Fragmentation and Genetic Diversity in Clinch Dace Populations

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2019-07-25
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Virginia Tech
Abstract

In 1999 Clinch Dace, Chrosomus sp. cf. saylori, was discovered in the Tennessee drainage of Virginia. Subsequent sampling of southwest Virginia and portions of Tennessee indicated that Clinch Dace populations are small, fragmented, and of questionable viability. Further, riparian land use and mining pose significant threats to critical habitat. As such, Clinch Dace were listed as a Federal Species of Concern and on Virginia’s Wildlife Action Plan as Tier I - Critical Conservation Need. A management plan and species description for Clinch Dace is of utmost importance, but data on distribution and life history are needed before these objectives can be realized. The objectives of this study were to: 1) Monitor known populations of Clinch Dace to characterize at fine-scale distribution and status. The latter will be addressed in terms of relative abundance. 2) Analyze distribution data using geographic information systems and other approaches to identify habitat and landscape features that isolate Clinch Dace and associated fish populations, 3) Map stream crossings and assess likely barriers to upstream passage and measurements of specific conductance, 4) Screen molecular genetic markers in order to define demographic and any evolutionarily significant units for the species. Molecular genetic variation will be screened at nuclear microsatellite loci to assess levels of molecular genetic variability and population-level differentiation. We will examine the effect of geographic distance on genetic differentiation (Botta et al. 2015). Habitat use will be compared to assess whether genetic differentiation relates to any observed differences in adaptive characters among populations. 5) Use these findings to define demographic and evolutionarily significant units for the species and work toward estimating effective population size and protocols for translocating individuals. We sampled 29 reaches on ten streams for fish with a three-pass depletion method and measured eight habitat variables which might inform conservation actions. We also conducted statistical analyses on six habitat and fish community variables to determine whether habitat rather than fragmentation was influencing Clinch Dace presence and abundance. We conclude that seven Clinch Dace populations vary in their degree of isolation, with some populations showing signs of recent admixture and others not. Populations with the least admixture, such as Hurricane Fork and Hart Creek in Russell County, may represent distinct management units. However, they are also among the largest populations found in 2017 and may therefore be the best candidates for donor population for translocations. The effects of road crossings in our study area was minimal and most crossings were not obvious barriers to fish passage. Instream habitat metrics that we measured also seemed to have little effect on Clinch Dace presence and abundance. We recommend that further management actions be taken with an adaptive management approach, as it is not clear from our results that translocations should be ruled out, but rather undertaken initially as a pilot study with follow-up monitoring to determine whether outbreeding depression is taking place as a result of moving locally adapted fish. Stream restoration activities may not be warranted, as the Clinch Dace shows some resilience to habitat degradation, such as sedimentation and lack of woody debris. We only found one culvert on Hart Creek which could be considered for a retrofit and that does seem to be acting as a barrier to Clinch Dace movement. Further research could measure temporal changes in abundance and characterize the relationship between population size and extinction risk and identify minimum viable population thresholds. Further monitoring should include the seven populations characterized as well as nine streams (Hess, Indian, Laurel, Left Fork Coal, Mudlick, Pine, Town Hill, and West Fork Big Creeks).

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Keywords
Clinch Dace, Clinch River
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