the yellowstone lake crisis: confronting a lake trout invasion › yell › planyourvisit › upload...

The Yellowstone Lake Crisis:Confronting a Lake Trout Invasion

A Report to the Director of the National Park Service

Publication of this report was funded inpart by generous grants from the Troutand Salmon Foundation, the Montana

Trout Foundation, along with additionalindividual donations to the Yellowstone

Fishery Fund.

The Yellowstone Lake Crisis:Confronting a Lake Trout Invasion

A Report to the Director of theNational Park Service

Edited by John D. Varley and Paul Schullery

Yellowstone Center for ResourcesNational Park Service, Yellowstone National Park, Wyoming

1995

ACKNOWLEDGMENTS

Many people assisted in the preparation of thisreport. We are especially grateful to JackMcIntyre for his assistance and guidance withmany aspects of the material published here, aswell as for his masterful direction of the laketrout workshop, whose results are summarizedbeginning on page 28. Yellowstone Park Su-perintendent Michael Finley's recognition of themagnitude of this crisis and his support of theproduction of a report of this scope were like-wise essential.

The workshop's arrangements and logistics weremanaged by Lauryl Mack, NPS. Additionalworkshop support was provided by the U.S. Fishand Wildlife Service Fishery Assistance Officein Yellowstone, under the Leadership of LynnKaeding, the NPS Yellowstone Center for Re-sources staff, especially Sue Consolo Murphyand Stu Coleman, and NPS Resource Manage-ment Operations Coordinator Tom Olliff and Re-source Management Coordinator Dan Reinhart.

The report by Kaeding et al., beginning on page

4, appears through special arrangement with theauthors, as it is also being published in theAmerican Fisheries Society journal Fisheries.

Renee Evanoff, NPS, designed the cover, SarahBroadbent, NPS, designed the rest of the report.Additional editorial and other support was pro-vided by Carrie Gray and Lauryl Mack.

More generally, we thank the many other peoplewho have given their time generously to helpwith this crisis: anglers, rangers, fishing guides,ecologists, fisheries managers, and many mem-bers of the public who have shown a specialconcern over this situation and have gone out oftheir way to volunteer information and support.

Publication of this report was made possible bya grant from the Montana Trout Foundation.Additional funds were provided by many indi-vidual donations to the Yellowstone FisheryFund of the Yellowstone Association.

Cover design by Renee Evanoff.Trout paintings by Michael Simon

TABLE OF CONTENTS

The Lake Yellowstone Trout Crisis Executive Summary ................................................................... 2

Lake Trout Discovered in Yellowstone Lake ................................................................................. 4by Lynn R. Kaeding, Glenn D. Boltz, and Daniel G. Carty

Editors's Note: Update on lake trout situation through June, 1996 ..................................................... 11

Cutthroat Trout and the Yellowstone Lake Ecosystem .................................................................... 12by Paul Schullery and John D. Varley

Socioeconomic Values Associated with the Yellowstone Lake Cutthroat Trout ....................................... 22by John D. Varley and Paul Schullery

Review and Assessment of Possibilities for Protecting the Cutthroat Trout ........................................... 28of Yellowstone Lake From Introduced Lake TroutProceedings of a workshop and information exchange held inGardiner, Montana, February 15-17, 1995by John D. McIntyre, Workshop Leader

A Draft Plan of Action for Controlling Expansion of the Lake Trout Population in Yellowstone Lake .......... 34by Tom Olliff

Authors and Workshop Participants .......................................................................................... 36

Yellowstone Lake is home of the premiersurviving inland cutthroat trout fishery in NorthAmerica. This fishery is threatened withdestruction by illegally introduced lake trout,which were discovered in 1994. The lake troutare known to exist in at least four and possibly asmany as six age groups, proof of a relativelysmall but reproducing population (Fig. 1). Theolder age groups are now able to reproduce, andthe lake trout population will almost certainlygrow rapidly.

The discovery of these non-native lake trout inYellowstone Lake caused great alarm amongfisheries biologists throughout the greaterYellowstone area because of the lake trout’sreputation for displacing species such ascutthroat trout in other western lakes. Parkadministrators sought to verify the “doomsday”opinion of local biologists by arranging anassessment of the situation by United States andCanadian specialists in population dynamicsand lake trout biology. The experts convened aninformation-sharing workshop in February1995, and concluded that the lake troutpopulation in Yellowstone Lake is likely toexpand and cause precipitous decline in thecutthroat trout population. The majority viewwas that the cutthroat trout are likely to declineto 10-20% of present abundance. Thesepercentages translate to a decline from anestimated 2.5 million trout of catchable size atpresent to 250,000-500,000 at some time in theforeseeable future.

Except for its strongholds in the upperYellowstone River area, the Yellowstonecutthroat trout is imperiled. Human activitieshave already reduced its range to 15% of itshistoric distribution. The appearance of laketrout in Yellowstone Lake has ominous

THE LAKE YELLOWSTONE TROUT CRISIS

EXECUTIVE SUMMARY

Fig. 1. Three age classes of lake trout captured at varioustimes in Yellowstone Lake in 1994, indicating ongoingreproduction in the introduced lake trout population. U.S.Fish and Wildlife Service photo.

implications for the continued viability of theYellowstone cutthroat trout as a subspecies.

The predicted decline of Yellowstone cutthroattrout will destroy the world-famous fisheries inthe lake and its tributaries, including the storiedfishery in the Yellowstone River between thelake and the Upper Falls; this latter fisherygained international prominence in the 1970s asthe site of pioneering advances in catch-and-release fishing, and remains one of the world'spremier destinations for trout fishermen. Fornearly 150 years, the lake itself has developedits own superlative reputation as a “troutcatchery.” Though a lake trout fishery willevolve in the lake consonant with the cutthroatdecline, it will be a highly specialized fishery ofinterest only to a comparatively few anglers andwill not occur at all on the rivers and streams.The replacement fishery will in no respect(ecologically, economically, or socially) re-place the fisheries it destroys.

The cutthroat trout decline will also causesevere disruption in the food supply for two

species listed under the Endangered SpeciesAct—the threatened grizzly bear and theendangered bald eagle—and will likewiseaffect many species of special concern,including the white pelican, otter, black bear,mink, osprey, and loon; an estimated 42 speciesof mammals and birds in all. Grizzly bear, whitepelican, and osprey abundance at YellowstoneLake, and perhaps other species as well, are allcorrelated with the abundance of YellowstoneLake cutthroat trout. Because of pronounceddifferences in the habits and habitat uses of laketrout and cutthroat trout, the lake trout will notserve as a replacement food source for theseaffected species of mammals and birds.

In reviewing current fishery technologies,workshop participants concluded that there islittle prospect that the lake trout can beeradicated from Yellowstone Lake. However,scientists from the Great Lakes region offeredsome hope that expansion of the lake troutpopulation might be contained through anaggressive gill-netting program such as thoseused by commercial fishing operations in theGreat Lakes. Following that lead, personnelfrom the National Park Service and the U.S.Fish and Wildlife Service’s Fishery AssistanceOffice at the park developed an action plan toinitiate a control program. The program’seffectiveness depends on an understanding ofwhere the lake trout populations are located ineach season so that they can be netted withoutharming the cutthroat trout population.

Initial efforts will proceed based on knowledgethat in the summer the lake trout generallyinhabit deeper waters than do cutthroat trout.As understanding of the location and move-ments of both species is refined, programeffectiveness will be increased. An importantfirst step is to import Great Lakes technology aswell as to obtain the additional financial

resources and personnel needed to implementand maintain these emergency measures. Therewas a consensus view among the workshopbiologists that only an aggressive lake troutcontrol program would protect the cutthroatpopulation and thus the ecological character ofthe entire Yellowstone Lake basin.

While the potential ecological losses arestaggering, the potential economic losses can besummarized as equally immense. The 1994value of the Yellowstone fisheries above thegreat falls, including the lake and its tributaries,is estimated at slightly more than $36 million.The cumulative 30-year value of the cutthroattrout sport fishery, assuming lake trout wereabsent, is estimated at more than a billiondollars ($1,080,000,000). Assuming lake troutare vigorously controlled, the consonant valuedeclines to $685 million. If lake trout are notcontrolled, the value declines to $439,950,000.The last value represents a three-decadeeconomic loss of $640 million, which can beconsidered the net economic effect of the illegallake trout introduction if no actions are taken tocontrol the species.

With lake trout control, at an estimated programcost of $9 million over 30 years, the effects oflake trout on the cutthroat trout population havea high probability of being ameliorated. Thebenefit-to-cost ratio for the lake trout controlprogram is a favorable 27:1.

If the effects of lake trout on cutthroat trout aregreater than projected by the experts, and theYellowstone cutthroat trout becomes rare ornearly extinct, the cost of the destruction of allfish life in the lake and its tributaries (the start-from-scratch alternative for restoring the nativefishery), and the subsequent reestablishment ofthe cutthroat trout population to its formercondition is estimated to be $32-181 million.

The Yellowstone Lake Crisis 3

Abstract: On July 30, 1994, lake trout(Salvelinus namaycush) were discovered inYellowstone Lake, Yellowstone NationalPark, Wyoming, the core of the remainingundisturbed, natural habitat for the nativeYellowstone cutthroat trout (Oncorhynchusclarki bouvieri). Data from this and other laketrout caught subsequently by anglers and theU.S. Fish and Wildlife Service suggest laketrout have reproduced in Yellowstone Lakesince at least 1989 and now number in thethousands, perhaps tens of thousands. A highlypiscivorous, nonnative species, lake trout willprobably thrive in Yellowstone Lake andreduce the lake’s cutthroat trout stockssubstantially unless preventive managementactions are taken.

Yellowstone Lake, Yellowstone NationalPark, Wyoming, is the core of the remainingundisturbed, natural habitat for the nativeYellowstone cutthroat trout (Oncorhynchusclarki bouvieri) (Varley and Gresswell 1988).During the past two decades in particular,fishery managers have used angling regulationsto greatly reduce angler harvest, considered aprincipal human threat to the cutthroat troutstocks of Yellowstone Lake (Gresswell andVarley 1988). As a result, the stocks haverecovered markedly from past overharvest and,to many managers, appeared safe from adversehuman activities (Jones et al. 1993).

The perception of Yellowstone Lake as asecure refuge for Yellowstone cutthroat troutchanged abruptly on July 30, 1994, when a laketrout (Salvelinus namaycush) was caught fromthe lake by an angler on a guided fishing trip.The fishing guide, aware that lake trout were

not known to occur in Yellowstone Lake,immediately contacted National Park Servicerangers. The angler and guide wereinterviewed, and the fish, 43 cm long, wasgiven to park authorities. On August 5, asecond lake trout (42 cm long) was caughtunder similar circumstances and given to parkauthorities.

A National Park Service press release datedAugust 11, 1994, described the discovery oflake trout in Yellowstone Lake; outlinedecological consequences that could result fromestablishment of this highly piscivorous,nonnative fish species; and offered a reward forinformation leading to the arrest and convictionof the person or persons responsible forillegally stocking the fish. Human culpabilitywas assumed because natural movement of laketrout into Yellowstone Lake from other parkwaters in which they are found was notpossible.

Extensive media coverage of the issue resultedin additional reports to the U.S. Fish andWildlife Service (FWS) (technical advisors tothe National Park Service) of lake troutcaptures from Yellowstone Lake. Twoexperienced anglers reported the capture onAugust 15, 1994, of three “roughly [46 cm] 18-inch” lake trout from Yellowstone Lake.Because the anglers believed the odor of fishmight attract bears to their backcountrycampsite, the putative lake trout were killedand returned to the lake. On August 20, a parkvisitor gave park authorities a photograph ofherself holding a lake trout 43 cm long that shehad caught from the lake July 21, 1994, andsubsequently consumed. A fishing guide

LAKE TROUT DISCOVERED

IN YELLOWSTONE LAKE

BY LYNN R. KAEDING, GLENN D. BOLTZ, AND DANIEL G. CARTY

reported that a lake trout < 33 cm long wascaught and kept by one of his clients in 1993.Two park employees, both experiencedanglers, reported that they caught and returnedto the lake a lake trout in the mid-1980s.

