 0.50 because of the stocks' unknown status relative to OSP.

PBR for each stock is given in Table I. 

ANNUAL HUMAN-CAUSED MORTALITY AND SERIOUS INJURY

An annual mean of 30 bottlenose dolphins with coefficient of variation (CV) = 0.21 stranded on the coast in

the U.S. Gulf of Mexico during the period 1988-1993, showing signs of fishery interactions such as net entanglement,

mutilation, gunshot wounds, etc. (Southeast U.S. Marine Mammal Stranding Network unpublished data). This

represented 9.6% of the total bottlenose dolphin strandings reported for the entire U.S. Gulf of Mexico. Morgan and

Patton (1990) reported that 12.9% of 116 cetacean carcasses examined by Mote Marine Laboratory's marine mammal

stranding response program on the west coast of Florida between 1984 and 1990 exhibited evidence of human-caused

mortality or serious injury.

 There are a number of difficulties associated with the interpretation of stranding data. It is possible that some

or all of the stranded dolphins may have been from a nearby coastal stock; however, the proportion of the stranded

dolphins belonging to another stock cannot be determined because of the difficulty of determining from where the

stranded carcass originated. Stranding data probably underestimate the extent of fishery-related mortality and serious

injury because not all of the dolphins which die or are seriously injured in fishery interactions wash ashore, nor will

all of those that do wash ashore necessarily show signs of entanglement or other fishery-interaction. Finally, the level

of technical expertise among stranding network personnel varies widely as does the ability to recognize signs of fishery

interaction.

Some of these stocks were the focus of a live-capture fishery for bottlenose dolphins which supplied dolphins

to the U.S. Navy and to oceanaria for research and for public display for almost two decades (NMFS unpublished data).

During the period between 1972-89, 490 bottlenose dolphins, an average of 29 dolphins annually, were removed from

a few locations in the Gulf of Mexico, including the Florida Keys. Mississippi Sound sustained the highest level of
162

removals and 202 dolphins were removed from this stock during this period, representing 41% of the total and an

annual average of 12 dolphins (compared to a current PBR of 13). The annual average number of removals never

exceeded the current PBR levels, but it may be biologically significant that 73% of the dolphins removed during 1982-

88 were females. The impact of those removals on the stocks is unknown. 

Fishery-related mortality and serious injury for each of these stocks is not known, but considering the evidence

from stranding data, the total fishery-related mortality and serious injury exceeds 10% of the total PBR and, therefore,

is not insignificant and approaching zero mortality and serious injury rate. This determination cannot be made for

specific fisheries until the implementing regulations for Section 118 of the MMPA have been reviewed by the public

and finalized. 

Fishery Information

Annual fishing effort for the shrimp trawl fishery in the U.S. Gulf of Mexico bays, sounds, and estuaries

during 1988-1993 averaged approximately 2.20 million hours of tows (CV = 0.11) (NMFS unpublished data). There

have been no reports of incidental mortality or injury in any of these stocks associated with the shrimp trawl fishery.

A fishery for blue crabs operates in estuarine areas throughout the Gulf of Mexico coast employing traps

attached to a buoy with rope. Bottlenose dolphins have been reported stranded with polypropylene rope around their

flukes (NMFS 1991; NMFS unpublished data) indicating the possibility of entanglement with crab pot lines; however,

entanglement has not been reported by fishermen. This fishery has not been monitored by observers and there are no

estimates of bottlenose dolphin mortality or serious injury for this fishery. 

Gillnets are not used in Texas, and gillnets over 46 m3 in area will not be allowed in Florida past July 1995,

but fixed and runaround gillnets are currently in use in Louisiana, Mississippi, and Alabama. These fisheries, for the

most part, operate year around. They are state-controlled and licensed, and vary widely in intensity and target species.

No marine mammal mortalities associated with gillnet fisheries have been reported in these states, but stranding data

suggest that gillnet and marine mammal interaction does occur, causing mortality and serious injury. 

Other Mortality

The nearshore habitat occupied by many of these stocks is adjacent to areas of high human population and

in some bays, such as Mobile Bay in Alabama and Galveston Bay in Texas, is highly industrialized. The area

surrounding Galveston Bay, for example, has a coastal population of over 3 million people. More than 50% of all

chemical products manufactured in the U.S. are produced there and 17% of the oil produced in the Gulf of Mexico is

refined there (Henningsen and Würsig 1991). Many of the enclosed bays in Texas are surrounded by agricultural lands

which receive periodic pesticide applications. 

Concentrations of chlorinated hydrocarbons and metals were examined in conjunction with an anomalous

mortality event of bottlenose dolphins in Texas bays in 1990, and were relatively low in most; however, some had

concentrations at levels of possible toxicological concern (Varanasi et al. 1992). No studies to date have determined

the amount, if any, of indirect human-induced mortality resulting from pollution or habitat degradation. A recent

assessment of the health of 35 bottlenose dolphins from Matagorda Bay, Texas, however, associated high levels of

chlorinated hydrocarbons with low health assessment scores (Reif et al., in preparation). 

STATUS OF STOCK

The status of these stocks relative to OSP is unknown and this species is not listed as threatened or endangered

under the Endangered Species Act. The occurrence of three anomalous mortality events among bottlenose dolphins

along the U.S. Gulf of Mexico coast since 1990 (NMFS unpublished data) is cause for concern; however, the effects

of the mortality events on stock abundance have not yet been determined. The available evidence suggests that

bottlenose dolphin stocks in the northern and western coastal portion of the U.S. Gulf of Mexico may have experienced

morbillivirus epidemic in 1993 (Lipscomb 1993; Lipscomb et al. 1994). Seven of 35 live-captured bottlenose dolphins

(20%) from Matagorda Bay, Texas, in 1992, tested positive for previous exposure to cetacean morbillivirus (Reif et

al., in preparation) and it is possible that other estuarine resident stocks have been exposed to the morbillivirus. 

Low-level monitoring surveys in Mississippi Sound indicated a significantly lower average summer bottlenose

dolphin abundance between 1985 and 1993 (NMFS unpublished data). The apparent decline in summer abundance

of bottlenose dolphins in Mississippi Sound is evidence of a possible downward trend in abundance; however, there

are insufficient data available with which to conduct a trend analysis. The relatively high number of bottlenose dolphin
163

deaths which occurred during the recent mortality events suggests that some of these stocks may be stressed. For these

reasons, and because the PBR for most of these stocks would be exceeded with the incidental capture of a single

dolphin, each of these stocks is a strategic stock. 

REFERENCES

Anon. 1994. Report of the PBR (Potential Biological Removal) workshop. June 27-29, 1994. NOAA, NMFS

Southwest Fisheries Science Center, La Jolla, California, 13 pp. + Appendices. 

Blaylock, R. A. and W. Hoggard. 1994. Preliminary estimates of bottlenose dolphin abundance in southern U.S.

Atlantic and Gulf of Mexico continental shelf waters. NOAA Tech. Mem. NMFS-SEFSC-356, 10 pp. 

Bräger, S. 1992. Untersuchungen zur Ortstreue und zum Vergesellschaftungmuster des Großen Tümmlers, Tursiops

truncatus (Montagu, 1821). Diploma thesis, Christian-Albrechts-Universität, Kiel, Germany, 97 pp. 

Bräger, S. 1993. Diurnal and seasonal behavior patterns of bottlenose dolphins (Tursiops truncatus). Mar. Mam. Sci.

9: 434-440.

Bräger, S., B. Würsig, Alejandro Acevedo, and T. Henningsen. 1994. Association patterns of bottlenose dolphins

(Tursiops truncatus) in Galveston Bay, Texas. J. Mamm. 75(2): 431-437. 

Buckland, S. T., D. R. Anderson, K. P. Burnham, and J. L. Laake. 1993. Distance sampling: Estimating abundance

of biological populations. Chapman & Hall, London, 446 pp. 

Duffield, D. A. and R. S. Wells. 1986. Population structure of bottlenose dolphins: Genetic studies of bottlenose

dolphins along the central west coast of Florida. Contract Report to National marine Fisheries Service,

Southeast Fisheries Center, Contract No. 45-WCNF-5-00366, 16 pp. 

Gruber, J. A. 1981. Ecology of the Atlantic bottlenosed dolphin (Tursiops truncatus) in the Pass Cavallo area of

Matagorda Bay, Texas. M. Sc. thesis. Texas A&M University, College Station, 182 pp. 

Henningsen, T. 1991. Zur Verbreitung und Ökologie des Großen Tümmlers (Tursiops truncatus) in Galveston, Texas.

Diploma thesis, Christian-Albrechts-Universität, Kiel, Germany, 80 pp. 

Henningsen, T. and B. Würsig. 1991. Bottle-nosed dolphins in Galveston Bay, Texas: Numbers and activities. Pages

36-38, in P. G. H. Evans (editor), European research on cetaceans - 5. Proceedings of the Fifth Annual

Conference of the European Cetacean Society, Sandefjord, Norway, 21-23 February, 1991. Cambridge, UK.

Laake, J. L., S. T. Buckland, D. R. Anderson, and K. P. Burnham. DISTANCE user’s guide, V2.0. Colorado

Cooperative Fish & Wildlife Research Unit, Colorado State University, Ft. Collins, Colorado, 72 pp. 

Lipscomb, T. P. 1993. Some answers to questions about morbillivirus. Pages 4-5 in R. A. Blaylock, B. Mase, and

D. K. Odell (editors), Strandings, Vol. 2, No. 3, SEFSC Miami Laboratory, Miami, Florida, 7 pp. 

Lipscomb, T. P. 1994. Morbilliviral disease in an Atlantic bottlenose dolphin (Tursiops truncatus) from the Gulf of

Mexico. Journal of Wildlife Diseases 30(4): 572-576. 

Lynn, S. K. 1995. Movements, site fidelity, and surfacing patterns of bottlenose dolphins on the central Texas coast.

M. Sc. thesis, Texas A&M University, College Station, 92 pp. 

McHugh, M. B. 1989. Population numbers and feeding behavior of the bottlenose dolphin (Tursiops truncatus) near

Aransas Pass, Texas. M. A. thesis. University of Texas, Austin, 97 pp. 

Morgan, M. A. and G. W. Patton. 1990. Human dolphin interactions on the west coast of Florida: Documentation

from MML's marine mammal response program. MML Technical Report #191, 9 pp. 

NMFS. 1991. Proposed regime to govern the interactions between marine mammals and commercial fishing

operations after October 1, 1993. Draft Environmental Impact Statement, June 1991. 

Reif, J. S., L. J. Hansen, S. Galloway, G. Mitchum, T. L. Schmitt. In preparation. The relationship between

chlorinated hydrocarbon contaminants and selected health parameters in bottlenose dolphins (Tursiops

truncatus) from Matagorda Bay, Texas, 1992. Colorado State University, Fort Collins, and NMFS, Southeast

Fisheries Science Center, Miami, Florida. 

Reilly, S. B. and J. Barlow. 1986. Rates of increase in dolphin population size. Fish. Bull., U.S. 84(3): 527-533. 

Scott, G. P. 1990. Management-oriented research on bottlenose dolphins by the Southeast Fisheries Center. Pages

623-639 in S. Leatherwood and R. R. Reeves (editors), The bottlenose dolphin. Academic Press, San Diego,

653 pp. 

Scott, M. D., R. S. Wells, and A. B. Irvine. 1990. A long-term study of bottlenose dolphins on the west coast of

Florida. Pages 235-244 in S. Leatherwood and R. R. Reeves (editors), The bottlenose dolphin. Academic

Press, San Diego, 653 pp. 
164

Shane, S. H. 1977. The population biology of the Atlantic bottlenose dolphin, Tursiops truncatus, in the Aransas Pass

area of Texas. M. Sc. thesis. Texas A&M University, College Station, 238 pp. 

Varanasi, U., K. L. Tilbury, D. W. Brown, M. M. Krahn, C. A. Wigren, R. C. Clark, and S-L. Chan. 1992. Pages

56-86 in L. J. Hansen (editor), Report on Investigation of 1990 Gulf of Mexico Bottlenose Dolphin Strandings,

Southeast Fisheries Science Center Contribution MIA-92/93-21, 219 pp. 

Wells, R. S. 1986a. Population structure of bottlenose dolphins: behavioral studies along the central west coast of

Florida. Contract report to NMFS, SEFSC. Contract No. 45-WCNF-5-00366, 58 pp. 

Wells, R. S. 1986b. Structural aspects of dolphin societies. Ph. D. dissertation. University of California at Santa

Cruz, Santa Cruz, 234 pp. 

Wells, R. S. 1992. The marine mammals of Sarasota Bay. Pages 9.1-9.23, in Sarasota Bay: Framework for action,

Sarasota Bay National Estuary Program, Sarasota, Florida. 
165

Figure 1. Distribution of Atlantic spotted dolphin sightings during NOAA Ship Oregon

II marine mammal surveys during 1991-1994 (filled circles) and during GOMEX

regional aerial surveys during 1992-1994 (unfilled circles). The straight lines show

transects during two ship surveys and are examples of typical ship survey transects. 

Isobaths are in 183 m (100 fm) intervals.

ATLANTIC SPOTTED DOLPHIN (Stenella frontalis):

Northern Gulf of Mexico Stock

STOCK DEFINITION AND GEOGRAPHIC RANGE

The Atlantic spotted dolphin is endemic to the Atlantic Ocean in warm temperate to tropical waters (Perrin

et al. 1987, 1994). Sightings of this species are concentrated along the continental shelf edge and also occur over the

continental shelf in the northern Gulf of Mexico [Fritts et al. 1983; Mullin et al. 1991; Southeast Fisheries Science

Center (SEFSC) unpublished data], but they have been reported as occurring around oceanic islands and far offshore

in other areas (Perrin et al. 1994). The island and offshore animals may be a different stock than those occurring on

the continental shelf (Perrin et al. 1994). Atlantic spotted dolphins were seen in all seasons during seasonal recent

GulfCet aerial surveys of the northern Gulf of Mexico during 1993-1995 (Davis et al., in preparation). Atlantic spotted

dolphins were seen in 1992 during regional aerial surveys conducted in the autumn of 1992-1994 over the U.S.

continental shelf [see Blaylock and Hoggard (1994) for a description of the areas surveyed in 1992-1993]. These

surveys were designed to estimate abundance of bottlenose dolphins and spotted dolphin abundance was not estimated.

It has been suggested that there may be a seasonal movement of this species onto the continental shelf in the spring,

but data supporting this hypothesis are limited (Caldwell and Caldwell 1966; Fritts et al. 1983). 

POPULATION SIZE

Estimates of abundance were derived through the application of distance sampling analysis (Buckland et al.

1993) and the computer program DISTANCE (Laake et al. 1993) to sighting data collected during 1991-1994 springsummer, visual sampling, line-transect vessel surveys of the northern Gulf of Mexico (Hansen et al. 1995) (Fig. 1),

which includes data collected as part of the GulfCet program (Davis et al., in preparation). These surveys were

conducted throughout the area from approximately the 200 m isobath along the U.S. coast to the seaward extent of the

U.S. Exclusive Economic Zone. The seasonal GulfCet aerial surveys included only a small portion of the stock range

and these data were not used for

abundance estimation. Estimated

abundance of Atlantic spotted

dolphins [coefficient of variation

(CV) in parentheses] by survey

year was zero in 1991, 4,527 in

1992 (0.65), 4,618 in 1993

(0.62), and 2,186 in 1994 (0.85)

(Hansen et al. 1995). Survey

effort-weighted estimated average

abundance of Atlantic spotted

dolphins for all surveys combined

was 3,213 (CV = 0.44) (Hansen

et al. 1995). This is probably an

underestimate and should be

considered a partial stock

estimate because the continental

shelf areas were not generally

covered by either the vessel or

GulfCet aerial surveys. 

Minimum Population Estimate

 The minimum population size was estimated using the average abundance estimate of Atlantic spotted

dolphins for all surveys combined which was 3,213 (CV = 0.44) (Hansen et al. 1995). The minimum population

estimate is the lower limit of the two-tailed 60% confidence interval of the log-normal distributed abundance estimate,

which is equivalent to the 20th percentile of the log-normal distributed abundance estimate as specified by NMFS

(Anon. 1994). The minimum population estimate is 2,255 Atlantic spotted dolphins. 
166

Current Population Trend

No trend was identified in the annual abundance estimates. There were no sightings of this stock during 1991.

The lack of sightings during 1991 may have been due to less sampling that year along the continental shelf edge where

sightings of this species were concentrated. The difference in abundance estimates during 1992-1994 were not

significant using the criteria of no overlap of log-normal 95 % confidence intervals. 

CURRENT AND MAXIMUM NET PRODUCTIVITY RATES

Current and maximum net productivity rates are not known for this stock; therefore, the default maximum

net productivity rate of 0.04 (Anon. 1994) was used for purposes of this assessment. 

POTENTIAL BIOLOGICAL REMOVAL

Potential biological removal level (PBR) was specified as the product of the minimum population size, one

half the maximum net productivity rate, and a recovery factor for endangered, threatened, or depleted stocks, or stocks

of unknown status relative to optimum sustainable population (OSP) (Anon. 1994). The recovery factor was set at 0.50

because the status of the stock relative to OSP is unknown. The resulting PBR, based on the partial estimate, for this

stock is 23 dolphins.

ANNUAL HUMAN-CAUSED MORTALITY AND SERIOUS INJURY

The level of past or current, direct, human-caused mortality of Atlantic spotted dolphins in the northern Gulf

of Mexico is unknown; however, interactions between spotted dolphins and fisheries have been observed in the

northern Gulf of Mexico.

There were two documented strandings of Atlantic spotted dolphins in the northern Gulf of Mexico during

1987-1994 which were classified as likely caused by fishery interactions. Stranding data probably underestimate the

extent of fishery-related mortality and serious injury because not all of the dolphins which die or are seriously injured

in fishery interactions wash ashore, nor will all of those that do wash ashore necessarily show signs of entanglement

or other fishery-interaction. Finally, the level of technical expertise among stranding network personnel varies widely

as does the ability to recognize signs of fishery interaction. 

Total estimated average annual fishing-related mortality and serious injury of spotted dolphins (both species)

is 1.5 spotted dolphins annually (CV = 0.33). Observed fishery-related mortality and serious injury for spotted dolphins

is less than 10% of PBR and can be considered insignificant and approaching zero mortality and serious injury rate

for this stock. This determination cannot be made for specific fisheries until the implementing regulations for Section

118 of the MMPA have been reviewed by the public and finalized. 

Fisheries Information

Pelagic swordfish, tunas, and billfish are the targets of the longline fishery operating in the U.S. Gulf of

Mexico. Total longline effort for the Gulf of Mexico pelagic fishery, including OCS edge, continental slope, and

Mexican territorial waters, based on mandatory logbook reporting, was 4,400 sets in 1991, 4,850 sets in 1992, and

3,260 sets in 1993 (Cramer 1994). This fishery has been monitored with about 5% observer coverage, in terms of trips

observed, since 1992. There were two observed incidental takes and releases of spotted dolphins in the Gulf of Mexico

during 1994, but no observed lethal takes of Atlantic spotted dolphins by this fishery in the Gulf of Mexico. 

Estimates of fishery-related mortality and serious injury were based on a generalized linear model (Poisson

error assumption) fit to the available observed incidental take for the entire Atlantic longline swordfish/tuna fishery

(which includes the Gulf of Mexico) (SEFSC, unpublished data). Takes observed throughout the range of this fishery

were used because the species occurs generally throughout the area of the fishery, but observed takes were infrequent

in any given region. Either spotted dolphin species may have been involved in the observed fishery-related mortality

and serious injury incidents, but because of the difficulty of species identification by fishery observers, they cannot

currently be separated. Estimated mortality and serious injury to spotted dolphins attributable to the longline fishery

for the entire fishery (including waters outside of the Gulf of Mexico) for 1993 was 16 (CV = 0.19). Estimated fisheryrelated mortality and serious injury for the Gulf of Mexico, based on proportionality of fishing effort (number of sets)

in 1993 was 4.4 spotted dolphins. Estimated average annual fishing-related mortality and serious injury of spotted

dolphins attributable to this fishery during 1991-1993 was 1.5 annually (CV = 0.33).
167

Pair trawl fishing gear has the potential to capture marine mammals, but there have been no reports of

mortality or serious injury to marine mammals in the Gulf of Mexico. This fishery has not been observed by NMFS

observers, and there are no other data available as to the extent of this fishery in the Gulf of Mexico. It is assumed that

it is very limited in scope and duration. 

