MANAGEMENT Walleye and Northern Pike: Boost or Bane to Northwest Fisheries?

By Thomas E. McMahon and David H. Bennett ABSTRACT Introductions of nonnative walleye (Stizostedion vitreum) and northern pike ( lucius) have created popular recreational fisheries in many Northwestern waters. Rising demand for expanded opportunities for these , especially walleye, has been met with growing concern about long- term risks associated with the introduction of a top predator. Proposed introductions are often con- troversial 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 introduc- tions of these species in the northwestern 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 shown to significantly alter entire in the Northwest illustrates that walleye (Stizostedion vit- communities, even in large weighing potential recreational and reum) and northern pike waterbodies (Colby et al. 1987; economic benefits derived from (Esox lucius) as sport Knight and Vondracek 1993). Coloni- introductions against potential long- has mushroomed in recent years in zation of new waters beyond the term ecosystem effects is fraught the northwestern United States point of release is an additional con- with complex biological and social (Conover 1986). The walleye fishery cern. Some western states prohibit considerations. In this article, we in Lake Roosevelt, , pro- stocking of walleye into certain review the current distribution of vides 200,000 angler-hours of waters ( Department of Fish walleye and northern pike in the annually at catch rates of 0.5 fish/h and [IDFG] 1982; Colby and region and summarize case studies with fish in the 2-kg to 5-kg size Hunter 1989). However, demand for describing how local systems have range commonly caught (Hallock angling opportunities continues to responded to pike and walleye intro- and Fletcher 1991). Northern pike in mount, especially for walleye, and ductions. Our aim is to outline Coeur d'Alene Lake, Idaho, exhibit Idaho (IDFG 1982) and approaches for evaluating risks and the highest growth rates of the (Colby and Hunter 1989) have con- benefits of proposed introductions species in , and catch- ducted environmental assessments and for curtailing illegal ones. es of fish >12 kg are common (Rich to guide stocking policies. Unfortu- 1993). These and other trophy fish- nately, while state agencies have ini- Current Distribution

Downloaded by [Montana State University Bozeman] at 09:06 02 April 2012 eries have received national publici- tiated detailed environmental re- Walleye and northern pike were ty in angling magazines and televi- views to evaluate risks and benefits first introduced to the Northwest in sion programs, thus fueling interest of proposed introductions, illegal the 1940s and 1950s (Brown 1971; for similar angling opportunities introductions of both species may be Beamesderfer and Nigro 1989) and elsewhere in the region. Proposed rising (Vashro 1990, 1995). now occur throughout the Columbia introductions are often controversial Throughout North America the and upper River basins due to perceived risk to the region's use of species introductions as a (Figure 1). Their range continues to prized salmonid fisheries (Conover management tool has come under expand as they colonize and are 1986). Managing such top predators increased scrutiny (Moyle et al. 1986; introduced into additional water- can be troublesome because poten- Spencer et al. 1991; Bain 1993). Wall- bodies. tial top-down effects have been eye and northern pike management Walleye Thomas E. McMahon is an associate professor in the Biology Department, Fish One of the more significant wall- and Wildlife Program,Montana State University, Bozeman, MT 59717-0346; eye introductions in the region was [email protected]. David H. Bennett is a professor in the Fish and to the upper Columbia River system Wildlife Resources Department, University of Idaho, Moscow, ID 83844-1136; (Figure 1). Although the history of [email protected]. its introduction is unclear, a popular

