Douglas et al. Seasonal distribution and abundance of cetaceans off Southern California 
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Figure 5 
Map of on-effort encounters with the fin whale ( Balaenoptera physalus) by season, recorded during 
the 16 shipboard line-transect surveys conducted quarterly during 2004-08 as part of the Cali- 
fornia Cooperative Oceanic Fisheries Investigation. The color of the triangle indicates the season: 
blue=winter, green=spring, red=summer, and yellow=fall. 
this species in our study area. Humpback whales off 
California, Oregon, and Washington migrate season- 
ally to wintering grounds off Baja, California, main- 
land Mexico, and Central America (Steiger et ah, 1991; 
Calambokidis et ah, 2000; Urban et ah, 2000). Clapham 
et al. (1997) and Forney and Barlow (1998) noted that 
in waters off California, a significantly greater propor- 
tion of the humpback whale population was found far- 
ther offshore in winter than in summer. We also found 
that more humpback whales occurred farther offshore 
and in deeper water in spring than during the sum- 
mer-fall seasonal period (Table 6). 
The thirdmost frequently encountered and abun- 
dant baleen whale within the study area, the blue 
whale, showed a distinct seasonal presence, a result 
that concurs with the findings from year-round aerial 
and ship-based surveys off Southern California. Forney 
and Barlow (1998) and Larkman and Veit (1998) found 
the greatest abundance of blue whales during August- 
October. Our abundance estimate of 288 blue whales 
(CV=0.23) was much lower than Barlow and Forney’s 
(2007) estimate of 842 individuals (CV=0.20) off South- 
ern California. The discrepancy between these esti- 
mates is likely due to a few factors, including interan- 
nual differences in proportion of the population found 
within the study area and our lack of a correction fac- 
tor for transect-line detection probability. Barlow and 
Forney’s (2007) estimate included surveys completed 
in 1991, 1993, and 1996, all years when much of the 
blue whale population was thought to be feeding along 
the California coast; however, in more recent years, evi- 
dence has indicated that blue whales are using more 
northerly, southerly, and offshore waters (Calamboki- 
dis and Barlow, 2004; Barlow and Forney, 2007; Calam- 
bokidis et ah, 2009). No blue whales were encountered 
in the study area during the winter— spring period — a 
finding that corresponds to their known migration pat- 
tern of feeding off California from May to November 
and migrating south to spend winter and spring off 
Mexico (Calambokidis et ah, 1990; Mate el al., 1999; 
Stafford et ah, 1999) and as far south as 6°N at the 
Costa Rica Dome (Wyrtki, 1964). 
Although known to be present year-round (Dohl 
et al. 5 ; Forney et ah, 1995; Barlow 3 ), minke whales 
5 Dohl, T. P., R. C. Guess, M. L. Duman, and R. C. Helm. 1983. 
Cetaceans of central and northern California, 1980-1983: 
status, abundance, and distribution. Part of investigator’s fi- 
