NOAA TECHNICAL MEMORANDUM NMFS-SEFSC-492 

A Marine Mammal Assessment Survey of the Southeast US Continental 

Shelf: February – April 2002 

Lance P. Garrison, Steven L. Swartz, Anthony Martinez, 

Carolyn Burks, and Jack Stamates

U.S. Department of Commerce 

National Oceanic and Atmospheric Administration 

NOAA Fisheries 

Southeast Fisheries Science Center 

75 Virginia Beach Drive 

Miami, Florida 33149 

January 2003 
NOAA TECHNICAL MEMORANDUM NMFS-SEFSC -492 

A Marine Mammal Assessment Survey of the Southeast US Continental 

Shelf: February – April 2002 

Lance P. Garrison, Steven L. Swartz, and Anthony Martinez, 

Southeast Fisheries Science Center, NOAA Fisheries 

75 Virginia Beach Drive, Miami Florida 33149 

Carolyn Burks 

2

 Southeast Fisheries Science Center, NOAA Fisheries 

Pascagoula Laboratory, 3209 Frederick Street, Pascagoula, Mississippi 39567 

Jack Stamates

3

 Atlantic Meteorological and Oceanographic Laboratory, NOAA, OAR 

4301 Rickerbacker Causeway, Miami Florida 33149 

U.S. DEPARTMENT OF COMMERCE 

Donald L. Evans, Secretary 

NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION 

Conrad C. Lautenbacher, Jr. 

Under Secretary for Oceans and Atmosphere 

 NATIONAL MARINE FISHERIES SERVICE 

 William T. Hogarth 

 Assistant Administrator for Fisheries 

January 2003 

This Technical Memorandum series is used for documentation and timely communication 

of preliminary results, interim reports, or 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 NOAA Fisheries (NMFS) does not approve, recommend or endorse any proprietary product 

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advertised product to be used or purchased because of NOAA Fisheries publication. 

This report should be cited as follows: 

Garrison, L.P., et al. 2002. A Marine Mammal Assessment Survey of the Southeast US 

Continental Shelf: February – April 2002. NOAA Technical Memorandum NOAA 

FISHERIES-SEFSC-492, 50 p. 

This report has an internal document No. PRD-01/02-13 

Copies of this report can be obtained from: 

Director, Protected Resources Branch or National Technical Information Center 

Southeast Fisheries Science Center 5825 Port Royal Road 

NOAA Fisheries Springfield, VA 22161 

75 Virginia Beach Drive (703) 605-6000, (800) 553-6847 

Miami, FL 33149 Http://www.ntis.gov/numbers.htm 
Abstract 

The Marine Mammal Protection Act (MMPA) requires frequent assessment of 

marine mammal stocks in US waters, with particular attention to “strategic” species that 

are classified as either endangered species or depleted relative to their optimum 

sustainable population size. To augment information on the winter spatial distribution 

and abundance of marine mammals in the mid-Atlantic region, the NOAA Fisheries 

SEFSC conducted a population assessment survey covering continental shelf and inner 

slope waters from Northern Florida to Delaware Bay during February-April 2002 that 

included both visual and passive hydroacoustic surveys. The survey was conducted 

under an interagency agreement between NOAA Fisheries and the US Navy that 

recognizes the need of both agencies for accurate information on the abundance and 

seasonal spatial distribution of marine mammal stocks. 

The primary objectives of the winter 2002 survey were to: 

1) Conduct a visual line transect survey of the mid-Atlantic continental shelf and 

inner slope waters from Northern Florida to Delaware Bay to determine the 

abundance and spatial distribution of marine mammals. 

2) Continue the development and application of passive hydroacoustic methods to 

detect marine mammals and augment visual observations. 

3) Opportunistically collect skin biopsy samples with particular focus on Atlantic 

bottlenose dolphin. 

There were a total of 287 marine mammal groups sighted during the survey from 24 

taxonomic groups and at least 15 species. These included Atlantic spotted dolphin, 

Atlantic bottlenose dolphin, common dolphin, Risso’s dolphin, pilot whale, sperm whale, 

fin whales, beaked whales, and a number of other species. Based upon visual survey 

effort, minimum estimates of abundance were derived for three major Naval operations 

areas on the US East Coast for the most commonly encountered species. Continental 

shelf waters from Cape Hatteras, NC to Florida generally support high abundances of 

dolphin species, in particular Atlantic spotted dolphin and bottlenose dolphin. North of 

Cape Hatteras, a much higher diversity of cetacean species was encountered and included 

significant numbers of fin whales. There is an apparent aggregation of cetacean species 

in intermediate temperature waters between the shelf break and the Gulf Stream during 

winter months. Continuing analyses will evaluate the utility of passive hydroacoustic 

detections to augment visual surveys and assess seasonal patterns in habitat use by 

cetaceans in US mid-Atlantic continental shelf waters. 
TABLE OF CONTENTS 

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

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

Methodology................................................................................... 3 

Survey Design and Regional Coverage....................................... . 3 

Visual Survey Methods............................................................ 3 

Conditionally Independent Observer........................................... 4 

Biopsy Skin Sample Collection................................................... 5 

Passive Acoustic Operations...................................................... 5 

Environmental Data................................................................. 6 

Analytical Methods – Visual Line Transect Abundance Estimation...... 7 

Results........................................................................................ 10 

Survey Effort....................................................................... 10 

Marine Mammal Sightings and Regional Distribution.................... 10 

Primary Abundance Estimates from Visual Surveys...................... 11 

Distribution with Respect to Habitat Variables............................. 14 

CIO Observations and Visibility Bias......................................... 15 

Passive Acoustic Observations.................................................. 15 

Biopsy Collections................................................................. 15 

Discussion.................................................................................... 16 

Common Dolphin.................................................................. 16 

Bottlenose Dolphin................................................................. 17 

Atlantic Spotted Dolphin.......................................................... 18 

Risso’s Dolphin..................................................................... 18 

Beaked Whales...................................................................... 19 

Pilot Whale.......................................................................... 20 

Fin Whale............................................................................ 20 

Continuing Analyses............................................................... 21 

Improvements in Future Surveys................................................ 21 

Future Survey Needs............................................................... 22 

Conclusions........................................................................... 23 

Acknowledgements........................................................................... 24 

Literature Cited.............................................................................. 24 

List of Tables and Figures.................................................................. 27 
Introduction 

 The Marine Mammal Protection Act (MMPA) requires frequent assessment of 

marine mammal stocks in US waters, with particular attention to “strategic” species that 

are classified as either endangered species or depleted relative to their optimum 

sustainable population size. The resulting abundance estimates and associated measures 

of uncertainty are used to determine minimum population sizes and set the maximum 

allowable mortality rates, termed potential biological removal (PBR), that will allow long 

term recovery and sustainability of each stock. In addition to direct estimates of 

abundance, these surveys also allow assessment of spatial distribution with particular 

attention to associations between marine mammal distribution and habitat variables such 

as temperature and depth. Most marine mammal species demonstrate seasonal changes 

in spatial distribution, and assessment surveys in multiple seasons provide a basis for 

evaluating the mechanisms underlying migration patterns. 

 The US mid-Atlantic continental shelf and inner slope is an area of high marine 

mammal occurrence including 23 stocks that are currently managed under the MMPA. 

Of these, 12 are defined as strategic under the MMPA guidelines either because they are 

classified as endangered, depleted, or the current mortality associated with human 

activities exceeds PBR (Waring et al., 2001). The most notable of these includes the 

northern right whale, Eubalaena glacialis, often described as one of the most endangered 

species of marine mammals in the world. The best estimate of stock size approaches 300 

individuals (Kruas et al., 2001), and extensive management actions are currently in place 

or are being developed to avoid mortality of this species associated with both ship strikes 

and entanglement in commercial fishing gear. These animals are present in shallow 

waters of the mid-Atlantic between South Carolina and northern Florida during winter 

months. 

 Another strategic stock of particular importance is the coastal morphotype of 

bottlenose dolphin, Tursiops truncatus. Two genetically distinct morphological forms of 

this species occur over the mid-Atlantic continental shelf, commonly referred to as the 

coastal and offshore forms. While the habitats of these morphotypes can be distinct, 

there is at least some overlap in spatial distribution, particularly in continental shelf 

waters less than 40m depth off the Georgia and South Carolina coasts (P. Rosel, NOAANOS, unpublished data). The coastal morphotype experiences mortality rates that exceed 

PBR in coastal fisheries along the U.S. coast, and has been the subject of recent 

management activities to reduce the impacts of these fisheries. However, the question of 

the relative spatial distribution of the two morphotypes has yet to be fully resolved. The 

two forms cannot be distinguished visually during surveys, and skin samples must be 

collected for genetic analysis to accurately determine the genetic type of any bottlenose 

dolphin encountered and to evaluate habitat differentiation between the two forms. Very 

few biopsy samples have been collected during winter months, and the relative 

distribution of the two morphotypes during winter remains highly uncertain. 

 The population estimates for the other primary strategic stocks in this region, fin 

whale (Balaenoptera physalus), sperm whale (Physter macrocephalus), and pilot whales 

(Globicephala sp.) are based upon results from shipboard and aerial surveys conducted 
solely during summer months (Waring et al. 2001). The Southeast Fisheries Science 

Center (SEFSC) last conducted a winter survey in the Atlantic in 1992, during which 

very little survey effort was accomplished due to poor weather conditions. Thus, the 

winter spatial distribution of these species in the mid-Atlantic region is largely unknown. 

 To augment information on the winter spatial distribution and abundance of 

marine mammals in the mid-Atlantic region, the NOAA Fisheries SEFSC conducted a 

marine mammal population assessment survey covering continental shelf and inner slope 

waters from northern Florida to Delaware Bay during February-April 2002. The survey 

was conducted under an interagency agreement between NOAA Fisheries and the U.S. 

Navy that recognizes the need of both agencies for accurate information on the 

abundance and seasonal spatial distribution of marine mammal stocks in this region. 

 In addition to population abundance estimates, the current survey continued the 

development of a passive hydroacoustic system for the detection of vocalizing marine 

mammals. Population estimates of marine mammals to date are almost exclusively based 

upon visual counts during surveys. However, these estimates suffer from a known 

negative bias in that some marine mammals are below the surface and are thus not 

available to a visual observer and/or animals may be on the surface but not seen by the 

observers due to poor viewing conditions or observer error. These sources of bias are 

collectively termed visibility bias (Marsh & Sinclair 1989). Passive hydroacoustics 

provides an alternative method for the detection of marine mammals that can augment 

visual methods. Diving sperm whales, for example, produce audible echolocation clicks, 

and animals beneath the surface will be available to the acoustic system that are not 

available to visual observers. The hydroacoustic system at the SEFSC has been 

developed during past surveys also supported through interagency agreement with the 

U.S. Navy (SEFSC, unpublished data). Where depth and weather conditions allowed, a 

passive hydroacoustic array was towed behind the vessel throughout the visual survey 

effort to provide a combined visual and acoustic survey of marine mammals in the midAtlantic. 

