Walleye and Northern Pike

Introductions of nonnative walleye (Stizostedion vitreum) and northern pike (Esox lucius) have created popular recreational fisheries in many Northwestern waters. Rising demand for expanded angling opportunities for these species, especially walleye, has been met with growing concern about longterm risks associated with the introduction of a top predator. Proposed introductions are often controversial because of potential prey depletions, reductions in salmonid populations, and long-range movements of the species from the point of release. We urge a cautious approach to future introductions of these species in the northwestern United States and outline some approaches for evaluating risks and benefits. Stricter risk assessment procedures for species introductions have been adopted by many states, but illegal introductions of both species are a continuing problem. Greater efforts are needed to educate the public about the risks of illegal transplants, and stronger statutes are necessary to discourage this activity. he popularity of nonnative walleye (Stizostedion vitreum) and northern pike (Esox lucius) as sport fishes has mushroomed in recent years in the northwestern United States (Conover 1986). The walleye fishery in Lake Roosevelt, Washington, provides 200,000 angler-hours of fishing annually at catch rates of 0.5 fish/h with fish in the 2-kg to 5-kg size range commonly caught (Hallock and Fletcher 1991). Northern pike in Coeur d'Alene Lake, Idaho, exhibit the highest growth rates of the species in North America, and catches of fish >12 kg are common (Rich 1993). These and other trophy fisheries have received national publicity in angling magazines and television programs, thus fueling interest for similar angling opportunities elsewhere in the region. Proposed introductions are often controversial due to perceived risk to the region's prized salmonid fisheries (Conover 1986). Managing such top predators can be troublesome because potential top-down effects have been shown to significantly alter entire fish communities, even in large waterbodies (Colby et al. 1987; Knight and Vondracek 1993). Colonization of new waters beyond the point of release is an additional concern. Some western states prohibit stocking of walleye into certain waters (Idaho Department of Fish and Game [IDFG] 1982; Colby and Hunter 1989). However, demand for angling opportunities continues to mount, especially for walleye, and Idaho (IDFG 1982) and Montana (Colby and Hunter 1989) have conducted environmental assessments to guide stocking policies. Unfortunately, while state agencies have initiated detailed environmental reviews to evaluate risks and benefits of proposed introductions, illegal introductions of both species may be rising (Vashro 1990, 1995). Throughout North America the use of species introductions as a management tool has come under increased scrutiny (Moyle et al. 1986; Spencer et al. 1991; Bain 1993). Walleye and northern pike management Thomas E. McMahon is an associate professor in the Biology Department, Fish and Wildlife Program, Montana State University, Bozeman, MT 59717-0346; [email protected]. David H. Bennett is a professor in the Fish and Wildlife Resources Department, University of Idaho, Moscow, ID 83844-1136; [email protected]. in the Northwest illustrates that weighing potential recreational and economic benefits derived from introductions against potential longterm ecosystem effects is fraught with complex biological and social considerations. In this article, we review the current distribution of walleye and northern pike in the region and summarize case studies describing how local systems have responded to pike and walleye introductions. Our aim is to outline approaches for evaluating risks and benefits of proposed introductions and for curtailing illegal ones. Current Distribution Walleye and northern pike were first introduced to the Northwest in the 1940s and 1950s (Brown 1971; Beamesderfer and Nigro 1989) and now occur throughout the Columbia and upper Missouri River basins (Figure 1). Their range continues to expand as they colonize and are introduced into additional waterbodies.