Objective
There was concern with regard to the effect of elevated temperatures on the reproduction of cold-water species such as Round Whitefish. While eggs exposed to small water temperature elevations due to discharge heating might experience some increased mortality if temperature increases exceed 3°C, the greatest adverse effect can occur from the advancement of hatching time, resulting in asynchrony of whitefish larvae and their early food supply.
Scope
Potential effects of the thermal discharge were determined through laboratory studies of constant and fluctuating temperatures. Mathematical models were developed to predict effects from periodic, or constant waste heat on egg incubation. Whitefish eggs were incubated in 16 combinations of constant and fluctuating regimes ranging from 1.8 to 10°C.
Results
Optimal survival occurred in the 4 to 6°C range. Survival declined only slightly (to 70%) at lower temperatures, but declined very rapidly at temperatures above 8°C, reaching less than 5% at constant 100°C incubation temperatures.
Throughout development, whitefish egg sensitivity to thermal stress changed. For example, the eggs were quite sensitive to both extreme high and low temperatures early in development.
Tentatively, it was suggested that continuous temperature rises of 1 to 2°C, or occasional heating by 3 to 4°C, would be unlikely to adversely affect egg survival or the timing of hatch.
