Barlow and Forney: Abundance and population density of cetaceans in the California Current ecosystem 511 



45°N - 



40° N - 



35°N - 



30°N 



45°N 



40°N 



35°N 



30° N 



i^^"^»—T' T I I I I 



1991/93^ ., Washington 



r 



; Oregon 



. 1996 



Pacific 

 Ocean 



2001 



Pacific 

 Ocean 



^'—1 1 1 r— T— ¥— ?- 



Washington 



. 2005 



Pacific 

 Ocean 



.. Washington 



r~,. W^. Oregon 



California 



Pacific 

 Ocean 



130°W 125°W 120°W 



130°W 125°W 120°W 



Figure 1 



Transect lines (gray) surveyed during 1991 and 1993, 1996, 2001, and 2005 

 surveys. Thick transect lines were surveyed in Beaufort sea states of 0-2 

 and thin lines in Beaufort sea states 3-5. Black lines on all maps indicate 

 the boundaries of the four geographic regions. 



Logarithms were used in Equation 1 because stan- 

 dard errors were found to be proportional to the mean. 

 Sightings were included in calculating indirect calibra- 

 tion coefficients if group size estimates were made by at 

 least two other directly calibrated observers. We use a 

 weighted geometric mean of the individual, calibrated 

 group-size estimates (weighted by the inverse of the 

 mean squared estimation error) as the best estimate 

 of overall group size in all of the analyses presented 

 here. 



Estimation of abundance from line-transect data 



Cetacean abundance was estimated by using line-tran- 

 sect methods (Buckland et al., 2001) with multiple covari- 



ates (Marques and Buckland, 2003). The entire study 

 area (1,141,800 km-) was divided into four geographic 

 strata (Fig. 1): 1) waters off Oregon and Washington 

 (322,200 km2 north of 42''N); 2) northern California 

 (258,100 km2 south of 42°N and north of Point Reyes 

 at 38°N); 3) central California (243,000 km^ between 

 Point Conception at 34.5°N and Point Reyes); and 4) 

 southern California (318,500 km^ south of Point Concep- 

 tion). The OR-WA region was not surveyed in 1991 or 

 1993 and thus received less survey effort. The density, 

 Z),, for a given species within geographic region i was 

 estimated as 



D.= 



1 ^fioizjysj 



2L, 



j=i 



^,(0) 



(2) 



