Shipping noise and vocal compensation by Southern Resident killer whales: Haro Strait as a study case.

Abstract

Southern resident killer whales (SRKWs) use acoustic signals to navigate, forage, and facilitate social dynamics. Researchers have published evidence that suggests SRKW compensate for increased background noise by increasing the source level and duration of their signals. Unpublished reports have also suggested that SRKW may compensate for background noise by repeating their signals and by preferentially using certain signal types. Most of this work has focused on noise from whale watching vessels or general background noise. Haro Strait is both the center of the summertime home range of the SRKW and an important shipping channel. From September 2009 to December 2010 almost 10 000 ships transited through Haro Strait with an average of 21 ships passing per day. Ship transits in Haro Strait can increase background noise by up to 20 dB and are detectable above background noise for up to 30 min. This may be impacting the ability of SRKW to detect and utilize their acoustic signals. A five hydrophone array and Automatic Identification System receiver located at the Lime Kiln Lighthouse were used to record passing ships and SRKW in Haro Strait. This project investigates signal compensation strategies in SRKW in correlation with increased noise from passing ships.