Migrations and Biological Characteristics of Adfluvial Coaster Brook Trout in a South Shore Lake Superior Tributary

Abstract

We used fish traps and electrofishing surveys to characterize the biology, life history traits, and potential biotic interactors important to the rehabilitation of native, adfluvial coaster brook trout Salvelinus fontinalis in Lake Superior. This study focused on the Salmon Trout River, Michigan, which is the site of the last known remnant population of adfluvial brook trout on the south shore of Lake Superior. The brook trout captured in passive traps (weirs) in the river ranged from 56 to 554 mm in total length (TL) and from 0 (young of the year) to 6 years of age. This population displayed a protracted 5-month migration into the river but one that included relatively few fish. Coaster brook trout in this population appear to initiate adfluvial migrations near age 3 and 300 mm TL. Relative weight values increased with fish length and therefore reproductive life stage, possibly indicating the shift from river to lake habitats. This population of coaster brook trout is small and subject to potential biotic interactions with exotic species and population limitation because of an active fishery in the lake and river. Migratory runs of brook trout coincided with large runs of coho salmon Oncorhynchus kisutch, and the instream juvenile salmonid composition included proportionately high densities of coho salmon and rainbow trout O. mykiss. In addition, Floy tag return data indicated that exploitation of reproductive-age Salmon Trout River coaster brook trout was at least 12% and may have been as high as 50% in the open waters of Lake Superior. A recent increase in the legal minimum length limit and reduction of the daily bag limit for recreational harvest may slow or reverse this trend.