NOTE Fulling et al.: Abundance and distribution of cetaceans in the US Gulf of Mexico 



927 



3 28- 



30- 



28- 



26- 



98 96 



Figure 2 



Locations of all on-effort sightings of Turswps truncatus (top), Stenelta frontalis 

 (center), Steno bredanensis, and T. truncatus+S. frontalis (bottom) in the northern U.S. 

 Gulf of Mexico outer continental shelf (20-200 m) during fall 1998-2001. Numbers of 

 sightings shown are prior to truncation. The 20- and 200-m isobaths (thin lines) are 

 shown (AL=Alabama, FL=Florida, LA=Louisiana, MS=Mississippi, TX=Texas). 



Abundance 



The abundance estimates for cetaceans reported in the 

 present study are the first ship-based estimates for the U.S. 

 GOM OCS. Abimdance estimates for T. truncatus on the OCS 

 (25,320; 0.26) are half the estimate in the pre-2002 SARs 

 (50,247; 0.18) (e.g. Waring et al, 2001), that were based on 

 aerial surveys conducted during fall 1992-94 (Blaylock et 

 al, 1994; Waring et al, 2001). The abundance estimate for 

 S. frontalis for the entire U.S. GOM in SARs prior to 2002 

 (3,213; 0.44) was based on data from ship surveys of OCS and 

 oceanic waters >100 m deep (Waring et al., 2001; Hansen et 

 al.'). Our current abundance estimate of S. frontalis (30,772; 

 0.27) for the OCS is almost an order of magnitude larger 



During the 1991-94 aerial surveys, there were 13 sight- 

 ings of S. frontalis groups and 10 sightings that were iden- 

 tified as T. truncatus+S. frontalis in OCS waters (SEFSC, 

 NMFS, Pascagoula, MS, unpubl. data). Using these sight- 

 ings and 139 T. truncatus sightings to estimate /(O), we esti- 

 mated the abundance of S. frontalis from the aerial survey 

 data to be 14,866 ( 0.37) for the U.S. GOM OCS [west, 3,526 

 (0.86); east, 11,340(0.40)]. 



There are several potential reasons for the differences in 

 abundances of the two species from ship and aerial surveys. 

 The U.S. GOM OCS east of 85.5°W makes up about 44% 

 of the U.S. GOM OCS. Aerial survey abundance estimates 

 in this area were based on a small number of transect 

 lines grouped in two places and most of the area was not 



