784 



Fishery Bulletin 92(4). 1994 



tocetes (e.g. Clarke, 1986; Barros and Odell, 1990; 

 Sekiguchi et al., 1992). However, very little is known 

 about the distribution and abundance of potential 

 prey species in Gulf oceanic waters beyond limited 

 information on cephalopods (e.g. Voss, 1971; Voss and 

 Brakoniecki, 1985) and records of the presence of 

 species (e.g. Hoese et al., 1977). 



Oceanographic features undoubtedly affect the 

 distribution of prey species and, ultimately, cetacean 

 diversity, abundance, and distribution. The Missis- 

 sippi River and its distributary, the Atchafalaya 

 River, enter the Gulf north of the area we surveyed 

 and account for nearly one-half of the total freshwa- 

 ter flow into the entire Gulf. The Loop Current, the 

 major oceanographic feature in the eastern Gulf, 

 carries 25-30 million m 3 of water per second into the 

 Gulf. At times, the Loop Current extends as far north 



as the Upper Mississippi Fan or the DeSoto Canyon. 

 As the Loop Current flows onto the continental slope 

 it causes nutrient-rich upwellings (Jones et al., 1973; 

 Weber et al., 1990). All these features interact with 

 the diverse bottom topography of the north-central 

 Gulf, making it a very dynamic area. 



In 1990, the Southeast Fisheries Science Center 

 began conducting annual cetacean shipboard surveys 

 of the entire oceanic U.S. Gulf of Mexico. Results to 

 date (775 herd sightings) suggest that the compara- 

 tively small maximum herd sizes and single species 

 herds found in this study in the Gulf are accurate 

 (SEFSC 7 ). Comparisons of the ecology of Gulf ceta- 

 ceans with those from other areas should provide an 

 excellent opportunity to understand the physical and 

 biological factors that affect cetacean diversity, dis- 

 tribution, abundance, herd sizes, and associations. 



Acknowledgments 



This cooperative study was supported by the U.S. 

 Minerals Management Service (MMS), Gulf of 

 Mexico Region; the NOAA Aircraft Operations 

 Center (AOC); and the SEFSC. R. Avent of the 

 MMS was instrumental in making this project a 

 success. We thank the AOC staff for all their help 

 and especially the Twin Otter pilots: Comdr. R 

 Wehling, Comdr. D. Eilers, Lt. T. Gates, Lt. T. 

 O'Mara, Lt. M. White, and Lt. BT This study could 

 not have been completed without the contributions 

 of SEFSC personnel J. Benigno, A. Shah, M. 

 McDuff, W. Stuntz, T. Henwood, and L. Hansen. 

 We thank J. Mead for providing the Gulf of Mexico 

 stranding data and T Jefferson for reviewing the 

 manuscript. The data for this paper were collected 

 under interagency agreement number 14- 12-000 1- 

 30398 between the MMS and the SEFSC. 



Literature cited 



Au, D. W., and W. L. Perryman. 



1985. Dolphin habitats in the eastern tropical 

 Pacific. Fish. Bull. 83:623-643. 

 Barron, G. L., and T. A. Jefferson. 

 1993. First records of the melon-headed whale (Pep- 

 onocephala electra) from the Gulf of Mexico. 

 Southwest. Nat. 38:82-85. 



7 SEFSC. 1990-93. Reports of NOAA ship Oregon II cruises 

 187, 194, 199, 203, and 204. U.S. Dep. Commer., NOAA, Nat. 

 Mar. Fish. Serv., Southeast Fish. Sci. Cent. Pascagoula Fa- 

 cility, P.O. Drawer 1207, Pascagoula, MS 39568. 



