Behavioral response of harbor porpoises to vessel noise in a tidal strait.

Abstract

Admiralty Inlet, a narrow channel in Puget Sound, WA, is the proposed location of a pilot tidal energy project. A pair of hydrokinetic turbines would be deployed, for evaluation, on the seabed in approximately 60 m of water. When extracting power from strong tidal currents, these turbines will also generate broadband noise. Harbor porpoises are known to exhibit strong avoidance behavior to loud noise and occur frequently in this area. Consequently, there is a concern that the project could cause local displacement of this species. Because Admiralty Inlet is a major shipping lane and traversed by a passenger ferry, there is already periodic, high intensity anthropogenic noise in the vicinity of the proposed tidal energy project. The behavioral response of harbor porpoises to these existing noise sources is evaluated to provide context for the potential impact from tidal turbine noise. This study combines data on shipping and ferry traffic from an automatic identification system receiver, received noise levels from broadband autonomous hydrophones, and current velocity from Doppler profilers. These are correlated with porpoise presence, as assessed by echolocations detected by Chelonia C‐Pods. Information collected over a full year provides insight into behavior at several time scales.