NOAA

GORDON GUNTER

Future Directions for Acoustic Marine Mammal Surveys:

Stock Assessment and Habitat Use

Report of a Workshop Held in La Jolla, California,

20–22 November 2002

NAT OI NAL OCEANIC AND ATMOSPHERIC ADMINISTRAT OI N

U.S. DEPARTMENT OF CO M MERCE Contribution 2557 from NOAA/Pacific Marine Environmental Laboratory

NOAA OAR Special Report

David Mellinger and Jay Barlow, co-convenors
On the cover: The bottlenose dolphin (photo: Jay Barlow) and 

humpback whale (photo: Barb Taylor) are known for their complex 

acoustic signals. Here their sounds are captured by instruments used 

for acoustic assessment: a hydrophone array towed behind a NOAA 

ship and a bottom-anchored autonomous hydrophone.
NOAA OAR Special Report

Future Directions for Acoustic Marine Mammal

Surveys: Stock Assessment and Habitat Use

Report of a Workshop Held in La Jolla, California,

20–22 November 2002

David Mellinger1 and Jay Barlow2, co-convenors

Pacific Marine Environmental Laboratory

7600 Sand Point Way NE

Seattle, WA 98115-6349

1Also at: CIMRS

Oregon State University

Hatfield Marine Science Center

2115 SE OSU Drive

Newport, OR 97365-5258

2National Marine Fisheries Service

Southwest Fisheries Science Center

8604 La Jolla Shores Drive

La Jolla, CA 92037-1508

March 2003

Contribution 2557 from NOAA/Pacific Marine Environmental Laboratory
NOTICE

Mention of a commercial company or product does not constitute an endorsement by

NOAA/OAR. Use of information from this publication concerning proprietary products

or the tests of such products for publicity or advertising purposes is not authorized.

Reference this document as follows:

Mellinger, D., and J. Barlow (2003): Future directions for

acoustic marine mammal surveys: Stock assessment and habitat use.

Report of a Workshop held in La Jolla, CA, 20–22 November 2002,

NOAA OAR Special Report, NOAA/PMEL Contribution No. 2557, 37 pp.

Contribution No. 2557 from NOAA/Pacific Marine Environmental Laboratory

For sale by the National Technical Information Service, 5285 Port Royal Road

Springfield, VA 22161

ii
Contents iii

Contents

Executive Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Workshop Participants . . . . . . . . . . . . . . . . . . . . . . . . . 3

Observers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Presentations (Wednesday, 20 November) . . . . . . . . . . . . . 5

I. Assessment: Abstracts of Presentations ............... 5

II. Acoustics: Abstract of Presentations . ............... 8

Discussion (Thursday, 21 November) . . . . . . . . . . . . . . . . 14

Discussion Topic I. Population Structure . . . . . . . . . . . . . . . . 14

Discussion Topic II. Abundance and Density . . . . . . . . . . . . . . 17

Discussion Topic III. Responses to Noise . . . . . . . . . . . . . . . . 19

Discussion Topic IV. Relative Density, Seasonal Distribution, and

Trends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Recommendations (Friday, 22 November) . . . . . . . . . . . . . . 24

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

Appendix A: Distance Sampling and Marine Mammal Acoustic

Surveys ............................... 31

Appendix B: Cetacean Detection and Assessment via Passive

Acoustics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

List of Figures

1 Locations of autonomous acoustic recorders deployed to monitor areas for North Pacific right whale (and other mysticete whale) calls

in the eastern Bering Sea (NMML/SIO) and in the northern Gulf of

Alaska (NMML/PMEL). . . . . . . . . . . . . . . . . . . . . . . . . . 37

List of Tables

1 Known acoustic population structures of some marine mammals. . . 16

2 Management-related needs for large whale populations that could be

assisted by acoustic (point source) monitoring. . . . . . . . . . . . . 23
iv Contents
Future Directions for Acoustic Marine Mammal Surveys: Stock

Assessment and Habitat Use

David Mellinger1 and Jay Barlow2, co-convenors

Executive Summary

Current uses of acoustics: Acoustic survey methods are now used primarily to augment visual sighting methods. During line-transect surveys,

acoustic observers who monitor towed hydrophone arrays routinely detect

more groups of animals than visual observers. In some cases, acoustic detections are being used to make more accurate estimates of marine mammal

populations than would be possible with visual methods alone. Autonomous

recorders are cost effective for use in regions that are difficult or expensive

to reach, such as Antarctica, the Indian Ocean, and areas far offshore in

the Atlantic and Pacific Oceans, and they are effective for seasonal coverage

when visual surveys are not feasible. They may also be useful to survey areas infrequently occupied by marine mammals, where routine visual surveys

would have a very high cost per sighting.

Future uses of acoustics: Acoustics holds eventual promise of gathering information about marine mammals at very low cost. Research is needed

in several areas to realize this possibility. Discussion at the workshop centered on these broad categories:

1. Population structure. If acoustic differences between populations of

marine mammals are tied to genetic differences, then acoustics would

offer a relatively fast and inexpensive method to assess population

structure. The foremost research need is to determine the relationship

between the population structures as indicated by acoustics and by

genetics.

2. Abundance and density. Acoustic observation can complement visual observation to provide more accurate estimates of marine mammal populations. This has been done for some populations, as for

example the Bering-Beaufort-Chukchi Sea stock of bowhead whales

and the eastern Pacific stock of sperm whales, but it could be done

more widely. For effective acoustic censuses, calibration methods must

be determined by joint visual-acoustic studies; determining such factors offers the promise of low-cost surveys for many species of marine

mammals using acoustic methods. Research is also needed in acoustic

species identification, particularly for smaller odontocetes.

3. Impacts of noise. Responses of marine mammal to natural noise have

not been well studied. Natural noise can include sounds of other ma1Also at: CIMRS, Oregon State University, Hatfield Marine Science Center, 2115 SE

OSU Drive, Newport, OR 97365-5258. 2NMFS/Southwest Fisheries Science Center, 8604 La Jolla Shores Dr., La Jolla, CA

92037-1508.
2 Mellinger and Barlow

rine mammals, especially conspecifics, as well as physical noise sources

such as from geological sound sources and wind. Responses of marine

mammals to anthropogenic noise was seen as a topic well covered by

other work; discussion here was limited to the contribution that passive

acoustics can make. Assisting in the constructing of an “ocean noise

map” was strongly supported, as was better public communication of

information on ocean noise levels.

4. Relative density, seasonal distribution, and trends. For determining relative density or abundance, and trends in abundance, many

of the same calibration factors are needed as for determining absolute

abundance. But in the absence of those calibration factors, acoustic

methods can offer estimates of minimum population size, and can be

used to track large-scale movement patterns.

Workshop discussion culminated in a list of recommendations for management, research, and field operations.
Future Directions for Acoustic Marine Mammal Surveys 3

Workshop Participants

Jay Barlow NMFS Southwest Fisheries Science Center

Phillip Clapham NMFS Northeast Fisheries Science Center

Chris Clark Cornell University

Chris Fox NOAA Pacific Marine Environmental Laboratory

Greg Fulling NMFS Southeast Fisheries Science Center

John Hildebrand Scripps Institution of Oceanography

Lance Garrison NMFS Southeast Fisheries Science Center

Jeff Laake NMFS Alaska Fisheries Science Center

Tony Martinez NMFS Southeast Fisheries Science Center

Mark McDonald Whale Acoustics, Inc.

Dave Mellinger Oregon State University and NOAA Pacific

Marine Environmental Laboratory

Sue Moore NMFS Alaska Fisheries Science Center

Debbie Palka NMFS Northeast Fisheries Science Center

Bill Perrin NMFS Southwest Fisheries Science Center

Sarah Mesnick NMFS Southwest Fisheries Science Center

Kate Stafford NMFS Alaska Fisheries Science Center

Barb Taylor NMFS Southwest Fisheries Science Center

Aaron Thode Scripps Institution of Oceanography

Observers

Eric Howarth San Diego State University

Megan Ferguson Scripps Institution of Oceanography

Melissa Hock Scripps Institution of Oceanography

Lisa Munger Scripps Institution of Oceanography

Tom Norris Science Applications International Corp.

Julie Oswald Scripps Institution of Oceanography

Erin Oleson Scripps Institution of Oceanography

Ana Siroviˇ  ́ c Scripps Institution of Oceanography

Sean Wiggins Scripps Institution of Oceanography
4 Mellinger and Barlow

Background

Although acoustics has been used for studying marine mammals for decades,

it has seldom been employed for assessing populations. The term assessment

is used here to describe the process of evaluating the status of a population

relative to some management goal. Assessment involves studies of the structure of populations, estimation of abundance and trends in abundance, and

the evaluation of anthropogenic impacts. The best example of the use of

acoustics in assessment to date is the long-term study of the Beaufort Sea

bowhead whale population, where combined visual and acoustic methods

have significantly improved the population estimate. The primary goal of

this workshop was to explore how acoustic methods might be more fully exploited for marine mammal assessment—that is, how might acoustic methods

provide assessment data unobtainable in other ways? In what ways might

acoustic methods provide roughly equivalent data at less cost? A secondary

goal was to explore how acoustic methods can be used to address the questions of how marine mammals respond to noise, especially anthropogenic

noise, and how effective any mitigation measures might be.
Future Directions for Acoustic Marine Mammal Surveys 5

Presentations (Wednesday, 20 November)

The workshop aimed to bring together two communities of marine mammal experts: those in assessment, and those in acoustics. The first day of

the workshop included presentations by most of the attendees to establish a

common base of knowledge. Assessment experts presented methods used in

the field and projects that have used them, discussed statistical techniques

for estimating populations from sets of observations, and covered the requirements needed for gathering necessary data to make statistically valid

population estimates. Acoustics experts discussed projects they had participated in, outlined the methods used, and explained capabilities of the

systems used and characteristics of data collected by these systems.

