Physiology in the service of fisheries science: Why thinking mechanistically matters

Behavioral responses of fishes to variability in environmental conditions and habitat quality are central to population-level demographic processes. Although field surveys can correlate abundance to habitat variables (physiochemical, biotic, and structural), they cannot provide mechanistic explanations. Moreover, field surveys are often stratified by time or geographic criteria relevant to humans, whereas fishes stratify by habitat variables relevant to them. If mechanisms underlying behavior are not explicitly understood, conclusions based on survey data can lead to biased inferences as to species-specific habitat requirements and preferences, as well as changes in stock size occurring over time. Because physiology is the transfer function that links specific environmental conditions to behavior and fitness, we argue great gains can be made through the integration of physiology and fisheries science. These are complementary disciplines, albeit ones that generally function at very different temporal and spatial scales, as well as different levels of biological organization. We argue more specifically that integrating physiological approaches with behavioral studies and traditional fisheries survey data (where each approach develops hypotheses to be tested in the other) can mechanistically link processes from cells through populations to place fisheries management in an appropriate ecosystem context. We further contend that population- and species-specific mechanistic understanding of physiological abilities and tolerances can significantly help to: improve stock assessments, describe essential fish habitat, predict rates of post-release mortality, develop effective bycatch reduction strategies, and forecast the population effects of increases in global temperatures and ocean acidification.