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sport fishery was established by the and Canyon Ferry Reservoir near the 62 contain northern pike (J. Vashro; 1960s in Lake Roosevelt, Washington headwaters of the Missouri River Montana Fish, Wildlife, and Parks (Hallock and Fletcher 1991). Walleye (Figure 1; Vashro 1995). [MFWP]; personal communication). are now widespread throughout the No known stockings of northern lower Columbia River basin, and Northern Pike pike have been made in the state of sport fisheries have developed in Northern pike were illegally Washington, but colonization from several reservoirs and tailwaters stocked into Coeur d'Alene Lake, Montana rivers has been recorded. (Hallock and Fletcher 1991; Tinus Idaho, in the early 1970s (Rich 1993) In Washington and , and Beamesderfer 1994). However, and have spread to several lowland pike are viewed as a threat to declin- concern about on salmo- lakes in northern Idaho. In Wyoming, ing stocks of salmonids because of nid smolts in the Columbia River northern pike occur only at Keyhole predation and possible transmission (Rieman et al. 1991) has led to a poli- Reservoir (Figure 1), where they of exotic parasites (J. Hammond, Bri- cy of no further introductions of were illegally stocked in the 1960s. tish Columbia Ministry of Fish and walleye into Oregon (A. Smith, Ore- Once established, annual stocking Wildlife, personal communication). gon Department of Fish and Wild- and length limits were instituted to Northern pike have not been intro- life, personal communication). Wash- reduce (Cyprinus carpio) popula- duced into Oregon, but some proba- ington is currently developing a tions and diversify angling opportu- bly occur in weedy sloughs of the walleye management policy (Doug nities (B. McDowell, Wyoming Game Columbia River as migrants from Fletcher, Washington Department of and Fish Department [WGFD], per- upstream. The state's current policy Fisheries, personal communication). sonal communication). is to eradicate pike when found Walleye were stocked into several Although native to Montana only (A. Smith, Oregon Department of southern Idaho reservoirs beginning in the River drainage, Fish and Wildlife, personal commu- in 1974 (IDFG 1982), but because of northern pike are now found state- nication). concern about anadromous salmo- wide in sloughs, backwaters, and nids, walleye introductions are pro- other clear waters with abundant Effects of Introductions hibited in the River drainage aquatic vegetation (Figure 1; Dos- Walleye (IDFG 1982). Santos 1991). Northern pike support The effects of walleye introduc- Walleye were first reported in popular sport fisheries in the lower tions and range expansion in the Wyoming in 1961 at Seminoe Reser- Flathead and Bitterroot rivers (Jones Northwest are complex and varied. voir, the uppermost reservoir on the 1990; DosSantos 1991), and unplanned Fisheries scientists have frequently North Platte River (Figure 1). During introductions and invasions of north- observed prey depletions, reduced high water in subsequent years, ern pike are a recurring problem. Of salmonid populations, and large walleye were flushed downstream 111 waters in northwest Montana shifts in fish community composition and colonized all seven North Platte that contain illegally introduced fish, (Colby and Hunter 1989). Seminoe River reservoirs throughout a range of 450 river kilometers (Figure 1; McMillan 1984). Walleye also have been stocked into other reservoirs in

the Missouri River drainage (Mar- >I

witz and Hubert 1995). n o In Montana, 40 million walleye 0 0

Downloaded by [Montana State University Bozeman] at 09:06 02 April 2012 fry are stocked annually into approx- imately 60 waterbodies. Stocking occurs primarily in large prairie reservoirs east of the Continental Divide, where natural reproduction is often limited (Colby and Hunter 1989). Walleye introductions are pro- hibited west of the Continental Divide because of the important native and nonnative salmonid pop- ulations (Colby and Hunter 1989). However, illegal introductions of walleye have resulted in self-sustain- ing populations in several reservoirs in western Montana, most recently in Noxon Rapids Reservoir on the Illegal introduction of walleye into Canyon Ferry Reservoir, Montana, has resulted in a Clark Fork of the Columbia River reproducing population, which managers expect will harm existing fisheries.

August 1996 Fisheries * 7 Figure 1 shows the range of nonnative wall- eye and northern pike, which has expanded greatly in northwestern states during the past 40 years. This map illustrates major waterbod- ies having known nonnative populations of northern pike and walleye, with the source of a population defined as an invasion (IN), legal plant (P), or illegal introduction (IL). Species locations, indicated by shading, are enlarged for emphasis. Bars indicate locations of major dams on the Columbia River, Oregon and Washington.

