Ship strikes on large whales in the Salish Sea, Washington State: Insights from recent strandings and two well-documented fatal strikes by Washington ferries

Abstract

Ship strikes on large whales are of growing concern around the world as shipping traffic and speeds have increased and whale populations have recovered. In most cases ship strikes go undocumented, neither observed by crew or a stranded carcass. We report the details on recent observations of ship strikes and strandings of humpback whales in the Salish Sea that provide insight into this issue. Humpback whale populations have increased on the US West Coast and in the late-2000s returned in numbers to the Salish Sea, where they were common prior to whaling in the early 1900s. On two separate occasions (28 May 2019 and 6 July 2020), humpback whales were hit and killed in Puget Sound by Washington State ferries and were observed by a combination of passengers, people on shore, and a whale-watch vessel. Unlike most ship strikes, there was good documentation of the location, speed, and identity of the whale involved. From dorsal fin and fluke images we tracked sightings of these whales prior to the strike and with follow-up, confirmed they were not seen again after. Both cases occurred inside protected waters where stranding would have the highest chance of being detected yet no carcass was ever found. For the last 40 years, all seven known strandings of humpback whales in Washington inside waters occurred starting in 2015, with at least 3 of them the result of ship strike (not including the two observed). The recent return/expansion of humpback whales into the Salish Sea puts them at added risk as these two ferry-strikes did not even occur at locations of greatest overlap of whale distribution and shipping traffic. The complete documentation of these two strikes and the absence of a carcass recovery illustrates why ship strikes are severely underreported and highlights the threats to recovering whale populations.

Poster for 24^th Biennial Conference for Society of Marine Mammalogy. Palm Beach, Florida Aug 1-5, 2022. ID: SMM20221061