 The primary objectives of the winter 2002 survey were to: 

1) Conduct a visual line transect survey of the mid-Atlantic continental shelf and 

inner slope waters from northern Florida to Delaware Bay to determine the 

abundance and spatial distribution of marine mammals. 

2) Continue the development and application of passive hydroacoustic methods to 

detect marine mammals and augment visual observations. 

3) Opportunistically collect skin biopsy samples with particular focus on bottlenose 

dolphin. 

. 
Methodology

 The survey was conducted aboard the NOAA ship Gordon Gunter, a 75m long 

oceanographic research vessel configured for both visual and acoustic marine mammal 

survey operations. The vessel draft allows it to operate in waters >10 m depth, and a 

flying bridge platform is affixed above the vessel’s bridge to provide a visual observation 

platform 14m above the water level. The Gordon Gunter is a converted naval vessel with 

acoustically quiet diesel-electric engines that generate relatively little low-frequency 

background noise providing enhanced acoustic signal detection. 

Survey Design and Regional Coverage

 The survey was designed to cover three primary areas of naval operations in the 

mid-Atlantic, the Virginia Capes area (VACapes), the Cherry Point area, and the 

Charleston/Jacksonville area (CHAS/JAX, Figure 1). The survey was designed to cover 

the continental shelf and inner continental slope for the VACapes and Cherry Point areas 

and concentrate on the continental shelf only in the CHAS/JAX region. Expected 

weather conditions made it unlikely to achieve reliable effort in the continental slope 

waters of this region which extend to the 200 mile limit of the U.S. economic exclusion 

zone (EEZ). The survey was designed in a “double saw-tooth” pattern to allow efficient 

and relatively uniform coverage of each operations area. A total of 4,291 km of trackline 

were planned in the initial design based upon the 62 day operational window for the 

survey and expected weather conditions (Table 1). 

Visual Survey Methods 

 Visual survey operations were conducted following standard SEFSC and NOAA 

Fisheries protocols for line transect surveys (Barlow et al., 1995). During “on effort” 

operations, the vessel proceeded at 10 knots along the designated tracklines. Two visual 

observers were stationed on the flying bridge and used 25x magnification “bigeye” 

binoculars to scan for marine mammals. Each of these observers was responsible for the 

90 quadrant from the bow to the beam on the left and right side of the vessel 

respectively. In addition, a third observer on the flying bridge served both as a data 

recorder and scanned the area immediately ahead of and relatively close to the vessel 

using unaided eye and 7x handheld binoculars. The maximum visual range for the 

bigeye observers was approximately 13.6 km (7.3 nautical miles) directly ahead of the 

vessel. Observers rotated every 40 minutes to avoid fatigue, and environmental 

information including weather, wind speed and direction, sun position, visibility 

conditions, swell height, and beaufort sea state were recorded both on rotations and when 

conditions changed. Visual effort was conducted during all daylight hours where weather 

and viewing conditions allowed safe and effective survey effort. In general, visual 

observations were suspended during very poor visibility associated with low-level fog, 

rain, and when sea state exceeded 5 on the beaufort scale. The ship’s location was also 

recorded at 30-second intervals through an independent GPS antenna connected to the 

data entry computer. 
 On observing a potential marine mammal cue such as a splash or blow, the 

position of the vessel, sighting angle, and distance to the cue was recorded. Distance was 

recorded using calibrated reticles in the bigeye binoculars or estimated for sightings by 

the center observer. The vessel continued surveying along the trackline until the cue was 

confirmed as a marine mammal or it was necessary to break away from standard search 

procedures to keep track of the sighting location. At that point the observers switched to 

an “off-effort” closing mode in which the vessel changed direction to approach the 

marine mammal group for species identification, group size estimation, and potential 

biopsy sample collection. The actual location of the group, group size, number of calves, 

sea surface temperature, and depth were recorded using a computerized data entry 

program. After recording all pertinent sighting information, the vessel returned to the 

trackline before the observers returned to on effort operations. 

 In addition to marine mammal sightings, a variety of ancillary observations are 

recorded including sea turtles, large sharks, pollution, and the presence of visually 

apparent surface fronts during the survey. These are recorded during survey operations 

on the computerized data entry system. 

Conditionally Independent Observer

An assumption of line-transect survey methods for abundance estimation is that 

all animals on the trackline are seen by visual observers. This assumption is known to be 

violated in almost all wildlife surveys, particularly in marine mammal surveys where 

animals are both difficult to see and are frequently submerged. There are two 

components to this bias that must be dealt with either analytically or through survey 

methods. Availability bias is typically related to animal behaviors, such as long dive 

times, that reduce the likelihood that they will be on the surface within the visual range of 

the observers. Perception bias is when animals are available to the observers, yet are not 

sighted due to factors including cryptic coloration of the animals, lack of visual cues, 

weather and sea state conditions, observer inexperience and observer fatigue. The 

presence of a second, independently searching visual observer or team of observers is the 

primary method for quantifying visibility bias. During this survey, we employed the 

conditionally independent observer (CIO) approach described by Barlow (1995). 

The CIO was stationed on the ship bridge or bridge wings below the primary team 

and operated throughout the survey. The CIO searched primarily ahead of the vessel and 

30 to the left and right of the trackline using both 7x binoculars and unaided eye. The 

CIO was aware of sightings by the primary team through its communication with bridge 

officers; however, the primary team was not aware of sightings by the CIO. 

 On sighting a marine mammal group that had not been identified by the primary 

team, the CIO noted the initial distance and bearing measurement along with position and 

environmental data. The CIO continued to track the group without notifying the primary 

team until it was either sighted or “missed” by the primary team. The group was defined 

as missed when either it 1) passed abeam of the ship, or 2) approached within 20 m of the 

vessel without being identified by the primary team. For each sighting, the CIO noted 

whether the group was subsequently sighted or missed by the primary team. Once the 
group was defined as missed, the CIO notified the primary team and the vessel went into 

“closing mode” to identify the group. Sightings made by bridge officers or other 

personnel were also included as CIO sightings. Animals first observed by either team 

riding the bow were also counted as missed groups. 

Biopsy Skin Sample Collection

 When possible, biopsy samples of skin and blubber were collected from marine 

mammals riding the vessel bow, with particular attention to collecting samples from 

Tursiops truncatus for stock identification. Given that biopsy collection was a low 

priority on this survey and the relative difficulty of collecting samples from the bow of 

the Gordon Gunter, marine mammal groups were rarely pursued for an extensive period 

of time. Samples were collected using a modified .22 caliber dart rifle fitted with custom 

designed biopsy heads that extract a small plug of tissue from the animals. Great care 

was taken to avoid significant injury to the animals, and all biopsy attempts and resulting 

animal behaviors were recorded as required under sampling permits. Both photographic 

and video records of biopsy attempts were taken during these operations. Biopsy 

sampling was attempted after all pertinent group size and biological information was 

recorded by the observer team. Biopsy samples were stored in DMSO and frozen at –

80C to preserve genetic material for later analysis. 

Passive Acoustic Operations

Passive acoustic operations were conducted in concert with the visual survey effort 

throughout the survey. The hydroacoustic arrays were used for the following purposes: 

1. To collect high quality examples of vocalizations from all available cetaceans, 

2. To collect data on the acoustic availability of cetacean species under varying 

conditions (i.e., during biopsy attempts), 

3. To determine presence or absence of cetaceans at times when visual survey effort 

was not possible, 

4. To determine how passive acoustics could best supplement visual survey 

methods, and 

5. Evaluate the utility of passive acoustics in the role of an independent observer 

during shipboard cetacean surveys. 

 The passive acoustics portion of the survey was conducted in conjunction with 

and along the same track as the visual survey, depth permitting. Additionally, there were 

periods during which no visual survey effort was underway due to high sea states and 

winds, or darkness, during which passive acoustics monitoring continued. These acoustic 

surveys did not necessarily coincide with the prescribed visual survey trackline. 
The primary passive acoustics collection tools used during this survey were a pair 

of towed hydrophone arrays. Array A1 was a two-element broadband array that could be 

trailed behind the ship at any distance up to 450 m astern. Array A2 was a five-element 

broadband array that could be set up to 800 m astern. Both arrays could be towed at any 

speed up to 11 knots. Array A1 was used in water depths from 20 m to 40 m, and array 

A2 was used in water deeper than 40 m. A1 was normally deployed 200 m astern of the 

Gordon Gunter while A2 was normally deployed 350 m astern. There was no acoustic 

effort in water shallower than 20 m to avoid damaging an array due to entanglement. The 

2 element array A1 is deployed by hand off the stern of the ship, while the five-element 

array A2 assembly is deployed from a hydraulic powered deck winch. 

 The towed arrays are 100-meter long Kevlar reinforced cable assemblies with 

high gain hydrophones spaced along the cable. Each element is a piezoelectric ceramic 

striped cylinder with the cable assembly and strength member passing through the center. 

Each sensor, along with its associated signal conditioning, filtering, and line drive 

electronics, is contained within a hydrodynamically shaped tow body assembly. The 

frequency response is essentially flat at –127 dB from about 2 kHz to 15 kHz then climbs 

to a resonance peak at about 35 kHz with a level of –121 dB, then drops off at roughly –

15 dB per octave after resonance. Below 1.5 kHZ, the sensors roll of at roughly 6 dB per 

octave to help reduce low frequency tow and impulse noise. 

 

The data from the arrays were fed into the acoustics lab for amplification, 

filtering, recording and monitoring. Digital audio tape recordings of signals of interest 

were made using multi-channel digital tape recorders. These tape recordings were limited 

to 10Hz – 24kHz in bandwidth. Digital recordings of up to 50 kHz were made directly to 

computer hard disk when warranted. The array signals were constantly monitored by two 

teams of operators. Signals were then passed from the recording equipment to a desktop 

computer for monitoring and high frequency recording. The software package “Ishmael” 

was used to monitor signals and make high bandwidth recordings. The bearings to signals 

of interest generated by “Ishmael” were then passed to a second PC for display. This PC 

was connected to a GPS receiver and loaded with the “WhalTrak” software package. 

“WhalTrak” displayed the ship’s current position and track in a graphics display window, 

overlaying lines of bearing as instructed by the operators. This provided the acoustics 

team with a clearer picture of how acoustic detections related to visual sightings of 

cetaceans and other possible sources of sound, such as ship traffic. “WhalTrak” was also 

employed to make time and position stamped flat ASCII files of the ship’s track, any 

bearings sent to it, and any comments entered by the acoustics team. 

Environmental Data

 Environmental data were collected during the survey to both calibrate sound 

propagation models for the acoustic signals and to examine the relationships between 

habitat characteristics and marine mammal spatial distribution. Vertical CTD profiles 

were made at the beginning and end of each survey day to provide hydrographic data to 

calculate sound velocity. During survey operations, continuous measures of sea surface 

temperature, water depth, salinity, air temperature, wind speed, and other variables were 
collected using a variety of shipboard sensors. These data were recorded at 60 second 

intervals throughout the cruise and are stored using the shipboard scientific computing 

system (SSCS). 

