.\
This paper not to be cited without prior reference to the author
ICES C.M. 1993/N:16
Marine Mammals Committee
Ref. B,D,G,H,J,K
International Council for
the Exploration of the Sea
SPATIAL PATTERNS OF SIX CETACEANS ALONG A LINEAR HABITAT
•
Gordon T. Waring
National Marine Fisheries Service
Northeast Fisheries Science Center
Woods Hole, MA 02543
ABSTRACT
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Results of a summer 1991 fine-scale survey of shelf edge waters
(200m to 2000m isobaths) off the northeastern USA indicate
latitudinal changes in small cetacean distribution. Sighting
rates (herds/km) for pilot whales (n=52), and common dolphins
(n=40) were higher east of Hudson Canyon, whereas sighting rates
for bottlenose (n=35), Risso's (n=15), striped (n=4), and spotted
dolphins (n=4) were higher west of this canyon area. Although,
contrary to observer's impressions, sighting rates were not
significantly different (P<0.05) between the two regions.
INTRODUCTION
Cetacean distribution along bathyrnetric features is generally
associated with spatial and temporal patterns in prey abundance
(Gaskin, 1985; Hui, 1985; Kenney and Winn, 1986; Kenney and Winn,
1987; Payne et al., 1986).
Studies conducted along continental
shelf margins off the united States have indicated that these
features form extensive linear high use cetacean habitats (CETAP,
1982; Hain et al., 1985; Mullin et al., 1991; Green et al.,
1992).
Off the U.S. east coast, this linear habitat is
characterized by numerous submarine canyons (Emery and Uchupi,
1972), and shelf- slope water characteristics are occasionally
influenced by Gulf Stream features (Olson and Backus, 1985;
Cornillon, 1985).
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Multiple seasonal surveys conducted from i979~1981 across the.
riertheast U.S~ contiriental shelf indicate cetacean distribution
patterns 'and density in slielf edge waters ~re highly varia1;>le "
(CETAP, 1982jKenney and winn, 1987)~ Seasonal patterns l~kely
reflect broadscale changes in prey migratioriarid environment.
coriditioris, although ephemeral events are also.important (CETAP,
1982; Waring et al.; 1993)~
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This paper.examines spatial patternsand observer's perceptions
of "a6tive" areas for pilot whales (Globicephala sp.), common
dolphins (Delphinus delphis), bottlenose dolphins (Tursiops.
truncatus), Risso's dolphins' (Grampus.griseus), spotteddolphins
(stenella frontalis),and stripeddolphins (5. coeruleoalba)based
ori a 1991 summer shelf edge shipboard survey~ Observer's views
of cetacean activity are meaningful, since they typi6ally become
part of the referenced anecdotal data base. ,Therefore, these,
perceptions should be examined using analytical
methods.
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METHODS
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During, June 8,to July 16, 1991, the National.oceanic arid
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Atmosplieric Administration (NOAA) 34-m leng
fisheries research
vessel RjV CHAPMAN was used to, coridtict a marine mammal sighting
survey, in shelf edge and offshore waters along the northeastern
U~S. coast (Waring et' al., 1992) •. This paper orlly, considers,
data collected iri transe6ts conducted.principally along theshelf
edge (200 - 2,000 m) waters (Figure 1).;
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The three legs of the surveyöccurred f':rom Cape' Hatteras to ..
HUdsori canyon region, oceanographer Canyon to waters south of
Cape Cod (70 0 20' W)i and Lydoriia canyon to-Northeast Channel(Figure 1). :A predetermiried ladder type cruise track was'
followed, although s6mesurvey, areas were not covered due t6
.military closures, .weather problems; and reprovisioning schedule.
These factors resulted in several,gaps in survey effort,
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particularly off the Delmarva region and between eastern Long,
Island and Cape Cod (Figure 1):
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Vessel speed under normal searching conditioris was 9~5-10.5kin~
Marine mammal sightings were collected daily between. 0700 arid"
1900
hr; .
conditions
permitting;
using
standard line transect 1' .
