Effects of Floods on Food Consumption and Production Rates of a Stream Brook Trout Population

Abstract

Food consumption and production rates were estimated for a stream population of brook trout, Salvelinus fontinalis Mitchill, over a two-year period (1965–1966) in which four severe floods occurred. Two year classes were nearly eliminated as producing components of the population. Standing crops of older age groups were reduced as a result of a decrease in the streamˈs carrying capacity after sand and debris carried into the stream by flood waters filled pools and blanketed riffle areas. Invertebrate populations were also severely damaged by floods, reducing the food supply and causing an apparent decrease in growth rates in 1965 when three of the four floods occurred. Results of laboratory feeding experiments at four different temperature-season combinations were used to estimate food consumption rates of the brook trout in their natural environment. Maintenance requirement increased with increasing temperature in the spring and summer and decreased with decreasing temperature in the fall and winter. Net efficiency of food utilization increased with increasing temperature in the spring and summer and decreased in the fall and winter. The smaller fish, <63 g, had a greater percentage maintenance at all temperature-season combinations except in the fall when they had a lower percentage maintenance requirement than the larger fish, 63 g and >. Annual production rates in 1965 and 1966 were 61.4 and 43.5 kg/ha respectively. Annual food consumption rates in the same two years were 855.6 and 370.1 kg/ha. The two year classes entering the population during the study contributed only 7 percent to the total accumulated production during the two-year study period.