Community Structure and Seasonal Changes in Standing Stocks of Fish in a Warm-water Stream

Abstract

A comprehensive study of the standing stocks of fish species in Glover Creek, Oklahoma, was conducted on a seasonal basis from 1977-1979. Community structure was described by biomass of species and feeding guilds and comparisons were made among seasons. Invertivore and invertivore-piscivore feeding guilds contained 79.9%o of the total fish standing stock. Guild structure differed among riffles and pools and varied less seasonally than between habitat types. The annual average total fish standing stocks were 60 and 90 kg/ha, for riffle and pool sites, respectively. Total standing stocks differed among seasons with the annual average occurring in April-May and October-November, and the maximum occurring during July-August. INTRODUCTION More reliable assessments of habitat impacts on streams could be made using a biological integrity approach rather than indicator species or diversity approaches (Cairns, 1977; Karr, 1981). Karr (1981) recently proposed a method to assess the biological integrity of stream fish communities. However, one of the basic assumptions of Karr's method is that biologists know what the structure of the fish community should be in unmodified habitats, and can then compare the observed community attributes with those expected under unmodified conditions. Although many studies have investigated how fish species richness varies with stream order (Huet, 1959; Sheldon, 1968), flow variability (Horwitz, 1978) and habitat structure (Gorman and Karr, 1978), relatively few investigators have attempted to quantify community trophic structure and seasonal changes in fish biomass in unmodified stream systems. For example, Funk (1975) found only seven studies of streams inhabited by black bass (Micropterus), in which composition of total fish biomass was estimated. Most of the studies reviewed by Funk (1975) suffered from four limitations: (1) smaller fish species were not considered; (2) estimates of total fish biomass were conducted only in pools; (3) population estimates were taken during one season giving no indication of typical seasonal variation, and (4) interpretation was complicated by the large number of species, even when smaller fishes were excluded. Schlosser (1982a) found that trophic structure was stable across both seasons and years in an unmodified stream, yet was seasonally unstable in a modified stream. Furthermore, Schlosser (1982b) attributed spatial variation in community organization to habitat structure and the temporal variability in habitat and food availability. However, few comparable studies assess the generality of Schlosser's findings. The objective of this study was to describe the structure of the fish community in an unmodified stream in relation to season and habitat type. Specifically, we ask: (1) Do fish communities in unmodified streams have a stable trophic structure? (2) Are there general differences in trophic structure between riffle and pool habitats? and (3) Does a typical seasonal pattern in total fish biomass exist? STUDY AREA The study area was located on Glover Creek in SE Oklahoma (Orth and Maughan, I Present address: Department of Fisheries and Wildlife Sciences, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061 2 Cooperators are the Oklahoma Department of Wildlife Conservation, Oklahoma State University, and the U.S. Fish and Wildlife Service.