Invasion genetics of the blue catfish (Ictalurus furcatus) range expansion into large river ecosystems of the Chesapeake Bay watershed

The blue catfish, Ictalurus furcatus (Ictaluridae), is ranked among the most invasive species in Chesapeake Bay.  Intentionally introduced  into three Bay tributaries and a number of impoundments in 1974 - 1989, blue catfish have subsequently spread to three additional tributaries.  The mode of range expansion is unknown and three scenarios are proposed: (1) dispersal from introduced tributary populations through the Bay corridor (2) intentional anthropogenic introduction and (3) escapement from impoundments. We evaluated 6 microsatellite loci in light of demographic data for the three introduced tributary populations (baseline) to elucidate the potential sources of the three colonizing populations using mixed stock analysis (n=1375).  The Bay populations were considerably more inbred (F ranged from 0.03 – 0.27) compared to native populations (all F = 0.03) and exhibited a 12% decrease in allelic diversity, evidence consistent with a founder effect.  Lack of evidence for bottlenecks and high effective migration rates suggest that there may be more movement of this species than previously thought.  Genetic and demographic data indicate that dispersal and escapement are likely primary modes for the recent range expansion and intentional introductions are unlikely to be the primary effective explanation for the sudden expansion of Potomac and Piankatank populations.