Growth of juvenile salmonids is a critical variable affecting survival and recruitment to successive life history stages, essentially affecting the strength of subsequent cohorts. Consumption and temperature are key variables affecting growth for fishes in general. Temperature dictates the metabolic efficiency of prey conversion to production, and is thus a primary variable affecting growth. Growth is an ideal indicator of habitat suitability, which is very informative for river restoration projects. However, temperature optima and thresholds are likely variable for Pacific salmon populations. Yet many researchers using bioenergetic approaches to understand growth use generalized temperature-dependent equations and coefficients for Chinook Salmon adults. This project addresses whether generalized bioengergetic coefficients are suitable for juveniles at the southern end of the species range. Our approach uses several lines of evidence to better understand relationships between temperature and growth. We focus this effort on juvenile Chinook Salmon in the San Joaquin River Restoration Program, which seeks to restore the southern-most run in North America. We used meta-analyses of growth rate and temperature relationships for wild populations, simulations with inSTREAM and bioenergetics models, and hatchery data. We are also using bomb calorimetry data to directly measure juvenile energy densities and very discrete levels of habitat temperatures to improve bioenergetic model accuracy.
Results from these multiple lines of evidence suggest that juvenile Chinook Salmon growth rates in southern rivers are quite robust, despite the degraded conditions of these ecosystems. We found that estimated scope for growth and consumption rates differ by ca. 35% by using direct versus published energy densities of juveniles. Further, temperatures in the restoration reach varied by as much as 10C during the rearing season, which greatly affects the estimated consumption rates of prey, which is valuable for establishing the carrying capacity of the restoration reach. Our broader main objectives are to generate population and habitat specific bioenergetics algorithms and encourage a broader use of population-specific relationships of temperature and growth rate. A focus on these approaches can help fisheries managers set realistic expectations for restoration projects.