NOAA Technical Memorandum NMFS-AFSC-76

U.S. DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric Administration

National Marine Fisheries Service

Alaska Fisheries Science Center

December 1996

Assessment of the Status of

Harbor Porpoise (Phocoena phocoena)

in Oregon and Washington Waters

by

S. Osmek, J. Calambokidis, J. Laake, P. Gearin,

R. Delong, J. Scordino, S. Jeffries, and R. Brown
NOAA Technical Memorandum NMFS

The National Marine Fisheries Service's Alaska Fisheries Science Center

uses the NOAA Technical Memorandum series to issue informal scientific and

technical publications when complete formal review and editorial processing

are not appropriate or feasible. Documents within this series reflect sound

professional work and may be referenced in the formal scientific and technical

literature.

The NMFS-AFSC Technical Memorandum series of the Alaska Fisheries

Science Center continues the NMFS-F/NWC series established in 1970 by the

Northwest Fisheries Center. The new NMFS-NWFSC series will be used by

the Northwest Fisheries Science Center.

This document should be cited as follows:

Osmek, S., J. Calambokidis, J. Laake, P. Gearin, R. DeLong, 

J. Scordino, S. Jeffries, and R. Brown. 1997. Assessment of the

status of harbor porpoise (Phocoena phocoena) in Oregon and

Washington waters. U. S. Dep. Commer., NOAA Tech. Memo. NMFSAFSC-76, 

46 p.

 

Reference in this document to trade names does not imply endorsement by

the National Marine Fisheries Service, NOAA.
December 1996

NOAA Technical Memorandum NMFS-AFSC-76

Assessment of the Status of

Harbor Porpoise (Phocoena phocoena)

in Oregon and Washington Waters

U.S. DEPARTMENT OF COMMERCE

William M. Daley, Secretary

National Oceanic and Atmospheric Administration

D. James Baker, Under Secretary and Administrator

National Marine Fisheries Service

Rolland A. Schmitten, Assistant Administrator for Fisheries

by

S. Osmek, J. Calambokidis, J. Laake, P. Gearin,

R. Delong, J. Scordino, S. Jeffries, and R. Brown

1 2 1 1

1 3 4 5

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National Marine Mammal Laboratory

Alaska Fisheries Science Center

7600 Sand Point Way N.E., BIN C-15700

Seattle, WA 98115-0070

Cascadia Research Collective

Waterstreet Building, Suite 201

218 1/2 West Fourth Avenue

Olympia, WA 98501

Northwest Regional Office

National Marine Fisheries Service

7600 Sand Point Way NE

Seattle, WA 98115

Washington Department of Fish and Wildlife

7801 Phillips Road

Tacoma, WA 98498

Oregon Department of Fish and Wildlife

2040 SE Marine Science Drive

Newport, OR 97365

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3

4

5
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111

ABSTRACT

The status of harbor porpoise, Phocoena phocoena, is reviewed for stocks in Oregon and

Washington waters, and the adjacent transboundary waters of southern British Columbia, Canada,

emphasizing the most recent data on their geographic range, population structure, distribution,

population size, trends in abundance, and reproductive biology. This information is used to

determine if the annual rate of incidental mortality and serious injury in gill-net fisheries from

1990-94 could be at a biologically significant level.

In the eastern North Pacific Ocean, harbor porpoise are found near the coast, generally in

water depths of less than 200 m. Differences in harbor porpoise mitochondrial DNA and

organochlorine pollutant ratios and concentrations indicate that porpoise movements and intrinsic

rates of mixing are sufficiently restricted to form geographically distinct groups, but not specific

stock boundaries. Two harbor porpoise transboundary management areas, the Inland Washington

Stock and the Oregon/Washington Coast Stock, are recommended because incidental takes of

harbor porpoise occur in commercial sockeye salmon gill-net fisheries of inland Washington

waters.

The corrected 1990-91 best and minimum abundance estimates are N = 3,352 (CV(N) =

0.270) and Nmin = 2,680 for inland Washington/southern British Columbia, and N = 26,175

(CV(N) = 0.206) and Nmin = 22,049 for coastal Oregon/Washington. Except for Puget Sound,

where a substantial decline in harbor porpoise abundance has occurred, there are no data to

determine population trends in Oregon and Washington waters. The aerial survey data collected

during the summer of 1990-91 for water depths less than 91 m (50 fathoms), indicated significant

differences (z = 6.9, P<O.OOl) in harbor porpoise mean densities (1.7 animals/km2 and 0.5
iv

animals/km2, respectively) between the waters of southern coastal Washington/Oregon and

northern coastal and inland Washington (i.e., the U.S. and Canadian portions of the Strait of Juan

de Fuca and San Juan Islands). Although incidental takes of this species in gill-net fisheries only

occur in the regions of lowest harbor porpoise densities, other factors such as variations in habitat

quality may be responsible for these observed density differences.

To determine if the annual number of incidental takes in gill-net fisheries was potentially

significant for a particular stock, an average mortality rate was calculated for 1990-94 and

compared to the stock’s calculated potential biological removal (PBR) level (i.e., the product of

the minimum population estimate, one-half the maximum theoretical productivity rate and a

population recovery factor). For the Inland Washington Stock, an estimated total of 16 harbor

porpoise are killed or seriously injured annually: 15 animals/year (90% C.I. = 2 - 58) are

incidentally taken in the commercial and tribal sockeye salmon drift gill-net fishery and 1 is

estimated to be taken annually in the tribal northwest Washington chinook salmon set gill-net

fishery. This combined rate is less than the PBR, but it exceeds 10% of the calculated PBR (27 x

0.1 = 2.7 animals). This tribal chinook salmon fishery also operates in the waters of the