STATUS OF STOCK

The status of this stock relative to OSP is unknown and there are insufficient data to determine population

trends. This species is not listed under the Endangered Species Act. The total level of human-caused mortality and

serious injury is unknown, but it is believed to be low relative to PBR; therefore, this is not a strategic stock.

REFERENCES

Anon. 1994. Report of the PBR (Potential Biological Removal) workshop. June 27-29, 1994. NOAA, NMFS

Southwest Fisheries Science Center, La Jolla, California, 13 pp. + Appendices. 

Blaylock, R. A. and W. Hoggard. 1994. Preliminary estimates of bottlenose dolphin abundance in southern U.S.

Atlantic and Gulf of Mexico continental shelf waters. NOAA Tech. Mem. NMFS-SEFSC-356, 10 pp. 

Buckland, S. T., D. R. Anderson, K. P. Burnham and J. L. Laake. 1993. Distance Sampling: estimating abundance

of biological populations. Chapman & Hall, London, 446 pp. 

Caldwell, D. K. and M. C. Caldwell. 1966. Observations on the distribution, coloration, behavior and audible sound

production of the spotted dolphin, Stenella plagiodon (Cope). Los Angeles County Museum Contribution to

Science, 104:1-28. 

Cramer, J. 1994. Large pelagic logbook newsletter - 1993. NOAA Tech. Mem. NMFS-SEFSC-352, 19 pp. 

Davis, R., G. Scott, B. Würsig, W. Evans, G. Fargion, L. Hansen, K. Mullin, N. May, T. Leming, B. Mate, J. Norris

and T. Jefferson. In preparation. Distribution and abundance of marine mammals in the north-central and

western Gulf of Mexico: Final Report. OCS Study #MMS 94-0003. Texas Institute of Oceanography and the

National Marine Fisheries Service. U.S. Dept. of the Interior, Minerals Mgmt. Service, Gulf of Mexico OCS

Region, New Orleans, Louisiana. 

Fritts, T. H., A. B. Irvine, R. D. Jennings, L. A. Collum, W. Hoffman and M. A. McGehee. 1983. Turtles, birds, and

mammals in the northern Gulf of Mexico and nearby Atlantic waters. U.S. Fish and Wildlife Service, Division

of Biological Services, Washington, D. C., FWS/OBS-82/65, 455 pp. 

Hansen, L. J., K. D. Mullin and C. L. Roden. 1995. Estimates of cetacean abundance in the northern Gulf of Mexico

from vessel surveys. Southeast Fisheries Science Center, Miami Laboratory, Contribution No. MIA-94/95-25,

9 pp. + tables and figures.

Laake, J. L., S. T. Buckland, D. R. Anderson, and K. P. Burnham. DISTANCE user’s guide, V2.0. Colorado

Cooperative Fish & Wildlife Research Unit, Colorado State University, Ft. Collins, Colorado, 72 pp. 

Mullin, K., W. Hoggard, C. Roden, R. Lohoefener, C. Rogers and B. Taggart. 1991. Cetaceans on the upper

continental slope in the north-central Gulf of Mexico. OCS Study/MMS 91-0027. U.S. Dept. of the Interior,

Minerals Management Service, Gulf of Mexico OCS Regional Office, New Orleans, 108 pp. 

Perrin, W. F., E. D. Mitchell, J. G. Mead, D. K. Caldwell, M. C. Caldwell, P. J. H. van Bree and W. H. Dawbin. 1987.

Revision of the spotted dolphins, Stenella spp. Mar. Mam. Sci. 3(2):99-170.

Perrin, W. F., D. K. Caldwell and M. C. Caldwell. 1994. Atlantic spotted dolphin Stenella frontalis (G. Cuvier,

1829). Pages 173-190 in S. H. Ridgway and R. Harrison (editors), Handbook of marine mammals, Vol. 5:

The first book of dolphins. Academic Press, London, 416 pp. 
168

Figure 1. Distribution of pantropical spotted dolphin sightings during NOAA Ship

Oregon II marine mammal surveys during 1991-1994. The straight lines show transects

during two surveys and are examples of typical survey transects. Isobaths are in 183 m

(100 fm) intervals. 

PANTROPICAL SPOTTED DOLPHIN (Stenella attenuata):

Northern Gulf of Mexico Stock

STOCK DEFINITION AND GEOGRAPHIC RANGE

The pantropical spotted dolphin is distributed worldwide in tropical and some sub-tropical oceans (Perrin et

al. 1987; Perrin and Hohn 1994). Sightings of this species occurred over the deeper waters of the northern Gulf of

Mexico, and rarely over the continental shelf or continental shelf edge [Mullin et al. 1991; Southeast Fisheries Science

Center (SEFSC) unpublished data]. Pantropical spotted dolphins were seen in all seasons during recent seasonal

GulfCet aerial surveys of the northern Gulf of Mexico during 1993-1995 (Davis et al., in preparation). Some of the

Pacific populations have been divided into different geographic stocks based on morphological characteristics (Perrin

et al. 1987; Perrin and Hohn 1994); however, there is no information on stock differentiation for the Atlantic

population. 

POPULATION SIZE

Estimates of abundance were derived through the application of distance sampling analysis (Buckland et al.

1993) and the computer program DISTANCE (Laake et al. 1993) to sighting data collected during 1991-1994 springsummer, visual sampling, line-transect vessel surveys of the northern Gulf of Mexico (Hansen et al. 1995) (Fig. 1),

which includes data collected as part of the GulfCet program (Davis et al., in preparation). These surveys were

conducted throughout the area from approximately the 200 m isobath along the U.S. coast to the seaward extent of the

U.S. Exclusive Economic Zone.

The seasonal GulfCet aerial

surveys included only a small

portion of the stock range and

these data were not used for

abundance estimation. Estimated

abundance of pantropical spotted

dolphins by survey year

[coefficient of variation (CV) in

parentheses] was 19,767 in 1991

(0.45), 15,280 in 1992 (0.36),

29,414 in 1993 (0.29), and

71,847 in 1994 (0.31) (Hansen et

al. 1995). Survey effortweighted estimated average

abundance of pantropical spotted

dolphins for all surveys

combined was 31,320 (CV =

0.20) (Hansen et al. 1995).

Minimum Population Estimate

The minimum population size was estimated from the average estimated abundance of pantropical spotted

dolphins which was 31,320 (CV = 0.20) (Hansen et al. 1995). The minimum population estimate is the lower limit

of the two-tailed 60% confidence interval of the log-normal distributed abundance estimate, which is equivalent to the

20th percentile of the log-normal distributed abundance estimate as specified by NMFS (Anon. 1994). The minimum

population estimate is 26,510 pantropical spotted dolphins. 

Current Population Trend

The 1994 abundance estimate was larger than the estimates for 1991-1993. The 1992 and 1994 estimates

were significantly different using the criteria of no overlap of log-normal 95% confidence intervals, but differences

within 1991-1993 estimates and differences between 1991, 1993, and 1994 were not significant. The observed
169

differences in abundance estimates may have been caused by inter-annual variation in distribution patterns and spatial

sampling, rather than changes in population size. 

CURRENT AND MAXIMUM NET PRODUCTIVITY RATES

Current and maximum net productivity rates are not known for this stock; therefore, the default maximum

net productivity rate of 0.04 (Anon. 1994) was used for purposes of this assessment. 

POTENTIAL BIOLOGICAL REMOVAL

Potential biological removal level (PBR) was specified as the product of the minimum population size, one

half the maximum net productivity rate, and a recovery factor for endangered, threatened, or depleted stocks, or stocks

of unknown status relative to optimum sustainable population (OSP) (Anon. 1994). The recovery factor was set at 0.50

because the status of the stock relative to OSP is unknown. The resulting PBR for this stock is 265 animals. 

ANNUAL HUMAN-CAUSED MORTALITY AND SERIOUS INJURY

The level of past or current, direct, human-caused mortality of pantropical spotted dolphins in the northern

Gulf of Mexico is unknown; however, interactions between spotted dolphins and fisheries have been observed in the

northern Gulf of Mexico.

There was one documented stranding of a pantropical spotted dolphin in the northern Gulf of Mexico during

1987-1994 which was classified as likely caused by fishery interactions. Stranding data probably underestimate the

extent of fishery-related mortality and serious injury because not all of the dolphins which die or are seriously injured

in fishery interactions wash ashore, nor will all of those that do wash ashore necessarily show signs of entanglement

or other fishery-interaction. Finally, the level of technical expertise among stranding network personnel varies widely

as does the ability to recognize signs of fishery interaction. 

Total estimated average annual fishing-related mortality and serious injury of spotted dolphins (both species)

is 1.5 spotted dolphins annually (CV = 0.33). Observed fishery-related mortality and serious injury for spotted dolphins

is less than 10% of PBR and can be considered insignificant and approaching zero mortality and serious injury rate

for this stock. This determination cannot be made for specific fisheries until the implementing regulations for Section

118 of the MMPA have been reviewed by the public and finalized. 

Fisheries Information

Pelagic swordfish, tunas, and billfish are the targets of the longline fishery operating in the U.S. Gulf of

Mexico. Total longline effort for the Gulf of Mexico pelagic fishery, including OCS edge, continental slope, and

Mexican territorial waters, based on mandatory logbook reporting, was 4,400 sets in 1991, 4,850 sets in 1992, and

3,260 sets in 1993 (Cramer 1994). This fishery has been monitored with about 5% observer coverage, in terms of trips

observed, since 1992. There were two observed incidental takes and releases of spotted dolphins in the Gulf of Mexico

during 1994, but no observed lethal takes of Atlantic spotted dolphins by this fishery in the Gulf of Mexico. 

Estimates of fishery-related mortality and serious injury were based on a generalized linear model (Poisson

error assumption) fit to the available observed incidental take for the entire Atlantic longline swordfish/tuna fishery

(which includes the Gulf of Mexico) (SEFSC, unpublished data). Takes observed throughout the range of this fishery

were used because the species occurs generally throughout the area of the fishery, but observed takes were infrequent

in any given region. Either spotted dolphin species may have been involved in the observed fishery-related mortality

and serious injury incidents, but because of the difficulty of species identification by fishery observers, they cannot

currently be separated. Estimated mortality and serious injury to spotted dolphins attributable to the longline fishery

for the entire fishery (including waters outside of the Gulf of Mexico) for 1993 was 16 (CV = 0.19). Estimated fisheryrelated mortality and serious injury for the Gulf of Mexico, based on proportionality of fishing effort (number of sets)

in 1993 was 4.4 spotted dolphins. Estimated average annual fishing-related mortality and serious injury of spotted

dolphins attributable to this fishery during 1991-1993 was 1.5 annually (CV = 0.33).

Pair trawl fishing gear has the potential to capture marine mammals, but there have been no reports of

mortality or serious injury to marine mammals in the Gulf of Mexico. This fishery has not been observed by NMFS

observers, and there are no other data available as to the extent of this fishery in the Gulf of Mexico. It is assumed that

it is very limited in scope and duration. 
170

STATUS OF STOCK

The status of this stock relative to OSP is unknown and there are insufficient data to determine population

trends. This species is not listed under the Endangered Species Act. The total level of human-caused mortality and

serious injury is unknown, but it is believed to be insignificant relative to PBR; therefore, this is not a strategic stock.

REFERENCES

Anon. 1994. Report of the PBR (Potential Biological Removal) workshop. June 27-29, 1994. NOAA, NMFS

Southwest Fisheries Science Center, La Jolla, California, 13 pp. + Appendices. 

Buckland, S. T., D. R. Anderson, K. P. Burnham and J. L. Laake. 1993. Distance Sampling: estimating abundance

of biological populations. Chapman & Hall, London, 446 pp. 

Cramer, J. 1994. Large pelagic logbook newsletter - 1993. NOAA Tech. Mem. NMFS-SEFSC-352, 19 pp. 

Davis, R., G. Scott, B. Würsig, W. Evans, G. Fargion, L. Hansen, K. Mullin, N. May, T. Leming, B. Mate, J. Norris

and T. Jefferson. In preparation. Distribution and abundance of marine mammals in the north-central and

western Gulf of Mexico: Final Report. OCS Study #MMS 94-0003. Texas Institute of Oceanography and the

National Marine Fisheries Service. U.S. Dept. of the Interior, Minerals Mgmt. Service, Gulf of Mexico OCS

Region, New Orleans, Louisiana. 

Hansen, L. J., K. D. Mullin and C. L. Roden. 1995. Estimates of cetacean abundance in the northern Gulf of Mexico

from vessel surveys. Southeast Fisheries Science Center, Miami Laboratory, Contribution No. MIA-94/95-25,

9 pp. + tables and figures.

Laake, J. L., S. T. Buckland, D. R. Anderson, and K. P. Burnham. DISTANCE user’s guide, V2.0. Colorado

Cooperative Fish & Wildlife Research Unit, Colorado State University, Ft. Collins, Colorado, 72 pp. 

Mullin, K., W. Hoggard, C. Roden, R. Lohoefener, C. Rogers and B. Taggart. 1991. Cetaceans on the upper

continental slope in the north-central Gulf of Mexico. OCS Study/MMS 91-0027. U.S. Dept. of the Interior,

Minerals Management Service, Gulf of Mexico OCS Regional Office, New Orleans, 108 pp. 

Perrin, W. F., E. D. Mitchell, J. G. Mead, D. K. Caldwell, M. C. Caldwell, P. J. H. van Bree, and W. H. Dawbin. 1987.

Revision of the spotted dolphins, Stenella spp. Mar. Mam. Sci. 3(2): 99-170.

Perrin, W. F. and A. A. Hohn. 1994. Pantropical spotted dolphin Stenella attenuata. Pages 71-98 in S. H. Ridgway

and R. Harrison (editors), Handbook of marine mammals, Vol. 5: The first book of dolphins. Academic

Press, London, 416 pp. 
171

Figure 1. Distribution of striped dolphin sightings during NOAA Ship Oregon II

marine mammal surveys during 1991-1994. The straight lines show transects during

two surveys and are examples of typical survey transects. Isobaths are in 183 m (100

fm) intervals. 

STRIPED DOLPHIN (Stenella coeruleoalba):

Northern Gulf of Mexico Stock

STOCK DEFINITION AND GEOGRAPHIC RANGE

The striped dolphin is distributed worldwide in tropical to warm temperate oceanic waters (Leatherwood and

Reeves 1983; Perrin et al. 1994). Sightings of these animals in the northern Gulf of Mexico occur primarily over the

deeper waters off the continental shelf [Mullin et al. 1991; Southeast Fisheries Science Center (SEFSC) unpublished

data]. Striped dolphins were seen in fall, winter, and spring during recent seasonal GulfCet aerial surveys of the

northern Gulf of Mexico during 1993-1995 (Davis et al., in preparation). There is no information on stock

differentiation for the Atlantic population. 

POPULATION SIZE

Estimates of abundance were derived through the application of distance sampling analysis (Buckland et al.

1993) and the computer program DISTANCE (Laake et al. 1993) to sighting data collected during 1991-1994 springsummer, visual sampling, line-transect vessel surveys of the northern Gulf of Mexico (Hansen et al. 1995) (Fig. 1),

which includes data collected as part of the GulfCet program (Davis et al., in preparation). These surveys were

conducted throughout the area from approximately the 200 m isobath along the U.S. coast to the seaward extent of the

U.S. Exclusive Economic Zone.

The seasonal GulfCet aerial

surveys included only a small

portion of the stock range and

these data were not used for

abundance estimation. Estimated

abundance of striped dolphins by

survey year [coefficient of

variation (CV) in parentheses]

was 3,483 in 1991 (0.76),

2,574 in 1992 (0.52), 4,160 in

1993 (0.63), and 8,147 in 1994

(0.60) (Hansen et al. 1995).

Survey effort-weighted estimated

average abundance of striped

dolphins for all surveys

combined was 4,858 (CV =

0.44) (Hansen et al. 1995).

Minimum Population Estimate

The minimum population size was estimated from the average estimate abundance which was 4,858 striped

dolphins (CV = 0.44) (Hansen et al. 1995). The minimum population estimate is the lower limit of the two-tailed 60%

confidence interval of the log-normal distributed abundance estimate, which is equivalent to the 20th percentile of the

log-normal distributed abundance estimate as specified by NMFS (Anon. 1994). The minimum population estimate

is 3,409 striped dolphins. 

Current Population Trend

The abundance estimates for 1991-1993 were less than the 1994 estimate. The abundance estimates were not

significantly different using the criteria of no overlap of log-normal 95% confidence intervals. The apparent

differences in abundance estimates may have been caused by small sample sizes; only 29 observations of herds of

striped dolphins were used in the distance sampling analysis. The differences in the estimates may also have been

caused by inter-annual variation in distribution patterns and spatial sampling, rather than changes in population size.
172

CURRENT AND MAXIMUM NET PRODUCTIVITY RATES

Current and maximum net productivity rates are not known for this stock; therefore, the default maximum

net productivity rate of 0.04 (Anon. 1994) was used for purposes of this assessment. 

POTENTIAL BIOLOGICAL REMOVAL

Potential biological removal level (PBR) was specified as the product of the minimum population size, one

half the maximum net productivity rate, and a recovery factor for endangered, threatened, or depleted stocks, or stocks

of unknown status relative to optimum sustainable population (OSP) (Anon. 1994). The recovery factor was set at 0.50

because the status of the stock relative to OSP is unknown. PBR for this stock is 34 striped dolphins. 

ANNUAL HUMAN-CAUSED MORTALITY AND SERIOUS INJURY

The level of past or current, direct, human-caused mortality of striped dolphins in the northern Gulf of Mexico

is unknown. Available information indicates there likely is little, if any, fisheries interaction with striped dolphins in

the northern Gulf of Mexico. There have been no logbook reports of fishery-related mortality or serious injury and no

fishery-related mortality or serious injury has been observed.

There were no documented strandings of striped dolphins in the northern Gulf of Mexico during 1987-1994

which were classified as likely caused by fishery interactions or other human-related causes. Stranding data probably

underestimate the extent of fishery-related mortality and serious injury because not all of the dolphins which die or are

seriously injured in fishery interactions wash ashore, nor will all of those that do wash ashore necessarily show signs

of entanglement or other fishery-interaction. Finally, the level of technical expertise among stranding network

personnel varies widely as does the ability to recognize signs of fishery interaction. 

Total known fishery-related mortality and serious injury for this stock is less than 10% of the calculated PBR

and, therefore, can be considered insignificant and approaching zero mortality and serious injury rate. This

determination cannot be made for specific fisheries until the implementing regulations for Section 118 of the MMPA

have been reviewed by the public and finalized. 

Fisheries Information

 Pelagic swordfish, tunas, and billfish are the targets of the longline fishery operating in the U.S. Gulf of

Mexico. Total longline effort for the Gulf of Mexico pelagic fishery, including OCS edge, continental slope, and

Mexican territorial waters, based on mandatory logbook reporting, was 4,400 sets in 1991, 4,850 sets in 1992, and

3,260 sets in 1993 (Cramer 1994). This fishery has been monitored with about 5% observer coverage, in terms of trips

observed, since 1992. There were no reports of mortality or serious injury to striped dolphins by this fishery. 

Pair trawl fishing gear has the potential to capture marine mammals, but there have been no reports of

mortality or serious injury to marine mammals in the Gulf of Mexico. This fishery has not been observed by NMFS

observers, and there are no other data available as to the extent of this fishery in the Gulf of Mexico. It is assumed that

it is very limited in scope and duration. 

