Tuesday, April 18, 2017

A Rare Peek at Clinch Dace Spawning, by Don Orth

Today, The American Midland Naturalist released a paper on spawning observations of Clinch Dace (Chrosomus sp. cf. saylori). Clinch Dace is a species of high conservation need due to a restricted distribution, low population densities, and modified stream habitats.  Clinch Dace occur in only 31.5 km of headwater streams and the global population size is below 10,000 individuals (Moore et al. 2017). Ten of these areas have abandoned mine sites with $12.5M in unfunded restoration costs.  Restoration of the streams will take decades, but in the meantime, we must characterize and protect the remaining genetic diversity.

Several years ago, Hunter Hatcher and Michael Moore noted that the Clinch Dace in standardized samples were becoming more colored up each day.  They literally stumbled across a small depression in a creek where they witnessed numerous Clinch Dace in breeding coloration.  In these small streams, small circular pits are created by Creek Chubs and Stonerollers.     
Clinch Dace.  Photo by Isaac Szabo
In the midst of a busy field schedule, they managed to capture videos over a three-day period. These observations provide a rare peek into the behavior of this small, rare fish.   Since so little is known about the Clinch Dace, any observations could prove helpful and may assist with future captive propagation efforts (Rakes et al. 2013).  A short portion of the hours of video obtained may be viewed by clicking here.

After the field season, Hunter and Michael watched the videos over and over again, taking notes, making observations, and asking more questions.  The behaviors of the Clinch Dace changed each day.  Hatcher et al. (2017)  speculated that the early behaviors were territorial pre-spawn behaviors.  The Clinch Dace were so brightly colored that it seemed that spawning would soon be underway.   Water temperature (21.8 C) was higher than observed by White and Orth (2014) in the only other field observation of the Clinch Dace spawning behavior.  Many behaviors were characterized, including the behaviors that include females being corralled and clasped by males.  Though gamete release was not confirmed from video observations, the videos likely bracketed actual breeding events.  

Habitat is an important determinant of nest location in other fine-scaled daces Chrosomus.  Other species of Chrosomus exhibit flexibility in type of nest used.  For the  blackside dace (Chrosomus cumberlandensis), a federally listed threatened species,  flow and depth were the most influential factors in determining nest location and nest activity, respectively, and nest activity was positively correlated with substrate size (Scherer et al. 2014).

The rare observation is important because it indicates that Clinch Dace are breeding.  Although the numbers of breeders was small, the aggregation behaviors appeared to be similar to that observed in other Chrosomus dace.   If they are unable to find suitable mates due to low population densities, reproductive isolating mechanisms may break down.   In one stream, a hybrid between Clinch Dace and Rosyside Dace.
Top: Clinch Dace. Middle: hybrid Clinch Dace x Rosyside Dace. Bottom: Rosyside Dace.   Photo by Michael J. Moore.
The first step in science is observation. This rare peek raises many questions. The questions asked and what comes next is up to us. I hope the future brings efforts to spawn and propagate the Clinch Dace in captivity to enhance small populations and restore populations to some stream segments.

Hatcher, H.R., M.J. Moore, and D.J. Orth. 2017.  Spawning observations of Clinch Dace: Comparison of Chrosomus spawning behavior.  The American Midland Naturalist 177:318-326.     
Rakes, P.L., M.A. Petty, J.R. Shute, C.L. Ruble, and H.R. Mattingly. 2013. Spawning and captive propagation of Blackside Dace, Chrosomus cumberlandensis. Southeastern Naturalist 12(Special issue 4): 162-170 .
White, S. L., and D. J. Orth. 2014. Reproductive biology of Clinch Dace, Chrosomus sp. cf. saylori. Southeastern Naturalist 13(4): 735-743.

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