Effect of Entrance-Pool Weir Elevation and Fish Density on Passage of Alewives (Alosa pseudoharengus) in a Pool and Weir Fishway

Abstract

A comparison of the rates of passage of alewives (Alosa pseudoharengus) into a pool and weir fish way throughout the peak of the alewife run (22 May-6 June) in a Nova Scotia river revealed that one entrance weir, built at an elevation 0.21 m (8.0 in) lower than the existing conventional weir, passed alewives at a significantly greater mean rate (56.25/min) than the conventional weir (23.25/min). The mean rate of passage of alewives from pool to pool within the fishway (37.59/min) was not significantly greater or less than the mean rate for either of the entrance weirs. Density tests at two intermediate fishway pools revealed that the relationship between alewife density and exit rate may be described by a curve that rises to a peak exit rate of 80/min at a density of 75/m3 and then levels off to 70/min at higher densities. It is concluded that crowding and delay is not likely to occur within the fishway at the peak of the alewife run. Values for substitution in the formula of Clay (1961) for calculating fishway capacity determined for the alewife show that this species does not require any more time per fishway pool than Pacific salmon and that the demands of alewives on water volume are about 6 times less than for Pacific salmon. These determinations permit more general application by fisheries resource biologists and engineers of the data presented on crowding, delay and capacity for alewives in a pool and weir fishway.