I. Assessment: Abstracts of Presentations

SWFSC Acoustic Survey Research for Marine Mammal Assessment

Jay Barlow, Julie Oswald, Erin Oleson, Shannon Rankin

At the Southwest Fisheries Science Center (SWFSC) we have been experimenting with the incorporation of acoustics in line-transect surveys since

1995. The CADDIS survey in 1995 looked at the acoustic detectability of

beaked whales and found that only Baird’s beaked whales made sounds that

could be readily detected (Dawson et al., 1998). The SWAPS survey in 1997

was our first combined visual and acoustic survey and provided density estimates of sperm whales using detections from both methods (Barlow and

Taylor, 1998). Starting in 1998, towed hydrophone arrays were used on dolphin line-transect surveys. We have worked with others (Thode et al., 2000;

Mellinger, 2001) to develop software to localize dolphins from their whistles. Results showed that dolphins could be detected at significantly greater

distances using acoustics. However, the inability to look directly forward

using a line array has hampered our ability to detect dolphins prior to their

being detected by visual observers. In collaborations with Scripps scientists,

sonobuoys have been used opportunistically on our surveys to make low-noise

recordings of sounds from a variety of species. Most notably, we were the first

to find that Bryde’s whales make stereotypical low-frequency calls similar to

blue whales and that the various call types show strong geographic patterns

(Oleson et al., in press). Recordings from sonobuoys and our towed array

have been used to examine the feasibility of determining species from dolphin whistles. Using two different classification methods (DFA and CART),

we have found that more than 50% of whistles from nine dolphin species can

be correctly classified to species (Oswald et al., in press), compared to an

11% correct classification by chance alone. Finally, in the last month, we

have tracked the mysterious “boing” down to its source and have found that

it is most probably a breeding call of the North Pacific minke whale. Future

research will concentrate on estimating g(0) for sperm whales, improving our

ability to listen in a forward direction using a towed hydrophone, estimating
6 Mellinger and Barlow

g(0) for dolphins, and estimating the density of calling minke whales from

their “boings” recorded on the 1997 sperm whale survey.

Barlow, J., and B.L. Taylor (1998): Preliminary abundance of sperm whales in the

northeastern temperate Pacific estimated from a combined visual and acoustic

survey. Int. Whal. Comm. Working Paper SC/50/CAWS20, 19 pp.

Dawson, S.M., J. Barlow, and D. Ljungblad (1998): Sounds recorded from Baird’s

beaked whale, Berardius bairdi. Mar. Mamm. Sci., 14(2), 335–344.

Mellinger, D.K. (2001): Ishmael 1.0 User’s Guide. NOAA Tech. Memo. OAR

PMEL-120, 26 pp.

Oleson, E.M., J. Barlow, J. Gordon, S. Rankin, and J.A. Hildebrand (in press):

Low frequency calls of Bryde’s whales. Mar. Mamm. Sci.

Oswald, J.N., J. Barlow, and T.F. Norris (in press): Acoustic identification of nine

delphinid species in the eastern tropical Pacific Ocean. Mar. Mamm. Sci.

Thode, A., T. Norris, and J. Barlow (2000): Frequency beamforming of dolphin

whistles using a sparse three-element towed array. J. Acoust. Soc. Am., 107(6),

3581–3584.

Distance Sampling and Marine Mammal Acoustic Surveys

Jeff Laake

Dr. Laake’s contribution comprised significantly more than an abstract, and

is included in this report as Appendix A.

Passive Hydroacoustic Detection of Marine Mammals at SEFSC

Lance Garrison (presenter), Steven Swartz, Anthony Martinez, Jack Stamates, John Proni, NOAA/NMFS/SEFSC and NOAA/OAR/AOML

The Southeast Fisheries Science Center (SEFSC), in cooperation with AOML

and the U.S. Navy, has been actively developing passive hydroacoustic methods to enhance assessment surveys for marine mammals in the Atlantic

Ocean, Gulf of Mexico, and Caribbean. The primary research vessel used on

marine mammal surveys, the NOAA ship Gordon Gunter, is ideally suited

for this task as it is acoustically quiet, provides ample space for acoustic data

acquisition and recording equipment, and has an excellent platform for visual

observations. Acoustic operations to date have primarily employed a fiveelement towed hydrophone array and a smaller two element array that can

be deployed in shallower water. In addition, sonobuoys were deployed extensively during cruises targeting humpback whales in the Caribbean. Acoustic

methods significantly enhanced the number of humpbacks detected during

these surveys.

More recently, SEFSC conducted a joint visual and acoustic survey of

the mid-Atlantic continental shelf. The hydroacoustic arrays were utilized

simultaneously with the visual survey effort except where limited by water

depths. The visual survey team operated independently of the acoustic effort

and were not notified of acoustic contacts. There were numerous cases where

acoustically detected marine mammals were not observed by the visual team.

Visual sightings were noted in the acoustic data logs, and these records are

currently being reviewed to match acoustic and visual detections.
Future Directions for Acoustic Marine Mammal Surveys 7

The hydroacoustic program is still in development. Significant research

challenges remain, such as developing and testing methods to calculate the

distance to acoustic signals, estimate the number of animals detected, and

verify species identifications. In addition, it is essential to develop a linked

database program to reducing the processing time required to match visual

and acoustic detections after the survey. During the next several cruises

during 2003 and 2004, we will continue to evaluate the best survey and theoretical methods to integrate passive acoustic detections into marine mammal

assessments.

Acoustic-Related Assessment Needs for Baleen Whales in the Waters of the Northeastern United States and Atlantic Canada

Phil Clapham

The waters off the northeastern coasts of the U.S. and adjacent areas of

Atlantic Canada contain important feeding habitats for several species of

mysticetes. These include North Atlantic right, humpback, fin, sei, minke,

and blue whales. Current knowledge of the distribution and abundance

of these species varies, and can be loosely categorized as follows: very good

(humpback whales); reasonably good with major gaps (right and fin whales);

fair (minke whales); and very poor (sei and blue whales). With some recent

exceptions (notably work by Clark and colleagues), acoustic techniques have

been used relatively little in studies of mysticete populations in this region.

Given that much of the distribution of mysticetes in the northeast is

centered in coastal and shelf waters, remote monitoring of calling whales

is constrained by shallow-water transmission loss. However, placement of

pop-ups or similar devices in areas known or thought to represent habitats

for mysticetes potentially allows for continual monitoring of the presence

of (calling) whales over extended periods, including at night, during poor

weather, and in locations that would be difficult to survey for much of the

year. This technique could fill significant gaps in knowledge concerning the

frequency with which certain species are found in more offshore areas. This

would be particularly valuable for whales for which winter distribution is

currently uncertain or unknown, which is an especially significant gap in our

knowledge of right whales. In addition, acoustic monitoring might help to

determine whether historically important but currently unsurveyed offshore

habitats for right whales (or other species) are still utilized today.

Acoustically derived data on distribution (and, if practicable, on relative abundance) would be potentially important in assessment of risk in

endangered populations. In particular, such data could help to determine

the occurrence of right whales in areas subject to human activities such as

shipping and fishing.

Problems with acoustic approaches to assessment include limited signal

range, lack of information on call characteristics of some species, and the potentially low frequency with which individuals may vocalize. For relatively

vocal species (such as right and humpback whales), additional research is required to establish whether correlations exist between calling rates and local
8 Mellinger and Barlow

abundance; this can potentially be accomplished by coordinating acoustic

monitoring with aerial or shipboard surveys in the same areas.

Using Passive Acoustics during Cetacean Abundance Surveys in

the Northwest Atlantic

Debra Palka

The Northeast Fisheries Science Center (NEFSC) estimates the abundance

of many cetacean species in the Northwest Atlantic using shipboard and

aerial line transect surveys. Abundance estimates derived from line transect

surveys may be biased due to animal availability (i.e., animals never surface

to be detected by visual observers), and human perception (i.e., observers

visually detect fewer animals in inclement weather conditions). To account

for these types of biases, the NEFSC has used the two “independent” team

method. However, this method does not fully account for animals that remain mostly submerged and so are seldom seen. One way to account for

this type of bias is to record the location of vocalizing animals in addition

to recording the location of visually detected animals. To evaluate this approach, sightings of harbor porpoises were made by three teams on the R/V

Abel-J in 1999 and simultaneously, harbor porpoises were acoustically detected using a high frequency hydrophone (125 kHz) trailed behind the ship.

During the 2001 R/V Delaware survey, cetaceans were visually detected by

two teams of observers and acoustically detected by a medium frequency

hydrophone (100 Hz to 22 kHz) trailed to the side and behind the ship.

Dr. David Borchers has developed a method to estimate abundance from

combined acoustic and visual data. Applying Borchers’ method to the 1999

harbor porpoise acoustic and visual data produced an abundance estimate

about 2.5 times higher than that obtained from a conventional visual line

transect analysis. These methods show promise but still need to be more

fully developed and tested. To record vocalizations from a variety of species,

a hydrophone system is now being constructed for use on NEFSC cetacean

surveys that records both high and medium frequencies. In the future, we

hope to use this hydrophone system and new analytical methods to produce

less biased abundance estimates for many cetacean species.

II. Acoustics: Abstract of Presentations

Acoustic Assessment of Marine Mammal Populations

John Hildebrand

Passive acoustic monitoring may be a useful technique for assessing marine

mammal populations, complementary to visual techniques. Acoustic and

visual techniques have different strengths and weaknesses for marine mammal monitoring. Acoustic techniques fundamentally monitor submerged animals, whereas visual techniques monitor animals during periods of surfacing.

Acoustic techniques have the ability to provide continuous temporal coverage

and thus information on seasonal presence, providing data that are difficult

or impossible to obtain with visual methods. Acoustic monitoring can be
Future Directions for Acoustic Marine Mammal Surveys 9

conducted relatively independent of daylight and weather, conditions that

severely affect visual surveys.

