Invasion Genetics of the Blue Catfish (Ictalurus Furcatus) Range Expansion into Large River Ecosystems of the Chesapeake Bay Watershed

Abstract

INVASION GENETICS OF THE BLUE CATFISH (ICTALURUS FURCATUS) RANGE EXPANSION INTO LARGE RIVER ECOSYSTEMS OF THE CHESAPEAKE BAY WATERSHED Colleen Beth Higgins, B.S., B.A. A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science at Virginia Commonwealth University. Virginia Corilmonwealth University, 2006 Director: Bonnie L. Brown, Ph.D., Associate Professor, Department of Biology The blue catfish, Ictalurus furcatus (Ictaluridae), is ranked among the most invasive, nonnative species of concern in the Chesapeake Bay watershed. This species, intentionally introduced to three major tributaries and a number of impoundments between 1974 and 1989 for sport fishing, has spread into three additional tributaries. Using samples from the introduced tributary populations as a baseline, we evaluated microsatellite genetic variation in light of demographic and ecological data to elucidate the potential sources of the invasive I. furcatus populations. In general, the populations surveyed in the Chesapeake 'Bay watershed were considerably more inbred ( F ranged from 0.03 0.27) than four native populations (all F = 0.03) and they exhibited 12% lower allelic diversity viii than native populations, showing evidence consistent with a founder effect. Lack of evidence for significant bottlenecks combined with high effective migration rates suggested that there may be a great deal more movement of this species within the Bay than was previously thought. Two proposed scenarios for expansion (dispersal from introduced populations and intentional surreptitious introductions) were evaluated. Although not inconceivable, genetic evidence did not support the Bubba mechanism as the primary mode of expansion and dispersal was found to be the most probable mode underlying the recent range expansion. However, a number of characteristics of the population genetic and mixed stock analyses indicate that a separate scenario, escapement from impoundments, is worth investigating as a substantial source of the expansion. The study has important implications for ecosystenl-based management because it is the first application of mixed stock analysis to an invasive species.