Reservoir, Wyoming, provides one of the more complete studies of changes in predator-prey interactions after wall- eye introduction (McMillan 1984). Seminoe was managed primarily as a put-grow-and-take rainbow (On- corhynchus mykiss) and a wild brown trout (Salmo trutta) fishery. The walleye population grew rapidly after its initial sighting in 1961, and caused sharp declines in native (Hybog- nathus spp.), darters (Etheostoma spp.), (Orconectes obscurus), and suckers (Catostomus spp.) by 1968. A popular fishery for walleye developed, with walleye averaging 45 cm long in 1973. As prey species declined in the early 1970s, predation on rainbow trout intensified. Walleye stomach samples indicated that most of the 500,000 fin- gerling trout stocked annually in the spring were eaten within a few weeks after planting (McMillan 1984). Man- agers tried dispersed stocking of fin- gerlings to increase trout survival, but the lack of alternate forage, combined with a growing walleye population, made success of this strategy short- lived. Walleye growth, condition, and

Downloaded by [Montana State University Bozeman] at 09:06 02 April 2012 abundance declined; in- creased; and recruitment failed as food supplies were overexploited. From 1973 to 1978, the percentage of walleye > 40 cm dropped from 52% to 9% of the population (McMillan 1984). The near-simultaneous collapse of walleye and trout populations led to sharp reductions in angler effort and harvest. Gizzard shad (Dorosoma cepedianum) and emerald shiner (Notropis atherinoides) were then stocked to bolster the prey base. The combination of an alternate forage base, decreased size of walleye, and especially the stocking of large trout 200 to 340 mm long that were less vulnerable to walleye predation led to

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increased survival of planted trout. A flavescens), is initially abundant. In Sal- limited, fishery (Colby and Hunter 1989). mixed walleye and trout fishery now mon Falls Creek Reservoir, Idaho, Walleye were recently stocked into exists in Seminoe Reservoir (Marwitz comprised 80% and walleye < Dailey Reservoir, Montana, to thin a and Hubert 1995), but the costs of man- 1% of the total numbers of sport fish stunted population and aging this fishery have increased be- caught in gill nets in 1975, shortly after into Cooney Reservoir, Montana, to cause of greater expense associated with walleye were introduced ( reduce abundant sucker populations. transporting and rearing larger trout 1988). But by 1987, perch and walleye Both effects have been achieved with (McMillan 1984; Wiley et al. 1993). percentages had reversed. Anglers minimal impacts to trout fisheries Managers have repeatedly observed caught state-record walleye in inter- (Venditti 1994; B. Shepard, MFWP, per- creation of a "predator trap," a large vening years, but numbers, maximum sonal communication). Managers are number of prey-limited piscivores sizes, and condition then declined. concerned that walleye will shift to (Peterman and Gatto 1978), after wall- Similar reversals in yellow perch and preying on trout if the current forage eye introduction in other systems. walleye abundances have been ob- base declines, but walleye reproduction Walleye predation led managers to served in Keyhole (Wichers 1981, 1986) is limited, and stocking could be stock larger trout or eliminate the trout and Glendo reservoirs, Wyoming reduced if trout fisheries become affect- fishery in Pathfinder (McMillan 1984), (WGFD 1990). ed in the future. Situations where wall- Keyhole (Wichers 1981), Alcova, and Glendo (WGFD 1990) reservoirs, Wyo- ming; and Falls Creek Reser- voir, Idaho (Partridge 1988). A survey of 15 major walleye-producing reser- voirs in Montana revealed that, al- though 3-4 reservoirs produce good walleye fisheries with catch rates near 0.3 fish/h, most are limited by inade- quate forage (Shepard 1991). Walleye appear prey-limited in most Wyoming reservoirs, with growth rate positively related to trout stocking density (Mar- witz and Hubert 1995). Managers did not anticipate nega- tive effects of walleye on salmonid fishes (Noble 1986); thus, walleye eye populations. fisheries since reports of walleye prey- deplete the food supply in years of low Information is scanty on walleye- ing on salmonids are not widespread forage abundance. Second, the lack of salmonid interactions in riverine sys- in the literature (Colby and Hunter cover in many reservoirs during sum- tems. Walleye are often seasonally 1989). In their native range, lakes with mer drawdown makes prey fishes abundant in tailwaters and reservoir both walleye and salmonids, such as highly vulnerable to walleye predation tributaries during spring spawning lake trout (Salvelinus namaycush), are even during years of high reproduction (McMillan 1984; Venditti 1994). The relatively rare (Johnson et al. 1977), and of prey (Swenson 1977). This effect is blue-ribbon rainbow trout and brown where they do co-occur, the species have exacerbated during successive years of trout fishery in river sections above little spatial overlap because of differ- poor reproductive success of prey and Seminoe and Pathfinder reservoirs

