Frequency of Pinniped-Caused Scars and Wounds on Adult Spring–Summer Chinook and Sockeye Salmon Returning to the Columbia River
At Bonneville Dam (Columbia River, 235 km from the mouth), the percentage of anadromous adult Pacific salmon Oncorhynchus spp. with abrasions (scars or wounds) caused by pinnipeds has increased from 2.8% in 1991 to 25.9% in 1996 for sockeye salmon O. nerka and from 10.5% in 1991 to as much as 31.8% in 1994 for spring–summer chinook salmon O. tshawytscha. Although there was a large increase in the percentage of salmonids with pinniped-caused abrasions between 1991 and 1996, fewer than 3% of the fish were judged to have abrasions sufficiently severe to adversely affect their survival to spawning. Larger, earlier-migrating chinook salmon were more likely to have abrasions than smaller, later-migrating fish. Similar trends were not found for sockeye salmon. Although these results suggest that pinniped predation may be an increasingly serious problem for Columbia basin salmonids, a lack of data that relates abrasions to pinniped-caused mortality makes it impossible to accurately estimate the magnitude of pinniped-caused mortality.
Fryer, J.K. 1998. Frequency of pinniped-caused scars and wounds on adult spring–summer Chinook and Sockeye Salmon returning to the Columbia River. North American Journal of Fisheries Management 18(1):46-51. Online at https://doi.org/10.1577/1548-8675(1998)018<0046:FOPCSA>2.0.CO;2.