Going against the flow: an examination of the propulsive movements made by young brook trout in streams

We examined the propulsive movements and behaviour of young-of-the-year (YOY) brook trout (Salvelinus fontinalis) swimming in their natal streams. Our findings demonstrated that swimming performance was influenced by temporal and spatial heterogeneity in water flow. Pectoral fins were used commonly, even by individuals swimming in fast flowing water. There also was spatial variation in the speed attained for a given tail-beat frequency and amplitude. After controlling statistically for variation in spatial location, fork length, and tail-beat amplitude, the swimming speeds brook trout attained for a given tail-beat frequency were lower than values expected from laboratory studies of steady swimming but higher than values expected from laboratory studies of unsteady swimming in standing water. Trout holding station made short-term adjustments in tail-beat frequency also suggesting a degree of unsteady swimming. A field experiment demonstrated that introduction of a current-velocity refuge reduced swimming costs by 10%, on average, without affecting the frequency of foraging attempts made.