Oregon/Washington Coast Stock. An average of 9 harbor porpoise (1990-93 data) are

incidentally taken or seriously injured annually. The annual incidental mortality is less than 10% of

the PBR (220 x 0.1 = 22) for the coastal stock.
V

CONTENTS

Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii

Introduction ................................................................................................................................ 1

Range and Stock Structure ......................................................................................................... 2

Estimates of Population Size and Regional Density. .................................................................... 7

Population Trends and Growth Rates ........................................................................................ 11

Current Biological Removals ..................................................................................................... 12

Potential Biological Removals and Status of Stocks................................................................... 18

Management Recommendations and Considerations ................................................................. 20

Acknowledgments ................................................................................................................... 22

Citations.................................................................................................................................. 23

Appendix - Description of Drift and Set Gillnets ........................................................................ 46
INTRODUCTION

In November 1988, the U.S. Congress passed a series of amendments to the Marine Mammal

Protection Act (MMPA) that established the Marine Mammal Exemption Program (MMEP) and

the Marine Mammal Assessment Program (MMAP). The MMEP was created to provide fisheries

that incidentally took marine mammals in the U. S. Exclusive Economic Zone (EEZ) with limited

exemptions from the MMPA regulations for 5 years. During that time, the National Marine

Fisheries Service (NMFS) and U.S. Fish and Wildlife Service (USFWS) were responsible for

determining the level of human-induced marine mammal mortality and serious injury for fisheries

suspected of incidentally taking marine mammals, and for gathering information on marine

mammal populations, distribution, abundance, stock structure, and trends for those species that

spend some portion of their time in the EEZ, These programs provided the requisite information

for the NMFS to calculate potential biological removal (PBR) levels and to estimate the potential

significance of human-caused impacts on marine mammal stocks. The PBR is defined as “the

maximum number of animals, not including natural mortalities, that may be removed from a

marine mammal stock while allowing that stock to reach or maintain its optimum sustainable

population (OSP)” (Barlow et al. 1995). Barlow et al. (1995) defined a “stock” as “the

fundamental [population] unit of legally mandated conservation efforts,” unless some biologically

significant data was available that would help delineate a specific stock boundary.

This document reviews information on the population status of harbor porpoise, Phocoena

phocoena, occupying Oregon/Washington marine waters (Osmek et al. 1992, 1993, 1994, 1995),

and recommends stocks for management purposes (i.e., stock boundaries do not necessarily

represent stocks of biological significance). General information regarding harbor porpoise
2

geographic distribution along the west coast of North America and their reproductive biology is

examined, while the subunits of this west coast population, abundance estimates, and regional

density differences are discussed more specifically for Oregon/Washington waters. This

information and the annual rates of incidental mortality and serious injury in commercial and tribal

gill-net fisheries are used to determine PBR levels and the potential significance of human-induced

impacts on two harbor porpoise stocks. The transboundary marine waters of southern British

Columbia are considered an important biological component of inland Washington waters and are

included in this stock (Fig. 1). The adjacent marine waters south of Oregon are divided into a

Northern California Stock and a Central California Stock of harbor porpoise These stocks are

discussed by Barlow and Hanan (1995).

RANGE AND STOCK STRUCTURE

Geographic Range and Seasonal Occurrence

In the eastern North Pacific Ocean, harbor porpoise are found coastally from north of Point

Barrow, Alaska, south to Point Conception, California, and are typically seen in groups of less

than 10 individuals. Harbor porpoise may occasionally frequent bays, the mouths of large rivers,

and at times, they ascend freshwater streams (Leather-wood and Reeves 1983). Some of the

earliest scientific observations of harbor porpoise in the northeast Pacific are from Lewis and

Clark, who reported sighting harbor porpoise in the Columbia River near its mouth during their

1804-6 expedition (Twaites 1904-5). Aerial survey data, collected out to the 91 m (50 fathoms)

isobath along coastal Oregon/Washing-ton (Calambokidis et al. 1992), suggests that the summer
3

1991 harbor porpoise distribution varied by depth with 65% of all group sightings (n=319)

occurring in waters shallower than 37 m (20 fathoms). They found no meaningful relationship to

water depth for the Strait of Juan de Fuca, but for the waters of the U.S./Canadian San Juan

Islands, harbor porpoise were found more often at depths greater than 91 m. Distribution by

depth in the five survey areas where harbor porpoise were observed was found to differ

significantly from the expected effort-corrected uniform pattern. Although the sample size of

sightings (n=88 animals) is small from a study by Green et al. (1992), their summer 1989-90

survey data indicate that most (68%) of the harbor porpoise individuals were found at water

depths shallower than 100 m and were rarely observed at depths greater than 200 m.

Few reliable data are available on seasonal changes in distribution or abundance of harbor

porpoise in the North Pacific Ocean. Catch per unit effort data from the 1988-89 northern

Washington salmon set gill-net fishery indicate that seasonal changes in distribution may regularly

occur around the Spike Rock fishing grounds (Fig. 2). Gear-in et al. (1994) reported that for gill

nets fished less than 1.6 km from shore (11-30 m deep), more harbor porpoise were incidentally

taken during July/August than during May/June. Both harbor porpoise and chinook salmon

(Uncorynchus tshawytscha) were found to consume primarily Pacific herring (Clupea pallasi),

market squid (Loligo opalescens), and smelts (Osmeridae). Harbor porpoise may follow prey into

shallower waters during July/August. Taylor and Dawson (1984) observed that the harbor

porpoise density (animals/km2

) in Sitakaday Narrows, Glacier Bay, Alaska, increased from 1.7

during summer to 5.9 during fall (P<O.OOl), and group size in this study area increased from

about 1 in July to greater than 3 in February. Taylor and Dawson surmise that these changes in

density and group size are related to changes in prey availability and feeding strategy
4

Harbor porpoise are present year-round in Oregon and Washington (Haley 1988,’ Green et al.

