Barlow and Forney: Abundance and population density of cetaceans in the California Current ecosystem 515 



The number of sightings of most species varied 

 among geographic regions (Table 2 I. Short- and long- 

 beaked common dolphins and striped dolphins were 

 seen much more frequently in central and southern 

 California. Ball's porpoises were seen much more 

 commonly in the northern California and Oregon- 

 Washington regions. The number of sightings of other 

 dolphin species (including Risso's dolphins, Pacific 

 white-sided dolphins, northern right whale dolphins, 

 and killer whales) showed no clear pattern with geo- 

 graphic region. Dolphin group sizes were generally 

 largest for the two species of common dolphin, but 

 Pacific white-sided dolphins were consistently found 

 in large groups in the central California region (Table 

 2). Blue whales were the most commonly seen baleen 



whale in the southern region, but were replaced by 

 fin whales and humpback whales as the most common 

 baleen whale in the northern regions (Table 2). The 

 sighting locations are illustrated in Figure 2 for some 

 common species. Locations of sightings of all species 

 have been provided in the reports for each survey (Hill 

 and Barlow, 1992; Mangels and Gerrodette, 1994; 

 Von Saunder and Barlow, 1999; Appier et al,. 2004; 

 Forney, 2007). 



Cetaceans were often found in mixed species assem- 

 blages. In some cases, species were obviously traveling 

 together in close association; in other cases, the indi- 

 vidual species may have been in the same area because 

 they were feeding on the same resource or were there 

 by coincidence. Some species (striped dolphins, bottle- 



