Movement patterns of large Brown Trout in the mainstream Au Sabl River, Michigan
Brown trout, trout, night, Gradient, activity, active, habitat
Journal or Book Title
Transactions of the American Fisheries Society
We used radiotelemetry to monitor spring and summer movements of 11 brown trout(Salmo trutta) (442-584 mm) for up to 904 d in a Michigan stream. Individual brown trout used afew specific locations near cover (referred to as home sites) as resting locations during the day,moved across various distances at night, and generally returned to the same home site the nextmorning. Home sites were predominantly artificial cover (88%) rather than natural sites, asnatural cover was very limited in the study area. Some fish used multiple home sites, and theaverage separation between multiple home sites for individual fish was over 500 m. Fish trackedfor more than 1 year used the same home sites each summer and generally exhibited similarbehaviour each year. Fish belonged to two general categories of daily movement behaviour:mobile or stationary. Mobile fish tended to move frequently and were found within their homesites only 43% of the time at night. Stationary fish did not move far from home sites, even atnight. There was a negative correlation between the average gradient and the maximum distancefish moved from their home sites during nocturnal periods. Stationary fish resided in areas ofsteeper gradient (usually about 0.20%) and moved less often nocturnally than did mobile fish.Three fish were tracked extensively over 36 d to quantify diel activity patterns. The hourly activityof fish increased dramatically at dusk, continued at a lower level overnight, and then increasedagain at dawn before declining to near zero during the day. This behaviour pattern was similaramong all individuals tracked and also between the months of June, July, and August for anindividual fish. Nocturnal movements involved significantly greater distances than diurnalmovements for these fish. The relationship between movement and gradient may indicateenergetic tradeoffs between the cost of moving against a current and the energy gained duringactive foraging. Also, the dominant use of artificial home sites has implications for the value ofhabitat improvements meant to increase abundance of large brown trout.