Community Indices, Parameters, and Comparisons

Understanding assemblages of fishes and how their numbers and compositions change over time and space has long been a fundamental interest of aquatic ecologists and has increasingly become recognized as an important component of fisheries science and management. Whereas much of traditional fisheries management may have focused on single-species approaches, targeting sport or commercial fishes, direct or indirect biotic interactions among fishes may strongly influence target populations. Furthermore, fisheries scientists may frequently be charged with sampling fish populations to detect changes in the aquatic environment, especially those effects related to human activities (e.g., pollution, altered hydrology, or nonnative introductions), and quantitative descriptors of the entire fish assemblage are required for this purpose. For fish assemblage descriptors to be ecologically relevant, they must be compared over time or among assemblages, and ecologists and biomathematicians have developed procedures to that end. Many of the indices and procedures that we include in this chapter have been developed for use with other taxonomic groups (e.g., plants, invertebrates, and terrestrial animals), or even engineering applications (e.g., communications, Shannon and Weaver 1949), but are equally applicable to the study of fishes. Many have been developed more thoroughly in flowing-water habitats, but the concepts and techniques transfer well to other aquatic systems. In this chapter, we outline, review, and demonstrate quantitative measures and techniques to describe and compare fish assemblages to assist the fisheries scientist in addressing practical research and management objectives.