Local and Regional Evaluation of Smallmouth Bass Population Genetic Structure in the Susquehanna River Basin

Smallmouth bass (Micropterus dolomieu) in the Susquehanna River basin have been displaying characteristics of disease and endocrine disruption (ED) for several years, including gross lesions and the presence of intersex. Since the initial observations of disease and ED, a wide range of potential environmental stressors have been identified including pathogens, water quality, and contaminants. Because of the life history characteristics of smallmouth bass in this system, which often spawn in smaller tributaries to the Susquehanna River and overwinter in the main-stem, it is challenging to link processes and ecological conditions in the river and the surrounding landscape that may be contributing to the observed disease and ED. To do so requires gaining an understanding of how smallmouth bass move throughout the river system and to define how they may function collectively as a population(s). Although a radio-telemetry study on two tributaries and a section of the Susquehanna River demonstrated movements relating to spawning and overwintering, resulting in intermixing of tributary and river-tagged fish, the population-level implications of these movements are unclear. One approach to address this question is through the use of highly variable genetic markers to quantify genetic variation within smallmouth bass from numerous sites within the Susquehanna River basin. This study aims to use population genetic tools to evaluate the structure and connectivity of smallmouth bass populations at both a local and regional scale across the Susquehanna River basin. Genetic samples were collected from 24 sites, including main-stem river sites that were paired with tributary locations to assess local gene flow between main-stem and tributary systems. A total of 1,034 fin clips were collected for genetic analysis during prespawn conditions and are being analyzed with microsatellite markers to investigate differences within and among populations. Laboratory analysis is currently underway, and results aim to provide information on the connectivity and genetic structure of populations as they may correlate to observed disease and other health characteristics and therefore aid in management