Although the evidence in late August 1994indicated that lake trout were present inYellowstone Lake, the origin of the lake troutpopulation was not clear. Some peoplespeculated that the lake trout caught by anglersin 1994 were part of a small group of fishillegally stocked into the lake as fingerlingsonly a few years earlier. Remarkably, ascenario similar to this was described in afictional magazine article (Parks 1991) that hadbeen brought to the attention of parkauthorities. Alternatively, it was possible thatthe lake trout caught by anglers had beenproduced in the lake from a founding parentstock that had been present there for manyyears.

In late August 1994 the FWS developed a planof action that had as its goal the elimination oflake trout from Yellowstone Lake. This goal isconsistent with National Park Service policy(NPS 1988) that directs the removal ofnonnative organisms from the park whenfeasible, especially when they present threats tonative organisms. Objectives of the plan wereto (1) characterize the lake trout population, (2)locate potential lake trout spawning areas, (3)determine the origin of the lake trout, and (4)identify remedial actions. This reportdescribes and interprets the data collectedunder Objectives 1 and 2.

YELLOWSTONE LAKE

AND CUTTHROAT TROUT

Yellowstone Lake lies 2,356 m above mean sealevel in east-central Yellowstone NationalPark. The lake has a surface area of 341␣km˝,shoreline length of 239 km, mean depth of48.5 m, and maximum depth of 107 m. A

thermocline forms in July and may persist inmid-September at a depth of 10-20 m. Thehypolimnion remains well-oxygenated duringstratification. Phytoplankton standing cropsare low and generally dominated by diatoms.Summer surface temperatures rarely exceed18°C, and ice covers the lake from mid-December through May or early June (Benson1961, Knight 1975, Kaplinski 1991).

Yellowstone cutthroat trout and longnose dace(Rhinichthys cataractae) are the native fishes ofYellowstone Lake, whereas longnose sucker(Catostomus catostomus), redside shiner(Richardsonius balteatus), and lake chub(Couesius plumbeus) are established, nonna-tive species. The minnow species inhabit onlywarm, vegetated bays and other littoral areas;cutthroat trout and longnose sucker are foundthroughout the lake (Benson 1961).

Yellowstone cutthroat trout are obligate streamspawners (Varley and Gresswell 1988).Approximately half of the lake’s 126 tributariesare known to be used for spawning by cutthroattrout from Yellowstone Lake. Cutthroat troutin Yellowstone Lake provide the most popularsportfishery in Yellowstone National Park(Jones et al. 1993), as well as food for grizzlybears, osprey, white pelicans, river otters, andother animals (Davenport 1974, Swenson1978, Reinhart and Mattson 1990).

PROCEDURES

Characterizing the Lake Trout PopulationGill nets, set perpendicular to the lake shore inrelatively shallow water in mid-September,have been used for more than two decades tomonitor trends in cutthroat trout and longnosesucker populations in Yellowstone Lake (Joneset al. 1993). That traditional monitoringprogram continued in 1994, and its techniqueswere also generally used in the search for laketrout in deeper water during the remainder ofthe field season.


6 Lake Trout Discovered

Gill nets used routinely are 38 m long, 1.8 mdeep, and have five 7.6-m panels of 19, 25, 32,38, and 51 mm mesh (bar measure)monofilament netting. For subsequentdeepwater gill netting, these nets and otherssimilar in construction but twice as long (i.e.,two “monitoring” nets attached end-to-end)were used. Gill nets were set during the dayand retrieved the next morning. Captured fishwere measured to total length and weighed.Captured lake trout (and those provided byanglers) were frozen and retained for age-growth, sexual maturation, and other analyses.

Angling was also used in attempts to capturelake trout. Downriggers were used to troll avariety of lures at depths shown by sonar to beoccupied by fish. Shallow trolling oftenaccompanied deep trolling with downriggers.Most of the angling effort was expended in lakeregions from which recreational anglers hadcaptured lake trout.

Locating Potential LakeTrout Spawning AreasVisual observation of substrates was used tolocate potential lake trout spawning areas.Observers in a boat moving slowly along thelake shoreline, in water 2-7 m deep, recordedsubstrate characteristics on topographic maps.

RESULTS

GillnettingAltogether, 1,368 Yellowstone cutthroat trout,630 longnose suckers, and 2 lake trout werecaught in gill nets set in many regions ofYellowstone Lake (Fig. 1). Catch rates forcutthroat trout and longnose suckers werehighest in shallow water and declined withincreasing depth (Table 1). Few longnosesuckers were found in water deeper than 30.5m. Lake trout were caught in nets that had theirshallow end in water about 36.6 m deep.

Range in lengths of individual cutthroat trout

Fig. 1. Locations of traditional gillnet sets (dots) anddeepwater gillnet sets (ovals), and capture locations forlake trout caught by anglers (A) and in gill nets (B),Yellowstone Lake, 1994. Stippled areas are islands.

varied little with depth, although few age-1+cutthroat trout (15-20 cm long) were caught inwaters 15.2-30.5 m deep (Fig. 2). Ranges inlengths were similar for longnose suckerscaught in waters 0-15.2 m and 15.3-30.5 mdeep (Fig. 3). The lake trout caught in gill netswere 20 and 32 cm long.

AnglingTwenty Yellowstone cutthroat trout (32 -53 cmlong) were caught by angling. Of these, sevenwere caught by downriggers at depths of 12.2-38.1 m; the remainder were caught at depths<6.1 m. No lake trout were caught. As manyas four lures were fished simultaneously duringthe 59 hours spent fishing between September7 and October 5, 1994.

Analyses of Individual Lake TroutAnalyses of scales revealed that the two laketrout (43 and 42 cm long) caught by the guidedanglers were five years old, whereas the two


Fig. 2. Length-frequency distributions for Yellowstonecutthroat trout caught in gill nets set in three ranges ofwater depth. Water depth is based on the depth of theshallow end of the gill net.

lake trout (32 and 20 cm long) caught in gillnets were four and two years old. The fishtherefore were of the 1989, 1990, and 1992year-classes, respectively (C. R. Bronte,National Biological Service, Ashland, Wis.,pers. commun.).

Analyses of gonadal tissue from the two largelake trout revealed that both fish were male.However, opinions on stage of reproductivematurity differed between the two analysts whoexamined the histological preparations. BethMacConnell (FWS, Bozeman, Mont., pers.commun.) indicated the fish were immature,whereas C. M. Kaya (Department of Biology,Montana State University, Bozeman, pers.commun.) saw evidence of early-stagespermatogenesis in both specimens. (Thetissue preparations had been considerablydistorted by freezing and thawing that occurredbefore tissue fixation.) Kaya also pointed outthat brook trout (Salvelinus fontinalis) at asimilar stage of gonadal development in Junecan spawn in October (Henderson 1962).

Potential Spawning HabitatVisual observation revealed that cobble,rubble, or boulder substrates occur in manyareas along the Yellowstone Lake shoreline(Fig. 4).

Table 1. Catch statistics for Yellowstone cutthroat trout, longnose suckers, and lake trout caught in 38- or 76-m-longgill nets in each of four ranges of water depth, Yellowstone Lake, fall 1994.

No. of sets Cutthroat trout Longnose suckers Lake trout

Deptha (m) 38 m 76 m N Catch rateb N Catch rateb N Catch rateb

0–15.2 61 4c 994 12.2 577 7.1 0 0

15.3–30.5 11 0 76 5.6 47 3.4 0 0

30.6–45.7 28 22 295 3.2 6 0.1 2 <0.1

45.8–61.0 1 3 3 0.3 0 0 0 0

a Water depth at the shallow end of the gill net.b Fish cautht per 30.5 linear m of net.c Gill nets entirely of 76 mm mesh netting.

DISCUSSION

All of the lake trout reported caught by anglersin 1994 were approximately 43 cm long andmight have been of one year-class produced in


1989. If so, these fish recruited into thesportfishery at age 5, the minimum age ofmaturity in wild lake trout (Healey 1978).Whether the 1989 year-class embodies the firstnatural reproduction of lake trout inYellowstone Lake is unknown. The presenceof these fish and additional, younger lake troutsuggests that lake trout have reproducedannually in Yellowstone Lake since at least1989.

On the basis of a mark-recapture (in gill nets)experiment that included more than 49,000marked, adult cutthroat trout, and extrapola-tion of areal densities of fish caught in purseseines set at many locations around the lake,Jones et al. (1980) concluded conservativelythat there were 1-4 million catchable cutthroattrout (>35 cm long) in Yellowstone Lake in

Fig. 3. Length-frequency distributions for longnosesuckers caught in gill nets set in three ranges of waterdepth. Water depth is based on the depth of the shallowend of the gill net.

Fig. 4. Shoreline areas (irregular ovals) where cobble,rubble, or boulder substrates occur in Yellowstone Lake.Stippled areas are islands.

1979. The total population of cutthroat troutwould be much larger, perhaps by a factor ofthree or more. If cutthroat trout are equallyabundant today, and they and lake trout aresimilar in their vulnerability to capture in gillnets, the approximate 1000:1 ratio of these fishin our gillnet catch suggests that lake troutnumber in the thousands, perhaps tens ofthousands, in Yellowstone Lake.

Such numbers of lake trout are too large to beexplained hypothetically by an introduction offingerling lake trout a few years ago. Instead,large numbers and multiple year-classes of laketrout indicate reproduction in YellowstoneLake. When the founding stock of parent laketrout began to reproduce is unknown, as is thereproductive history of their progeny. Laketrout in Yellowstone Lake were unknown topark authorities prior to 1994 because thepopulation of catchable-size lake trout wasmuch smaller, the few anglers who caught laketrout did not bring the fish or other substantialevidence to park authorities, and traditionalmonitoring programs were designed to sample


cutthroat trout in shallow water in early fall(when lake trout are likely to be in deep waterbecause the lake has not yet undergonetemperature destratification).

Lake trout are capable of rapid populationincrease (Curtis 1990) and are likely to thrive inYellowstone Lake unless preventive manage-ment actions are taken. Lake temperatures andwater quality are ideal for lake trout, andsubstrates ostensibly suitable to lake troutspawning (areas of cobble and rubble with littleor no fine sediments [Thibodeau and Kelso1990, Edsall et al. 1992]) occur at manylocations. Reproduction by the 1989 year-classof lake trout in Yellowstone Lake could rapidlyincrease the population.

The extent that the cutthroat trout population ofYellowstone Lake might be reduced by laketrout competition or predation is unknown butpotentially substantial. Macroinvertebratefoods of cutthroat trout and longnose sucker(Benson 1961, Benson and Bulkley 1963) alsoare eaten by young lake trout (Elrod 1983,Elrod and O’Gorman 1991), and cutthroat troutand longnose suckers themselves would befood for juvenile and adult lake trout.Individual lake trout in Yellowstone Lake growslowly, similar to lake trout in nearby (10highway km) Lewis Lake, where the specieswas introduced officially in 1890, and anabundant population has developed (Jones et al.1983). This suggests that competition for foodalready occurs among lake trout and other fishspecies in Yellowstone Lake.

Predation on cutthroat trout by lake trout mightbecome especially significant in YellowstoneLake because, as our data suggest, manycutthroat trout, including young fish, occupydeep water, the habitat of lake trout. Incontrast, the other potential prey species,longnose sucker, occurs primarily in shallowwater.

Introduced lake trout have been implicated inthe extinction of Lahontan cutthroat trout (O. c.henshawi) in Lake Tahoe (Cordone and Frantz1966). Benson et al. (1961) stated thatintroduced lake trout eliminated nativecutthroat trout in several large, deep lakes inthe Rocky Mountain region but provided nosupportive data. In Heart Lake, YellowstoneNational Park, the native Yellowstonecutthroat trout may have declined markedlyafter lake trout of unknown origin becameestablished (Dean and Varley 1974). InJackson Lake, Wyoming, substantial decline inthe native Yellowstone cutthroat troutaccompanied colonization of the lake by laketrout (Behnke 1992). Lake trout also have beenshown to eliminate native bull trout (S.confluentus) in lakes (Donald and Alger 1993).

