Mullin et al.: Cetaceans of the north-central Gulf of Mexico 



781 



10% of the total survey effort occurred. The Missis- 

 sippi Canyon region is probably an important ceta- 

 cean habitat. Eight species or species groups were 

 sighted there and when herd sighting rates were 

 calculated for each survey block (Mullin et al. 5 ), it 

 had the highest sighting rate of any block. 



The region near the 1,000-m isobath on the Upper 

 Mississippi Fan appeared to be an important habi- 

 tat for sperm whales. Most sperm whale herd 

 sightings (72%, 31/43) occurred on the Upper Mis- 

 sissippi Fan (Blocks Al, B3, and B4) but only 40% of 

 the total effort occurred there. Fall may have been a 



5 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. Outer Continental Shelf Study/ 

 MMS 91-0027. U.S. Dep. Interior, Minerals Mgmt. Service, Gulf 

 of Mexico OCS Regional Office, New Orleans, LA, 108 p. 



time of increased sperm whale abundance on the 

 Upper Mississippi Fan. Of the total effort, 20% oc- 

 curred in fall on the Upper Mississippi Fan and 

 yielded 47% (20/43) of the total sperm whale herd 

 sightings. Of course the same animals could have 

 been seen repeatedly, but even if that were true, it 

 indicates that a very small area (Fig. 2) could be 

 important to some animals for a period of at least 

 several months. 



Our study was confined to the outer continental 

 shelf and the upper continental slope and did not 

 cover the entire range of water depths that each spe- 

 cies inhabits. However, our results do not conflict 

 with what is generally known about the water depth 

 distribution of each species (Leatherwood and 

 Reeves, 1983 ). While the supposition that only bottle- 

 nose dolphins and Atlantic spotted dolphins inhabit 