1992). Observations of harbor porpoise on the east coast of North America indicate that a

seasonal migration occurs, with the animals moving south and possibly offshore during winter

(Gaskin 1977, Gaskin and Watson 1985). Annual migrations have also been described for harbor

porpoise in Danish waters, where animals were driven into traps and captured (Heel 1962) and in

British waters where seasonal differences in the number of harbor porpoise strandings have been

documented (Easton et al. 1982). In the northeast Pacific, however, no strong seasonal migration

has been documented.

Biological Subunits of the Population

Various methods have been used to determine population stock structure of harbor porpoise

along North America. In the western North Atlantic, four major sub-populations of harbor

porpoise are proposed (Gaskin 1984) based, in part, on differences in cranial morphology

(Yurick and Gaskin 1987). Genetic and contaminant analyses have been used to investigate the

stock structure of harbor porpoise in the northeast Pacific.

Genetics

Subunits of the population were analyzed using mitochondrial DNA (mtDNA) from samples

collected along the west coast (Rose1 1992). Two distinct mtDNA groupings exist. One group is

present in California, Washington, British Columbia, and Alaska. (No samples were available from

Oregon.) A second group exists only in California and Washington waters. When an analysis of

genetic variance was conducted with these data and data from additional samples from these

regions, Rose1 et al. (1995) found significant differences for four of the six pair-wise comparisons.
5

These results demonstrate that harbor porpoise along the west coast of North America are not

panmictic and genetic differences have evolved. Sample sizes were insufficient to determine

whether genetic differences also exist between harbor porpoise of coastal Washington and the

inland Washington waters of the Strait of Juan de Fuca, San Juan Islands, and Puget Sound

(Fig. 1).

Contaminants

Geographic differences in organochlorine pollutant residue (OPR) ratios and concentrations

have been used to assess harbor porpoise stock discreteness along the west coast of North

America (Calambokidis and Barlow 1991, Osmek et al. 1994). Calambokidis and Barlow (1991)

found decreasing concentrations of DDE in harbor porpoise blubber for those beach cast or

incidentally caught individuals collected from coastal California north to coastal Washington

waters. A similar decrease in DDE concentration with an increase in latitude was reported by

Osmek et al. (1994) for samples collected in Oregon, Washington, and British Columbia waters,

Calambokidis and Barlow (1991) showed that through discriminant analysis of OPR ratios, the

state from which the harbor porpoise was collected from could be accurately predicted for 86% of

the samples. These observed differences in OPR ratios illustrate that harbor porpoise movements

are not coastwide. However, no specific boundaries can be identified from these genetic and

contaminant data to determine biologically discrete subunits.

Recommended Stocks for Management

In the absence of evidence to define stocks of biological significance, management

boundaries must be selected in a way to reasonably protect harbor porpoise so their populations
6

can be maintained within OSP, or if depleted, can be restored to OSP. It is recommended that a

conservative approach be used to assign harbor porpoise stock boundaries in Oregon and

Washington waters. The biological evidence indicates harbor porpoise movements are not rangewide in the northeast Pacific Ocean even though specific boundaries have not been empirically

substantiated. The lack of a stock boundary within Oregon/Washington waters could result in an

inappropriately large PBR being used for fisheries concentrated in northern Washington that may

result in a local depletion of porpoise. Conversely, a harbor porpoise management plan that is too

conservative is undesirable because a biologically significant stock could be repeatedly split which

may result in commercial fishing activities being unnecessarily restricted.

It is recommended that Oregon and Washington waters be divided into two harbor porpoise

stocks, Inland Washington and Oregon/Washington Coast, using a boundary located at the

western end of the Strait of Juan de Fuca. This boundary extends north from Tatoosh Island,

Washington, to Bonilla Point, British Columbia (approximately long. 124.43.5°W, Fig. 1). This

boundary is also used by the Washington Department of Fish and Wildlife (WDFW) to manage

commercial fisheries operating in Areas 4 and 4B (Fig. 2). A stock boundary at this location

protects harbor porpoise in most areas where animal densities are relatively low and includes all

non-tribal commercial gill net fisheries that are known to incidentally take harbor porpoise. This

boundary, however, does not include all of the tribal gill-net fisheries that incidental take harbor

porpoise along northern Washington of the Oregon/Washington Coast Stock.
7

ESTIMATES OF POPULATION SIZE AND REGIONAL DENSITY

Cooperative efforts between NMFS and various state and private organizations have focused

on aerial and shipboard surveys and a correction factor to provide the best estimate of harbor

porpoise abundance for Oregon, Washington, and southern British Columbia waters, Aerial linetransect surveys were flown during 1984-85 (Barlow et al. 1988) 1989 (Turnock et al In press.),

1990 (Calambokidis et al. 1991), 1991 (Calambokidis et al. 1992) and 1994 (Osmek et al. 1995).

Vessel surveys were conducted during 1984-86 (Barlow 1988), 1988-89 (Calambokidis In press),

and 1994 (Osmek et al. 1995). The aerial survey data collected by Calambokidis et al. (1992) are

best suited for estimating harbor porpoise abundance for both stocks because these surveys had

the most complete coverage of Oregon, coastal/inland Washington, and the transboundary waters

of southern British Columbia.

