7212 - Laserfiche WebLink

Home Browse Search

spatial partitioning to be less structured in a desert stream in Oklahoma. Their study area is more similar to the low gradient areas of the Green River than the lakes and more structured streams studied by the other investigators. Water 'velocity, found to be important in the Green River, tended to be important in other stream environments (Matthews and Hill 1980; Baker and Ross 1981). I The high spatial and dietary overlap observed between the small Colorado squawfish and red shiner may provide some support for the hypothesis that competition between these two species may be an important factor in the decline ' in Colorado squawfish abundance. However, our ability to address the effects of competition in a field study such as this where the availability of resources to the fishes in question was not measured was limited. Competition between two species for resources requires the satisfaction of at least three factors (Li 1979): 1) important resources must be limited; 2) these resources must be shared; and 3) the sharing of these resources results in an 1 adverse influence on one of the two species -- perhaps impaired reproductive success or decreased survival. Although we observed sharing of resources among the specs we EE_i .ed, we did not measure the availability of those resources, hence we do not know if a factor was limiting. In addition, the documentation of an adverse effect to one or both species would require a more controlled experiment conducted over a longer time period. However, some inferences may be made by comparing our results with data provided by other investigators. Holden and Crist (1981) studied the invertebrate community in the upstream portion of our study area. They observed a seasonal fluctuation in invertebrate abundance with lowest densities occurring during the spring-runoff period (partially attributed to sampling problems during high water) and highest densities occurring during early fall. Furthermore, l' they observed that dipterans were a very important component of the invertebrate high density. Thus, the dietary overlap between small Colorado sawfish and red shiner and to a lesser extent channel catfi?s that we observed may reflect the mut, ual use of an abundant r souse rather than competition for food beween these ,species. ACKNOWLEDGMENTS We would like to thank the many people who participated in this study; Bob Burdick, Ken Harper, Randy McNatt, Susan Henne, Fred Hagstrom, Joe Krakker, James Krietlow, Wally Polinski, Marion Smith and Kurt Welke who assisted with the field work; Bill Miller and Don Archer who provided administrative support; and Gerald and Donna Jacobi who performed the stomach analyses. Funding was provided by the U. S. Bureau of Reclamation. LITERATURE CITED Archer, D. L., H. Tyus, and R. Valdez. 1980. Field methodologies of the Fish and Wildlife Service's Colorado River Fisheries Project. Transactions of the Bonneville Chapter of the American Fisheries Society. 1980:13-36. Baker, J. A., and S. T. Ross. 1981. Spatial and temporal resource utilization by southeastern cyprinids. -Copeia 1981:178-189. Behnke, R. J., and D. E. Benson. 1983 Endangered and threatened fishes of.the Upper Colorado River Basin. Cooperative Extension Service, Bulletin 503A. Colorado State University, Fort Collins, Colorado. r 1y 52