Barlow and Forney: Abundance and population density of cetaceans in the California Current ecosystem 517 



45°N - 



40°N 



35°N 



30°N 



45°N 



40°N 



35'N 



30°N 



I ' ' ' \^^'-^'^ 



,\ Washington 

 , y^!k Oregon 



^ *4L Californ 



Pacific 

 Ocean 



Dall's porpoise 



Pacific 

 Ocean 



Short-beaked common dolphin 



Washington 



Oregon 



California 



Pacific 

 Ocean 



Pacific white-sided dolphin 



4- 



^ • Washington 

 Oregon 



I ,, ,* California 



. « mk. * 



Pacific 

 Ocean 



Risso's dolphin 



130°W 125'W 120°W 130°W 125''W 120°W 



Figure 2 (continued) 



Estimation of abundance from line-transect data 



Short-beaked common dolphins dominated the abun- 

 dance estimates for all regions except Oregon-Wash- 

 ington (Table 5), both because of the large number of 

 sightings and the large group sizes for this species. 

 Balls porpoise was, by far, the most abundant small 

 cetacean in the Oregon-Washington region (Table 5). 

 Short-beaked common dolphins and DalTs porpoises 

 together represented approximately 81% of all del- 

 phinoids and 79% of all cetaceans, and baleen whales 

 (mysticetes) represented only about 1% of the total 

 estimated cetacean individuals along the U.S. west 

 coast (Table 6). 



The estimated abundance of most species varied 

 considerably among years (Tables 7 and 8). In large 

 part, the year-to-year variation in abundance for most 

 species could be attributed to low sample size and sam- 

 pling variation; however, the distributions of all spe- 



cies extended beyond the boundaries of the study area 

 and some of the annual variation was likely due to a 

 different portion of a larger population being in the 

 study area within a given year (Forney and Barlow, 

 1998). Because all years and all regions were pooled 

 for estimating the line-transect parameters, the abun- 

 dance estimates for different regions (Table 5) and for 

 different years (Tables 7 and 8) were correlated and 

 these estimates cannot be used in standard statistical 

 tests of difference among regions or among years. 



The most important covariates, z, for estimating line- 

 transect function f(Oiz) varied among species and spe- 

 cies groups (Table 4). Covariates appearing in more 

 than one model were Bino, Beauf, LnTotGS, Ship, and 

 RainFog. In addition to these, a covariate that coded 

 for difference among species within a group (SppGrp) 

 was chosen in the model for delphinids (large vs. small 

 delphinids) and for small whales (beaked whales vs. 

 Kogia spp. vs. minke whales). The mean ESWs for most 



