Will a Fish's Perspective Improve the Ecological Relevance of River Connectivity Metrics?

Structural indices of aquatic connectivity typically focus on the spatial arrangement of barriers to fish movement. Here, we describe a method that adapts the widely applied structural Dendritic Connectivity Index (DCI) into a functional index (DCI F ) that constrains connectivity measurements to biologically relevant scales (e.g., based on fish movement behavior). We compare fish communities in five Ontario watersheds to empirically test the hypothesis that they are better explained when connectivity is measured using the DCI F . We test the response of fish abundance grouped by swimming abilities and morphology, along with fish community assemblage as a whole. We expected the DCI F to better explain the abundance of the weakest swimmer groups and overall community assemblage than the structural index. At the spatial scales examined, the DCI F provided modest improvements in explaining the abundance of some fish functional groups. Conversely, we found little to no improvement over the structural index in explaining community structure. Regardless, our paper illustrates a new approach that explicitly incorporates ecologically relevant scales into connectivity measures within watersheds. These scale effects can be significant, and the approach presented here can be applied to aquatic systems at various spatial extents. Our case study suggests that managers may not always need to gather data on fish movement or other biological parameters, and instead can focus on variables that may better explain the effect of barriers on fish community patterns.