Fishery and Hatchery Effects on an Endangered Salmon Population with Low Productivity

We estimated the natural spawner–fry stock–recruitment relationship and juvenile survival rates for Sacramento River winter Chinook Salmon Oncorhynchus tshawytscha in California and used these estimates to examine the expected numbers of spawners and fishing mortality under different fishing mortality rates and levels of hatchery supplementation. A stochastic, age-structured population dynamics model was fit to fry and female spawner abundance data for the years 1996–2010. Estimated survival rates of fry through the end of the first year in the ocean were generally <0.5%. Estimated survival rates of hatchery-origin fish from egg to the end of the first year in the ocean were on average about four times greater than the estimated maximum rate for natural-origin fish. The hatchery program was estimated to increase the number of spawners returning to natural spawning areas and thereby increase the fishing mortality rate that could be sustained. Assessing the past or future net effect of the hatchery on the size of the natural population would require quantifying any potential reduction in the productivity of the natural population as a result of reduced fitness of hatchery-origin fish spawning in natural spawning areas.

Received February 21, 2013; accepted December 14, 2013.