Evaluation of Blue Catfish Populations in Four Midwestern Power Cooling Reservoirs

Blue Catfish (Ictalurus furcatus) are the largest catfish in North America and as such angler desire for trophy fisheries have grown in addition to harvest fisheries. The Illinois Department of Natural Resources (IDNR) has stocked Blue Catfish into several reservoirs in the state including four that have powerplants that utilize the water for cooling and discharge it back into the reservoir at increased temperatures. This study explored the potential impacts of these warm water effluents on Blue Catfish population demographics, as well as whether management changes need to be implemented in these systems. I sampled Powerton, LaSalle, Springfield, and Clinton Lakes via low pulse electrofishing in the summer and fall of 2020. Additional data was provided from the IDNR including low pulse electrofishing, gill net, and fishing tournament data from 2019 and 2020. Clinton Lake yielded only two Blue Catfish and was removed from analysis in this study. Blue Catfish in Powerton Lake had the largest mean lengths and the oldest population of all reservoirs for 2020 low pulse electrofishing. The Blue Catfish in Springfield Lake were significantly smaller in 2019 and 2020 compared to Powerton Lake in low pulse electrofishing surveys, but with small sample sizes on Springfield Lake population trends are difficult to determine. However, large individuals are still present in Springfield Lake as seen in gill net sampling, but did not recruit to our electrofishing sampling efforts. Growth was similar for both Powerton and LaSalle Lakes with faster growth rates compared to other Blue Catfish fisheries in the United States. These same trends were not seen in LaSalle Lake, which had the lowest mean lengths and relative weight values of all the systems, although it is similar in size and construction to Powerton. Age data shows Blue Catfish in LaSalle are getting older without successive increases in length indicating potential stunting and density-dependent issues. Springfield Lake’s data showed that gill nets and fishing tournaments can provide alternative sampling strategies that provide additional data to low pulse electrofishing sampling but do suffer from size selectivity. Overall, some of these systems have Blue Catfish populations that have fast growth and are reaching large sizes. Whether or not thermal effluents are the causal factor of this growth is yet undetermined. More robust data will be needed for sound management decisions to be implemented. Our results indicate a need for more efficient and standardized low pulse electrofishing sampling in the future but show promise for having strong Blue Catfish fisheries in these powerplant reservoirs in the state of Illinois.