The role of the pectoral fins in station-holding of Atlantic salmon Parr (Salmo salar L.)

Benthic fish resist downstream displacement in a current by balancing drag, the force orientated downstream, with the friction force. The friction force is μ (Wo—L), where μ is the friction coefficient, Wo the weight force of the fish in water (N), and L the lift force (N) acting on the body and fins (Arnold and Weihs, 1978). Above a critical speed, friction is insufficient to counteract drag and the fish must either swim or seek shelter from the flow. This note reports tests of the commonly proposed hypothesis (e.g. Kalleberg, 1958; Keenleyside and Yamamoto, 1962; Jones, 1975; Wankowski, 1981) that the pectoral fins are important to station-holding in Atlantic salmon, acting as hydrofoils generating negative lift.