STATUS OF STOCK

The status of this stock relative to OSP is unknown and there are insufficient data to determine population

trends. This species is not listed under the Endangered Species Act. The total level of human-caused mortality and

serious injury is unknown, but it is believed to be insignificant relative to PBR; therefore, this is not a strategic stock.

REFERENCES

Anon. 1994. Report of the PBR (Potential Biological Removal) workshop. June 27-29, 1994. NOAA, NMFS

Southwest Fisheries Science Center, La Jolla, California, 13 pp. + Appendices. 

Buckland, S. T., D. R. Anderson, K. P. Burnham and J. L. Laake. 1993. Distance Sampling: estimating abundance

of biological populations. Chapman & Hall, London, 446 pp. 

Cramer, J. 1994. Large pelagic logbook newsletter - 1993. NOAA Tech. Mem. NMFS-SEFSC-352, 19 pp. 
173

Davis, R., G. Scott, B. Würsig, W. Evans, G. Fargion, L. Hansen, K. Mullin, N. May, T. Leming, B. Mate, J. Norris

and T. Jefferson. In preparation. Distribution and abundance of marine mammals in the north-central and

western Gulf of Mexico: Final Report. OCS Study #MMS 94-0003. Texas Institute of Oceanography and the

National Marine Fisheries Service. U.S. Dept. of the Interior, Minerals Mgmt. Service, Gulf of Mexico OCS

Region, New Orleans, Louisiana. 

Hansen, L. J., K. D. Mullin and C. L. Roden. 1995. Estimates of cetacean abundance in the northern Gulf of Mexico

from vessel surveys. Southeast Fisheries Science Center, Miami Laboratory, Contribution No. MIA-94/95-25,

9 pp. + tables and figures.

Laake, J. L., S. T. Buckland, D. R. Anderson, and K. P. Burnham. DISTANCE user’s guide, V2.0. Colorado

Cooperative Fish & Wildlife Research Unit, Colorado State University, Ft. Collins, Colorado, 72 pp. 

Leatherwood, S. and R. R. Reeves. 1983. The Sierra Club handbook of whales and dolphins. Sierra Club Books, San

Francisco, 302 pp. 

Mullin, K., W. Hoggard, C. Roden, R. Lohoefener, C. Rogers and B. Taggart. 1991. Cetaceans on the upper

continental slope in the north-central Gulf of Mexico. OCS Study/MMS 91-0027. U.S. Dept. of the Interior,

Minerals Management Service, Gulf of Mexico OCS Regional Office, New Orleans, 108 pp. 

Perrin, W. F., C. E. Wilson and F. I. Archer II. 1994. Striped dolphin Stenella coeruleoalba (Meyen, 1833). Pages

129-159 in S. H. Ridgway and R. Harrison (editors), Handbook of marine mammals, Vol. 5: The first book

of dolphins. Academic Press, London, 416 pp. 
174

Figure 1. Distribution of spinner dolphin sightings during NOAA Ship Oregon II

marine mammal surveys during 1991-1994. The straight lines show transects during

two surveys and are examples of typical survey transects. Isobaths are in 183 m (100

fm) intervals. 

SPINNER DOLPHIN (Stenella longirostris):

Northern Gulf of Mexico Stock

STOCK DEFINITION AND GEOGRAPHIC RANGE

The spinner dolphin is distributed worldwide in tropical to warm temperate waters in the world's oceans

(Leatherwood and Reeves 1983; Perrin and Gilpatrick 1994). Sightings of these animals in the northern Gulf of

Mexico occur primarily over the deeper waters off the continental shelf [Southeast Fisheries Science Center (SEFSC)

unpublished data]. Spinner dolphins were seen in winter, spring and summer during recent seasonal GulfCet aerial

surveys of the northern Gulf of Mexico during 1993-1995 (Davis et al., in preparation). Different geographic stocks

have been identified in the Pacific based on morphological characteristics (Perrin and Gilpatrick 1994); however, there

is no information on stock differentiation for the Atlantic population. 

POPULATION SIZE

Estimates of abundance were derived through the application of distance sampling analysis (Buckland et al.

1993) and the computer program DISTANCE (Laake et al. 1993) to sighting data collected during 1991-1994 springsummer, visual sampling, line-transect vessel surveys of the northern Gulf of Mexico (Hansen et al. 1995) (Fig. 1),

which includes data collected as part of the GulfCet program (Davis et al., in preparation). These surveys were

conducted throughout the area from approximately the 200 m isobath along the U.S. coast to the seaward extent of the

U.S. Exclusive Economic Zone.

The seasonal GulfCet aerial

surveys included only a small

portion of the stock range and

these data were not used for

abundance estimation .

Estimated abundance of spinner

dolphins by survey year

[coefficient of variation (CV) in

parentheses] was zero in 1991,

2,593 in 1992 (0.63), 2,336 in

1993 (0.62), and 15,995 in 1994

(0.67) (Hansen et al. 1995).

Survey effort-weighted estimated

average abundance of spinner

dolphins for all surveys

combined was 6,316 (CV =

0.43) (Hansen et al. 1995).

Minimum Population Estimate

The minimum population size was estimated from the average estimate abundance which was 6,316 spinner

dolphins (CV = 0.43) (Hansen et al. 1995). The minimum population estimate is the lower limit of the two-tailed 60%

confidence interval of the log-normal distributed abundance estimate, which is equivalent to the 20th percentile of the

log-normal distributed abundance estimate as specified by NMFS (Anon. 1994). The minimum population estimate

is 4,465 spinner dolphins. 

Current Population Trend

The abundance estimates for 1992 and 1993 were approximately the same and the 1994 estimate was

considerably larger; however, the estimates were not significantly different using the criteria of no overlap of lognormal 95% confidence intervals. The apparent differences in abundance estimates may have been caused by less

sampling effort during 1991 (Hansen et al. 1995), or by inter-annual variation in distribution patterns or spatial

sampling patterns, rather than changes in population size. 
175

CURRENT AND MAXIMUM NET PRODUCTIVITY RATES

Current and maximum net productivity rates for this stock are not known; therefore, the default maximum

net productivity rate of 0.04 (Anon. 1994) was used for purposes of this assessment. 

POTENTIAL BIOLOGICAL REMOVAL

Potential biological removal level (PBR) was specified as the product of the minimum population size, one

half the maximum net productivity rate, and a recovery factor for endangered, threatened, or depleted stocks, or stocks

of unknown status relative to optimum sustainable population (OSP) (Anon. 1994). The recovery factor was set at 0.50

because the status of the stock relative to OSP is unknown. PBR for this stock is 45 spinner dolphins. 

 

ANNUAL HUMAN-CAUSED MORTALITY AND SERIOUS INJURY

The level of past or current, direct, human-caused mortality of spinner dolphins in the northern Gulf of

Mexico is unknown. Available information indicates there likely is little, if any, fisheries interaction with spinner

dolphins in the northern Gulf of Mexico. There have been no logbook reports of fishery-related mortality or serious

injury and no fishery-related mortality or serious injury has been observed.

There were no documented strandings of spinner dolphins in the northern Gulf of Mexico during 1987-1994

which were classified as likely caused by fishery interactions or other human-related causes. Stranding data probably

underestimate the extent of fishery-related mortality and serious injury because not all of the dolphins which die or are

seriously injured in fishery interactions wash ashore, nor will all of those that do wash ashore necessarily show signs

of entanglement or other fishery-interaction. Finally, the level of technical expertise among stranding network

personnel varies widely as does the ability to recognize signs of fishery interaction. 

The total known fishery-related mortality and serious injury for this stock is less than 10% of the calculated

PBR and, therefore, can be considered insignificant and approaching zero mortality and serious injury rate. This

determination cannot be made for specific fisheries until the implementing regulations for Section 118 of the MMPA

have been reviewed by the public and finalized. 

Fisheries Information

Pelagic swordfish, tunas, and billfish are the targets of the longline fishery operating in the U.S. Gulf of

Mexico. Total longline effort for the Gulf of Mexico pelagic fishery, including OCS edge, continental slope, and

Mexican territorial waters, based on mandatory logbook reporting, was 4,400 sets in 1991, 4,850 sets in 1992, and

3,260 sets in 1993 (Cramer 1994). This fishery has been monitored with about 5% observer coverage, in terms of trips

observed, since 1992. There were no reports of mortality or serious injury of spinner dolphins by this fishery. 

Pair trawl fishing gear has the potential to capture marine mammals, but there have been no reports of

mortality or serious injury to marine mammals in the Gulf of Mexico. This fishery has not been observed by NMFS

observers, and there are no other data available as to the extent of this fishery in the Gulf of Mexico. It is assumed that

it is very limited in scope and duration. 

STATUS OF STOCK

The status of this stock relative to OSP is unknown and there are insufficient data to determine population

trends. This species is not listed under the Endangered Species Act. The total level of human-caused mortality and

serious injury is unknown, but it is believed to be insignificant relative to PBR; therefore, this is not a strategic stock.

REFERENCES

Anon. 1994. Report of the PBR (Potential Biological Removal) workshop. June 27-29, 1994. NOAA, NMFS

Southwest Fisheries Science Center, La Jolla, California, 13 pp. + Appendices. 

Buckland, S. T., D. R. Anderson, K. P. Burnham and J. L. Laake. 1993. Distance Sampling: estimating abundance

of biological populations. Chapman & Hall, London, 446 pp. 

Cramer, J. 1994. Large pelagic logbook newsletter - 1993. NOAA Tech. Mem. NMFS-SEFSC-352, 19 pp. 
176

Davis, R., G. Scott, B. Würsig, W. Evans, G. Fargion, L. Hansen, K. Mullin, N. May, T. Leming, B. Mate, J. Norris

and T. Jefferson. In preparation. Distribution and abundance of marine mammals in the north-central and

western Gulf of Mexico: Final Report, OCS Study #MMS 94-0003. Texas Institute of Oceanography and the

National Marine Fisheries Service. U.S. Dept. of the Interior, Minerals Mgmt. Service, Gulf of Mexico OCS

Region, New Orleans, Louisiana. 

Hansen, L. J., K. D. Mullin and C. L. Roden. 1995. Estimates of cetacean abundance in the northern Gulf of Mexico

from vessel surveys. Southeast Fisheries Science Center, Miami Laboratory, Contribution No. MIA-94/95-25,

9 pp + tables and figures. 

Laake, J. L., S. T. Buckland, D. R. Anderson, and K. P. Burnham. DISTANCE user’s guide, V2.0. Colorado

Cooperative Fish & Wildlife Research Unit, Colorado State University, Ft. Collins, Colorado, 72 pp. 

Leatherwood, S. and R. R. Reeves. 1983. The Sierra Club handbook of whales and dolphins. Sierra Club Books, San

Francisco, 302 pp. 

Perrin, W. F. and J. W. Gilpatrick, Jr. 1994. Spinner dolphin Stenella longirostris (Gray, 1828). Pages 99-128 in S.

H. Ridgway and R. Harrison (editors), Handbook of marine mammals, Vol. 5: The first book of dolphins.

Academic Press, London, 416 pp.
177

Figure 1. Distribution of rough-toothed dolphin sightings during NOAA Ship Oregon

II marine mammal surveys during 1991-1994. The straight lines show transects during

two surveys and are examples of typical survey transects. Isobaths are in 183 m (100

fm) intervals. 

ROUGH-TOOTHED DOLPHIN (Steno bredanensis):

Northern Gulf of Mexico Stock

STOCK DEFINITION AND GEOGRAPHIC RANGE

The rough-toothed dolphin is distributed worldwide in tropical to warm temperate waters (Leatherwood and

Reeves 1983; Miyazaki and Perrin 1994). Sightings of these animals in the northern Gulf of Mexico occur primarily

over the deeper waters off the continental shelf [Southeast Fisheries Science Center (SEFSC) unpublished data].

Rough-toothed dolphins were seen in all seasons during recent seasonal GulfCet aerial surveys of the northern Gulf

of Mexico during 1993-1995 (Davis et al., in preparation). There is no information on stock differentiation for the

Atlantic population. 

POPULATION SIZE

Estimates of abundance were derived through the application of distance sampling analysis (Buckland et al.

1993) and the computer program DISTANCE (Laake et al. 1993) to sighting data collected during 1991-1994 springsummer, visual sampling, line-transect vessel surveys of the northern Gulf of Mexico (Hansen et al. 1995), which

includes data collected as part of the GulfCet program (Davis et al., in preparation). These surveys were conducted

throughout the area from approximately the 200 m isobath along the U.S. coast to the seaward extent of the U.S.

Exclusive Economic Zone. The

seasonal GulfCet aerial surveys

included only a small portion of

the stock range and these data

were not used for abundance

estimation. Estimated abundance

of rough-toothed dolphins by

survey year [coefficient of

variation (CV) in parentheses]

was 545 in 1991 (1.15), 758 in

1992 (0.58), 1,192 in 1993

(0.48), and 527 in 1994 (0.86)

(Hansen et al. 1995). Survey

effort-weighted estimated average

abundance of rough-toothed

dolphins for all surveys combined

was 852 (CV = 0.31) (Hansen et

al. 1995).

Minimum Population Estimate

The minimum population size was estimated from the average estimate abundance which was 852 roughtoothed dolphins (CV = 0.31) (Hansen et al. 1995). The minimum population estimate is the lower limit of the twotailed 60% confidence interval of the log-normal distributed abundance estimate, which is equivalent to the 20th

percentile of the log-normal distributed abundance estimate as specified by NMFS (Anon. 1994). The minimum

population estimate is 660 rough-toothed dolphins. 

Current Population Trend

The 1993 abundance estimate was greater than the 1991, 1993, and 1994 estimates; however, the abundance

estimates were not significantly different using the criteria of no overlap of log-normal 95% confidence intervals. The

apparent differences in abundance estimates may have been caused by small sample sizes (Hansen et al. 1995) or by

inter-annual variation in distribution patterns or spatial sampling patterns, rather than changes in population size. 
178

CURRENT AND MAXIMUM NET PRODUCTIVITY RATES

Current and maximum net productivity rates are not known for this stock; therefore, the default maximum

net productivity rate of 0.04 (Anon. 1994) was used for purposes of this assessment. 

POTENTIAL BIOLOGICAL REMOVAL

Potential biological removal level (PBR) was specified as the product of the minimum population size, one

half the maximum net productivity rate, and a recovery factor for endangered, threatened, or depleted stocks, or stocks

of unknown status relative to optimum sustainable population (OSP) (Anon. 1994). The recovery factor was set at 0.50

because the status of the stock relative to OSP is unknown. The resulting PBR for this stock is 6.6 rough-toothed

dolphins. 

ANNUAL HUMAN-CAUSED MORTALITY AND SERIOUS INJURY

The level of past or current, direct, human-caused mortality of rough-toothed dolphins in the northern Gulf

of Mexico is unknown. Available information indicates there likely is little, if any, fisheries interaction with roughtoothed dolphins in the northern Gulf of Mexico. There have been no logbook reports of fishery-related mortality or

serious injury and no fishery-related mortality or serious injury has been observed.

There were no documented strandings of rough-toothed dolphins in the northern Gulf of Mexico during 1987-

1994 which were classified as likely caused by fishery interactions or other human-related causes. Stranding data

probably underestimate the extent of fishery-related mortality and serious injury because not all of the marine mammals

which die or are seriously injured may wash ashore, nor will all of those that do wash ashore necessarily show signs

of entanglement or other fishery-interaction. Finally, the level of technical expertise among stranding network

personnel varies widely as does the ability to recognize signs of fishery interaction. 

Total fishery-related mortality and serious injury for this stock is less than 10% of the calculated PBR and,

therefore, can be considered insignificant and approaching zero mortality and serious injury rate. This determination

cannot be made for specific fisheries until the implementing regulations for Section 118 of the MMPA have been

reviewed by the public and finalized. 

Fisheries Information

Pelagic swordfish, tunas, and billfish are the targets of the longline fishery operating in the U.S. Gulf of

Mexico. Total longline effort for the Gulf of Mexico pelagic fishery, including OCS edge, continental slope, and

Mexican territorial waters, based on mandatory logbook reporting, was 4,400 sets in 1991, 4,850 sets in 1992, and

3,260 sets in 1993 (Cramer 1994). This fishery has been monitored with about 5% observer coverage, in terms of trips

observed, since 1992. There were no reports of mortality or serious injury of rough-toothed dolphins by this fishery.

Pair trawl fishing gear has the potential to capture marine mammals, but there have been no reports of

mortality or serious injury to marine mammals in the Gulf of Mexico. This fishery has not been observed by NMFS

observers, and there are no other data available as to the extent of this fishery in the Gulf of Mexico. It is assumed that

it is very limited in scope and duration. 

STATUS OF STOCK

The status of this stock relative to OSP is unknown and there are insufficient data to determine population

trends. This species is not listed under the Endangered Species Act. The total level of human-caused mortality and

serious injury is unknown, but it is believed to be insignificant relative to PBR; therefore, this is not a strategic stock.

REFERENCES

Anon. 1994. Report of the PBR (Potential Biological Removal) workshop. June 27-29, 1994. NOAA, NMFS

Southwest Fisheries Science Center, La Jolla, California, 13 pp. + Appendices. 

Buckland, S. T., D. R. Anderson, K. P. Burnham and J. L. Laake. 1993. Distance Sampling: estimating abundance

of biological populations. Chapman & Hall, London, 446 pp. 

Cramer, J. 1994. Large pelagic logbook newsletter - 1993. NOAA Tech. Mem. NMFS-SEFSC-352, 19 pp. 
179

Davis, R., G. Scott, B. Würsig, W. Evans, G. Fargion, L. Hansen, K. Mullin, N. May, T. Leming, B. Mate, J. Norris

and T. Jefferson. In preparation. Distribution and abundance of marine mammals in the north-central and

western Gulf of Mexico: Final Report. OCS Study #MMS 94-0003. Texas Institute of Oceanography and the

National Marine Fisheries Service. U.S. Dept. of the Interior, Minerals Mgmt. Service, Gulf of Mexico OCS

Region, New Orleans, Louisiana. 

Hansen, L. J., K. D. Mullin and C. L. Roden. 1995. Estimates of cetacean abundance in the northern Gulf of Mexico

from vessel surveys. Southeast Fisheries Science Center, Miami Laboratory, Contribution No. MIA-94/95-25,

9 pp. + tables and figures. 

Laake, J. L., S. T. Buckland, D. R. Anderson, and K. P. Burnham. DISTANCE user’s guide, V2.0. Colorado

Cooperative Fish & Wildlife Research Unit, Colorado State University, Ft. Collins, Colorado, 72 pp. 

Leatherwood, S. and R. R. Reeves. 1983. The Sierra Club handbook of whales and dolphins. Sierra Club Books, San

Francisco, 302 pp. 

Miyazaki, N. and W. F. Perrin. 1994. Rough-toothed dolphin Steno bredanensis (Lesson, 1828). Pages 1-21 in S.

H. Ridgway and R. Harrison (editors), Handbook of marine mammals, Vol. 5: The first book of dolphins.

Academic Press, London, 416 pp.
180

Figure 1. Distribution of clymene dolphin sightings during NOAA Ship Oregon II

marine mammal surveys during 1991-1994. The straight lines show transects during

two surveys and are examples of typical survey transects. Isobaths are in 183 m (100

fm) intervals. 

CLYMENE DOLPHIN (Stenella clymene):

Northern Gulf of Mexico Stock

STOCK DEFINITION AND GEOGRAPHIC RANGE

The Clymene dolphin is endemic to tropical and sub-tropical waters of the Atlantic (Leatherwood and Reeves

1983; Perrin and Mead 1994). Sightings of these animals in the northern Gulf of Mexico occur primarily over the

deeper waters off the continental shelf (Mullin et al. 1994). Clymene dolphins were seen in the winter, spring and

summer during recent seasonal GulfCet aerial surveys of the northern Gulf of Mexico during 1993-1995 (Davis et al.,

in preparation). There is no information on stock differentiation for the Atlantic population. 

