Abstract
During 2017, the Vancouver Fraser Port Authority's Enhancing Cetacean Habitat and Observation program carried out a two-month voluntary vessel slowdown trial to determine whether slowing to 11 knots was an effective method for reducing underwater radiated vessel noise. The trial was carried out in Haro Strait, British Columbia, in critical habitat of endangered southern resident killer whales. During the trial, vessel noise measurements were collected next to shipping lanes on two hydrophones inside the Haro Strait slowdown zone, while a third hydrophone in Strait of Georgia measured vessels noise outside the slowdown zone. Vessel movements were tracked using the automated identification system (AIS), and vessel pilots logged slowdown participation information for each transit. An automated data processing system analyzed acoustical and AIS data from the three hydrophone stations to calculate radiated noise levels and monopole source levels (SLs) of passing vessels. Comparing measurements of vessels participating in the trial with measurements from control periods before and after the trial showed that slowing down was an effective method for reducing mean broadband SLs for five categories of piloted commercial vessels: containerships (11.5 dB), cruise vessels (10.5 dB), vehicle carriers (9.3 dB), tankers (6.1 dB), and bulkers (5.9 dB).
Highlights
Marine shipping has long been recognized as a major source of underwater noise (Wenz, 1962) and is often the predominant source of man-made noise near major ports and shipping routes (NRC, 2003)
A total of 2765 vessel source levels (SLs) measurements were collected during the control and trial periods on the two hydrophone stations in Haro Strait and on the Strait of Georgia Underwater Listening Station (ULS)
A total of 920 transits in the pilot logs were matched to vessel measurements during the slowdown trial period
Summary
Marine shipping has long been recognized as a major source of underwater noise (Wenz, 1962) and is often the predominant source of man-made noise near major ports and shipping routes (NRC, 2003). Marine shipping is the dominant source of underwater ambient noise (Bassett et al, 2012) Key among these species is the endangered southern resident killer whale (SRKW), with a population of only 74 individuals as of 2018 (Center for Whale Research, 2018). This population was designated as endangered under Canada’s Species at Risk Act in 2001, which initiated the development of a recovery strategy (DFO, 2011, 2016) and an action plan (DFO, 2017) to address the current threats to northern resident killer whales and SRKWs in Canadian Pacific waters This recovery strategy designates much of the Salish Sea as SRKW critical habitat—the habitat necessary for the survival or recovery of the species. Under the U.S Endangered Species Act, critical habitat has been designated over much of the U.S waters of the Salish Sea
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