Creative Commons License

Creative Commons License
This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License.

Preferred Name

Alaina C Esposito

Date of Award

Summer 2015

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Department of Biology

Advisor(s)

Christine L. May

Abstract

The critically endangered James Spinymussel (Pleurobema collina) is a species of freshwater mussel endemic to Virginia’s James and Dan River basins. In the last 20 years, P. collina has experienced a substantial decline in numbers and currently occupies approximately 10% of its original habitat; however, little information is known about this species to assist in conservation. A 230-meter reach of transitional habitat in Swift Run was selected for repeat observations to estimate detection probabilities using a Capture-Mark-Recapture framework. In June 2014, visual scouting began to locate and tag P. collina (including other mussels in the community) with PIT tags. Repeat surveys were conducted bi-weekly for three months to relocate tagged individuals, record their position, visibility on the surface, and relevant habitat characteristics. On average, 76% of all tagged bivalves were detected with the PIT tag reader, and 7.5% of those encountered were visible on the surface. The best-fitting logistic regression model to estimate P. collina’s visual detection probability incorporates mussel length, substrate grain size, and sampling season (AIC=94.8), and predicts that 14.0% of all P. collina are visually detectable during baseline flow conditions in the summer. Temporal variation in surface expression rates of P. collina did not vary significantly (p-value=0.90) but did significantly vary for V. constricta (p-value=0.001), indicating that there is heterogeneous expression on the surface for V. constricta. Multistate analyses similarly estimated the PIT tag reader detection of P. collina at 78%-79% and survival at 100%, during any sampling period. Multistate analyses also predict 8% of P. collina will move from a subsurface to a surface state, while 70% will move from a surface to a subsurface state during any sampling interval. Movement analyses of P. collina indicated that individuals occupying sandier habitats do not move more than those in more stable pebble/gravel habitats (p-value=0.61). Raster-analysis of the surrounding watershed show no land use changes from 2001-2006, and that natural vegetation and agriculture dominate the landscape, covering 9.5 km2 and 7 km2, respectively. This information will assist in estimating population sizes, and understand the dynamics between P. collina and their habitat, to aid managers in furthering conservation efforts.

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