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.

Freshwater fishes have been introduced outside their native range to establish recreational fisheries, but management conflicts arise when such introductions also result in potentially harmful effects on native species. In this case study, we focus on Blue Catfish Ictalurus furcatus, which were introduced in the Chesapeake Bay region and are now considered invasive. In many tidal tributaries, Blue Catfish have increased dramatically in abundance, expanded into high‐salinity habitats (up to 21.8 psu), and negatively affected native species, prompting calls for the development of an effective management plan. However, management of this conflict species is complicated by multiple competing objectives, including control of population size, maintenance of trophy fisheries, and expansion of commercial fisheries for Blue Catfish. Seven management recommendations were advanced by the Invasive Catfishes Work Group to control the spread and limit the ecological impacts of Blue Catfish on native species. We highlight opportunities for addressing these complex management issues and guide our suggestions using results from research on invasive Blue Catfish ecology and population dynamics, as well as management of invasive species in general. A formal approach, such as structured decision analysis, is required to resolve conflicts among user groups and to address the wicked problem of Blue Catfish in the Chesapeake Bay region.

Blue Catfish Ictalurus furcatus were purposefully introduced into freshwater tributaries to Chesapeake Bay in the past, and populations have subsequently spread to new areas, negatively impacting native communities and causing concern for resource managers. To aid development of management strategies, we implemented a multiyear (2012)(2013)(2014)(2015) tagging study of invasive Blue Catfish in a 40-km stretch of the Potomac River to estimate survival and assess movement patterns. Blue Catfish (N = 1,237) were captured by electrofishing and double-tagged to allow us to estimate tag retention rates; we used reward tags to increase reporting rates. Recaptured fish (N = 104; 8.4% return rate) were at large for between 2 and 1,208 d. Tag retention rates were 0.88 (SE = 0.045) after 1 year and declined to 0.31 (SE = 0.107) after 2.7 years. The mean minimum distance moved by fish was 24.1 km (range = 0.0-112.6 km). Most (63%) fish displayed downriver movements, but distance moved was unrelated to fish size or days at large. Greater distances were observed among fish that moved downriver (34.4 km) than those that moved upriver (6.7 km). These results suggest high variability in movement behaviors for Blue Catfish inhabiting the tidal Potomac River from freshwater reaches to estuarine habitats. We estimated an annual apparent survival rate of 0.56 (SE = 0.057; Brownie tag-return model) across the study period. This survival rate is lower than survival rates reported from their native range. Long-distance movements of Blue Catfish in the Potomac River indicate that robust, large-scale control measures will be needed to reduce population abundance and minimize negative impacts of this species on native communities.

Choice of management spatial scale is a critical step of any stock assessment, but deciding on a conservative criterion is difficult because of risks associated with any choice. For example, if one large unit is selected when distinct sub‐stocks exist, then some population components may disappear over time. Alternatively, choosing several small management units when one well‐mixed stock exists may lead to costly and ineffective management. We consider the example of tautog (Tautoga onitis). Mortality estimated for a single stock using virtual population analysis has exceeded the target and resulted in mandated reductions in fishing. In Virginia, tag returns and catch curve analyses are consistent with a localized mortality rate that is less than the target. Therefore, reductions of fishing effort in Virginia may not alleviate overfishing elsewhere and might not be conservative. Thus, simple models used for localized assessment can have advantages over sophisticated models applied to an entire stock complex when multiple stocks exist.

Aquatic resource surveys that span multiple decades provide valuable information about fish population responses to environmental and human-induced changes. Often, surveys are altered as scientific objectives change or in response to management needs. These modifications usually result in inconsistencies in the time series, which must be addressed for proper analysis of fish community data. Since 1997, juvenile fishes in Virginia tributaries of Chesapeake Bay have been captured monthly using a bottom trawl at both fixed and random sites. Previous surveys in these tributaries were conducted at fixed sites only; thus, an understanding of the effect of this design change would allow us to infer fish community status through multiple decades. We compared samples from the fixed site design with those from the stratified random design in the James, York, and Rappahannock rivers and examined species composition, biodiversity, relative abundance estimates, and size distributions to understand the effects of survey design on these metrics. Catches from random sites were characterized by consistently higher species richness than those from fixed sites; biodiversity metrics varied by sampling site type (fixed versus random) and river. For most select species, we observed similar trends in relative abundance regardless of site type; however, for some species we noted differences in magnitude among years and between sampling site types. Community metrics, such as taxonomic diversity and distinctness, revealed subtle differences about fish species assemblages compared with traditional diversity metrics demonstrating that community metrics can characterize biodiversity of fishes at higher taxonomic levels. Thus, species-specific and community metrics derived from assemblage data from fixed-site surveys may not fully represent the magnitude of change in demersal fish assemblages, but can provide reliable indicators of patterns of change in abundance through time.