POPULATION SIZE

Estimates of abundance were derived through the application of distance sampling analysis (Buckland et al.

1993) and the computer program DISTANCE (Laake et al. 1993) to sighting data collected during 1991-1994 springsummer, visual sampling, line-transect vessel surveys of the northern Gulf of Mexico (Hansen et al. 1995) (Fig. 1),

which includes data collected as part of the GulfCet program (Davis et al., in preparation). These surveys were

conducted throughout the area from approximately the 200 m isobath along the U.S. coast to the seaward extent of the

U.S. Exclusive Economic Zone.

The seasonal GulfCet aerial

surveys included only a small

portion of the stock range and

these data were not used for

abundance estimation. Estimated

abundance of Clymene dolphins

by survey year [coefficient of

variation (CV) in parentheses]

was 1,936 in 1991 (0.69), 3,390

in 1992 (0.48), 6,486 in 1993

(0.46), and 12,255 in 1994 (0.62)

(Hansen et al. 1995). Survey

effort-weighted estimated

average abundance of Clymene

dolphins for all surveys combined

was 5,571 (CV = 0.37) (Hansen

et al. 1995). 

Minimum Population Estimate

The minimum population size was estimated from the average estimate abundance which was 5,571 Clymene

dolphins (CV = 0.37) (Hansen et al. 1995). The minimum population estimate is the lower limit of the two-tailed 60%

confidence interval of the log-normal distributed abundance estimate, which is equivalent to the 20th percentile of the

log-normal distributed abundance estimate as specified by NMFS (Anon. 1994). The minimum population estimate

is 4,120 Clymene dolphins. 

Current Population Trend

The abundance estimates showed an increasing trend during 1991-1994; however, the estimates were not

significantly different using the criteria of no overlap of log-normal 95% confidence intervals. The apparent

differences in abundance estimates may have been caused by small sample sizes (Hansen et al. 1995) or by inter-annual

variation in distribution patterns or spatial sampling patterns, rather than changes in population size. 

CURRENT AND MAXIMUM NET PRODUCTIVITY RATES

Current and maximum net productivity rates are not known for this stock; therefore, the default maximum

net productivity rate of 0.04 (Anon. 1994) was used for purposes of this assessment. 
181

POTENTIAL BIOLOGICAL REMOVAL

Potential biological removal level (PBR) was specified as the product of the minimum population size, one

half the maximum net productivity rate, and a recovery factor for endangered, threatened, or depleted stocks, or stocks

of unknown status relative to optimum sustainable population (OSP) (Anon. 1994). The recovery factor was set at 0.50

because the status of the stock relative to OSP is unknown. PBR for this stock is 41 Clymene dolphins. 

ANNUAL HUMAN-CAUSED MORTALITY AND SERIOUS INJURY

The level of past or current, direct, human-caused mortality of Clymene dolphins in the northern Gulf of

Mexico is unknown. Available information indicates there likely is little, if any, fisheries interaction with Clymene

dolphins in the northern Gulf of Mexico. There have been no logbook reports of fishery-related mortality or serious

injury and no fishery-related mortality or serious injury has been observed.

There were no documented strandings of Clymene dolphins in the northern Gulf of Mexico during 1987-1994

which were classified as likely caused by fishery interactions or other human-related causes. Stranding data probably

underestimate the extent of fishery-related mortality and serious injury because not all of the marine mammals which

die or are seriously injured may wash ashore, nor will all of those that do wash ashore necessarily show signs of

entanglement or other fishery-interaction. Finally, the level of technical expertise among stranding network personnel

varies widely as does the ability to recognize signs of fishery interaction. 

The total known fishery-related mortality and serious injury for this stock is less than 10% of the calculated

PBR and, therefore, can be considered insignificant and approaching zero mortality and serious injury rate. This

determination cannot be made for specific fisheries until the implementing regulations for Section 118 of the MMPA

have been reviewed by the public and finalized. 

Fisheries Information

Pelagic swordfish, tunas, and billfish are the targets of the longline fishery operating in the U.S. Gulf of

Mexico. Total longline effort for the Gulf of Mexico pelagic fishery, including OCS edge, continental slope, and

Mexican territorial waters, based on mandatory logbook reporting, was 4,400 sets in 1991, 4,850 sets in 1992, and

3,260 sets in 1993 (Cramer 1994). This fishery has been monitored with about 5% observer coverage, in terms of trips

observed, since 1992. There were no reports of mortality or serious injury to Clymene dolphins by this fishery. 

Pair trawl fishing gear has the potential to capture marine mammals, but there have been no reports of

mortality or serious injury to marine mammals in the Gulf of Mexico. This fishery has not been observed by NMFS

observers, and there are no other data available as to the extent of this fishery in the Gulf of Mexico.

STATUS OF STOCK

The status of this stock relative to OSP is unknown and there are insufficient data to determine population

trends. This species is not listed under the Endangered Species Act. The total level of human-caused mortality and

serious injury is unknown, but it is believed to be insignificant relative to PBR; therefore, this is not a strategic stock.

REFERENCES

Anon. 1994. Report of the PBR (Potential Biological Removal) workshop. June 27-29, 1994. NOAA, NMFS

Southwest Fisheries Science Center, La Jolla, California, 13 pp. + Appendices. 

Buckland, S. T., D. R. Anderson, K. P. Burnham and J. L. Laake. 1993. Distance Sampling: estimating abundance

of biological populations. Chapman & Hall, London, 446 pp. 

Cramer, J. 1994. Large pelagic logbook newsletter - 1993. NOAA Tech. Mem. NMFS-SEFSC-352, 19 pp. 

Davis, R., G. Scott, B. Würsig, W. Evans, G. Fargion, L. Hansen, K. Mullin, N. May, T. Leming, B. Mate, J. Norris

and T. Jefferson. In preparation. Distribution and abundance of marine mammals in the north-central and

western Gulf of Mexico: Final Report. OCS Study #MMS 94-0003. Texas Institute of Oceanography and the

National Marine Fisheries Service. U.S. Dept. of the Interior, Minerals Mgmt. Service, Gulf of Mexico OCS

Region, New Orleans, Louisiana. 

Hansen, L. J., K. D. Mullin and C. L. Roden. 1995. Estimates of cetacean abundance in the northern Gulf of Mexico

from vessel surveys. Southeast Fisheries Science Center, Miami Laboratory, Contribution No. MIA-94/95-25,

9 pp. + tables and figures. 
182

Laake, J. L., S. T. Buckland, D. R. Anderson, and K. P. Burnham. DISTANCE user’s guide, V2.0. Colorado

Cooperative Fish & Wildlife Research Unit, Colorado State University, Ft. Collins, Colorado, 72 pp. 

Leatherwood, S. and R. R. Reeves. 1983. The Sierra Club handbook of whales and dolphins. Sierra Club Books, San

Francisco, 302 pp. 

Mullin, K. D., L V. Higgins, T. A. Jefferson, and L. J. Hansen. 1994. Sightings of the Clymene dolphin (Stenella

clymene) in the Gulf of Mexico. Mar. Mam. Sci. 10(4): 464-470.

Perrin, W. F. and J. G. Mead. 1994. Clymene dolphin Stenella clymene (Gray, 1846). Pages 161-171 in S. H. Ridgway

and R. Harrison (editors), Handbook of marine mammals, Vol. 5: The first book of dolphins. Academic

Press, London, 416 pp.
183

Figure 1. Distribution of Fraser’s dolphin sightings during NOAA Ship Oregon II

surveys during 1991-1994 (filled circle) and during GulfCet seasonal aerial surveys

(unfilled circles). The straight lines show transects during two ship surveys and are

examples of typical survey transects. Isobaths are in 183 m (100 fm) intervals.

FRASER'S DOLPHIN (Lagenodelphis hosei):

Northern Gulf of Mexico Stock

STOCK DEFINITION AND GEOGRAPHIC RANGE

Fraser's dolphin is distributed worldwide in tropical waters (Perrin et al. 1994). Sightings of these animals

in the northern Gulf of Mexico occur primarily over the deeper waters off the continental shelf (Leatherwood et al.

1993). Fraser's dolphins have been observed recently in the northern Gulf of Mexico during the spring, summer, and

fall (Leatherwood et al. 1993), and also were seen in the winter during recent seasonal GulfCet aerial surveys of the

northern Gulf of Mexico during 1993-1995 (Davis et al., in preparation). There is no information on stock

differentiation for the Atlantic population. 

POPULATION SIZE

Estimates of abundance were derived through the application of distance sampling analysis (Buckland et al.

1993) and the computer program DISTANCE (Laake et al. 1993) to sighting data collected during 1991-1994 springsummer, visual sampling, line-transect vessel surveys of the northern Gulf of Mexico (Hansen et al. 1995) (Fig. 1),

which includes data collected as part of the GulfCet program (Davis et al., in preparation). These surveys were

conducted throughout the area

from approximately the 200 m

isobath along the U.S. coast to

the seaward extent of the U.S.

Exclusive Economic Zone. The

seasonal GulfCet aerial surveys

included only a small portion of

the stock range and these data

were not used for abundance

estimation. Estimated abundance

of Fraser’s dolphins by survey

year [coefficient of variation

(CV) in parentheses] was zero in

1991, 443 in 1992 (0.92), and

zero in 1993 and 1994 (Hansen

et al. 1995). Survey effortweighted estimated average

abundance of Fraser's dolphins

for all vessel surveys combined

was 127 (CV = 0.90) (Hansen et al. 1995).

Minimum Population Estimate

The minimum population size was estimated from the average estimate abundance which was 127 Fraser’s

dolphins (CV = 0.90) (Hansen et al. 1995). The minimum population estimate is the lower limit of the two-tailed 60%

confidence interval of the log-normal distributed abundance estimate, which is equivalent to the 20th percentile of the

log-normal distributed abundance estimate as specified by NMFS (Anon. 1994). The minimum population estimate

is 66 Fraser’s dolphins. 

Current Population Trend

No trend was identified in the annual abundance estimates. There were no observations of Fraser's dolphins

during 1991 and 1993 vessel surveys, and the 1992 estimate is based on only one observation (Hansen et al. 1995);

however, five other sightings of Fraser's dolphins were documented in the northern Gulf of Mexico during other

surveys in 1992, 1993 and 1994 (Leatherwood et al. 1993, SEFSC unpublished data). The apparent differences in

abundance estimates may have been caused by low sampling intensity relative to population size (Hansen et al. 1995)

or by inter-annual variation in distribution patterns or spatial sampling patterns, rather than changes in population size.
184

CURRENT AND MAXIMUM NET PRODUCTIVITY RATES

Current and maximum net productivity rates are not known; therefore, the default maximum net productivity

rate of 0.04 (Anon. 1994) was used for purposes of this assessment. 

POTENTIAL BIOLOGICAL REMOVAL

Potential biological removal level (PBR) was specified as the product of the minimum population size, one

half the maximum net productivity rate, and a recovery factor for endangered, threatened, or depleted stocks, or stocks

of unknown status relative to optimum sustainable population (OSP) (Anon. 1994). The recovery factor was set at 0.50

because the status of the stock relative to OSP is unknown. PBR for this stock is 0.7 Fraser’s dolphins. 

ANNUAL HUMAN-CAUSED MORTALITY AND SERIOUS INJURY

The level of past or current, direct, human-caused mortality of Fraser's dolphins in the northern Gulf of

Mexico is unknown. Available information indicates there likely is little, if any, fisheries interaction with Fraser’s

dolphins in the northern Gulf of Mexico. There have been no logbook reports of fishery-related mortality or serious

injury and no fishery-related mortality or serious injury has been observed.

There were no documented strandings of Fraser's dolphins in the northern Gulf of Mexico during 1987-1994

which were classified as likely caused by fishery interactions or other human-related causes. Stranding data probably

underestimate the extent of fishery-related mortality and serious injury because not all of the marine mammals which

die or are seriously injured may wash ashore, nor will all of those that do wash ashore necessarily show signs of

entanglement or other fishery-interaction. Finally, the level of technical expertise among stranding network personnel

varies widely as does the ability to recognize signs of fishery interaction. 

 Available information indicates there likely is little, if any, fisheries interaction with Fraser's dolphins in the

northern Gulf of Mexico. The total known fishery-related mortality and serious injury for this stock is less than 10%

of the calculated PBR and, therefore, can be considered insignificant and approaching zero mortality and serious injury

rate. This determination cannot be made for specific fisheries until the implementing regulations for Section 118 of

the MMPA have been reviewed by the public and finalized. 

Fisheries Information

Pelagic swordfish, tunas, and billfish are the targets of the longline fishery operating in the U.S. Gulf of

Mexico. Total longline effort for the Gulf of Mexico pelagic fishery, including OCS edge, continental slope, and

Mexican territorial waters, based on mandatory logbook reporting, was 4,400 sets in 1991, 4,850 sets in 1992, and

3,260 sets in 1993 (Cramer 1994). This fishery has been monitored with about 5% observer coverage, in terms of trips

observed, since 1992. There were no reports of mortality or serious injury of Fraser’s dolphins by this fishery. 

Pair trawl fishing gear has the potential to capture marine mammals, but there have been no reports of

mortality or serious injury to marine mammals in the Gulf of Mexico. This fishery has not been observed by NMFS

observers, and there are no other data available as to the extent of this fishery in the Gulf of Mexico.

STATUS OF STOCK

The status of this stock relative to OSP is unknown and there are insufficient data to determine population

trends. This species is not listed under the Endangered Species Act. The total level of human-caused mortality and

serious injury is unknown, but it is believed to be insignificant relative to PBR; therefore this is not a strategic stock.

REFERENCES

Anon. 1994. Report of the PBR (Potential Biological Removal) workshop. June 27-29, 1994. NOAA, NMFS

Southwest Fisheries Science Center, La Jolla, California, 13 pp. + Appendices. 

Buckland, S. T., D. R. Anderson, K. P. Burnham and J. L. Laake. 1993. Distance Sampling: estimating abundance

of biological populations. Chapman & Hall, London, 446 pp. 

Cramer, J. 1994. Large pelagic logbook newsletter - 1993. NOAA Tech. Mem. NMFS-SEFSC-352, 19 pp. 
185

Davis, R., G. Scott, B. Würsig, W. Evans, G. Fargion, L. Hansen, K. Mullin, N. May, T. Leming, B. Mate, J. Norris

and T. Jefferson. In preparation. Distribution and abundance of marine mammals in the north-central and

western Gulf of Mexico: Final Report. OCS Study #MMS 94-0003. Texas Institute of Oceanography and the

National Marine Fisheries Service. U.S. Dept. of the Interior, Minerals Mgmt. Service, Gulf of Mexico OCS

Region, New Orleans, Louisiana. 

Hansen, L. J., K. D. Mullin and C. L. Roden. 1995. Estimates of cetacean abundance in the northern Gulf of Mexico

from vessel surveys. Southeast Fisheries Science Center, Miami Laboratory, Contribution No. MIA-94/95-25,

9 pp. + tables and figures. 

Laake, J. L., S. T. Buckland, D. R. Anderson, and K. P. Burnham. DISTANCE user’s guide, V2.0. Colorado

Cooperative Fish & Wildlife Research Unit, Colorado State University, Ft. Collins, Colorado, 72 pp. 

Leatherwood, S., T. A. Jefferson, J. C. Norris, W. E. Stevens, L. J. Hansen, and K. D. Mullin. 1993. Occurrence and

sounds of Fraser's dolphin in the Gulf of Mexico. The Texas Journal of Science, 45(4):349-354. 

Perrin, W. F., S. Leatherwood and A. Collet. 1994. Fraser's dolphin Lagenodelphis hosei (Fraser 1956). Pages 225-

240 in S. H. Ridgway and R. Harrison (editors), Handbook of marine mammals, Vol. 5: The first book of

dolphins. Academic Press, London, 416 pp.
186

Figure 1. Distribution of killer whale sightings during NOAA Ship Oregon II marine

mammal surveys during 1991-1994. The straight lines show transects during two

surveys and are examples of typical survey transects. Isobaths are in 183 m (100 fm)

intervals.

KILLER WHALE (Orcinus orca):

Northern Gulf of Mexico Stock

STOCK DEFINITION AND GEOGRAPHIC RANGE

The killer whale is distributed worldwide from tropical to polar regions (Leatherwood and Reeves 1983).

Sightings of these animals in the northern Gulf of Mexico occur primarily over the deeper waters off the continental

shelf [Southeast Fisheries Science Center (SEFSC) unpublished data]. Killer whales were seen only in the summer

during recent seasonal GulfCet aerial surveys of the northern Gulf of Mexico during 1993-1995 (Davis et al., in

preparation) and in the late spring during vessel surveys (SEFSC unpublished data). Different stocks have been

identified in the northeastern Pacific based on morphological, behavioral, and genetic characteristics (Bigg et al. 1990;

Hoelzel 1991). There is no information on stock differentiation for the Atlantic population, although an analysis of

vocalizations of killer whales from Iceland and Norway indicated that stocks from these areas may represent different

stocks (Moore et al. 1988). 

POPULATION SIZE

Estimates of abundance were derived through the application of distance sampling analysis (Buckland et al.

1993) and the computer program DISTANCE (Laake et al. 1993) to sighting data collected during 1991-1994 springsummer, visual sampling, line-transect vessel surveys of the northern Gulf of Mexico (Hansen et al. 1995), which

includes data collected as part of the GulfCet program (Davis et al., in preparation). These surveys were conducted

throughout the area from approximately the 200 m isobath along the U.S. coast to the seaward extent of the U.S.

Exclusive Economic Zone. The

seasonal GulfCet aerial surveys

included only a small portion of

the stock range and these data

were not used for abundance

estimation. Estimated killer

whale abundance by survey year

[coefficient of variation (CV) in

parentheses] was zero in 1991,

138 in 1992 (0.96), 641 in 1993

(0.50), and 193 in 1994 (1.12)

(Hansen et al. 1995). Survey

effort-weighted estimated average

abundance of killer whales for all

surveys combined was 277 (CV

= 0.42) (Hansen et al. 1995).

Minimum Population Estimate

The minimu m

population size was estimated from the average estimate abundance which was 277 killer whales (CV = 0.42) (Hansen

et al. 1995). The minimum population estimate is the lower limit of the two-tailed 60% confidence interval of the lognormal distributed abundance estimate, which is equivalent to the 20th percentile of the log-normal distributed

abundance estimate as specified by NMFS (Anon. 1994). The minimum population estimate is 197 killer whales. 

Current Population Trend

The abundance estimates were highest during 1993; however, there were no observations of this species during

1991, and the 1992-1994 estimates were not significantly different using the criteria of no overlap of log-normal 95%

confidence intervals. The apparent differences in abundance estimates may have been caused by lower sampling effort

during 1991, and by low sampling intensity relative to population size (Hansen et al. 1995) or by inter-annual variation

in distribution patterns or spatial sampling patterns, rather than changes in population size. Preliminary analysis of
187

existing photo-identification data shows that some individual whales have been seen during more than one survey

(SEFSC unpublished data). 

CURRENT AND MAXIMUM NET PRODUCTIVITY RATES

Current and maximum net productivity rates for this stock are not known; therefore, the default maximum

net productivity rate of 0.04 (Anon. 1994) was used for purposes of this assessment. 

POTENTIAL BIOLOGICAL REMOVAL

Potential biological removal level (PBR) was specified as the product of the minimum population size, one

half the maximum net productivity rate, and a recovery factor for endangered, threatened, or depleted stocks, or stocks

of unknown status relative to optimum sustainable population (OSP) (Anon. 1994). The recovery factor was set at 0.50

because the status of the stock relative to OSP is unknown. PBR for this stock is 2.0 killer whales. 

ANNUAL HUMAN-CAUSED MORTALITY AND SERIOUS INJURY

The level of past or current, direct, human-caused mortality of killer whales in the northern Gulf of Mexico

is unknown. Available information indicates there likely is little, if any, fisheries interaction with killer whales in the

northern Gulf of Mexico. There have been no logbook reports of fishery-related mortality or serious injury and no

fishery-related mortality or serious injury has been observed.

