Henderson et al.: Effects of sea-surface temperature on the occurrence of small cetaceans off Southern California 
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Figure 1 
Map of the study area located off Southern California in the eastern North Pacific Ocean, south of Point Conception and incor- 
porating the Channel Islands, in which small cetacean distributions were recorded during 1979-2009. Colored areas indicate 
500-m depth contours. The blue area (mean depth <1 100 in, maximum depth <2000 m) was considered the inshore and island 
region, the green area (mean depth of 1000-3200 m, within a depth range of 500-3500 m) was considered the slope region, 
and the yellow area (mean depth >3500 m, maximum depth >4000 m) was considered the offshore region. 
We analyzed data from visual sightings of marine 
mammals from 105 separate survey cruises conducted 
by both CalCOFI and SWFSC from 1979 to 2009 (Fig. 
2). During CalCOFI cruises from May 1987 to April 
2004 (CalCOFIa) marine mammals were recorded as 
part of standardized CalCOFI top predator surveys 
that were focused primarily on marine birds. The 
strip-transect methods of Tasker et al. (1984) were fol- 
lowed. Observations were made with the naked eye by 
a single observer stationed on one side of the flying 
bridge or outside the main bridge. Marine mammals 
were recorded only if they occurred within the 300-m 
strip transect used for birds or within 1000 m of the 
vessel for large cetaceans. Each CalCOFI transect line 
extended from directly in front of the ship to 90° on 
the observation side. Group sightings of marine birds 
and mammals were summarized into 3-km bins, with 
the latitude and longitude determined for the centroid 
of each bin. Additional details of field methods are pro- 
vided in Veit et al. (1996; 1997), Hyrenbach and Veit 
(2003), and Yen et al. (2006). 
In July 2004, 2 dedicated marine mammal visual 
observers were added to the CalCOFI cruises (CalCO- 
Flb), and a standard line-transect protocol replaced the 
strip-transect protocol (Burnham et al., 1980; Buckland 
et al., 2001). A complete description of survey methods 
can be found in Soldevilla et al. (2006). Each observer 
monitored a 90° field of view from bow to abeam, one 
on each side of the ship, and alternated between scan- 
ning with Fujinon 1 7x50 binoculars (Fujifilm Corp., To- 
kyo) and with the naked eye. Survey effort was calcu- 
lated on the basis of latitude and longitude at the start 
and end of each trackline. 
For all CalCOFI surveys, observations were made 
on daytime tracklines between stations, and no visual 
observation effort was conducted while the vessel was 
stationary. All visual effort was conducted in sea state 
conditions rated 5 or less on the Beaufort scale. Data 
used for analyses were generally from 4 surveys per 
year from 1987 to 2009, 1 survey per season (typically 
in the same month but with some variation). In 5 of 
these years, only 3 surveys were conducted. In 1998, 
surveys were carried out monthly to capture a time 
series of oceanographic measures in a strong El Nino 
year. However, to be consistent across all years for pur- 
poses of analysis, these cruise data were combined into 
1 Mention of trade names or commercial companies is for iden- 
tification purposes only and does not imply endorsement by 
the National Marine Fisheries Service, NOAA. 
