Analysis and Interpretation of Freshwater Fisheries Data

13: Fish Population Bioassessment

Michael Power


Approaches to detecting, interpreting, and reporting the significance of stressors on fish populations vary. The tools described in Chapters 4 through 10 may all be used alone, or in combination, to yield insights into how fluctuations in environmental variables or anthropogenic stressors such as exploitation, habitat degradation, and pollution—or some combination of both—may affect abundance, reproductive potential, or growth. Despite general agreement in the fisheries literature that an understanding of the population level effects of stressors is of paramount importance, relatively few studies have attempted to estimate stressor effects systematically (Barnthouse 1993) or to link changes explicitly at lower levels of biological organization to changes at the population level (Shuter and Regier 1989). Most investigations have followed the pioneering lead of Selye (1976), who defined stress as the measurable biological response of an individual to an external stimulus (stressor), and are based on laboratory experimentation aimed at determining individual responses to acute or chronic stressors (Adams 2002). Although valuable for achieving the specific objectives of determining whether a measurable response exists, studies focused at the individual level lack ecological realism and do not necessarily predict or facilitate understanding the consequent effects of stress at the population level (Power and McCarty 1997).