There were no documented strandings of killer whales in the northern Gulf of Mexico during 1987-1994

which were classified as likely caused by fishery interactions or other human-related causes. Stranding data probably

underestimate the extent of fishery-related mortality and serious injury because not all of the marine mammals which

die or are seriously injured may wash ashore, nor will all of those that do wash ashore necessarily show signs of

entanglement or other fishery-interaction. Finally, the level of technical expertise among stranding network personnel

varies widely as does the ability to recognize signs of fishery interaction. 

The total known fishery-related mortality and serious injury for this stock is less than 10% of the calculated

PBR and, therefore, can be considered insignificant and approaching zero mortality and serious injury rate. This

determination cannot be made for specific fisheries until the implementing regulations for Section 118 of the MMPA

have been reviewed by the public and finalized. 

Fisheries Information

Pelagic swordfish, tunas, and billfish are the targets of the longline fishery operating in the U.S. Gulf of

Mexico. Total longline effort for the Gulf of Mexico pelagic fishery, including OCS edge, continental slope, and

Mexican territorial waters, based on mandatory logbook reporting, was 4,400 sets in 1991, 4,850 sets in 1992, and

3,260 sets in 1993 (Cramer 1994). This fishery has been monitored with about 5% observer coverage, in terms of trips

observed, since 1992. There were no reports of mortality or serious injury of killer whales by this fishery. 

Pair trawl fishing gear has the potential to capture marine mammals, but there have been no reports of

mortality or serious injury to marine mammals in the Gulf of Mexico. This fishery has not been observed by NMFS

observers, and there are no other data available as to the extent of this fishery in the Gulf of Mexico. It is assumed that

it is very limited in scope and duration. 

STATUS OF STOCK

The status of this stock relative to OSP is unknown and there are insufficient data to determine population

trends. This species is not listed under the Endangered Species Act. The total level of human-caused mortality and

serious injury is unknown, but it is believed to be insignificant relative to PBR; therefore, this is not a strategic stock.

REFERENCES

Anon. 1994. Report of the PBR (Potential Biological Removal) workshop. June 27-29, 1994. NOAA, NMFS

Southwest Fisheries Science Center, La Jolla, California, 13 pp. + Appendices. 
188

Bigg, M. A., P. F. Olesiuk, G. M. Ellis, J. K. B. Ford and K. C. Balcomb. 1990. Social organization and genealogy

of resident killer whales (Orcinus orca) in the coastal waters of British Columbia and Washington State.

Pages 383-405 in P. S. Hammond, S. A. Mizroch and G. P. Donovan (editors), Individual recognition of

cetaceans: Use of photoidentification and other techniques to estimate population parameters, Rep. Int. Whal.

Commn., Special Issue 12, Cambridge, 440 pp. 

Buckland, S. T., D. R. Anderson, K. P. Burnham and J. L. Laake. 1993. Distance Sampling: estimating abundance

of biological populations. Chapman & Hall, London, 446 pp. 

Cramer, J. 1994. Large pelagic logbook newsletter - 1993. NOAA Tech. Mem. NMFS-SEFSC-352, 19 pp. 

Davis, R., G. Scott, B. Würsig, W. Evans, G. Fargion, L. Hansen, K. Mullin, N. May, T. Leming, B. Mate, J. Norris

and T. Jefferson. In preparation. Distribution and abundance of marine mammals in the north-central and

western Gulf of Mexico: Final Report. OCS Study #MMS 94-0003. Texas Institute of Oceanography and the

National Marine Fisheries Service. U.S. Dept. of the Interior, Minerals Mgmt. Service, Gulf of Mexico OCS

Region, New Orleans, Louisiana. 

Hansen, L. J., K. D. Mullin and C. L. Roden. 1995. Estimates of cetacean abundance in the northern Gulf of Mexico

from vessel surveys. Southeast Fisheries Science Center, Miami Laboratory, Contribution No. MIA-94/95-25,

9 pp. + tables and figures. 

Hoelzel, A. R. 1991. Analysis of regional mitochondrial DNA variation in the killer whale; implications for

conservation. Pages 225-233 in A. R. Hoelzel (editor), Genetic ecology of whales and dolphins, Rep. Int.

Whal. Commn. Special Issue 13, Cambridge, 311 pp. 

Laake, J. L., S. T. Buckland, D. R. Anderson, and K. P. Burnham. DISTANCE user’s guide, V2.0. Colorado

Cooperative Fish & Wildlife Research Unit, Colorado State University, Ft. Collins, Colorado, 72 pp. 

Leatherwood, S. and R. R. Reeves. 1983. The Sierra Club handbook of whales and dolphins. Sierra Club Books, San

Francisco, 302 pp. 

Moore, S. E., J. K. Francine, A. E. Bowles and K. B. Ford. 1988. Analysis of calls of killer whales, Orcinus orca, from

Iceland and Norway. Rit. Fiskideild. 11:225-250.
189

Figure 1. Distribution of false killer whale sightings during NOAA Ship Oregon II

marine mammal surveys during 1991-1994 (filled circles) and during GulfCet seasonal

aerial surveys (filled circles). The straight lines show transects during two surveys and

are examples of typical survey transects. Isobaths are in 183 m (100 fm) intervals. 

FALSE KILLER WHALE (Pseudorca crassidens):

Northern Gulf of Mexico Stock

STOCK DEFINITION AND GEOGRAPHIC RANGE

The false killer whale is distributed worldwide throughout warm temperate and tropical oceans (Leatherwood

and Reeves 1983). Sightings of this species in the northern Gulf of Mexico occur primarily over the deeper waters off

the continental shelf [Southeast Fisheries Science Center (SEFSC) unpublished data]. False killer whales were seen

only in the summer during recent seasonal GulfCet aerial surveys of the northern Gulf of Mexico during 1993-1995

(Davis et al., in preparation) and in the late spring during vessel surveys (NMFS unpublished data). There is no

information on stock differentiation for the Atlantic population. 

POPULATION SIZE

Estimates of abundance were derived through the application of distance sampling analysis (Buckland et al.

1993) and the computer program DISTANCE (Laake et al. 1993) to sighting data collected during 1991-1994 springsummer, visual sampling, line-transect vessel surveys of the northern Gulf of Mexico (Hansen et al. 1995) (Fig. 1),

which includes data collected as part of the GulfCet program (Davis et al., in preparation). These surveys were

conducted throughout the area from approximately the 200 m isobath along the U.S. coast to the seaward extent of the

U.S. Exclusive Economic Zone.

The seasonal GulfCet aerial

surveys included only a small

portion of the stock range and

these data were not used for

abundance estimation .

Estimated abundance of false

killer whales by survey year

[coefficient of variation (CV) in

parentheses] was 661 in 1991

(0.88), 196 in 1992 (1.00), 77 in

1993 (1.08), and 744 in 1994

(1.14) (Hansen et al. 1995).

Survey effort-weighted estimated

average abundance of false killer

whales for all surveys combined

was 381 (CV = 0.62) (Hansen et

al. 1995). 

Minimum Population Estimate

The minimum population size was estimated from the average estimate abundance which was 381 false killer

whales (CV = 0.62) (Hansen et al. 1995). The minimum population estimate is the lower limit of the two-tailed 60%

confidence interval of the log-normal distributed abundance estimate, which is equivalent to the 20th percentile of the

log-normal distributed abundance estimate as specified by NMFS (Anon. 1994). The minimum population estimate

is 236 false killer whales. 

Current Population Trend

No trend was identified in the annual abundance estimates, and the differences in the abundance estimates

were not significant using the criteria of no overlap of log-normal 95% confidence intervals. The apparent differences

in abundance estimates may have been caused by lower sampling effort during 1991, by low sampling intensity relative

to population size (Hansen et al. 1995), or by inter-annual variation in distribution patterns or spatial sampling

patterns, rather than changes in population size. 
190

CURRENT AND MAXIMUM NET PRODUCTIVITY RATES

Current and maximum net productivity rates are not known; therefore, the default maximum net productivity

rate of 0.04 (Anon. 1994) was used for purposes of this assessment. 

POTENTIAL BIOLOGICAL REMOVAL

Potential biological removal level (PBR) was specified as the product of the minimum population size, one

half the maximum net productivity rate, and a recovery factor for endangered, threatened, or depleted stocks, or stocks

of unknown status relative to optimum sustainable population (OSP) (Anon. 1994). The recovery factor was set at 0.50

because the status of the stock relative to OSP is unknown. PBR for this stock is 2.4 false killer whales.

 

ANNUAL HUMAN-CAUSED MORTALITY AND SERIOUS INJURY

The level of past or current, direct, human-caused mortality of false killer whales in the northern Gulf of

Mexico is unknown. Available information indicates there likely is little, if any, fisheries interaction with false killer

whales in the northern Gulf of Mexico. There have been no logbook reports of fishery-related mortality or serious

injury and no fishery-related mortality or serious injury has been observed.

There were no documented strandings of false killer whales in the northern Gulf of Mexico during 1987-1994

which were classified as likely caused by fishery interactions or other human-related causes. Stranding data probably

underestimate the extent of fishery-related mortality and serious injury because not all of the marine mammals which

die or are seriously injured may wash ashore, nor will all of those that do wash ashore necessarily show signs of

entanglement or other fishery-interaction. Finally, the level of technical expertise among stranding network personnel

varies widely as does the ability to recognize signs of fishery interaction. 

The total known fishery-related mortality and serious injury for this stock is less than 10% of the calculated

PBR and, therefore, can be considered insignificant and approaching zero mortality and serious injury rate. This

determination cannot be made for specific fisheries until the implementing regulations for Section 118 of the MMPA

have been reviewed by the public and finalized. 

Fisheries Information

Pelagic swordfish, tunas, and billfish are the targets of the longline fishery operating in the U.S. Gulf of

Mexico. Total longline effort for the Gulf of Mexico pelagic fishery, including OCS edge, continental slope, and

Mexican territorial waters, based on mandatory logbook reporting, was 4,400 sets in 1991, 4,850 sets in 1992, and

3,260 sets in 1993 (Cramer 1994). This fishery has been monitored with about 5% observer coverage, in terms of trips

observed, since 1992. There were no reports of mortality or serious injury of false killer whales by this fishery. 

Pair trawl fishing gear has the potential to capture marine mammals, but there have been no reports of

mortality or serious injury to marine mammals in the Gulf of Mexico. This fishery has not been observed by NMFS

observers, and there are no other data available as to the extent of this fishery in the Gulf of Mexico. It is assumed that

it is very limited in scope and duration. 

STATUS OF STOCK

The status of this stock relative to OSP is unknown and there are insufficient data to determine population

trends. This species is not listed under the Endangered Species Act. The total level of human-caused mortality and

serious injury is unknown, but it is believed to be insignificant relative to PBR; therefore, this is not a strategic stock.

REFERENCES

Anon. 1994. Report of the PBR (Potential Biological Removal) workshop. June 27-29, 1994. NOAA, NMFS

Southwest Fisheries Science Center, La Jolla, California, 13 pp. + Appendices. 

Buckland, S. T., D. R. Anderson, K. P. Burnham and J. L. Laake. 1993. Distance Sampling: estimating abundance

of biological populations. Chapman & Hall, London, 446 pp. 

Cramer, J. 1994. Large pelagic logbook newsletter - 1993. NOAA Tech. Mem. NMFS-SEFSC-352, 19 pp. 
191

Davis, R., G. Scott, B. Würsig, W. Evans, G. Fargion, L. Hansen, K. Mullin, N. May, T. Leming, B. Mate, J. Norris

and T. Jefferson. In preparation. Distribution and abundance of marine mammals in the north-central and

western Gulf of Mexico: Final Report. OCS Study #MMS 94-0003. Texas Institute of Oceanography and the

National Marine Fisheries Service. U.S. Dept. of the Interior, Minerals Mgmt. Service, Gulf of Mexico OCS

Region, New Orleans, Louisiana. 

Hansen, L. J., K. D. Mullin and C. L. Roden. 1995. Estimates of cetacean abundance in the northern Gulf of Mexico

from vessel surveys. Southeast Fisheries Science Center, Miami Laboratory, Contribution No. MIA-94/95-25,

9 pp. + tables and figures. 

Laake, J. L., S. T. Buckland, D. R. Anderson, and K. P. Burnham. DISTANCE user’s guide, V2.0. Colorado

Cooperative Fish & Wildlife Research Unit, Colorado State University, Ft. Collins, Colorado, 72 pp. 

Leatherwood, S. and R. R. Reeves. 1983. The Sierra Club handbook of whales and dolphins. Sierra Club Books, San

Francisco, 302 pp.
192

Figure 1. Distribution of pygmy killer whale sightings during NOAA Ship Oregon II

marine mammal surveys during 1991-1994. The straight lines show transects during

two surveys and are examples of typical survey transects. Isobaths are in 183 m (100

fm) intervals. 

PYGMY KILLER WHALE (Feresa attenuata):

Northern Gulf of Mexico Stock

STOCK DEFINITION AND GEOGRAPHIC RANGE

The pygmy killer whale is distributed worldwide in tropical and subtropical waters (Ross and Leatherwood

1994). Sightings of these animals in the northern Gulf of Mexico occur primarily over the deeper waters off the

continental shelf [Southeast Fisheries Science Center (SEFSC) unpublished data]. Pygmy killer whales and melonheaded whales (Peponocephala electra) are difficult to distinguish and sightings of either species are often categorized

as pygmy killer/melon-headed whales. Sightings of this category were documented in all seasons during recent

seasonal GulfCet aerial surveys of the northern Gulf of Mexico during 1993-1995 (Davis et al., in preparation). There

is no information on stock differentiation for the Atlantic population. 

POPULATION SIZE

Estimates of abundance were derived through the application of distance sampling analysis (Buckland et al.

1993) and the computer program DISTANCE (Laake et al. 1993) to sighting data collected during 1991-1994 springsummer, visual sampling, line-transect vessel surveys of the northern Gulf of Mexico (Hansen et al. 1995) (Fig. 1),

which includes data collected as part of the GulfCet program (Davis et al., in preparation). These surveys were

conducted throughout the area from approximately the 200 m isobath along the U.S. coast to the seaward extent of the

U.S. Exclusive Economic Zone.

The seasonal GulfCet aerial

surveys included only a small

portion of the stock range and

these data were not used for

abundance estimation .

Estimated abundance of pygmy

killer whales by survey year

[coefficient of variation (CV) in

parentheses] was 2,347 in (0.81),

356 in 1992 (0.73), 153 in 1993

(1.13), and zero in 1994 (Hansen

et al. 1995). Survey effortweighted estimated average

abundance of pygmy killer

whales for all surveys combined

was 518 (CV = 0.81) (Hansen et

al. 1995).

Minimum Population Estimate

The minimum population size was estimated from the average estimated abundance which was 518 pygmy

killer whales (CV = 0.81) (Hansen et al. 1995). The minimum population estimate is the lower limit of the two-tailed

60% confidence interval of the log-normal distributed abundance estimate, which is equivalent to the 20th percentile

of the log-normal distributed abundance estimate as specified by NMFS (Anon. 1994). The minimum population

estimate is 285 pygmy killer whales. 

Current Population Trend

A declining trend was identified in the annual abundance estimates; however, the 1991-1993 abundance

estimates were not significantly different using the criteria of no overlap of log-normal 95% confidence intervals. There

were no observations of this species during the 1994 survey. The apparent differences in abundance estimates may have

been caused by lower sampling effort during 1991, by low sampling intensity relative to population size (Hansen et al.

1995), or by inter-annual variation in distribution patterns or spatial sampling patterns, rather than changes in

population size. 
193

CURRENT AND MAXIMUM NET PRODUCTIVITY RATES

Current and maximum net productivity rates are not known; therefore, the default maximum net productivity

rate of 0.04 (Anon. 1994) was used for purposes of this assessment. 

POTENTIAL BIOLOGICAL REMOVAL

Potential biological removal level (PBR) was specified as the product of the minimum population size, one

half the maximum net productivity rate, and a recovery factor for endangered, threatened, or depleted stocks, or stocks

of unknown status relative to optimum sustainable population (OSP) (Anon. 1994). The recovery factor was set at 0.50

because the status of the stock relative to OSP is unknown. PBR for this stock is 2.8 pygmy killer whales. 

ANNUAL HUMAN-CAUSED MORTALITY AND SERIOUS INJURY

There has historically been some take of this species in small cetacean fisheries in the Caribbean (Caldwell

and Caldwell 1971); however, the level of past or current, direct, human-caused mortality of pygmy killer whales in

the northern Gulf of Mexico is unknown. Available information indicates there likely is little, if any, fisheries

interaction with pygmy killer whales in the northern Gulf of Mexico. There have been no logbook reports of fisheryrelated mortality or serious injury and no fishery-related mortality or serious injury has been observed.

There were no documented strandings of pygmy killer whales in the northern Gulf of Mexico during 1987-

1994 which were classified as likely caused by fishery interactions or other human-related causes. Stranding data

probably underestimate the extent of fishery-related mortality and serious injury because not all of the marine mammals

which die or are seriously injured may wash ashore, nor will all of those that do wash ashore necessarily show signs

of entanglement or other fishery-interaction. Finally, the level of technical expertise among stranding network

personnel varies widely as does the ability to recognize signs of fishery interaction.

The total known fishery-related mortality and serious injury for this stock is less than 10% of the calculated

PBR and, therefore, can be considered insignificant and approaching zero mortality and serious injury rate. This

determination cannot be made for specific fisheries until the implementing regulations for Section 118 of the MMPA

have been reviewed by the public and finalized. 

Fisheries Information

Pelagic swordfish, tunas, and billfish are the targets of the longline fishery operating in the U.S. Gulf of

Mexico. Total longline effort for the Gulf of Mexico pelagic fishery, including OCS edge, continental slope, and

Mexican territorial waters, based on mandatory logbook reporting, was 4,400 sets in 1991, 4,850 sets in 1992, and

3,260 sets in 1993 (Cramer 1994). This fishery has been monitored with about 5% observer coverage, in terms of trips

observed, since 1992. There were no reports of mortality or serious injury of pygmy killer whales by this fishery. 

Pair trawl fishing gear has the potential to capture marine mammals, but there have been no reports of

mortality or serious injury to marine mammals in the Gulf of Mexico. This fishery has not been observed by NMFS

observers, and there are no other data available as to the extent of this fishery in the Gulf of Mexico. It is assumed that

it is very limited in scope and duration. 

STATUS OF STOCK

The status of this stock relative to OSP is unknown and there are insufficient data to determine population

trends. This species is not listed under the Endangered Species Act. The total level of human-caused mortality and

serious injury is unknown, but it is believed to be insignificant relative to PBR; therefore, this is not a strategic stock.

REFERENCES

Anon. 1994. Report of the PBR (Potential Biological Removal) workshop. June 27-29, 1994. NOAA, NMFS

Southwest Fisheries Science Center, La Jolla, California, 13 pp. + Appendices. 

Buckland, S. T., D. R. Anderson, K. P. Burnham and J. L. Laake. 1993. Distance Sampling: estimating abundance

of biological populations. Chapman & Hall, London, 446 pp. 

Caldwell, D. K. and M. C. Caldwell. 1971. The pygmy killer whale, Feresa attenuata, in the western Atlantic, with

a summary of world records. J. Mamm. 52:206-209. 

Cramer, J. 1994. Large pelagic logbook newsletter - 1993. NOAA Tech. Mem. NMFS-SEFSC-352, 19 pp. 
194

Davis, R., G. Scott, B. Würsig, W. Evans, G. Fargion, L. Hansen, K. Mullin, N. May, T. Leming, B. Mate, J. Norris

and T. Jefferson. In preparation. Distribution and abundance of marine mammals in the north-central and

western Gulf of Mexico: Final Report. OCS Study #MMS 94-0003. Texas Institute of Oceanography and the

National Marine Fisheries Service. U.S. Dept. of the Interior, Minerals Mgmt. Service, Gulf of Mexico OCS

Region, New Orleans, Louisiana. 

