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SC/69A/IST/02
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Resource ID
20024
Access
Open
Document Number
SC/69A/IST/02
Full Title
Ship strikes and entanglements of gray whales in the North Pacific Ocean, 1924-2021
Author
Jonathan Scordino, Gen Nakamura, Hyun Woo Kim, Jorge Urban, And Paul Cottrell
Authors Summary
Paper SC/68D/ISTXX provides an updated assessment of all known reports of gray whale non-hunting, human-caused injuries and mortalities (NHHCIM) during 1924-2021. The paper provides new data for 2019 to 2021 and adds additional cases that were not documented in past assessments that occurred prior to 2019 (Scordino et al. 2020). The primary sources of NHHCIM are entanglements and ship strikes. Reporting of NHHCIM was most common in the regions of California and northern California through northern British Columbia, likely due to well-established stranding networks in those regions. During the five most recent years of data collection (2017-2021) there were an average of 14.3 NHHCIM per year, which was substantially more than during the previous five-year period of 2012-2016 which had 9.9 NHHCIM per year.
Publisher
IWC
Publication Year
2024
Abstract
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 humans 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 513 reports of NHHCIM of gray whales for the time period of 1924 through 2021. The majority of reports were from the time period of 1980 through 2021 when stranding networks were established along the US west coast. Of the 513 reports, 194 documented whale deaths. The remaining 319 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 and found that 250 documented serious injuries and 69 were non-serious injuries. Responders in the USA, Canada, and Mexico successfully disentangled 50 whales which resulted in the whale receiving non-serious injury. The sum of serious injuries and mortalities was 388.44 gray whales. The primary regions for reports were California (58%) and Northern California through Northern British Columbia (24%). 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 were pot fishery gear and entanglements of an unknown source. During the 2020s, unknown entanglements and ship strikes were the most common source of NHHCIM. During the five most recent years of data collection (2017-2021) there was an average of 14.3 NHHCIM per year which was substantially more than the previous five-year period of 2012-2016 which had 9.9 NHHCIM per year. 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.