Correction Factor

A correction factor for harbor porpoise aerial surveys was needed to compensate for the

number of animals missed by observers on the survey trackline. Aerial-line transect theory

assumes that animal sightability is 100% near the transect line (g(0) = l), but decreases as a

function of distance from the trackline. If factors such as animal submergence, sea state, cloud

cover, water turbidity, and glare reduce visibility near the line (g(O)<l), abundance estimates will

be negatively biased. To correct for these biases, a calibration experiment was conducted in

August 1992 to estimate the probability that all porpoise groups are detected near the aerial

trackline (Calambokidis et al. 1993a). Shore-based observers visually tracked porpoise groups
8

using theodolites and recorded locations, group sizes, and surfacing rates while the same twinengine aircraft, used during the 1990-91 surveys, flew transects through the San Juan Islands

study area. The shore and aerial sighting data were compared to determine whether a group at or

near the surface was seen by aerial observers. Of the 92 groups located from shore within 100 m

of the aerial trackline, 28 (30.4%) were seen by the aerial observers. With a point estimate of

g(0) = 0.324 (SE = 0.056, var = 0.003), the correction factor was calculated at

3.1 (l/g(O)).

Best Estimate of Abundance

The summer 1991 surveys (Figs. 3b-d) provide the most recent abundance estimates and used

aerial survey methods identical to the 1990 surveys (Fig. 3a). Therefore, these data were pooled

by Calambokidis et al. (1993b) to estimate abundace. During these 1990-91 surveys, two sidewindow observers and one belly window observer reported harbor porpoise sightings to the data

recorder while the aircraft flew a sawtooth configuration of line transects at an altitude of 183 m

(600 ft) and a speed of 167 kmhr (90 knots). Along coastal Oregon/Washington, survey

tracklines were primarily flown out to the 91 m isobath (50 fathoms). The exception was Heceta

Bank, along coastal Oregon (Fig. 3b), where waters out to 182 m (100 fathoms) deep were

sampled to provide complete coverage of the coastal waters where harbor porpoise commonly

occur This survey design, however, excluded some harbor porpoise in Oregon/Washington

coastal waters distributed at depths greater than 91 m (Green et al. 1992). All water depths were

surveyed along inland Washington and southern British Columbia. Calambokidis et al. (1993b)

estimated harbor porpoise abundance following the methods described by Buckland et al. (1993),
9

using the program DISTANCE (Laake et al. 1993). Only effort and group sightings from oneffort periods with optimal sighting conditions (Beaufort Wind Scale <_ Force 2 and cloud cover 5

25%) were used. The Hazard-rate model, with one cosine adjustment term, was used in the

analysis to estimate the probability of detection with perpendicular distance from the track line

(Fig. 4). The coefficient of variation (CV) for the corrected abundance estimates are below 0.30,

an objective of Ferrero and Fowler (1992).

The estimate of harbor porpoise abundance for the Inland Washington Stock is 3,352

(CV = 0.270)(Table 1). It is important to note, however, that this may be a slight overestimate of

abundance because the 1991 surveys were conducted before the Tatoosh-Bonilla harbor porpoise

stock boundary was defined. Approximately 10% of the survey area was located outside (west) of

this stock boundary and is part of the Coastal Oregon/Washington stock (Fig. 3c)(The amount of

geographic area added to the coastal stock is 1% and is considered an inconsequential addition).

Another important factor to consider is that an additional 20 % of the stock area lies in the waters

of British Columbia outside the EEZ. Consequently, about 30% of the Inland Washington survey

area lies either outside U.S. waters or the stock boundary line.

The best abundance estimate for the Oregon/Washington Coast Stock is 26,175 (CV = 0.206)

harbor porpoise. No harbor porpoise were sighted in the mouth of the Columbia River, Grays

Harbor, Willapa Bay, Hood Canal or Puget Sound in 1991 (Fig. 3d).

Minimum Population Estimate

The minimum population estimate (NG) is the 20th percentile of a log-normal distribution

based on the estimate of the number of animals in a stock. Nmin is calculated using Equation 1
10

from the 27-29 June 1994 PBR Workshop (see Barlow et al. 1995):

Nmin = N/exp(0.842*[ln(1+[CV(N)]2)]1/2)

where N is the abundance estimate. The minimum estimates of abundance are 2,680 for the Inland

Washington Stock and 22,049 for the Oregon/Washington Coast Stock (Table 2).

Regional Differences in Density

We compared the density data from the five subregions that comprised the study area of

Calambokidis et al. 1991 (Table 1). Harbor porpoise density in northern Washington (0.5

animals/km2

) is lower than the density in southern Washington (1.7 animals/km2)(Z = 6.9,

P<O.OOl). The aerial survey boundary separating these two water bodies occurs approximately

one-quarter of the way down the Washington coast near the mouth of the Hoh River (Fig. 3b).

Southern Washington had the highest density of porpoise with Oregon waters ranking second

(Table 1). Barlow (1988) and Green et al. (1992) also reported a relatively high density in the .

waters off southern Washington and northern Oregon, (around the Columbia River mouth), with a

much lower density occurring along the northern Washington coast. The only other dramatic

difference was for the inland Washington waters of Hood Canal, and south Admiralty Inlet, in

Puget Sound, where no harbor porpoise were observed.

The reasons for these disparities are unknown, but it may be related to differences in habitat or

the location where incidental takes in gillnet fisheries occur. Fisheries-related incidental takes have

only been reported from the waters of coastal northern Washington and the inland waters of

Washington and British Columbia where densities are lowest.
11

POPULATION TRENDS AND GROWTH RATES

Population Trend

There are currently no reliable data on population trends of harbor porpoise for the waters of

coastal Oregon/Washington, British Columbia, and most of inland Washington. In Puget Sound,

however, it is known that a substantial decline in harbor porpoise abundance has occurred. During

the 194Os, harbor porpoise were considered common in Puget Sound (Scheffer and Slipp 1948).

Though quantitative data for this area are lacking, marine mammal survey effort (Everitt et al.

