The Yellowstone Lake Crisis: Confronting a Lake Trout Invasion
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The Yellowstone Lake Crisis: Confronting a Lake Trout Invasion A Report to the Director of the National Park Service Publicationofthisreportwasfundedin partbygenerousgrantsfromtheTrout andSalmonFoundation,theMontana TroutFoundation,alongwithadditional individualdonationstotheYellowstone FisheryFund. The Yellowstone Lake Crisis: Confronting a Lake Trout Invasion A Report to the Director of the National Park Service Edited by John D. Varley and Paul Schullery Yellowstone Center for Resources National Park Service, Yellowstone National Park, Wyoming 1995 ACKNOWLEDGMENTS Manypeopleassistedinthepreparationofthis 4,appearsthroughspecialarrangementwiththe report.WeareespeciallygratefultoJack authors,asitisalsobeingpublishedinthe McIntyreforhisassistanceandguidancewith AmericanFisheriesSocietyjournalFisheries. manyaspectsofthematerialpublishedhere,as wellasforhismasterfuldirectionofthelake ReneeEvanoff,NPS,designedthecover,Sarah troutworkshop,whoseresultsaresummarized Broadbent,NPS,designedtherestofthereport. beginningonpage28.YellowstoneParkSu- Additionaleditorialandothersupportwaspro- perintendentMichaelFinley'srecognitionofthe videdbyCarrieGrayandLaurylMack. magnitudeofthiscrisisandhissupportofthe productionofareportofthisscopewerelike- Moregenerally,wethankthemanyotherpeople wiseessential. whohavegiventheirtimegenerouslytohelp withthiscrisis:anglers,rangers,fishingguides, Theworkshop'sarrangementsandlogisticswere ecologists,fisheriesmanagers,andmanymem- managedbyLaurylMack,NPS.Additional bersofthepublicwhohaveshownaspecial workshopsupportwasprovidedbytheU.S.Fish concernoverthissituationandhavegoneoutof andWildlifeServiceFisheryAssistanceOffice theirwaytovolunteerinformationandsupport. inYellowstone,undertheLeadershipofLynn Kaeding,theNPSYellowstoneCenterforRe- Publicationofthisreportwasmadepossibleby sourcesstaff,especiallySueConsoloMurphy agrantfromtheMontanaTroutFoundation. andStuColeman,andNPSResourceManage- Additionalfundswereprovidedbymanyindi- mentOperationsCoordinatorTomOlliffandRe- vidualdonationstotheYellowstoneFishery sourceManagementCoordinatorDanReinhart. FundoftheYellowstoneAssociation. ThereportbyKaedingetal.,beginningonpage Cover design by Renee Evanoff. Trout paintings by Michael Simon TABLEOFCONTENTS TheLakeYellowstoneTroutCrisisExecutiveSummary ................................................................... 2 LakeTroutDiscoveredinYellowstoneLake ................................................................................. 4 byLynnR.Kaeding,GlennD.Boltz,andDanielG.Carty Editors'sNote:UpdateonlaketroutsituationthroughJune,1996 ..................................................... 11 CutthroatTroutandtheYellowstoneLakeEcosystem .................................................................... 12 byPaulSchulleryandJohnD.Varley SocioeconomicValuesAssociatedwiththeYellowstoneLakeCutthroatTrout ....................................... 22 byJohnD.VarleyandPaulSchullery ReviewandAssessmentofPossibilitiesforProtectingtheCutthroatTrout ........................................... 28 ofYellowstoneLakeFromIntroducedLakeTrout Proceedingsofaworkshopandinformationexchangeheldin Gardiner,Montana,February15-17,1995 byJohnD.McIntyre,WorkshopLeader ADraftPlanofActionforControllingExpansionoftheLakeTroutPopulationinYellowstoneLake .......... 34 byTomOlliff AuthorsandWorkshopParticipants .......................................................................................... 36 THE LAKE YELLOWSTONE TROUT CRISIS EXECUTIVE SUMMARY Yellowstone Lake is home of the premier surviving inland cutthroat trout fishery in North America. This fishery is threatened with destruction by illegally introduced lake trout, which were discovered in 1994. The lake trout are known to exist in at least four and possibly as many as six age groups, proof of a relatively small but reproducing population (Fig. 1). The older age groups are now able to reproduce, and the lake trout population will almost certainly grow rapidly. Fig. 1. Three age classes of lake trout captured at various The discovery of these non-native lake trout in times in Yellowstone Lake in 1994, indicating ongoing Yellowstone Lake caused great alarm among reproduction in the introduced lake trout population. U.S. fisheries biologists throughout the greater Fish and Wildlife Service photo. Yellowstone area because of the lake trout’s reputation for displacing species such as implications for the continued viability of the cutthroat trout in other western lakes. Park Yellowstone cutthroat trout as a subspecies. administrators sought to verify the “doomsday” opinion of local biologists by arranging an The predicted decline of Yellowstone cutthroat assessment of the situation by United States and trout will destroy