Analytical Methods – Visual Line Transect Abundance Estimation

The standard theory for line-transect sampling is well developed and has been 

routinely applied in a variety of wildlife population assessments in both terrestrial and 

marine habitats (Buckland et al. 1993). Given a random distribution of a survey line 

relative to the distribution of a population of interest, then the probability of observing an 

animal at any distance away from the transect line is equal. Assuming that all animals or 

groups of animals within a particular distance (W = strip width) on either side of the line 

are observed, then the density of animals in the area is: 

(1) LW

n D

2  , 

where n is the number of groups observed and L is the length of the transect line. 

However, line transect theory as described in Buckland et al. (1993) recognizes 

that the probability of observing an animal or group generally declines with increasing 

distance away from the trackline. The distance sampling approach therefore examines 

the distribution of sighting frequency as a function of distance away from the trackline 

and corrects the density estimate for the sighting function, g(x). The sighting function 

can take any integrable form, however in practice it is generally constrained to be 

monotonically decreasing vs. the distance away from the trackline, x. The probability of 

sighting an animal within a strip is then the area under this function divided by the total 

strip width: 

(2) W

g x dx

P

w

a

  0 ( ) . 

 To calculate the probability of sighting an animal at any distance away from the 

trackline, the sighting function is rescaled to the probability distribution function (pdf), 

f(x) as: 

(3) 



 w

g x dx

g x f x

0 ( )

( ) ( ) . 

The assumption is made that the sighting probability on the trackline is unity (g(0) = 1) 

allowing one to solve for the pdf at x = 0 as: 
(4) 



 w

g x dx

f

0

( )

1 (0) , 

and the quantity , or the effective strip half-width is: 

(5)  

w

g x dx

0

 ( ) , 

alternatively expressed as  = Pa W. The group density estimate given in eqn. 1 is 

therefore modified to: 

(6) L

n D

2  . 

 This approach makes the assumption that the probability of sighting animals on 

the trackline, g(0), is 1. This is required to accomplish the formulation of eqn. 4 and the 

solution for the effective strip width. In practice, it is likely that some animals will be 

missed on the trackline, and therefore g(0) is < 1. The failure of this assumption 

introduces a direct, negative bias in the density estimate. This source of bias is termed 

“visibility bias”. 

 In the case of marine mammal surveys, the relevant measure is the perpendicular 

distance from the trackline to the center of a group of animals. To calculate the absolute 

abundance of animals within a region of area, A, equation 6 is modified by multiplying 

by the average group size for the species, E(s): 

(7) L

nAE s N

2

( )  . 

 Variance in the abundance estimate is calculated following the delta method 

outlined by Seber (1982) for combining uncorrelated variances. Thus, the variance in the 

density estimate is given as: 

(8) 











 	    

2 2 2

2

( )

var( ( ))

(0)

var( ) var( (0)) var( ) E sE s

f

f

n

n D D 

where var(x) indicates the variance of the respective quantities. The variance of mean 

group size [var(E(s))] is calculated using the standard expression for variance and the 

variance of the inverse sighting function [f(0)] is calculated based upon the maximum 

likelihood fitting procedure used to derive the sighting function. The quantity var(n) is 
the variance of the expected number of animals observed during the survey. The 

sampling unit in for the current survey is considered a single transect line or a single 

day’s effort. For each of k defined effort units where li is the length of each unit and L is 

the sum of all transect lengths, then var(n) is estimated as: 

(9) var( ) ( 1)

2

1

 













    

k

L

n

l

n

n L l

k

i i

i

i , 

 

where ni is the number of groups seen on transect i and n is the total number of groups 

observed during the survey. This variance estimator assumes both independence of 

encounter rates between transect lines and that the mean encounter rates (n/l) are 

normally distributed. Severe violations of these assumptions due to spatial contagion 

may result in inaccurate variance estimation. To account for these factors, variance may 

also be calculated through non-parametric bootstrap resampling of sampling units 

(Buckland et al. 1993). 
Results 

Survey Effort

 The survey covered the majority of the planned tracklines, however lower than 

expected effort occurred in both the Cherry Point and Virginia Capes regions where 

consistently high winds and bad weather occurred throughout the survey period (Table 1, 

Figure 2). However, due to favorable weather in the southern part of the survey, 

additional effort was expended in the continental slope area of the Chas/JAX region 

(Figure 2), and survey effort was accomplished inside a naval operations area in the 

eastern Gulf of Mexico (Figure 3). 

Marine Mammal Sightings and Regional Distribution

 There were a total of 287 marine mammal groups sighted during the entire survey 

from 24 taxonomic groups and at least 15 species (Table 2). The most common species 

were Atlantic spotted dolphin (Stenella frontalis) and bottlenose dolphin (Tursiops 

truncatus). In the Charleston/Jacksonville region, the vast majority of sightings were 

from these two species, reflecting the concentration of survey effort on the continental 

shelf in this region (Table 3a). Pilot whales (Globicephala sp.), false killer whale 

(Psuedorca cassidens), one Northern right whale (Eubalaena glacialis), and one sperm 

whale (Physeter macrocephalus) were also sighted. The Cherry Point region sightings 

were also dominated by Atlantic spotted and bottlenose dolphins, and included sightings 

of dwarf/pygmy sperm whales (Kogia sp.), pilot whale, and both Mesoplodon and 

Ziphiid beaked whales (Table 3a). A greater diversity of marine mammal species were 

encountered in the Virginia capes region and included common dolphin (Delphinus 

delphi), bottlenose dolphin, Risso’s dolphin (Grampus griseus), and striped dolphins 

(Stenella coeruleoalba). Large and medium whales including fin whale (Balaenoptera 

physalus), sperm whale, and pilot whales were also encountered with relative frequency 

in this area (Table 3b). Very few sightings were made during the effort in the Gulf of 

Mexico region, and these included Atlantic spotted, bottlenose, and Risso’s dolphin 

(Table 3b, Figure 3). 

 Atlantic spotted dolphin was very frequently encountered in the relatively shallow 

continental shelf waters between 10-50m depth, particularly south of Cape Fear, North 

Carolina. Their abundance declined at higher latitudes, and only one spotted dolphin 

group was encountered north of Cape Hatteras (Figure 4). Likewise, bottlenose dolphin 

were abundant in shallow waters in the Charleston/Jacksonville area, and were found 

progressively further offshore with increasing latitude (Figure 4). Risso’s dolphins were 

encountered primarily in deep water just off the continental shelf in the Virginia capes 

area, but one group was also encountered over the continental slope in the 

Charleston/Jacksonville region (Figure 4). The remaining identified dolphin species 

including common dolphin, striped dolphin, and Clymene’s dolphins were encountered 

only in the Virginia Capes region. Common dolphin occurred across the depth range, 

while the two Stenellid species occurred in deep waters of the continental slope (Figure 

5). 
 

 Beaked whales, Kogia sp., melonheaded whale, and false killer whale were 

infrequently observed during the survey. This is consistent with previous surveys where 

these species have been collectively described as “cryptic” species (Barlow 1995, Mullin 

in press) because they generally surface for very short intervals, have a relatively small 

body size, and often have cryptic coloration. Of these species, the beaked whales and 

Kogia sp. were observed in continental slope water of the Cherry Point region (Figure 6). 

Two false killer whales were sighted in the continental slope area of the 

Charleston/Jacksonville region (Figure 6). 

 The large whales and pilot whale were most often encountered in the Virginia 

Capes region (Figure 7). Fin whales (Balaenoptera physalus) and other unspecified 

baleen whales (Balaenoptera sp.) were the most commonly encountered large whale. 

The majority of fin whale sightings occurred in a cluster near the continental shelf break 

in the northern edge of this region, while the Balaenoptera sp. sightings occurred in deep 

waters of the continental slope. Sperm whales were also sighted in deeper slope waters 

of the Virginia capes region, along with pilot whales (Figure 7). Sperm whale and pilot 

whale sightings also occurred in the deeper waters of the Charleston/Jacksonville region, 

and one right whale sighting occurred in the very nearshore waters off of Georgia (Figure 

7). 

Preliminary Abundance Estimates from Visual Surveys

Data Selection and Analysis stratification

 Animal size and behavior are primary factors that effect both availability to and 

detection probabilities for visual observers. Ideally, the sighting functions developed for 

the line transect analysis of abundance would be done independently for each species to 

reflect these differences; however, in practice sample sizes for individual species 

generally preclude individual sighting functions. To address this issue Barlow (1995) 

recommended grouping species by these characteristics and applying a common sighting 

function within groups. This process has been previously applied by SEFSC researchers 

(Mullin, in press) and was similarly applied here (Table 4, Table 5). In addition, 

abundance estimates were only developed for species with >2 on effort sightings. With 

fewer than 2 sightings, variability in the encounter rates is extremely high and the 

calculated variance for mean group size is highly uncertain or cannot be estimated. 

 Group size may also have a significant effect on the availability and probability of 

sighting a marine mammal group during a visual survey. In a sufficiently large group of 

dolphins, for example, there is a high probability that at least one animal will be on the 

surface at all times, and therefore the entire group is available to the survey team. Group 

size bias can be addressed through regression of sighting distance vs. group size 

(Buckland et al. 1993). However, where there is no clear pattern in this relationship, the 

regression procedure may not demonstrate a statistically significant result. Therefore, 

Barlow (1995) recommended post-stratifying the analyses by group size where sample 

size allows to avoid biasing the abundance estimates and improve precision, particularly 
in cases where there is large variation in group size. Based upon a preliminary evaluation 

of the sighting data, we have post-stratified analyses for dolphin species based upon 

group sizes less than and greater than or equal to 20 animals. 

 A fundamental assumption of line transect analyses is that animals are observed 

prior to responding to the survey platform. The analysis stems from the assumption that 

line transects are placed randomly with respect to animal distribution, and this 

assumption is clearly violated if there is strong positive or negative response to the vessel 

(Buckland et al. 1993). This is a common difficulty encountered in ship board marine 

mammal surveys, as dolphin species in particular, may be attracted to the vessel at 

considerable distances (Palka & Hammond, 2001). There is strong evidence of attraction 

to the vessel during the current survey as evinced by a strongly skewed sighting function, 

particularly for dolphin species (Figure 8). In some cases, animals that were feeding or 

milling at the time of first observation changed their behavior and turned to approach the 

vessel at distances greater than 2 km (L. Garrison, personal observation). Particularly in 

southern areas with Atlantic spotted dolphins and/or during poor viewing conditions, a 

considerable number of survey sightings occurred when animals surfaced within 400m of 

the vessel and were already approaching to bowride. These animals were clearly 

demonstrating attractive behavior and were seen only because they chose to approach the 

vessel. To avoid potentially serious positive biases in the abundance estimates, we have 

chosen not to use sightings of dolphins that were first observed within 500m radial 

distance from the vessel. These animals were effectively missed by the primary visual 

observers using bigeye binoculars that have a visual range of several miles from the 

vessel. The presence of these missed animals in the viewing area indicates a significant 

degree of visibility bias during the survey and a resulting negative bias in the derived 

abundance estimates. 

