Response of Sport Fishes to Thermal Discharges into the Great Lakes: Is Somerset Station, Lake Ontario, Different?

Abstract

To assess potential thermal impacts of Somerset Generating Station on sport fishes, the frequencies and durations of encountering the thermal discharge at Somerset Station were determined by tagging 121 salmonines and 58 centrarchids with temperature-sensing radiotransmitters. Encounters of the Lake Ontario shoreline occupied by Somerset Station averaged 0.7 and 0.1 per fish for salmonines and centrarchids, respectively. Salmonines averaged 5.5 h at the station per encounter. Four centrarchids established residence areas in the lake near the station for 29-79 d; others averaged 3.5 d at the station. Salmonines and centrarchids occupied waters off Somerset Station on 6.7% and 16.0% respectively, of the days they were tracked. No temperatures occupied by fish at the station exceeded critical thermal maxima for salmonines (20 - 25 degrees C) or centrarchids (30 - 37 degrees C). Salmonines occupied heated water >2 degrees C above ambient lake temperatures on 1.3% of the 1,983 occasions when temperatures were recorded, while centrarchids averaged 0.1% of 1,773 observations. Rare encounters of and lack of attraction to the thermal discharge were attributed to characteristics of the discharge (600+ m offshore, small delta T, small volume/area), to unremarkable lake habitat (flat bottom, physically similar to other regions of southcentral Lake Ontario), and to the generally wide-ranging movements of fishes in Lake Ontario. Comparing results from Somerset Station with similar studies at other Great Lakes power stations suggests that discharge design and lake habitat importantly influence the extent of fish attraction to thermal discharges.