Use of a novel richness-weighted abundance index of age-0 fishes to identify key features for habitat conservation and restoration

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Prioritizing sites for conservation or setting goals for enhancement and restoration projects is often difficult due to limited knowledge about relations between habitat characteristics and faunal assemblages. We tested the utility of a novel richness-weighted abundance (RWA) index as a tool for guiding habitat conservation and restoration for native fishes and compared its utility to established indices of abundance and diversity (i.e., Shannon diversity index, Simpson diversity index, species richness, total catch). Habitat and fishes were sampled in the upper Niagara River during late summer, 2013–2015. We used multivariate adaptive regression splines to model the relation between each index of abundance or diversity of native age-0 fish and aquatic habitat features, and compared R2 values among models to determine the strength of the relationship between each index and aquatic habitat features. Our RWA index had the strongest relation with habitat features (R2 = 0.40) and Shannon and Simpson indices were unrelated to habitat features. We found the best habitats for native fishes (i.e., highest RWA scores) contained substantial submerged aquatic vegetation extending into the water column (>20%), low water velocities (<0.1 m/s), and fine to very fine substrates. Our approach of valuing habitat based on an RWA index allows researchers and practitioners to assess the quality of native fish assemblages and determine which habitat characteristics are associated with supporting those assemblages. This index should be applicable to other ecosystems, and has value for ranking existing sites for conservation and for setting clear goals for enhancement and restoration projects.