Effects of seismic exploration activities on bowhead whale call distribution in the Alaskan Beaufort Sea.

Abstract

Airgun use during seismic exploration activities is known to cause a decrease in call detection rates (used here as a proxy for calling rates) in migrating bowhead whales. However, the received airgun sound levels at the whales, at which behavioral changes occur, are not known. To address this question 40 directional autonomous seafloor acoustic recorders (DASARs) were deployed in autumn 2008 at five sites along the migration corridor of bowhead whales during ongoing marine seismic exploration activities. Over 440 000 whale calls were detected and localized by triangulation. Concurrently, over 100 000 airgun pulses were detected and analyzed. The study area was divided into a hexagonal grid (hexagon width 1.75 km). The received level (SPL and cumulative SEL) of airgun sounds was modeled for each hexagon in the study area and each 15‐min period over the entire season, using information on the timing and location of airgun activities, the size of the airgun array being used, the depth of the DASARs recording the airgun sounds, and other covariates. Logistic regression was then used to model occurrence of whale calls as a function of received level, distance offshore, and other covariates. [Work supported by Shell Exploration and Production Company.]