 Finally, abundance estimates were stratified by naval operations area. For the 

Charleston/Jacksonville area only survey effort and sightings on the continental shelf 

(<200 m depth) was used given that the vast majority of survey effort was expended in 

this habitat, and sighting rates are thus most representative of the continental shelf in this 

region. 

 

Abundance Estimates-Dolphin Species

 A common sighting probability function was fit for all dolphin species across the 

three survey regions; however, separate sighting functions were fit for dolphin group 

sizes <20 and >= 20 individuals. As discussed above, all groups first seen at radial 

distances < 500 m from the vessel were removed from the analysis. As outlined in 

Buckland et al. (1993) the number of sightings as a function of perpendicular distance 

from the trackline was examined to identify a right truncation distance beyond which the 

sighting rate dropped off dramatically. For groups <20 animals, the truncation distance 

corresponded to 1600 m from the trackline resulting in removal of 20/112 on effort 

groups. The truncation distance for group sizes >= 20 was 2300 m resulting in truncation 

of 9/45 on effort groups. 
 The sighting function for each group size was fit by selection of either hazard rate 

or half-normal key functions with cosine or polynomial adjustment terms. The bestfitting model was selected using the minimum Akaike’s Information Criterion (AIC, 

Buckland et al. 1993). For group sizes <20, the best fitting function was a half-normal 

key function with 2nd and 3rd order cosine adjustment terms (Figure 9a). This model 

provided a good fit to the sighting data as indicated by a non-significant goodness of fit 

chi-square (Chi-square = 3.916, df = 4, p = 0.4113). The effective half strip width 

(ESW) for this function was 740.77 m (coefficient of variation (CV) = 15.96 %). 

 The best fitting sighting function for group sizes >= 20 was likewise a halfnormal key function but with 2nd order cosine adjustment terms (Figure 9b). The model 

provided a good fit to the data (Chi-square = 7.423, df = 5, p = 0.1904). The calculated 

ESW was predictably higher than that for groups <20 animals and was 1,172.7 m (CV = 

20.91 %). 

 Regional abundance estimates for Atlantic spotted dolphin, bottlenose dolphin, 

common dolphin, and striped dolphin are presented in Table 4. Across the entire survey 

are, the total abundance estimate for spotted dolphin was 19,812 (%CV = 27.3) and that 

for bottlenose dolphin was 17.727 (%CV = 25.9). The estimate for common dolphin was 

79,229 (%CV = 81.8) and 45,237 (%CV = 68.4) for striped dolphin in the Virginia Capes 

region (Table 4). 

Abundance Estimates – Large Whales 

 Due to the lack of on effort sightings in other regions, the abundance estimates for 

the large whales and pilot whales are restricted to the Virginia Capes area. There was 

relatively little variation in group size for these species, and preliminary analysis 

indicated no significant effect of group size on sighting distances. Unlike the dolphin 

species, there was no indication or expectation of attraction to the vessel for the large 

whale species. However, there was one sighting of a fin whale that occurred within 

500m of the vessel when the animal surfaced nearly directly ahead of the boat. This 

sighting was retained in the analysis. In addition to the 7 identified Fin whale sightings, 

there were two additional sightings that could only be classified as Balaenoptera sp. As 

the other baleen whales including sei whales, blue whales, and minke whales are much 

less common in this area than fin whales, these unclassified Balaenoptera sp. sightings 

were included in the abundance estimate for fin whale. 

 A common sighting function was fit across all on effort sightings of sperm whale, 

fin whale (including Balaenoptera sp.), unidentified large whale, and pilot whale 

sightings in the Virginia Capes region, a total of only 21 on effort sightings. An initial 

evaluation of the sighting distribution suggested a right truncation distance of 8,000m, 

removing 1 unidentified large whale sighting from the analysis. Due to the small sample 

size, the sightings were grouped into wide 2000m distance intervals to fit the sighting 

function. Several alternative functions including adjustment terms were fit to the sighting 

data, and the best function (minimum AIC) was the half-normal key with no adjustment 
terms (Figure 10). This function provided a good fit to the data (Chi-square = 0.3257, 3 

df, p = 0.8497) and the resulting effective strip width was 3,693 m (CV = 17.89 %). 

 

 Abundance estimates and associated variance for the large whales in the Virginia 

capes region are shown in Table 5. The estimate for fin whale (including Balaenoptera 

sp.) was 230 animals (CV = 48.26%), for sperm whale the estimate was 142 (CV = 

85.36%), and for pilot whale 727 (CV = 73.65%, Table 5). 

 Summary abundance estimates for both dolphin and whale species across the 

entire survey region are shown in Table 6. 

 

Distribution with Respect to Habitat Variables 

 

 Environmental variables including temperature, depth, and the presence of frontal 

zones likely have a strong effect on the seasonal spatial distribution of marine mammals. 

Furthermore, it is likely that different stocks within the same species demonstrate 

different responses to habitat variables and therefore spatial distribution. In this 

preliminary analysis, we examined the relationships between sea surface temperature and 

depth and the number of sightings for five species of dolphins commonly encountered in 

the survey: Atlantic spotted dolphin, bottlenose dolphin, common dolphin, striped 

dolphin, and Risso’s dolphin. 

The majority of bottlenose dolphin sightings occurred in waters of relatively high 

temperature, though there were apparent regional differences in distribution relative to 

temperature (Figure 11a-c). In the Charleston/Jacksonville region, the peak in bottlenose 

dolphin sightings occurred in the 19-21C temperature range (Figure 11a). Bottlenose 

dolphin were more commonly found in warmer waters >22 C in the Cherry Point region 

(Figure 11b), and to some extent in the Virginia Capes region though there were very few 

sightings in the northern area (Figure 11c). The depth distribution also reflects this 

regional difference, as bottlenose dolphin were found most commonly in progressively 

deeper water with increasing latitude (Figure 12). 

Atlantic spotted dolphin distributions also suggest regional differences in habitat 

preferences. Spotted dolphins were found primarily in the 18-20 degree temperature 

range in the Charleston/Jacksonville region in very shallow waters (Figure 11a), but 

seemed to have a broader temperature and depth distribution in the Cherry Point region 

(Figure 11b, Figure 12). 

Those species that were observed primarily in the Virginia Capes region most 

commonly occurred in intermediate temperature waters between 9-14 C (Figure 11c). 

However, common dolphin were also present in shallow, cold water in this region. This 

temperature range corresponds to a broad depth range in slope waters off the continental 

shelf between 200-3000 m depth (Figure 12c). 

This intermediate temperature region seemed to be a particular area of 

aggregation for both dolphins and large whale species. The region just south of 38 N 
latitude off the shelf break was an area where many different species were encountered 

in close proximity including common dolphin, Risso’s dolphin, striped dolphin, and 

Balaenoptera whales (Figure 4, Figure 7). To further evaluate spatial patterns, we show 

the distribution of marine mammal sightings in the Virginia Capes region with respect to 

a satellite derived sea surface temperature image from March 1, 2002 corresponding to 

the timing of the majority of these sightings. This image demonstrates the importance of 

the region between the cold continental shelf waters and the very warm gulf stream 

waters as an area of aggregation for these species (Figure 13). Bottlenose dolphin, pilot 

whale and to a lesser extent sperm whale were more strongly associated with warmer gulf 

stream water (Figure 13). 

CIO observations and visibility bias

 

In most cases, sightings made by the CIO were of animals that surfaced within 

300 meters of the vessel and were approaching the ship to bowride. These included 

primarily Atlantic spotted and bottlenose dolphins, but also included 2 sightings of false 

killer whale and an unidentified small cetacean, possibly Kogia sp. The vast majority of 

CIO sightings were also seen by the primary team prior to the animals coming within 20 

meters of the bow. There are too few (<20) CIO-only sightings to generate a reliable 

sighting function and thereby directly estimate sighting probabilities during the survey. 

However, the frequency of CIO sightings and primary team sightings of animals that first 

appeared within 600 meters of the vessel do provide information on sighting 

probabilities. The frequency of these types of sightings in combination with the CIO 

sightings will be used to evaluate the factors that may contribute to reduced sighting 

probabilities. These include weather conditions such as sea state and swell and regional 

differences in animal behavior. These analyses are currently underway and will be used 

to guide and improve future survey efforts. 

Passive acoustic observations

 A large number of passive acoustic detections occurred during the survey of the 

many dolphin species encountered, sperm whales, and pilot whales. The majority of the 

visual sightings were accompanied by either initial or subsequent acoustic detection. In 

addition, there were many acoustic detections that were not detected by the visual 

observers. The acoustic signals collected during the survey are currently being analyzed 

and reconciled with the visual sighting records. The results from this comparison will 

include an initial analysis of the utility of acoustic detections to evaluate visibility bias. 

Biopsy collections

 36 skin biopsy samples were collected during the survey from common dolphin, 

spotted dolphin, and bottlenose dolphin (Figure 14). This includes 22 samples collected 

from bottlenose dolphin that will be used to augment the assessment of stock 

identification for the animals encountered during this survey and during aerial surveys of 

nearshore waters also conducted during winter 2002. 
Discussion 

 The species encountered during the current survey and resulting abundance 

estimates are generally consistent with the findings from previous surveys on the US 

Atlantic continental shelf. Continental shelf waters from Cape Hatteras, NC to Florida 

generally support high abundances of dolphin species, in particular Atlantic spotted 

dolphin and bottlenose dolphin. North of Cape Hatteras in the Virginia Capes region, a 

much higher diversity of cetacean species was encountered and included significant 

numbers of fin whales. There is an apparent aggregation of cetacean species in 

intermediate temperature waters between the shelf break and the Gulf Stream during 

winter months. Results for major species of interest in Atlantic waters are discussed 

below. 

 In addition to the survey effort expended on the Atlantic continental shelf, 

opportunistic sampling of the eastern Gulf of Mexico continental shelf was undertaken 

with a particular focus on a naval operations area near the west coast of Florida. Very 

few animals were encountered during the survey effort in this region, but included 

spotted dolphin, bottlenose dolphin, and Risso’s dolphin. Throughout the transit along 

the eastern Gulf of Mexico, very few cetaceans were encountered or observed. However, 

this region was an area of relatively frequent occurrence of sperm whales, including 

mother-calf pairs, in this area during early spring of 2001 (SEFSC Unpublished data). 

An anomalous “black water” event associated with an algal bloom was occurring along 

the Gulf coast of Florida during the survey period, perhaps contributing to the relatively 

low encounter rates of cetaceans during the current survey. 

