159 
Abstract— The link between ocean 
temperature and spatial and tempo- 
ral distribution patterns of 8 species 
of small cetaceans off Southern Cali- 
fornia was examined during the period 
1979-2009. Averages and anomalies 
of sea-surface temperatures (SSTs) 
were used as proxies for SST fluctua- 
tions on 3 temporal scales: seasonal, El 
Nino-Southern Oscillations (ENSO), 
and Pacific Decadal Oscillations (PDO). 
The hypothesis that cetacean species 
assemblages and habitat associations 
in southern California waters co-vary 
with these periodic changes in SST was 
tested by using generalized additive 
models. Seasonal SST averages were 
included as a predictor in the models 
for Dali’s porpoise ( Phocoenoides dalli), 
and common dolphins ( Delphinus spp.), 
northern right whale dolphin ( Lisso - 
delphis borealis), and Risso’s dolphin 
( Grampus griseus). The ENSO index 
was included as a predictor for north- 
ern right whale, long-beaked common 
(Delphinus capensis ), and Risso’s dol- 
phins. The PDO index was selected 
as a predictor for Dali’s porpoise and 
Pacific white-sided (Lagenorhynchus 
obliquidens), common, and bottlenose 
( Tursiops truncatus) dolphins. A metric 
of bathymetric depth was included in 
every model, and seafloor slope was 
included in 5 of the 9 models, an indi- 
cation of a distinctive spatial distribu- 
tion for each species that may repre- 
sent niche or resource partitioning in 
a region where multiple species have 
overlapping ranges. Temporal changes 
in distribution are likely a response 
to changes in prey abundance or dis- 
persion, and these patterns associated 
with SST variation may foreshadow 
future, more permanent shifts in dis- 
tribution range that are due to global 
climate change. 
Manuscript submitted 1 April 2013. 
Manuscript accepted 28 March 2014. 
Fish. Bull. 112:159-177 (2014). 
doi:10.7755/FB.112.2-3.5 
The views and opinions expressed or 
implied in this article are those of the 
author (or authors) and do not necessarily 
reflect the position of the National 
Marine Fisheries Service, NOAA. 
Effects of fluctuations in sea-surface 
temperature on the occurrence of small 
cetaceans off Southern California 
E. Elizabeth Henderson 1 
Karin A. Forney 2 
Jay P. Barlow 3 
John A. Hildebrand 1 
Annie B. Douglas 4 
John Calambokidis 4 
William J. Sydeman 5 
Email address for contact author: elizabeth.henderson@nmmpfoundation.org 
1 Scripps Institution of Oceanography 
University of California, San Diego 
9500 Gilman Drive Mailcode 0905 
La Jolla, California 92093 
Present address for contact author: National Marine Mammal Foundation 
2240 Shelter Island Drive, Suite 200 
San Diego, California 92106 
2 Marine Mammal and Turtle Division 
Southwest Fisheries Science Center 
National Marine Fisheries Service, NOAA 
1 10 Shaffer Road 
Santa Cruz, California 95060 
3 Marine Mammal and Turtle Division 
Southwest Fisheries Science Center 
National Marine Fisheries Service, NOAA 
8901 La Jolla Shores Drive 
La Jolla, California 92037 
4 Cascadia Research Collective 
2181/2 W. 4 th Ave. 
Olympia, Washington 98501 
5 Farallon Institute for Advanced Ecosystem 
Research 
101 H Street, Suite Q 
Petaluma, California 94952 
Highlands, New Jersey 07732 
Cetaceans are higher-trophic-level 
marine predators whose movement 
patterns and habitat preferences are 
typically related to the distribution 
of their prey (Wishner et ah, 1995; 
Gowans et al. 2007). Unlike baleen 
whales, small cetaceans (porpoises, 
dolphins, and small-toothed whales) 
generally do not undertake ocean- 
scale annual migrations to track 
prey or to move between breeding 
and feeding grounds. Rather, small 
cetaceans may display a high degree 
of site fidelity, or they may move sea- 
sonally inshore and offshore or along 
regional-scale coastlines (Leather- 
wood et ah, 1984; Dohl et ah, 1986; 
Shane et ah, 1986; Forney and Bar- 
low, 1998). 
Although many small cetacean 
species may overlap in any one re- 
gion of their total range, they often 
differ in their occurrence or habitat- 
use patterns, perhaps reflecting com- 
petitive exclusion or niche partition- 
ing. This separation of habitat and 
resources often occurs along depth, 
slope, and sea-surface temperature 
(SST) gradients (Reilly, 1990; Forney, 
2000; Ballance et ah, 2006; MacLeod 
et al., 2008). Habitat preferences 
likely reflect differences in preferred 
prey. Dolphins may follow prey habi- 
tats as they shift not only season- 
ally but through large-scale climate- 
driven changes such as the El Nino- 
Southern Oscillation (ENSO) or the 
Pacific Decadal Oscillation (PDO) 
(Shane, 1995; Defran, 1999; Benson 
et ah, 2002; Ballance et ah, 2006). 
We examined the distribution and 
relative abundance of multiple spe- 
cies of small cetaceans across shift- 
ing temperature regimes off South- 
