Relationship between Bioenergetics and Behavior in Anadromous Fish Migrations

Abstract

Minimizing energetic cost per unit distance is often considered the major criterion that anadromous migrants seek to optimize during upstream migration. To test this theory, we documented energetic expenditures and travel speeds of 15 anadromous fish populations involving 9 species observed during their upstream migration. Parameters that characterized fish migratory behavior and the spawning river were calculated for each population. In most cases, cost per unit distance is not minimized and migratory strategy does not conform to the theoretical optimum. Populations that make long or difficult migrations are more efficient in their use of energy reserves than populations that make shorter migrations. Only populations that need all their energy to complete the migration swim at speeds that approach the theoretical optimum. Migration length may lead to improved migratory efficiency by selecting for larger body size, more accurate upstream orientation, and travel speeds that optimize energy efficiency. The failure to minimize energy expenditures is sometimes due to environmental constraints that exceed the physiological capacities of migrants. Minimizing the probablity of death due to exhaustion may be the major factor determining migratory behavior. Selection for energetic efficiency appears important only in cases where energy reserves are exhausted during migration.