Seasonal movement, growth and survival of brook trout in sympatry with brown trout in Midwestern US streams

Seasonal patterns in growth, survival and movement of brook trout Salvelinus fontinalis were monitored in two southeastern Minnesota streams divided into study reaches based on brown trout Salmo trutta abundance. We estimated survival and movement while testing for effects of stream reach and time using a multistrata Cormack-Jolly-Seber model in Program MARK. Multistrata models were analysed for three age groups (age-0, age-1 and age-2+) to estimate apparent survival, capture probability and movement. Survival varied by time period, but not brown trout abundance and was lower during flood events. Age-0 brook trout emigrated from reaches with low brown trout abundance, whereas adult brook trout emigrated from downstream brown trout-dominated reaches. Growth was highest in spring and summer and did not differ across streams or reaches for the youngest age classes. For age-2+ brook trout, however, growth was lower in reaches where brown trout were abundant. Interspecific interactions can be age or size dependent; our results show evidence for adult interactions, but not for age-0. Our results suggest that brook trout can be limited by both environmental and brown trout interactions that can vary by season and life stage.