1980; Dale Rice, NMML, unpublished data), stranding records since the early 1970s (NW Marine

Mammal Stranding Network, unpublished data) and the results of harbor porpoise surveys of

1991 (Calambokidis et al 1992) and 1994 (Osmek et al. 1995) indicate that harbor porpoise have

become increasingly rare, Although declines in abundance have not been quantified elsewhere in

inland Washington or British Columbia, anecdotal information suggests that abundance is

declining in those areas (Flaherty and Stark 1984, Calambokidis and Baird 1994, T. Guenther,

Marine Mammal Research Group, Box 6244, Victoria, BC, V8P 5L5, pers. commun., June

1995).

The cause(s) of the decline in Puget Sound are unidentified, but they are possibly related to

several factors, including mortality associated with entanglement in gill-net fisheries, decreased

reproductive output, immunosuppression, anthropogenic contaminants, human-generated noises,

recreational and commercial sea-going vessel traffic, and possibly changes in prey availability and

competition with Dall’s porpoise (Phocoenoides dalli), a species that has likely increased in

numbers within Puget Sound (Osmek et al. 1995).
12

Maximum Net Productivity

The maximum net productivity rate (Rmax) has never been measured for free-ranging harbor

porpoise. Barlow and Boveng (1991), using a female age at first birth of 4-years old, calculated a

theoretical upper bound for Rmax of 9.4% per year. Woodley and Read (1991) calculated a harbor

porpoise Rmax value of 5% per year, using the reproductive and survival rates of a Himalayan thar,

Hemitragus jemlahicus. This terrestrial species is thought to exhibit a maximum reproductive

potential similar to harbor porpoise because it also produces an average of one offspring annually,

starting at age 4, and is not long-lived.

Barlow and Boveng (1991) recommended that their Rmax value not be used for managing

harbor porpoise populations because the objective of their study was to develop an exploratory

model and not one for immediate application. It was decided the Rmax value of Himalayan thars

also should not be used to calculate PBR because the appropriateness of these data has not been

fully evaluated. The default cetacean Rmax, rate of 4% will be employed for Oregon/Washington

harbor porpoise until additional data become available (Barlow et al. 1995).

CURRENT BIOLOGICAL REMOVALS

Incidental Mortality and Serious Injury

To maintain consistency with other MMAP documents that describe the status of marine

mammal populations, the following estimates of incidental mortality and serious injury are based

on observer data from five fishing seasons, 1990-94. For the set gill-net fishery along northwest
13

Washington, incidental mortality data since 1988, the year when this program was initiated, is

provided to illustrate the dynamics of this tribal fishery in terms of annual variability in fishing

effort and the number of annual incidental takes (Table 3). A description of the drift gillnets and

set gillnets used in the salmon fisheries is provided in the Appendix.

Inland Washington Fisheries

In recent years, harbor porpoise have been incidentally taken from inland Washington waters

in two gillnet fisheries: the Area 7/7A commercial/tribal San Juan Islands sockeye salmon

(Oncorynchs nerka), drift gill-net fishery (Fig. 5) and the Area 4B/5 northwest Washington

chinook salmon set gill-net fishery (Fig. 2). During August/September 1993-94, NMFS, in

cooperation with the WDFW and the Northwest Tribes, conducted observer programs to monitor

incidental takes of marine mammals in commercial drift gill-net and purse-seine activities within

the U.S. waters of the Strait of Juan de Fuca and the San Juan Islands. One mortality was

observed in Area 7 during the 1994 drift gillnet fishery near the San Juan Islands (Pierce et al.

1996). During this 1994 fishery, another harbor porpoise was observed entangled and released

alive, presumably uninjured. Using one observed harbor porpoise mortality and over 600 observed

gill-net sets in Areas 7 (almost 7% observer coverage), an incidental take estimate of 15 (90%

C.I. = 2 - 58) harbor porpoise per year was calculated for an estimated total of 6,521 (SE=614)

commercial sets and 2,824 (SE=286) tribal sets (Pierce et al. 1996).

Harbor porpoise are also known to be incidentally taken in the U.S. waters of the western

Strait of Juan de Fuca in Area 4B/5 (Gearin et al. 1994, and NMFS, Northwest Region,

unpublished data)(Fig. 2). This northwest Washington chinook salmon set gill-net fishery is

exclusively tribal and is authorized by the Makah Tribe to operate annually from May through

September. Most fishing activity, however, occurs from late May or early June through the middle
14

of August. From 1988 to 1993,61.4% of the total fishing effort (5,429 net days) was expended in

the western Strait of Juan de Fuca with the remainder spent along coastal northern Washington of

the Oregon/Washington Coast Stock. One harbor porpoise was reported taken by a tribal

fisherman during 1989 and one was observed taken by a NMFS fishery observer during 1991.

That single take was used to extrapolate the mortality rate estimate of two for 1991 (Table 3).

Excluding 1994, when no observer data was available for this fishery, the 1990-93 average annual

take rate is one (2 kills/4 years = 0.5).

During October 1992, a harbor porpoise was incidentally killed in a tribal salmon gillnet in

southern Puget Sound; the Tribe’s reaction to the entanglement was one of surprise, probably

indicating that such mortalities, like sightings of live animals, are infrequent (Osmek et al. 1995).

Harbor porpoise incidental takes also occur in fisheries of inland British Columbia (Stacey et al.

1990, Baird et al. 1994a), but because observer programs are also lacking in these areas, no

reliable annual take rates exist.

Oregon/Washington Coast Fisheries

Within the Oregon/Washington Coast Stock, harbor porpoise are incidentally taken in the

Area 4/4A northwest Washington chinook salmon set gill-net fishery. Although much of the set

gill-net fishing effort has recently been expended within the western Strait of Juan de Fuca,

incidental take levels are much higher along the northern Washington coast. Since 1988, all but

two harbor porpoise (n = 156) were incidentally taken from coastal Washington waters (Table 3).

