Upper Mississippi Center

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Fish species diversity is a widely used indicator of stream health, however, the relationship between the functional diversity of fish communities and stream health is less documented. Although functional and species diversity are often related, it is also the case that functional diversity may reveal levels of community health or impairment that species based approaches may miss. Functional diversity has been previously defined as the diversity of functional traits, such as fin length. We will define functional diversity as the variance of fish trophic guilds according to the IA DNR reference. Fish were categorized as benthic invertivore, filter, generalist, herbivore, insectivore, omnivore, parasite, top carnivore, or N/A. Nineteen sampling sites were selected, making sure to select an even mix of urbanized, agricultural, and protected sites. Geographic Information Systems (GIS) was used to delineate the watersheds of the 19 sites across the area. An ETS Electrofishing Systems AbP-4-MR-HP Pulsed-DC backpack unit for collecting fish in the field. A 50 meter reach was sampled at each site, measured along the streambank following the water’s edge. Seine nets were placed across the entire width of the stream at the top and lower end of the sampling reach. Fish were identified to the species level. Predators were the least common guild identified and included: Micropterus salmoides, Micropterus dolomieu, and Esox americanus. We assessed each community for fish functional diversity through Shannon's diversity calculation based on guild membership rather than species identity. A multiple regression model using entrenchment ratio, chloride, and stream width as predictors of Shannons index was significant (R2 = .744, F = 11.598, p < .001). In this model, stream width was the variable most tightly linked with functional diversity (t=3.998), while entrenchment ratio and chloride concentrations were less influential (t = -2.803, -2.494 respectively). Our results suggest that geomorphology may be a stronger predictor of functional diversity in these assemblages than water quality, and geomorphic variables may limit the presence of top predators in these assemblages. Specifically, stream width could be used as an indicator to predict whether a top carnivore will be present in a stream.