Ship strikes and entanglements of gray whales in the North Pacific Ocean, 1924-2018
Jonathan Scordino, Dennis Litovka, Hyun Woo Kim
International Whaling Commission
Non-hunting, human-caused injuries and mortalities (NHHCIM) can have significant impacts on cetacean populations. Gray whales are likely more vulnerable than most whale populations to interactions with fishing gear due to their nearshore migratory and feeding behavior. We compiled all known sources of data on NHHCIM of gray whales in the North Pacific to document the frequency and source of NHHCIM. Data was compiled from national stranding and human-interaction databases, published reports, and newspaper articles. We documented 449 reports of NHHCIM of gray whales for the time period of 1924 through 2018. The majority of reports were from the time period of 1980 through 2018 when stranding networks were established along the US west coast. Of the 449 reports, 173 documented whale deaths. The remaining 245 reports were assessed using the policy developed by NOAA for distinguishing serious from non-serious injuries and prorating a probability of death to seriously injured whales. The sum of serious injuries and mortalities was 343.6 gray whales. The primary regions for reports were California (61.7%) and Northern California through Northern British Columbia (23.6%). The most common form of NHHCIM in gray whales was entanglement in net fisheries in the 1980s and 1990s. In the 2000s and 2010s the most common cause of NHHCIM was entanglement in pot fisheries (assuming most unknown entanglements were from pot fisheries). NHHCIM correlates with gray whale abundance suggesting that the high occurrences of NHHCIM in 2016 through 2018 was in part driven by high abundance in those years. This report represents a minimum estimate of the number of NHHCIM because it is difficult to definitively determine the cause of death of stranded whales, stranding networks had poor spatial coverage during all or part of the reporting time period, and because injured or killed whales not documented at sea may not wash to shore or be reported at-sea.