Science activity

Sacramento River winter-run Chinook salmon have been endangered since 1994. Historically, the fish spawned during summer in cool tributaries upstream of Sacramento, but dams have limited spawning habitat to a small reach of the river. Today, survival of their offspring is heavily dependent on cool summer water releases from reservoirs, which also provide critical water supplies for irrigation, municipal, and industrial needs, as well as providing flood control and hydropower generation. During drought, this can lead to difficult management decisions. Understanding how winter run Chinook salmon respond to drought and water temperature is therefore vital to the management of this endangered population. This project tackled two outstanding questions about winter-run salmon ecology. The first was how winter-run Chinook use different rearing habitats during drought and non-drought periods, and the second was to explore which habitats provide enhanced growth during drought and non-drought periods. To answer these questions, UC Berkeley post-doc Pedro Morais used isotopic analysis of otoliths, or fish ear bones, which grow continuously throughout their lives and therefore carry a record of their environment and growth. Using otoliths, researchers can reconstruct details of fishes’ lives, including water temperature and migration patterns.