Distribution of Candy Darter Reflects Range-Wide Variation in Stream Temperature Regime and Substrate Composition

The candy darter Etheostoma osburni is endemic to central and northern portions of the New River drainage in Virginia and West Virginia. Non-targeted surveys suggest the species is extirpated from much of its southern range, where three isolated populations occur, but little is known about its life history or the mechanisms of its decline. We hypothesized the apparent decline could be due to low detectability and/or higher stream temperatures and embedded substrate.  We used a hierarchical occupancy framework to examine occurrence patterns among riffles, segments, and watersheds. Occurrence data came from repeated electrofishing of 43 stream segments across candy darter’s historical range.  Our objectives were to 1) estimate the species’ detection probability while using targeted methods, 2) search for unknown populations, and 3) examine relations among occupancy, stream temperature, and instream habitat.  Candy darters are highly detectable using our sampling protocol. We discovered one new population but collected none from sites where they were purportedly extirpated. Additionally, streams with confirmed populations feature cooler temperatures and less fine sediment than those where darters were not detected. Managers can use detection probability and habitat association findings to customize survey methods and identify suitable areas for the reintroduction and recovery of the species.