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Fishery Bulletin 112(2-3) 
300 
E 
1 200 
O 
CD 
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c 
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t 100 
0 | 
Winter Spring Summer Fall 
Season 
Figure 6 
Box-and-whisker plot showing distance to land by season for fin 
whales (Balaenoptera physalus) within the study area for line- 
transect surveys conducted off Southern California during 2004- 
OS for 16 quarterly California Cooperative Oceanic Fisheries In- 
vestigation cruises. In each box, the middle horizontal line shows 
the median value and the upper and lower lines show the 75th 
and 25th percentiles. Ends of the upper and lower whiskers indi- 
cate the minimum and maximum data values; an * indicates the 
outlier and the vertical lines extend to a maximum of 1.5 times 
the interquartile range. 
* 
(Balaenoptera acutorostrata) are difficult to sight even 
in very good sea conditions. The sample size of this 
species in the 6 CalCOFI surveys was insufficient for 
an abundance estimate, but it is worth noting that we 
encountered minke whales in low numbers from spring 
to fall, and a peak in encounter rates occurred during 
the spring (Table 4) that cannot be explained by bet- 
ter sea conditions in spring. Although sei whales were 
historically the fourth-most commonly captured whale 
along coastal California during whaling activity in the 
1950s and 1960s (Rice, 1974), they now are considered 
rare in California waters (Dohl et al. 5 ; Mangels and 
Gerrodette, 1994; Forney et al., 1995; Barlow 3 ). Our 
results support findings that they are not commonly 
encountered off southern California with only a sin- 
gle sighting of a sei whale and a sighting of one other 
individual that was either a sei whale or a Bryde’s 
whale. 
Odontocetes We encountered 16 species of odontoce- 
tes, with sufficient sightings of 8 species to calculate 
seasonal abundance and density and examine seasonal 
trends. The most commonly encountered odontocete 
species along Southern California are present year- 
nal report, Marine Mammal and Seabird Study, central and 
northern California, Contract No. 14-12-0001-29090. Pre- 
pared by Center for Marine Sciences, Univ. California, Santa 
Cruz, for the Pacific OCS Region, Minerals Management 
Service, OCS Study MMS 84-0045, 284 p. 
round, although some of them undergo sea- 
sonal shifts in abundance; the Dali’s porpoise 
and Risso’s dolphin have been recognized as 
moving seasonally into Southern California 
waters during the winter months. Such sea- 
sonal shifts of abundance out of Southern 
California waters during winter months in- 
creases the likelihood that these species were 
regionally underrepresented in previous es- 
timates (Barlow and Forney, 2007; Carretta 
et al., 2011b) of density and abundance that 
were generated from sighting data collected 
during summer-fall ship-based surveys. 
Sufficient sample size allowed for density 
and abundance estimation of sperm whales; 
however, mean group size (2.7 individuals) 
was significantly lower than the 8.1 indi- 
viduals reported off Southern California from 
pooled sightings collected over 5 years of 
SWFSC surveys (Barlow and Forney, 2007). 
In our study, group-size estimates were very 
likely negatively biased by the constraints 
of conducting a survey in passing mode, in- 
stead of using the protocol for the SWFSC 
line-transect surveys of conducting multiple 
counts over 90 min to enumerate asynchro- 
nously diving whales (Barlow and Taylor, 
2005; Barlow and Forney, 2007). We encoun- 
tered sperm whales year-round and in both 
depth categories, but we observed this spe- 
cies primarily during the summer-fall period in depths 
>2000.5 m — findings similar to earlier analyses of year- 
round survey effort (Dohl et al. 5 ; Barlow, 1995; Forney 
et al., 1995). 
Even with our relatively high number of common 
dolphin sightings that could not be identified to spe- 
cies, we found that short-beaked common dolphins were 
the most abundant and widely distributed cetacean in 
our study area — a finding that is consistent with previ- 
ously published results from cetacean survey effort off 
Southern California (Leatherwood et al., 1982; Dohl et 
al., 1986; Smith et al., 1986; Barlow, 1995; Forney et 
al., 1995). Moreover, our stratified abundance estimates 
provide clear evidence of seasonal shifts in habitat use. 
We found that, during the summer-fall period, short- 
beaked common dolphins were fairly evenly spread 
throughout the study area, and, during the winter- 
spring period, there was a surge in abundance of this 
species into offshore waters (mean group size: 127.7 in- 
dividuals; abundance: 101,900 individuals [CV=0.45]). 
The greatest seasonal abundance estimate (170,151 in- 
dividuals [CV=0.14]) was from the summer-fall period, 
a level that is very close to Barlow and Forney’s (2007) 
estimate for that seasonal period of 165,400 individu- 
als (CV=0.19). From aerial and ship-based line-transect 
surveys, the abundance of short-beaked common dol- 
phins off California has been shown to change on sea- 
sonal and interannual times scales (Dohl et al., 1986; 
Barlow, 1995; Forney et al., 1995). 