Downloaded by [Montana State University Bozeman] at 09:06 02 April 2012 ing habitat requirements (MacLean and low water levels (Partridge 1988; declined after walleye were intro- Magnuson 1977). However, the oppor- WDFG 1990). Third, when recruitment duced, but exact causes of the decline tunity for spatial segregation is limited of one prey species is low, alternate for- are unknown (B. Wichers, WGFD, per- in many western reservoirs due to a age is often not available because of sonal communication). Walleye are lack of strong thermal stratification and typically low prey diversity in western estimated to consume 2 million salmon small littoral area (Colby and Hunter reservoirs (Wydoski and Bennett 1981). smolts annually in the Columbia River, 1989). Fingerling trout are particularly Although many western states gen- approximately one-third of total preda- vulnerable to predation by walleye erally avoid introducing walleye into tion loss. Recreational and economic because stocking typically occurs in the salmonid waters (IDFG 1982), man- benefits of a walleye fishery must be spring, when post-spawning walleye agers have not observed prey deple- balanced with this potential harm to have high forage demands, but other tions and harm to salmonids in all declining salmon populations (Tinus suitable-sized prey are often scarce cases. Walleye have had minimal im- and Beamesderfer 1994). (Ney and Orth 1986). pact on trout fisheries in some Mon- Stable walleye fisheries generally tana reservoirs where limited - Northern Pike have been difficult to maintain in ing habitat or high flushing rates keep Few studies have documented Northwest reservoirs even when their walleye densities low, yet recruitment effects of northern pike introductions favored prey, yellow perch (Perca is sufficient to provide a stable, albeit in the region, but like walleye, pike

August 1996 Fisheries * 9 MANAGEMENT

piscivory has the potential to impose McMahon 1992) using habitat suitabili- marked declines in condition and large-scale changes in fish communities, ty models developed for walleye (Mc- abundance of brown trout in Seminoe including species elimination (He and Mahon et al. 1984) and northern pike Reservoir after the expanding walleye Kitchell 1990; Vashro 1990). Northern (Inskipp 1982) is another approach. population significantly reduced cray- pike introduced into small lakes and Determining the adequacy of the fish, brown trout's favored prey. Man- ponds in Montana typically deplete forage base is difficult yet vital to risk agers should estimate tradeoffs in their prey and stunt, hence the nick- assessment since either species could sport-fish harvest and use. Although name "hammer handles." Generally, deplete an abundant prey base. Prey walleye are popular sport fish, signifi- northern pike do not pose a serious biomass, growth and size structure, cant reductions in angler harvest and predation threat to existing fish com- seasonal availability, and prey habitat use have been reported following their munities throughout much of the re- suitability are important considerations introduction (McMillan 1984). Walleye gion because of specialized habitat (Kohler et al. 1986; Ney and Orth 1986; are harder to catch and, as top-level requirements, resulting in limited dis- McMahon 1992). Water-level fluctua- predators, are less numerous than mid- tribution (Jones 1990; DosSantos 1991). tions are believed to be key variables level predators such as rainbow trout, which are easier to catch and tend to support higher angler use (B. Wichers, WGFD, personal communication). The establishment of walleye and pike populations by invasion from other waters (Figure 1) illustrates that move- ment from introduction sites should be anticipated. Given their expanding distribution and increasing popularity with anglers, fishery managers will continue to be called on to predict and manage effects of walleye and northern pike introduc- tions. A case in point was the proposal to introduce walleye into the 14,250-ha present, pike apparently eliminated and sucker populations. Walleye prey Canyon Ferry Reservoir, near the head- most other fishes except the deep-bod- on young suckers and carp when other waters of the Missouri River, site of the ied, spiny-rayed pumpkinseed (Lepomis forage is lacking (Wichers 1981; most popular trout and yellow perch gibbosus). Northern pike have been im- McMillan 1984), and managers have lake fishery in Montana (Lere 1991). plicated in the decline of native west- observed large declines in small suck- Walleye were proposed for introduc- slope cutthroat trout (0. clarki lewisi) ers and carp after walleye introduction tion to expand angling opportunities and bull trout (Salvelinus confluentus) in (McMillan 1984; Fredenberg and Poore and reduce nongame fishes. In re- Upper and Lower Stillwater lakes, 1987). Walleye can prey on fish almost sponse, Montana Fish, Wildlife, and Montana (J. Vashro, MFWP, personal half their size (Colby et al. 1979; Parks hosted a workshop on walleye communication). McMillan 1984), and under heavy wall- and trout interactions, performed a eye predation, remaining sucker and preference survey of 1,831 anglers Evaluating Proposed carp populations shift rapidly to a size (MFWP 1992), and conducted a pre-

