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 ava ilability or better thermal conditions at the front, but a quantitativ e evaluation of the effects of fronts on fish has yet to be done. Bioe nergetics 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 f ronts of different temperatures and prey concentrations. The distribut ions of growth rate potentials across these fronts depended on fish ph ysiology, the temperatures encompassed by the front, and prey distribu tions 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 we re better for growth if prey availability was low. Increased food avai lability at the front enhanced fish growth rate potential at the front . Actual growth rates depended on whether the fish behaviorally select ed habitats by temperature, food, or growth rate potential. Results il lustrate that prey patchiness and the nonlinearities inherent in the r elationship of fish growth to temperature and prey availability must b e considered in order to evaluate how a population of fish might respo nd to a front and how the front might affect fish growth and productio n.