An Inexpensive Modified Emergent-Fry Trap for Lake-Spawning Salmonids

Abstract

Emergent-fry traps, designed for sampling salmonid fry, have been particularly valuable for evaluating the reproductive success of stocked lake trout Salvelinus namaycush in the Great Lakes. Traditional fry traps are constructed with a welded iron base and riveted walls and are therefore heavy and bulky as well as expensive. We describe an inexpensive new design with a semi-rigid base and soft, fabric walls that requires few specialized tools for construction. The soft design and light weight of the traps allow for easy stacking and transport. The weight can also be adjusted to suit sampling requirements. We deployed 15 rigid and 14 soft fry traps at two sites in Lake Champlain, Vermont and New York. Of the 286 fry collected, 187 were collected in rigid traps and 99 in soft traps. The numbers of fry collected per unit effort did not differ significantly between rigid and soft traps at either site. At one site, significantly greater numbers of soft traps than rigid traps contained fry (chi-square test, P < 0.0005). The new fry trap design provides a convenient, inexpensive method for determining locations of salmonid hatch and for estimating relative fry production.