Seasonality of blue and fin whale calls and the influence of sea ice in the Western Antarctic Peninsula
Ana Širovića, John A. Hildebranda, Sean M. Wigginsa, Mark A. McDonaldb, Sue E. Moorec, and Deborah Thieled
aScripps Institution of Oceanography,
bWhale Acoustics, Bellvue,
Marine Mammal Laboratory,
Seasonality of blue (Balaenoptera musculus) and fin whale (B. physalus) calls off the west Antarctic Peninsula shelf break was compared to satellite derived sea ice coverage and chlorophyll a concentration data. The calling seasonality was assessed using acoustic data recorded on eight autonomous acoustic recording packages (ARPs) deployed from March 2001 to February 2002. Blue whale calls were detected on the ARPs year-round, but showed variable calling rates by site and season. The highest blue whale calling rates were in late January and early February and also in May and November. Temporal patterns in call rates suggest some blue whales remained close to the ice edge throughout the austral winter while another segment of the population was possibly migrating. Fin whale calls suggest a strong seasonal presence, with a peak in the autumn and absence of fin whale calls through the spring and summer. Relatively higher call counts for both species occurred at northern sites in autumn and more calls were detected at the southern sites in the summer. Both whale species show highest call counts later in the season than anticipated. Late seasonal presence could be related to the relatively late formation of ice in 2001. Phyoplankton blooms, as indicated by chlorophyll a measures, occurred at all sites during spring, after the ice melted.