THE EFFECT OF THERMAL FRONTS ON FISH GROWTH - A BIOENERGETICS EVALUATION OF FOOD AND TEMPERATURE

Fish aggregations at fronts may be caused by either increased food availability or better thermal conditions at the front, but a quantitative evaluation of the effects of fronts on fish has yet to be done. Bioenergetics models were used to evaluate the growth rate potential of a cool-water fish, the chinook salmon (Oncorhynchus tshawytscha), and a warm-water fish, the striped bass (Morone saxatilis), across thermal fronts of different temperatures and prey concentrations. The distributions of growth rate potentials across these fronts depended on fish physiology, the temperatures encompassed by the front, and prey distributions across the front. When food was distributed uniformly across the front, the growth rates of both species were highest at their optimal temperatures, if sufficient prey was available. Lower temperatures were better for growth if prey availability was low. Increased food availability at the front enhanced fish growth rate potential at the front. Actual growth rates depended on whether the fish behaviorally selected habitats by temperature, food, or growth rate potential. Results illustrate that prey patchiness and the nonlinearities inherent in the relationship of fish growth to temperature and prey availability must be considered in order to evaluate how a population of fish might respond to a front and how the front might affect fish growth and production.