Range, activity, and habitat of large, freeranging brown trout in a Michigan stream.
activity, habitat, Brown trout, trout, radio telemetry, telemetry, upstream, fishing, regulations, night, active, food
Journal or Book Title
Transactions of the American Fisheries Society
Little is known about behaviour patterns and habitat use of large (400+ mm totallength) brown trout (Salmo trutta). We used radio telemetry to monitor the movements of eightlarge (437-635 mm), free-ranging brown trout for up to 346 d. Total range of movement upstream and downstream varied from 370 m to 33,420 m. At some time during the year, six of the fishmoved out of an area protected with no-kill fishing regulations, even though none of them weretagged and released closer than 2 km from its boundaries. However, four of five fish trackedduring the height of the fishing season spent 87% of their time in the protected area. The fishappeared to have separate winter and summer ranges. Five of six fish tracked during autumn–winter moved upstream about 10 km to slower, deeper parts of the river between August andNovember, and remained there at least through the following April. The part of the river used asautumn–winter range was considered only marginal habitat for brown trout during summer due towarm water temperatures. Individuals used as many as four specific home sites within theirspring–summer range; average separation between home sites was 386 m. The fish typicallyrotated among sites, spending 2–3 d at one site before moving, usually at night, to anothersection of river. Activity was divided into two categories: active displacement – long-range travelfrom one part of the range to another; and foraging – short-range movements that might occurwhen searching for food. Active displacement appeared to be correlated with stream discharge,Fish displaced themselves an average of 239 m between telemetry observations in spring–summer and 3,103 m in autumn–winter; only 11% of this variation was attributable to variations inthe length of time between telemetry observations in spring–summer and autumn–winter. Dailyforaging activity varied by month and appeared to be related to light level, food availability, andwater temperature, In spring–summer, fish typically moved to midstream to forage at night, thenreturned to cover at specific home sites during the day. The sites they selected in daytime werecharacterized by deep (>30 cm), slow (< 10 cm/s) water with heavy log cover and silt substrate.