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Fishery Bulletin 112(2-3) 
ern California by using a unique coupled cetacean- 
oceanographic long-term data set. This data set enables 
a rare opportunity to assess interdecadal changes in 
cetacean distribution over a broad spatial extent. The 
co-occurrence of cold- and warm-water cetacean species 
makes this location an ideal one at which to examine 
potential effects of climate variation on regional dis- 
tribution patterns at different temporal scales (intra- 
annual, annual, and decadal). 
The Southern California region represents the con- 
vergence of warm- and cold-water masses and supports 
populations of both warm- and cold-water, small ceta- 
cean species (Forney and Barlow, 1998). During the 
summer, the cold, equatorward flowing California Cur- 
rent system has a seasonal maximum (7.8 Sverdrups 
[Sv], -7.8 million m 3 s _1 ). The California Current turns 
shoreward (poleward) at approximately 32°N and be- 
comes the California Countercurrent. The California 
Countercurrent and California Undercurrent also have 
a seasonal maximum in late summer and into the fall 
and, therefore, dominate the Southern California Bight, 
with a combined maximum transport in October of 1.8 
Sv. The California Undercurrent reaches its minimum 
(0.8 Sv) and turns equatorward in the spring. The Cali- 
fornia Countercurrent turns equatorward then as well; 
therefore, all flow through the Southern California re- 
gion becomes equatorward in the spring, allowing the 
California Current to dominate and transport cooler 
water farther south (Hickey, 1993; Hickey et ah, 2003). 
In the California Current system, strong El Nino 
years in the positive ENSO phase have been linked to 
increased downwelling, warmer SSTs, and a deepening 
of the thermocline observed off Southern California 
(Sette and Isaacs, 1960; McGowan, 1985; Caldeira et 
ah, 2005). During the warm, positive phase of the PDO, 
the California Current is weakened and the Counter- 
current is strengthened. This intensified current brings 
warmer waters farther north and west into and beyond 
the Southern California region, creating warm SST 
anomalies along the California coast. In contrast, dur- 
ing the cool, negative PDO phase, the California Cur- 
rent is stronger, bringing cool water farther south and 
east into the region (Mantua and Hare, 2002). A PDO 
regime shift from cool to warm occurred around 1977, 
before our study, and a shift back to a cool PDO may 
have occurred during the last decade starting in 1998- 
99 (Peterson and Schwing, 2003; Zhang and McPhaden, 
2006; Wang et al., 2010). 
Two long-term sets of ship-based surveys have been 
conducted in Southern California waters, making it an 
ideal region for this investigation. The California Coop- 
erative Oceanic Fisheries Investigations (CalCOFI) has 
been conducting quarterly cruises that have sampled a 
breadth of oceanographic and lower-trophic-level bio- 
logical data since 1949. Marine bird and mammal ob- 
servations were added in 1987 (Hyrenbach and Veit, 
2003; Sydeman, et al., in press). The NOAA Southwest 
Fisheries Science Center (SWFSC) also regularly has 
conducted marine mammal abundance surveys that 
have included this region since 1979. 
Changes in SST have been linked to changes in all 
levels of the food web, from immediate phyto- and zoo- 
plankton responses to lagged alterations in numbers, 
diet, and even reproductive success of higher-level or- 
ganisms, such as Ashes, seabirds, and marine mammals 
(Tibby, 1937; Hubbs, 1948; McGowan, 1985; McGowan 
et ah, 2003; Sydeman et al., in press). It follows that 
small cetacean populations would respond to such vari- 
ations in SST, likely as a response to changes in prey 
populations, as has been shown for seabirds (Hyren- 
bach and Veit, 2003). In addition, population-level re- 
sponses to these fluctuations in temperature may pre- 
dict their reaction to future ocean conditions as global 
ocean temperatures rise. 
We investigated such responses by 8 species of small 
cetaceans across 30 years, using SST averages and 
anomaly indices as a proxy for environmental varia- 
tion on 3 temporal scales: seasonal (yearly), ENSO 
(2-7 years) and PDO (-30 years). We predicted that 
patterns in small cetacean occurrence and distribution 
within Southern California waters would follow simi- 
lar trends reported for seabirds (Hyrenbach and Veit, 
2003; Yen et al., 2006; Sydeman et al., in press) and 
other cetaceans (Forney and Barlow, 1998; Becker et 
al., 2012). For small cetaceans off Southern Califor- 
nia, the following trends were predicted: 1) species as- 
semblages will differ depending on the dominant SST 
regime, 2) cold-water-associated species will be more 
abundant and broadly distributed when cold-water con- 
ditions prevail, 3) warm-water-associated species will 
dominate during warm-water conditions, and 4) the lat- 
ter 2 patterns will be compounded when SST fluctua- 
tions co-occur on multiple scales. 
Materials and methods 
Study area and survey methods 
Our study area was situated between 117°W and 125°W 
longitude and from 30°N to 35°N latitude (Fig. 1) and 
includes the Southern California Bight as well as 
deeper offshore waters. The Southern California Bight 
is a region of complex bathymetric features, including 
the Channel Islands and a series of deep basins and 
shallow ridges (Dailey et al., 1993). Beyond the steep 
2000-m slope lies the ocean basin, with a mean depth 
of >3500 m. Three regions, associated with depth, were 
defined in the analyses for this study (Fig. 1): 1) the 
inshore and island region (with a mean depth <1100 
m and a maximum depth <2000 m; 2) the slope region 
(with a mean depth of 1000-3200 m and a depth range 
of 500-3500 m); and the offshore region (with a mean 
depth >3500 m and a maximum depth >4000 m). The 
terms for these three regions will be used throughout 
the study. 
