Fathead Minnows, Aquatic Invertebrates, and Mallard Duckling Interactions in Man-Made Ponds

Activity traps have been commonly used in qualitative invertebrate studies. The effect of the orientation of the trap on catch has not been tested. Aquatic invertebrates were collected in horizontally and vertically oriented activity traps in experimental ponds in 1990 to test trap orientation effectiveness. Horizontal traps caught the most invertebrates, vertical traps caught more Coenagrionidae. Fathead minnows have the potential to affect invertebrate populations in wetlands. Stocking minnows in formerly fishless wetlands may negetatively affect duckling growth and survival. In 1991, 5 pairs of ponds (cells) were used to test what effect minnows had on the invertebrate population and duckling growth. Fathead minnows were stocked in half of the cells. Mallard ducklings were placed on both stocked and control cells. Nine 5-week-old ducklings were used in the analysis. The presence of fathead minnows did not affect duckling growth rates, presumably because by this age the ducklings used plant foods. Chaoboridae, Amphipoda, Cladocera, Copepoda, and total macroinvertebrate catch were negetatively affected by minnow presence . Fewer Chironomidae, Baetidae, Ceratopogonidae, and Coenagrionidae were caught in stocked cells, but numbers were not significantly different. Average length of Chironomidae were larger in stocked cells, while Corixidae were larger in control cells. Results demonstrate that fathead minnows can have an effect on invertebrate populations in semipermanent wetland conditions. Horizontally placed activity traps are adequate to analyze the effects of minnows on invertebrate numbers. Recommendations are made for futher research on fish/waterfowl interactions in prairie wetlands