774 



Fishery Bulletin 92(4). 1994 



contribute to the demise of endangered species or to 

 the depletion of marine mammal populations. To as- 

 sess potential impacts of oil and gas activities on 

 marine mammal populations, it is imperative that 

 we know when, where, and how many marine mam- 

 mals may be vulnerable to such activities. 



Only limited data from strandings, opportunistic 

 sightings (Schmidly, 1981; Mead 3 ), and aerial sur- 

 veys (Fritts et al., 1983) are currently available to 

 assess these parameters for oceanic cetaceans in the 

 Gulf. In July 1989, the U.S. Minerals Management 



3 Mead, J. G. 1992. Marine mammal strandings. National Mu- 

 seum of Natural History, Smithsonian Institution, Washington, 

 D.C. 20560. Unpubl. data. 



Service and the Southeast Fisheries Science Center 

 (SEFSC) began aerial surveys of cetaceans on the 

 upper continental slope in the north-central Gulf. The 

 objectives of the surveys were 1) to determine which 

 species were present; 2) to document temporal and 

 spatial distribution for each species; and 3) to esti- 

 mate relative abundance for each species. 



Methods 



The study was conducted in two phases. Phase 1 was 

 a five-month pilot study carried out from July 

 through November 1989. The primary objective of 

 Phase 1 was to determine which species of cetaceans, 



97 58 

 32 39' 



24 05 



97 58' 



24 05' 

 79°46' 



26''23■ 



8Z;48' OOV 



30°46 1 30°46' 



26^23' 



90°34' 



87°48' 



Figure 1 



Location of the area surveyed for cetaceans in the north-central Gulf of Mexico (top panel). The locations of the 

 survey blocks for Phase 1 (July-November 1989) are shown in the lower left panel and for Phase 2 (January-June 

 1990), in the lower right panel. 



