Michigan Department of Natural Resources
Institute for Fisheries Research Report No.1763, 1970
Age, Growth, and Downstream Migration of Juvenile Rainbow Trout in the Black-River, Michigan
Thomas M. Stauffer
Abstract.-Juvenile rainbow trout were examined during 1951-59 while they lived in upstream areas of the Black River and also when on migration to Lake Michigan. Their growth rate in the stream was about 3 inches per year. The body-scale relationship was: L (inches) = 0.16 + .0826S (mm x107). The relationship between length (mm) and weight (g) was: W = .00001384L3.0426. On the average, the parr in upper sections of the river in autumn were 68% age O, 29% age I and 3% age II. Annual variations in age composition were related to year class strength. For a given migratory season, age composition varied according to year class strength, and the older parr migrated first. On the average, the downstream migration was 64% age-I fish, 34% age II and 2% age III. Lengths of downstream migrants averaged 4.4 inches for age I, 7.1 for age II and 8.9 for age III. Most migration occurred between May 21 and June 30, at night, on subsiding water levels, and at water temperatures