In Yellowstone Lake, the lake trout is apotential keystone predator (sensu Paine 1966),an organism that greatly influences ecosystemprocesses as a result of its feeding activity.Among the ecosystem processes likely to beaffected by lake trout is energy flow from theaquatic to the terrestrial ecosystem. Today,this energy transfer includes Yellowstonecutthroat trout eaten by grizzly bears, whitepelicans, river otters, ospreys, and otherterrestrial animals. Because cutthroat troutspawn in tributaries and use other shallow-water habitats during other times of the year inYellowstone Lake, they are vulnerable to suchpredation. In contrast, the habits of lake troutmake them almost entirely unavailable toterrestrial predators.

ACKNOWLEDGMENTS

D. L. Mahony (FWS), N. Rowe, andnumerous National Park Service personnelassisted in data collection. We thank R. E.Gresswell, J. D. McIntyre, and J. D. Varleyfor their constructive reviews of a draft of thisreport.


LITERATURE CITED

Behnke, R. J. 1992. Native trout of westernNorth America. Am. Fish. Soc. Mono.

Benson, N. G. 1961. Limnology ofYellowstone Lake in relation to thecutthroat trout. U.S. Fish Wildl. Serv.,Res. Rep. 56.

_____, J. R. Greeley, M. I. Huish, and J. H.Kuehn. 1961. Status of management ofnatural lakes. Trans. Am. Fish. Soc.90:218-224.

_____, and R. V. Bulkley. 1963. Equilibriumyield and management of cutthroat trout inYellowstone Lake. U.S. Fish Wildl. Serv.,Res. Rep. 62.

Cordone, A. J., and T. C. Frantz. 1966. TheLake Tahoe sport fishery. Calif. FishGame 52(4):240-274.

Curtis, G. L. 1990. Recovery of an offshorelake trout population in eastern LakeSuperior, USA and Canada. J. Gt. LakesRes. 16(2):279-287.

Davenport, M. B. 1974. Piscivorous avifaunaon Yellowstone Lake, Yellowstone Na-tional Park. Master Sci. Thesis. MontanaState Univ., Bozeman.

Dean, J. L., and J. D. Varley. 1974.Yellowstone fishery investigations. U.S.Fish Wildl. Serv., Yellowstone NationalPark.

Donald, D. B., and D. J. Alger. 1993.Geographic distribution, species displace-ment, and niche overlap for lake trout andbull trout in mountain lakes. Can. J.Zool.71(2):238-247.

Edsall, T. A., C. L. Brown, G. W. Kennedy,and J. R. P. French III. 1992. Surficialsubstrates and bathymetry of five historicallake trout spawning reefs in nearshorewaters of the Great Lakes. Gt. Lakes Fish.Comm. Tech. Rep. 58:1-53.

Elrod, J. H. 1983. Seasonal food of juvenilelake trout in U.S.waters of Lake Ontario. J.Gt. Lakes Res. 9(3):396-402.

_____, and R. O’Gorman. 1991. Diet of

juvenile lake trout in southern Lake Ontarioin relation to abundance and size of preyfishes, 1979-1987. Trans.Am. Fish. Soc.120(3):290-302.

Gresswell, R. E., and J. D. Varley. 1988.Effects of a century of human influence onthe cutthroat trout of Yellowstone Lake.Am. Fish. Soc. Sym. 4:45-52.

Healey, M. C. 1978. The dynamics ofexploited lake trout populations andimplications for management. J. Wildl.Manage. 42(2):307-328.

Henderson, N. E. 1962. The annual cycle inthe testis of the eastern brook trout,Salvelinus fontinalis (Mitchell). Can. J.Zool. 40:631-641.

Jones, R. D., R. E. Gresswell, D. E. Jennings,S. M. Rubrecht, and J. D. Varley. 1980.Fishery and aquatic management programin Yellowstone National Park. U.S. FishWildl. Serv., Yellowstone National Park.

_____, P. E. Bigelow, R. E. Gresswell, L. D.Lentsch, and R. A. Valdez. 1983. Fisheryand aquatic management program inYellowstone National Park. U.S. FishWildl. Serv., Yellowstone National Park.

_____, Boltz, D. G. Carty, L. R. Kaeding, D.L. Mahony, and T. Olliff. 1993. Fisheryand aquatic management program inYellowstone National Park. U.S. FishWildl. Serv., Yellowstone National Park.

Kaplinski, M. A. 1991. Geomorphology andgeology of Yellowstone Lake, YellowstoneNational Park, Wyoming. Master Sci.thesis. Northern Ariz. Univ., Flagstaff.

Knight, J. C. 1975. The limnology of the WestThumb of Yellowstone Lake, YellowstoneNational Park, Wyoming. Master Sci.Thesis, Montana State Univ., Bozeman.

NPS (National Park Service). 1988.Management policies. U.S. Dep. Int.,National Park Service.

Paine, R. T. 1966. Food web complexity andspecies diversity. Am. Nat. 100(910):65-75.


Parks, G. 1991. Fish story. Grays SportingJournal. Summer :64-70.

Reinhart, D. P., and D. J. Mattson. 1990.Bear use of cutthroat trout spawningstreams in Yellowstone National Park. Int.Conf. Bear Res. Manage. 8:343-350.

Swenson, J. E. 1978. Prey and foragingbehavior of ospreys on Yellowstone Lake,Wyoming. J. Wildl. Manage. 42:87-90.

EDITORS'S NOTE: UPDATE ON LAKE TROUT

SITUATION THROUGH JUNE, 1996

During the summers of 1995 and 1996,additional data was gathered on lake trout inYellowstone Lake. Experimental gillnettingconducted by the U.S. Fish and Wildlife Servicehas yielded several hundred additional lake troutfrom 7 inches up to 32 inches (12.5 lbs.)

National Park Service staff received anglerreports of nearly 100 additional lake trout, mostcaught by anglers from the lake shore. Most ofthese fish were in the 16-19 inch size range, withseveral ranging up to 23 inches. Lake trout werecomparatively common along the shore and in

surface waters until the middle of July when theymoved to deep water.

Both the numbers and the distribution of theselake trout serve to strengthen the prevailingopinion that the situation is grave and alarming.It is now clear that there are many lake trout ofa variety of age classes in the lake, and that oneor more age class is capable of spawning. It islikewise clear that the fish are distributedthroughout the lake, as these fish were caughtin many locations. The situation is, if anything,more troubling than previously imagined.

Thibodeau, M. L., and J. R. M. Kelso. 1990.An evaluation of putative lake trout(Salvelinus namaycush) spawning sites inthe Great Lakes. Can. Tech. Rep. Fish.Aquat. Sci. 1739:1-20.

Varley, J. D., and R. E. Gresswell. 1988.Ecology, status, and management ofYellowstone cutthroat trout. Am. Fish.Soc. Sym. 4:13-24.

Yellowstone Lake is the last great refuge of theonce widespread Yellowstone cutthroat trout,Oncorhynchus clarki bouvieri. Though heavilyexploited by recreational and commercialfishing between 1890 and 1970, recent changesin fishing regulations have restored robustnumbers and population structure (Gresswelland Varley 1988). Yellowstone Lake and itstributaries and outlet stream have becomeworld-renowned as examples of intensivelyused yet healthy fisheries (Varley and Schullery1983), and the potential effects of an illegallyintroduced population of lake trout, Salvelinusnamaycush, therefore causes considerableanxiety among managers, scientists, and thepublic.

All the roles played by cutthroat trout in thelake’s ecosystem have not been examined, butmany have, and the accumulated informationallows cautious predictions of the consequencesof a collapse of the cutthroat trout population.For example, we know there are 42 species ofmammals and birds that are known or suspectedof using cutthroat trout for food in theYellowstone Lake area (Table 1). Thesemammals and birds take all ages of fish, in allparts of the lake and in the tributary streams.Their predation on living trout is best known(e.g., osprey) but the consumption of carcassesof migratory salmonids, particularly in spawn-ing streams, has been shown to be ecologicallysignificant (Cederholm et al. 1989). Thisconsumption, or scavenging, is apparently quitecomplex, and may reach quite far into theterrestrial food chain.

We cannot look into the future and say that anyof these bird or mammal species would

themselves be extirpated as a consequence ofthe collapse of cutthroat trout population, butknowing the importance of the native trout tothese species, we must assume that some ofthem would be seriously diminished, if notimperiled.

Ecologists have noted the extraordinaryprecision of resource partitioning amongpredators on the Yellowstone Lake cutthroattrout (Davenport 1974, Varley and Schullery1983). The many avian and mammalianpredators who depend wholly or in part uponthis resource are surprisingly specialized in thesize of the fish they take, with the result that fishof all ages are subjected to predation, and aretherefore of importance to some or severalpredators. Thus any alteration of the agestructure of the trout population will begin tohave effects on some predators before it affectsothers, but eventually, as the trout populationdeclines, all predators will be affected.

A LAST STRONGHOLD OF YELLOWSTONE

CUTTHROAT TROUT AT RISK

When white settlers first began colonizing thewestern United States there were probably 14subspecies of cutthroat trout (Onchorhynchusclarki spp.) in various levels of abundance(Behnke 1979). After several centuries ofcivilized “progress,” two subspecies are extinctand eight of the remaining groups are listed bythe American Fisheries Society (1989) asendangered, threatened, or of special concern.In this sad history of neglect and extermination,the preservation of two subspecies, the coastalcutthroat trout (O. clarki clarki), and Yellow-stone cutthroat trout (O. clarki bouvieri), gavethe public some cause for celebration. But then

CUTTHROAT TROUT AND THE

YELLOWSTONE LAKE ECOSYSTEM

BY PAUL SCHULLERY AND JOHN D. VARLEY

Table 1. Checklist of birds and mammals known or suspected to utilize Yellowstone cutthroat troutas a food source in the Yellowstone Lake drainage.

Species Known Suspected

Mammals:Water shrew Sorex palustris XMasked shrew Sorex cinereus XDusky shrew Sorex monticolus XDeer mouse Perimyscus maniculatus XRed squirrel Tamiasciurus hudsonicus XUinta chipmunk Tamias umbrinus XFlying squirrel Glaucomys sabrinus XMuskrat Ondatra zibethicus XErmine Mustela erminea XLongtailed weasel Mustela frenata XMink Mustela vison XMarten Martes americana XStriped skunk Mephitis mephitis XOtter Lutra canadensis XWolverine Gulo gulo XBadger Taxidea taxus XCoyote Canis latrans XBobcat Lynx rufus XCougar Felis concolor XBlack bear Ursus americanus XGrizzly Bear Ursus horribilus XRaccoon Procyon sp. X

Birds:White pelican Pelecanus occidentalis XCommon merganser Mergus merganser XBlue heron Ardea herodias XCalifornia gull Larus californicus XEared grebe Podiceps caspicus XLoon Gavia immer XCaspian tern Hydroprogne caspia XBarrows goldeneye Bucephala islandica XBufflehead Bucephala albeola XDble. crest. cormorant Phalacrocorax auritus XWestern grebe Aechmophorus occidentalis XRedtailed hawk Buteo jamaicensus XBald eagle Haliaeetus leucocephalus XOsprey Pandion haliaetus XBelted kingfisher Megaceryle alcyon XDipper Cinclus mexicanus XGray Jay Perisoreus canadensis XStellers jay Cyanocitta stellari XCrow Corvus brachyrhynchos XRaven Corvus corax X


14 Cutthroat Trout and the Yellowstone Lake Ecosystem

91% of the remaining range of the Yellowstonecutthroat trout is located in YellowstoneNational Park, and practically all of that is in theYellowstone Lake and River (Fig. 1, Varley andGresswell 1988). The report by McIntyre (thisvolume) now causes us considerable concernfor the fate of these cutthroat trout in their lastmajor stronghold.

