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

Abstract

The link between ocean temperature and spatial and temporal 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 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 (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 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 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.