Hansen, L. J., K. D. Mullin and C. L. Roden. 1995. Estimates of cetacean abundance in the northern Gulf of Mexico

from vessel surveys. Southeast Fisheries Science Center, Miami Laboratory, Contribution No. MIA-94/95-25,

9 pp. + tables and figures. 

Laake, J. L., S. T. Buckland, D. R. Anderson, and K. P. Burnham. DISTANCE user’s guide, V2.0. Colorado

Cooperative Fish & Wildlife Research Unit, Colorado State University, Ft. Collins, Colorado, 72 pp. 

Ross, G. J. B. and S. Leatherwood. 1994. Pygmy killer whale Feresa attenuata (Gray, 1874). Pages 387-404 in S. H.

Ridgway and R. Harrison (editors), Handbook of marine mammals, Vol. 5: The first book of dolphins.

Academic Press, London, 416 pp. 
195

Figure 1. Distribution of all Kogia sightings (unfilled circles) and sightings identified

as dwarf sperm whales (filled circles) during NOAA Ship Oregon II marine mammal

surveys in 1991-1994. The straight lines show transects during two surveys and are

examples of typical survey transects. Isobaths are in 183 m (100 fm) intervals. 

DWARF SPERM WHALE (Kogia simus):

Northern Gulf of Mexico Stock

STOCK DEFINITION AND GEOGRAPHIC RANGE

The dwarf sperm whale appears to be distributed worldwide in temperate to tropical waters (Caldwell and

Caldwell 1994). Sightings of these animals in the northern Gulf of Mexico occur primarily along the continental shelf

edge and over the deeper waters off the continental shelf (Mullin et al. 1991; Southeast Fisheries Science Center,

SEFSC, unpublished data). Dwarf sperm whales and pygmy sperm whales (Kogia breviceps) are difficult to distinguish

and sightings of either species are often categorized as Kogia spp. Sightings of this category were documented in all

seasons during recent seasonal GulfCet aerial surveys of the northern Gulf of Mexico during 1993-1995 (Davis et al.,

in preparation). There is no information on stock differentiation. 

POPULATION SIZE

Estimates of abundance of Kogia spp. were derived through the application of distance sampling analysis

(Buckland et al. 1993) and the computer program DISTANCE (Laake et al. 1993) to sighting data collected during

1991-1994 spring-summer, visual sampling, line-transect vessel surveys of the northern Gulf of Mexico (Hansen et

al. 1995) (Fig. 1), which includes data collected as part of the GulfCet program (Davis et al., in preparation). These

surveys were conducted throughout the area from approximately the 200 m isobath along the U.S. coast to the seaward

extent of the U.S. Exclusive Economic Zone. The seasonal GulfCet aerial surveys included only a small portion of the

stock range and these data were

not used for abundance

estimation. Estimate d

abundance of Kogia spp. by

survey year [coefficient of

variation (CV) in parentheses]

was 109 in 1991 (0.68), 1,010

in 1992 (0.40), 580 in 1993

(0.45), and 162 in 1994 (0.61)

(Hansen et al. 1995). Survey

effort-weighted estimated

average abundance of Kogia

spp. for all surveys combined

was 547 (CV = 0.28) (Hansen

et al. 1995). Estimates of dwarf

sperm whale abundance cannot

be provided due to uncertainty

of species identification at sea. 

Minimum Population Estimate

A minimum population estimate was not calculated because of uncertainty of species identification at sea. 

Current Population Trend

A declining trend is evident in the annual abundance estimates since 1992; however, the 1991, 1993 and 1994

abundance estimates were not significantly different using the criteria of no overlap of log-normal 95% confidence

intervals. The apparent differences in abundance estimates may have been caused by lower sampling effort during

1991, and by low sampling intensity relative to population size (Hansen et al. 1995), or by inter-annual variation in

distribution patterns, rather than changes in population size. 

CURRENT AND MAXIMUM NET PRODUCTIVITY RATES

Current and maximum net productivity rates are not known. 
196

POTENTIAL BIOLOGICAL REMOVAL

Potential biological removal level (PBR) was not calculated because the minimum population size cannot be

calculated. 

ANNUAL HUMAN-CAUSED MORTALITY AND SERIOUS INJURY

The level of past or current, direct, human-caused mortality of dwarf sperm whales in the northern Gulf of

Mexico is unknown. Available information indicates there likely is little, if any, fisheries interaction with dwarf sperm

whales in the northern Gulf of Mexico. There have been no logbook reports of fishery-related mortality or serious

injury and no fishery-related mortality or serious injury has been observed.

There were no documented strandings of dwarf sperm whales in the northern Gulf of Mexico during 1987-

1994 which were classified as likely caused by fishery interactions, but there have been stranding investigation reports

of dwarf sperm whales which may have died as a result of other human-related causes. Stranding data probably

underestimate the extent of fishery-related mortality and serious injury because not all of the marine mammals which

die or are seriously injured may wash ashore, nor will all of those that do wash ashore necessarily show signs of

entanglement or other fishery-interaction. Finally, the level of technical expertise among stranding network personnel

varies widely as does the ability to recognize signs of fishery interaction. 

Although the PBR cannot be calculated, there is no known fishery-related mortality or serious injury to this

stock and, therefore, total fishery-related mortality and serious injury can be considered insignificant and approaching

zero mortality and serious injury rate. This determination cannot be made for specific fisheries until the implementing

regulations for Section 118 of the MMPA have been reviewed by the public and finalized. 

Fisheries Information

Pelagic swordfish, tunas, and billfish are the targets of the longline fishery operating in the U.S. Gulf of

Mexico. Total longline effort for the Gulf of Mexico pelagic fishery, including OCS edge, continental slope, and

Mexican territorial waters, based on mandatory logbook reporting, was 4,400 sets in 1991, 4,850 sets in 1992, and

3,260 sets in 1993 (Cramer 1994). This fishery has been monitored with about 5% observer coverage, in terms of trips

observed, since 1992. There were no reports of mortality or serious injury of dwarf sperm whales by this fishery. 

Pair trawl fishing gear has the potential to capture marine mammals, but there have been no reports of

mortality or serious injury to marine mammals in the Gulf of Mexico. This fishery has not been observed by NMFS

observers, and there are no other data available as to the extent of this fishery in the Gulf of Mexico. It is assumed that

it is very limited in scope and duration. 

Other Mortality

A total of at least nine dwarf sperm whale strandings were documented in the northern Gulf of Mexico from

1987-present; one of these animals had a plastic bag in its stomach. 

STATUS OF STOCK

The status of this stock relative to OSP is unknown and there are insufficient data to determine population

trends. This species is not listed under the Endangered Species Act. The total level of fishery-related mortality and

serious injury is unknown, but it is believed to be insignificant. Upon the advice of the Atlantic Scientific Review

Group this stock has been designated a strategic stock because PBR cannot be determined and there is an unknown

amount of possible human-caused mortality from the ingestion of marine debris such as plastic bags. 

REFERENCES

Anon. 1994. Report of the PBR (Potential Biological Removal) workshop. June 27-29, 1994. NOAA, NMFS

Southwest Fisheries Science Center, La Jolla, California, 13 pp. + Appendices. 

Buckland, S. T., D. R. Anderson, K. P. Burnham and J. L. Laake. 1993. Distance Sampling: estimating abundance

of biological populations. Chapman & Hall, London, 446 pp. 

Caldwell, D. K. and M. C. Caldwell 1989. Pygmy sperm whale Kogia breviceps (de Blainville, 1838): dwarf sperm

whale Kogia simus Owen, 1866. Pages 235-260 in S. H. Ridgway and R. Harrison (editors), Handbook of

marine mammals, Vol. 4: River dolphins and the larger toothed whales. Academic Press, San Diego. 

Cramer, J. 1994. Large pelagic logbook newsletter - 1993. NOAA Tech. Mem. NMFS-SEFSC-352, 19 pp. 
197

Davis, R., G. Scott, B. Würsig, W. Evans, G. Fargion, L. Hansen, K. Mullin, N. May, T. Leming, B. Mate, J. Norris

and T. Jefferson. In preparation. Distribution and abundance of marine mammals in the north-central and

western Gulf of Mexico: Final Report. OCS Study #MMS 94-0003. Texas Institute of Oceanography and the

National Marine Fisheries Service. U.S. Dept. of the Interior, Minerals Mgmt. Service, Gulf of Mexico OCS

Region, New Orleans, Louisiana. 

Hansen, L. J., K. D. Mullin and C. L. Roden. 1995. Estimates of cetacean abundance in the northern Gulf of Mexico

from vessel surveys. Southeast Fisheries Science Center, Miami Laboratory, Contribution No. MIA-94/95-25,

9 pp. + tables and figures. 

Laake, J. L., S. T. Buckland, D. R. Anderson, and K. P. Burnham. DISTANCE user’s guide, V2.0. Colorado

Cooperative Fish & Wildlife Research Unit, Colorado State University, Ft. Collins, Colorado, 72 pp. 

Mullin, K., W. Hoggard, C. Roden, R. Lohoefener, C. Rogers and B. Taggart. 1991. Cetaceans on the upper

continental slope in the north-central Gulf of Mexico. OCS Study/MMS 91-0027. U.S. Dept. of the Interior,

Minerals Management Service, Gulf of Mexico OCS Regional Office, New Orleans, Louisiana 108 pp. 
198

Figure 1. Distribution of all Kogia sightings (unfilled circles) and sightings identified

as pygmy sperm whales (filled circles) during NOAA Ship Oregon II marine mammal

surveys in 1991-1994. The straight lines show transects during two surveys and are

examples of typical survey transects. Isobaths are in 183 m (100 fm) intervals.

PYGMY SPERM WHALE (Kogia breviceps):

Northern Gulf of Mexico Stock

STOCK DEFINITION AND GEOGRAPHIC RANGE

The pygmy sperm whale appears to be distributed worldwide in temperate to tropical waters (Caldwell and

Caldwell 1994). Sightings of these animals in the northern Gulf of Mexico occur primarily along the continental shelf

edge and over the deeper waters off the continental shelf (Mullin et al. 1991; Southeast Fisheries Science Center,

SEFSC, unpublished data). Pygmy sperm whales and dwarf sperm whales (Kogia simus) are difficult to distinguish

and sightings of either species are often categorized as Kogia spp. Sightings of this category were documented in all

seasons during recent seasonal GulfCet aerial surveys of the northern Gulf of Mexico during 1993-1995 (Davis et al.,

in preparation). There is no information on stock differentiation. 

POPULATION SIZE

Estimates of abundance of Kogia spp. were derived through the application of distance sampling analysis

(Buckland et al. 1993) and the computer program DISTANCE (Laake et al. 1993) to sighting data collected during

1991-1994 spring-summer, visual sampling, line-transect vessel surveys of the northern Gulf of Mexico (Hansen et

al. 1995) (Fig. 1), which includes data collected as part of the GulfCet program (Davis et al., in preparation). These

surveys were conducted throughout the area from approximately the 200 m isobath along the U.S. coast to the seaward

extent of the U.S. Exclusive Economic Zone. The seasonal GulfCet aerial surveys included only a small portion of the

stock range and these data were

not used for abundance

estimation. Estimated abundance

of Kogia spp. by survey year

[coefficient of variation (CV) in

parentheses] was 109 in 1991

(0.68), 1,010 in 1992 (0.40), 580

in 1993 (0.45), and 162 in 1994

(0.61) (Hansen et al. 1995).

Survey effort-weighted estimated

abundance of Kogia spp. for all

surveys combined was 547 (CV

= 0.28) (Hansen et al. 1995).

Estimates of pygmy sperm whale

abundance cannot be provided

due to uncertainty of species

identification at sea. 

Minimum Population Estimate

A minimum population estimate could not be calculated because of uncertainty of species identification at sea.

Current Population Trend

A declining trend is evident in the annual abundance estimates since 1992; however, the 1991, 1993 and 1994

abundance estimates were not significantly different using the criteria of no overlap of log-normal 95% confidence

intervals. The apparent differences in abundance estimates may have been caused by lower sampling effort during

1991, and by low sampling intensity relative to population size (Hansen et al. 1995), or by inter-annual variation in

distribution patterns or spatial sampling patterns, rather than changes in population size. 

CURRENT AND MAXIMUM NET PRODUCTIVITY RATES

Current and maximum net productivity rates are not known. 
199

POTENTIAL BIOLOGICAL REMOVAL

Potential biological removal level (PBR) was not calculated because the minimum population size cannot be

calculated. 

ANNUAL HUMAN-CAUSED MORTALITY AND SERIOUS INJURY

The level of past or current, direct, human-caused mortality of pygmy sperm whales in the northern Gulf of

Mexico is unknown. Available information indicates there likely is little, if any, fisheries interaction with pygmy

sperm whales in the northern Gulf of Mexico. There have been no logbook reports of fishery-related mortality or

serious injury and no fishery-related mortality or serious injury has been observed.

There have been no documented strandings of pygmy sperm whales in the northern Gulf of Mexico during

1987-1994 which have been classified as likely caused by fishery interactions, but there have been stranding

investigation reports of pygmy sperm whales which may have died as a result of other human-related causes. Stranding

data probably underestimate the extent of fishery-related mortality and serious injury because not all of the marine

mammals which die or are seriously injured may wash ashore, nor will all of those that do wash ashore necessarily

show signs of entanglement or other fishery-interaction. Finally, the level of technical expertise among stranding

network personnel varies widely as does the ability to recognize signs of fishery interaction.

Although the PBR cannot be calculated, the total known fishery-related mortality and serious injury for this

stock is zero and, therefore, can be considered insignificant and approaching zero mortality and serious injury rate.

This determination cannot be made for specific fisheries until the implementing regulations for Section 118 of the

MMPA have been reviewed by the public and finalized. 

Fisheries Information

Pelagic swordfish, tunas, and billfish are the targets of the longline fishery operating in the U.S. Gulf of

Mexico. Total longline effort for the Gulf of Mexico pelagic fishery, including OCS edge, continental slope, and

Mexican territorial waters, based on mandatory logbook reporting, was 4,400 sets in 1991, 4,850 sets in 1992, and

3,260 sets in 1993 (Cramer 1994). This fishery has been monitored with about 5% observer coverage, in terms of trips

observed, since 1992. There were no reports of mortality or serious injury of pygmy sperm whales by this fishery. 

Pair trawl fishing gear has the potential to capture marine mammals, but there have been no reports of

mortality or serious injury to marine mammals in the Gulf of Mexico. This fishery has not been observed by NMFS

observers, and there are no other data available as to the extent of this fishery in the Gulf of Mexico. It is assumed that

it is very limited in scope and duration. 

Other Mortality

At least 13 pygmy sperm whale strandings were documented in the northern Gulf of Mexico from 1987-

present; one of these animals had a plastic bag in its stomach and another stranded apparently due to injuries inflicted

by impact, possibly with a vessel. 

STATUS OF STOCK

The status of this stock relative to OSP is unknown and there are insufficient data to determine population

trends. This species is not listed under the Endangered Species Act. The total level of fishery-related mortality and

serious injury is unknown, but it is believed to be insignificant. Upon the advice of the Atlantic Scientific Review

Group this stock has been designated a strategic stock because PBR cannot be determined and there is an unknown

amount of possible human-caused mortality from the ingestion of marine debris such as plastic bags and possibly from

collision with vessels. 

REFERENCES

Anon. 1994. Report of the PBR (Potential Biological Removal) workshop. June 27-29, 1994. NOAA, NMFS

Southwest Fisheries Science Center, La Jolla, California, 13 pp. + Appendices. 

Buckland, S. T., D. R. Anderson, K. P. Burnham and J. L. Laake. 1993. Distance Sampling: estimating abundance

of biological populations. Chapman & Hall, London, 446 pp. 
200

Caldwell, D. K. and M. C. Caldwell 1989. Pygmy sperm whale Kogia breviceps (de Blainville, 1838): dwarf sperm

whale Kogia simus Owen, 1866. Pages 235-260 in S. H. Ridgway and R. Harrison (editors), Handbook of

marine mammals, Vol. 4: River dolphins and the larger toothed whales. Academic Press, San Diego. 

Cramer, J. 1994. Large pelagic logbook newsletter - 1993. NOAA Tech. Mem. NMFS-SEFSC-352, 19 pp. 

Davis, R., G. Scott, B. Würsig, W. Evans, G. Fargion, L. Hansen, K. Mullin, N. May, T. Leming, B. Mate, J. Norris

and T. Jefferson. In preparation. Distribution and abundance of marine mammals in the north-central and

western Gulf of Mexico: Final Report. OCS Study #MMS 94-0003. Texas Institute of Oceanography and the

National Marine Fisheries Service. U.S. Dept. of the Interior, Minerals Mgmt. Service, Gulf of Mexico OCS

Region, New Orleans, Louisiana. 

Hansen, L. J., K. D. Mullin and C. L. Roden. 1995. Estimates of cetacean abundance in the northern Gulf of Mexico

from vessel surveys. Southeast Fisheries Science Center, Miami Laboratory, Contribution No. MIA-94/95-25,

9 pp. + tables and figures. 

Laake, J. L., S. T. Buckland, D. R. Anderson, and K. P. Burnham. DISTANCE user’s guide, V2.0. Colorado

Cooperative Fish & Wildlife Research Unit, Colorado State University, Ft. Collins, Colorado, 72 pp. 

Mullin, K., W. Hoggard, C. Roden, R. Lohoefener, C. Rogers and B. Taggart. 1991. Cetaceans on the upper

continental slope in the north-central Gulf of Mexico. OCS Study/MMS 91-0027. U.S. Dept. of the Interior,

Minerals Management Service, Gulf of Mexico OCS Regional Office, New Orleans, Louisiana 108 pp. 
201

Figure 1. Distribution of melon-headed whale sightings during NOAA Ship Oregon II

marine mammal surveys in 1991-1994. The straight lines show transects during two

surveys and are examples of typical survey transects. Isobaths are in 183 m (100 fm)

depth intervals. 

MELON-HEADED WHALE (Peponocephala electra):

Northern Gulf of Mexico Stock

STOCK DEFINITION AND GEOGRAPHIC RANGE

The melon-headed whale appears to be distributed worldwide in tropical to sub-tropical waters (Perryman et

al. 1994). Sightings of these animals in the northern Gulf of Mexico occur primarily over the deeper waters off the

continental shelf (Mullin et al. 1994). Melon-headed whales and pygmy killer whales (Feresa attenuata) are difficult

to distinguish and sightings of either species are often categorized as pygmy killer/melon-headed whales. Sightings

of this category were documented in all seasons during recent seasonal GulfCet aerial surveys of the northern Gulf of

Mexico during 1993-1995 (Davis et al., in preparation). There is no information on stock differentiation for the

Atlantic population. 

POPULATION SIZE

Seasonal aerial survey data were insufficient for estimating abundance. Estimates of abundance were derived

through the application of distance sampling analysis (Buckland et al. 1993) and the computer program DISTANCE

(Laake et al. 1993) to sighting data collected during 1991-1994 spring-summer, visual sampling, line-transect vessel

surveys of the northern Gulf of Mexico (Hansen et al. 1995) (Fig.1), which includes data collected as part of the

GulfCet program (Davis et al., in preparation). These surveys were conducted throughout the area from approximately

the 200 m isobath along the U.S. coast to the seaward extent of the U.S. Exclusive Economic Zone. The seasonal

GulfCet aerial surveys included

only a small portion of the stock

range and these data were not

used for abundance estimation.

Estimated abundance of melonheaded whales by survey year

[coefficient of variation (CV) in

parentheses] was zero in 1991,

3,174 in 1992 (0.54), 827 in

1993 (0.70) and 10,586 in 1994

(0.48) (Hansen et al. 1995). The

survey effort-weighted estimated

average abundance of melonheaded whales for all surveys

combined was 3,965 (CV =

0.39) (Hansen et al. 1995).