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procedures . (Burnham; Anderson, and Laake, 1980);
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The s~ght~ng team.cons~sted of three observers, (port,. center,· and.
starboard) that searched from the catwalkof the pilot house '(eye
height about 6m 'above sea level); Individuals,were randomly
.
assigried to.each position atthe" start 'of each day. observcrs
maintained45 min watchcswith a 15 min rest period and15.min
data recordirig period .. positions ware rotated avery, 15 min; ':.
Primary searchingwas donc with thc na~ed"cyci but 7X50
e
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binoculars wer~ used to confirmiriitial sightings,. and for.
determining species identification, group size, and swimmirig
direction. Visual estimates were made of the radial distance to
each sighing. Sighting angle was determined using apelorus that
was mounted at each observer station.
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M~an sighting ~ates (herds/km) for:each species withiri two shelf
edge regions were compared using a. t-test (Zar, 1974)., Region 1
was from Cape Hatteras.to Hudson Canyoni and region 2 was waters
east of Hudson Canyon. ,Areal partitioning wasbased on a major
break ~oint in·survey effort, and 6bserver's perceptionsof "lo~"
small cetaceanactivity in the moresouthern.region. Observers's
perceptions were revealed during informal scientific team
meetings. '
RESULTS
Survey transects covered 2,774kmof shelf edge waters,_
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principallY.200 to 2,000 m, from,capc Hatteras,to Georges Bank.
Forty-four transects covering 1,184.km (43%) were conducted in
the region betwecn Cape Hatteras and Hudson Canyon (i.e., west of
72° 00 W).' East of Hudson canyon, 54 transects (1,590 km, 57%)
, were made. "
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A total of 150 sightings of 6 small cetaceans were made, with 94
percent of the sightings made in sea state of Beaufort 3 or'less
(Table 1) ~ "pilot, whales were the most frequently sighted species
(35%); Commori dolphins, bottlenose dolphins"Risso's dolphins, ,
respectively comprised.27%, '23%, and 10% of these sightings~ The
number of spotted dolphins; and striped dolphins sightirigswere
low, each about3 %.
"
Distribution
pilot whale.shelf-edge' sightings west of HUdson canyon were
concentrated off Cape Hatteras (Figure 2a). 'East of Hudson, ,
animals.were clustered betweeri Hydrographer and Lydortia canyons;
and GeorgesaridCorsair Canyons along the southern edge of-_
Ge6rges_Bank~ Few sightings were,made in shelf edge waters north
of Cape Hatteras to southwester!1 Georges Bank (Figure 2a)~
Overali; the'distribution of cominon dolphin sightings (Figure 2b)
was similar to pilot whales, a.lthough, common dolphins were
sighted around Hudson Canyon. 'Further; common dolphin sightings
generally bracketed pilot whale sightings alorig the southern edge
of Georges Bank.
Bottlenose dolphin sightings were conccntra.ted near Cape Hatteras
and in Hudson canyori; and to a.lesser extent along the'southern"
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edge of Georges Bank (Figura 3a). Few dightings were made
between Cape Hatteras and' Hudson' canyon.;,
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Sightings of Risso's, or Grampus dolphins, were clustered in and
to the west of Hudson Canyon (Figure 3b);.· No sightings .were made
off Cape Hatteras and between Ihidson and Oceanographer Canyons.
Further, sightings along Georges Bank were more restricted
compared to pilot whales and common dolphins~
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spotted and striped dolphins were only sighted between Cape,;
Hatteras arid Hudson canyon (Figures 4a, !4b) ~ .. In addition; . the
riorthern and southern extent of spotted land striped dolphin
sightings, respectively, overlapped near Baltimore canyon.
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sighting rates
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Overall meari sighting rates for six cetaceans in both regions
were very low; ranging from o,to 0.300herds/km, and standard'
errors were large (>27%) (Table 2).
Mean sighting rates for
bottlenose,Risso's, spotted,and stripcid dolphins were higher in
region 1, whereas rates forpilot whales and common dolphins were
higher east of Hudson Canyon. Mean siglitirig rates between,the '
two regions, however ware not sigriificantly'different
(P <0.05).