Common Dolphin

 Common dolphin was encountered in the Virginia Capes region and was broadly 

distributed across the continental shelf and along the continental shelf break. Only 20 

groups of common dolphin were sighted; however, many of these groups were extremely 

large. Several groups were over 150 animals, and the largest group was estimated at 798 

animals. This large variation in group size contributed to the high degree of uncertainty 

in the abundance estimates for common dolphin derived from this survey. The combined 

estimate was 45,237 animals with a 68.7% coefficient of variation (CV). This is within 

the range of the entire population estimate based upon summer surveys from Maryland to 

the Gulf of St. Lawrence of approximately 31,000 animals (CV = 32%, Waring et al.,

2001). During the summer surveys, common dolphins occurred solely along the shelf 

break, the southern flank of Georges Bank, and in the Gulf of Maine north of Delaware 

Bay (Waring, et al., 2001). In a summer 1998 survey of shelf and slope waters south of 

Delaware Bay no common dolphins were observed (Mullin, in press) , and only two 

small groups were observed in summer 1999 (SEFSC, unpublished data). These results 

suggest that a significant portion of the common dolphin population migrates southward 

onto the mid-Atlantic continental shelf and slope during winter months, consistent with 

findings from aerial surveys conducted during winter in the early 1980s (CETAP, 1982). 
Common dolphin is currently defined as a strategic stock under the MMPA 

because mortality rates due to fishery activities greatly exceed PBR (Waring et al. 2001). 

Common dolphin is taken relatively frequently in gillnet and bottom trawl fisheries in the 

mid-Atlantic and northeast United States and are also hooked in pelagic longline 

fisheries. The current study suggests that the bulk of the population may be vulnerable to 

fishing and other human activities in mid-Atlantic continental shelf and inner slope 

waters during winter. 

 

Bottlenose Dolphin

 Bottlenose dolphin was encountered throughout the survey range and was the 

second most common species seen during the survey. There are two genetically, 

morphometrically, and ecologically distinct types of bottlenose dolphin in mid-Atlantic 

continental shelf waters (Hersh & Duffield, 1990). It is probable that the bulk of the two 

populations do not overlap with one another, however spatial overlap between the two 

morphotypes has been demonstrated in waters <30m depth over the continental shelf off 

of Georgia and South Carolina (P. Rosel, NOAA, unpublished data). The coastal 

morphotype has been the subject of considerable recent management action as it suffers a 

significant level of mortality in coastal gillnet fisheries in nearshore waters of North 

Carolina and Virginia (Waring et al. 2001). The bulk of the coastal morphotype 

population likely resides in waters <10m depth and therefore outside of the coverage of 

the current survey. 

One notable spatial pattern in bottlenose dolphin distribution is that they occurred 

progressively further offshore with increasing latitude. This is consistent with the 

findings of previous summer surveys (SEFSC, unpublished data) and suggests that the 

coastal and offshore morphotype populations diverge at higher latitudes. During summer 

north of Cape Hatteras, NC previous surveys have observed a high abundance of 

bottlenose dolphins close to shore in waters <25 m depth, a region of very low abundance 

between 25-100m depth, and then a high abundance of presumably offshore morphotype 

animals along the continental shelf break and inner slope (Kenney, 1990; SEFSC, 

unpublished data). During winter, the coastal form migrates south of Cape Hatteras, a 

pattern confirmed by aerial surveys also conducted during winter 2002 where no 

bottlenose dolphins were observed in nearshore waters north of Manteo, NC (SEFSC, 

unpublished data). In the Virginia Capes region during the current survey, bottlenose 

dolphins were observed in deeper water at the continental shelf break, and it is likely that 

these animals were of the offshore morphotype. In the Cherry Point region, bottlenose 

dolphins were also encountered in primarily warm, deep waters on the outer continental 

shelf. However, during the winter 2002 aerial survey, there was a very high abundance 

of dolphins close to shore between Cape Hatteras and Cape Lookout NC (SEFSC, 

unpublished data). Preliminary results of biopsy samples collected during fall and winter 

of 2002 indicated that the offshore morphotype occurred close to shore in this region (A. 

Hohn, SEFSC, unpublished data) suggesting potential mixing of the two populations in 

this area. In the Charleston/Jacksonville region, it is very likely that the two populations 

overlap with each other, particularly in water <40m depth. Continued analysis of genetic 

samples collected during the current survey and in localized sampling efforts during 
winter 2002 will allow a more complete analysis of the relative distribution of the two 

morphotypes in during winter months. 

 The vast majority of the bottlenose dolphin encountered during this survey are 

most likely from the offshore morphotype. The current coastwide abundance estimate of 

17,727 (CV = 26.3%) is not significantly different from an estimate of 13,944 (CV = 

38%) for offshore bottlenose dolphin based upon a shipboard survey during the summer 

1998 (Mullin in press). The 1998 survey covered the same general latitudinal range, but 

also included survey effort on the outer continental slope to the US EEZ suggesting that 

the majority of the offshore bottlenose dolphin population occurs on the continental shelf 

or inner slope in mid-Atlantic waters. Offshore morphotype bottlenose dolphin also 

occur in waters further north on the continental shelf and southern flank of Georges 

Bank, and their abundance during summer was estimated at 16,689 (CV = 32%, Waring 

et al., 2001) resulting in a coast wide estimate for the offshore morphotype of 30,633 (CV 

= 25%) animals. It is likely, however, that at least a small proportion of the animals 

encountered during both the current survey and the 1998 survey were of the coastal 

morphotype and the resulting abundance estimates may therefore be positively biased. 

However, the surveys did not include waters <10m depth where the majority of the 

coastal stock occurs, particularly in the waters of South Carolina and Georgia. 

Atlantic Spotted Dolphin

 Atlantic spotted dolphin were observed primarily over continental shelf waters 

south of Cape Hatteras. This is also consistent with the summer distribution of spotted 

dolphins based upon the 1998 (Mullin in press) and 1999 (unpublished data) SEFSC ship 

surveys. As with bottlenose dolphin, there are two genetically distinct morphotypes of 

spotted dolphin in US Atlantic waters (Perrin et al. 1994). North of Cape Hatteras, 

spotted dolphins are observed in very deep waters (>1000m) well off the shelf break, and 

this likely represents the bulk of the offshore stock (Waring et al. 2001). With limited 

effort in the deeper continental slope waters off of Florida, two groups of spotted 

dolphins were observed and likewise several spotted dolphin groups were observed in 

this region during the 1998 survey (Mullin in press). It remains unclear whether these 

animals are of the offshore or coastal morphotype, and further genetic sampling in this 

region is required to better delineate the habitat preferences of the two stocks. 

 The current abundance estimate of 19,812 (CV = 26.9%) animals is very similar 

to the estimate of 20,326 (CV = 60%) animals for the 1998 summer survey (Mullin in 

press). Spotted dolphin is rarely taken in commercial fishing operations and other 

activities, and the species is not currently defined as a strategic or depleted stock (Waring 

et al. 2001). 

Risso’s Dolphin

 Risso’s dolphin most commonly occurs along the shelf break and inner 

continental slope in the northwest Atlantic. The bulk of observations during summer 

months occurred along the southern flank of Georges Bank and in shelf break waters 
north of New Jersey (Waring et al. 2001, CETAP 1982). In winter, the range in the 

northeast US extends further offshore into oceanic waters north of Cape Hatteras. 

Risso’s dolphin has shown a strong association with shelf-break waters in a number of 

different ocean basins. In the northern Gulf of Mexico, Risso’s dolphin were strongly 

associated with regions with strong gradients in bathymetry, and it was hypothesized that 

they concentrated in frontal systems along the shelf where intermediate water 

temperatures and high food concentration occurred (Baumgartner 1997, Baumgartner et 

al. 2001). The Risso’s dolphins observed in the Virginia Capes region during the current 

study were also observed near the shelf-break in waters of intermediate temperatures. 

The high abundance of fin whales and other species within this area suggests that food 

availability or some other factor likely associated the shelf-break frontal system results in 

a concentration of marine mammals in this region. 

Beaked Whales

 There are four species of beaked whales from the genus Mesoplodon that occur in 

Northwest Atlantic waters: M mirius (True’s beaked whale), M. europaeus (Gervais’ 

beaked whale, M. densirostris (Blainville’s beaked whale), and M. bidens (Sowerby’s 

beaked whale). These four species in addition to Cuvier’s beaked whale (Ziphius 

cavirostris) are difficult to distinguish at sea and are thus assessed as undifferentiated 

beaked whales (Waring et al. 2001). As in previous assessments, these species are 

classified as cryptic due to their relatively small body size, short surfacing intervals, and 

long dive times (Barlow 1995). Thus, these animals are difficult to observer during 

visual surveys and are rarely encountered. 

 During the current survey, three beaked whales were observed in the continental 

slope waters of the Cherry Point region. This is consistent with the general finding that 

beaked whales primarily are observed in deep waters near the continental shelf break 

(Waring et al 2001). In addition, beaked whales of all species are commonly stranded 

along the North Carolina coastline (SEFSC, unpublished data). The bulk of beaked 

whale sightings during summer surveys have occurred in continental slope waters 

between Delaware and the southern flank of Georges Bank, with occasional sightings in 

southern areas (Waring et al. 2001). Based upon 8 sightings during the 1998 summer 

survey, beaked whale abundance was estimated at 596 (CV = 50%) animals (Mullin in 

press); however, it is likely that this estimate is negatively biased because it was not 

corrected for the long dive times of these species. 

 Beaked whales are currently considered a strategic stock due to the high degree of 

uncertainty in the abundance estimates and stock structure. There is also significant 

concern with these species due to documented mortality events in other regions 

associated with sound production during naval activities (Waring et al., 2001). 

Considerable additional research is necessary to adequately assess beaked whale stocks in 

Atlantic waters. 
Pilot Whale

 There are two species of pilot whale on the US continental shelf and inner slope 

waters. Long-finned pilot whale (Globicepahla melas) is generally distributed in the 

northern end of the range from Florida to the Gulf of Maine while short-finned pilot 

whale (Globicephala macrorhynchus) occurs in the southern portion of the range. The 

species boundary is generally considered to be in the North Carolina – New Jersey region 

(Waring et al. 2001), corresponding roughly to the Virginia Capes area in the current 

study. Since the two species cannot be distinguished visually during surveys, it is unclear 

which species, or whether a mix of the two were observed in the Virginia Capes area 

during the current survey. It is likely that the pilot whales observed over the continental 

slope off of Florida were short-finned pilot whales. 

 The abundance estimate for the current survey of 727 animals (CV = 0.74) is 

considerably lower than a combined estimate of 14,254 (CV = 0.30) encompassing the 

area from the Gulf of St. Lawrence to Florida. The bulk of the pilot whale population 

likely occurs north of the survey area. Pilot whales are generally found in association 

with high relief areas and submerged banks or along the northern edge of the Gulf stream 

wall (Waring et al. 1992). The pilot whales observed in the current survey in the Virginia 

Cape region were associated with very warm Gulf Stream water. Seasonal movements of 

pilot whales suggest a spring and summer northern migration onto Georges Bank and the 

Gulf of Maine, and perhaps a southern and offshore migration during winter (Payne & 

Heinemann, 1993). The association of pilot whales with warm water during this study is 

consistent with those movement patterns. Likewise, the occurrence of pilot whales, 

likely G. macrorhynchus, in deep continental slope waters in the southern regions is 

consistent with studies during summer months (Waring et al., 2001). 

