Effects of fluctuations in sea-surface temperature on the occurrence of small cetaceans off Southern California


Henderson, E. Elizabeth, Karin A. Forney, Jay P. Barlow, John A. Hildebrand, Annie B. Douglas, John Calambokidis, and William J. Sydeman
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The link between ocean temperature and spatial and temporal distribution patterns of 8 species of small cetaceans off Southern California was examined during the period 1979–2009. Averages and anomalies of sea-surface temperatures (SSTs) were used as proxies for SST fluctuations on 3 temporal scales: seasonal, El Niño–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 Dall’s porpoise (Phocoenoides dalli), and common dolphins (Delphinus spp.), northern right whale dolphin (Lissodelphis borealis), and Risso’s dolphin (Grampus griseus). The ENSO index was included as a predictor for northern right whale, long-beaked common (Delphinus capensis), and Risso’s dolphins. The PDO index was selected as a predictor for Dall’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 indication of a distinctive spatial distribution for each species that may represent 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 dispersion, and these patterns associated with SST variation may foreshadow future, more permanent shifts in distribution range that are due to global climate change.