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DISCUSSION
Distribution of·six small cetaceans alorig shelf edge waters were
generally similar to those reported by CETAP (1982). Althougli,
general spatial gaps in small cetacean distribution observed in
this studY,are not evident in CETAP composite maps.Thesegaps
are partially attributable to survey constraints (i.e: areal :
closures, weather coriditions, and'port calls), that prevented .
sampling along all proposed transect lines. Cetacean
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aggregations in tlie, three disparate regions (i.e~, ,Cape Hatteras,
Hudson Canyon, and Georges Bank) are likely related to prey
abundance, enhanced by oceanographic conditions. Tha Gulf. Stream
bordars the·shelf adga off ,Capa Hatteras, a warm core ring was
adjacent to Hudson Canyon during thesurvey period, and'the
southerri edge ofGeorges Bank is delineated bya series'of
'
Canyons (Emery and Uchupi;' 1972;. Cornillon, 1985; wäring et al;,
1993)~
Further, pilot whale and bottlenose dolphin stock
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structures may have contributed to patterns observed for ,these
species.'· sightings near Cape Hatteras.may'comprise short-finned
pilot whales Globicephala macrorhynchyus, and thc nearshore form
of b6ttlenose dolphins (Leatherwood et ~l~, 1976i Kenney;. 199~);
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Contrary to observer's impressions, sighting rates for six small
cetaceans.were not significantly different between two'portions
of the study area. Their conceptof catacean active areas are.
likely biased by several factors including survey course, weather
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days, sighting cvcnts, cctaccan bchavior, etc.
For, exarnple, the
survcy began off Cape Hatteras andcndcd on Georgcs·bank, areal
closures,orily occurred south of Hudsoncanyon, and animals were
frcqucntly associated with numcrou~ fixcd ge~r marke~s on Georges
Bank. Overall, obscrver's views are important, because they
typicallYbccomc part of thc referenced anecdotal data base.'
Forexample, contrary. to results,of an informal poll,ef marine
mammal researchers, Kenney and Winn (1987) did not di~cern);my
significant difference'in cetacean biomass between canyon and
intercariyon areas along the northeastshelf. Thcrcfore, whcn
possible these impressions should be considcred in post~ survcy
data analysis.
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REFERENCES
Burnham, K.P., D.R. Anderson and J.L. Laakc~ i980~ Estimation of
density from line transect sampling of biological
popula~ions. Wildf. Monog. 72:1-202.
CETAP. 1982.A characterization of marine mammals and turtles in
the mid-. and north-Atlantic areas of the ,U. S. outer ,
,',.
continental' ShEÜf. Final Report ofthe Cetaceari arid Turtle
Assessment Program, Bureau of Land Management, Contract No.
AA551-CT~48, U~S.Dept; Int., washirigton D.C., USA. 450 pp.'
•
cornillon; P. 1985~ , Gulf' stream envelope arid mean path between
, 75° Wand 58° W. In: Gulf streamWorkshop proceedings, help
23-26 April 1985 at the Graduate School of oceanography;
Univcrsity of Rhode Island, Kingston RI~ 548 pp.
.
.
,
Emery, K.O. ·and E; Uchupi. 1972. western North Atlantic ocean
topography rocks, structure, water life and sediments., '
Am. Assoe. Pet~· and Geol. Mem. '17: 1-532 ~
.
Gaskin, h.E. 1985. Thc ecology of whales an~ dOlphins. ,
Heinemann, London and Portsmouth, New Hampstiire. 459 pp.
Green; G.A., J~J. Brueggeman,.c.E. Bowlby, R.A. Grotefendt, M;L.
Bonnell, ,and K.T. Balcomb, III. 1991. Cetacean distribution
and abundance off oregon and Washington, '1989-1990~ Final
Report, OCS Study MMS 91-0093. U.S. Dcpt~ Int., Min.
Mangt~ Ser., Pacific OCS Region, Los Angeles, CA. 100 pp.
Hain, J.H.W., M.A.M. Hirnan; R~D. Kenney and H.E~ Wirin. 1985. Tbc
role of cetaceans in the shelf-cdge region of the
riortheastcrn uriitcd Statcs. Mar; Fish. Rcv~ 47:13-17;
Hui, C~A. 1985~ Undcrsca topography and thc comparativc
distributions of two pclagic cetaceans. Fish. Bull.' (U.S.)
83:472-475.
.