Long-term acoustic monitoring is best conducted from fixed sites, either

from seafloor acoustic recording packages or cable-connected hydrophones

such as the SOSUS arrays. Because of this, acoustic techniques are best

applied to a small locale. Visual surveys are typically designed to cover a

broad region, and thereby provide a synoptic assessment of the total population. The mismatch of these two scales, local for acoustic and regional for

visual, must be reconciled before a good comparison can be made between

these two techniques. Another important issue is whether whales detected

visually can also be detected acoustically, and vice versa. There is some evidence that calling whales are stealthy (difficult to detect visually) and that

easily seen whales are rarely vocalizing.

Examples are presented of acoustic monitoring for baleen whales in the

southern California offshore region and in the Antarctic. Using automated

call detection algorithms, blue whale calling seasonality at both sites can

be described. In southern California, blue whale calling begins in early

June, peaks from August through October, and decreases through the fall.

Aerial visual survey data from southern California suggests that there is

a mismatch in the seasonality of blue whales detected visually and those

detected acoustically. More whales are visually detected early in the summer,

while acoustic detections peak late in the summer. A diurnal calling pattern

is observed with 30% more calls at dawn and dusk than at other times of the

day. In the Antarctic, blue whale calling is detected year-round in a region

where no visual sightings of blue whales have been confirmed for the past

decade.

Status of NOAA/PMEL Acoustic Observing Systems

Christopher G. Fox

NOAA’s Pacific Marine Environmental Laboratory (NOAA/PMEL) collects

a variety of digital underwater acoustic recordings in support of NOAA’s

Vents Program. Since August 1991, NOAA/PMEL has collected continuous recordings from the U.S. Navy SOSUS arrays in the North Pacific,

and this effort will continue into the foreseeable future with ten arrays currently collected. Numerous SOSUS arrays exist in the Atlantic which are not

collected by PMEL, although the expertise exists to tap into those arrays.

There are also several SOSUS arrays that have been abandoned by the Navy

that could be occupied by NOAA. In May 1996, the Vents acoustic monitoring effort was expanded through the use of PMEL-developed autonomous

hydrophones deployed in the eastern equatorial Pacific (8◦S–8◦N, 110◦W–

95◦W), and later to the central North Atlantic between 15◦N and 35◦N

(March 1999), the Gulf of Alaska (October 1999–July 2002), and the North

Atlantic between 40◦N and 50◦N (June 2002). These arrays are generally

deployed for seismic studies (with the exception of the Gulf of Alaska blue

whale study) and are therefore collected in relatively low frequency bands

(1–100 Hz) with some higher sampling (1–450 Hz). Natural seismicity in the
10 Mellinger and Barlow

Pacific produces nearly 10,000 events per year with source levels exceeding

200 dB (re 1 μPa @ 1 m), with about 3,500 events per year exceeding this

level in the North Atlantic. Significant contributions from manmade sources

are present throughout the data but have not been quantified. Recordings

from the North Atlantic arrays are dominated by noise from seismic airgun

profilers working offshore Canada, Brazil, and West Africa. In September

2001, a cabled vertical hydrophone array was installed at Pioneer Seamount,

offshore central California, which provided continuous, unclassified acoustic

data (in the range of 1–450 Hz) to the research community in real time. Unfortunately, a cable break in Fall 2002 ended the experiment. Future plans

call for the expansion of the NOAA monitoring effort to other opportunities

worldwide and making the raw data available to the community via the internet. Areas being targeted for future monitoring include (1) the Eastern

Tropical Pacific near 9–10◦N, 104◦W, with spacing of about 20 km, capable

of tracking marine mammals through the area, (2) the Lau Basin region of

the Southwest Pacific near 20◦S, 180◦W, and (3) the Marianas Islands region

of the western Pacific. Currently, the inventory of portable hydrophones totals 35 units, some of which could be made available for marine mammal

studies.

Seasonal Patterns of Large Whale Occurrence in the North Pacific

Kate Stafford (presenter), Sue Moore, and Chris Fox

In collaboration with the National Marine Mammal Lab, NOAA’s Pacific

Marine Environmental Lab has been supporting the study of low-frequency

whale calls both through access to the U.S. Navy’s west coast SOSUS data

and through development of autonomous moored hydrophones (Fox et al.,

2001). Specific results include documenting seasonal and geographic variation in reception of fin whale calls from five sites in the North Pacific (Moore

et al., 1998); establishing the northern (Gulf of Alaska) and southern (equatorial eastern tropical Pacific) extents of northeastern Pacific blue whale

calls and suggesting migratory patterns from these data (Stafford et al.,

1999a); documenting that there are at least two geographically distinct call

types that may be attributed to blue whales in the North Pacific (Stafford

et al., 2001); showing that the eastern tropical Pacific is used by blue whales

from both the southern and northern hemisphere and probably by fin whales

(Stafford et al., 1999b). Long-term monitoring of ambient noise in the ocean

has shown that most large whale species produce calls year-round. Although

the behavioral function of calling remains little understood for most species,

this research shows that call reception can be used reliably to determine

presence/absence of large whales across broad temporal and spatial scales.

Remote monitoring of cetacean calls is clearly a powerful tool for monitoring

macro-scale seasonal and geographic patterns of large whale occurrence.

Fox, C.G., H. Matsumoto, and T.K.A. Lau (2001): Monitoring Pacific Ocean seismicity from an autonomous hydrophone array. J. Geophys. Res., 106(B3),

4183–4206.

Moore, S.E., K.M. Stafford, M.E. Dahlheim, C.G. Fox, H.W. Braham, J.J. Polovina,
Future Directions for Acoustic Marine Mammal Surveys 11

and D.E. Bain (1998): Seasonal variation in reception of fin whale calls at five

geographic areas in the North Pacific. Mar. Mamm. Sci., 14, 617–627.

Stafford, K.M., S.L. Nieukirk, and C.G. Fox (1999a): An acoustic link between blue

whales in the Northeast Pacific and the eastern tropical Pacific. Mar. Mamm.

Sci., 15, 1258–1268.

Stafford, K.M., S.L. Nieukirk, and C.G. Fox (1999b): Low-frequency whale sounds

recorded on hydrophones moored in the eastern tropical Pacific. J. Acoust. Soc.

Am., 106, 3687–3698.

Stafford K.M., S.L. Nieukirk, and C.G. Fox (2001): Geographic and seasonal variation of blue whale calls in the North Pacific. J. Cetacean Res. Manage., 3,

65–76.

Two Times the Trouble, Five Times the Fun: Using Two Towed

Arrays for Dolphin and Sperm Whale Localization

Aaron Thode (presenter), Eric Howarth

Single towed arrays are typically used to estimate bearings during marine

mammal survey work. The deployment of a second towed array, separated

from the first array by 150 to 500 m, can yield range and even depth information, if surface reflections can be exploited. Two examples of such work

will be shown, including 3D tracking of close-range sperm whales in the Gulf

of Mexico, and automated bearing-range dolphin tracking using data from

a February 2002 SE Fisheries survey cruise off the East Coast.

Acknowledgments: Tony Martinez, Jack Stamates, Steve Swartz, Matt Grund,

Mark Johnson, Peter Tyack

Song of Blue and Fin Whales Applied to Population Identification,

Distribution and Seasonal Movements

Mark McDonald (presenter), John Hildebrand, Sarah Mesnick

Blue whale song has been divided into nine types worldwide, excluding variations within some types. Seven of the nine song types have been recorded

repeatedly over many years and are unchanging in character, though all

have been shifting downward in frequency over the 40 years of recording.

The frequency change may be related to recovery from whaling. There are

presently three song types in the Indian Ocean, two in the North Pacific, one

in the North Atlantic, one in the Antarctic, two in the South Pacific and no

data in the South Atlantic. More song types will undoubtedly be discovered

and some regions where blue whales are common lack acoustic recordings.

Blue whales from some regions are known to sing year around, though the

amount of singing for a given animal density is believed to vary by season.

Approaches to estimating both minimum and absolute population density

from recordings will be discussed.
12 Mellinger and Barlow

Acoustic Surveys and Acoustic Detection Distance

David K. Mellinger

On recent sperm whale surveys in the Gulf of Mexico, towed hydrophone

arrays and sonobuoys were used to gather data. The software used includes

Ishmael, a multipurpose tool for recording, displaying, and analyzing sounds;

WhalTrak, a program for plotting and logging bearings to vocalizing whales;

RainbowClick, a powerful tool for locating sperm whales; and Matlab, a programming environment used for many purposes. Another acoustic technique

is the use of autonomous hydrophone recorders, instruments that collect data

for months to years at a time. The large quantity of data makes automatic

call recognition an attractive option. A case study is presented in which

sperm whale sounds in the Gulf of Alaska are automatically detected, with

the detections used to show seasonal and geographic differences in calling.

A further step is to use acoustic data for assessment, for which we must

estimate acoustic detection distances. This can be done by use of acoustic

propagation models, which in turn need environmental information (sound

speed profile, bottom characteristics, noise levels, etc.), whale depth, and

information about whale calling behavior. The result of the propagation

model—transmission loss as a function of range and depth—can then be used

in a model of whale calling and diving behavior to estimate the probability

of detection as a function of range.

Acoustics for Marine Mammal Surveys

Christopher W. Clark

The application of passive acoustic mechanisms for detecting and identifying marine mammals and the integration of visual and acoustic methods for

population surveys are long overdue. Acoustic mechanisms are advancing

rapidly and costs are decreasing continually. The breadth of engineering

and oceanographic talent is steadily increasing. All the basic tools and talent are there. Visual survey methods have reached their limits. For many

species known to be vocally active, the application of passive acoustics offers an immediate and obvious benefit at relatively modest cost. It is no

longer a matter of proving the concept of dual-mode surveys, it is a matter

of making them effective and pro forma. It is a matter of finding the right

combination of people skills and technology and applying these to some real

problems. The bowhead whale census is an excellent example of visual and

acoustic techniques successfully merged for population assessment and trend

analysis. The major challenge for application in other scenarios (e.g., vesselbased surveys) resides in (a) developing robust statistical methodologies to

estimate abundance from vessel-based sightings and acoustic detections, (b)

understanding levels of variability in acoustic behaviors, and (c) developing

a suite of standardized tools for collecting, analyzing, and interpreting bioacoustic data. In cases where visual surveys are impractical, passive acoustic

mechanisms offer ways of sampling large areas of the ocean for long periods

of time at low cost. To better interpret such bioacoustic data we need to
Future Directions for Acoustic Marine Mammal Surveys 13

better understand the whys and hows of marine mammal vocal production

and behavioral ecology. We need to integrate distributions and densities

with ocean productivity.

