Brydeʹs whale seasonal range expansion and increasing presence in the Southern California Bight from 2000 to 2010

Brydeʹs whales (Balaenoptera edeni) are commonly found in tropical and subtropical regions of the Pacific Ocean, but few studies have explored the presence of Brydeʹs whales at the boundary of their distribution range. Such studies are increasingly relevant as climate impact models predict the range expansion of warm water species towards the poles in response to ocean warming. Like other baleen whales, Brydeʹs whales produce distinct low frequency (<60 Hz) calls, which can be used for long-term acoustic monitoring of whale presence in an area. Autonomous passive acoustic recorders deployed at five sites in the Southern California Bight (SCB) were used to investigate the presence of Brydeʹs whales in temperate waters from 2000 to 2010. Calling Brydeʹs whales were observed in the SCB from summer to early winter, indicating a seasonal poleward range expansion. There was a significant increase in the presence of calling Brydeʹs whales in the SCB between 2000 and 2010, but no significant correlation was found between Brydeʹs whale presence and local sea surface temperature. Brydeʹs whale occurrence is likely driven by prey availability within the California Current ecosystem, which is affected by seasonal and inter-annual changes in climate and oceanographic conditions. Continued monitoring of Brydeʹs whales and their prey in the eastern North Pacific is needed to provide a longer time series and determine the full effect of climate variability and ocean warming on the distribution of this species.