Canister for Releasing Marked Fish at Depth in Hydroelectric Dam Gatewells and Forebays

Abstract

At Pacific Northwest hydroelectric dams, surface containers or hose systems have been used to release marked juvenile Pacific salmon Oncorhynchus spp. for fish passage studies. Because these release methods introduce marked fish to unknown depths and hydraulic conditions, they may compromise study results. We constructed a canister and frames for releasing marked fish at predetermined depths and locations in the gatewells and forebays of hydroelectric dams. The canister performed as anticipated, avoiding injury to fish and allowing them to acclimate to depth prior to release. Acclimation is accomplished by slowly lowering the canister to the desired depth and holding the canister for a period of time before release. A total of 1,000 yearling and subyearling chinook salmon O. tshawytscha were released with this canister over a 2-year period in studies of guidance and orifice passage systems. About 98% of these fish were recaptured, with no injury or descaling attributed to the release canister. This release method allows time for acclimation as well as repeatable positioning of the canister for release of fish at depth for studies at hydroelectric dams on the Columbia and Snake rivers.