Characterizing Yearling Chinook Salmon Migration Behavior

Juvenile yearling Chinook salmon emigrating from the Columbia River, USA, tend to migrate north towards British Columbia and Alaska.  However, coastal currents in this area generally flow southward during spring and summer.  Do salmon initiate an energetically-expensive positive rheotactic migration with the genetic ‘knowledge’ that feeding conditions are better in the north?  Or do they solely respond to local conditions to maximize growth or survival, inadvertently selecting small-scale currents and depth-specific flows to passively migrate north?  We combined output from a 3-D oceanographic model with an individual-based model of Chinook salmon migration and growth.  By comparing the spatial distribution of simulated salmon to empirical information obtained from ocean sampling and otolith analyses, we evaluated a suite of potential behavioral mechanisms used by salmon.  We show that overly-simplistic behavioral rules, such as passive migration or a single compass bearing, are inadequate.  Although invalidation of behavioral rules is easier than validation, with this tool we can gain insight into the types of behavioral mechanisms likely required for salmon to migrate at realistic rates and with appropriate spatial distributions.