Nesting biology, chronology, and hybridization risks of the rare barrens darter (Etheostoma forbesi)

The Barrens darter (Etheostoma forbesi) is a rare Catonotus darter endemic to the Caney Fork River system in middle Tennessee. Hybridization with the closely related fringed darter ( E. crossopterum) has been assumed as a risk to the Barrens darter. To assess chronology and similarity of nesting habitat between these species, nests of each egg-clustering darter were observed through the spring nesting seasons in four streams during 2008 and 2009.Thirty-nine Barrens darter nests were monitored at Duke Creek in Cannon County, and 28 fringed darter nests were monitored at West Fork Hickory Creek in Coffee County in 2008. Twenty-three Barrens darter nests were monitored in Lewis Creek in Cannon County, and 78 fringed darter nests were monitored in Meadow Branch Creek in Coffee County in 2009. Nesting chronology and clutch sizes were similar between species, with spawning periods similar to those reported for other Catonotus darters and clutch sizes up to 2,000 eggs/nest. Nests were present from March through early June at Duke, Lewis, and Meadow Branch creeks, but spawning was delayed by approximately two weeks at West Fork Hickory Creek, the largest and only spring-fed stream in the study. Nests were observed from one to six times each, with mean nest persistence ranging from 11 to 17 days at mean stream temperatures from 14.5ºC to 15.2ºC.Microhabitat variables associated with nests exhibited evidence of headwater specialization by the Barrens darter that may isolate spawning populations from fringed darters. Barrens darter nest rocks at both Duke and Lewis creeks had a significantly smaller bottom surface area where eggs were deposited than fringed darter nest rocks at Hickory Creek and Meadow Branch Creek (P < 0.01). Water depth where Barrens darter nest rocks were located at both Duke and Lewis creeks was significantly shallower than where fringed darter nests rocks were located in West Fork Hickory and Meadow Branch creeks (P < 0.001). Barrens darter nests were located in swifter stream velocities at 60% depth in all comparisons (P < 0.01) and at nest level in three of four comparisons (P = 0.003). Suitable nest rocks occurred at significantly different densities in the four streams (P = 0.004), with the highest densities at Lewis Creek and lowest at West Fork Hickory Creek, but nest rock availability did not appear limiting in any of the streams. Barrens and fringed darters did not nest in the same streams in this study, and distinct differences in nesting parameters suggest a reduced risk of hybridization.