During 1988, 1989, 1990, and 1991, NMFS fishery observers saw 22, 14, 13, and 14 harbor

porpoise incidentally taken, respectively. Fishing effort has decreased each year along coastal

Washington from 1988 to 1993, when no effort was expended on the coast. This decline in fishing

effort and incidental takes was primarily due to declining salmon runs. Though no observer
15

program was conducted during 1994; it is known that harbor porpoise were incidentally taken

from the Oregon/Washington Coast Stock,

The total annual estimate of mortalities, using the percent observer coverage and the number

of harbor porpoise observed taken by NMFS observers, was 33 (CV = 0.26), 16 (CV = 0.27), and

19 (CV = 0.29) for 1989, 1990, and 1991, respectively (Table 3). In 1988, no reasonable estimate

of incidental mortality could be extrapolated because observer coverage was low and

concentrated on one vessel that fished in the waters of Spike Rock, an area where incidental

mortalities are highest (Gearin et al. 1994). It is known that 102 harbor porpoise were incidentally

taken during 1988; the minimum estimate for 1992 and 1993 is 2 and 0, respectively. Because the

1994 data is currently unavailable, annual take estimates from 4 years (1990-93) were used to

calculate the average incidental mortality rate of 9 harbor porpoise. Although gillnets are used in

Oregon, the Columbia River, Willapa Bay, and Grays Harbor, no harbor porpoise incidental takes

have been reported for these fisheries.

Sex and Age Distribution of Incidental Takes

Reproduction and population growth of harbor porpoise could be dramatically reduced if high

numbers of adult females are removed from a population. Gearin et al. (1994) reported the sex

and age structure of harbor porpoise recovered and necropsied from the tribal northwest

Washington chinook salmon set gill-net fishery between 1988 and 1990 (Fig. 6). Of the 44

females examined, 3 1 (70.5%) were reproductively immature while 13 (29.5%) were mature. Of

the 55 males sampled, 4 (7.3%) were calves, 28 (50.9%) were reproductively immature males and

23 (41.8%) mature males. It is not apparent from these data whether this fishery is removing

harbor porpoise of each age and sex categories at proportions other than their relative occurrence
16

in the wild (Table 4). However, it does show that all sex and age classes are susceptible to

entanglement in gillnets.

Other Human-Induced Mortality Causes

Subsistence Take

No directed subsistence takes of harbor porpoise presently occurs in Oregon or Washington

waters. There are recent reports of fisherman in British Columbia (Stacey et al. 1990) and tribal

fisherman in Washington who have eaten incidentally caught porpoise, but it appears this was

done on an opportunistic basis and is probably uncommon. Historically, subsistence takes of

harbor porpoise by harpooning along northwest Washington (Swan 1870) and shooting have

occurred on the west coast (Scammon 1874, Scheffer and Slipp 1948). Because these methods of

take are presumably difficult, relying on a porpoise to approach within shooting range, harvest

levels of harbor porpoise by the northern tribes of the west coast were not thought to be great.

Illegal Killing and Intentional Harassment

Illegal takes of harbor porpoise are not known to occur and are considered unlikely because

harbor porpoise are not known to feed on fish caught by fishing gear and therefore are not viewed

as a menace by fisherman. This species currently does not provide products of commercial value

which would encourage directed takes.

Live Capture

Free-ranging harbor porpoise are not easily live-captured using an active approach (Heel

1962, Silbers et al. 1990) and therefore have not been taken from the wild in large numbers. Only
17

live-stranded neonates, recovered from Oregon/Washington beaches and rehabilitated at the Point

Defiance Zoo and Aquarium, Tacoma, Washington, have been taken from the wild.

Unusual Mortality Events

Other causes of mortality that have the potential for affecting large numbers of harbor

porpoise have been noted in the waters of Washington and British Columbia. During October

1992, five dead harbor porpoise in fresh condition were found along several kilometers of

Washington’s Long Beach Peninsula, near the mouth of the Columbia River (NMML,

unpublished data). The stomach contents from two of these harbor porpoise were tested for

paralytic shellfish poisoning (PSP), an assortment of biotoxins produced by dinoflagelates

(Alexandrium spp.) responsible for causing red-tides. Paralytic shellfish poisoning was found at

low concentrations (40 pg/lOO g and 41 pg/lOO g) below the U.S. Food and Drug Administration

regulatory closure level of 80 pg./100 g for seafood (J. Wekell, NMFS, Northwest Fisheries

Science Center, Utilization Research Division (URD), Seattle, WA, pers. commun January

1996). Northern anchovy, Engraulis morahx, was a common prey item found in both stomachs

and is thought to be the source of the PSP toxicity. During the same time period as the strandings,

a red-tide event was observed along the coast of Washington/Oregon and higher levels of PSP

were detected in mackerel (90 pg/lOO g) sampled 111 km (60 nm) offshore of Newport, Oregon,

and razor clams from southern Washington (M. Eklund, URD, pers. commun., May 1995). The

total number of porpoise affected (if they are affected at all by PSP) or the length of time these

animals were exposed to the low PSP levels is unknown. Additional analysis of stomach contents
18

for demoic acid, another biotoxin, and tissues selected for histopathological examinations,

provided no information on the cause of these mortalities.

From April to May 1993, Baird et al. (1994b) collected the carcasses of 13 harbor porpoise,

10 Dall’s porpoise and 1 unidentified porpoise along the beaches of Victoria, Vancouver Island,

British Columbia (Fig. 1.). This number of stranded small cetaceans in this vicinity was relatively

high compared to the average for an entire year (about 0 to 4 small cetaceans carcasses). Most of

these porpoise had enlarged mesenteric lymph nodes, but the cause could not be investigated

thoroughly, so the deaths could not be related to PSP or other disease agents. The total number of

harbor porpoise affected by this event was undetermined.

