“…The sub-sampling techniques of scoop traps (Meehan, 1964), dip traps (Mason, 1966) and fyke nets (Craddock, 1959) make them unsuitable for research in which a high recovery of marked stocked fish is required. Wolf traps (Wolf, 1950) and inclined screen traps (McLain and Manion, 1967) were designed to catch all downstream migrants, but the size and permanent nature of these designs made them unsuitable for the investigations, briefly reported here, because of their cost and lack of portability.…”