Minimum Population Estimate

The minimum population size was estimated from the average abundance estimate which was 3,965 (CV =

0.39) (Hansen et al. 1995). The minimum population estimate is the lower limit of the two-tailed 60% confidence

interval of the log-normal distributed abundance estimate, which is equivalent to the 20th percentile of the log-normal

distributed abundance estimate as specified by NMFS (Anon. 1994). The minimum population estimate is 2,888

melon-headed whales.

Current Population Trend

No trend was identified in the annual abundance estimates; however, the 1994 estimate was more than ten

times larger than the 1993 estimate and the difference was significant using the criteria of no overlap of log-normal

95% confidence intervals. No melon-headed whales were sighted during 1991, and the differences between the 1992

and 1993 estimates and between the 1993 and 1994 estimates were not significant. The apparent differences in

abundance estimates may have been caused by lower sampling effort during 1991, and by low sampling intensity

relative to population size (Hansen et al. 1995), or by inter-annual variation in distribution patterns or spatial sampling

patterns, rather than changes in population size. 
202

CURRENT AND MAXIMUM NET PRODUCTIVITY RATES

Current and maximum net productivity rates are not known; therefore, the default maximum net productivity

rate of 0.04 (Anon. 1994) was used for purposes of this assessment. 

POTENTIAL BIOLOGICAL REMOVAL

Potential biological removal level (PBR) was specified as the product of the minimum population size, one

half the maximum net productivity rate, and a recovery factor for endangered, threatened, or depleted stocks, or stocks

of unknown status relative to optimum sustainable population (OSP) (Anon. 1994). The recovery factor was set at 0.50

because the status of the stock relative to OSP is unknown. PBR for this stock is 29 melon-headed whales. 

ANNUAL HUMAN-CAUSED MORTALITY AND SERIOUS INJURY

There has historically been some take of this species in small cetacean fisheries in the Caribbean (Caldwell

et al. 1976); however, the level of past or current, direct, human-caused mortality of melon-headed whales in the

northern Gulf of Mexico is unknown. Available information indicates there likely is little, if any, fisheries interaction

with melon-headed whales in the northern Gulf of Mexico. There have been no logbook reports of fishery-related

mortality or serious injury and no fishery-related mortality or serious injury has been observed.

There were no documented strandings of melon-headed whales in the northern Gulf of Mexico during 1987-

1994 which were classified as likely caused by fishery interactions or other human-related causes. Stranding data

probably underestimate the extent of fishery-related mortality and serious injury because not all of the marine mammals

which die or are seriously injured may wash ashore, nor will all of those that do wash ashore necessarily show signs

of entanglement or other fishery-interaction. Finally, the level of technical expertise among stranding network

personnel varies widely as does the ability to recognize signs of fishery interaction.

The total known fishery-related mortality and serious injury for this stock is less than 10% of the calculated

PBR and, therefore, can be considered insignificant and approaching zero mortality and serious injury rate. This

determination cannot be made for specific fisheries until the implementing regulations for Section 118 of the MMPA

have been reviewed by the public and finalized. 

Fisheries Information

Pelagic swordfish, tunas, and billfish are the targets of the longline fishery operating in the U.S. Gulf of

Mexico. Total longline effort for the Gulf of Mexico pelagic fishery, including OCS edge, continental slope, and

Mexican territorial waters, based on mandatory logbook reporting, was 4,400 sets in 1991, 4,850 sets in 1992, and

3,260 sets in 1993 (Cramer 1994). This fishery has been monitored with about 5% observer coverage, in terms of trips

observed, since 1992. There were no reports of mortality or serious injury to melon-headed whales by this fishery. 

Pair trawl fishing gear has the potential to capture marine mammals, but there have been no reports of

mortality or serious injury to marine mammals in the Gulf of Mexico. This fishery has not been observed by NMFS

observers, and there are no other data available as to the extent of this fishery in the Gulf of Mexico. It is assumed that

it is very limited in scope and duration. 

STATUS OF STOCK

The status of this stock relative to OSP is unknown. This species is not listed under the Endangered Species

Act. There are insufficient data to determine population trends. The total level of fishery-related mortality and serious

injury is unknown, but it is believed to be insignificant relative to PBR; therefore, this is not a strategic stock. 

REFERENCES

Anon. 1994. Report of the PBR (Potential Biological Removal) workshop. June 27-29, 1994. NOAA, NMFS

Southwest Fisheries Science Center, La Jolla, California, 13 pp. + Appendices. 

Buckland, S. T., D. R. Anderson, K. P. Burnham and J. L. Laake. 1993. Distance Sampling: estimating abundance

of biological populations. Chapman & Hall, London, 446 pp. 

Caldwell, D. K., M. C. Caldwell and R. V. Walker. 1976. First records for Fraser's dolphin (Lagenodelphis hosei)

in the Atlantic and the melon-headed whale (Peponocephala electra) in the western Atlantic. Cetology 25:

1-4. 

Cramer, J. 1994. Large pelagic logbook newsletter - 1993. NOAA Tech. Mem. NMFS-SEFSC-352, 19 pp. 
203

Davis, R., G. Scott, B. Würsig, W. Evans, G. Fargion, L. Hansen, K. Mullin, N. May, T. Leming, B. Mate, J. Norris

and T. Jefferson. In preparation. Distribution and abundance of marine mammals in the north-central and

western Gulf of Mexico: Final Report. OCS Study #MMS 94-0003. Texas Institute of Oceanography and the

National Marine Fisheries Service. U.S. Dept. of the Interior, Minerals Mgmt. Service, Gulf of Mexico OCS

Region, New Orleans, Louisiana. 

Hansen, L. J., K. D. Mullin and C. L. Roden. 1995. Estimates of cetacean abundance in the northern Gulf of Mexico

from vessel surveys. Southeast Fisheries Science Center, Miami Laboratory, Contribution No. MIA-94/95-25,

9 pp. + tables and figures. 

Laake, J. L., S. T. Buckland, D. R. Anderson, and K. P. Burnham. DISTANCE user’s guide, V2.0. Colorado

Cooperative Fish & Wildlife Research Unit, Colorado State University, Ft. Collins, Colorado, 72 pp. 

Mullin, K. D., T. A. Jefferson, L. J. Hansen and W. Hoggard. 1994. First sightings of melon-headed whales

(Peponocephala electra) in the Gulf of Mexico. Mar. Mam. Sci. 10(3): 342-348. 
204

Figure 1. Distribution of Risso’s dolphin sightings during NOAA Ship Oregon II

marine mammal surveys during 1991-1994. The straight lines show transects during

two surveys and are examples of typical survey transects. Isobaths are in 183 m (100

fm) intervals. 

RISSO'S DOLPHIN (Grampus griseus):

Northern Gulf of Mexico Stock

STOCK DEFINITION AND GEOGRAPHIC RANGE

Risso's dolphin is distributed worldwide in tropical to warm temperate waters (Leatherwood and Reeves 1983).

Sightings of these animals in the northern Gulf of Mexico occur primarily along the continental shelf and continental

slope (Mullin et al. 1991; Southeast Fisheries Science Center, SEFSC, unpublished data). Risso's dolphin were seen

in all seasons during recent seasonal GulfCet aerial surveys of the northern Gulf of Mexico during 1993-1995 (Davis

et al., in preparation) and in the late spring during vessel surveys (SEFSC, unpublished data). There is no information

on stock differentiation for the Atlantic population. 

POPULATION SIZE

Seasonal aerial survey data were insufficient for abundance estimation. Estimates of abundance were derived

through the application of distance sampling analysis (Buckland et al. 1993) and the computer program DISTANCE

(Laake et al. 1993) to sighting data collected during 1991-1994 spring-summer, visual sampling, line-transect vessel

surveys of the northern Gulf of Mexico (Hansen et al. 1995) (Fig.1), which includes data collected as part of the

GulfCet program (Davis et al., in preparation). These surveys were conducted throughout the area from approximately

the 200 m isobath along the U.S.

coast to the seaward extent of the

U.S. Exclusive Economic Zone.

The seasonal GulfCet aerial

surveys included only a small

portion of the stock range and

these data were not used for

abundance estimation .

Estimated abundance of Risso’s

dolphins by survey year

[coefficient of variation (CV) in

parentheses] was 667 in 1991

(0.95), 2,325 in 1992 (0.34),

1,408 in 1993 (0.41), and 6,332

in 1994 (0.45) (Hansen et al.

1995). Survey effort-weighted

average abundance of Risso's

dolphins estimated for all surveys

combined was 2,749 (CV =

0.27) (Hansen et al. 1995). 

Minimum Population Estimate

The minimum population size was estimated from the average abundance estimate which was 2,749 Risso’s

dolphins (CV = 0.27) (Hansen et al. 1995). The minimum population estimate is the lower limit of the two-tailed 60%

confidence interval of the log-normal distributed abundance estimate, which is equivalent to the 20th percentile of the

log-normal distributed abundance estimate as specified by NMFS (Anon. 1994). The minimum population estimate

is 2,199 Risso’s dolphins. 

Current Population Trend

No trend was identified in the annual abundance estimates. The 1994 abundance estimate was greater than

the other annual estimates, but no annual estimates differed significantly using the criteria of no overlap of log-normal

95% confidence intervals. The apparent differences in abundance estimates may have been caused by lower sampling

effort during 1991 (Hansen et al. 1995) or by inter-annual variation in distribution patterns or spatial sampling

patterns, rather than changes in population size. 
205

CURRENT AND MAXIMUM NET PRODUCTIVITY RATES

Current and maximum net productivity rates for this stock are not known; therefore, the default maximum

net productivity rate of 0.04 (Anon. 1994) was used for purposes of this assessment. 

POTENTIAL BIOLOGICAL REMOVAL

Potential biological removal level (PBR) was specified as the product of the minimum population size, one

half the maximum net productivity rate, and a recovery factor for endangered, threatened, or depleted stocks, or stocks

of unknown status relative to optimum sustainable population (OSP) (Anon. 1994). The recovery factor was set at 0.50

because the status of the stock relative to OSP is unknown. PBR for this stock is 22 Risso’s dolphins. 

ANNUAL HUMAN-CAUSED MORTALITY AND SERIOUS INJURY

The level of past or current, direct, human-caused mortality of Risso's dolphins in the northern Gulf of Mexico

is unknown. This species has been taken in the U.S. longline swordfish/tuna fishery in the northern Gulf of Mexico

and in the U.S. Atlantic (Lee et al. 1994). Estimated average annual fishery-related mortality and serious injury

attributable to the longline swordfish/tuna fishery in the Gulf of Mexico during 1992-1993 was 19 Risso’s dolphins

annually (CV = 0.20). 

There were no documented strandings of Risso' dolphins in the northern Gulf of Mexico during 1987-1994

which were classified as likely caused by fishery interactions or other human-related causes. Stranding data probably

underestimate the extent of fishery-related mortality and serious injury because not all of the marine mammals which

die or are seriously injured may wash ashore, nor will all of those that do wash ashore necessarily show signs of

entanglement or other fishery-interaction. Finally, the level of technical expertise among stranding network personnel

varies widely as does the ability to recognize signs of fishery interaction.

The total estimated fishery-related mortality and serious injury for this stock is not less than 10% of the

calculated PBR and, therefore, cannot be considered insignificant and approaching zero mortality and serious injury

rate. This determination cannot be made for specific fisheries until the implementing regulations for Section 118 of

the MMPA have been reviewed by the public and finalized. 

Fisheries Information

Interactions between the U.S. longline swordfish/tuna fishery and Risso' dolphins have been documented in

the northern Gulf of Mexico (Lee et al. 1994). Pelagic swordfish, tunas, and billfish are the targets of the longline

fishery operating in the U.S. Gulf of Mexico. Total longline effort for the Gulf of Mexico pelagic fishery, including

OCS edge, continental slope, and Mexican territorial waters, based on mandatory logbook reporting, was 4,400 sets

in 1991, 4,850 sets in 1992, and 3,260 sets in 1993 (Cramer 1994). This fishery has been monitored with about 5%

observer coverage, in terms of trips observed, since 1992. One Risso's dolphin was observed taken and released alive

during 1992; the extent of injury to the animal was unknown (SEFSC, unpublished data). One lethal take of a Risso's

dolphin by the fishery was observed in the Gulf of Mexico during 1993 (SEFSC, unpublished data). Annual fisheryrelated mortality and incidental injury was estimated using a generalized linear model (Poisson error assumption) fit

to the available observed incidental take data for the entire fishery and partitioned on the fishery effort (number of sets)

in the Gulf of Mexico. Estimated total mortality and serious injury to Risso’s dolphins (CV in parentheses) in the Gulf

of Mexico in 1992 was 24 (0.19), and in 1993 it was 13 (0.20). Estimated average annual fishery-related mortality

and serious injury attributable to the longline swordfish/tuna fishery in the Gulf of Mexico during 1992-1993 was 19

Risso’s dolphins annually (CV = 0.20). 

Pair trawl fishing gear has the potential to capture marine mammals, but there have been no reports of

mortality or serious injury to marine mammals in the Gulf of Mexico. This fishery has not been observed by NMFS

observers, and there are no other data available as to the extent of this fishery in the Gulf of Mexico. It is assumed that

it is very limited in scope and duration. 

STATUS OF STOCK

The status of this stock relative to OSP is unknown. This species is not listed under the Endangered Species

Act and there are insufficient data to determine population trends. This is not a strategic stock because fishery-related
206

mortality and serious injury does not exceed PBR; however, fishery-related mortality and serious injury is very close

to PBR and requires close monitoring. 

REFERENCES

Anon. 1994. Report of the PBR (Potential Biological Removal) workshop. June 27-29, 1994. NOAA, NMFS

Southwest Fisheries Science Center, La Jolla, California, 13 pp. + Appendices. 

Buckland, S. T., D. R. Anderson, K. P. Burnham and J. L. Laake. 1993. Distance Sampling: estimating abundance

of biological populations. Chapman & Hall, London, 446 pp. 

Cramer, J. 1994. Large pelagic logbook newsletter - 1993. NOAA Tech. Mem. NMFS-SEFSC-352, 19 pp. 

Davis, R., G. Scott, B. Würsig, W. Evans, G. Fargion, L. Hansen, K. Mullin, N. May, T. Leming, B. Mate, J. Norris

and T. Jefferson. In preparation. Distribution and abundance of marine mammals in the north-central and

western Gulf of Mexico: Final Report. OCS Study #MMS 94-0003. Texas Institute of Oceanography and the

National Marine Fisheries Service. U.S. Dept. of the Interior, Minerals Mgmt. Service, Gulf of Mexico OCS

Region, New Orleans, Louisiana. 

Hansen, L. J., K. D. Mullin and C. L. Roden. 1995. Estimates of cetacean abundance in the northern Gulf of Mexico

from vessel surveys. Southeast Fisheries Science Center, Miami Laboratory, Contribution No. MIA-94/95-25,

9 pp. + tables and figures. 

Laake, J. L., S. T. Buckland, D. R. Anderson, and K. P. Burnham. DISTANCE user’s guide, V2.0. Colorado

Cooperative Fish & Wildlife Research Unit, Colorado State University, Ft. Collins, Colorado, 72 pp. 

Leatherwood, S. and R. R. Reeves. 1983. The Sierra Club handbook of whales and dolphins. Sierra Club Books, San

Francisco, 302 pp. 

Mullin, K., W. Hoggard, C. Roden, R. Lohoefener, C. Rogers and B. Taggart. 1991. Cetaceans on the upper

continental slope in the north-central Gulf of Mexico. OCS Study/MMS 91-0027. U.S. Dept. of the Interior,

Minerals Management Service, Gulf of Mexico OCS Regional Office, New Orleans, Louisiana, 108 pp. 
207

Figure 1. Distribution of short-finned pilot whale sightings during NOAA Ship Oregon

II surveys during 1991-1994. The straight lines show transects during two surveys and

are examples of typical survey transects. Isobaths are in 183 m (100 fm) intervals.

SHORT-FINNED PILOT WHALE (Globicephala macrorhynchus):

Northern Gulf of Mexico Stock

STOCK DEFINITION AND GEOGRAPHIC RANGE

The short-finned pilot whale is distributed worldwide in tropical to warm temperate waters (Leatherwood and

Reeves 1983). Sightings of these animals in the northern Gulf of Mexico occur primarily along the continental shelf

and continental slope [Mullin et al. 1991; Southeast Fisheries Science Center (SEFSC) unpublished data]. Short-finned

pilot whales were seen in all seasons during recent seasonal GulfCet aerial surveys of the northern Gulf of Mexico

during 1993-1995 (Davis et al., in preparation). There is no information on stock differentiation for the Atlantic

population. 

POPULATION SIZE

Abundance was estimated using distance sampling analysis (Buckland et al. 1993) and the computer program

DISTANCE (Laake et al. 1993) with sighting data collected during 1991-1994 spring-summer, visual sampling, linetransect vessel surveys of the northern Gulf of Mexico (Hansen et al. 1995) (Fig. 1), which includes data collected as

part of the GulfCet program (Davis et al., in preparation). These surveys were conducted throughout the area from

approximately the 200 m isobath along the U.S. coast to the seaward extent of the U.S. Exclusive Economic Zone. The

seasonal GulfCet aerial surveys

included only a small portion of

the stock range, so those data

were not used for abundance

estimation. Estimated

abundance of short-finned pilot

whales by survey year

[coefficient of variation (CV) in

parentheses] was zero in 1991,

909 in 1992 (0.62), 103 in 1993

(1.20), and 240 in 1994 (1.03)

(Hansen et al. 1995). Survey

effort-weighted estimated

average abundance of shortfinned pilot whales for all

surveys combined was 353 (CV

= 0.89) (Hansen et al. 1995). 

Minimum Population Estimate

The minimum population size was estimated from the average abundance estimate which was 353 pilot whales

(CV = 0.89) (Hansen et al. 1995). The minimum population estimate is the lower limit of the two-tailed 60%

confidence interval of the log-normal distributed average abundance estimate, which is equivalent to the 20th percentile

of the log-normal distributed abundance estimate as specified by NMFS (Anon. 1994). The minimum population

estimate is 186 pilot whales. 

Current Population Trend

The annual abundance estimates were not significantly different using the criteria of no overlap of log-normal

95% confidence intervals. The variation in abundance estimates that was observed may have been caused by lower

sampling effort during 1991, by low sampling intensity relative to population size (Hansen et al. 1995), or by interannual variation in distribution patterns or spatial sampling patterns, rather than changes in population size. 

CURRENT AND MAXIMUM NET PRODUCTIVITY RATES

Current and maximum net productivity rates are not known for this stock; therefore, the default maximum

net productivity rate of 0.04 (Anon. 1994) was used for purposes of this assessment. 
208

POTENTIAL BIOLOGICAL REMOVAL

Potential biological removal level (PBR) was specified as the product of the minimum population size, one

half the maximum net productivity rate, and a recovery factor for endangered, threatened, or depleted stocks, or stocks

of unknown status relative to optimum sustainable population (OSP) (Anon. 1994). The recovery factor was set at 0.50

because the status of the stock relative to OSP is unknown. PBR for this stock is 1.9 short-finned pilot whales. 

ANNUAL HUMAN-CAUSED MORTALITY AND SERIOUS INJURY

The level of past or current, direct, human-caused mortality of short-finned pilot whales in the northern Gulf

of Mexico is unknown. This species has been taken in the U.S. longline swordfish/tuna fishery in U.S. Atlantic waters

(Lee et al. 1994) and there is a logbook report of a fishery-related mortality or serious injury in the northern Gulf of

Mexico (NMFS unpublished data); however, fishery-related mortality or serious injury has not been observed. Total

known fishery-related mortality or serious injury is estimated to be 0.3 short-finned pilot whales per year based upon

the logbook report. 

There were no documented strandings of short-finned pilot whales in the northern Gulf of Mexico during

1987-1994 which were classified as likely caused by fishery interactions or other human-related causes. Stranding data

probably underestimate the extent of fishery-related mortality and serious injury because not all of the marine mammals

which die or are seriously injured may wash ashore, nor will all of those that do wash ashore necessarily show signs

of entanglement or other fishery-interaction. Finally, the level of technical expertise among stranding network

personnel varies widely as does the ability to recognize signs of fishery interaction.

