923 



Abundance and distribution of cetaceans 

 in outer continental shelf waters of the 

 U.S. Gulf of Mexico 



Gregory L. Fulling 



Keith D. Mullin 



Carrie W. Hubard 



Southeast Fisheries Science Center 



National Marine Fisheries Service, NOAA 



3209 Frederic Street 



Pascagoula, Mississippi 39567 



E-mail address (for G. L Fulling) Greg Fulling(a)noaa, gov 



The U.S. Marine Mammal Protection 

 Act (MMPA) requires that stocks of 

 marine mammal species in U.S. waters 

 be maintained at or above their opti- 

 mum sustainable population (OSP) 

 level, defined as the number of animals 

 that results in the maximum net pro- 

 ductivity. To meet this requirement for 

 each stock, the U.S. National Marine 

 Fisheries Service (NMFS) estimates 

 annual human-caused mortality and 

 potential biological removal (PBR), the 

 maximum number of animals that may 

 be removed from a stock due to human 

 activities (e.g. fisheries bycatch) while 

 allowing the stock to reach or maintain 

 its OSP PBR is calculated by follow- 

 ing specific criteria and using the 

 estimated abundance of the stock, its 

 maximum net productivity rate (theo- 

 retical or estimated), and a recovery 

 factor (Barlow et al., 1995; Wade and 

 Angliss, 1997). The NMFS is required 

 to prepare an annual stock assessment 

 report (SAR) for each stock to update 

 abundance, stock structure, maximum 

 net productivity, human-caused mor- 

 tality, PBR, and status (e.g. Waring et 

 al.,2001). 



Cetaceans in the U.S. Gulf of Mexico 

 (U.S. GOM) occur in two species assem- 

 blages that overlap in upper continen- 

 tal slope waters (-200-1000 m). The 

 oceanic waters (>200 m) are routinely 

 inhabited by 20 species that, in most 

 cases, inhabit deep warm-temperate to 

 tropical waters throughout the world. 

 Bottlenose dolphins iTursiops trim- 

 catus) and Atlantic spotted dolphins 

 [Stenella frontalis) are the only two 

 species commonly found in continen- 



tal shelf waters (<200 m) (Mulhn and 

 Hansen, 1999). 



In the U.S. GOM the distribution of T. 

 fruncatiis ranges from inshore waters 

 to deep waters of the continental slope 

 (Blaylock and Hoggard, 1994; Hansen 

 et al.'; Mullin and Hoggard'^). In the 

 U.S. GOM, the NMFS divides T. trun- 

 catus into 38 stocks: 33 inshore stocks 

 (bays, sounds, and estuaries); 3 coastal 

 stocks (western, northern, and eastern) 

 from shore to 9 km seaward of the 18-m 

 (10-fm) isobath; 1 outer continental 

 shelf (OCS) stock from the coastal 

 boundary to 9 km seaward of the 183-m 

 (100-fm) isobath; and 1 continental 

 shelf edge and slope stock from the 

 OCS boundary out to the U.S. Exclu- 

 sive Economic Zone (FEZ) (Waring et 

 al., 2001). The abundance estimate for 

 the OCS T. truncatus stock is 50,247 

 dolphins (CV=0.18) and is based on 

 aerial surveys conducted during fall 

 which covered all the U.S. GOM shelf 

 waters over 3 years in sections, west, 

 central, and east, in 1992, 1993, and 

 1994, respectively (Blaylock and Hog- 

 gard, 1994; Waring et al., 2001). 



One U.S. GOM S. frontalis stock is 

 recognized, and the abundance, 3213 

 dolphins (CV=0.44), is estimated from 

 ship surveys of shelf edge and oceanic 

 waters >100 m deep conducted from 

 1991-94 (Hansen et al.M. Abundance 

 estimates for S. frontalis for the U.S. 

 GOM OCS were not made from the 

 1992-94 aerial surveys although S. 

 frontalis groups were sighted (War- 

 ing et al., 2001). The majority of S. 

 frontalis are thought to inhabit the 

 shelf-edge region. However, data from 



opportunistic sightings (e.g. Mills and 

 Rademacher, 1996) and a summer 1994 

 ship survey of the eastern GOM (Hof- 

 stetter, 2002) have indicated that they 

 are common throughout eastern GOM 

 shelf waters >10 m deep, and in oceanic 

 waters <500 m. 



The NMFS Southeast Fisheries Sci- 

 ence Center (SEFSC) conducts annual 

 spring and fall ichthyoplankton sur- 

 veys in the U.S. GOM. The spring sur- 

 vey targets the entire oceanic portion 

 of the U.S. GOM, and the fall survey 

 focuses on shelf waters from the U.S.- 

 Mexico border to southern Florida. 

 Since 1991, abundance estimates of 

 oceanic cetacean species in the U.S. 

 GOM have been based primarily on 

 data collected during annual spring 

 surveys (Hansen et al.'; Mullin and 

 Hoggard'^; Mullin and Fulling^). Be- 

 cause of the lack of current assessment 

 information on and the uncertainty of 

 abundance estimates for T. truncatus 

 and S. frontalis in OCS waters, ceta- 

 cean surveys were conducted during 

 the fall ichthyoplankton surveys from 

 1998 to 2001. From these surveys, we 

 report the abundance and distribution 

 of cetaceans in OCS waters (20-200 m 

 deep) ofthe U.S. GOM. 



1 Hansen, L. J., K. D. Mullin, and C. L. 

 Roden. 1995. Unpublished report. Es- 

 timates of cetacean abundance in the 

 northern Gulf of Mexico from vessel sur- 

 veys, 20 p. Southeast Fisheries Science 

 Center, 3209 Frederic St., Pascagoula, MS 

 .39.567. 



2 Mullin, K.D., and W. Hoggard. 2000. Vi- 

 sual surveys of cetaceans and sea turtles 

 from aircraft and ships. In Cetaceans, 

 sea turtles and seabirds in the northern 

 Gulf of Mexico: Distribution, abundance 

 and habitat associations. Volume II: Tech- 

 nical report (R.W. Davis, W. E. Evans, and 

 D. Wursig, eds.), p. 111-172. OCS Study 

 MMS 96-0027. Minerals Management 

 Service, Gulf of Mexico OCS Region, New 

 Orleans, LA. 70123. 



3 Mullin, K.D., and G.L. Fulling. 2003. Un- 

 published report. Abundance of ceta- 

 ceans in the oceanic northern Gulf of 

 Mexico, 1996-2001, 35 p. Southeast 

 Fisheries Science Center, 3209 Frederic 

 Street, Pascagoula, MS 39567. 



Manuscript approved for publication 

 10 July 2003 by Scientific Editor. 



Manuscript received 20 July 2003 at 

 NMFS Scientific Publications Office. 



Fish. Bull. 101:923-932 (2003). 