This subspecies is worthy of preservation in itsown right; it is part of the planet’s biodiversity.But there are many other reasons for preservingthis trout population. The cutthroat trout is acelebrity among the trout family (e.g., Trotter1987) due to its popularity with sport fishermen.As an all-around sport fish it has few peers: itgrows to a fairly large average size, is highlyvulnerable to sport fishing, even by noviceanglers, and it has high susceptibility torepeated catches when released (Varley 1984,Gresswell and Liss 1995). Cutthroat trout, morethan any other trout species, is the archetype ofwestern trout fishing. These traits are also thereasons that it is so vulnerable to overexploitationand the main reason so many of the cutthroatsubspecies are declining.

All of this is very important, of course, but theYellowstone cutthroat trout is also important inthe fabric of something very much larger: theecosystem in which it lives. It is this dimensionwe explore here.

OTHER FISHES

For the past 10,000 years or so, only thelongnose dace (Rhinichthys cataractae) sharedYellowstone Lake with the native cutthroat(Varley and Schullery 1983). As a result of theactivities of modern humans, the Yellowstonecutthroat trout now share Yellowstone Lakewith several other introduced fish species:redside shiners (Richardsonius balteatus),longnose sucker (Catostomus catostomusgriseus), lake chub (Couseus plumbeus), andmost recently, lake trout (Salvelinus namaycush).

Fig. 1. Probable past (pre-1880s) and presentdistributions of native Yellowstone cutthroat trout (lightshading). Dark shading in Wyoming is the probabledistribution of the fine-spotted Snake River cutthroat trout,which has not been scientifically described or named.From J. D. Varley, and R. E. Gresswell, 1988, Ecology,status, and management of the Yellowstone cutthroat trout.Am. Fish. Soc. Symp. 4:13-24.

Prior to the advent of the lake trout, the survivalof the native cutthroat trout did not appear to beaffected by the nonindigenous newcomers. Infact, cutthroat trout are occasionally known tofeed heavily on some of these fish (Brown1974). The effects of a collapse of the cutthroattrout population on these other species is notknown, nor is the effect of lake trout predationon these species predictable. We can speculatethat lake trout might prey heavily on the suckerbecause both are hypolimnetic (deep-dwelling,bottom-oriented) species, but all age and sizegroups of all species (including cutthroat trout)would be potentially vulnerable to lake trout

Montana

Wyoming

Idaho

Utah

Montana

Wyoming

Idaho

Utah

Past

Present


predation, depending upon their preferredhabitats.

BIRDS

We know or suspect that a minimum of 20 birdspecies in the Yellowstone Lake ecosystem(Table 1) have evolved using the cutthroat troutas a primary or significant source of food. Thespecies diversity is as complex as it isfascinating. The stream-dwelling dipper(Cinclus mexicanus), for instance, is an efficientpredator of trout fry as they emerge from thegravel and migrate lakeward. Based on this fact,we can speculate about the effect no cutthroatspawners, or greatly diminished spawningactivity, might have on this species. Whatfollows are short case histories of the birdspecies we have the most knowledge of, and thepotential effects of the lake trout disruption.

The bald eagle (Haleaeetus leucocephalus) iswidely thought of as a predominantly fish-eating species, but studies in Yellowstone showthat only about 25% of its diet is fish (Davenport1974, Swenson et al. 1986), and only about halfof the fish it eats are trout (Davenport 1974).This does not mean that trout are unimportant tothe bald eagle, of course; its status over the pastseveral decades has often been precarious, andany change or reduction in its food base,especially protein- and fat-rich fish, could becritically significant. As well, some of its otherprey, especially waterfowl, are themselves inpart dependent upon fish, and so in effect theeagle’s reliance on fish is higher than mightappear from an examination only of itsimmediate prey. Davenport (1974) estimatedthat the daily consumption of fish per bald eaglewas 0.09 lb. per day. Lake trout are not expectedto be vulnerable to bald eagle predation.

The osprey (Pandion haliaetus) lives almostentirely on fish, and most of the fish are trout(Fig. 2). Yellowstone Lake and River hostnumerous breeding pairs of ospreys. Swenson

(1978) found that 93% of the fish bonesidentified near osprey nests were from trout, andthe rest were from Longnose suckers. Longnosesuckers may have been overrepresented in thissample because their bones are heavier andmore likely to endure and be found. Swenson(1978) also determined these birds selectivelypreyed on cutthroat trout about 11 inches inlength. Davenport (1974) estimated thatospreys averaged 0.88 lb. of fish per day onYellowstone Lake. Because they live at a fargreater depth than cutthroat trout, lake trout willhardly ever be available to ospreys. Afterseveral decades of struggle, osprey are doingrelatively well in Yellowstone National Park(Fig. 3), but past experience indicates theirsusceptibility to stress.

White pelicans (Pelecanus occidentalis) areamong the most-studied species of animals inYellowstone National Park (Fig. 4, Diem andCondon 1967). The nesting colony inYellowstone is the only known colony in anAmerican national park, and is the highestelevation colony known anywhere (Fig. 5). In1994, a record 739 white pelican nests wereinitiated on the Molly Islands, but nestingsuccess was low (T. McEneaney, NPS, pers.commun., 1995). In 1922, Ward estimated thatvirtually all of the pelican diet in YellowstoneLake was trout, but since then the introduction

Fig. 2. Osprey are obligate fish-eaters in YellowstoneLake. NPS photo.


several recent studies that indicate that whitepelicans consume 2 to 4 pounds of fish per day.

Davenport (1974) estimated that 72% of the dietof great blue herons (Ardea herodias) aroundYellowstone Lake was trout, and that theyconsumed an estimated 1.93 lb. of food each perday. While the population of herons isrelatively small (several dozen) the birdsaverage about 1,000 “heron-use days” in thecourse of the summer season. Unlike manyspecies of fish-eating animals, but like thepelicans, herons take fish of many sizes, from 2to 16 inches in length. Lake trout are notexpected to be vulnerable to herons.

The common merganser (Mergus merganser),though not as large or glamorous as the above-named species, may in some years actuallyconsume more fish than any of them because thepopulation is fairly large (400-800 birds, 62,000use-days) and they spend a long season on thelake (Davenport 1974). Davenport (1974)estimated that mergansers averaged 1.0 lb. oftrout eaten per day.

Fig. 4. Number of white pelicans fledged, 1890-1991, with known human influences. From J. D. Varley, and P.Schullery, in press, Yellowstone Lake and its cutthroat trout, in W. L. Halvorson, and G. E. Davis, eds., The evolutionof ecosystem management in America’s National Parks. University of Arizona Press, Tucson.

and proliferation of the longnose sucker hasprobably shifted the percentage of non-salmonids consumed to some extent. Pelicansfish in shallow water for trout and suckersbetween 6 and 16 inches, and it is unlikely laketrout will be vulnerable in this way to the birdsin the future. Davenport (1974) summarized

Fig. 3. Osprey breeding pairs in Yellowstone Lake, 1924-1991, with known human influences. From J. D. Varley,and P. Schullery, in press, Yellowstone Lake and itscutthroat trout, in W. L. Halvorson, and G. E. Davis, eds.,The evolution of ecosystem management in America’sNational Parks. University of Arizona Press,Tucson.

30 -

25 -

20 -

15 -

10 -

5 -

0 -

—- - - -

—- - - -

—- - - -

—- - - -

—- - - -

—- - - -

—

1924 1965 1970 1975 1980 1985 1990

Yellowstone LakeShoreline

Frank Island

Nu

mb

er

of

Bre

ed

ing

Osp

rey

Pa

irs

DDT Banned in

Greater YellowstoneEcosystem

DDT Bannedin USA

TroutRestoration

Campsite ClosuresNear Nests

Island Closures

Nu

mb

er

of W

hite

Pe

lica

ns

Fle

dg

ed

700 -

600 -

500 -

400 -

300 -

200 -

100 -

0 -

Human Disturbance on Molly Islands

Pelican Pop. Control

Year

Trout RestorationBoat Disturbance

Permitted Near Islands

Islands Free of Human Impacts

DDT Banned in USA

—- - - - - - - - -

—- - - - - - - - -

—- - - - - - - - -

—- - - - - - - - -

—- - - - - - - - -

—- - - - - - - - -

—- - - - - - - - -

—- - - - - - - - -

—- - - - - - - - -

—- - - - - - - - -

—

1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990


According to Davenport’s (1974) estimate oftrout consumption in 1973 and 1974, theCalifornia gull (Larus californicus), whosepopulation was estimated between 1,400 and2,000 (160,000 bird-days use) and whose diet is50% trout, consumed as much trout as didpelicans. The eared grebe (Podiceps caspicus),whose numbers ranged from 2,500 to 3,000(100,000 bird-days use) depended entirely upontrout for its diet, and consumed 0.31 lb. per day.The common loon (Gavia immer) and thecaspian tern (Hydroprogne caspia), occur insmaller numbers (15 and 35, respectively) butboth depend entirely upon trout for their food,and consume 1.91 and 0.7 lb. of food per day(Davenport 1974). Other bird species that eattrout include the Barrow’s goldeneye (Bucephalaislandica), bufflehead (Bucephala albeola), andbelted kingfisher (Megaceryle alcyon). None ofthe above species are expected to utilize lake

trout because of the fish’s deep water habits.

Double-crested cormorants (Phalacrocoraxauritus) are another prominent fish-eater onYellowstone Lake (Fig. 6). Cormorantsapparently consume few trout, and may nothave inhabited the lake at all until after theintroduction of longnose suckers (Davenport1974). If cormorants are profundal predators, asa diet of suckers suggests, they may consumelake trout in Yellowstone Lake. It is not knownif the presence of lake trout, who willthemselves prey on longnose suckers, willenhance or decrease cormorant population size.

All of the above species of birds, with thepossible exception of the cormorant, prey onfish within a few feet of the surface ofYellowstone Lake, along the lake shoreline, orin the shallower waters of the lake’s tributaries

Fig. 5. The white pelican nesting islands in the Southeast Arm of Yellowstone Lake have been intermittently monitoredsince the late 1800s. NPS photo.


Schullery 1991), it is assumed that prior to thecreation of Yellowstone National Park, grizzlybears (Ursus arctos) preyed heavily onspawning cutthroat trout in the tributary streamsof Yellowstone Lake. During the extendedperiod of open-pit garbage dumps in Yellow-stone (roughly 1890-1970), when increasingnumbers of bears devoted much of theirattention to feeding at these concentrated foodsources, relatively few reports were made ofbears feeding on these spawning runs, a notableexception being bears that discovered easyconcentrations of fish at spawner collectionweirs operated by hatchery managers. By the1960s, when the first ecological study ofYellowstone grizzly bears was undertaken, theYellowstone Lake cutthroat trout populationwas severely depressed and garbage feeding bybears was at its height (Schullery 1992). TheCraighead research team observed no feedingby grizzly bears on spawning trout in the 1960s(J. Craighead, pers. commun., 1984).

In the late 1960s, a general overhaul of parkfishing regulations allowed the cutthroat troutpopulation to begin a rapid recovery, withconcurrent increase in grizzly bear activityalong spawning streams (Fig. 7). YellowstoneLake has 124 tributaries, at least 59 of which areknown to have cutthroat trout spawning runs.Surveys in 1974 and 1975 revealed bear activityon 17 streams, and clear evidence of bear fishingon 11 (Hoskins 1975). Surveys in 1985-1987revealed that 93% of the streams now hadevidence of bear activity, and 61% “hadconclusive evidence of bear fishing” (Fig. 8,Reinhart and Mattson 1990). An estimatedminimum of 44 bears used these spawning runsin 1987 (Reinhart and Mattson 1990), andsometimes this use was substantial; Yellow-stone Grizzly Foundation researchers observedan adult female grizzly bear maintain an averageharvest of 100 fish per day (average fish weight= 1.3 lbs) for 10 days (S. French, pers. commun.,1989).

