Results of Predator Reduction on Brook Trout and Brown Trout in 4.2 Miles (6.76 km) of the North Branch of the Au Sable River

Abstract

Abstract During the autumns of 1964, 1965 and 1966, brown trout 12.0–25.1 inches (305–638 mm) in length were removed from 4.2 miles (6.76 km) of the North Branch of the Au Sable River (Dam 2-County Line), and American mergansers were harassed in the same area each winter as time permitted. The objective was to decrease losses among the smaller salmonids which would otherwise be eaten by the large trout and mergansers. Effects of control efforts were assayed by comparison of 1965–1967 angling results and population estimates with similar data accumulated on the test section and two other stream sections of the North Branch during 1961–1964 when predator manipulation was not carried on. In 1964, 561 large brown throut (66% of the estimated population) were removed. In 1965 and 1966, the actual removals were 346 and 104, or 63 and 40% of the population, respectively. The only major change noted was an increase during 1965, 1966 and 1967 in numbers of brook trout larger than 9 inches (229 ram) in the populati...