Influence of Environmental Variables and Species Interactions On Sport Fish Communities in Small Missouri Impoundments

Small impoundments (<400 ha) are numerous and provide close-to-home fishing opportunities for anglers but may not support optimal sport fisheries.  Most of these fisheries are managed by harvest regulations but watershed and impoundment characteristics, poor water quality, or detrimental species interactions can also influence the desirability of fisheries.  We examined the relative importance of watershed characteristics, impoundment morphology, water quality, and species interactions in explaining differences in relative abundance, growth, and size structure of largemouth bass Micropterus salmoides, bluegill Lepomis macrochirus, redear sunfish L. microlophus, white crappie Pomoxis annularis, and black crappie P. nigromaculatus among 89 small Missouri impoundments spanning a large fertility gradient.  Using regression analysis, we found variables associated with predation, competition, and lake fertility were most important in explaining variation in sport fish demographics.  Watershed and impoundment morphology variables were typically less important.  Lakes with dense largemouth bass populations commonly contained sunfish and crappie populations with desirable size structure and growth implying that predation was a strong structuring force.  Density dependent growth was common among all sport fish species.  White crappies and black crappies had better growth or size structure in lakes with fewer bluegills, suggesting competition among these species.  Lakes containing common carp Cyprinus carpio had fewer largemouth bass and slower-growing black crappies than lakes without common carp.  Gizzard shad Dorosoma cepedianum benefitted largemouth bass populations but negatively affected bluegill and black crappie populations. Growth and size structure of sport fishes usually improved with increasing lake fertility.  Predation and competition seemed most important in structuring sport fish communities in these impoundments provided that lake fertility was adequate to sustain acceptable abundances and growth rates of these fishes.