Fig. 6. The double-crested cormorant is one of very fewaquatic bird species on Yellowstone Lake that may not bebe adversely affected by the collapse of the cutthroat troutpopulation. NPS photo.

and outlet stream. Cutthroat trout, who preferthese same habitats, are thus vulnerable to thispredation. Lake trout spend almost all of theirlives at depths too great to be reached by thesepredators. In the event of a collapse of thecutthroat trout population and an increase in thelake trout population, the lake trout are notexpected to provide a replacement prey.

MAMMALS

With the exception of grizzly bears, the use ofcutthroat trout by mammals has not received theamount of study attention birds have received;yet a surprising number of mammal species—22—are known or suspected of using cutthroattrout as a primary or significant food item(Table 1). For species like otters there is littledoubt of the potential impact of lake trout.Observers on Yellowstone Lake have reportedthey seem to be able to catch cutthroat trout atwill. The deep-dwelling lake trout will certainlybe less available and accommodating. Whatfollows are short discussions and somespeculation on the effect of lake trout on ourbest-known mammal species.

Though the historical record is sketchy due tothe shortage of observers and changing patternsof human use (Skinner 1927, Whittlesey 1988,


Fig. 7. Percent of Yellowstone Lake tributary streamsfished by grizzly bears in three periods: 1953-1970, 1974-1975, and 1985-1987. From J. D. Varley, and P.Schullery, in press, Yellowstone Lake and its cutthroattrout, in W. L. Halvorson, and G. E. Davis, eds., Theevolution of ecosystem management in America’sNational Parks. University of Arizona Press, Tucson.

Fig. 8. Grizzly bear fishing Flat Mountain Arm Creekduring cutthroat trout spawning run. NPS photo.

(Streubel 1989), and has been a commonlyobserved denizen of the lake since the park’searliest history. As predators in YellowstoneLake, they are trout specialists but are alsothought to eat longnose suckers. It is not knownwhether a shift of biomass in the lake fromcutthroat to lake trout will have an effect onotters, but given the observed vulnerability ofthe cutthroat trout to otters, we suspect the shiftwill be negative.

The above-described birds and mammals arethe best-known consumers of Yellowstonecutthroat trout, because we have research data inhand on them. But there are many more specieswho are known or assumed (either from localanecdotal information or from the scientificliterature) to use these fish (Table 1). In all,some 42 species of birds and mammals areknown or suspected to depend on theYellowstone cutthroat trout to some extent. Thelist could undoubtedly be extended with theinclusion of reptiles, amphibians, invertebrates,bacteria, and fungi. It is obvious from the abovediscussion and from Table 1 that theYellowstone cutthroat trout is the central, orkeystone, species in the Yellowstone Lakeecosystem, and that its decline or disappearancewould have disastrous consequences for muchof the remaining animal life.

Black bears (Ursus americanus) also fish thesespawning streams, though they are notobserved as often as are grizzly bears. Most useof spawning runs has been by grizzly bears, butReinhart and Mattson (1990) noted that “blackbear use of streams was also increasinglycommon, progressing from the east shore to thewest shore.” The presence of grizzly bears on astream apparently deterred black bears fromfishing more.

Gunther (1995) noted that “cutthroat trout are animportant, high quality food source for grizzlybears that have home ranges adjacent toYellowstone Lake. Unlike cutthroat trout, laketrout do not move up tributary streams to spawn,but spawn within the lake at depths makingthem unavailable to many terrestrial predatorssuch as grizzly bears.” It is not possible toquantify the effects of this loss of an importantnutritional source with much precision, butthose effects will obviously be substantial.

Unlike the bears, the river otter (Lutracanadensis) is “almost entirely carnivorous”

***

**

*** Estimated Use

Confirmed Use

1953–1970 1974–1975 1985–1987

100

75

50

25

0

Per

cent

of S

trea

ms

Fis

hed

by G

rizzl

y B

ears


LITERATURE CITED

American Fisheries Society. 1989. Fishes ofNorth America, endangered, threatened, orof special concern. Fisheries 14(6):2-38.

Behnke, R. 1979. The native trouts of thegenus Salmo of western North America.Report to the U.S. Fish and WildlifeService, Denver, Colo.

Brown, R. R. 1974. The predation of cutthroattrout on redside shiners in Pelican Creek.Pages 124-131 in U.S. Fish and WildlifeService, Division of Planning and Assis-tance, Annual Project Report YellowstoneFishery Investigations, Yellowstone Na-tional Park, Calendar Year 1973, June 10,1974. Yellowstone National Park.

Cederholm, C. J., D. B. Houston, D. L. Cole,and W. J. Scarlett. 1989. Fate of cohosalmon (Onchorhynchus kisutch) carcassesin spawning streams. Can. Jour. of Fish. andAquatic Sci. 46(8):1347-1355.

Davenport, M. B. 1974. Piscivorous avifaunaon Yellowstone Lake, Yellowstone Na-tional Park. Yellowstone National Park,U.S. Fish and Wildlife Service internal rep.62pp.

Diem, K. L., and D. D. Condon. 1967. Bandingstudies of water birds on the Molly IslandsYellowstone Lake, Wyoming. YellowstoneLibrary and Museum Association, Yellow-stone National Park. 41pp.

Gresswell, R. E., and J. D. Varley. 1988.Effects of a century of human influence onthe cutthroat trout of Yellowstone Lake.Am. Fish. Soc. Symp. 4:45-52.

Gresswell, R. E., and W. J. Liss. 1995. Valuesassociated with management of Yellow-stone cutthroat trout in YellowstoneNational Park. Cons. Biol. 9(1):159-165.

Gunther, K. A. 1995. Grizzly bears andcutthroat trout: potential impacts of theintroduction of non-native lake trout toYellowstone Lake. Bear ManagementOffice, Yellowstone National Park, Infor-mation Paper No. BMO-8. 3pp.

Hoskins, W. P. 1975. Yellowstone Laketributary survey project. U.S.D.I. Inter-agency Grizzly Bear Study Team, Yellow-stone National Park, unpubl. rep. 10pp.

Kaeding, L. R., D. G. Carty, D. L. Mahony, G.Boltz, and S. M. Anderson. 1995. Fisheryand aquatic management program inYellowstone National Park. U.S. Fish andWildlife Service, Yellowstone NationalPark, Tech. Rep. for 1994. 38pp.

Reinhart, D. P., and D. J. Mattson. 1990. Bearuse of cutthroat trout spawning streams inYellowstone National Park. Int. Conf. BearRes. and Manage. 8:343-350.

Schullery, P., ed. 1991. Yellowstone bear tales.Roberts Rinehart, Niwot, Colo. 212pp.

Schullery, P. 1992. The bears of Yellowstone.High Plains Publishing Company, Worland,Wyo. 318pp.

_____, and J. D. Varley. 1994. Fires and fish,the fate of Yellowstone waters since 1988.Trout 35(2):16-23.

Skinner, M. P. 1927. The predatory and fur-bearing animals of Yellowstone Park.Roosevelt Wildl. Bull. 4(2):163-282.

Streubel, D. 1989. Small mammals of the Yel-lowstone ecosystem. Roberts Rinehart,Boulder. 152pp.

Swenson, J. 1978. Prey and foraging behaviorof ospreys on Yellowstone Lake, Wyoming.J. Wildl. Manage. 42(1):87-90.

_____, K. L. Alt, and R. L. Eng. 1986. Ecologyof bald eagles in the greater Yellowstoneecosystem. Wildl. Monogr. No. 95, 1-46.

Trotter, P. 1987. Cutthroat: Native trout of thewest. Colorado Associated UniversityPress, Boulder. 219pp.

Varley, J. D. 1984. The use of restrictiveregulations in managing wild salmonids inYellowstone National Park, with particularreference to cutthroat trout, Salmo clarki.Pages 145-156 in J. M. Walton, and D. B.Houston, eds. Proceedings of the Olympicwild fish conference, Mar. 23-25, 1983, PortAngeles, Wash.


_____, and R. E. Gresswell. 1988. Ecology,status, and management of the Yellowstonecutthroat trout. Am. Fish. Soc. Symp. 4:13-24.

_____, and P. Schullery. 1983. Freshwaterwilderness: Yellowstone fishes and theirworld. Yellowstone Library and MuseumAssociation, Yellowstone National Park.

132pp.Ward, H. B. 1922. Food habits of the pelican.

Yellowstone National Park, unpubl. rep.25pp.

Whittlesey, L. H. 1988. Yellowstone placenames. Montana Historical Society, Helena.178pp.

SOCIOECONOMIC VALUES ASSOCIATED

WITH THE YELLOWSTONE LAKE CUTTHROAT TROUT

BY JOHN D. VARLEY AND PAUL SCHULLERY

The study of the social and economic dimen-sions of fish and wildlife in our country is arelatively young discipline, even for sport spe-cies harvested or otherwise of great interest topeople, but especially when applied tononconsumptive activities such as wildlife view-ing or hearing. We know, for example, thatwildlife observation is “the single most impor-tant activity” for 94% of Yellowstone NationalPark visitors (Duffield 1992), eclipsing even thestoried geysers. From this information, wecan conclude that wildlife viewing is sociallyvaluable. A dollar valuation for this enormouslyimportant activity, however, has never been es-tablished. Though fish viewing has seldom beenheld in the same esteem as wildlife observa-tion, the social significance of a robust popula-tion of nonharvested cutthroat trout recentlybecame obvious to park managers. In recentyears, cutthroat trout viewing at Fishing Bridgeand LeHardys Rapids (Fig. 1), for instance,attracted more than a third of a million visitors,about 10% of the total annual park visitation(Gresswell and Liss 1995). What is particu-larly surprising is that in Yellowstone NationalPark, an area famous for its trout fishing, thenonconsumptive fish viewing public exceeds thetotal number of anglers (Fig. 2).

SOCIAL ANDECONOMIC VALUESFish and wildlife are recognized as having sev-eral types of economic values besides those as-sociated with their direct consumption (e.g.,hunting, trapping, or fishing harvest). Thesevalues include use value, which is how muchan individual is willing to pay to enjoy wildlife,either firsthand, or through some media; optionvalue, which is how much an individual is will-ing to pay just to ensure that the wildlife existsin case the individual some day may choose togo view it; existence value, which is how much

Fig. 1. LeHardys Rapids, where cutthroat trout arefrequently visible during their spawning run, has becomea significant visitor attraction emphasizing anonconsumptive use of the fishery. NPS photo.

an individual is willing to pay just to know thatan animal continues to thrive in the wild; andbequest value, which is how much an individualis willing to pay to know that an animal willsurvive for the enjoyment of future generations(Swanson et al. 1994). Except for wolf recov-ery, whose future regional net economic im-pact is on the order of $43 million a year(Duffield 1992), these values have not up to nowbeen computed for any species in the Yellow-stone Lake ecosystem, but are quite high in othernature reserves (Swanson et al. 1994).

Though wolf recovery analyses and data fromother reserves may by suggestive, or even com-pelling, nontraditional economic values remainpoorly considered and frequently neglected,merely because they have not been as well quan-tified as have many other types of resources.For example, if the existence value of the griz-zly bear to all Americans and all other peoplewith a concern for wildlife were to be calcu-lated, it would at least seriously compete withthe better-known values of many other tradi-tionally recognized resources, and in fact might

exceed them. An example given by Duffield etal. (1987) concluded that stream fisheries inMontana compared favorably economically withmarketed resources such as timber, coal, or graz-ing. The current plight of the Yellowstone Lakecutthroat trout, with its consequences for manyother species of wildlife, is an excellent exampleof why more analyses of these values are needed.Until now, no attempt has been made to esti-mate at least some of the lost spiritual, scien-tific, or recreational values should the Yellow-stone Lake cutthroat trout population be reducedor destroyed.

