Douglas et al. Seasonal distribution and abundance of cetaceans off Southern California 
199 
124°W 
l 
122“W 
_l 
120°W 
l 
1 18°W 
l 
116°W 
i 
Santa Barbara 
Los Angeles 
Study area zones 
167.087 km 2 ; Deep (>=2000 5 m) 
71,407 km 2 Shallow (<2000 5 m) 
Survey effort 
■ CalCOFI stations 
Bathymetry contour (500 m) 
N 
I 1 1 1 1 
0 25 50 100 km 
San Diego 
l). S. A._ 
MEXICO 
CANADA 
124°W 
122°W 
120°W 
118°W 
116°W 
Figure 1 
Map of the study area and 6 southern transect lines of 16 quarterly California Cooperative Oceanic 
Fisheries Investigation (CalCOFI) surveys conducted from July 2004 to April 2008 off Southern Cali- 
fornia. Shallow survey area (<2000.5 m) is lighter gray and deep survey area (>2000.5 m) is dark gray. 
Dark squares on CalCOFI transect lines indicate oceanographic sampling stations. The CalCOFI study 
area (238,494 km 2 ) occurs completely inside the larger southern stratum (318,500 km 2 ) of the South- 
west Fisheries Science Center shipboard surveys that extends farther to the northwest. 
winter and spring months (Dohl et al. 1 ; Forney and Bar- 
low, 1998; Becker, 2007). In this study, new estimates 
of cetacean abundance were calculated off Southern 
California with marine mammal sighting data collected 
during 16 cruises undertaken as part of the California 
Cooperative Oceanic Fisheries Investigation (CalCOFI) 
(Bograd et al., 2003; Ohman and Venrick, 2003; Soldev- 
illa et al., 2006). Marine mammal surveys on CalCOFI 
cruises are conducted quarterly, along predetermined 
transect lines between oceanographic water sampling 
stations (Fig. 1). The depth of the study area is ex- 
tremely variable, with shallow waters inshore of the 
Channel Islands, a steep slope west of these islands, 
and an expansive deepwater plain offshore. Almost 
1 Dohl, T. P., K. S. Norris, R. C. Guess, J. D. Bryant, and M. 
W. Honig. 1980. Summary of marine mammal and seabird 
surveys of the Southern California Bight area, 1975-1978. 
Part II. Cetacea of the Southern California Bight. Final 
report to the Bureau of Land Management, NTIS Rep. No. 
PB81248189, 414 p. 
30% of CalCOFI transect lines occur in water depths 
of 20-2000 m, and 69% of them occur in water depths of 
3001-4600 m, and there is minimal (1%) coverage with 
transect lines in water depths of 2001-3000 m owing 
to the steep slope and orientation of the transect lines. 
Therefore, this study provides information on seasonal 
and interannual presence of cetaceans in both coastal 
and deep offshore waters. Such information is important 
to understanding and potentially mitigating effects of 
human activities on cetacean populations off Southern 
California. 
Materials and methods 
Data collection 
Dedicated visual observers conducted line-transect 
surveys for marine mammals (Buckland et al., 1993; 
Kinzey and Gerrodette, 2003) during 16 quarterly Cal- 