 Pilot whales are taken frequently in bottom trawl, gillnet, and pelagic longline 

fisheries along the US mid-Atlantic and north Atlantic coasts (Yeung, 1999; Waring et 

al., 2001). The association of pilot whales with frontal zones and relief areas is likely 

correlated with high abundances of fish prey species and their predators. The fisheries 

that target these large pelagic predators including tunas and swordfish thus have 

considerable overlap with pilot whale distributions and potential interactions. Notably, 

one group of pilot whales was observed during this survey in very close association (< 

200m) from a pelagic longline off the coast of North Carolina. 

Fin Whale

 Fin whales are the most common large whales observed in US mid-Atlantic 

continental shelf waters (Hain et al. 1993, Waring et al. 2001). During spring, summer 

and fall, fin whales are broadly distributed across the continental shelf and along the shelf 

break, and tend to aggregate in the great south channel of Georges Bank and inshore Gulf 

of Maine (Hain et al. 1993, Waring et al. 2001). Fin whale was less common on the 

continental shelf during winter (Hain et al. 1993). During the current survey, fin whales 

were encountered aggregated in a localized area near the continental shelf break. This 

was a region of intermediate temperature waters between 9-13 C. This temperature 
range corresponds to the modal temperature of 12-14 C of fin whale sightings during the 

1982 CETAP aerial surveys. The findings of the current study are consistent with those 

of the CETAP data showing that the deep continental shelf waters off of Delaware bay 

are an important area of winter aggregation for fin whales (Hain et al., 1993) 

The abundance estimate from the current survey of 230 animals (CV = 48.3%) is 

well below the population estimate of 2,814 animals used in the current assessment 

(Waring et al., 2001). This is not surprising as the bulk of the fin whale population likely 

occurs well north of the study area on the Nova Scotian shelf and/or in waters further 

offshore. 

Continuing Analyses

 The results presented here provide a broadscale assessment of the occurrence and 

abundance of marine mammals in three large areas of the US Atlantic continental shelf. 

All of these abundance estimates should be considered minimum estimates as they are 

not corrected for dive times and visibility bias. In addition to the visual effort, passive 

hydroacoustic effort was accomplished through much of the survey and included many 

acoustic detections, particularly of large whales, that were not observed visually. The 

additional acoustic detections will be used to augment presence/absence information 

derived from visual sightings, and will be incorporated into analyses of sighting 

probabilities. We are also continuing our analysis of sighting probabilities based upon 

the conditionally independent observer sightings for incorporation into corrected 

abundance estimates. Finally, we are exploring more detailed modeling efforts to 

evaluate habitat associations of the major species encountered during this survey. These 

analyses will allow a more detailed assessment of the habitats and localized spatial areas 

where aggregations of marine mammals are likely to occur. Results from the current 

survey represent the first assessment of winter habitat preferences for these species in 

mid-Atlantic waters in the last 10 years. In combination with results from the summer 

1998 and 1999 efforts, the surveys will form the basis of habitat preference models for 

cetaceans over the US mid-Atlantic continental shelf. 

Improvements in Future Surveys

 The primary limitation of the current survey methodology employed by SEFSC is 

an inability to account for visibility bias in abundance estimation. As a result, all 

abundance estimates derived solely from visual effort should be considered minimal 

estimates. In addition, using current methodologies, it is difficult to account for changes 

in animal visibility under varying survey conditions. This is particularly relevant for 

winter surveys where a significant amount of effort must be expended under marginal 

sighting conditions. There are two methods to adequately address these issues, both of 

which will be incorporated into future SEFSC marine mammal assessment surveys. First, 

the passive hydroacoustic approach provides an additional source of marine mammal 

detections that does not face the same limitations as the visual survey. The results from 

the hydroacoustic effort expended during the survey will be directly compared to those 

from the visual effort to provide a preliminary analysis of sighting probabilities under 
varying conditions. The appropriate application of acoustic detections to augment visual 

surveys is an area of active research within both the SEFSC and other NOAA fisheries 

regions. 

Second, the incorporation of a second independent team of visual observers will 

greatly improve the abundance estimates resulting from visual surveys. A second team of 

visual observers during a survey provides an independent estimate of abundance from the 

same sighting platform and allows application of a suite of approaches based upon markrecapture statistics to quantify visibility bias during the survey (e.g., Laake 1999; 

Borchers et al. 1998a). A second team of observers also allows a more flexible analysis 

of the role of environmental factors on sighting probabilities (e.g., Borchers et al. 1998b) 

and can be used to account for animal attraction to the vessel (Palka & Hammond, 2001). 

The Gordon Gunter is an ideal platform for incorporating a second team of observers. 

Bigeye binoculars can be affixed on bridge wings several meters below the flying bridge 

that would allow full visibility on either side of the vessel and are still approximately 

10m above the water surface. SEFSC has recently incorporated the two-team methods 

into aerial surveys for bottlenose dolphins with considerable success and plans to 

incorporate this approach into all future assessment surveys. 

Future Survey Needs

 The results of the current survey and previous assessment surveys indicate a 

consistent association of cetacean species with major oceanographic features along the 

shelf-break front and the boundary between Gulf Stream and continental slope waters. 

These frontal zones are likely areas where oceanographic processes such as upwelling 

and convergence zones create local patches of high primary and secondary production, 

high fish biomass, and therefore high abundances of marine mammals. The resulting 

spatially patchy distribution of marine mammals contributes to the relatively low 

encounter rates and high uncertainty associated with abundance estimates. For example, 

much of the variability in the common dolphin abundance estimate resulted from the 

extreme variation in group size. As previously noted, in one instance a group of 

approximately 800 animals was encountered, and this within the same general region 

where fin whales, Risso’s dolphin, and large groups of striped dolphins occurred. 

Likewise, pilot whales have shown a strong association with boundary regions of the 

Gulf Stream in the Atlantic and in frontal zones in other basins. Due to the concentration 

of pelagic fish and squid species, these frontal zones are often an area of high fishery 

activity as well, perhaps contributing to interactions with marine mammals. 

 The broadscale design of past assessment surveys has resulted in relatively little 

effort within frontal zones. As a result, there are usually few encounters with species 

associated with these areas and high uncertainty in abundance estimates. Further, there 

has been no directed effort to evaluate the oceanographic processes and prey fields that 

supports these localized aggregations of marine mammals in the mid-Atlantic. An 

integrated physical and biological evaluation of marine mammal habitat was recently 

conducted in the Gulf of Mexico (Davis et al. 2002) and a survey concentrating on the 

shelf break zone along the southern flank of Georges Bank is currently being planned by 
the Northeast Fisheries Science Center (G. Waring, NEFSC, personal communication). 

Future surveys will include integrated effort to characterize the physical and biological 

habitat that supports large aggregations of marine mammals. 

 

 

Conclusions

 The winter 2002 marine mammal survey provided an assessment of the winter 

distribution of cetaceans in mid-Atlantic continental shelf and inner slope waters between 

Florida and Delaware Bay. Minimum abundance estimates for major Naval operations 

areas have been derived based upon visual survey effort. In addition, biopsy samples 

from Atlantic bottlenose dolphin were collected during the survey that will be used to 

better define the winter habitat boundaries for the coastal and offshore morphotypes. 

Continuing analyses include evaluation of habitat associations, environmental factors 

influencing sighting probabilities, and assessing the utility of passive hydroacoustic 

detections to augment visual survey efforts. 
Acknowledgments 

 The winter 2002 assessment survey could not have been conducted without the 

dedication of numerous individuals who planned and participated in the surveys. This 

included Dr. Keith Mullin, Wayne Hoggard and Carol Roden of the SEFSC Pascagoula, 

MS laboratory. Diligent visual observers are essential to accomplishing the mission of 

these surveys, and we recognize the work of observers Chris Andrews, Dr. Joel Bell, 

Maria Cordona, Carol Fairfield, Paul Felts, Kathy Foley, Annie Gorgone, Dean Landi, 

Lanora Lang, Jennifer Lawrence, Aaron Mooney, Laura Morse, Dr. Debra Palka, Grisel 

Rodriguez, Carrie Sinclair, Aaron Thode, Juan Carlos Salinas Vargas, and Eric Zolman. 

The officers and crew of the NOAA ship Gordon Gunter provide consistent, highly 

professional mission support and contribute significantly to the quality of assessment 

surveys conducted by SEFSC. Biopsy samples were collected under permit from NOAA 

fisheries Office of Protected Resources #779-1633-00 and the survey was conducted 

SEFSC’s research permit #779-1339. The survey was supported by the Chief of Naval 

Operations, Environmental RDT&E Program (Code N45) under an interagency 

agreement with NOAA Fisheries Southeast Fisheries Science Center, Miami Laboratory. 

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 Academic Press. 653 p. 

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In: The Bottlenose Dolphin. S Leatherwood and RR Reeves (eds.). Academic 

Press. 653 p. 

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Parameters of the North Atlantic Right Whale. J. Cetacean. Res. 

Manage. (special issue) 2: 231-236. 

Laake JL (1999) Distance sampling with independent observers: Reducing bias from 

heterogeneity by weakening the conditional independence assumption. Pgs. 137-

149 In: Garner GW, Amstrup SC, Laake JL, Manly BFJ, McDonald LL, and 

Robertson DG (eds). Marine Mammal Survey and Assessment Methods. AA 

Balekma, Rotterdam, 287 p. 

Marsh H, Sinclair DF (1989) Correcting for visibility bias in strip transect aerial survey 

of aquatic fauna. J. Wildl. Management 53: 1017-1024 

Mullin KD (in press) Abundance and distribution of cetaceans in the southeastern US 

Atlantic ocean during summer, 1998. Fish. Bull. U.S. 

Palka DL and Hammond PS (2001) Accounting for responsive movement in line transect 

estimates of abundance. Can. J. Fish. Aquat. Sci. 58: 778-787. 

Payne PM and Heinemann DW (1993) The distribution of pilot whales (Golbicephala 

sp.) in shelf/shelf edge and slope waters of the northeastern United States, 1978-

1988. Rep. Int. Whale. Comm (Special Issue) 14: 51-68. 

Perrin WF, Caldwell DK, and Caldwell MC (1994) Atlantic spotted dolphin. In: 
Ridgeway SH and Harrison R (eds.), Handbook of Marine Mammals, Volume 5: 

The first book of dolphins. Academic Press, San Diego, 418 pp. 

Seber GAF (1982) The estimation of animal abundance and related parameters. 

MacMillin, New York. 

Waring GT, Quintal JM, and Swartz SL (2001). US Atlantic and Gulf of Mexico Marine 

Mammal Stock Assessments 2001. NOAA Tech. Mem. NMFS-NE-168, 310 p. 

Yeung C (1999) Estimates of marine mammal and marine turtle bycatch by the US 

Atlantic pelagic longline fleet in 1998. NOAA Tech. Mem. NMFS-SEFSC-430, 

26 p. 
List of Tables and Figures 

Table 1. Summary of planned and executed survey effort during the winter 2002 

marine mammal survey. 

Table 2. Survey of all marine mammal sightings during the mid-Atlantic cetacean 

survey, February-April 2002. “On-Effort” indicates the total number of marine 

mammal herds observed while on trackline during survey operations. 

