Abstract
The introduction of a non-native freshwater fish, blue catfish Ictalurus furcatus, in tributaries of Chesapeake Bay resulted in the establishment of fisheries and in the expansion of the population into brackish habitats. Blue catfish are an invasive species in the Chesapeake Bay region, and efforts are underway to limit their impacts on native communities. Key characteristics of the population (population size, survival rates) are unknown, but such knowledge is useful in understanding the impact of blue catfish in estuarine systems. We estimated population size and survival rates of blue catfish in tidal habitats of the James River subestuary. We tagged 34,252 blue catfish during July–August 2012 and 2013; information from live recaptures (n = 1177) and dead recoveries (n = 279) were used to estimate annual survival rates and population size using Barker’s Model in a Robust Design and allowing for heterogeneity in detection probabilities. The blue catfish population in the 12-km study area was estimated to be 1.6 million fish in 2013 (95% confidence interval [CI] adjusted for overdispersion: 926,307–2,914,208 fish). Annual apparent survival rate estimates were low: 0.16 (95% CI 0.10–0.24) in 2012–2013 and 0.44 (95% CI 0.31–0.58) in 2013–2014 and represent losses from the population through mortality, permanent emigration, or both. The tagged fish included individuals that were large enough to exhibit piscivory and represented size classes that are likely to colonize estuarine habitats. The large population size that we estimated was unexpected for a freshwater fish in tidal habitats and highlights the need to effectively manage such species.
Highlights
In river-dominated estuaries, the continuum between freshwater and marine environments provides a potential conduit for the encroachment of freshwater species into brackish and saline habitats
Higher salinities are believed to serve as a barrier to freshwater fishes (Scott et al 2008), some species exhibit salinity tolerances that allow them to successfully colonize estuarine habitats
Blue catfish Ictalurus furcatus (Schloesser et al 2011), Rio Grande cichlids Herichthys cyanoguttatus (Lorenz et al 2016), African jewelfish Hemichromis letourneuxi (Rehage et al 2015), largemouth bass Micropterus salmoides (Norris et al 2010), and pikeperch Sander lucioperca (Scott et al 2008) are freshwater species that are found in estuarine environments
Summary
In river-dominated estuaries, the continuum between freshwater and marine environments provides a potential conduit for the encroachment of freshwater species into brackish and saline habitats. Blue catfish Ictalurus furcatus (Schloesser et al 2011), Rio Grande cichlids Herichthys cyanoguttatus (Lorenz et al 2016), African jewelfish Hemichromis letourneuxi (Rehage et al 2015), largemouth bass Micropterus salmoides (Norris et al 2010), and pikeperch Sander lucioperca (Scott et al 2008) are freshwater species that are found in estuarine environments Some of these freshwater fishes are non-native and considered invasive because they threaten the biodiversity of aquatic ecosystems (Arthington et al 2016) through direct predation effects or indirectly by competition for limited resources with native fauna. In Chesapeake Bay tributaries, diadromous fishes such as American shad Alosa sapidissima and alewife Alosa pseudoharengus, which have experienced significant coastwide declines in abundance, are vulnerable to predation by invasive blue catfish
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