Predation on Sockeye Salmon Fry by Juvenile Coho Salmon in the Chignik Lakes, Alaska: Implications for Salmon Management

Abstract

-The consumption of recently emerged sockeye salmon Oncorhynchus nerka by juvenile coho salmon O. kisutch in Chignik Lake, Alaska, was estimated for 15 May–5 August, 1985–1987. Estimated daily consumption of sockeye salmon fry by individual coho salmon in Chignik Lake, based on a stomach evacuation method, increased from about 2.0 fry in late May to 3.3 fry in June, then it declined in July and early August to 1.1 fry. Average consumption during each year, based on a bioenergetic approach, was within 14% (range, 15–20%) of the stomach evacuation method estimates, whereas bioenergetic estimates on a given day generally were within 30% of the stomach evacuation method estimates. Few coho salmon were captured in nearby Black Lake, where consumption of sockeye salmon fry per juvenile coho salmon was low. Estimates of sockeye salmon fry consumed by coho salmon in Chignik Lake, based on two independent estimates of juvenile coho salmon abundance, were 68 million, 24 million, and 78 million, which represented approximately 59% of the average population of sockeye salmon fry for 1985, 1986, and 1987. Numbers of adult sockeye salmon returning per spawner in Chignik Lake were generally high during brood years 1971–1976 relative to 1977–1984. This pattern was opposite that of sockeye salmon adults returning to Black Lake and other sockeye salmon systems in western and central Alaska. Greater abundance of juvenile coho salmon in the Chignik lakes during recent years, as indicated by greater abundance of adult coho salmon, and the large number of sockeye salmon fry consumed by coho salmon in this field study suggest that juvenile coho salmon reduced returns of sockeye salmon to Chignik Lake, A management strategy resulting in a fixed spawning escapement of coho salmon, combined with the currently fixed escapement of sockeye salmon, is recommended to reduce and stabilize predation by juvenile coho salmon on sockeye salmon fry in Chignik Lake.