Demographic status and population genetic differentiation of Candy Darter populations in Virginia
July 2016 - April 2020
- Virginia Department of Game and Inland Fisheries
Candy Darter are narrowly restricted to medium-size streams with cold-cool temperatures, high-velocity riffles, and silt-free substrates. Absences in fish surveys over the last half-century indicate that the species has declined or is extirpated from many former localities, probably due to warming water temperatures or excessive siltation.
Enhanced understanding of the viability and dynamics of extant populations and evaluation of biologically defensible options for translocation of individuals or augmentation of populations would inform management planning for the species, enhance cost-effectiveness of management actions, and may obviate the need to formally list the species as imperiled.
(1)Document spatiotemporal shifts in occupancy and suitability of riffles in Stony Creek and Cripple Creek.
(2)Monitor populations to estimate relative population size for use in demographic projections and assessment of population viability.
(3)Estimate life-history attributes such as fecundity, age-specific survival, annual recruitment, and age structure.
(4)Analyze molecular and life-history data to define demographic and evolutionarily significant units for the species and to estimate genetic diversity and effective population size.
Site occupancy remained constant throughout the study duration in both Cripple and Stony creeks. Sites outside the known distribution of Candy Darter were unoccupied throughout the study. Results of multi-season occupancy models were not interpretable, likely resulting from small sample sizes, few absences and little variation in covariate values.
Relative abundance was estimated using Cormack-Jolly-Seber models for mark-recapture surveys and catch-per-unit-effort (CPUE) for all surveys. Capture probabilities for mark-recapture data were generally low, which resulted in low precision in abundance and survival estimates.
Molecular data support the view that Candy Darter populations historically occurred throughout the New River drainage, but extant populations have been demographically isolated for some time. Mitochondrial and microsatellite DNA markers revealed high levels of population differentiation and strong evidence of recent population genetic bottlenecks.
Molecular genetics evidence supports the interpretation that all populations of Candy Darter in Virginia might benefit from genetic augmentations. The Cripple Creek, Laurel Creek, and Stony Creek populations had similar levels of genetic diversity and demographic stability, which make them viable options as source populations.