Energetic Constraints of Juvenile Chum Salmon (<i>Oncorhynchus keta</i>) Migrating in Estuaries

Experiments on fish feeding behavior, field measures of fish sizes, migration rate, and prey resources, and an energetic growth model are used to evaluate the growth of juvenile chum salmon (Oncorhynchus keta) during outmigration in an estuary. Fish growth is defined as the difference between energy intake and metabolic costs. Energy intake is estimated from prey densities and foraging parameters, namely pursuit swimming speeds and energetic expenditures, and prey handling and encounter rates. Relationships for foraging parameters as functions of fish sizes and field prey abundance are used to evaluate energy intake by fish in the estuary. This information and calculations of metabolic costs allow predictions of fish growth during the migration. Results show that metabolic costs of maintenance and migration lie in a delicate balance with food intake and growth. Growth efficiencies exceeding 20% occur when metabolic expenditures decline and energy intake rates permit growth without depletion of the food supply. Defining such energetic balances facilitates characterization of carrying capacities of coastal ecosystems and has implications for enhancement of juvenile fish growth and, in turn, fish survival and production at sea.