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SC/69A/IST/03
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Resource ID
20026
Access
Open
Document Number
SC/69A/IST/03
Full Title
Preliminary findings: Anthropogenic and killer whale (Orcinus orca) scarring on Pacific Coast Feeding Group gray whales (Eschrichtius robustus) in northwest Washington
Author
Ryan P. Walsh, Elizabeth M. Allyn, Jonathan J. Scordino
Authors Summary
Paper SC/68D/IST/XX assesses the rate of anthropogenic and killer whale scarring on live PCFG gray whales observed in northwest Washington during 2014-2020 and compares the observed rates of scarring to published studies of scarring of Sakhalin Island gray whales due to anthropogenic sources (Bradford et al., 2009) and killer whale attacks (Weller et al., 2018). The study found that of 139 PCFG gray whales, 11.5% had scarring from entanglements, 5% had scarring from vessel strikes, and 21.6% had scarring from killer whale attacks. The observed rates of entanglement scarring of PCFG whales were less than was previously reported for Sakhalin Island gray whales (Bradford et al., 2009) and was slightly greater for PCFG whales for vessel strikes, but the differences were not statistically significant. A significantly greater proportion of gray whales observed at Sakhalin Island had killer whale scars than did PCFG gray whales observed in northwest Washington. This study, Bradford et al. (2009), and Weller et al. (2018), all likely underreport the true frequency that gray whales were scarred due to poor photo coverage of the posterior portion of the caudal peduncle and of the fluke which are the body regions of the whale most commonly scarred by entanglement injuries and killer whale attacks. The finding of no significant differences in scarring from anthropogenic sources between PCFG and Sakhalin Island whales suggests that whales in the two regions likely have similar mortality rates from non-hunting anthropogenic sources.
Publisher
IWC
Publication Year
2026
Abstract
Gray whales face many threats to their survival that are multi-faceted and difficult to document. In this study, we evaluate scarring of Pacific Coast Feeding Group gray whales photographed during 2014–2020 off northwest Washington to document the occurrence of scarring from vessel strikes, entanglements, and killer whale attacks. We found that of the 139 PCFG whales evaluated, 11.5% had scarring from entanglements, 5.0% had scarring from vessel strikes, and 21.6% had scarring from killer whale attacks. We found no difference in scarring rates between males and females. Our observed rates of scarring from entanglements were less than previously observed at Sakhalin Island while our scarring rates from vessel strikes were slightly greater, but the differences were not statistically significant. Gray whales observed at Sakhalin Island had a significantly higher frequency of having scars due to killer whale attacks than the PCFG whales assessed in this study. Our estimates of anthropogenic and killer whale scarring are likely biased low because we had poor photographic coverage of the posterior caudal peduncle and tail region where scarring from killer whale attacks and entanglements are most commonly observed. Our methods were similar to past studies at Sakhalin Island, suggesting the studies had similar biases. Our finding of no significant differences in anthropogenic scarring between PCFG whales and Sakhalin Island whales can be used to evaluate if current models of gray whale threats from anthropogenic sources for the two groups are presenting plausible mortality estimates.