Downloaded by [Montana State University Bozeman] at 09:06 02 April 2012 Introductions structure comprised primarily of indi- introduction risk assessment (Mc- Relying on post-introduction case viduals too large to be eaten (McMillan Mahon 1992). Based on this informa- studies to evaluate potential introduc- 1984; Fredenberg and Poore 1987). An tion, MFWP decided in 1992 not to tions has recognized limitations but abundant supply of young-of-the-year introduce walleye into the reservoir provides the best available information (preferably soft-rayed) fishes < 12.5 cm due to high risk to the fishery, inade- (Mundie and Bell-Irving 1986; Colby et is needed to support an abundant wall- quacy of the forage base, and angler al. 1987; Bain 1993). Key to evaluating eye population (Knight and Vondracek preference. However, walleye were ille- the potential for harm is determining 1993). Examples of forage depletion gally introduced and have increased whether walleye and northern pike reinforce the need to assess the possi- rapidly, with fingerlings to large will establish a self-sustaining popula- bility of future introductions of prey, (737 mm), mature adults being collected tion. Applying a walleye habitat model which pose their own set of risks in recent years (D. Yerk and R. Spoon, by Bennett and McArthur (1990) is a (Wydoski and Bennett 1981; DeVries et MFWP, personal communication). useful first step in assessing the likeli- al. 1991), to maintain good quality hood of establishing a self-sustaining walleye and pike fisheries. Curtailing Illegal walleye population. Comparing repro- Compatibility of introductions with Introductions ductive requirements with conditions existing fisheries is another important As the above case illustrates, "buck- in the proposed introduction site (e.g., consideration. McMillan (1984) found et biologists" can easily circumvent

