219 
Abstract— Surveys were conducted in 
the northern Gulf of Mexico during the 
spring seasons of 1992, 1993, and 1994 
to determine the distribution, abun- 
dance, and habitat preferences of oce- 
anic cetaceans. The distributions of 
bottlenose dolphins ( Tursiops trunca- 
tus ), Risso’s dolphins ( Grampus griseus ), 
Kogia spp. (pygmy [Kogia breviceps] 
and dwarf sperm whales [ Kogia s/mo]), 
pantropical spotted dolphins (Stenella 
attenuata ), and sperm whales ( Physe - 
ter maerocephalus)'were examined with 
respect to depth, depth gradient, surface 
temperature, surface temperature vari- 
ability, the depth of the 15°C isotherm, 
surface chlorophyll concentration, and 
epipelagic zooplankton biomass. Bottle- 
nose dolphins were encountered in two 
distinct regions: the shallow continen- 
tal shelf (0-150 m) and just seaward 
of the shelf break (200-750 m). Within 
both of these depth strata, bottlenose 
dolphins were sighted more frequently 
than expected in regions of high sur- 
face temperature variability which sug- 
gests an association with ocean fronts. 
Risso’s dolphins were encountered over 
the steeper sections of the upper con- 
tinental slope (200-1000 m), whereas 
the Kogia spp. were sighted more fre- 
quently in waters of the upper conti- 
nental slope that had high zooplankton 
biomass. The pantropical spotted dol- 
phin and sperm whale were similarly 
distributed over the lower continental 
slope and deep Gulf (>1000 m), but 
sperm whales were generally absent 
from anticyclonic oceanographic fea- 
tures (e.g. the Loop Current, warm-core 
eddies) characterized by deep occur- 
rences of the 15°C isotherm. Habitat 
partitioning, high-use areas, species 
accounts, environmental sampling lim- 
itations, and directions for future hab- 
itat work in the Gulf of Mexico are 
discussed. 
Manuscript accepted 11 October 2000. 
Fish. Bull. 99:219-239 (2001). 
Cetacean habitats in the northern GuSf of Mexico 
Mark F. Baumgartner 
Southeast Fisheries Science Center 
National Marine Fisheries Service 
Bldg. 1 103, Room 218 
John C. Stennis Space Center, Mississippi 39529 
Present address: College of Oceanic and Atmospheric Sciences 
Oregon State University 
104 Ocean Administration Building 
Con/allis, Oregon 97331 
E-mail address: mbaumgar@oce.orst edu 
Keith D. Mullin 
Southeast Fisheries Science Center 
National Marine Fisheries Service 
PO. Drawer 1207 
Pascagoula, Mississippi 39568 
L. Nelson May 
Thomas D. Leming 
Southeast Fisheries Science Center 
National Marine Fisheries Semce 
Bldg. 1103, Room 218 
John C. Stennis Space Center, Mississippi 39529 
Studies of cetacean distribution in the 
northern Gulf of Mexico have largely 
relied on stranding, opportunistic sight- 
ing, and limited survey data (Jefferson 
and Schiro, 1997) until recently (Mullin 
et ah, 1994; Davis and Fargion 1 ; Davis 
et al. 2 ). During the past decade, both 
aerial and shipboard assessment sur- 
veys in the oceanic (>200 m depth) 
northern Gulf have identified and char- 
acterized the abundance and distribu- 
tion of 20 species of cetaceans, all but 
one of which were odontocetes (Mullin 
et al., 1994; Mullin and Hansen, 1999; 
Hansen et al. 3 ; Mullin and Hoggard 4 ). 
Only two of these species, the bottle- 
1 Davis, R. W., and G. S. Fargion. 1996. 
Distribution and abundance of cetaceans 
in the north-central and western Gulf 
of Mexico: final report, vol. I: executive 
summary. LIS. Department of the Inte- 
rior, Minerals Management Service, OCS 
Study MMS 96-007, 29 p. [Available from 
Public Information Office, MS 5034, Gulf 
of Mexico Region, Minerals Management 
Service, 1201 Elmwood Park Blvd., New 
Orleans, LA 70123-2394.] 
2 Davis, R. W., W. E. Evans, and B. Wiirsig. 
2000. Cetaceans, sea turtles and seabirds 
in the northern Gulf of Mexico: distribution, 
2 ( continued ) abundance and habitat asso- 
ciations, vol. I: executive summary. U.S. 
Department of the Interior, Geological Sur- 
vey, Biological Resources Division, LTSGS/ 
BRD/CR- 1999-0006 and Minerals Man- 
agement Service, OCS (outer continental 
shelf) Study MMS 2000-003, 27 p. (Avail- 
able from Public Information Office, MS 
5034, Gulf of Mexico Region, Minerals 
Management Service, 1201 Elmwood Park 
Blvd., New Orleans, LA 70123-2394.] 
3 Hansen, L J , K. D. Mullin, T. A. Jefferson, 
and G. P. Scott. 1996. Visual surveys 
aboard ships and aircraft In Distribution 
and abundance of cetaceans in the north- 
central and western Gulf of Mexico: final 
report, vol. II: technical report (R. W. Davis 
and G. S. Fargion, eds.), p. 55-128. LIS. 
Department of the Interior, Minerals 
Management Service, OCS Study MMS 
96-007. [Available from Public Information 
Office, MS 5034, Gulf of Mexico Region, Min- 
erals Management Service, 1201 Elmwood 
Park BlvcL, New Orleans, LA 70123-2394.] 
4 Mullin, K. D., and W. Hoggard. 2000. 
Visual surveys of cetaceans and sea turtles 
from aircraft and ships. In Cetaceans, sea 
turtles and seabirds in the northern Gulf of 
Mexico: distribution, abundance and habitat 
associations, vol. II: technical report (R. W. 
Davis, W. E. Evans, and B. Wiirsig, eds. ), p. 
11 1-171 U.S. Department of the Interior, 
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