The Effects of impoundment depth and isolation on fish species diversity and fish size

Abstract

A problem for many fisheries managers is trying to maintain a diverse prey base while maximizing predator size. To test the effects of water depth and impoundment isolation on fish size and species composition, two rock-quarry ponds were sampled at the Great Ape Trust in central Iowa during the fall of 2005. One impoundment was shallow and small compared to an adjacent impoundment that was relatively deep and large. The impoundments were isolated from one another for the majority of the year by an extremely shallow, narrow band of water that was subject to lateral transfer from the Des Moines River. We hypothesized that fish of each species will be greater in the larger, deeper pond. Specimens were collected using a throw net, lengths were recorded with a tailors tape, and capture locations were marked using GPS. Two-tailed t-tests were then used to analyze data sets that were standardized using log transformations to assume for normality. Although species composition was found to be identical in both impoundments, significant differences in mean length were only found in two of the five species, bluegill and the common carp. We conclude that factors other than pond depth play a greater role in influencing body size such as dissolved oxygen content and inter- and intra-specific competition.