Population Characteristics and Summer-to-Autumn Survival of Juvenile Rainbow Trout and Coho
Salmon in Two Lake Superior Tributaries, 1969-1972
Thomas M. Stauffer
Abstract.-Population estimates of age-0 and age-I rainbow trout and age-0 coho salmon were made during June-November in the Little Garlic River (1969-70) and in Chinks Creek (1971-72). Estimates were made and growth data were obtained, usually monthly, on a 305-m section of each stream. Numbers of age-0 rainbow trout ranged from 607 to 6,327 fish and density was on the order of 1-4 trout per square meter during August to November. Biomass in the two streams was about 1-3 g/m2, and production was 0.72- 1.29 g /m2 for Chinks Creek and 1.542.31 g /m2 for the Little Garlic River. Age-0 rainbow trout in the two streams grew to 62 mm (TL) by November. Numbers of age-0 rainbow trout declined rapidly during August-November. August, September and October populations were 44, 60 and 80%, respectively, of that present in November. These values can be used for comparative purposes, to estimate the numbers ultimately present in November. Age-I rainbow trout numbers ranged from a very few to 724 (0.43 /m2) during June-November. The Little Garlic had by far the largest population. Biomass was 1-3 g/m2 in the Little Garlic River whereas it was much less in Chinks Creek. Production in the Little Garlic was 2.0 g/m2. By November, Little Garlic trout averaged 127 mm long and Chinks Creek averaged 138 mm. Rainbow trout numbers declined during June-August, probably due to downstream migration, but did not change in September, October or November. The numbers of age-0 coho salmon ranged from a very few to 1, 590 during July-November. Density and biomass were much higher in Chinks Creek (0.22-1.23 fish per square meter and 1.09-2.51 g/m2) than in the Little Garlic River (maximum of 0.09 fish per square meter and 0.39 g/m2). Maximum production (1.89 g/m2) occurred in Chinks Creek in 1972. By November coho averaged 77 mm long. Numbers declined rapidly and average survival of the three cohorts to November was 49, 56, 67 and 83%, respectively, for salmon present at the beginning of July, August, September and October. These values can be used to estimate the numbers ultimately present in November.