166 
Fishery Bulletin 112(2-3) 
Table 2 
Summary of sightings, including the number of cruises con- 
ducted by the California Cooperative Oceanic Fisheries Inves- 
tigations and the NOAA Southwest Fisheries Science Center 
in which each species was encountered and the total number 
of groups sighted in 1979-2009 in Southern California wa- 
ters for each studied species of small cetacean: short-beaked 
common dolphin (Delphinus delphis), long-beaked common 
dolphin ( D . capensis), Risso’s dolphin (Grampus griseus), 
northern right whale dolphin (LissocLelphis borealis ), Pacific 
white-sided dolphin ( Lagenorhynchus obliquidens), Dali’s por- 
poise ( Phocoenoides dalli), striped dolphin ( Stenella coeruleo- 
alba), and bottlenose dolphin ( Tursiops truncatus ). Because 
the short- and long-beaked common dolphins were not rec- 
ognized formally as distinct until 1994, data for both species 
were used in a combined category in analyses. 
Number of Number of 
Species cruises groups 
Short-beaked common dolphin 
29 
387 
Long-beaked common dolphin 
22 
93 
Both common dolphins 
105 
1537 
Risso’s dolphin 
74 
227 
Northern right whale dolphin 
32 
71 
Pacific white-sided dolphin 
62 
217 
Dali’s porpoise 
64 
240 
Striped dolphin 
22 
28 
Bottlenose dolphin 
50 
180 
ed during later SWFSC (1991-2005) cruises, mak- 
ing Survey Type an important predictor variable. 
Bottlenose dolphin 
Bottlenose dolphin groups tended to display a 
strong inshore and island association. They gen- 
erally were sighted over the continental shelf, 
although they were occasionally observed farther 
offshore, as shown in the depth residuals plots 
(Fig. 5). The PDO variable was significant, indi- 
cating that a slight increase in sightings occurred 
with negative PDO anomalies. 
Northern right whale dolphin 
Northern right whale dolphin is 1 of 3 cold-tem- 
perate species strongly associated with the Cali- 
fornia Current system. Therefore, the extent of 
this species into the Southern California study 
area was expected to correlate with cold-water 
intrusions. Sightings were associated with cool 
SSTs as expected. However, sightings were asso- 
ciated also with both positive and negative ENSO 
anomalies. Groups of northern right whale dol- 
phins showed a strong association with the slope 
region, with most sightings located at depths be- 
tween 2000 and 4000 m, as shown in the depth 
residuals plot (Fig. 6). 
Risso's dolphin 
Risso’s dolphins were largely observed inshore, al- 
though they were occasionally observed offshore and 
in areas of shallow depths and steep slope, as shown 
in the partial residuals plots for depth and slope (Fig. 
5). Sightings peaked slightly during warmer seasonal 
SSTs, around 18°C, but occurred least frequently in the 
summer. ENSO also was included in the model and in- 
dicated slightly more sightings during positive ENSO 
phases. 
Striped dolphin 
Striped dolphins are a tropical and warm-temperate 
species associated with warm water masses, and dol- 
phins of this species were predominantly observed off- 
shore of the 2000-m depth contour with a deep min- 
imum depth (Fig. 5). Because of this strong offshore 
distribution, only 28 groups were sighted during 22 
cruises. This low number of sightings is in part due 
to the limitation of including only sightings made in 
sea states rated 3 or less on the Beaufort scale; be- 
cause most striped dolphin sightings occurred offshore, 
many were made in higher-rated sea states and were, 
therefore, not included. Because of that exclusion, most 
sightings included for analyses came from data collect- 
Dall's porpoise 
Sightings of Dali’s porpoise, another cold-temperate 
species, peaked during the spring, fall, and winter (Fig. 
6), and groups of Dali’s porpoises were associated with 
cool SSTs. However, they were associated with slightly 
positive PDO phases, as well. They were distributed 
inshore and offshore, in areas of slightly shallower 
slopes, as shown in the depth and slope residuals plots. 
Pacific white-sided dolphin 
Results were unexpected for Pacific white-sided dol- 
phin, the final cold-temperate species the sighting 
rates of which were anticipated to increase in cooler 
temperatures. Sightings peaked slightly during the 
spring quarter when the water temperature was cool- 
er. However, they also exhibited an association with 
slightly positive PDO indices (Fig. 6). This species was 
distributed largely inshore, as shown in the depth re- 
siduals plot. 
Discussion 
Patterns of seasonal sea-surface temperatures 
Patterns of encounter rate related to seasonal SSTs were 
largely consistent with past studies within this region 
