Fishery Bulletin 93(1). 1995 



very close to the present estimate of 626 and is 

 well within its 95% confidence interval. 



For two species, new estimates of abun- 

 dance appear to be substantially different 

 from previous estimates. For the late 1970's, 

 the combined summer and fall estimate of 

 common dolphin abundance was 57,270 

 (CV=0.17) (Dohl et al., 1986). Although the 

 methods used were very different and the 

 area surveyed was smaller in that study, es- 

 timates for other small cetaceans are simi- 

 lar in the two studies. A large increase in 

 common dolphin abundance is likely. This 

 could have resulted as an effect of the 1991— 

 92 El Nino. Although there were no surface 

 temperature manifestations of El Nino in the 

 study area at the time of the survey, it is pos- 

 sible that common dolphins were moving into 

 California waters from farther south as a 

 result of El Nino changes there. Since 1980, 

 a decline has been noted in the abundance of 

 the northern stock of common dolphins south 

 of 30°N (Anganuzzi et al., 1993), and those 

 authors hypothesize that this could have 

 been caused by a general northward move- 

 ment of that stock. This interpretation is con- 

 sistent with the increases noted here, but the 

 magnitude of the decrease in the south (from 

 approximately 500,000 in 1980 to approxi- 

 mately 100,000 in 1991 [Anganuzzi et al. 

 1993]) is greater than the entire estimated 

 population in California waters. 



The abundance of blue whales, based on the 

 current line-transect data (2,250), is also 

 much higher than recent estimates made 

 from individual-identification mark-recap- 

 ture techniques (904 based on left-side pho- 

 tographs and 1,112 based on right-side pho- 

 tographs). 1 Although some mark-recapture 

 estimates may be biased low because of geo- 

 graphic heterogeneity in habitat use by indi- 

 vidual whales (Hammond, 1990), the meth- 

 ods used for mark-recapture should have 

 minimized those effects. 1 South of the present 

 study area, the abundance of blue whales was 

 estimated to be 1,415 (CV=0.24) based on line- 

 transect ship surveys in the eastern tropical 

 Pacific from 1986 to 1990 (Wade and Ger- 

 rodette, 1993). The latter study included 

 sightings made along the coast of Baja Califor- 

 nia (which probably belong to the California 

 feeding population) as well as sightings made 

 near the Costa Rica Dome and along the Equa- 

 tor (which are likely to be part of a different 

 population; Reilly and Thayer [1990]). 