 The total known fishery-related mortality and serious injury for this stock is greater than 10% of the

calculated PBR and, therefore, cannot be considered insignificant and approaching zero mortality and serious injury

rate. This determination cannot be made for specific fisheries until the implementing regulations for Section 118 of

the MMPA have been reviewed by the public and finalized. 

Fisheries Information

Pelagic swordfish, tunas, and billfish are the targets of the longline fishery operating in the U.S. Gulf of

Mexico. Interactions between the U.S. longline swordfish/tuna fishery and short-finned pilot whales have been

reported in the northern Gulf of Mexico (SEFSC, unpublished logbook data), but have not been observed by NMFS

fishery observers. Total longline effort for the Gulf of Mexico pelagic fishery, including OCS edge, continental slope,

and Mexican territorial waters, based on mandatory logbook reporting, was 4,400 sets in 1991, 4,850 sets in 1992, and

3,260 sets in 1993 (Cramer 1994). This fishery was been monitored with about 5% observer coverage in both the

Atlantic Ocean and the Gulf of Mexico, in terms of trips observed, in 1992-1993. There was one logbook report of

a fishery-related injury of a pilot whale in the northern Gulf of Mexico in 1991, but no fishery interactions were

observed during 1992-1993. Total known fishery-related mortality or serious injury is estimated to be 0.3 short-finned

pilot whales per year based upon the logbook report. 

Pair trawl fishing gear has the potential to capture marine mammals, but there have been no reports of

mortality or serious injury to marine mammals in the Gulf of Mexico. This fishery has not been observed by NMFS

observers, and there are no other data available as to the extent of this fishery in the Gulf of Mexico. It is assumed that

it is very limited in scope and duration. 

STATUS OF STOCK

The status of this stock relative to OSP is unknown and there are insufficient data to determine population

trends. This species is not listed under the Endangered Species Act. The total level of estimated fishery-related

mortality and serious injury is unknown, but because there is a record of a fishery-related mortality or serious injury

and because of the extremely low estimated stock size, this is a strategic stock.

REFERENCES

Anon. 1994. Report of the PBR (Potential Biological Removal) workshop. June 27-29, 1994. NOAA, NMFS

Southwest Fisheries Science Center, La Jolla, California, 13 pp. + Appendices. 

Buckland, S. T., D. R. Anderson, K. P. Burnham and J. L. Laake. 1993. Distance Sampling: estimating abundance

of biological populations. Chapman & Hall, London, 446 pp. 
209

Cramer, J. 1994. Large pelagic logbook newsletter - 1993. NOAA Tech. Mem. NMFS-SEFSC-352, 19 pp. 

Davis, R., G. Scott, B. Würsig, W. Evans, G. Fargion, L. Hansen, K. Mullin, N. May, T. Leming, B. Mate, J. Norris

and T. Jefferson. In preparation. Distribution and abundance of marine mammals in the north-central and

western Gulf of Mexico: Final Report. OCS Study #MMS 94-0003. Texas Institute of Oceanography and the

National Marine Fisheries Service. U.S. Dept. of the Interior, Minerals Mgmt. Service, Gulf of Mexico OCS

Region, New Orleans, Louisiana. 

Hansen, L. J., K. D. Mullin and C. L. Roden. 1995. Estimates of cetacean abundance in the northern Gulf of Mexico

from vessel surveys. Southeast Fisheries Science Center, Miami Laboratory, Contribution No. MIA-94/95-25,

9 pp. + tables and figures. 

Laake, J. L., S. T. Buckland, D. R. Anderson, and K. P. Burnham. DISTANCE user’s guide, V2.0. Colorado

Cooperative Fish & Wildlife Research Unit, Colorado State University, Ft. Collins, Colorado, 72 pp. 

Leatherwood, S. and R. R. Reeves. 1983. The Sierra Club handbook of whales and dolphins. Sierra Club Books, San

Francisco, 302 pp. 

Lee, D. W., C. J. Brown, A. J. Catalano, J. R. Grubich, T. W. Greig, R. J. Miller and M. T. Judge. 1994. SEFSC

pelagic longline observer program data summary for 1992-1993. NOAA Tech. Mem. NMFS-SEFSC-347,

19 pp. 

Mullin, K., W. Hoggard, C. Roden, R. Lohoefener, C. Rogers and B. Taggart. 1991. Cetaceans on the upper

continental slope in the north-central Gulf of Mexico. OCS Study/MMS 91-0027. U.S. Dept. of the Interior,

Minerals Management Service, Gulf of Mexico OCS Regional Office, New Orleans, Louisiana, 108 pp. 
210

INDEX

agricultural runoff: 148

Alabama: 148, 151, 152, 155, 157, 160

Apalachee Bay: 150, 154, 158

Apalachicola Bay: 158

Aransas Bay: 158

Arctic: 21, 31, 112, 119, 122

Atchafalaya Bay: 158

Atlantic spotted dolphin: 82, 83, 85, 86, 89, 163, 165

Balaenoptera acutorostrata: 16, 19

Balaenoptera borealis: 13-15

Balaenoptera musculus: 21, 22

Balaenoptera physalus: 9, 11, 12

Barataria Bay: 158

Basque whalers: 1

Bay Boudreau: 158

Bay of Fundy: 1, 3, 10, 16, 18, 19, 32, 35, 36, 62, 63,

70-72, 76, 106-108, 110, 112, 113, 115, 117, 120,

123

billfish: 58, 63, 68, 79, 83, 87, 91, 95, 126, 129, 132,

135, 138, 141, 144, 164, 167, 170, 173, 176, 179,

182, 185, 188, 191, 194, 197, 200, 203, 206

Blainville’s beaked whale: 134

blue runners: 152, 156

blue whale: 21, 22

Bonsecour Bay: 158

bottlenose dolphin: 96-104, 140, 142, 143, 145-155,

157-162, 165

Brevortia tyrannus: 103, 148, 152, 156

Bryde’s whale: 128, 129

Calcasieu Lake: 158

Caloosahatchee River: 158

Canada: 3, 11, 13, 18, 19, 21, 22, 32, 36, 38, 39, 42,

43, 46, 50, 51, 54, 55, 59, 62, 64, 65, 68, 73, 74,

76, 80, 81, 84, 88, 92, 95, 99, 108, 110-120,

122-124

Canadian East Coast: 16, 18

Canadian fisheries: 79, 107

Cape Cod Bay: 1, 4, 7

Cape Hatteras: 3, 6, 7, 9, 13, 16, 23-25, 27-30, 33, 34,

38, 40-42, 44-46, 48-50, 52-54, 56, 58, 60, 61, 63,

64, 66-68, 70, 72, 73, 75, 77-79, 82-84, 86-88,

90-92, 94-102, 104, 108, 109, 114, 117

Charlotte Harbor: 157, 158

Chesapeake Bay: 70, 82, 109

chlorinated hydrocarbons: 65, 103, 148, 160

Choctawhatchee Bay: 158

Chokoloskee Bay: 158

cigarfish: 152, 156

Clearwater Harbor: 158

clymene dolphin: 178, 180

coastal gillnet: 103, 107, 109, 155

cod traps: 3, 18, 19, 62, 63, 113, 117, 120, 123

common dolphin: 77-80

Compano Bay: 158

Connecticut: 103, 119, 122

contaminants: 64, 65, 103, 105, 110, 147-149, 152,

153, 156, 161

Corpus Christi Bay: 158

Crystal Bay: 158

Cystophora cristata: 121-124

DDE: 146, 148, 152, 156

DDT: 64, 73, 146, 152

Delaware: 5, 63

Delphinus delphis: 77, 80, 81

drift gillnet: 3, 7, 25, 27, 28, 30, 34, 37, 38, 41, 42,

45, 46, 49, 50, 53, 54, 57, 58, 62, 63, 67, 72, 78,

79, 83, 84, 87, 88, 92, 95, 98, 109

dwarf sperm whale: 27-30, 193, 194, 198

East Bay: 158

ecotype: 96, 100, 140, 143, 146, 150, 154

entanglement: 2, 3, 6, 7, 11, 14, 17, 28, 29, 33, 63,

67, 73, 102, 109, 113, 114, 117, 126, 129, 132,

135, 138, 147, 148, 151, 152, 155, 156, 159, 160,

164, 167, 170, 173, 176, 179, 182, 185, 188, 191,

194, 197, 200, 203, 206

epidemic: 149, 152, 160

Erysipelas spp.: 148, 152, 156

Espirito Santo Bay: 158

Estero Bay: 158

estuaries: 157, 158, 160

Eubalaena glacialis: 1, 4

false killer whale: 187

Feresa attenuata: 33, 34, 190-192, 199

fin whale: 9-12, 22

Florida: 1, 3, 18, 21, 27-30, 33, 37, 44, 48, 52, 56, 66,

67, 77, 82, 86, 94, 96, 100-106, 122, 133, 134,

137, 140, 143, 148, 149, 152-162

Florida Keys: 96, 102, 140, 158, 160

foreign fishing: 6, 10, 11, 40, 44, 48, 52, 58, 62, 64,

70, 72, 79, 83, 87, 91, 98

Fraser’s dolphin: 181

Galveston Bay: 158, 160, 161
211

Galveston Island: 148, 157

Gasparilla Sound: 158

Georges Bank: 1, 3, 5, 7, 8, 10, 11, 13, 16-18, 23-25,

28, 30, 34, 38, 40-42, 44-46, 48-50, 52-54, 56-58,

60, 61, 63, 67, 70-72, 77-79, 84, 88, 90, 92,

95-98, 109

Georgia: 103, 112

Gervais’ beaked whale: 46, 137

gillnet: 3, 4, 7, 18-20, 25, 27, 28, 30-32, 34, 37-39,

41-43, 45-47, 49-51, 53-55, 57-59, 62, 63, 67,

71-74, 76, 78-80, 83-85, 87-89, 91, 92, 94, 95, 98,

103, 104, 107-111, 113-115, 117, 118, 120, 123,

124, 148, 152, 155, 160

Globicephala macrorhynchus: 66, 205

Globicephala melas: 60, 63, 65, 66

Grampus griseus: 56, 59, 202

gray seal: 115-118

Great South Channel: 1, 2, 4, 13, 63, 67

Greenland: 1, 5, 16, 19, 25, 35, 62, 70, 72, 75, 79,

106, 112, 113, 117, 119, 120, 122

groundfish: 3, 7, 19, 27, 30, 34, 38, 42, 46, 50, 54, 57,

62-64, 67, 68, 71, 72, 76, 78, 83, 87, 91, 92, 99,

108, 109, 113, 117, 120, 123

Gulf of Maine: 1, 3, 5-8, 10-18, 20, 22, 27, 30-32, 34,

56, 60, 61, 70, 71, 73-75, 77, 106-108, 110, 111,

113-118

Gulf of Mexico: 1, 4, 16, 21, 26-30, 32-34, 37, 44, 58,

63, 66, 68, 69, 77, 79, 82-84, 86-88, 90, 91,

93-95, 98, 104, 125-144, 146, 148-152, 154-207

Gulf Stream: 23, 24, 26, 40, 41, 44, 45, 48, 49, 52,

53, 56, 59-61, 66, 77, 81, 82, 85, 90, 93, 95, 96,

100, 101

Gullivan Bay: 158

gunshot wounds: 102, 147, 151, 155, 159

Halichoerus grypus: 116, 118

harbor porpoise: 10, 12, 20, 74, 106-111, 114

harbor seal: 110, 112-115

harp seal: 119-121

haul seine: 103

health assessment: 103, 148, 160

herring weirs: 3, 18, 111, 113, 117

hooded seal: 122, 123

humpback whale: 5-8

Hyperoodon ampullatus: 35, 36

Indian/Banana River: 96, 100

Key West: 103, 143, 154, 158

killer whale: 31-34, 184, 186, 187, 190-192

Kogia breviceps: 28-30, 193, 194, 196, 198

Kogia simus: 27, 28, 30, 193, 194, 196, 198

ladyfish: 152, 156

Lagenodelphis hosei: 181, 183, 200

Lagenorhynchus acutus: 70, 74, 81

Lagenorhynchus albirostris: 65, 75, 76

Laguna Madre: 158

Lemon Bay: 158

Little Sarasota Bay: 158

lobster-pot: 11

Long Island: 100, 112

longline fishery: 18, 30, 57-59, 62, 63, 68, 79, 83, 87,

91, 95, 98, 126, 129, 132, 135, 138, 141, 144,

164, 167, 170, 173, 176, 179, 182, 185, 188, 191,

194, 197, 200, 203, 206

long-finned pilot whale: 60, 63-67

Louisiana: 28, 30, 69, 88, 127, 130, 133, 136, 139,

148, 151, 152, 155, 157, 160, 165, 168, 171, 174,

177, 179, 183, 186, 189, 192, 195, 198, 201, 204,

207

mackerel: 5, 7, 11, 18, 58, 62, 64, 65, 68, 72, 73, 78,

79, 98, 99, 113

Maine: 1, 3, 5-8, 10-20, 22, 27, 30-32, 34, 56, 60, 61,

70, 71, 73-75, 77, 106-119, 122

mark-recapture: 119, 120, 157

Maryland: 4, 102

Massachusetts: 1, 2, 4-6, 9, 12, 20, 22, 26, 31, 32, 64,

65, 73, 74, 108, 110, 111, 114-119, 122

matrilines: 1

Megaptera novaeangliae: 5, 7, 8, 22

melon-headed whale: 199, 200

menhaden: 103, 148, 152, 155, 156

Mesoplodon bidens: 52, 55, 135, 138

Mesoplodon densirostris: 48, 51, 134

Mesoplodon europaeus: 44, 137

Mesoplodon mirus: 40, 43

metals: 148, 160

minke whale: 16-19

Mississippi: 146-148, 150-152, 155, 157, 158, 160,

161

Mississippi River: 146, 147, 150, 152, 158

Mississippi River Delta: 152, 158

Mississippi Sound: 150, 157, 158, 160, 161

Mobile Bay: 158, 160

morbillivirus: 148, 149, 152, 153, 156, 160, 161

mutilation: 109, 147, 151, 155, 159

net entanglement: 2, 147, 151, 155, 159

New England: 1, 5, 9, 14, 16, 18, 23, 27, 30, 31, 34,

38, 42, 46, 50, 52, 54, 57, 58, 62, 64, 68, 72-75,

78, 82, 83, 87, 91, 92, 99, 103, 108-110, 112-118

New Jersey: 7, 60, 66, 100, 101, 103, 109, 119
212

New York: 11, 22, 26, 36, 43, 44, 47, 51, 55, 73, 80,

92, 99, 103, 106, 109, 112, 119-122, 137

North Carolina: 5, 7, 13, 16, 24, 27-30, 33, 40, 44,

48, 52, 56, 60, 66, 67, 70, 75, 77, 82, 86, 90, 94,

96, 100, 102, 103, 106, 109

northern bottlenose whale: 35, 36

Nueces Bay: 158

Orcinus orca: 31, 32, 184, 186

organochlorines: 110

pair trawl: 8, 20, 26, 27, 30, 34, 37-39, 41-43, 45-47,

49-51, 53-55, 57, 58, 62, 63, 72, 76, 78, 80, 83,

84, 87, 88, 91, 92, 98, 99, 108, 111, 126, 129,

132, 135, 138, 142, 144, 145, 165, 167, 170, 173,

176, 179, 182, 185, 188, 191, 194, 197, 200, 203,

206

pantropical spotted dolphin: 82, 86, 87, 89, 166-168

Passage Key Inlet: 157

pathology: 110

PCBs: 64, 73, 110

Peponocephala electra: 190, 199-201

Perdido Bay: 158

Phoca groenlandica: 119, 121, 124

Phoca vitulina: 112, 114, 115

Phocoena phocoena: 106, 110, 111

photo-identification: 1, 2, 6, 157, 185

Physeter macrocephalus: 23, 26, 125, 127

Pine Sound: 158

Plymouth: 1

polychlorinated biphenyls: 18, 64, 73, 110

population growth rate: 2, 4, 107

pound net: 102

pseudorabies virus: 148, 156

Pseudorca crassidens: 187

pygmy killer whale: 33, 34, 190-192

pygmy sperm whale: 27-30, 194, 196-198

Redfish Bay: 158

right whale: 1-4, 13

Risso’s dolphin: 56, 58, 202

Sabine Lake: 158

salmon gillnets: 18, 62, 113, 117

San Antonio Bay: 158

Sarasota Bay: 157, 158, 162

Scotian Shelf: 1, 13, 17, 23, 24, 41, 45, 49, 53, 57, 61,

71, 77, 78, 97

sei whale: 13, 14

shark: 27, 30, 34, 38, 42, 46, 50, 54, 58, 63, 72, 78,

80, 83, 87, 91, 98, 108

ship collisions: 2, 3, 11

ship strikes: 2, 3, 6, 11, 19

short-finned pilot whale: 60, 63, 64, 66-68, 205

shrimp trawl: 103, 141, 148, 151, 155, 160

sink gillnet: 18, 27, 30, 31, 34, 38, 42, 46, 50, 54, 57,

62, 72, 73, 78, 83, 87, 91, 103, 108, 110, 114, 117

South Carolina: 94

South Padre Island: 146, 157

Southeast U.S. Marine Mammal Stranding Network:

102, 103, 147, 149, 151, 153, 155, 159

Sowerby’s beaked whale: 134, 135, 137, 138

Spanish sardine: 152, 156

sperm whale: 23-30, 125-127, 193, 194, 196-198

spinner dolphin: 94, 95, 172, 174

squid: 18, 57, 58, 62, 64, 65, 68, 72, 73, 78, 79, 98,

99

St. Andrew Bay: 158

St. Georges Sound: 158

St. John's Sound: 158

St. Joseph Bay: 158

St. Vincent Sound: 158

Staphylococcus spp.: 148, 152, 156

Stellwagen Bank: 13, 18, 73, 114

Stenella attenuata: 83, 86, 89, 166, 168

Stenella clymene: 77, 178, 180

Stenella frontalis: 82, 86, 163, 165

Stenella longirostris: 94, 172, 174

Strait of Belle Isle: 1, 21

striped dolphin: 90-92, 169, 171

swordfish: 3, 6, 8, 20, 25-28, 30, 34, 38, 39, 42, 43,

46, 47, 50, 51, 54, 55, 58, 63, 67, 68, 72, 76,

78-80, 83, 84, 87, 88, 91, 92, 95, 98, 99, 108, 111,

126, 129, 132, 135, 138, 141, 142, 144, 145, 164,

167, 170, 173, 176, 179, 182, 185, 188, 191, 194,

197, 200, 203, 206

Tampa Bay: 156-158

Ten Thousand Islands: 158

TerreBonne Bay: 158

Texas: 4, 94, 103, 105, 127, 130, 133, 136, 139,

146-149, 152, 153, 155-157, 160-162, 165, 168,

171, 174, 177, 179, 183, 186, 189, 192, 195, 198,

201, 204, 207

thread herring: 152, 156

Timbalier Bay: 158

Trinity Bay: 158

tunas: 58, 63, 68, 79, 83, 87, 91, 95, 126, 129, 132,

135, 138, 141, 144, 164, 167, 170, 173, 176, 179,

182, 185, 188, 191, 194, 197, 200, 203, 206

Tursiops truncatus: 96, 99, 100, 104, 105, 140, 143,

146, 149, 150, 153, 154, 157, 161, 162
213

Vermillion Bay: 158

Virginia: 1-5, 8, 63, 64, 67, 68, 102, 104, 109

Waccasassa Bay: 158

West Bay: 158

West Cote Blanche Bay: 158

Whitewater Bay: 158

white-beaked dolphin: 75

white-sided dolphin: 70-74

Withlacoochee Bay: 158

Ziphius cavirostris: 37, 39, 131, 133, 134, 137