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careful and thorough environmental and (fines, suspension of fishing privileges, that highlights hazards of illegal intro- public pre-introduction reviews. Of the and liability for cost of restoring a fish- ductions. Portraying the costs and lost 33 major waters containing walleye and ery) for illegally transplanting fish, and recreational opportunities from illegal pike populations (Figure 1), 7 (21%) are rewards have been offered for individ- introductions could be effective (Vash- known to be the result of illegal intro- uals reporting such cases. Laws pre- ro 1990, 1995). In addition, fish and ductions. Fishery managers whom we venting transport of live fish from a game regulation booklets could be surveyed noted that illegal introduc- waterbody have passed in numerous used to educate anglers about risks of tions of walleye, northern pike, and states (e.g., , Idaho, Wyoming, illegal introductions, and angler sur- yellow perch pose one of their more Oregon, and western Montana) but veys could assess knowledge about the serious and perplexing management may face considerable public opposi- impacts of illegal introductions and problems. Although there is little data, tion (H. Johnson, MFWP, personal gauge initial responses to proposed the number of illegal introductions communication). legislation as a basis for directing may be increasing. In Montana, 50 of Public education and involvement future educational efforts. 210 documented cases of illegal fish are essential. As with wildlife poach- introductions have occurred in the last ing, managers must appeal to recre- Conclusions 5 years (Vashro 1995). The problem is ationists to help locate and discourage Purposeful introductions or un- considered more acute now that mod- potential violators. Montana has re- planned invasions of walleye and ern angling boats equipped with live- cruited angler organizations to help northern pike have been a "boost" to wells facilitate such transfers. curb illegal introductions and, with Northwest fisheries by creating popu- Although identifying the source of their financial support, has expanded lar sport fisheries and enhancing local unplanned introductions is difficult the state hotline to include economies, but they also have been a (Was an introduction a deliberate effort reports of illegal introductions. Work- "bane" due to the difficulty of sustain- to add a new species to the fishery? An shops, news releases, and public meet- ing an adequate prey base for these top innocent dumping of a bait bucket or ings also could be used to inform predators, the potential for significant livewell? A result of "contaminated" anglers of the risks of illegal introduc- reduction of existing salmonid fisheries stockings by a fishery agency? An tions. For example, the Wyoming and native species, and the coloniza- invasion from a nearby waterbody that Game and Fish Department used the tion of new waters well beyond the was legally stocked?), we believe that discovery of walleye in Lake DeSmet, a point of release. Managers should greater enforcement efforts are needed valuable wild rainbow trout fishery, to approach future introductions with to address the problem. Statutes related publicize the risks of illegal introduc- caution. We encourage independent to illegal fish introductions and fish tions (B. McDowell, WGFD, personal review of risk assessments and stock- transportation should be strengthened communication). Oregon State Univer- ing plans to help deflect the sometimes if necessary. For example, the 1991 sity recently released an educational strong public pressure fishery man- Montana legislature stiffened penalties video, "Strangers in Our Waterways," agers face for introducing these species Downloaded by [Montana State University Bozeman] at 09:06 02 April 2012