Cetacean Detection and Assessment via Passive Acoustics

Sue Moore

[This is the abstract of a significantly longer work, which is included as

Appendix B.]

From 1999 through 2002, the National Marine Mammal Laboratory (NMML)

conducted collaborative projects focused on the advancement of passive

acoustics for detection of large whales. The NMML focused its efforts on

long-term deployments of autonomous recording packages (ARPs) for detection of large whales in Alaskan waters. Four ARPs were deployed in the

eastern Bering Sea in October 2000 to monitor waters where critically endangered North Pacific right whales (Eubalaena japonica) have been seen

each July since 1996. Two other recorders, fabricated by NOAA/PMEL,

were deployed southeast of Kodiak Island near an area where one North

Pacific right whale was seen in July 1998. In addition, NMML collaborated

with researchers using the U.S. Navy’s SOund SUrveillance System (SOSUS)

assets to locate blue whales in the North Pacific to conduct a provisional seasonal habitat analysis by integrating the call location data with bathymetry

and remotely sensed data (i.e., sea surface temperature (SST), chlorophyll

a, altimetry) using a geographic information system (GIS). Results of these

analyses were presented at the 13th Biennial Marine Mammal Conference in

2000 and subsequently published in Oceanography 15(3), 2001.
14 Mellinger and Barlow

Discussion (Thursday, 21 November)

The theme of this day of the workshop was “Directions for the Future.” The

day was organized as four discussion sessions on topics important to either

performing assessment or understanding responses of marine mammals to

noise. Each discussion session was moderated by a member of the workshop;

the goal of the discussion was to determine what acoustics might contribute

toward the topic at hand, and what the group might recommend toward that

end. The recommendations were further discussed and refined on Friday.

Below is a summary of the day’s discussion.

Discussion Topic I. Population Structure

Jay Barlow, moderator

Management aspects of population structure

The appropriate subdivision of a species into “management units” or “stocks”

varies with different management frameworks and objectives. The U.S. Marine Mammal Protection Act (MMPA) has a requirement that species be

maintained as functioning elements of their ecosystems, and this has been

interpreted to mean that there should be no fragmentation or contraction

of the range of any species. To meet this objective, a species would have to

be managed on the basis of smaller units (to prevent local extirpation) than

if the management objective were to prevent the extinction of the species.

The Endangered Species Act (ESA) refers to Distinct Population Segments

(DPS) of a species which are typically larger than the “population stocks”

which are managed under the MMPA. The U.S. Fish and Wildlife Service

and NMFS, which are responsible for enforcing the ESA, have interpreted

these legal requirements to mean that a DPS must be genetically distinct

and must occupy unique habitat. If conservation of populations is successful,

the evolutionary potential of a species is preserved.

Studies of population structure for cetaceans have mainly used genetics, tagging, and photo-identification. To a lesser extent, gaps in distribution have been used as indicators of separate populations. It may be useful to use one technique—for example, differences in vocalization types—to

form hypotheses about population structure, and another technique—say,

genetics—to test the hypotheses.

Although the above principles have been widely discussed in the conservation biology community, there has been little uniformity in how the principles are applied across species. The International Whaling Commission

(IWC) has a Working Group on stock identification. That group decided

that the term “stock” was confusing because it means different things to

different people; the IWC chose the term “unit to conserve” instead. Some

examples:

 Under the U.S. ESA, gray whales are divided into eastern and western

stocks, with the eastern stock considered recovered and the western

stock still endangered.
Future Directions for Acoustic Marine Mammal Surveys 15

 The appropriate population structure for Bryde’s whales in the Pacific

is unknown. Some within the IWC have suggested a structure with

three populations: one near Japan, one made up of pygmy Bryde’s,

and the third encompassing all other Bryde’s whales.

 The appropriate structure for Atlantic minke whales is likewise unknown. Separation into an oceanic population and a coastal Norway

population has been suggested.

Time scale

Management typically operates on a time scale of years or decades. Traditional use of genetics to define populations has focused on differences between

populations that build up on an evolutionary time scale and is inappropriate for defining management units. Genetics can now be used for estimating

dispersal rates to answer the question, “If a species has been extirpated in

one area, does repopulation happen in 10 years or 200?” As an example of

this dilemma, the southern resident population of killer whales in the Puget

Sound area has been declining. If this population dies out, will the northern residents repopulate the area? There is little to no genetic interchange

between the southern and northern residents, but the northern residents

do come into the southern area sometimes. Other examples include places

where whaling eliminated a population, and re-population has not occurred:

Spitsbergen bowhead whales, South Georgia blue whales, and South Georgia

fin whales.

Acoustically defined populations

It may be reasonable to investigate populations as defined acoustically (Table

1), i.e., by vocalization characteristics. As an example, blue whale vocalizations in different areas appear to have different time/frequency contours.

Such differences may sometimes be sufficient, for instance, for defining a

Distinct Population Segment under the ESA. Acoustic differences have been

used to define stocks by NMFS: the Eastern Pacific stock of blue whales was

recognized because of its unique call type. At the same time, acoustic differences are not a necessary condition for defining a stock; humpback whale

genetics has shown maternal fidelity to breeding sites—enough difference

has been found to define separate stocks—but acoustically, these populations would be lumped into one stock. There is simply more difference in

genetics than in song.

The amount of data available for investigating this question varies widely

between species. For instance, Bryde’s whale sounds have not been acoustically sampled throughout much of their range, and the variation in call types

is not known. Taxonomists are now suggesting that Bryde’s whale be split

into at least two or three species, and perhaps more; the extent to which

these species splits correlate with acoustic differences will remain unknown

until more acoustic data can be collected.

It was strongly suggested that we think in terms of evolutionary biology
16 Mellinger and Barlow

Table 1: Known acoustic population structures of some marine mammals.

Number of Temporal

Species Geographic structure populations stability Citation

blue whale

B. musculus

large fixed differences

between populations

9–12 30–40 year Stafford (1999, 2001);

McDonald, pers. comm.

fin whale

B. physalus

statistically detectable

differences between

populations

? ? Thompson and Freidl (1982)

Bryde’s whale

B. edeni

large fixed differences

between populations

8–? ≥2 year Oleson et al., to appear

common minke

B. acutorostrata

fixed differences between

populations

2–3 ≥40 year Winn and Perkins (1976);

Mellinger et al. (2000);

Gedamke et al. (2001)

humpback whale

M. novaeangliae

within a season, fixed

differences between

populations

4–? 1–3 year Payne and Payne (1983);

Noad et al. (2000); Cerchio

(2002)

right whales

E. glacialis,

australis, japonica

none? ? ? Clark (1982); Clark et al.

(2000); McDonald and

Moore (2002)

bowhead whale

B. mysticetus

none? ? ? Clark and Johnson (1984);

W ̈ursig and Clark (1993)

gray whale

E. robustus

? ? ? Crane and Lashkari (1996);

Moore and Ljungblad

(1984); Dahlheim (1987)

sperm whale

P. macrocephalus

statistically detectable

differences between

populations

? ? Watkins and Schevill (1977);

Weilgart and Whitehead

(1993); Pavan et al. (2000)

orca

O. orca

large fixed differences

between populations

>>6 ≥30 year Ford (1991)

beluga

D. leucas

unknown; some data exist ? ? Sjare and Smith (1986);

Angiel (1997)

other delphinids statistically detectable

difference between species

>>100 ? e.g., Steiner (1981); Rendell

et al. (1999); Oswald et al.

(2003)

bearded seal

E. barbatus

unknown; some data exist ? ? Ajmi (1996)

harbor seal

P. vitulina

fixed differences >>6 ≥30 year Hanggi and Schusterman

(1994); Van Parijs et al.

(2000); Van Parijs et al., in

press
Future Directions for Acoustic Marine Mammal Surveys 17

about why there are acoustic differences, and about how fast vocalizations

change.

It was reiterated several times during the workshop, and agreed by all or

nearly all present, that a combined approach to studying populations (and

assessment in general) is needed. By a combined approach, we mean using

all appropriate methodologies, including but not limited to acoustics, visual

surveys, genetics, behavior study, tagging, etc.

Discussion of population structure culminated in several recommendations, which are covered below as item R1 of Friday’s topics.

Discussion Topic II. Abundance and Density

Phil Clapham, moderator

The estimation of marine mammal density or abundance using acoustics

is similar to estimation by visual methods in several regards. The estimation methods for either are likely to involve the application of some form of

“distance sampling”: either line-transect or point-transect methods. These

methods require the estimation of detection distances from either a moving

platform or a single stationary point (respectively). For both, important factors include those that affect the production of cues (surfacings, blows, etc.

for visual surveys; vocalizations for acoustic surveys) and those that affect

the detection of cues (e.g., equipment used, sea state, etc.). For visual surveys, all individuals produce at least some cues at regular intervals (animals

must surface to breathe); whereas, for acoustic surveys, there may be much

more variation in the rate of cue production between different individuals

(e.g., gender, age, and seasonal differences). Therefore, for acoustic surveys,

there may need to be greater emphasis in the measurement of factors that

are related to the production of cues. In contrast, the detection of cues is

much more easily understood for acoustic detection methods than for visual

methods. For visual surveys, detection distances are estimated empirically,

and there has been very little progress in the mathematical modeling of visual detection distance. For acoustic detection methods, there is a much

greater contribution that modeling can make to improve our understanding

of detection distances.

