Use of Strain, Season of Stocking, and Size at Stocking to Improve Fisheries for Rainbow Trout in Reservoirs with Walleyes

Abstract

We evaluated stockings of rainbow trout Oncorhynchus mykiss in Pathfinder and Alcova reservoirs, Wyoming, to determine what combination of strain, season of stocking, and size at stocking maximized angler catch in the presence of walleyes Stizostedion vitreum. Coded wire tags were used to identify individual rainbow trout to stock group. Angler catch of Kamloops rainbow trout and fall rainbow trout in Pathfinder Reservoir exceeded returns of Eagle Lake rainbow trout. Differences in strain performance in Alcova Reservoir were less pronounced. The importance of season of stocking was identified with fall-stocked (Aug–Oct) rainbow trout returning to anglers in higher numbers than those stocked during spring (Mar–Jun). Size-at-stocking evaluations indicate that large, catchable-size (>208 mm total length) rainbow trout maximize use of hatchery facilities over stocking greater numbers of small, catchable (178–207 mm) or subcatchable (127–177 mm) sizes. Pond feeding trials conducted with three walleye size-classes and three rainbow trout sizes showed that 127-mm rainbow trout were highly vulnerable to walleyes as small as 330–378 mm. Intermediate-size rainbow trout (178 mm) were not readily consumed by 381–432-mm walleyes, but they were vulnerable to 483–533-mm walleyes. At 229 mm, rainbow trout appeared invulnerable to walleyes in the largest size-class (483–533 mm) we studied. Rainbow trout stocked at large, catchable sizes are probably vulnerable to fewer walleyes compared with small, catchable and subcatchable sizes, allowing greater numbers to survive predation and recruit to the sport fishery.