Human-Mediated Evolution in a Threatened Species?

A third of historic Pacific salmon populations in the Pacific Northwest have been extirpated, and half of the remainder are federally protected under the U.S. Endangered Species Act (ESA).  A great deal of time, effort, and money has been spent on evaluating the ecological/demographic factors that caused the declines or are impeding recovery (e.g., what fraction of adults are taken in sport, commercial, and tribal fisheries?  How many juveniles are killed at each Columbia River dam?  How much is egg-smolt survival reduced by poor land-uses practices?).  However, all of these human-modifications to salmon ecosystems also change the types of salmon that survive and reproduce, and this leads to evolutionary change that can have profound consequences for conservation and management.  In this study, we use parentage analysis to determine whether an observed change in life history traits in an ESA-listed species (a change from subyearling to yearling smolt migration in Snake River fall Chinook salmon) is at least partially under genetic control.  After controlling for other factors that can influence juvenile growth rate, we show that parents that themselves migrated to sea as subyearlings produce faster-growing offspring than parents that migrated as yearlings—the result expected if the trait is at least partially heritable.  Results of this ongoing study have important implications for current and future management of the Columbia River hydropower system.