}
6
Kenney, R.D. 1990. The bottlenose dolphins off the northeastern
United states. In: The Bottlenose Dolphin, (S. Leatherwood
and R.R. Reeves, eds., Academic Press, Inc., San Diego, CA.
653 pp.
Kenney, R.D. and H.E. Winn. 1986. Cetacean high-use habitats of
the northeast united States continental shelf. Fish. Bull.
(U.S.) 84:345-357.
Kenney, R.D. and H.E. Winn. 1987. Cetacean biomass densities near
submarine canyons compared to adjacent shelf/slope areas.
Cont. Shelf Res. 7:107-114.
Mullin, K., W. Hoggard, C. Roden, R. Lohoefener, C. Rogers and B.
Taggart. 1991. Cetaceans on the upper continental slope in
the North-Central Gulf of Mexico. oes Study/MMS 91-0027.
U.S. Dept. Int., Min. Mangt. Sero Gulf of Mexico oes
Regional Office, New Orleans, LA. 108 pp.
•
Olson, D.B. and R.H. Backus. 1985. The concentrating of organisms
at fronts: A cold-water fish and a warm-core Gulf Stream
ring. J. Mar. Res., 43:113-137.
Payne, P.M., J.R. Nicolas, L. O'Brien and K.D. Powers. 1986. The
distribution of the humpback whale, Megaptera novaeangliae,
in Georges Bank and in the Gulf of Maine in relation to
densities of the sand eel, Ammodytes americanus. Fish. Bull.
(U.S.) 84:271-277.
Waring, G.T., C.P. Fairfield, C.M. Ruhsam and M. Sano. 1993.
Sperm whales associated with Gulf Stream features off the
north-eastern USA shelf. Fish. Ocean., 2:2, 101-105.
•
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Table 1.
Number of six small cetaceans sighted by Beaufort scale
during R/V CHAPMAN 1991 Marine Mammal Survey.
Beaufort
Species
--------------------------------------------0
1
2
3
4
5+
Total
0
2
0
0
-0
0
10
16
2
0
1
15
10
9
3
1
21
12
12
3
0
1
15
3
0
1
0
1
1
0
2
0
1
0
0
35
40
15
4
4
52
2
44
52
43
6
3
150
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e
Bottlenose dolphins
Common dolphins
Risso's dolphins
Spotted dolphins
striped dolphins
pilot whales
Total
Table 2.
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Mean sighting rates (herds/km) for six small cetaceans
from R/V CHAPMAN 1991 Marine Mammal Survey.
Species
Bottlenose dolphins
Common dolphins
Risso's dolphins
Spotted dolphins
striped dolphins
pilot whales
West of 72° OO'W
Mean
SE
0.030
0.012
0.008
0.002
0.002
0.014
0.013
0.007
0.003
0.002
0.001
0.008
East of 72°00'W
Mean
SE
0.010
0.026
0.002
0
0.001
0.018
0.003
0.007
0.001
0
0.001
0.005
n = 44 and 54 transects, respectively west of 72° 00' W and east
of 72° OO'W
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1991 R/V OlAPMAN Transea Lincs
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NO =Norfolk
BA = Bdtimcxc.
WI
=WiI.m.i.D.ttoo
I-IU =HudsOD
IN = H)'dn'onrber
LY = L)'dooia
CO=COfS:I.ir
Figure 7. Distribution of R/V Chapman 1991 Marine Mammal survey
transect lines.
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+44
2b
Commoo dolphins
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+
42
Figures 2a, 2b. Distribution of all on effort pilot whale (top) and common
dolphin sightings du ring R/V Chapman 1991 Marine Mammal survey.
10
+44
3a
BoaJcnose dolphios
+
42
•
+44
3b
Risso's dnlphins
+
•
42
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Figur s 3a, 3b. Di tribution of all on ffort bottlenose dolphin (top)
and Risso's dolphin sightings during R/V Chapman 1991 Marine Mammal Survey.
4
,
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11
4a
+44
Spolted dolphins
+
42
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4b
+44
Slriped dolphins
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+ 42
A(
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Figures 4a, 4b.
Distribution of all on effort spotted dolphin(top) and striped
dolphin sightings during R. V. Chapman 1991 Marine Mammal survey.