Population Dynamics Modeling and Management Strategy Evaluation for an Invasive Catfish

Blue Catfish were introduced in the tidal tributaries of the Chesapeake Bay in the 1970s and 1980s to establish new fisheries during a time period when many fisheries were in decline due to pollution, habitat alteration, disease, overfishing, and environmental catastrophes. Having expanded their range to most Bay tributaries, the species has drawn concern from many stakeholders and scientists for its effects on at-risk and economically important native and naturalized species. My study focused on understanding the dynamics of this species based on multiple long-term monitoring data and evaluating potential management strategies to meet stakeholder needs. I sought to understand how is growth variability was partitioned over time and space, how Blue Catfish populations changed from 1994 to 2016, and how predation on native species and fishery-based performance measures may respond to management intervention. As Blue Catfish length-at-age is exceptionally variable in Virginia tributaries of the Chesapeake Bay, I evaluated the variability in growth using candidate non-linear mixed effects models that described variability in growth over time and space. Linear trend tests supported declines in growth over time within river systems, but did not support the presence of synchronous growth responses among river systems. To better understand population dynamics of Blue Catfish in the Chesapeake Bay watershed, I developed a statistical catch-at-length model for the James River to estimate population size, instantaneous fishing mortality, and size structure over time. The statistical catch-at-length model estimated that Blue Catfish abundance increased slowly and peaked in the mid-2000s before undergoing a recent decline. The model estimated a large spike in abundance due to an estimated large recruitment event in 2011, but may be an artifact of missing data in 2012 in both relative abundance indices examined. The newly developed statistical catch-at-length model provides most detailed information on population dynamics of Blue Catfish in the James River and can be expanded and updated as new data become available. Based on results of the statistical catch-at-length model, I examined population responses to unregulated, maximum length limit (60 cm), and harvest slot limit regulations (harvest allowed 25 –60 cm) in a management strategy evaluation framework. The management strategy evaluation supported that the James River Blue Catfish population could be reduced with increased harvest, but trophy-size fish would decline. Consequently, fishery managers tasked with invasive species management must consider this tradeoff of fishery economic benefits and predation on native populations, especially those prey in which population sizes are unknown.