AU and FERRYMAN: DOLPHIN HABITATS 



The spinner dolphin appears to be distributed like 

 the spotted dolphin, with westerly extending lobes 

 of distribution in similar latitudes (Fig. 4). Schools 

 were infrequent along the Equator, more so than 

 were those of spotted dolphin. The eastern spinner 

 was encountered frequently off southern Mexico, 

 where its main population center appeared to be 

 relatively localized. However, eastern spinner 

 dolphins were seen as far offshore as long. 126°W 

 near lat. 10°N and also nearly to the Equator within 

 a broad, 600 nmi coastal belt off Central America. 

 The whitebelly form of spinner dolphin (Perrin 

 1975a, b; Perrin et al. 1977) occurred in a broad 

 range north and south of the Equator and at the 

 southern and western portions of the total spinner 

 dolphin range Large schools (>300) were seen most- 

 ly off southern Mexico (eastern spinner) and south 

 of the Equator (whitebelly spinner). 



Striped and common dolphins seem to have a 

 distribution pattern qualitatively different from that 

 of spotted and spinner dolphins (Fig. 5). A distinct 

 distributional lobe, consisting primarily of common 

 dolphins, occurred off Baja California, with exten- 

 sions around the Revilla Gigedo Islands (ca. lat. 



19°N, long. 111°W). Between lat. 5° and 12°N, off 

 Central America, there was a second lobe made up 

 of both species. This lobe attenuated to the west 

 along lat. 10°N, but appeared to re-intensify past 

 long. 130°W. Only striped dolphins were seen in the 

 intermediate interval between long. 100°W and 

 130°W along this lobe A third lobe appeared to 

 originate off Peru. It merged somewhat with the 

 outer portions of the Central American lobe, and 

 then extended westward along the Equator. 

 Equatorial waters were frequented by both species 

 out to about long. 100°W, beyond which striped 

 dolphins apparently predominate. The striped 

 dolphin is the more widespread of the two species; 

 however, its school sizes are small (Tkble 1). Large 

 schools (>300) of the common dolphin occurred 

 within each of the three main centers of its 

 distribution. 



The above sighting data were adjusted to show the 

 distributions of relative abundance of schools by cor- 

 recting for searching effort. Effort is calculated as 

 miles searched = time searched x ship speed. 

 Relative abundance of schools was expressed as 

 schools per 100 nmi searched (approximately the 



170° 

 30° 



ISO* 



— T" 



120» 



— r 



90- 



80" 



70° 

 30" 



Hawaiian Itlandt 



Christmas Island * 



Marquasa* Islands 



I I 



• EASTERN SPINNER 



O WHITEBELLY SPINNER 



O CD O 



Figure 4.— Distribution of spinner doipliin schools, eastern and whitebelly forms, seen during the January-March research cruises. Larger 



circles indicate schools >300 animals. 



627 



