Mullln and Fulling: Abundance of cetaceans in the southern Atlantic Ocean 



605 



of the primary team. Mixed-species groups were uncom- 

 mon (five of 217 sightings) and group-size estimates were 

 made separately for each species. 



Species identification 



Cetaceans were identified to the lowest taxonomic level 

 possible from descriptions in field guides and scientific 

 Uterature (e.g. Leatherwood and Reeves, 1983; Jefferson 

 et ah, 1993; Carwardine, 1995) (Table 1). An observer's 

 ability to make identifications depended on weather and 

 animal behavior. The study area was potentially inhabited 

 by short-finned pilot whales (Globicephala inacrorhynchus), 

 which are thought to occur within the study area from about 

 Virginia south, and long-finned pilot whales (G. melas), 

 thought to occur from near Cape Hatteras north (Pa3me and 

 Heinemann, 1993). Because the two species cannot be reli- 

 ably distinguished at sea, they were recorded simply as pilot 

 whales. Two forms of the Atlantic spotted dolphin (Stenella 

 frontalis) were tentatively identified: the larger, more 

 coastal form, and the smaller offshore form (Perrin et al.. 



1994 ). Abundances were estimated for each form and for all 

 Atlantic spotted dolphins combined because only one stock 

 is currently designated for U.S. Atlantic waters. Coastal and 

 offshore forms of bottlenose dolphins (Hersh and Duffield, 

 1990), which constitute the two stocks, were recorded, but 

 most sightings could not be clearly categorized; therefore, 

 all bottlenose dolphin sightings were pooled for one overall 

 abundance estimate. Bottlenose and Atlantic spotted dol- 

 phins could not always be distinguished at large distances 

 and a separate estimate was made for animals that could 

 not be approached and were identified as ''Tursiops or S. 

 frontalis." Overall abundances for the genus Kogia and the 

 genus Mesoplodon were estimated. Dwarf sperm whales (K. 

 sima) and pygmy sperm whales (K. breviceps) were difficult 

 to distinguish and stranding records of both species are 

 numerous from U.S. Atlantic shores (Schmidly''). Based on 



5 Schmidly, D. J. 1981. Marine mammals of the southeastern 

 United States and the Gulf of Mexico. U.S. Dep. Interior, U.S. 

 Fish and Wildlife Service Biological Services Program FWS/ 

 OBS-80/41, 165 p. 