To date, there has been greater emphasis on visual than acoustic methods of estimating marine mammal density or abundance. There are many

abundance estimates based on visual methods alone, but none based solely

on acoustic methods. However, there have been published estimates based

on the integration of visual and acoustic methods (e.g., bowhead whales

and sperm whales), and in these cases, the addition of acoustic methods

have greatly improved the abundance estimation. Some members of the

workshop envisioned a day when acoustic survey methods would completely

replace visual methods; however, most participants felt that the greatest

immediate benefits might be obtained by using the best attributes of each

method in an integrated survey.

One key factor in the use of acoustic survey methods must be species

identification. In this area, more progress has been made with baleen whales
18 Mellinger and Barlow

than with the toothed whales. There are many baleen whales for which

species can be determined unequivocally from at least some call types (e.g.,

blue whales, fin whales, minke whales, humpback whales, and right whales);

whereas there are few toothed whales for which this is true (e.g., sperm

whales and killer whales). In a recent study of nine dolphin species, the

percentage of correctly identified individuals (from a single whistle) was only

about 50%, and, clearly, if acoustics are to be a valuable survey tool, methods

should be investigated to improve this. A working group of Dave Mellinger,

Kate Stafford, and Julie Oswald was identified to review the state of species

identification from cetacean calls.

Another key factor in the use of acoustic survey methods is the need

to estimate detection distances. For this, there are two general approaches:

empirical and theoretical. The empirical approach involves measuring the

actual location of vocalizing animals for a large sample and fitting some

function to describe the probability of detection as a function of range. The

localization of vocalizing whales can be purely acoustical using hydrophone

arrays or by utilizing multi-path information (bottom/surface bounces) or

other aspects of sound propagation. The theoretical approach involves modeling of detection distance using knowledge of source levels, propagation

conditions, and ambient noise. It was pointed out that 20 dB variations in

source level could have a 10-fold effect in detection distance, so additional

efforts are needed to quantify source level variation. There is considerable

variation in published estimates of source level for many species, and these

need to be evaluated to determine whether this represents measurement error

or natural variation. Chris Clark mentioned that he has data on variation in

source level of right whales in the Atlantic. It was agreed that both empirical

and theoretical approaches to estimating detection distance have merit, and

that there should be efforts to validate the theoretical models using empirical

methods.

The relative merits of moving platform (line-transect) surveys vs. fixed

point surveys were discussed. In distance sampling, there is a common assumption that the speed of the survey platform is fast relative to the speed of

the animals being surveyed. This is clearly violated for fixed-point surveys.

In order for fixed-point surveys to work for estimating density, the residency

time within the detection range needs to be addressed. Currently there is no

well-defined method for doing this in a rigorous quantitative framework. It

is possible that cue counting methods (a sub-set of distance sampling) can

be used from fixed points, but cue rates would have to be well known and

additional analytical developments are probably required. It is also possible

that fixed-point surveys can be used in a narrow migration route to enumerate migrants, however this method is quite different. A common aspect

of both line-transect and point-transect methods is that transects must be

placed randomly with respect to the animals. The current array of fixed sampling points is probably inadequate to meet this assumption because they

are placed in a physical environment that was chosen to optimize reception,

and these physical factors are also likely to affect whale distribution. Also, a

large number of fixed points would likely be necessary to adequately sample

a species’ range. For a mobile platform, it is easier to meet the assumption
Future Directions for Acoustic Marine Mammal Surveys 19

of randomness with respect to whale distribution, but if a systematic survey

grid is used, care should be exercised to ensure a random starting point is

selected. The strength of fixed point monitoring (e.g., bottom recorders) is

the much greater temporal/seasonal coverage. The strength of mobile platform monitoring (e.g., ship line-transect surveys) is the broader geographic

coverage. Participants agreed that there is value in both of these general

approaches.

One area that clearly needs more work for the advancement of acoustic

surveys is to understand variation in vocalization rates. Likely factors that

affect vocalization rates are gender, age, seasonality, location, time-of-day,

and associated behaviors (e.g., feeding vs. breeding). Fixed hydrophones

or (especially) hydrophone arrays matched with detailed visual observations

may also be extremely useful in quantifying vocalization rates. Oleson and

Hildebrand described an experiment planned in association with FLIP and a

moored hydrophone array to study blue whale vocalization rates in southern

California next summer. The development of acoustic recording tags may

allow great advances to be made in the near future. The information from

acoustic tags can be greatly enhanced if the tag is designed to retain a small

sample of skin for genetic analyses of gender and population structure. It was

pointed out also that the value of acoustic tags is greatly enhanced if they can

be applied to a random sample of the population; the deliberate sampling

of vocalizing animals would result in a biased estimate of vocalization rates

for the population as a whole.

Because methods for purely acoustic surveys are not well developed, emphasis should be placed on integrating visual and acoustic survey methods

to improve estimates of abundance. Acoustic methods can provide improvements by extending search range, by allowing survey at night, by detecting

submerged animals, and by estimating the fraction of animals missed by

visual methods. If visual and acoustic detections can be considered to be

independent, the fraction of animals missed can be estimated with markrecapture methods. If there is a negative correlation between the probabilities of acoustic detection and visual detection, mark-recapture methods will

result in an overestimation of abundance; in such cases it may be better to

pool visual and acoustic detections to minimize the negative bias in either

one without risking a positive bias in abundance estimates. However abundance is estimated, there is a need to match visual and acoustic detections

to determine whether the animals seen are the same ones being heard. This

is best done in the field, but analytical procedures that assign a probability

of a match are also being developed. The purely acoustic estimation of the

number of individuals in a large group remains problematic, and here visual

methods are still essential.

Discussion Topic III. Responses to Noise

Sue Moore, moderator

How can acoustics be used to study responses of marine mammals to noise?

One obvious answer is that one must measure the noise in order to under-
20 Mellinger and Barlow

stand any responses to it, but beyond that, acoustics may be useful in other

ways as well.

Marine mammals may respond to both natural and manmade noise.

Natural Noise

There are several ways the issue of responses to natural noise can be

viewed, depending on the type of noise and the response.

 Animals may respond to calling by conspecifics by changing their own

vocalization behavior. If so, this bears directly on efforts toward an

acoustic census, in which the number of individuals is to be estimated

from acoustic data. Sometimes individuals of a species may respond by

increasing their own rate of vocalizations; right whales, for instance, are

known to increase their vocalization rates when other right whales are

present and vocalizing. Another response could be decreased average

call rates, such as when an individual needs to make fewer contact

calls to a herd when other members of the herd are themselves calling

nearby. This topic needs significantly more study before acoustics can

become widely used for censuses.

 Animals may respond to increased noise by increasing the intensity of

their vocalizations. This may happen regardless of whether the noise

is from conspecifics, other natural sound sources, or manmade sound

sources.

One subject open to investigation is how whales respond to earthquake

sounds, which are very low in frequency. This question could be studies using long-term recordings of SOSUS arrays, which are available

at NOAA/PMEL, or using recordings from autonomous hydrophones

that have been deployed by several researchers. It would probably

make the most sense to investigate response to earthquakes in whale

species that use very-low-frequency sound, such as blue and fin whales.

 An animal may respond to a noise source by moving toward or away

from it. As an example, fin whales have been seen to move away from

vessels emitting seismic profiling airgun sounds; similarly, seismic profilers operating off the coast of Africa have displaced some species.

(These are obviously not natural noise sources, but they illustrate responses that could be studied using acoustic methods.) Again, data already exist from autonomous hydrophones and fixed arrays that could

be used to address these questions.

In order to address the above questions quantitatively, it would help to have

a prioritized listing including species, areas, and data sets.

Anthropogenic Noise

The topic of responses of marine mammals to anthropogenic noise is quite

large, and is being addressed by a National Research Council panel. The
Future Directions for Acoustic Marine Mammal Surveys 21

relatively brief discussion at this workshop revolved around ways in which

passive acoustics could be employed to address this topic.

One suggestion would be to use passive acoustics to quantify the noise

field—to come up with a “noise budget” for the oceans. Constructing such

a budget would necessarily be a huge undertaking, as the noise would need

to be characterized by geographic location, time, and frequency (spectrum),

and probably further by other properties such as duration of transients,

variation over time, etc. Data sets already exist for constructing such a

noise budget, but many more recordings will be needed.

As a first step toward creating such a budget, it was suggested that

all passive acoustic recordings be made using calibrated equipment (hydrophones, amplifiers, etc.). This will, at minimum, make the collected

data usable for analysis of noise budgets.

The suggestion was also made that it would help greatly to have some

device to communicate to the public what ocean noise levels are like. For

instance, this could be a graphic device like a thermometer showing averaged

noise levels. It is also necessary to communicate to the public that the ocean

is not a pristine sound environment; some level of natural sound is always

present, and manmade sounds are present much of the time. The level of

manmade sounds has been going up over the last several decades (see paper

by Rex Andrews in JASA-Online).

Many workshop participants recognized that seismic airguns emit quite

high levels of sound. For instance, seismic survey ships operating near Sable

Island, Nova Scotia dominate the sound field recorded along the Mid-Atlantic

Ridge thousands of miles away. There are alternatives to airguns (of unknown effectiveness and cost); marine vibro-seis technology was developed

in the 1970’s but has not been used widely. (Vibro-seis machines shake the

ground, delivering a vibratory signal of longer duration but much lower peak

intensity than an airgun.) If there is a large impact of airgun sounds on marine mammals, and people start asking whether there are alternatives, it

helps to have “yes” as an answer.

Discussion Topic IV. Relative Density, Seasonal Distribution,

and Trends

Jeff Laake, moderator

There is much interest in the use of “relative density” from vocalizations as

a measure of trends in abundance or to infer seasonal movement pattern.

Interpreting the number of calls or the summed intensity of calls as “relative

density” requires that the factors that affect call production and call detection be the same in the two samples being compared. In most cases, this will

not be known, and it would be extremely tenuous to make this assumption.

