How to Survive a Drought: Modeling Shows Evidence of the Importance of Foraging Plasticity to Juvenile Salmon

Most models for assessing and predicting the growth of juvenile salmon in rivers only incorporate activity costs for drift foraging.  I propose that models (and fish) may need to include benthic foraging to reconsile energy needs under certain situations; such as when prey are scarce, difficult to find, or if low water velocities do not promote high drift delivery. To investigate this I compared growth rates from empirical data and model simulations.  Empirical data are from a cohort of wild juvenile Chinook Salmon (Onchorhyncus tschawytscha) in the San Joaquin River, while simulations were from the individual based model inSTREAM.  Stable isotope analyses suggested a significant portion of total assimilated biomass was in the form of oligochaetes, confirming model predictions of benthic foraging.  The model was then used to simulate a variety of river discharge and prey production scenarios.  Results from these scenarios suggest that prey production has the most significant effect on growth and survival, while any discharge level above critically low is beneficial for growth and survival.  These results highlight the importance of foraging plasticity to the survival and growth of juvenile salmon in unfavorable drift conditions, and the importance of including benthic foraging in simulations of such conditions.