August 1996 Fisheries * 11 MANAGEMENT

into new, sometimes inappropriate Colby, P. J., P. A. Ryan, D. H. Schupp, Kohler, C. C., J. J. Ney, and W. E. Kelso. waters. More detailed monitoring stud- and S. L. Serns. 1987. Interactions in 1986. Filling the void: development of ies of predator-prey interactions after north-temperate lake fish communi- a pelagic fishery and its consequences introductions (e.g., Marwitz and Hu- ties. Can. J. Fish. Aquat. Sci. to littoral fishes in a Virginia main- bert 1995) would aid successful man- 44:104-128. stem reservoir. Pages 166-177 in G. E. agement. Greater efforts also are needed Conover, M. C. 1986. Stocking cool-water Hall and M. J. Van Den Avyle, eds. to stem the tide of illegal introduction. species to meet management needs. Reservoir for A combination of enforcement and Pages 31-39 in R. H. Stroud, ed. Fish the 80s. American Fisheries Society, culture in fisheries management. Amer- Bethesda, MD. education, as outlined, could be con- ican Fisheries Society, Bethesda, MD. Lere, M. 1991. Statewide fisheries investi- ducted with minimal added expense DeVries, D. R., R. A. Stein, and J. G. Mi- gations, survey and inventory of cold- and substantial benefit to existing fish- ner. 1991. Stocking threadfin shad: con- water lakes, Canyon Ferry, Hauser, eries and native fish communities. )4 sequences for young-of-the-year fishes. and Holter reservoirs study. Montana Trans. Am. Fish. Soc. 120:368-381. Dept. Fish, Wildl., and Parks, Job Acknowledgments DosSantos, J. M. 1991. Ecology of a river- Progr. Rep. F-46-R-1, Helena. We thank the many individuals ine pike population. Pages 155-159 in MacLean, J. H., and J. J. Magnuson. who provided vital information and J. L. Cooper, ed. Warmwater Fisheries 1977. Influences on species interac- comments: J. DosSantos, B. Hill, H. Symposium I. U.S. For. Serv. Gen. tions in percid communities. J. Fish. Johnson, S. Leathe, M. Lere, B. Shep- Tech. Rep. RM-207. Res. Board Can. 34: 1941-1951. ard, R. Spoon, G. Thomas, J. Vashro, Fredenberg, W. A., and M. D. Poore. Marwitz, T. D., and W. A. Hubert. 1995. D. Vincent, D. Workman, D. Yerk, 1987. Southcentral Montana fisheries Descriptions of walleye stocks in high- and A. Zale (Montana); E Partridge study, inventory of waters of the pro- elevation Wyoming reservoirs. Prairie and B. Rich (Idaho); A. Smith (Ore- ject area. Montana Dept. Fish, Wildl., Nat. 27:101-114. gon); S. Bonar and D. Fletcher (Wash- and Parks, Job Progr. Rep. F-20-31, McMahon, T. E. 1992. Potential impacts ington); and W. Hubert, B. McDowell, Billings. of the introduction of walleye to the and B. Wichers (Wyoming). Reviews Hallock, M., and D. Fletcher. 1991. A fishery of Canyon Ferry Reservoir and by W. Hubert, J. Vashro, A. Zale, review of walleye in the lower Colum- adjacent waters. Montana Dept. Fish, and an anonymous referee were es- bia River reservoirs. Washington Dept. Wildl., and Parks, Helena. pecially helpful in improving the Wildl. Rep. 91-9, Olympia. McMahon, T. E., J. W. Terrell, and P. C. paper. M. A. Madsen drew the dis- He, X., and J. F Kitchell. 1990. Direct and Nelson. 1984. Habitat suitability tribution map. indirect effects of predation on a fish information: walleye. U.S. Fish Wildl. community: a whole-lake experiment. Serv. FWS-OBS-82/10.56, Washing- Trans. Am. Fish. Soc. 119:825-835. ton, DC. References IDFG (Idaho Department of Fish and McMillan, J. 1984. Evaluation and en- Bain, M. 1993. Assessing impacts of Game). 1982. Evaluation of walleye hancement of the trout and walleye introduced aquatic species: grass carp for an expanded distribution in Idaho. fisheries in the North Platte River sys- in large systems. Environ. Manage. IDFG, Boise. tem of Wyoming with emphasis on 17:211-224. Inskipp, P. 1982. Habitat suitability Seminoe Reservoir. Wyoming Game Beamesderfer, R. C., and A. A. Nigro. index models: northern pike. U.S. and Fish Dept., Laramie. 1989. Status, biology, and alternatives Fish Wildl. Serv. FWS-OBS-82/10.17, MFWP (Montana Fish, Wildlife, and for management of walleye in John Washington, DC. Parks). 1992. Canyon Ferry Reservoir/ Day Reservoir: a review. Oregon Johnson, M. G., J. H. Leach, C. K. Minns, Missouri River fisheries management Dept. Fish Wildl., Info. Rep. 89-2, and C. H. Olver. 1977. Limnological plan. MFWP, Helena.

Downloaded by [Montana State University Bozeman] at 09:06 02 April 2012 Portland. characteristics of lakes in rela- Moyle, P. B., H. W. Li, and B. A. Barton. Bennett, D. H., and T. J. McArthur. 1990. tion to associations of walleye (Stizo- 1986. The Frankenstein effect: impact Predicting success of walleye stocking stedion vitreum vitreum), northern pike of introduced fishes on native fishes in programs in the United States and (Esox lucius), lake trout (Salvelinus North America. Pages 415-426 in R. H. . Fisheries 15(4):19-23. namaycush), and smallmouth Stroud, ed. Fish culture in fisheries Brown, C. J. D. 1971. Fishes of Montana. (Micropterus dolomieui). J. Fish. Res. management. American Fisheries Soci- Big Sky Books, Bozeman, MT. Board Can. 34:1592-1601. ety, Bethesda, MD. Colby, P., and C. Hunter. 1989. Environ- Jones, T. S. 1990. Floodplain distribution Mundie, J. H., and R. Bell-Irving. 1986. mental assessment of the introduction of fishes of the Bitterroot River, with Predictability of the consequences of of walleye beyond their current range emphasis on introduced populations the Kemano hydroelectric proposal for in Montana. Montana Department of of northern pike. Master's thesis. Uni- natural salmon populations. Can. Fish, Wildlife, and Parks, Helena. versity of Montana, Missoula. Water Resour. J. 11:14-25. Colby, P. J., R. E. McNicol, and R. A. Knight, R. L., and B. Vondracek. 1993. Ney, J. J., and D. J. Orth. 1986. Coping Ryder. 1979. Synopsis of biological Changes in prey fish populations in with future shock: matching predator data on the walleye (Stizostedion v. vit- western , 1969-88, as related stocking programs to prey abundance. reum) (Mitchill 1818). Food and Agri- to walleye, Stizostedion vitreum, Pages 81-92 in R. H. Stroud, ed. Fish culture Organization (FAO) Fish. predation. Can. J. Fish. Aquat. Sci. culture in fisheries management. Amer- Synop. 119, Rome, . 50:1289-1298. ican Fisheries Society, Bethesda, MD. 12 * Fisheries Vol. 21, No. 8 MANAGEMENT

