Hierarchical Bayesian Approach to Standardize Catch Rates of Blue Catfish in Tidal Rivers of Virginia from Multiple Surveys Using Multiple Gears

Blue Catfish, introduced into tidal waters of Virginia from 1970s to mid-1980s, have rapidly expanded into many major tributaries in the Chesapeake Bay watershed. This expansion necessitates the need for monitoring abundance of the Blue Catfish. A hierarchical Bayesian delta model was applied to examine the relative influence of environmental, spatial and temporal factors on Blue Catfish catches from annual surveys conducted in tidal rivers of Virginia because of the high percentage of zero observations and sparse data. The analyses were based on three datasets, collected from a bottom-trawl survey by the Virginia Institute of Marine Science and low- and high-frequency electrofishing surveys by the Virginia Department of Game and Inland Fisheries. Data collected from multiple tributaries by the same type of survey were treated as hierarchically structured. We found the catch rates of Blue Catfish in the trawl survey were significantly influenced by the salinity, temperature, season and site locations. Standardized catch rates were highly variable and increased over time significantly in the trawl survey and the low-frequency electrofishing survey, indicating that the abundance of Blue Catfish increased across years. We recommend continued monitoring in these and other tidal rivers to permit evaluation of control strategies of Blue Catfish.