SIGNIFICANCE OF THEYELLOWSTONE LAKE ECOSYSTEMYellowstone Lake, the waters tributary to it,and its outlet downstream to the Upper Yellow-stone Falls are the most popular and heavilyused fisheries in the park (Fig. 3), together sup-porting more than 264,000 cutthroat trout“catches” annually and almost 50% of the totalparkwide fishing interest. Yellowstone Lakehas more than 100 tributary streams and a half-dozen lakes in its immediate watershed withinthe park boundary. It must be emphasized thatfish populations and fishing in the tributarystreams (e.g., Pelican Creek, Upper Yellow-stone River) and in the world-famous section ofthe Yellowstone River between Fishing Bridgeand the Upper Yellowstone Falls will be as se-verely affected by lake trout as will Yellow-stone Lake.

In 1994, 237,700 angler days were reported onall parkwide waters, and 78,169 (33% of theparkwide total) of those were spent on Yellow-stone Lake (Kaeding et al. 1995). Extrapolat-ing from data and interpretations for the Yel-lowstone Lake ecosystem presented in Varleyet al. (1976) and the 1994 sport fishery datafrom Kaeding et al. (1995), we estimate the1994 use on the Yellowstone River between thefalls and the lake at 33,500 (14%) angler days,and the lakes and streams flowing into Yellow-stone Lake at 3,400 (1.4%) angler days. Thus,we can estimate about 115,069 angler days,which in the past have been totally supportedby cutthroat trout, to be in some way jeopar-dized by the advent of lake trout in this ecosys-tem.

The U.S. Fish and Wildlife Service annual re-ports for the past several decades have quanti-fied extremely high levels of angler satisfactionwith the fishing experiences produced by theYellowstone Lake ecosystem. For example,in 1994, more than two-thirds of all anglerslanded one or more cutthroat trout per outing,and those fish averaged more than 15 inches inlength. Seventy-eight percent of the anglersresponding to questionnaires reported satisfac-tion with their angling experience (Kaeding etal. 1995). Most fishermen and fishing writersspeak of these kinds of angling adventures insuperlatives.

There are accepted ways to derive an economicvalue for sport fisheries and we have done thathere to underscore the importance of exactlywhat is at risk in the Yellowstone Lake ecosys-tem. To a great extent we have followed themethod and calculations of Duffield et al. (1987),a part of which is known as a regional TravelCost Model (TCM). The TCM approach is rec-ommended by both the Water Resources Coun-cil (1979, 1983) and the U.S. Department ofthe Interior (1986) as a preferred technique. An-other technique reported by Duffield et al. (1987)focuses on angler expenditure data per trip,sometimes called the “trickle-down model,”

Fig. 2. Fish-watching from Fishing Bridge, at the outletof Yellowstone Lake. NPS photo.

The Yellowtone Lake Crisis 23

24 Socioeconomic Values

wild trout fishery with a hatchery-supported fish-ery would cost $281,200 annually. He furtherestimated, based on actual hatchery productioncosts, that each wild cutthroat trout was worth$72.63 over the span of its projected three-yearcatchable life. Varley (1984) concluded that torecreate a fishery supported solely by hatcheryfish equal to the Yellowstone River could notlikely be done because the costs per fish weretoo high for any public agency to bear, or foranglers to tolerate paying for.

No specific economic analysis has been con-ducted of angler benefits or expenditures on theYellowstone River, but calculations have beenmade for similar, close-by waters in the state ofMontana and Wyoming. The economic datagenerated from fisheries in the two states arefairly comparable. For the sake of simplicityand relevance to the present, we have usedMontana’s figures. The 1987 study by Duffieldet al. calculated total recreational value per dayfor many Montana waters. Based on a reportedtravel cost of $.36 per mile, the statewide aver-age for all stream fisheries was $135.38, butthe data on the “blue-ribbon” Yellowstone Riverin Montana was higher, amounting to $276.74.Using the 1994 estimate of use on the Yellow-stone River downstream from Fishing Bridgeof 33,500 angler days, and Montana’s calcula-tion for their portion of the Yellowstone, yieldsa 1994 value of $9,270,800 for this portion ofthe Yellowstone River.

It is worth noting that among all Montanastreams, those nearest Yellowstone NationalPark (Upper Yellowstone, Upper Yellowstonetributaries, Madison, Madison tributaries) hadthe highest values per day in the state.

Yet another significant measure of economicvalue of fisheries is angler expenditure per out-ing. Duffield et al. (1987) calculated that totalangler expenditure per day for Montana resi-dents on streams was $29.45. For nonresidentsthe daily expenditure on streams was $153.61.Yellowstone Park fishermen are essentially all

which can be additive to those figures derivedfrom the TCM. Both techniques, according toDuffield et al. (1987) “are the appropriate val-ues to use in benefit/cost analysis or where eco-nomic efficiency decisions are being made.” Athird model (Varley 1984) focuses on the costof replacing or duplicating a wild fishery re-source in “avoided fish hatchery costs.” Be-cause the calculations from the above modelsare based on inflated dollars, all dollar figurespresented in this report have been converted to1994 U.S. dollars using the Consumer PriceIndex (U.S. Bureau of Labor Statistics).

THE YELLOWSTONE RIVER BETWEENFISHING BRIDGE AND UPPERYELLOWSTONE FALLSThis portion of the Yellowstone River arguablyhas more fame than any other trout stream inthe Rocky Mountains (Fig. 4). Because thissection of river is largely populated by cutthroattrout from Yellowstone Lake, the fortunes ofthe river are closely tied to the viability andhealth of the stock in the lake. Varley (1984)examined the 8.9 mile section of the Yellow-stone River between Fishing Bridge and the Up-per Falls, and concluded that to reproduce this

Fig. 3. The cutthroat trout population of the YellowstoneRiver (between Fishing Bridge and the Upper Falls) isthreatened by the lake trout invasion, because thesecutthroats spend the winter in the lake and are thereforevulnerable to predation. This river fishery is world-famousas the site of pioneering work in special regulations, andwould be severely reduced in quality if the lake trout thrivein Yellowstone Lake. NPS photo.


nonresidents in terms of their expenditures andso the angler expenditure for the YellowstoneRiver equates to $5,145,900.

YELLOWSTONE LAKE TRIBUTARYSTREAMS AND LAKESThe rivers, streams and lakes tributary to Yel-lowstone Lake are often cited by fishermen andwriters as notable fisheries in their own right.Well-known streams such as the Upper Yellow-stone River (above the lake), Thorofare Creek,Pelican Creek, plus literally dozens of others,and lakes such as Alder, Trail, Riddle and Syl-van, are expected to be seriously affected bythe introduction of lake trout in YellowstoneLake. Almost all of these fisheries are signifi-cantly tied to the fortunes of the cutthroat troutof Yellowstone Lake, mostly because of the an-nual spawning migrations from the “motherlake,” and the resultant redistribution of troutbiomass. Using the economic factors detailedabove, plus the Duffield et al. (1987) figuresfor lakes in the “Madison [River] Area” near

Yellowstone Park, we estimate the total recre-ational value per day for these fisheries to be onthe order of $809,700.

In terms of the average nonresident angler ex-penditure per day, an additional $365,300 canbe added to the annual value of the fisheriesassociated with the lakes and streams tributaryto Yellowstone Lake.

YELLOWSTONE LAKE FISHERYThe Yellowstone Lake fishery has been consid-ered peerless since it was discovered by mod-ern anglers in the middle of the last century.Since its popularity with Euroamericans began,literally tens of millions of cutthroat trout havebeen harvested, although catch-and release regu-lations in recent years have reduced that har-vest to fewer than 100,000 annually (Fig. 5).

We have estimated the value of the YellowstoneLake fishery in several ways. In the first model,we have used Varley’s (1984) figures from the

Fig. 4. Each wild cutthroat trout in the famous “catch-and-release” water of the Yellowstone River between FishingBridge and the Upper Falls has a calculated recreational value of about $72.00.NPS photo.

26 Socioeconomic Values

Yellowstone River catch-and-release section onthe value of each catchable cutthroat trout, andthe estimate quoted in McIntyre et al. (this vol-ume) on the number of catchable trout in thelake to compute an average “catchable stock.”Thus, the estimate of 2.5 million catchable cut-throat trout in the lake with a nominal value of$72.63 per fish yields a value of $181,575,000for the current catchable stock in terms of “re-placement or duplication value” and “avoidedfish hatchery costs.”

Using the Montana valuation figures (Duffieldet al. 1987) for total recreational value, weproject that the 1994 estimates of 78,169 anglerdays spent on Yellowstone Lake, and a value of$194.74 per angler day, yield an estimated valueof $15,222,600 for that year. Using the figurescalculated by Duffield et al. (1987) for averagenonresident expenditure on quality lakes nearYellowstone Park an additional figure of$5,257,600 can be estimated.

ECONOMIC VALUE OF THEYELLOWSTONE LAKE ECOSYSTEMBased upon the above figures for the Yellow-stone River, Yellowstone Lake, and the tribu-taries to the lake, summed to a grand total, weconservatively estimate that the nominal one year(1994) economic value of the sport fisheries inthe Yellowstone Lake ecosystem is $36,021,900.

The effect of lake trout on the Yellowstone Lakeecosystem has been projected out over a 30-yearhorizon, so given the following assumptions,we can project the economic effect over the nextthree decades. We assume 1) no lake trout con-trol is implemented, and 2) the demise of thecutthroat trout occurs as predicted by McIntyreet al. (this report). We falso factored in theexpectation that during the decline of cutthroattrout, lake trout will offer a replacement sportfishery at least on par with the Lewis Lake laketrout fishery in the park. Given these assump-tions, we project that in 30 years (2024) theYellowstone Lake ecosystem sport fisheries willdecline from the 1994 value of $36,000,000 to

an annual value of $8,492,300.

Consequently, the cumulative 30-year value ofthe cutthroat trout sport fishery assuming theintroduction of lake trout had not occurred isestimated at more than a billion dollars($1,080,000,000). The consonant value assum-ing lake trout populations are vigorously con-trolled and do not exceed 20-30% of the troutbiomass in the lake is $685,000,000. If no sig-nificant lake trout control is carried out and theirpopulation approaches 70-80% of the trout bio-mass, the 30-year value of the sport fishery isexpected to decline to $439,950,000. This lastscenario represents a three decade economic ero-sion of $640 million, which we consider thelong-term net economic effect of the introduc-tion of lake trout if park managers fail to takeaction.

Further, if the surge of lake trout is greater thanproje and the decline in cutthroat trout is worsethan expected, and this results in the cutthroattrout population becoming extinct or nearly soat the end of 30 years, we estimate that the totalecological restoration of the cutthroat trout inYellowstone Lake, its outlet stream, and itstributaries, would have a one-time cost of a mini-mum of $31,250,000, or a multiple year “re-placement-in-kind” of $181,575,000. If the cut-throat decline was severe enough, the subspe-cies may warrant listing under the Endangered

Fig. 5. Yellowstone Lake is the west’s premier cutthroattrout lake fishery, which has a calculated annualrecreational value of more than $15 million.NPS photo.


Species Act, which would increase the restora-tion costs cited above.

By any measure it is obvious that saving thenative ecosystem would be the desired courseof action on both biological and economicgrounds. Elsewhere in this volume, a lake troutcontrol program is presented that uses a combi-nation of sport angler exploitation and inten-sive, large-scale gillnetting and trapping to sig-nificantly suppress their population. This typeof program, which would have to be carriedout indefinitely (assuming no technologicalbreakthroughs occur), would cost approximately$300,000 per year (30 years = $9,000,000).Thus, the lake trout control program and pres-ervation of as much of the cutthroat trout fish-ery as possible would result in a highly favor-able benefit:cost ratio of 27:1.

Through this brief presentation of social and eco-nomic dimensions of lake trout invasion, wehave attempted to add a useful perspective onsome of the values at risk. Though we wereonly able to speculate about option, existence,and bequest values, it is clear to us they wouldbe substantial if those figures were available.However, by any measure the angler-use pro-jections, while partially presumptive, demon-strate a resource of extraordinary scope, qual-ity, and value. The fishery at risk is held ingreat esteem by the public and is very valuableto the local and regional economy. The Yel-lowstone Lake cutthroat trout population fits thedefinition of extraordinary significance: in theirown right because they are now an imperiledsubspecies, for the fishing experience they pro-vide, on behalf of the charismatic wildlife spe-cies they feed, for the scientific laboratory theyare a part of, and for the economic bonanzathey provide the region.

