1997 Horseshoe Lake Survey: The Warmwater Fish Community Before Chemical Precipitation of Phosphorus and Increase Dilution of the Lake

The warmwater fish community of Horseshoe Lake (Cowlitz/Clark County) was studied during late summer 1997 before the application of aluminum sulfate ('alum') and final upgrade to the lake's inlet pump station. In terms of biomass, the lake was dominated by non-game species, primarily largescale sucker and common carp. However, in terms of abundance, the lake was clearly dominated by juvenile largemouth bass. Catch rates for stock-size (varies by species) warmwater fish were below average while electrofishing yet above average when gill netting. Growth of warmwater fish was generally consistent with or below the state average for each species. Relative weight, an index of fish condition, was generally high indicating abundant forage. Traditional stock density indices suggest that Horseshoe Lake is naturally suited for a panfish fishery. Management strategies that might improve the warmwater fishery at Horseshoe Lake include reevaluating the aquatic plant control contingency plan, stocking tiger muskellunge to control forage fish and non-game species, changing fishing rules to increase the size structure of largemouth bass, and continued monitoring of the warmwater fish community. The baseline information presented here will be useful when monitoring the long-term effects of the chemical precipitation of phosphorus and increased dilution of Horseshoe Lake.