Abstract
We made estimates of annual production of stream trout in two Lake Superior tributaries in northeastern Minnesota in 1977–1978. The Caribou River (total alkalinity, 34 mg/L as CaCO3) drains part of the north shore of Lake Superior in an igneous rock geology. The Blackhoof River (total alkalinity, 83 mg/L) drains glacial drift and lake clay at the western end of Lake Superior. Annual production of brook trout Salvelinus fontinalis in the Caribou River was estimated to be 58.0 kg (wet weight) per hectare, reflecting low water fertility. In the Blackhoof River, annual production was 43.5 kg of brown trout Salmo trutta and 95.7 kg of juvenile rainbow trout Oncorhynchus mykiss per hectare, The total salmonid production of 139.2 kg/hectare in the Blackhoof River appeared to reflect an intermediate level of water fertility. Ratios of annual production: mean standing stock (P/B) were calculated to be 2.2 for juvenile rainbow trout, 1.7 for brook trout, and 0.9 for brown trout. These values suggest an inverse relation between P/B and number of age-groups present (three for rainbow trout, four for brook trout, and six for brown trout).
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