208 
Fishery Bulletin 112(2-3) 
Table 4 
Encounter rate, the number of encounters (Enc) per 1000 km, and number of sightings n of cetacean species by season on 
the 6 southern transect lines during 16 quarterly California Cooperative Oceanic Fisheries Investigation (CalCOFI) cruises 
conducted from 2004 to 2008 off Southern California, for species seen on 10 or more occasions. The value under each season 
represents the combined length of the transect lines surveyed. 
Winter 
Spring 
Summer 
Fall 
All seasons 
(4165 km) 
(4904 km) 
(6211 km) 
(4716 km) 
(19,996 km) 
Species 
Enc/1000 km, n 
Enc/1000 km, n 
Enc/1000 km, n Enc/1000 km, n 
Enc/1000 km, n 
Humpback whale 
0,0 
2.2, 11 
1.6, 10 
2,7, 13 
1.7,34 
Blue whale 
0,0 
0,0 
3.1, 19 
1.3, 6 
1.3,25 
Fin whale 
0.7,3 
1.0, 5 
3.7,23 
4.7, 22 
2.7,53 
Minke whale 
0,0 
1.4, 7 
0.3, 2 
0.2, 1 
0.5, 10 
Sperm whale 
1.0, 4 
0.4, 2 
1.9, 12 
0.4, 2 
1.0,20 
Short-beaked common dolphin 
7.2,30 
0.8,4 
9.5,59 
6.1, 29 
6.1, 122 
Long-beaked common dolphin 
Common dolphin (unknown short- 
0.2, 1 
0.2, 1 
1.3,8 
1.5,7 
0.9, 17 
or long-beaked) 
2.6, 11 
1.6,8 
5.5,34 
4.0, 19 
3.6, 72 
Pacific white-sided dolphin 
2.6, 11 
4.7, 23 
1.1, 7 
1.1, 5 
2.3, 46 
Risso’s dolphin 
0.7,3 
1.6,8 
0.2, 1 
0.4, 2 
0.7, 14 
Bottlenose dolphin 
0.5,2 
1.0, 5 
0.2, 1 
0.8,4 
0.6, 12 
Northern right whale dolphin 
0.2, 1 
1.8,9 
0,0 
0,6,3 
0.7, 13 
Dali’s porpoise 
2.6, 11 
7.1,35 
0.2, 1 
0.4, 2 
2.5,49 
highest encounter rate (Table 4) and were the most 
abundant of large whales in the study area (Table 5), 
with the greatest density estimate from summer-fall 
surveys in shallow water, 3.67 individuals/1000 km 2 
(CV=0.30) (Tables 6 and 7), and with the greatest abun- 
dance during the summer-fall surveys in deep water. 
Fin whales were the only whale species that showed 
a significant difference in depth, distance to land, and 
distance to shelf by seasonal period (Table 7; Figs. 5 
and 6). Humpback whale density was highest during 
the summer-fall surveys in shallow water with 3.08 
individuals/1000 km 2 (CV=0.36) (Table 5). Least abun- 
dant of the large whales, blue whales were encountered 
only during the summer-fall surveys, with the greatest 
density and abundance in shallow water, 3.20 individu- 
als/1000 km 2 and 228 individuals (CV=0.26) (Table 5). 
Odontocetes Although sperm whales were most abun- 
dant during the summer-fall surveys in deep water, 
158 individuals (CV=0.36) (Table 5), density was simi- 
lar for both shallow areas (0.94 individuals/1000 km 2 
[CV=0.44]) and deep areas (0.95 individuals/1000 km 2 
[CV=0.36]) for that seasonal period. Short-beaked com- 
mon dolphins were the most abundant cetacean spe- 
cies, encountered in all seasons and at all depths; the 
highest encounter rate was observed in the summer 
months (Table 4) and the greatest density estimate 
was obtained from summer-fall surveys in shallow wa- 
ter, 1319.69 individuals/1000 km 2 (CV=0.24) (Table 5). 
Long-beaked common dolphins were the second-most 
abundant cetacean species; however, this species was 
encountered only in shallow water and, seasonally, 
there was a dramatic shift in density with 22 times 
more long-beaked common dolphins observed during 
the summer-fall surveys than during the winter- 
spring surveys (Table 5). Because of the difficulty of 
distinguishing between short- and long-beaked common 
dolphins from a survey conducted in passing mode, 72 
out of 211 on-effort common dolphin sightings were 
not identified to species (Table 3). Densities of Pacific 
white-sided, northern right whale, and Risso’s dolphins 
were greatest during the winter-spring period in shal- 
low water, and Dali’s porpoises were most abundant 
during the winter-spring seasonal period in deep wa- 
ter; these species were least abundant during the sum- 
mer-fall period. Abundance of Dali’s porpoises varied 
strongly by seasonal period but not by depth. Beaked 
whales were encountered on 6 occasions, with Cuvier’s 
beaked whale ( Ziphius cavirostris) the most commonly 
encountered (3 occasions). 
Discussion 
Monitoring and management of marine mammal spe- 
cies off Southern California has often relied heavily 
on abundance estimates generated from line-transect 
surveys conducted during the summer and fall, despite 
year-round anthropogenic activities and significant sea- 
sonal spatial movements of many species (Forney and 
Barlow, 1998). Our observations from the 16 CalCOFI 
surveys conducted between 2004 and 2008 provide the 
most current and consistent data set on seasonal shifts 
in movements and abundance for the most commonly 