the world-famous fisheries in Canadian specialists in population dynamics the lake and its tributaries, including the storied and lake trout biology. The experts convened an fishery in the Yellowstone River between the information-sharing workshop in February lake and the Upper Falls; this latter fishery 1995, and concluded that the lake trout gained international prominence in the 1970s as population in Yellowstone Lake is likely to the site of pioneering advances in catch-and- expand and cause precipitous decline in the release fishing, and remains one of the world's cutthroat trout population. The majority view premier destinations for trout fishermen. For was that the cutthroat trout are likely to decline nearly 150 years, the lake itself has developed to 10-20% of present abundance. These its own superlative reputation as a “trout percentages translate to a decline from an catchery.” Though a lake trout fishery will estimated 2.5 million trout of catchable size at evolve in the lake consonant with the cutthroat present to 250,000-500,000 at some time in the decline, it will be a highly specialized fishery of foreseeable future. interest only to a comparatively few anglers and will not occur at all on the rivers and streams. Except for its strongholds in the upper The replacement fishery will in no respect Yellowstone River area, the Yellowstone (ecologically, economically, or socially) re- cutthroat trout is imperiled. Human activities place the fisheries it destroys. have already reduced its range to 15% of its historic distribution. The appearance of lake The cutthroat trout decline will also cause trout in Yellowstone Lake has ominous severe disruption in the food supply for two The Yellowstone Lake Crisis 3 species listed under the Endangered Species resources and personnel needed to implement Act—the threatened grizzly bear and the and maintain these emergency measures. There endangered bald eagle—and will likewise was a consensus view among the workshop affect many species of special concern, biologists that only an aggressive lake trout including the white pelican, otter, black bear, control program would protect the cutthroat mink, osprey, and loon; an estimated 42 species population and thus the ecological character of of mammals and birds in all. Grizzly bear, white the entire Yellowstone Lake basin. pelican, and osprey abundance at Yellowstone Lake, and perhaps other species as well, are all While the potential ecological losses are correlated with the abundance of Yellowstone staggering, the potential economic losses can be Lake cutthroat trout. Because of pronounced summarized as equally immense. The 1994 differences in the habits and habitat uses of lake value of the Yellowstone fisheries above the trout and cutthroat trout, the lake trout will not great falls, including the lake and its tributaries, serve as a replacement food source for these is estimated at slightly more than $36 million. affected species of mammals and birds. The cumulative 30-year value of the cutthroat trout sport fishery, assuming lake trout were In reviewing current fishery technologies, absent, is estimated at more than a billion workshop participants concluded that there is dollars ($1,080,000,000). Assuming lake trout little prospect that the lake trout can be are vigorously controlled, the consonant value eradicated from Yellowstone Lake. However, declines to $685 million. If lake trout are not scientists from the Great Lakes region offered controlled, the value declines to $439,950,000. some hope that expansion of the lake trout The last value represents a three-decade population might be contained through an economic loss of $640 million, which can be aggressive gill-netting program such as those considered the net economic effect of the illegal used by commercial fishing operations in the lake trout introduction if no actions are taken to Great Lakes. Following that lead, personnel control the species. from the National Park Service and the U.S. Fish and Wildlife Service’s Fishery Assistance With lake trout control, at an estimated program Office at the park developed an action plan to cost of $9 million over 30 years, the effects of initiate a control program. The program’s lake trout on the cutthroat trout population have effectiveness depends on an understanding of a high probability of being ameliorated. The where the lake trout populations are located in benefit-to-cost ratio for the lake trout control each season so that they can be netted without program is a favorable 27:1. harming the cutthroat trout population. If the effects of lake trout on cutthroat trout are Initial efforts will proceed based on knowledge greater than projected by the experts, and the that in the summer the lake trout generally Yellowstone cutthroat trout becomes rare or inhabit deeper