The effects of vessel slowdowns on foraging habitat of the southern resident killer whales

The Enhancing Cetacean Habitat and Observation (ECHO) Program, a collaborative program led by Vancouver Fraser Port Authority, coordinated voluntary slowdowns for commercial shipping traffic in Haro Strait in the summers of 2017 and 2018, to better understand the relationship between vessel speed and source level, and how this may effect noise levels and foraging of the southern resident killer whales. With a speed target of 11 knots in 2017, a 61% participation rate of piloted ships was reported, resulting in a median broadband ambient noise level reduction of 1.7 dB re 1μPa, and a 22% reduction in “lost foraging time”, compared to baseline traffic conditions. In 2018 the slowdown aimed to increase participation by increasing target speeds to 15 knots and 12.5 knots, based on vessel type, thus decreasing operational and economic barriers to participation. This resulted in 87% of piloted vessels reporting participation, an ambient noise reduction of 1.5 dB re 1μPa, and a modelled reduction in “lost foraging time” on the order of 15%. These slowdown efforts indicate that voluntary operational measures by the shipping industry may be an effective means of reducing underwater noise in the foraging habitat of southern resident killer whales.