The work to validate the assumptions required to interpret “relative density”

is, in general, the same work that would be necessary to estimate absolute

abundance, so there is seldom a compelling reason to concentrate research

on relative density alone. The assumption that call rates are proportionate

to animal density is likely to hold up best when comparing within one season
22 Mellinger and Barlow

and geographic area, such as for breeding-related calls made on the breeding

grounds.

It was pointed out that acoustic surveys can provide additional information even when they are not able to provide unbiased estimates of density

or abundance. For example, the density of calling whales may be estimated

using a maximum estimate of calling rate and a maximum estimate of detection distances; such an estimate can be useful as a minimum estimate of

density. Surveys of vocalizing animals also can be used to define the range

of species and help define their breeding areas. Although it might be hard

to use calls to quantify movement patterns, the geographic “big picture” of

seasonal movements might be more obvious from acoustics than any other

available method.

Management needs for acoustic surveys, especially to provide better

knowledge of seasonal distribution, are shown in Table 2.
Future Directions for Acoustic Marine Mammal Surveys 23 Table 2: Management-related needs for large whale populations that could be assisted by acoustic (point source) monitoring. In some cases, positive results from such monitoring could be used to focus dedicated surveys in the areas concerned. Species Location Period Issue Notes Priority E. glacialis Unsurveyed and/or historic habitats Year-round Are these habitats still utilized? Where does much of the population go in winter? Where do non-Fundy females go in summer? In order of priority: Scotian Shelf (Roseway Basin, Emerald Basin), mid-Atlantic states, Flemish Cap, Cintra Bay, Labrador coast, Cape Farewell Ground, Hebrides, Maury distribution. High Known major habitats Seasonal What is the occurrence and distribution of whales? What is the frequency of ship traffic? Areas include Great South Channel, Roseway Basin, Bay of Fundy, Cape Cod Bay, U.S. mid-Atlantic states, southeastern U.S. High U.S. mid-Atlantic states Winter/spring Movement and locations of migrating animals Density may be low (so low call rates?) Important for ship-strike management. High E. japonica Historic habitats, eastern North Pacific Year-round Are these habitats still utilized? Where are whales at any time? Current distribution poorly known. Areas include: Bering Sea, Gulf of Alaska, Aleutians. High Historic habitats, western North Pacific Year-round Are these habitats still utilized? Where are whales at any time? Current distribution poorly known. Areas include: Kurils, Commanders, Okhotsk Sea (Sakhalin). Logistically and politically difficult. Medium M. novaeangliae U.S. mid-Atlantic states Winter Frequency of occurrence Area has high mortality and whales from at least two feeding grounds. High M. novaeangliae B. musculus B. physalus South Georgia Spring-fall Has the area been recolonized? All three species virtually extirpated in this area by whaling. Medium M. novaeangliae New Zealand Winter Ditto Ditto Medium B. musculus Japan Summer? Ditto Ditto Medium B. physalus Gibraltar Year-round? Ditto Ditto Medium B. mysticetus Spitsbergen Year-round Ditto Ditto Medium Any Any marine mammal habitat in which noisy human activity is likely in the future Year-round What is the baseline ambient noise and distribution of whales in the area? Collection of baseline data for assessment of impact of future industrial or other human activities (e.g., in lease-sale areas). High
24 Mellinger and Barlow

Recommendations (Friday, 22 November)

Discussion culminated in a set of recommendations for future research, survey methods, changes to marine mammal management policies, and changes

to field operations procedures. Within each category (e.g., within R1), these

recommendations are ordered from highest to lowest priority.

R1. Examine vocalization types as an indicator of population

identity

In some species, there are identifiable differences between vocalizations recorded in different regions. For example, blue whales worldwide have several

distinct vocalization types (e.g., Cummings and Thompson, 1971; McDonald

et al., 1995; Ljungblad et al., 1998; Stafford et al., 1999). To what degree

are such differences useful as indicators of population identity—for example,

do acoustic differences correlate well with genetic differences? If they do, it

would facilitate determining the seasonal distributions of the various populations. In a small number of cases, acoustic differences have been found to be

correlated with genetic differences; one such case is fin whales in the Mediterranean and in the North Atlantic. Some populations—for example, humpback whales breeding in different regions of the North Atlantic—evidence

genetic differences but not acoustic ones.

R1a. Literature Review Recommendation: Compile example spectrograms of diagnostic species-specific or population-specific marine mammal sounds. Spectrograms need to be made at several time scales to

ease comparison with sounds that may be observed later (and other

spectrogram parameters need to be specified). This would be a research tool rather than a field guide for casual observers.

R1b. Literature Review Recommendation: Examine the time scales

and geographic extent of vocalization types as shown by existing literature (and recordings?), with particular attention to identifiable categories that can be associated with certain species/areas (see Table 1).

Identify gaps (many of them large) in knowledge.

R1c. Management Recommendation: Use evidence of diagnostic differences in vocalizations between areas as the null hypothesis for population structure instead of thorough mixing when making management

decisions. However, lack of evidence of acoustic differences should not

necessarily be interpreted to indicate a lack of population structure.

R1d. Management Recommendation: Recognizing that acoustics may

be useful for only a subset of marine mammals, the pairing of acoustics

with other indicators of population structure should be prioritized both

by the conservation concerns and by the likelihood of success. The

latter can be assessed using available data on whether species segregate

by age and/or sex.
Future Directions for Acoustic Marine Mammal Surveys 25

R1e. Field Operations Recommendation: Researchers deploying acoustic tags should collect skin samples from tagged animals, and process

and store the samples in such a way that they can be analyzed genetically.

R1f. Field Operations Recommendation: When possible, obtain biopsy

samples from targeted species when collecting data with ship-based

acoustic systems, including towed arrays and sonobuoys.

R1g. Research Recommendation: Using the data collected from skin

samples and biopsies, investigate genetic and acoustic population structures and the relationships between them. With skin samples from

acoustic tags, differences between individuals making known vocalization can be compared; with biopsy samples, only comparisons between

populations making different vocalizations are usually possible.

R1h. Research Recommendation: Because existing data indicate that

some discrete populations mix either during migration or on feeding

grounds, it is recommended that, when practical, data should be first

collected on breeding grounds when genetic populations should be well

segregated.

R2. Include acoustic monitoring on NMFS ship-based marine

mammal surveys

R2a. Survey Recommendation: Routinely use acoustics on all NMFS

ship-based surveys.

R2b. Survey Recommendation: Use calibrated hydrophones and amplifiers for all towed hydrophones.

R2c. Survey Recommendation: Establish and document recommended

standards for the five NMFS regions for

 data collection tools and equipment (e.g., array connectors/pinouts, calibration standards),

 data collection methods (e.g., record and make static all amplifier/sample rate/filter configurations for calibration; collect data

on sound speed profiles from CTD/XBT, data on behavior, estimates of group size, noise data from other sources),

 data collection software,

 data analysis methods (e.g., estimation of bearings and ranges

to detected individuals; combination of successive locations into

tracks; estimation of detection ranges).

R2d. Survey Recommendation: Develop a protocol for integrating visual

and acoustic data from line-transect surveys (operational procedures,

data recording, analysis).
26 Mellinger and Barlow

R3. Investigate the acoustic detectability of vocalizing marine

mammals. (Separate detection distance/source levels/depth/

orientation/beam pattern/environment from vocalization

rates?)

What proportion of the time can different species of vocalizing marine mammals be detected using passive acoustics? While empirical field studies (e.g.,

Barlow and Taylor, 1998) and theoretical models (e.g., Mellinger et al.,

2002) have been used to study this question in a preliminary way, to date

no directed investigations have been done for either towed-array systems,

sonobuoys, or fixed acoustic sensors.

R3a. Research Recommendation: Study acoustic detection distance—

how far away can a calling animal be heard?—and statistical modeling

of calling and diving behavior, movement of animal and possibly of the

sensor, environmental conditions, background noise levels, etc. Studies

should be done both theoretically and empirically.

R3b. Research Recommendation: Determine the best (lowest-cost) way

to localize whales at one site with the minimum number of hydrophones

and recording devices.

R4. Study the relation between the number of vocalizations

heard (or number of animals tracked) and the number present

How can acoustic data be used to estimate the number of animals present in

a given area? One approach involves relating the number of calls received to

the number of individuals estimated by visual surveys. This method requires

estimates of calling rates, which can be derived from either acoustic tags or

joint acoustic-visual surveys. Another approach involves acoustic tracking of

individual animals; it requires estimating the proportion of individuals that

produce sound.

R4a. Research Recommendation: Use acoustic tags to estimate calling

rates of individual animals. Application of a tag to an animal should

be done independently of the animal’s acoustic behavior; in particular,

these animals should not be located acoustically.

R4b. Research Recommendation: Use joint acoustic/visual surveys to

estimate the proportion of animals that produce sound. This may vary

with season, area, year, age, and sex of the animals, behavioral state,

density of animals, and background noise, so all of these factors must

at least be recorded.

R4c. Research Recommendation: Develop ways of estimating abundance from fixed autonomous recorders.

R4d. Research Recommendation: Develop and investigate statistical

models for estimating detection probability from joint visual and acoustic surveys. Evaluate relationships between surfacing and calling from

acoustic tag data.
Future Directions for Acoustic Marine Mammal Surveys 27

R4e. Research Recommendation: Develop and evaluate methods for

estimating group size from acoustic data. Where practical, deploy a

second array in vicinity of large groups to enable precise tracking of

individuals in groups.

R5. Use autonomous acoustic recorders to monitor trends in

abundance

Although several researchers (e.g., Fox, Clark, Hildebrand, Moore) have deployed autonomous acoustic recorders for gathering data about cetacean

occurrence, NMFS has yet to deploy these instruments systematically.