Table 3a. Number of marine mammal herds sighted by the survey region during 

mid-Atlantic cetacean survey, February-April 2002. “On-Effort” indicates the 

total number of marine mammal herds observed while on trackline during survey 

operations. 

Table 3b. Number of marine mammal herds sighted by the survey region during 

mid-Atlantic cetacean survey, February-April 2002. “On-Effort” indicates the 

total number of marine mammal herds observed while on trackline during survey 

operations. 

Table 4a. Abundance estimates for Atlantic spotted and bottlenose dolphin in the 

Charleston/Jacksonville and Cherry Point regions. 

Table 4b. Abundance estimates for Atlantic spotted and bottlenose dolphin in the 

Virginia Capes region. 

Table 5. Abundance estimates for large whale species and pilot whale in the 

Virginia capes region. 

Table 6. Summary of abundance estimates from the winter 2002 marine mammal 

survey. 

Figure 1. Planned tracklines for the winter 2002 marine mammal survey. Survey 

regions corresponding to naval operations areas and bathymetry to 200m depth 

are shown. 

Figure 2. On effort tracklines on the US Atlantic continental shelf during the 

winter 2002 marine mammal survey. Survey regions corresponding to naval 

operations areas and bathymetry to 200m depth are shown. 

Figure 3. Additional survey effort in the eastern Gulf of Mexico and sightings of 

spotted, bottlenose, and Risso’s dolphin. 

Figure 4. Sightings of Atlantic spotted dolphin, bottlenose dolphin, and Risso’s 

dolphin in the mid-Atlantic during the winter 2002 survey. 
Figure 5. Sightings of common dolphin, short-snouted spinner dolphin, striped 

dolphin, and unspecified dolphin classes in the mid-Atlantic during the winter 

2002 survey. 

Figure 6. Sightings of cryptic species and beaked whales in the mid-Atlantic 

during the winter 2002 survey. 

Figure 7. Sightings of pilot whales and large whales in the mid-Atlantic during the 

winter 2002 survey. 

Figure 8. Number of dolphin groups sighted in 100m intervals of perpendicular 

sighting distance. Groups initially sighted <1500m radial distance from the vessel 

are indicated in grey. These groups were not included in the abundance estimates 

to avoid biases associated with attraction to the survey vessel prior to detection. 

Figure 9. Sighting probability as a function of perpendicular distance from the 

trackline for dolphin group sizes A) < 20 animals and B) >= 20 animals. The line 

indicates the fitted sighting function. Bars indicate sighting frequencies at binned 

distance intervals. Sighting data were right-truncated at 1600 m PSD for groups < 

20 animals and 2300 m PSD for groups >= 20 animals. 

Figure 10. Sighting probability as a function of perpendicular distance from the 

trackline for large whales and pilot whale. The line indicates the fitted sighting 

function. Bars indicate sighting frequencies at binned distance intervals. 

Sighting data were right-truncated at 8000 m PSD. 

Figure 11. The proportion of sightings for dolphin species in 1C temperature 

intervals in the A) Charleston/Jacksonville, B) Cherry Point, and C) Virginia 

Capes regions. 

Figure 12. The proportion of dolphin sightings by water depth intervals for the A) 

Charleston/Jacksonville, B) Cherry Point, and C) Virginia Capes regions. Note 

the difference in depth category for the Charleston/Jacksonville region. 

Figure 13. A) Dolphin and B) whale sightings in the Virginia Capes region and 

sea surface temperature. SST image is from an AVHRR image collected on 

March 1, 2002 available through the NOAA CoastWatch program Southeast 

Region. 

Figure 14. Skin biopsy samples collected during the winter 2002 marine mammal 

survey. 
Table 1. Summary of planned and exectued survey effort during the winter 2002 marine 

mammal survey. 

* Charleston/Jacksonville total effort includes unplanned trackline opportunistically 

sampled in waters > 200 m depth. Due to limited effort, the given region area and all 

abundance estimates are based only upon effort and sightings on the continental shelf. 

1902.1 km of survey effort was accomplished on the continental shelf in this region. 

Region Region area 

(km2

) 

Planned 

Effort (km) Actual Effort (km) 

Charleston / Jacksonville 72,054* 1891 2343.9* 

Cherry Point 65,580 1123 880.3 

Virginia Capes 125,930 1277 961.5 

Gulf of Mexico N/A 0 406.8 

Total 4,291 4,592.4 
Table 2. Summary of all marine mammal sightings during mid-Atlantic cetacean survey, 

February-April 2002. “On-Effort” indicates the total number of marine mammal herds 

observed while on trackline during survey operations. 

Species Name Common Name Number of 

Groups On-Effort 

Stenella frontalis Atlantic spotted dolphin 94 65 

Balaenoptera sp. Rorqual Whales 3 2 

Tursiops truncatus Bottlenose dolphin 62 50 

Delphinus delphis Common Dolphin 20 17 

Balaenoptera physalus Fin Whale 8 7 

Kogia sp. Pygmy/Dwarf Sperm Whale 2 1 

Peponocephala electra / Kogia sp. Melonheaded Whale/Pygmy Sperm Whale 1 1 

Peponocephala electra Melonhead 1 1 

Mesoplodon sp. Mesoplodon Beaked Whales 1 1 

Globicephala sp. Pilot Whale 10 7 

Pseudorca crassidens False Killer Whale 2 0 

Eubalaena glacialis Northern Right Whale 1 1 

Grampus griseus Risso's Dolphin 9 8 

Stenella clymene Clymene Dolphin 1 1 

Physeter macrocephalus Sperm Whale 5 4 

Stenella sp. Un-id Stenella Dolphin 4 2 

Stenella coeruleoalba Striped Dolphin 11 9 

Tursiops truncatus/Stenlla frontalis Bottlenose or Spotted Dolphin 7 5 

Un-identified Beaked Whale Un-id Beaked Whale 1 1 

Un-identified Dolphin Un-id Dolphin 31 25 

Un-identified Large Whale Un-id Large Whale 6 4 

Un-identified Odontocete Un-id Toothed Whale 4 3 

Un-identified Small Whale Un-id Small Whale 2 2 

Ziphius sp. Ziphiid beaked whales 1 1 

Total 287 218 
Table 3a. Number of marine mammal herds sighted by survey region during midAtlantic cetacean survey, February-April 2002. “On-Effort” indicates the total number of 

marine mammal herds observed while on trackline during survey operations. 

Species Name Common Name Number of 

Groups On-Effort 

Charleston/Jax Region

Stenlla frontalis Atlantic spotted dolphin 73 51 

Tursiops truncatus Bottlenose dolphin 39 34 

Globicephala sp. Pilot Whale 2 1 

Pseudorca crassidens False Killer Whale 2 0 

Eubalaena glacialis Northern Right Whale 1 1 

Grampus griseus Risso's Dolphin 1 1 

Physeter macrocephalus Sperm Whale 1 1 

Stenella sp. Un-id Stenella Dolphin 3 2 

Tursiops truncatus/Stenlla frontalis Bottlenose or Spotted Dolphin 6 4 

Un-identified Dolphin Un-id Dolphin 16 12 

Un-identified Small Whale Un-id Small Whale 1 1 

 

Cherry Point Region 

Stenlla frontalis Atlantic spotted dolphin 15 10 

Tursiops truncatus Bottlenose dolphin 13 8 

Kogia sp. Pygmy/Dwarf Sperm Whale 2 1 

Mesoplodon sp. Mesoplodon Beaked Whales 1 1 

Globicephala sp. Pilot Whale 1 0 

Stenella sp. Un-id Stenella Dolphin 1 0 

Tursiops truncatus/Stenlla frontalis Bottlenose or Spotted Dolphin 1 1 

Un-identified Beaked Whale Un-id Beaked Whale 1 1 

Un-identified Dolphin Un-id Dolphin 4 3 

Un-identified Large Whale Un-id Large Whale 1 1 

Un-identified Small Whale Un-id Small Whale 1 1 

Ziphius sp. Ziphiid beaked whales 1 1 
Table 3b. Number of marine mammal herds sighted by survey region during midAtlantic cetacean survey, February-April 2002. “On-Effort” indicates the total number of 

marine mammal herds observed while on trackline during survey operations. 

Species Name Common Name Number of 

Groups On-Effort 

Virginia Capes Region

Stenlla frontalis Atlantic spotted dolphin 2 2 

Balaenoptera sp. Rorqual Whales 3 2 

Tursiops truncatus Bottlenose dolphin 9 7 

Delphinus delphis Common Dolphin 20 17 

Balaenoptera physalus Fin Whale 8 7 

Peponocephala electra / Kogia sp. Melonheaded Whale/Pygmy Sperm 

Whale 1 1 

Peponocephala electra Melonheaded Whale 1 1 

Globicephala sp. Pilot Whale 7 6 

Grampus griseus Risso's Dolphin 7 6 

Stenella clymene Clymene’s Dolphin 1 1 

Physeter macrocephalus Sperm Whale 4 3 

Stenella coeruleoalba Striped Dolphin 11 9 

Un-identified Dolphin Un-id Dolphin 11 10 

Un-identified Large Whale Un-id Large Whale 5 3 

Un-identified Odontocete Un-id Toothed Whale 4 3 

 

Gulf of Mexico Region 

Stenlla frontalis Atlantic spotted dolphin 4 2 

Tursiops truncatus Bottlenose dolphin 1 1 

Grampus griseus Risso's Dolphin 1 1 
Table 4a. Abundance estimates for Atlantic spotted and bottlenose dolphin in the 

Charleston/Jacksonville and Cherry Point regions. 

Charleston/Jacksonville Region 

Number 

of 

Groups 

Encounter 

Rate N/L 

(%CV) 

Mean 

Group 

Size 

(%CV) 

Group 

Density 

(% CV) 

groups 

km-2

Animal 

Density 

(%CV) 

n km-2

Abundance 

Estimate 

Abundance 

95 % CI 

Atlantic Spotted Dolphin 

Group Size 

< 20 27 0.014 (30.1) 8.2 (11.9) 0.0096 (34.1) 

0.0784 

(36.0) 5,648 2,905-10,978 

Group Size 

 >= 20 11 0.006 (42.9) 36.8 (17.9) 0.0025 (47.7) 

0.0907 

(50.1) 6,539 2,615 – 16,346 

Total 0.1691 

(31.2) 12,187 6,816 – 21,789 

 

Bottlenose Dolphin 

Group Size 

< 20 23 0.012 (33.2) 6.3 (16.5) 0.0082 (36.8) 

0.0511 

(40.3) 3,679 1,755 – 7,714 

Group Size 

 >= 20 3 0.002 (98.1) 60.7 (24.1) 0.0006 (102.1) 

0.0408 

(103.1) 2,938 580 – 14,875 

Total 0.0918 

(49.5) 6,617 2,647 – 16,540 

 

Cherry Point Region 

Atlantic Spotted Dolphin 

Group Size 

< 20 5 0.005 (32.7) 8.6 (29.6) 0.0038 (36.4) 

0.0329 

(46.9) 2,162 924 – 5,058 

Group Size 

 >= 20 3 0.006 (61.8) 57.3 (10.5) 0.0015 (65.2) 

0.0833 

(66.1) 5,463 1,734 – 17,120 

Total 0.116 

(49.2) 7,625 3,140 – 8,960 

 

Bottlenose Dolphin 

Group Size 

< 20 1 0.0011 (75.4) 16.0 (8.5*) 0.0008 (77.1) 

0.0123 

(77.5) 804 217 – 2,974 

Group Size 

 >= 20 4 0.045 (39.8) 30.8 (8.5) 0.0019 (44.9) 

0.0596 

(45.7) 3,906 1,703 – 8,960 

Total 0.0718 

(40.1) 4,711 2,255 – 9,842 
Table 4b. Abundance estimates for Atlantic spotted and bottlenose dolphin in the Virginia Capes 

region.