LITERATURE CITEDDuffield, J., J. Loomis, and R. Brooks. 1987. The net

economic value of fishing in Montana. Montana De-partment of Fish, Wildlife and Parks.

Duffield, J. 1992. An economic analysis of wolf recov-ery in Yellowstone: park visitor attitudes and values.-87 in Wolves for Yellowstone? A report tothe U.S. Congress, Vol. IV, J. D. Varley and W. G.Brewster, eds. National Park Service.

Gresswell, R. E., and W. J. Liss. 1995. Values associ-ated with Management of Yellowstone Cutthroat Troutin Yellowstone National Park. Conserv. Biol.9(1):159-165.

Kaeding, L. R., D. G. Carty, D. L. Mahony, G. Boltz,and S. M. Anderson. 1995. Fishery and aquaticmanagement program in Yellowstone National Park.U.S. Fish and Wildlife Service, Yellowstone NationalPark, Tech. Rep. for 1994. 38pp.

Swanson, C. S., D. W. McCollum, and M. Maj. 1994.Insights into the economic value of grizzly bears inthe Yellowstone recovery zone. Int. Conf. Bear Res.and Manage. 9(1):575-582.

U.S. Bureau of Labor Statistics. 1995. Consumer PriceIndex, 1970-1994. Washington, D.C. 1p.

Varley, J. D. 1983. The use of restrictive regulations inmanaging wild salmonids in Yellowstone NationalPark, with particular reference to cutthroat trout.Pages 145-156 in J. M. Walton and D. B. Houston,eds. Proceedings of the Olympic Wild Fish Confer-ence, Penninsula College, Port Angeles, Wash.

Varley, J.D., R.E. Gresswell, S.M. Hoskins, R.B.Mathias, D.E. Jennings, M.D. Carpenter, and J.Dolan. 1976. Annual project report for 1975, fish-ery and aquatic program, Yellowstone Park. U.S.Fish and Wildlife Service, Yellowstone Park, tech.report. 148pp.

U.S. Department of the Interior. 1986 Natural Resourcedamage assessments: final rule. 43 CFR Part 11,Federal Register 51(148), Aug. 1, 1986.

U.S. Water Resources Council. 1979. Procedures forevaluation of national economic development (NED)benefits and costs in water resources planning. FinalRule, Federal Register 44(242), Dec. 14, 1979.

U.S. Water Resources Council. 1983. Economic and en-vironmental principles and guidelines for water andrelated land resources. Mar. 10, 1983.

REVIEW AND ASSESSMENT OF POSSIBILITIES

FOR PROTECTING THE CUTTHROAT TROUT

OF YELLOWSTONE LAKE FROM INTRODUCED LAKE TROUT

PROCEEDINGS OF A WORKSHOP AND INFORMATION EXCHANGE HELD INGARDINER, MONTANA, FEBRUARY 15-17, 1995

BY JOHN D. MCINTYRE, WORKSHOP LEADER

Chairman), Reginald Reisenbichler (Seattle,Washington), Bruce Rieman (Boise, Idaho),James Selgeby (Ashland, Wisconsin), andJames Vashro (Kalispell, Montana). Additionalinformation was provided by David Donald(Regina, Saskatchewan) and Robert Behnke(Ft. Collins, Colorado), who were unable toattend the meeting.

The team was directed to an exploration of theavailable information concerning fish commu-nity dynamics in Yellowstone Lake and in otherlakes where lake trout have been introduced.Based on these discussions and on theirpersonal experience and background, eachmember judged the likelihood that lake troutcan be eliminated from Yellowstone Lake, thelikelihood that the lake trout population can becontrolled, and the expected percent loss in thecutthroat trout population with and withoutsuppression of lake trout. Team members werealso asked to identify potentially usefulmanagement methods and to judge the potentialeffectiveness of each. Finally, they were askedto describe information needed to address theproblem and to monitor the result of actions thatmay be taken by the National Park Service(NPS).

PROGNOSIS

The team concluded there is only a slight chancethat lake trout can be eliminated fromYellowstone Lake (Fig. 1A), but they all judgedthere to be at least a 50% chance that substantial

INTRODUCTION

Lake trout (Salvelinus namaycush) werecaptured in Yellowstone Lake, YellowstoneNational Park in 1994. Lake trout are notindigenous to the lake and their predatory habitsare perceived to be a threat to the nativeYellowstone cutthroat trout (Oncorhynchusclarki bouvieri) and to all other aquatic andterrestrial species that depend on the presence ofa robust population of cutthroat trout. As part ofan action plan to address the problem,administrators of Yellowstone National Parkconvened a team of scientists to helpcharacterize the threat to the cutthroat trout andto identify and judge the potential effectivenessof management actions to reduce that threat.

The team met in Gardiner, Montana, inFebruary 1995. Members were selected so thatas a whole the team had demonstrated capacityfor objective analysis and broad experiencewith cutthroat trout, lake trout, populationbiology, management techniques, and manage-ment strategies. This is a report of their findingsand judgments.

PARTICIPANTS AND PROCEEDINGS

Participants included Frederick Binkowski(Milwaukee, Wisconsin), Theodore Bjornn(Moscow, Idaho), Jon Erickson (Jackson,Wyoming), Robert Gresswell (Corvallis, Or-egon), Michael Healey (Vancouver, BritishColumbia), Leo Marnell (Glacier NationalPark, Montana), John McIntyre (Boise, Idaho,

control of lake trout population’s expansion wasfeasible (Fig. 1B).

If the lake trout population is not suppressed,most participants judged the loss of cutthroattrout from present levels would equal or exceed50% within the next 20 years (Fig. 2A). Theyjudged that suppression of the lake troutpopulation might limit that loss to less than 30%of present levels (Fig. 2B).

In the absence of some action to limit lake trout,most team members judged the number ofcutthroat trout would be reduced by 70% ormore within 100 years (Fig. 2C). Theexpectation of loss in 100 years with lake troutsuppression was variable, but five of eightrespondents judged that it may be possible tolimit the loss of cutthroat trout to 10-20% ofpresent levels (Fig. 2D).

It is not a foregone conclusion that lake troutpopulation will cause a catastrophe for thecutthroat trout. One participant concluded thateven with no suppression of lake trout, cutthroattrout are likely to be reduced only by 20% in the

Fig. 1. Frequency distributions of estimated probabilities that lake trout canbe eliminated from Yellowstone Lake (A), and that lake trout abundance canbe effectively controlled in Yellowstone Lake (B).

short term (Fig. 2A) or the long term (Fig. 2C).Most concluded otherwise, however, andjudged that protection of a robust population ofcutthroat trout may require aggressive action onthe part of NPS managers to suppress lake trout.

Suppression of the lake trout population wasjudged possible, and the cutthroat troutpopulation remaining within 100 years may be 2to 4 times as large as is likely if the lake trout arenot suppressed.

POSSIBLE CONTROL METHODS

The following methods for suppressing the laketrout population were identified by the team orwere otherwise brought to its attention. Optionsthat received no more than a 0.5 chance ofsuccess by half or more of the team members aredescribed first. Methods judged likely to bemore effective are described second.

Status Quo AnglingPresent angling regulations include killing anycaptured lake trout and reporting the catch topark authorities. Most team members judgedthat the present sport fishery of Yellowstone

A

B

Probability of Success


Freq

uenc

yFr

eque

ncy

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

6 —

4 —

2 —

0 —

6 —

4 —

2 —

0 —

— — — — — — — — — — —

— — — — — — — — — — —


Review and Assessment of Possibilities30

Lake had less than a 50% chance of effectivelylimiting the lake trout population. The presentopen season, no-limit regulations for lake troutwill continue to raise public awareness andprovide an additional monitoring tool.

Killing Lake Trout EmbryosThis proposal included covering spawningareas with polyethylene sheeting, or withscreens to collect and subsequently destroyspawn, killing developing embryos withtoxicants or smothering (e.g., sand), use ofmechanical removal methods (e.g., suctiondredge), or use of concussion to destroyembryos. Locating and covering all of thepotential spawning areas did not seem to be aviable strategy for Yellowstone Lake. Themajority of the team judged there to be less thana 30% chance that any of these alternatives is aviable method for suppressing lake trout inYellowstone Lake.

Provide Cover for Juvenile Cutthroat TroutThe proposal was to construct artificial cover

near the outlet of major spawning tributaries toprotect cutthroat trout fry as they enter the lake.None of the participants judged this tool ashaving a chance for success of even 20%. Theadditional cover was thought to be as likely toprovide cover for waiting predators, includinglake trout, as well as for migrating cutthroattrout fry.

Release Sterile Sea Lampreysin Yellowstone LakeDiscussion of this proposal included anacknowledgment that there is no source ofsterile sea lamprey. Further, there is concernthat use of such a tool cannot be applied withoutcausing additional risk to cutthroat trout andother endemic species. No participant gave thisproposal more than a 10% chance for successfulcontrol of lake trout at the present time.

Attract Lake Trout to Sound or ChemicalsExperimental evidence exists that fish can beattracted to sound and to chemicals (includingpheromones), captured, and removed. Given

Fig. 2. Frequency distributions of estimates of reduction of cutthroat trout inYellowstone Lake within 20 years if lake trout are not suppressed (A), within20 years if lake trout are suppressed (B), within 100 years if lake trout arenot suppressed (C), and within 100 years if lake trout are suppressed (D).


the absence of evidence that large numbers oflake trout could be attracted from substantialdistances, the team judged that there was nomore than a 30% chance of success with soundor chemical attractants.

Trap-netMore than half the team members judged the useof trap-nets to have at least a 40% chance ofsuccessfully suppressing the lake trout popula-tion. The main disadvantage of the method ishigh expense of operation.

Long-line FishingNine participants judged that long-line fisherieswould have only between 10 and 30% chance ofsuccess in controlling lake trout abundance.One participant judged long-line fishing to havea 60% chance for success. Disadvantages of themethod include the need for use of cut-baits, andthis technique is more labor intensive thannetting and trapping techniques.

Use of Divers or RemotelyOperated Vehicles to Kill Lake TroutThese methods offer little hope for success inkilling large numbers of lake trout. Norespondent judged that even a 30% chance forsuccess exists.

Supplementation ofCutthroat Trout PopulationIncreasing the number of cutthroat trout inYellowstone Lake by stocking hatchery-rearedcutthroat trout was viewed as only contributingto an even greater food supply for lake trout. Norespondent judged supplementation to havemore than a 20% chance of reducing theperceived risk to the cutthroat trout populationin Yellowstone Lake.

Stocking “Buffer Species”The general conclusion was that the effects ofadding new species to the lake community weretoo unpredictable. Most team members judged

this proposition to have only a 10% chance ofsuccessfully diverting the lake trout’s dietaryhabits and reducing risk for cutthroat trout.

Use of Chemical ToxicantsThere was no support for use of chemicaltreatment of Yellowstone Lake to eliminate thelake trout. Disadvantages include the non-selectivity of potential chemicals and theinfeasibility of treating such a large lake.

Use of “Judas Fish”The proposal was to obtain and sterilize malelake trout from Lewis Lake. These males wouldthen be fitted with radio or ultrasonictransmitters and released in Yellowstone Lakewhere they would help to locate the spawninggrounds. The team judged that such venturesmight be useful but should begin with fishcaptured from Yellowstone Lake.

Use of Sterile Male Lake TroutThe proposal was to stock large numbers ofsterile males according to protocols developedfor insect pest control. The ensuing discussiongenerally discounted the proposal because theneeded technology for fish has not beendeveloped.

The following methods were judged to have atleast a 50% chance of being successful inreducing lake trout abundance by more than halfof the respondents.

Directed Angling (Fig. 3A)This option included use of anglers experiencedin catching lake trout. Cut bait, echo location,ice fishing, and other approaches known to beeffective in catching lake trout would be used.