POTENTIAL BIOLOGICAL REMOVALS AND STATUS OF STOCKS

PBR Calculations

Under the 1994 re-authorization of the MMPA, PBR is the product of the minimum

population estimate (Nmin), one-half the maximum theoretical net productivity (Rmax)

,

rate, and a recovery factor (F,):

The F, for this stock is 0.50, the value for cetacean stocks with unknown population status

(Barlow et al. 1995). Using an Rmax, value of 0.04, the PBR is 27 for the Inland Washington Stock

and 220 for the Oregon/Washington Coast Stock (Table 2).
19

Determination of Significance

Barlow et al. (1995) interpreted the zero-rate mortality goal of the MMPA to be met if the

level of incidental mortality from commercial fishing operations is below 10% of PBR. If the level

,

of incidental mortalities exceeds 10% of PBR, these takes cannot be considered an insignificant

level. If the mortality level exceeds PBR then the number of takes are significant and the affected

stock is defined as strategic.

For the Inland Washington Stock, total fishery mortality and serious injury, 16 (15+1),

exceeds 10% of the calculated PBR (27 x 0.1 = 2.7) and, therefore, this take rate can not be

considered insignificant. When the PBR is reduced by 30% (27 x (1.0 - 0.30) = 19), the amount of

survey area outside the boundaries of this stock, stock status is unchanged because the take rate is

still below 19. The incidental take level of 9 animals per year for the Oregon/Washington Coast

Stock is insignificant because 9 is less than 10% of PBR (220 x 0.1 = 22).

Stock Status Relative to OSP and K

The status of these stocks relative to the OSP and carrying capacity (K) have not been

determined because no reliable estimates of these parameters are available for comparison with

the most recent (1991) abundance estimates for Oregon/Washington waters.
20

MANAGEMENT RECOMMENDATIONS AND CONSIDERATIONS

Future harbor porpoise studies should be conducted primarily in the transboundary waters of

Washington and British Columbia, Canada where most fisheries incidental takes are known to

occur and where harbor porpoise densities are low. It is recommended that NMFS and the

Department of Fisheries and Oceans develop cooperative programs to assess harbor porpoise

abundance and incidental take levels in those waters under their jurisdiction. For the next aerial

surveys planned for inland Washington and coastal Oregon and Washington, the Tatoosh-Bonilla

stock boundary and the international boundary should be used to define survey regions. Based on

the results of these surveys, updated estimates of animal density, and ongoing studies of harbor

porpoise stock structure, the best location(s) for a stock boundary should be reevaluated.

Inland Washington Stock

The potential effect of the sockeye salmon drift gill-net fishery takes on the status of this stock

should be reviewed again when separate estimates of harbor porpoise abundance are available for

both inland Washington and inland southern British Columbia. Until then, a conservative

management approached for this stock is needed because:

1). The estimated mean level of incidental take can not be considered an insignificant annual

mortality rate.

2). The upper 90% confidence interval for the incidental mortality estimate (n=58) exceeds twice

the PBR (n=27).
21

3). The abundance estimate, and hence the PBR value, may be inappropriately large because

approximately 30% of the 1991 survey area was inside British Columbia waters or west of the

stock boundary line.

4). It is known that dramatic declines in harbor porpoise abundance have occurred in Puget

Sound (Osmek et al. 1995).

Oregon/Washington Coast Stock

Emphasis should be placed on developing measures to mitigate incidental takes of harbor

porpoise, particularly along coastal northwest Washington where monthly rates can exceed

0.7 mortalities per net day (Gearin et al. 1994). If the fishing effort increases to 1988-89 levels

without mitigation, the annual number of harbor porpoise killed in this tribal fishery could rise to

biologically significant levels (>lO% of PBR = 22). Such take levels could also negatively affect

the status of the adjacent Inland Washington Stock because animals likely cross over the boundary

that separates these two harbor porpoise management areas.
22

ACKNOWLEDGMENTS

The authors are grateful for the efforts of the many people who assisted in gathering data and

the NMFS Office of Protected Resources for funding this research. Robin Baird and Tamara

Guenther, MMRG, provided all of the tissues samples from British Columbia to greatly increase

the sample size for the stock determination research. Rich Ferrero, Jack Cesarone, and others

from NMML provided the harbor porpoise PSP samples and Mel Ekhmd and John Wekell from

URD provided the results of the PSP analysis from the October 1992 unusual mortality event. We

would also like to thank the Makah Tribe, Tribal Fisheries Office, Makah Tribal biologists and

fisherman for fully cooperating with our harbor porpoise research over the years. Jack Cesarone,

Darlene DeGhetto, Doug DeMaster, Brad Hanson, Rod Hobbs, Harriet Huber, and Bob Small

reviewed this manuscript and provided helpful comments.
23

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75.
Table l.--Harbor porpoise abundance estimates by survey area and stock for Oregon/Washington waters (Calambokidis et al. 1993b).

Aerial surveys were conducted during summer 1990-9 1 off the coast to a minimum depth of 9 1 m (50 fins). All inland water

depths were surveyed.
Table 2.-- Corrected abundance estimates (1990-91), PBRs, and annual incidental take rates for two Washington

harbor porpoises stocks. The PBRs were calculated using Rmax and Fr values of 0.04 and 0.5, respectively

*Includes approximately 30% of the survey area located outside the Stock boundary.

**Incidental takes were only observed in the 1994 commercial drift gill-net fishery for sockeye salmon. The number

of takes is significant because it exceeds 10% of the PBR (3).

***The number of incidental takes in the 1990-93 Tribal salmon set gill-net fishery may be an insignificant level.
Table 3.-- The NMFS observer program results by Fishery Management Area for the northwest Washington chinook salmon set gill-net

fishery. During 1994, several harbor porpoises were known to be incidentally taken, but the final results are unavailable.