Virginia Capes Region 

Number 

of 

Groups 

Encounter 

Rate N/L 

(%CV) 

Mean 

Group 

Size 

(%CV) 

Group 

Density 

(% CV) 

groups 

km-2

Animal 

Density 

(%CV) 

n km-2

Abundance 

Estimate 

Abundance 

95 % CI 

Bottlenose Dolphin 

Group Size 

< 20 2 0.002 (56.3) 12.5 (20.0) 0.0014 (58.5) 

0.0176 

(61.8) 2,210 747 – 6,536 

Group Size 

 >= 20 3 0.003 (47.5) 25 (10.4) 0.0013 (51.8) 

0.0333 

(52.9) 4,188 1,625 – 10,791 

Total 0.0508 

(40.7) 6,398 3,035 – 13,487 

 

Common Dolphin 

Group Size 

< 20 5 0.005 (47.8) 7.4 (22.8) 0.0035 (50.4) 

0.0259 

(55.3) 3,271 1,221 – 8,760 

Group Size 

 >= 20 6 0.006 (72.4) 226.7 (40.1) 

0.0026 

(75.3) 

0.6032 

(85.3) 75,958 18,562 – 310,830 

Total 0.6292 

(81.8) 79,229 20,252 – 309,957 

 

Striped Dolphin 

Group Size 

< 20 1 0.001 (63.3) 19 (12.3*) 0.0007 (65.2) 

0.0134 

(66.4) 1,679 531 – 5,312 

Group Size 

 >= 20 4 0.004 (67.1) 195 (12.3) 0.0018 (70.3) 

0.346 

(71.3) 43,558 12,834 – 147,830 

Total 0.359 

(68.7) 45,237 13,829 – 147,972 
Table 5. Abundance estimates for large whale species and pilot whale in the Virginia 

Capes regions

Virginia Capes Region 

Number of 

Groups 

Encounter 

Rate N/L 

(%CV) 

Mean 

Group 

Size 

(%CV) 

Group 

Density 

(% CV) 

groups 

km-2

Animal 

Density 

(%CV) 

n km-2

Abundance 

Estimate 

Abundance 

95 % CI 

Fin Whale 9 0.0094 

(41.6) 

1.44 

(16.8) 

0.0013 

(45.3) 

0.0018 

(48.3) 230 84 - 631 

Sperm Whale 3 0.0031 

(82.5) 

2.67 

(12.5) 

0.0004 

(84.4) 

0.0011 

(85.4) 142 25 - 816 

Pilot Whale 6 0.0062 

(67.6) 

6.83 

(23.1) 

0.0008 

(69.9) 

0.0058 

(73.7) 727 159 - 3,317 
Table 6. Summary of abundance estimates from the winter 2002 marine mammal survey. 

Figure 1. Planned tracklines for the winter 2002 marine mammal survey. Survey 

regions corresponding to naval operations areas and bathymetry to 200m depth are 

shown. 

Species 

Charleston/ 

Jacksonville 

(%CV) 

Cherry Point 

(%CV) 

Virginia 

Capes 

(%CV) 

Total 

Abundance 

(% CV) 

Total Abundance 

95% CI 

Dolphin Species 

Atlantic Spotted 

Dolphin 

12,187 

(31.2) 

7,625 

(49.2) - 19,812 (26.9) 11, 971 – 32,788 

Bottlenose 

Dolphin 

6,617 

(50.9) 

4,711 

(40.1) 

6,398 

(40.7)

17,727 

(26.3) 10,828 – 29,020 

Common 

Dolphin - - 79,229 (81.8) 

79,229 

(81.8) 20,252 – 309,957 

Striped Dolphin - - 45,237 

(68.7) 

45,237 

(68.7) 13,829 – 147,972 

Whale Species 

Fin Whale - - 230 

(48.3) 

230 

(48.3) 84 - 631 

Sperm Whale - - 142 

(85.4) 

142 

(85.4) 25 - 816 

Pilot Whale - - 727 

(73.7) 

727 

(73.7) 159 - 3,317 

36° 36°

38° 38°

84° 82° 80° 78° 76° 74° 72°

VA
ii 

Figure 2. On effort tracklines on the US Atlantic continental shelf during the winter 

2002 marine mammal survey. Survey regions corresponding to naval operations areas 

and bathymetry to 200m depth are shown. 

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iii 

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spotted, bottlenose, and Risso’s dolphin.

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and unspecified dolphin classes in the mid-Atlantic during the winter 2002 survey. 

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Short-snouted 

spinner dolphin 

Striped Dolphin 

Stenella sp. 

Spotted or 

Bottlenose 

Un-identified 

dolphin 
vi 

Figure 6. Sightings of cryptic species and beaked whales in the mid-Atlantic during the 

winter 2002 survey. 

S

#

%U

V&

(

%

$

$T $T

%

30°

30°

32°

32°

34°

34°

36°

36°

38°

38°

84°

84°

82°

82°

80°

80°

78°

78°

76°

76°

74°

74°

72°

72°

Ziphiid Beaked 

Whale

Dwarf/Pygmy Sperm 

Whale 

Mesoplodon Beaked 

Whale 

Melonheaded Whale 

Un-id

Beaked 

 Whale 

False Killer 

Whale 

Melonhead/

Kogia.
vii 

Figure 7. Sightings of pilot whales and large whales in the mid-Atlantic during the 

winter 2002 survey 

V&

V&

V&

S

#

#

&

$

#

&

$

#

&

#

#

$

$T

# #

S#$

&

%U

%

%U

%

%

%

%

%

%

V&

S&

#&

$#

%

%

%

30°

30°

32°

32°

34°

34°

36°

36°

38°

38°

84°

84°

82°

82°

80°

80°

78°

78°

76°

76°

74°

74°

72°

72°

Un-id Large

Whale 

Pilot Whale

Fin Whale

Sperm Whale 

Rorqual 

Whales 

Right Whale

Un-id Small

Whale

Un-id Toothed 

Whale 
viii 

Figure 8. Number of dolphin groups sighted in 100m intervals of perpendicular sighting 

distance. Groups initially sighted <500 m radial distance from the vessel are indicated in 

grey. These groups were not included in the abundance estimates to avoid biases 

associated with attraction to the survey vessel prior to detection.

0

5

10

15

20

25

30

35

40

45

<100

100-200

200-300

300-400

400-500

500-600

600-700

700-800

800-900

900-1000

1000-1100

1100-1200

1200-1300

1300-1400

1400-1500

1500-1600

>1600

Perpendicular Sighting Distance (m)

Number of Groups

<= 500m radial distance

> 500m radial distance
ix 

Figure 9. Sighting probability as a function of perpendicular distance from the trackline 

for dolphin group sizes A) < 20 animals and B) >= 20 animals. The line indicates the 

fitted sighting function. Bars indicate sighting frequencies at binned distance intervals. 

Sighting data were right-truncated at 1600 m PSD for groups < 20 animals and 2300 m 

PSD for groups >= 20 animals. 

0

0.2

0.4

0.6

0.8

1

1.2

0

100

200

300

400

500

600

700

800

900

1000

1200

1300

1400

1500

1600

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0

200

400

600

800

1000

1200

1400

1600

1800

2000

2200

Perpendicular Sighting Distance (m)

Sighting Probability

A

B
x 

Figure 10. Sighting probability as a function of perpendicular distance from the trackline 

for large whales and pilot whale. The line indicates the fitted sighting function. Bars 

indicate sighting frequencies at binned distance intervals. Sighting data were righttruncated at 8000 m PSD.

0

0.2

0.4

0.6

0.8

1

1.2

0

500

1000

1500

2000

25003000

3500

400045005000

5500

6000

6500

7000

7500

8000

Perpendicular Sighting Distance (m)

Sighting Probability
xi 

Figure 11. The proportion of sightings for dolphin species in 1C temperature intervals 

in the A) Charleston/Jacksonville, B) Cherry Point, and C) Virginia Capes regions.

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

Spotted Dolphin

Bottlenose Dolphin

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

Spotted Dolphin

Bottlenose Dolphin

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

>7

7-88-9

9-10

10-1111-1212-1313-1414-1515-1616-1717-1818-1919-2020-2121-2222-2323-2424-2525-2626-27

>27

Bottlenose Dolphin Com m on Dolphin

Risso's Dolphin Striped Dolphin

A. Chas/Jax

B. Cherry Point

C. Va. Capes

Proportion of Sightings

Water Temperature C 
xii 

Figure 12. The proportion of dolphin sightings by water depth intervals for the A) 

Charleston/Jacksonville, B) Cherry Point, and C) Virginia Capes regions. Note the 

difference in depth category for the Charleston/Jacksonville region.

0

0.1

0.2

0.3

0.4

0.5

0.6

<10 10-20 20-30 30-40 40-50 50-60 60-70 70-80 80-90 90-100 >100

Spotted D olphin

Bottlenose D olphin

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

<25 25-50 50-100 100-

200

200-

500

500-

1000

1000-

1500

1500-

2000

2000-

2500

2500 -

3000

>3000

S potted D olphin

B ottlenose D olphin

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

<25 25-50 50-100 100-200 200-500 500-

1000

1000-

1500

1500-

2000

2000-

2500

2500 -

3000

>3000

B ottlenose D olphin

C ommon D olphin

Risso's D olphin

S triped D olphin

Proportion of Sightings

A. Chas/Jax

B. Cherry Point

C. Va. Capes

Depth (m) 
xiii 

Figure 13. A) Dolphin and B) whale sightings in the Virginia Capes region and sea 

surface temperature. SST image is from an AVHRR image collected on March 1, 2002 

available through the NOAA CoastWatch program Southeast Region. 

Balaenoptera sp.

Sperm Whale

Pilot Whale

Bottlenose Dolphin

Common Dolphin

Risso’s Dolphin

Striped Dolphin
xiv 

 

Figure 14. Skin biopsy samples collected during the winter 2002 marine mammal 

survey. 

#

$

#

%

$ $ %

$

%

%

$

%$

$

%%%

$

$$ $ $ $

30° 30°

32° 32°

34° 34°

36° 36°

38° 38°

84°

84°

82°

82°

80°

80°

78°

78°

76°

76°

74°

74°

72°

72°

Common Dolphin 

Bottlenose Dolphin

Spotted Dolphin