Evaluating the Impact of an Altered Thermal Regime on Sport Fish Assemblages

A site specific rule change granted by The Illinois Pollution Control Board to Ameren Energy Generating Co. allows increased thermal loading in May and October on Coffeen Lake, a reservoir utilized by a power station capable of generating 945 megawatts of electricity.  The goal of this project is to monitor the biological impacts on the sport fish populations of the lake.  Sampling was done during fall 2010 and consisted of 6.25 hours of three-phase AC electrofishing from 5 separate sites on the reservoir. Species sampled were largemouth bass, bluegill, redear sunfish, white crappie, black crappie, and channel catfish.  Using relative weight (W_r) as an index of condition, we found largemouth bass were robust throughout the reservoir (W_r =101.0).  Relative density of largemouth bass was low in the cooling loop (22 fish/hour) compared to the lower temperature upper pool (70 fish/hour).  Bluegill (426 fish/hour) and redear sunfish (75 fish/hour) were caught in all sites in high numbers.  Average size for both bluegill (67.5 mm) and redear sunfish (106.0mm) was low in this reservoir.  We had low catch rates of both white crappie (3.2 fish/hr) and black crappie (2.9 fish/hr) in all reaches.  During winter and spring 2011 we will increase effort to include additional electrofishing and trapnetting to increase sample sizes of black crappie, white crappie, and channel catfish.