(Source: NOAA, NMFS, Northwest Region and NMML, Seattle, WA, unpublished data.)
36

Table 4 --Mean total lengths, body weights, and ranges for 99 harbor porpoise incidentally

caught in the Tribal northwest chinook salmon set gill-net fishery, July 1988 through

August 1990 (Gearin et al. 1994).
Figure 1 .--The Oregon/Washington Coast Stock and the Inland Washington Stock are separated

by the Tatoosh Island-Bonnila Point line located off Cape Flattery, Washington. The

cross-hatching represents the waters where harbor porpoise rarely occur.
38

Figure 2.-- The Tribal northwest Washington chinook salmon set gill-net fishery operates in the

waters of both the Oregon/Washington Coast Stock (Area 4/4A) and the Inland

Washington Stock (Area 4B/5)(Fig. 1 from Gearin et al. 1995).

38
39

Figure 3a.-- 1990 survey tracklines flown along coastal Washington to determine harbor porpoise

abundance (Fig. 11 from Calambokidis et al. 1993b).
40

127 126 125 124 123,

Figure 3b.- 1991 survey tracklines flown along coastal Oregon and Washington to determine

harbor porpoise abundance (Fig. 13 from Calambokidis et al. 1993b).
48

125 124 123 122

Figure 3c.-- 1991 survey tracklines flown along inland Washington and southern British Columbia

to determine harbor porpoise abundance (Fig. 14 from Calambokidis et al. 1993b).
42

Figure 3d.-- 1991 aerial survey tracklines for the waters of Grays Harbor, Willapa Bay and the

Columbia River (Fig. 3 from Calambokidis et al. 1992). No harbor porpoises were

seen in these waters.
Figure 4.-- Perpendicular sighting distances for pooled 1990-91 aerial survey data (Fig. 3 from

Calambokidis et al. 1993b). Fitted hazard rate model with one cosine adjustment term

is shown. The number of sightings are above the bars.
44

Figure 5.-- Location of the 7/7A drift gill-net sockeye salmon fishery within Inland Washington.
Figure 6.-- Age and sex distribution of harbor porpoises recovered from the Tribal northwest

Washington chinook salmon set gill-net fishery during 1988-90. DeMaster (1978)

calculated the mean age of reproductive maturity for harbor porpoises at 3.9 for

females and 3.5 for males.
46

APPENDIX

Description of Drift and Set Gillnets

The drift and set gillnets used for fishing salmon in Oregon and Washington waters are similar to

one another, but vary somewhat because of how and where they are fished. The drift gillnets used

within inland Washington waters are made of a 12.7 cm (5 inch) stretched-mesh, multi-strand,

monofilament with a maximum net length of 549 m (300 fathoms). Drift nets hang down from the

corkline in the water column to a depth of 19.1-25.4 m (150-200 meshes) as it moves with the

fishing vessel in the current. Drift-nets are frequently fished at night and are checked for fish after

several hours of fishing. Over 1,000 vessels are licensed by the State to fish drift gillnets in these

waters, and about 500-600 actually fish each year. The tribal set gillnets, fished along coastal and

inland Washington waters, are constructed of a 17.8-20.3 cm (7-8 inch) stretched-mesh, multistrand, monofilament with a maximum net length of 183 m (100 fathoms). These set nets are

fished 7.1-18.3 m (40-90 meshes) above a heavy lead-line (0.25-0.50 kg/m (1-2 lb/fathom) which

is anchored to the bottom, usually near shore, at a water depth ranging from 4 to 30 m deep.

Weather permitting, set nets are checked for fish daily.
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EBBERTS, B. D., and B. L. WING. 1997. Diversity and abundance of neustonic zooplankton in the north

Pacific subarctic frontal zone, 34 p. NTIS No. PB97-138218.

SINCLAIR, E.H. (editor). 1996. Fur seal investigations, 1994, 144 p. NTIS No. PB97-129456.

MERRICK, R. L., T. R. LOUGHLIN, and D. G. CALKINS. 1996. Hot branding: A technique for long-term

marking of pinnipeds, 21 p. NTIS No. PB97-124226.

LANG, G M., and P. A. LIVINGSTON. 1996. Food habits of key groundfish species in the eastern Bering

Sea slope region, 111 p. NTIS No. PB97-124010.

KINOSHITA, R. K., and J. M. TERRY. 1996. Oregon, Washington, and Alaska exports of edible fishery

products, 1995,48 p. NTIS No. PB96-214663.

HONKALEHTO T., and N. WILLIAMSON. 1996. Echo integration-trawl survey of walleye pollock

(Theragra chalcogramma) in the Southeastern Aleutian Basin during February and March 1995, 57 p.

NTIS No. PB96-202726.

TYNAN, C. 1996. Characterization of oceanographic habitat of cetaceans in the Southern Indian Ocean

between 82° - 115° E: Cruise report from World Ocean Circulation Experiment (WOCE) 18S and l9S,

53 p. NTIS No. PB96-192786.

KINOSHITA, R. K., and J. M. TERRY. 1996. Oregon, Washington, and Alaska exports of edible fishery

products, 1994, 49 p. NTIS No. PB96-183553.

KINOSHITA, R. K., A. GRIEG, and J. M. TERRY. 1996. Economic status of the groundfish fisheries off

Alaska, 1994, 108 p. NTIS No. PB96-178595.

PELLA, J., M. MASUDA, and S. NELSON. 1996. Search algorithms for computing stock composition of

a mixture from traits of individuals by maximum likelihood, 68 p. NTIS No. PB96-154653.

YANG, M-S. 1996. Diets of the important groundfishes in the Aleutian Islands in summer 1991, 105 p.

NTIS No. PB96-147582.