Population Densities of the Threatened Blackside Dace, Chrosomus cumberlandensis, in Kentucky and Tennessee

Abstract

Chrosomus cumberlandensis (Blackside Dace) is a rare cyprinid fish restricted to small tributaries in the upper Cumberland River drainage in southeastern Kentucky and northeastern Tennessee. One hundred and nineteen 200-m reaches within 55 streams were sampled during June–August 2003, 2005, and 2006 via AC and pulsed-DC singlepass backpack electrofishing, thereby representing the most comprehensive quantitative survey conducted for this species to date. Dace were found to inhabit 43 of 55 streams and 78 of 119 reaches, although in two-thirds of the reaches the species was either not detected or was present in low numbers (i.e., catch rates ≤10 dace per 200 m). For the 78 reaches where the dace was detected, single-pass electrofishing catch rates ranged from 1 to 151 (mean ± SD = 27 ± 34) dace per 200 m. Petersen mark-recapture population estimates conducted on 16 reaches within 12 streams were used to build a regression model to calibrate single-pass electrofishing catch for the remaining 62 reaches inhabited by dace. Population estimates for the 78 reaches harboring Blackside Dace averaged 90 ± 121 dace per 200 m, and associated densities averaged 14.1 ± 19.4 dace per 100 m2. Electrofishing sampling efficiency for Blackside Dace was 0.30 as revealed through our mark-recapture efforts. The small population sizes documented in many streams coupled with restricted distributions and relatively limited mobility may render many populations susceptible to local extinction due to stochastic events, poor recruitment, or additional habitat degradation.