Baumgartner et al.: Cetacean habitats in the northern Gulf of Mexico 
237 
and eddies at the northern and eastern sides of the Loop 
Current (Vukovich and Maul, 1985). These cyclonic fea- 
tures are usually much smaller than the Loop Current 
itself or the warm-core features of the central and west- 
ern Gulf (Cochrane, 1972). Along the latitude of 27°N and 
within 40 km of the Loop Current (near 88.8°W) in late 
spring, 1993, for instance, the satellite-borne AVHRR de- 
tected surface temperatures 1.5°C cooler than the Loop 
Current itself, but the vertical temperature structure, sur- 
face chlorophyll and zooplankton biomass associated with 
this narrow feature were not captured because of the 
coarse sampling strategy (Figs. 2 and 3). The recent Gulf- 
Cet II program (Davis et al. 16 ) examined cetacean habitat 
associations in the vicinity of cyclonic-anticyclonic eddy 
pairs in the northeastern Gulf of Mexico and demonstrat- 
ed that these mesoscale hydrographic features can indeed 
influence cetacean distribution. In addition to the cyclonic 
features associated with the Loop Current, the CTD and 
XBT sampling strategy of our study did not resolve other 
potentially productive features that occur on smaller spa- 
tial scales, such as nutrient-rich Mississippi River plume 
waters entrained at the edge of the Loop Current (Maul, 
1977; Miiller-Karger et al., 1991) and shelf break fronts. 
Future studies of cetacean habitats in the Gulf of Mexi- 
co should continue to consider these smaller scale features 
as potential sites of large cetacean aggregations because 
of their high levels of biological activity. These features 
could potentially 1 ) have high rates of primary productiv- 
ity that is converted into prey biomass over short tempo- 
ral and spatial scales, 2) concentrate prey through solely 
physical mechanisms or through physical-biological inter- 
actions or 3) make local prey more accessible to surface- 
bound cetaceans. Although investigating these processes 
is undoubtedly a challenge, it is important to elucidate 
what processes affect cetacean distribution and at what 
spatial and temporal scales these processes operate if we 
are to understand how oceanographic conditions affect ce- 
tacean ecology. 
Acknowledgments 
This work was supported by the National Marine Fisher- 
ies Service’s Marine Mammal Program. Additional fund- 
ing was provided by the Minerals Management Service 
under contract 14-35-0001-30619 and Interagency Agree- 
ment 16197 (GulfCet Program). Portions of the environ- 
mental data and all of the zooplankton data were collected 
under the Southeast Area Monitoring and Assessment 
Program (SEAMAP) and were generously provided by J 
Shultz. We would like to acknowledge the hard work and 
dedication of the marine mammal observers, the officers 
and crew of the NOAA Ship Oregon II, and the staff of the 
Southeast Fisheries Science Center. Special thanks go to 
C. Roden for managing the marine mammal surveys and 
M. McDuff for technical guidance and support. S. Ander- 
son and R. Weller of the Woods Hole Oceanographic Insti- 
tution graciously provided computing resources. We also 
thank three anonymous reviewers for criticizing earlier 
drafts of this manuscript. 
Literature cited 
Barlow, J. 
1995. The abundance of cetaceans in California waters. Part 
I: ship surveys in summer and fall of 1991. Fish. Bull. 
93:1-14. 
Baumgartner, M. F. 
1997. The distribution of Risso’s dolphins (G)-ampus gri- 
seus) with respect to the physiography of the northern Gulf 
of Mexico. Mar. Mamm. Sci. 13:614-638. 
Berzin, A. A. 
197 1 The sperm whale. Pischevaya Promyshlennost, Mos- 
cow, 394 p. [Translated from Russian by E. Hoz and Z. 
Blake, Israel Program for Scientific Translations, Ltd.] 
Biggs, D. C. 
1992. Nutrients, plankton, and productivity in a warm-core 
ring in the western Gulf of Mexico. J. Geophys. Res. 
97:2143-2154. 
Biggs, D. C., R. R. Leben, and J. G. Ortega-Ortiz. 
2000. Ship and satellite studies of mesoscale circulation 
and sperm whale habitats in the northeast Gulf of Mexico 
during GulfCet II. Gulf of Mexico Science 18:15-22. 
Blaylock, R. A., J. W. Hain, L. J. Hansen, D. L. Palka, and 
G. T. Waring. 
1995. U.S. Atlantic and Gulf of Mexico marine mammal stock 
assessments. U.S. Dep. Commer., NOAA Tech. Memo. 
NMFS-SEFSC-363, 211 p. 
Blaylock, R. A., and W. Hoggard. 
1994. Preliminary estimates of bottlenose dolphin abun- 
dance in southern U.S. Atlantic and Gulf of Mexico con- 
tinental shelf waters. U.S. Dep. Commer., NOAA Tech. 
Memo. NMFS-SEFSC-356, 10 p. 
Clarke, M. R. 
1986. Cephalopods in the diet of odontocetes. In Research 
on dolphins (M. M. Bryden and R. Harrison, eds.), p. 281-321. 
Oxford Univ. Press, Oxford. 
1996. Cephalopods as prey. III: Cetaceans. Philos. Trans. 
R. Soc. Lond. (ser B.) Biol. Sci. 351:1053-1065. 
Cochrane, J. D 
1972. Separation of an anticyclone and subsequent develop- 
ments in the Loop Current (1969). In Contributions on 
the physical oceanography of the Gulf of Mexico (L. R. A. 
Capurro and J. L. Reid, eds.), p. 91-106. Gulf Publishing, 
Houston, TX. 
Conover, W. J. 
1980. Practical nonparametric statistics. John Wiley and 
Sons, Inc, New York, NY, 493 p. 
Curry, B. E., and J. Smith. 
1997. Phylogeographic structure of the bottlenose dolphin 
( Tursiops truncatus): stock identification and implications 
for management. In Molecular genetics of marine mam- 
mals (A. E. Dizon, S. J. Cbivers and W. F. Perrin, eds.), 
p. 227-247. Society for Marine Mammalogy. 
Dagg, M. J., P B. Ortner, and F. Al-Yamani. 
1988. Winter-time distribution and abundance of copepod 
nauplii in the northern Gulf of Mexico. Fish. Bull. 86:219- 
230. 
Davis, R. W., G. S. Fargion, L. N. May, T. D. Leming, 
M. F. Baumgartner, W. E. Evans, L. J. Hansen, and K. Mullin. 
1998. Physical habitat of cetaceans along the continental 
slope in the north-central and western Gulf of Mexico. Mar. 
Mamm. Sci. 14:490-507. 
Dowling, T. E., and W. M. Brown. 
1993. Population structure of the bottlenose dolphin ( Tur- 
siops truncatus) as determined by restriction endonuclease 