Noble, R. L. 1986. Predator-prey interac- Shepard, B. 1991. Walleye management habitat utilization of rainbow trout tions in reservoir communities. Pages in Montana. In Walleye/trout work- and juvenile walleye in Cooney Reser- 137-143 in G. E. Hall and M. J. Van shop. Montana Dept. Fish, Wildl., and voir, Montana. Master's thesis. Mon- Den Avyle, eds. Reservoir fisheries Parks video proceedings, Helena. tana State University, Bozeman. management for the 80s. American Spencer, C. N., B. R. McClelland, and Wichers, W. F 1981. Fishery manage- Fisheries Society, Bethesda, MD. J. A. Stanford. 1991. stocking, ment investigations (fisheries prob- Partridge, F. E. 1988. Lake and reservoir salmon collapse, and eagle displace- lems in Keyhole Reservoir). Wyoming investigations, alternative fish species ment. BioScience 41:14-21. Game and Fish Dept., Job Progr. Rep. and strains for fishery development. Swenson, W. A. 1977. Food consumption of F-44-R-04, Cheyenne. Idaho Fish. Res. Rep. F-73-R-10, Boise. walleye (Stizostedion vitreum vitreum) and . 1986. Keyhole Reservoir fisher- Peterman, R. M., and M. Gatto. 1978. (S. canadense) in relation to food man use and harvest, 1985. Estimation of functional responses of availability and physical conditions in Wyoming Game and Fish Dept., Fish. predators on juvenile salmon. J. Fish. , , Shaga- Div. Rep. 3085-02-8501, Cheyenne. Res. Board Can. 35:797-808. wa Lake, and western . Wiley, R. W., R. A. Whaley, J. B. Satake, Rich, B. A. 1993. Population dynamics, J. Fish. Res. Board Can. 34:1643-1654. and M. Fowden. 1993. Assessment of food habits, movement and habitat Tinus, E. S., and R. C. Beamesderfer. stocking hatchery trout: a Wyoming use of northern pike in the Coeur 1994. An update on the distribution, perspective. N. Am. J. Fish. Manage. d'Alene River system. Master's thesis. fisheries, and biology of walleye in the 13:160-170. University of Idaho, Moscow. lower Columbia River. Oregon Dept. Wydoski, R. S., and D. H. Bennett. 1981. Rieman, B. E., R. C. Beamesderfer, S. Fish Wildl., Info. Rep. 94-3, Portland. Forage species in lakes and reservoirs Vigg, and T. P. Poe. 1991. Estimated Vashro, J. 1990. Illegal aliens. Montana of the western United States. Trans. loss of juvenile salmonids to predation Outdoors 21(4):35-37. Am. Fish. Soc. 110:764-771. by northern squawfish, walleyes, and --. 1995. The "bucket brigade" is WGFD (Wyoming Game and Fish De- in John Day Reser- ruining our fisheries. Montana Out- partment). 1990. Annual fisheries pro- voir, Columbia River. Trans. Am. Fish. doors 26(5):34-37. gress report on the 1989 work sched- Soc. 120:448-458. Venditti, D. A. 1994. Diet overlap and ule. WGFD, Cheyenne. Downloaded by [Montana State University Bozeman] at 09:06 02 April 2012

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