Trends in propeller strike-induced mortality in harbor seals

An article published in the Journal of Wildlife Diseases in 2021 describes research documenting injuries among harbor seals in the Salish Sea caused by boat propeller strikes. The number of strikes increased significantly between 2002 and 2019, as did vessel traffic.

Several harbor seals lying on a rock
Harbor seals. Photo: Tony Cyphert (CC BY-NC-ND 2.0)


Documenting human impacts on marine mammals is critical for understanding and mitigating harm. Although propeller strike injuries in small marine mammals are often debilitating and fatal, little is known about the occurrence or demographics of these types of injuries in pinniped populations. Using data of stranded harbor seals (Phoca vitulina) in the Salish Sea from 2002–19, we identified 27 cases of fatal propeller strikes. Weaned pups were the most frequently affected (64% of cases) with a much higher rate of propeller strikes than expected for the age class. Although they do represent animal welfare concerns, harbor seals in the Salish Sea probably are not threatened by these types of injuries at the population level; nevertheless, propeller strike cases increased significantly over the time of this study period, indicating increased interactions between boats and seals in the region. Continued monitoring and increased efforts to consistently quantify vessel traffic in the area are recommended to create and monitor long-term effectiveness of mitigation measures.

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About the Author: 
Jennifer K. Olson,1,6 ; Dyanna M. Lambourn,2; Jessica L. Huggins,3; Stephen Raverty,4; Alyssa A. Scott,1; and Joseph K. Gaydos5 1The Whale Museum,Friday Harbor, WA, USA; 2Washington Department of Fish & Wildlife, Tacoma, WA, USA; 3Cascadia Research Collective,Olympia, WA, USA; 4Animal Health Center, Abbotsford, BC, Canada; 5SeaDoc Society, Eastsound, WA, USA