Correlates of the Whole-System Distribution of a Reservoir Predator (Blue Catfish, Ictalurus furcatus)

Few comprehensive evaluations exist of correlates for the whole system distribution of mobile sportfish.  Here, we used a monthly manual acoustic telemetry survey throughout Milford Reservoir, KS, to quantify whole-system distribution of Blue Catfish (N = 75 fish).  In addition to fish distribution, we also collected data on 15 variables within three groups of correlates (1. microhabitat, 2. mesohabitat, 3. biotic) at our 57 telemetry survey locations. Using both model selection and regression tree approaches, the strongest correlates of Blue Catfish whole-reservoir distribution were mesohabitat variables (i.e., river kilometer from the dam, distance to channel) and a biotic variable (i.e., Secchi depth, which was empirically related to primary productivity). Monthly analysis confirmed these across-season relationships. In summary, Blue Catfish distribution was driven by conditional, interactive relationships among multiple variables across scales. For example, Blue Catfish avoided extremely low dissolved oxygen concentrations that can cause physiological stress during the warmest months, were more abundant near the underwater channel (an area of bathymetric heterogeneity that may offer a foraging advantage), and were concentrated at locations with increased primary productivity. Our research supports a growing body of evidence that whole-system approaches are needed to understand and effectively manage mobile sportfish.