Associations Between Emigration Strategy, Habitat Use and Survival to Adulthood for Central Valley Winter-Run Chinook Salmon

As juvenile winter-run Chinook salmon migrate from the Sacramento River through the San Francisco Estuary into the Pacific Ocean, their growth, migration, and survival are heavily affected by water temperature and flow dynamics. Yet the relative importance and use of habitats within the winter-run migration corridor is poorly understood. Unique chemical markers within a watershed may be able to provide insight into the habitat usage and migratory behavior of juvenile salmonids. Here we examine the use of otolith microchemistry to reconstruct spatiotemporally explicit migration histories and habitat use of individual Central Valley Winter-run Chinook salmon. This project makes use of a high-resolution model of water chemistry to generate isotopic landscapes (isoscapes) of strontium and oxygen isotopes for the entire range of Winter-run habitat from the Sacramento River to the ocean. The ratio of strontium isotopes (⁸⁷Sr/⁸⁶Sr) of a watershed is determined by the geological age of the rock, while the ratio of oxygen isotopes (δ¹⁸O) depends on the average temperature and salinity of the water. The isoscape model will be driven by input from recently developed physical models of the river and estuary that provide hourly estimates of water temperature and salinity. These isotopic values are readily incorporated into the otoliths of teleost fishes, and are measured through laser ablation techniques in order to describe aspects of emigration behavior such as rearing in floodplain or estuarine habitats. With these isotopic values we are able to probabilistically map individuals onto the modeled isoscape and determine the habitat use and migration strategy of individuals through the migration corridor. This will dramatically increase our understanding of how habitat may influence the growth, long-term survival, and reproductive success of these anadromous fishes.