518 



Fishery Bulletin 105(4) 



45°N - 



40°N 



35"N 



30°N 



45°N - 



40°N 



35°N - 



30°N 



Pacific 

 Ocean 



Northern right whale dolphin 



H — I — I — I I I — I — I J I I I — I — I — I — I — I- 



Washlngton 

 ^^:^~pS: Oregon 



California 



Pacific 

 Ocean 



Cuvier's beaked whale 



Striped dolphin 



4—1 — I — I — I — I — I — I J I I — I — I — I — I — I — I — 1- 



Washington 



Pacific 

 Ocean 



Mesoplodont beaked whales 



130 W 125 W 120'W 130"W 125'W 120'W 



Figure 2 (continued) 



species were between 2 and 3 km (Table 1). Dalls por- 

 poise and Kogia species had the narrowest effective 

 strip widths (~1 km), and humpback whales had the 

 greatest values (-3.2 km). 



Discussion 



Abundance and density of cetaceans 



Delphinidae Delphinids off the U.S. west coast can be 

 classified as warm-temperate (short- and long-beaked 

 common dolphins, striped dolphins, and short-finned 

 pilot whales), cold-temperate (Pacific white-sided 

 dolphins and northern right whale dolphins), or cos- 

 mopolitan (Risso's dolphin, bottlenose dolphins, and 

 killer whales). The warm temperate species are gener- 

 ally more common in southern and central California, 



and the cold-temperate species are more common 

 in the northern California and Oregon-Washington 

 regions. In 1996, when waters were relatively cool 

 off California, the abundance of striped dolphins 

 (the most tropical species) was lower than average 

 and the abundance of the two cold-temperate species 

 was higher. Four of the five sightings of short-finned 

 pilot whales were in 1993, a warm year. All four spe- 

 cies have distributions that extend outside our study 

 area. These changes in abundance are consistent with 

 shifts in the distribution of these species into and out 

 of our study area with changes in water temperature. 

 The tendency for these species to change distribu- 

 tion with water temperature is also seen in seasonal 

 distribution changes (Forney and Barlow, 1998). The 

 abundance of common dolphins and the cosmopolitan 

 species did not vary consistently with warm and cold 

 years (Table 7). 