R5a. Research Recommendation: Pick areas in which some species of interest occur (see Table 2), make several successive 1-year deployments

of arrays of recorders, and analyze the results for trends in number of

vocalizing animals or the number of vocalizations detected. Knowledge

of acoustic detection distances is a prerequisite to estimating trends in

abundance.

R5b. Field Operations Recommendation: Use calibrated hydrophones

for all deployments. Re-calibrate regularly.

R5c. Recommendation: Share and compare information on automatic

signal detectors. Published descriptions of detectors should be as explicit as possible.

R6. Fill in gaps in knowledge about unknown sound types

and unknown cetacean populations

R6a. Field Operations Recommendation: Collect acoustic and visual

data in such a way that definitive identification of animal(s) making

unknown or poorly-known vocalizations is possible. (Primarily this

means that visual observers need to record animal location as frequently as possible.)

R6b. Literature Review and Research Recommendation: Determine

the significant gaps in knowledge about distribution and seasonality of

marine mammal populations; go to suspected or likely locations and

obtain recordings. Conversely, investigate some of the unknown sounds

that are recorded.

R7. Study responses of marine mammals to natural noise

Marine mammal species may respond acoustically to natural noise sources,

including wind/wave noise, earthquakes, and sounds from conspecifics. They

might, for instance, increase or decrease the rate or intensity of their vocalization. Existing data sets, principally from cabled arrays and autonomous

recorders, could be used to investigate these responses.
28 Mellinger and Barlow

R7a. Literature Review Recommendation: Develop a list of species,

existing data sets, and geographic areas in which responses to natural

noise could be investigated.

R7b. Research Recommendation: Choose one or more items from this

list and do the study.

R8. Support efforts to quantify the noise field

Recognizing that ambient noise is an important part of marine mammal

environment and is an essential component of assessing marine mammals by

acoustic methods....

R8a. Management Recommendation: Support efforts to map ambient

noise fields throughout the world.

R9. Assess the effects of seismic airgun surveys and mitigation

measures on marine mammals

The International Association of Geophysical Contractors (IAGC) and Minerals Management Service are looking for research recommendations on reducing the potentially harmful effects of airgun emissions (which may be

funded by oil companies).

R9a. Research Program Recommendation: Assess the potentially harmful effects of airgun emissions on marine mammal populations.

R9b. Recommendation: Contribute to monitoring the effects of mitigation measures on ambient noise levels.
Future Directions for Acoustic Marine Mammal Surveys 29

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Future Directions for Acoustic Marine Mammal Surveys 31

Appendix A: Distance Sampling and Marine

Mammal Acoustic Surveys

Jeff Laake

Estimation of animal abundance or density, in its simplest form, requires

correctly counting the number of animals in a sample region of known size.

For example, n animals could be counted within a strip of length L and

width 2w and the density (D) for this strip transect sample would be

D = n

2wL

Typically, the effectiveness of methods to detect animals, whether they

are visual, auditory, or otherwise, declines as the distance between the animal

and receiver (e.g., observer, acoustic receiver, etc.) increases. Thus, if an

observer traversed the rectangular region by traveling down the centerline

and could not detect all animals within a lateral (perpendicular) distance of

w, animals would be missed and the density estimator would be negatively

biased. One option would be to make the strip more narrow such that no

animals were missed. However, this would exclude many potentially useful

observations detected beyond the strip boundary and would require a strip

that was sufficiently narrow such that the assumption of perfect detection

was satisfied for all conditions that would be encountered.

A more complete use of the data is accomplished with distance sampling

(line and point) (Buckland et al., 2001) which originated with visual surveys

of animals but has been extended into numerous other applications (e.g.,

sonar, underwater video) due to the generality of the underlying concept.

The fundamental construct of distance sampling is the detection function,

g(x), which is the probability of detecting (e.g., visual or auditory) an animal

that is at a lateral (perpendicular) distance x from the centerline or at a

radial distance x from a point (e.g., sonobuoy). If g(0) = 1 (all animals on

the line or at the point close to the receiver are detected), lines or points are

selected independent of the animal distribution and animals do not move

prior to detection, then the expected proportion of animals detected within

a strip is

p =

 w

0 g(x)dx

w

and the abundance estimator is

D = n/p

2wL.

Likewise, for point (circular) samples,

p =

 w

0 xg(x)dx

w2
32 Mellinger and Barlow

and for k points the abundance estimator is

D = n/p

kπw2 .

Acoustic (auditory) sampling is often used in bird sampling, and in forest

habitats it is the primary mechanism for locating birds that are not visible

or difficult to see. Thus, it is quite natural to consider applying distance

sampling to acoustic surveys of marine mammals or joint acoustic and visual surveys. The acoustic and visual sampling methods are complementary

because marine mammals are available for acoustic sampling when they vocalize and are not visible beneath the surface and they are available for visual

sampling when they are at the surface and they are not vocalizing.

Standard distance sampling is only unbiased if all marine mammals on

the line or at the point are detected (g(0) = 1). In visual surveys, marine

mammals are detected if they are at the surface (available) when in view of

the observer and they are observed (perceived) and identified by the observer.

In acoustic surveys, marine mammals are detected if they vocalize (available)

and the vocalization is within the detection range of the acoustic receiver

(perceived) and identified based on its vocalization. Thus, it is unlikely that

g(0) = 1 for either method for many marine mammals and large whales in

particular. The expected value for the abundance estimator is g(0)D, which

is negatively biased unless g(0) = 1.

Several alternatives are possible to remove or minimize the bias due to

g(0) < 1. One approach used with visual surveys is to develop an estimate of g(0) based on a model for availability (e.g., surfacing interval) and

the observation process (Barlow, 1999) or incorporating surfacing interval

data within an estimation model from the observed data (Schweder, 1999).

Similar approaches could be used with acoustic surveys if data on the vocalization process were available. These approaches assume that the externally

derived process data (e.g., surfacing interval) applies to the survey data that

are typically collected at a different time and place. Another approach that

avoids that assumption uses survey data collected from “independent observers” (IO) during the course of the survey (Buckland and Turnock, 1992;

Borchers et al., 1998; Laake, 1999). The independent observers can be on the

same survey platform (e.g., ship or plane) or on different platforms (e.g., one

on a ship and the other on a helicopter in front of the ship). The analysis

is a form of mark-recapture (sighting and re-sighting) and requires knowing which observations are detected by both observers or that assessment

must be incorporated into the likelihood (Hiby and Lovell, 1998). If the

timing for the observations is nearly coincident (e.g., two observers in the

same aircraft) then the IO method will not correct for “availability bias”

(e.g., whales beneath the surface) but can correct for reductions in g(0) due

to “perception bias” (e.g., visible whales that are missed) as long as there

is a non-zero probability that one of the observers can detect every whale.

In some situations (e.g., high Beaufort states) it is not possible to correct

entirely for “perception bias” because neither observer has a non-zero probability of detection and the estimator will remain negatively biased under

those circumstances. If observers are in separate platforms that survey se-
Future Directions for Acoustic Marine Mammal Surveys 33

quentially and separated sufficiently in time (Buckland and Turnock, 1992;

Laake et al., 1997; Hiby and Lovell, 1998; Carretta et al., 1998), both “availability” and “perception” bias can be eliminated. Similar approaches could

be used with “independent” acoustic surveys, but a better approach would

be to combine visual and acoustic surveys as the “independent” sampling

methods. A joint visual/acoustic survey would enable estimation of g(0) for

both methods as long as the availability processes (surfacing and vocalizing) were independent. In general for two sampling methods, the expected

value of the conditional probability of detection of one method (1) given an

observation from another (2) can be expressed as:

E[Pr(detected by 1 | detected by 2)]

= cov[Pr(detected by 1), Pr(detected by 2)]

p2

+ p1

If the process covariance is 0, the correct answer (p1) is obtained. If the covariance is positive, detection probability will be over-estimated and abundance will be negatively biased. But, if the covariance is negative, abundance will be positively biased. When the same survey method is used for

both “independent” observers the covariance is typically positive because

what affects the visibility for one observer affects the other in the same way.

However, with visual and acoustic sampling methods the covariance is not

necessarily positive and may be negative depending on the surfacing and

vocalizing processes. If whales vocalize at depth and vocalizing whales are

unlikely to be at the surface within the field of view of the visual observer

and surfacing whales were unlikely to vocalize within the range of the receiver, the processes would be negatively correlated and abundance would be

positively biased, possibly severely so. A better understanding of the relationship between surfacing and vocalization is needed before any confidence

is placed in g(0) estimates derived from joint visual and acoustic sampling.

An alternative approach for a joint visual/acoustic survey is to pool the

unique observations from the sampling methods. This will reduce but not

eliminate the bias due to g(0) < 1. If gv(0) and ga(0) are the g(0) values

for the visual and acoustic methods, respectively, then g(0) for the pooled

data would be bounded between max [gv(0), ga(0)] and 1. The former would

occur if the observations from one method were a subset of the other and

the latter could occur if there was no overlap between the observations of

the two methods.

Barlow, J. (1999): Trackline detection probability for long-diving whales. Marine

Mammal Survey and Assessment Methods, Rotterdam, A.A. Balkema, 209–221.

Borchers, D.L., W. Zucchini, and R.M. Fewster (1998): Mark-recapture models for

line transect surveys. Biometrics, 54(4), 1207–1220.

Buckland, S.T., and B.J. Turnock (1992): A robust line transect method. Biometrics 48(3), 901–909.

Buckland, S.T., D.R. Anderson, K.P. Burnham, and J.L. Laake (2001): Introduction to Distance Sampling: Estimating Abundance of Biological Populations.

Oxford, Oxford University Press, [i]-xv + 432 pp.

Carretta, J.V., K.A. Forney, and J.L. Laake (1998): Abundance of southern Cali-
34 Mellinger and Barlow

fornia coastal bottlenose dolphins estimated from tandem aerial surveys. Mar.

Mamm. Sci., 14(4), 655–675.

Hiby, L., and P. Lovell (1998): Using aircraft in tandem formation to estimate

abundance of harbour porpoise. Biometrics 54(4), 1280–1289.

