Monitoring Climate Impacts: Survival and Migration Timing of Summer Chum Salmon in Salmon Creek, Washington

Abstract

AbstractIn rivers of the Pacific Northwest, climate change is predicted to increase flow variability and water temperature, which may ultimately affect salmonid survival and the seasonal timing of key life history transitions. Summer Chum Salmon Oncorhynchus keta, native to tributaries flowing into Hood Canal and Strait of Juan de Fuca in Washington State, are particularly vulnerable to flow and temperature changes given their early spawn timing, yet relatively little is known regarding their juvenile life history. We investigated how flow and incubation temperatures influenced juvenile survival and timing of Chum Salmon in Salmon Creek between 2008 and 2016. Egg‐to‐migrant survival ranged from 0.9% to 46.3%, and was negatively related to the peak flow experienced during egg incubation from November 1 to January 31. Warm temperatures advanced emergence timing, as the number of days between the median spawning date and the median juvenile migration date was negatively related to average stream temperature during the same period. We used empirical data to estimate the range of accumulated temperature units (TUs) and survival that best explained the observed juvenile migration in the spring. The model indicated that incubating eggs experiencing warmer temperatures (2010, 2015, and 2016) accrued more TUs before emigration than did eggs incubating during colder years (2008, 2009, and 2014). Although the population exhibited some ability to compensate for warmer temperatures and stabilize emergence timing by increasing TU thresholds, our analysis, when combined with climate projections, suggests that warming temperature trends could significantly advance the timing of marine entry by weeks or more. Such a change could carry a corresponding impact on marine survival if emigration timing becomes desynchronized with spring zooplankton blooms in the marine environment, the primary source of nutrition for juvenile summer Chum Salmon.Received December 21, 2016; accepted April 16, 2017 Published online July 31, 2017