Evaluating a Reintroduced Freshwater Mussel Population in the Upper Clinch River

The Clinch River is part of the Upper Tennessee River Basin; originating in Tazewell, Virginia and flowing southwest into northeastern Tennessee. It has been described as one the most biologically diverse river systems in the United States and is a biological hotspot for rare and imperiled species—many of which are unique to the drainage^1–4. Notably, the Clinch River system supports 46 extant freshwater mussel species, including 24 federally listed species⁴. This taxa has faced significant declines in the last century and is considered one of the most imperiled taxa in the North America^3,5.

In recent years, translocation and captive propagation methods have increasingly been used as a species recovery tool to reestablish extirpated mussel populations into historically occupied habitats and augment declining populations in the Upper Clinch River. Once commonly distributed throughout the upper Clinch, the federally endangered oyster mussel (Epioblasma capsaeformis) had reached undetectable densities by the mid-1980’s and was considered likely extirpated. In 2006, VDGIF (in collaboration with USFWS and Virginia Tech) began recovery efforts to reestablish oyster mussel to the river at a site called Cleveland Islands in Russell County. By 2013, over 4,500 uniquely marked oyster mussels had been reintroduced to the site through translocation and captive propagation efforts.

In 2011 and 2012, post-reintroduction monitoring to assess restoration success was initiated using quadrat and capture-mark-recapture (CMR) survey methods. This study documented successful settlement, high post-release survival, and evidence of recruitment (two individuals)—criteria representing three short-term measures of reintroduction success. Though these reintroductions were considered to be a short-term success, long-term reintroduction success could not be assessed in 2011–2012 surveys due to the time frame of the project, i.e., monitoring immediately followed reintroductions and consequential natural recruitment can take several years before it is self-sustaining and evident. Based on predicted age-class-structures, it was determined that recruitment should be observable by 2015. Hence, further surveying was needed to evaluate oyster mussel recruitment at Cleveland Islands and assess whether rates are occurring at self-sustaining levels—a measure of long-term reintroduction success^5,6.

This summer (2016), CMI researchers at Virginia Tech returned to Cleveland Islands to reevaluate the reintroduced oyster mussel population. Using methods consistent with the 2011 and 2012 sampling design, we conducted CMR over three capture occasions. These capture histories will be integrated with 2011–2012 survey data and used in capture-recapture models to investigate trends and obtain estimates of abundance, apparent survival, and recruitment. Results from this follow-up monitoring (and future) efforts will improve our understanding of oyster mussel vital rates and provide data on effective population sizes and demographics structures required to make informed decisions for future recovery projects.