Laake, J.L., J. Calambokidis, S.D. Osmek, and D.J. Rugh (1997): Probability

of detecting harbor porpoise from aerial surveys: Estimating g(0). J. Wildl.

Manage., 61(1), 63–75.

Laake, J. (1999): Distance sampling with independent observers: Reducing bias

from heterogeneity by weakening the conditional independence assumption.

Marine Mammal Survey and Assessment Methods, Rotterdam, A.A. Balkema,

137–148.

Schweder, T. (1999): Line transecting with difficulties; lessons from surveying minke

whales. Marine Mammal Survey and Assessment Methods, Rotterdam, A.A.

Balkema, 149–166.
Future Directions for Acoustic Marine Mammal Surveys 35

Appendix B: Cetacean Detection and Assessment

via Passive Acoustics

Sue E. Moore

Abstract

From 1999 through 2002, the National Marine Mammal Laboratory (NMML)

conducted collaborative projects focused on the advancement of passive

acoustics for detection of large whales. The NMML focused its efforts on

long-term deployments of autonomous recording packages (ARPs) for detection of large whales in Alaskan waters. Four ARPs were deployed in the

eastern Bering Sea in October 2000 to monitor waters where critically endangered North Pacific right whales (Eubalaena japonica) have been seen

each July since 1996. Two other recorders, fabricated by NOAA/PMEL,

were deployed southeast of Kodiak Island near an area where one North

Pacific right whale was seen in July 1998. In addition, NMML collaborated

with researchers using the U.S. Navy’s SOund SUrveillance System (SOSUS)

assets to locate blue whales in the North Pacific to conduct a provisional seasonal habitat analysis by integrating the call location data with bathymetry

and remotely sensed data (i.e., sea surface temperature (SST), chlorophyl

a, altimetry) using a geographic information system (GIS). Results of these

analysis were presented at the 13th Biennial Marine Mammal Conference in

2000 and subsequently published in Oceanography, 15(3) 2001.

Introduction

Since 1999, the National Marine Mammal Laboratory has collaborated with

scientists at the NOAA Pacific Marine Environmental Laboratory (PMEL)

and Oregon State University (OSU) in Newport, OR, Scripps Institution of

Oceanography (SIO), La Jolla, CA, and Woods Hole Oceanographic Institution (WHOI), Woods Hole, MA, and to leverage their expertise in underwater acoustic techniques and analysis. The focus of acoustic studies at

NMML was on long-term deployment of autonomous acoustic recorders to

monitor the SE Bering Sea and waters offshore Kodiak Island for mysticete

whale (especially, North Pacific right whale) calls.

North Pacific right whales were a species of particular focus due to their

status as a critically endangered species and the on-going photo-identification

studies conducted by the Southwest Fisheries Science Center (SWFSC) in

the eastern Bering Sea. The sighting of a lone right whale among humpback

whales southeast of Kodiak Island in 1998 provided impetus for placement

of two recorders there also. In addition, NMML was able to collaborate on

an on-going acoustic study of blue whales in the North Pacific basin using

the U.S. Navy’s SOSUS, and to augment that work though application of

GIS technology. A brief synopsis of each collaborative project is provided

below.
36 Mellinger and Barlow

Acoustic Monitoring for Right Whales in the Eastern Bering

Sea: Collaboration with SIO

Four autonomous recorders were deployed on 1 October 2000 in the eastern

Bering Sea at locations where SWFSC researchers have photographed North

Pacific right whales (Eubalaena japonica) during aerial surveys each July

since 1998 (Fig. 1: NMML/SIO). The ARPs sample acoustic data at 500

Hz and have 36 Gbytes of data storage capacity. Two of the four ARPs were

recovered and two replacement recorders deployed in late August 2001. Of

necessity, this was a particularly shallow-water deployment (∼70 m) and it

was uncertain if storms or drag by fishing gear had caused the “loss” of two of

the instruments. Subsequently, both “lost instruments” were recovered; one

on the beach at Nelson Lagoon (Alaska Peninsula) and one by a fisherman

working near the IDL in the central Bering Sea. So, although 2 ARPs were

recovered in an unconventional way, data from four instruments are now

available for analysis. Data analysis is ongoing, via contract to Dr. Mark

McDonald, and SIO graduate student Lisa Munger (under the direction of

Dr. John Hildebrand). Dr. McDonald is using calls recorded from North

Pacific right whales in 1999 (McDonald and Moore, 2002) to aid in the

detection and enumeration of recorded calls.

North Pacific Right Whales in the Gulf of Alaska: Collaboration with NOAA/PMEL

After a North Pacific right whale was sighted off Kodiak Island in July 1998,

an acoustic search for right whales was conducted (Waite et al., 2002). In

May 2000, an autonomous recorder, similar to instruments used by PMEL

for seismicity detection (Fox et al., 2001), was placed on the seafloor at the

location of the sighting, 57◦ 08.20

N and 151◦ 51.00W. A second recorder

was deployed farther offshore to listen for right whales and to complement a

broad array of six recorders deployed in the Gulf of Alaska by PMEL (Fig.

1: NMML/PMEL). The first instrument was recovered in early September

2000, but sea conditions have thus far prevented recovery of the second

recorder. The first instrument recorded sound continuously to a magnetic

disk from 26 May to 11 September 2000. After recovery of the instrument,

all sounds that could potentially be right whale calls were detected by a

computer. This was done by measuring energy in the frequency band of

right whale calls, 50 Hz to 400 Hz. Whenever the total energy was above

the background noise level for at least 0.6 sec (so short thumps and clicks

would not be detected), but not more than 3 sec (so long tones would not

be detected), the sound was extracted and saved as a separate sound file.

A total of 10,729 potential right whale sounds were detected and extracted using this method. Next, a spectrogram of each sound file was examined visually to determine whether it was similar to other up-type calls

that have been recorded from North Pacific right whales (McDonald and

Moore, in press). Upon examination, 6,364 (59%) were found to be humpback whale (Megaptera novaeangliae) sounds, with most of the rest being

various sounds from fish and other, unknown sources. A few sounds were
Future Directions for Acoustic Marine Mammal Surveys 37

0 300 600 km

NMML/PMEL

NMML/SIO

PMEL

Gulf of

Alaska

Alaska

Bering

Sea

160° 150° 140°

55°

60°

50°

Figure 1: Locations of autonomous acoustic recorders deployed to monitor areas for North Pacific right

whale (and other mysticete whale) calls in the eastern Bering Sea (NMML/SIO) and in the northern Gulf

of Alaska (NMML/PMEL). The two recorders in the Gulf of Alaska complement six recorders deployed by

PMEL to monitor deep-water areas for blue whales.

somewhat similar to right whale calls but could not be identified with certainty because some of the calls made by humpbacks that summer were very

similar to right whale up-type calls. This made it difficult to determine with

certainty what species produced these calls—especially since the right whale

seen in 1998 was among humpbacks. Improvements to the algorithm used

to detect right whale calls in 2001, resulted in 10s of calls, recorded during the last week of deployment being identified as being from right whales.

While calls were few, it is cause to re-double efforts to find right whales near

Kodiak Island, a former “key” whaling ground for the species.

Blue Whales in the Northwest Pacific Ocean: Collaboration

with WHOI

Dr. Bill Watkins at WHOI heads an on-going study (since 1995) of mysticete

whale calls in the North Pacific, based upon SOSUS signal reception at the

U.S. Navy NAVFAC/Whidbey Island (Watkins et al., 2000a, b). In FY00,

NMML contracted with GIS-analyst Jeremy Davies to construct call-maps

for blue whales in the North Pacific and collate call location and seasonal
38 Mellinger and Barlow

occurrence with bathymetry and remotely sensed data (e.g., SST, chlorophyl

a). Preliminary results of this analysis were first provided in an oral presentation at the 13th Biennial Marine Mammal Conference, December 1999,

with final results presented in Oceanography (Moore et al., 2002). Here, the

focus was on blue whale call detection in the Northwestern Pacific, an area

of the ocean virtually unsurveyed for large whales since the era of commercial whaling. The strong seasonal signal of blue whale calling corresponds

with seasonal changes in SST and chlorophyl a, although it is the association

with ocean height (altimetry) and eddys that appear the strongest. This paper is designed to augment an earlier presentation of seasonal occurrence of

blue, fin, and humpback whales in the North Pacific, as derived by SOSUS

reception of calls (Watkins et al., 2000a).

Fox C.G., H. Matsumoto, and T.A. Lau (2001): Monitoring Pacific Ocean seismicity

from an autonomous hydrophone array. J. Geophys. Res., 106, 4183–4206.

McDonald, M.A., and S.E. Moore (2002): Calls recorded from North Pacific right

whales in the Eastern Bering Sea. J. Cetacean Res. Manage., 4(3), in press.

Moore, S.E., W.A. Watkins, J.R. Davies, M.A. Daher, and M.E. Dahlheim (2002):

Blue whale habitats in the Northwest Pacific: analysis of remotely-sensed data

using a Geographic Information System. Oceanography, 15(3), 20–25.

Waite, J.M., K. Wynne, and D.K. Mellinger (2003): Documented sighting of a North

Pacific right whale in the Gulf of Alaska and post-sighting acoustic monitoring.

Northwestern Naturalist, to appear.

Watkins, W.E., MA. Daher, G.M. Reppucci, J.E. George, D.L Martin, N.A. DiMarzio, and D.P. Gannon (2000a): Seasonality and distribution of whale calls

in the North Pacific. Oceanography, 13, 62–67.

Watkins, W.E., J.E. George, M.A. Daher, K. Mullin, D.L. Martin, S.H. Haga, and

N.A. DiMarzio (2000b):. Whale call data for the North Pacific November 1995

through July 1999: Occurrence of calling whales and source locations from

SOSUS and other acoustic systems. WHOI-00-02, 160 pp.
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7600 Sand Point Way NE

Seattle, WA 98115