Effects of airgun sounds on bowhead whale calling rates in the Alaskan Beaufort Sea

This study assesses effects of airgun sounds on bowhead calling behavior during the autumn migration. In August-October 2007, 35 directional acoustic recorders (DASARs) were deployed at five sites in the Alaskan Beaufort Sea. Location estimates were obtained for >137,500 individual calls; a subsample of locations with high detection probability was used in the analyses. Call localization rates (CLRs) were compared before, during, and after periods of airgun use between sites near seismic activities (median distance 41-45km) and sites relatively distant from seismic activities (median distance >104km). At the onset of airgun use, CLRs dropped significantly at sites near the airguns, where median received levels from airgun pulses (SPL) were 116-129 dB re 1 Pa (10-450 Hz). CLRs remained unchanged at sites distant from the airguns, where median received levels were 99-108 dB re 1 Pa. This drop could result from a cessation of calling, deflection of whales around seismic activities, or both combined, but call locations alone were insufficient to differentiate between these possibilities. Reverberation from airgun pulses could have masked a small number of calls near the airguns, but even if masking did take place, the analysis results remain unchanged.