Benefits of voluntary vessel slowdowns to acoustic space reduction for killer whales

Abstract

Underwater noise from marine vessels can reduce the acoustic space that is available to marine mammals for performing critical life functions. Likewise, measures such as speed reductions that decrease vessel radiated noise can limit the extent to which acoustic space is affected by marine traffic. To investigate the benefits of voluntary summer vessel slowdowns in Haro Strait and Boundary Pass, the Enhancing Cetacean Habitat and Observation (ECHO) program commissioned a modelling study of acoustic space reduction which focused on two frequency bands relevant to resident killer whales: a communication band (0.5–5 kHz), using a metric termed Listening Space Reduction (LSR) and an echolocation band (15–100 kHz), using a metric termed Echolocation Space Reduction (ESR). The LSR and ESR metrics calculate a relative percent change from the maximum listening or echolocation space under natural ambient conditions to the reduced space caused by anthropogenic noise. Percent LSR and ESR was calculated in the study area at fine spatial (200 m) and temporal (1 min) resolution for scenarios representing baseline and slowdown traffic conditions. Results of this study demonstrate the benefits of voluntary vessel slowdowns on lost listening and echolocation space for resident killer whales.