Increasing Predation through Walleye Fingerling Stocking: A Recovery Tool for Saginaw Bay, Lake Huron
David G. Fielder
Abstract.—The walleye Sander vitreus fishery in Saginaw Bay was historically the second largest in the Great Lakes. It collapsed in the mid 1940s. Modern-day limitations to natural recruitment are offshore spawning habitat degradation (sedimentation of reefs), blockage by dams to tributary spawning grounds, and likely the predatory effects of nonnative planktivores such as alewives Alosa pseudoharengus and rainbow smelt Osmerus mordax. Walleyes have always been the principal predator in the bay’s ecosystem, and with their numbers depressed, the fish community is overpopulated with prey fish species precipitating a variety of ecological problems. Stocking of about 0.8 million spring walleye fingerlings per year, beginning in the early 1980s, helped to re-establish a walleye population and fishery. Some natural recruitment has returned, mostly from spawning in rivers below the first impoundment. Research, however, has determined that the walleye population remains heavily dependent on stocking, with about 80% of the local recruitment attributed to hatchery propagated fish. The walleye population is still well below the carrying capacity of the bay’s habitat for adult walleyes and the prey base. New recovery initiatives have been developed recently for walleyes in the bay with emphasis on restoration of access to tributary spawning grounds. These measures, however, may be limited in their benefit as long as nonnative planktivores remain abundant in the bay. Increased predation rates on the alewife and rainbow smelt populations are needed so as to encourage better survival of naturally reproduced walleye fry. Increased stocking is rationalized as the best means with which to initially achieve a balance of predator and prey in the bay, thereby setting up a more favorable environment for natural recruitment. While walleye stocking is a common practice in North America, this approach is somewhat novel in that the objectives are not just to contribute to the creel, but to increase predatory pressure on an overabundant prey base, especially the nonnative planktivores. The goal is to help manipulate the fish community biologically to an assemblage that favors native prey species thereby minimizing some of the obstacles to better survival of naturally reproduced walleye larvae. Higher predation rates may also make the Saginaw Bay ecosystem more resistant and resilient to the effects of any future exotic invaders.