Aggregation of two imperfectly detected imperilled freshwater fishes: understanding community structure and co-occurrence for multispecies conservation

Abstract

Characterizing critical habitat for endangered species is the first step for effective conservation and relies on knowledge of the abiotic conditions that promote species occurrence. Knowledge of biotic interactions, a component of species habitat, can also provide vital information for the conservation of endangered species by identifying conditions and/or locations suitable for multispecies conservation. We investigated site-level species co-occurrence patterns for 2 federally protected fish species in Canada, eastern sand darter Ammocrypta pellucida and silver shiner Notropis photogenis, to determine if management measures applied to one species could confer benefits to the other species. Using repeat surveys of fish communities in the Grand River, Ontario, we developed 2-species occupancy models to control for imperfect detection while evaluating species co-occurrence patterns and related those patterns to abiotic habitat covariates. We also used a principal component analysis (PCA) to characterize observed fish community structure and fit abiotic variables to PCA axes to explain observed patterns. Results indicated aggregation between the 2 federally protected species in the Grand River; the probability of occupancy for N. photogenis was higher at sites where A. pellucida was present. Results from the PCA and cooccurrence models confirmed the importance of depth, water clarity, and water velocity for both species. The result of site-level aggregation after correcting for imperfect detection suggests that management measures applied to one species could confer benefits to the other; however, the mechanisms underlying co-occurrence remain poorly understood.