Lake-wide Gillgetting (Fig. 3B)Commercial fisheries in the Great Lakes caneffectively harvest and depress targeted stocksof lake trout. Locations and movements of laketrout tend to be predictable, thus making the fish

Review and Assessment of Possibilities32

vulnerable to such fishing. Removal of largefish is an effective means of limiting lake troutreproduction because they do not mature untilattaining a body length of 15 to 18 inches. Netfisheries should be able to avoid cutthroat troutfor the most part by fishing when lake trout andcutthroat trout are separated by depth, andwhere together, by targeting lake trout that arelarger than cutthroat trout.

Capture on Spawning Grounds (Fig. 3C)This method includes location of lake troutspawning grounds through use of radio orultrasonic tagging, and use of intensive nettingor other techniques to capture or destroy thecongregated fish.

ConclusionsBased on these results, the team concluded thatuse of mechanical removal methods, eithergillnetting or some combination of gillnettingand trapping is likely to provide the greatestsuccess in controlling lake trout abundance.Initial control measures can be initiated in 1995field season along with an experimentalgillnetting program for obtaining the informa-

tion needed to improve the effectiveness of theprogram. Adaptive management strategies toincorporate new information and understandingon a continuing basis. Some of the reviewedmethods or other ideas may become useful inthe future, either by themselves or incombination with other methods.

Control of the lake trout population is likely torequire a perpetual effort. In the short term, thelake trout population is expected to continueexpanding limited by the effectiveness of thecontrol effort. In the long term, the lake troutpopulation presumably will tend to stabilize at alevel also dictated by the effectiveness of thecontrol program. The effort (including costsand other resources) needed to control the laketrout population at that level can then beestimated. A carefully developed and managedlake trout control program can provide theinformation needed to evaluate its success.

INFORMATION NEEDS

The team concluded that most informationneeded to implement an effective program canbe obtained by initiating an aggressive

Fig. 3. Frequency distributions of estimated probabilities that directed angling(A), lake-wide gillnetting (B), and removal of adults on spawning areas (C)can provide effective control of lake trout.

A


Freq

uenc

y

3 —

2 —

1 —

0 —

— — — — — — — — — — — —

Freq

uenc

y

Freq

uenc

y

3 —

2 —

1 —

0 —

3 —

2 —

1 —

0 —

— — — — — — — — — — — —

— — — — — — — — — — — —

Probability of Success0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1


B

C


experimental gillnetting program for lake troutand refining the existing monitoring programfor cutthroat trout. Elaborate and expensivenew program elements are not needed over andabove the gillnetting program. Primaryinformation needs are data to assess the status(abundance indices and distribution in spaceand time) of the lake trout and to monitorimpacts on Yellowstone cutthroat trout.Accurate information to assess abundancetrends of cutthroat trout is most important.Present gill-netting, creel census, and censusmethods in spawning streams need to be refinedto enable cohort and catch-curve analyses.Extensive surveys of spawning streams com-bined with intensive investigation of threespawning streams in separate locations aroundthe lake would help to improve the presentdatabase. Information needed to monitor laketrout abundance and to develop their populationdynamics (age-determination, mortality, re-cruitment, spawning dynamics, diet) andgrowth rates was considered the next mostimportant task.

Appropriate locations and time periods for themost effective removal of lake trout withoutfurther harming cutthroat trout are unknowns.Accordingly, adaptive management must beseen as an integral component of the lake troutcontrol program.

Depth distribution may be the most appropriatecriterion for separating cutthroat trout and laketrout because considerable overlap in their sizedistributions is expected in Yellowstone Lake.Almost no cutthroat trout are found at depthsgreater than 30 m, and lake trout may preferdepths near 40-60 m. These criteria can be usedto begin a control program, and target depthscan be verified from netting, tagging, and radiotracking. Captured lake trout might be fittedwith radio tags to facilitate locating thespawning grounds. As information comes

available to show the most effective sizes,locations, and seasons for use of nets, anincreasingly aggressive program can bedeveloped to control lake trout abundance.

Additional information to assess the source andreproductive success of the lake trout inYellowstone Lake, to describe the geneticstructure of the cutthroat trout metapopulation,and to partition sources of cutthroat troutmortality were also identified as important forunderstanding the dynamics of the system, butnot as critical to the immediate need as theinformation described earlier.

SUMMARY

1. Although there is a slight chance that laketrout will not threaten the Yellowstone Lakecutthroat trout, chances are high that lake troutcannot be eliminated and will seriously reducethe cutthroat trout population in YellowstoneLake.

2. The probability that lake trout abundance canbe limited by initiating an aggressive controlprogram using mechanical means of removal ishigh, but there is little chance that lake trout canbe eliminated. Consequently, a long-termcommitment is required to maintain control laketrout abundance.

3. The cutthroat trout population is likely to bereduced whether or not the lake trout aresuppressed, but suppression of lake trout mayreduce the expected loss of cutthroat trout by50% or more.

4. Most information needed to increase theeffectiveness of initial control measures can beobtained from the control program itself. Somemodification of the present monitoring programis required to enable detection of changes in thecutthroat trout population.

INTRODUCTION

In the absence of complete knowledge of thebehavior and habits of lake trout in YellowstoneLake, we intend to develop a program forlimiting their expansion based on availableknowledge coupled with careful monitoring andapplication of adaptive management strategies.Control will begin by gillnetting at depthswhere cutthroat trout do not occur, andsecondarily by experimental gillnetting de-signed primarily to gain information on laketrout distribution in space and time. Monitoringprovides the basis for assessing the success orfailure of alternative management actions andprovides the basis for making real-timeadjustments needed to help reduce deleteriouseffects in the cutthroat trout population.

Our long-term goal is to develop and maintain aprogram for controlling lake trout abundancethat will limit the loss of cutthroat trout to lessthan 20% of present levels. Proposed levels ofeffort may be initially too conservative orexcessive, but rigorous application of adaptivemanagement will enable us to make appropriateadjustments as the program develops insubsequent years.

We identify the fact that additional resources areneeded if our present fishery program is toremain intact. We have, however, elevated theperceived crises caused by the lake trout to ourmost important problem for fishery investiga-tions. If we cannot successfully secure theadditional funding required for this effort, wewill redirect existing resources for aquaticecosystem work to the following program.

A DRAFT PLAN OF ACTION FOR CONTROLLING

EXPANSION OF THE LAKE TROUT POPULATION

IN YELLOWSTONE LAKE

BY TOM OLLIFF

1995 OBJECTIVES

1. We will attempt to secure $50,000 of newfunding to finance the 1995 experimentalprogram.

2. We will take action to secure a permanentaddition of $300,000/year to base funding forthe fishery program to maintain the controlprogram.

3. Present monitoring efforts for cutthroat troutwere designed only to detect long-term changesin the population and must be supplemented toattain the desired result. The cutthroat troutpopulation needs to be monitored at a level ofrigor that will provide the statistical sensitivityneeded to detect changes in abundance in atimely manner. Consequently, we will expandspawning ground surveys to all importantspawning streams, and increase the intensivemonitoring presently conducted only at ClearCreek to three runs by including two additionaltributaries.

4. We want to prevent existing lake trout fromattaining spawning size. We will accordinglymove aggressively to remove as many lake troutfrom deep water as time and personnel permit.

5. We will develop a suitable index formonitoring lake trout abundance in Yellow-stone Lake. Data from Objectives (4) and (6)will help to attain this objective.

6. We will improve our effectiveness inremoving lake trout. This objective requiresthat we develop an understanding of lake trout


OBJECTIVES FOR 19971. We will maintain an expanded spawningground survey on all important spawningstreams, and intensively monitor runs in threeimportant tributaries.

2. We will continue efforts to prevent as manylake trout as we can from attaining spawningsize by gillnetting in deep water and otherlocations where it is shown from work in 1995Objective (5) and 1996 Objective (4) that laketrout can be captured without harming cutthroattrout. We will continue to develop a suitableindex for monitoring lake trout abundance inYellowstone Lake.

3. We will continue to improve our effective-ness in removing lake trout via an experimentalgill-netting program designed to assess whereand when lake trout can be effectively capturedwithout harming cutthroat trout. The objectiveincludes description of lake trout age-structure,mortality, recruitment, and behavior.

4. To the extent that by 1997 adaptivemanagement has enabled us to redirectresources and personnel to some additionalendeavors, we will initiate studies to locatespawning locations and to assess spawningsuccess for lake trout, to describe the structureof the cutthroat trout metapopulation, and topartition the sources of mortality for cutthroattrout.

population dynamics. An experimental gill-netting program will be initiated to begin anassessment of where and when lake trout can beeffectively captured without harming cutthroattrout. We will use the data obtained here and in(4) to describe age-structure, mortality, recruit-ment, and behavior of lake trout.

OBJECTIVES FOR 19961. We will attempt to secure permanent funds(estimated at $300,000/year) added to our basefunding to maintain the control program.

2. We will maintain an expanded spawningground survey on all important spawningstreams, and intensively monitor runs in threeimportant tributaries.

3. We will continue preventing as many laketrout as we can from attaining spawning size bygillnetting in deep water and other locationswhere it is shown from work in 1995 Objective(5) that lake trout can be captured withoutharming cutthroat trout. We will continue workand analysis to develop a suitable index formonitoring lake trout abundance in Yellow-stone Lake.

4. We will continue to improve our effective-ness in removing lake trout via an experimentalgill-netting program designed to assess whereand when lake trout can be effectively capturedwithout harming cutthroat trout. The objectiveincludes description of lake trout age-structure,mortality, recruitment, and behavior.

36

AUTHORS

Glenn D. Boltz, U.S. Fish and Wildlife Service,Yellowstone Fishery Assistance Office, P.O.Box 184, Yellowstone National Park, WY82190

Daniel G. Carty, U.S. Fish and Wildlife Service,Yellowstone Fishery Assistance Office, P.O.Box 184, Yellowstone National Park, WY82190

Lynn R. Kaeding, U.S. Fish and Wildlife Ser-vice, Yellowstone Fishery Assistance Office,P.O. Box 184, Yellowstone National Park, WY82190

John D. McIntyre, U.S. Forest Service (retired)P.O. Box 1651 Boise, Idaho 83701

Tom Olliff, National Park Service, Division ofResource Management and Visitor Protection,P.O. Box 168, Yellowstone National Park, WY82190

Paul Schullery, National Park Service, Yellow-stone Center for Resources, P.O. Box 168, Yel-lowstone National Park, WY 82190

John D. Varley, National Park Service, Yellow-stone Center for Resources, P.O. Box 168, Yel-lowstone National Park, WY 82190

WORKSHOP PARTICIPANTS OR ATTENDEES

Workshop MembersBob Behnke, Department of Fish and Wildlife

Biology, Colorado State University, FortCollins, Colorado 80523 (participated throughe-mail).

Fred Binkowski, Center for Great Lakes Stud-ies, 600 East Greenfield Ave, University ofWisconsin, Milwaukee, Wisconsin 53204

Ted Bjornn, National Biological Service, IdahoCooperative Fish and Wildlife Research Unit,University of Idaho, Moscow, Idaho 83844-1136

Jon Erikson, Wyoming Game and Fish Depart-ment (retired), P. O. Box 1054 Jackson, Wyo-ming 83001

Bob Gresswell, U.S. Forest Service, PacificNorthwest Forest Sciences Lab, 3200Jefferson Way, Corvallis, Oregon 97331

Mike Healey, West Water Research Center, Uni-versity of British Columbia 1933 West Mall,Vancouver, British Columbia Canada V6T 1Z2

Leo Marnell, National Biological Service, Gla-cier Field Unit, West Glacier, Montana 59936

John D. McIntyre, U.S. Forest Service (retired)P.O. Box 1651 Boise, Idaho 83701

Bruce Reiman, U.S. Forest Service, Boise For-est Sciences Lab, 316 E. Myrtle Street, Boise,Idaho 83702

Reg Reisenbichler, National Biological ServiceLaboratory, Building 204, Naval Station, Se-attle Washington 98115

James Selgeby, National Biological Service,Ashland Field Station, Route 1 Box 24, IronRiver, Wisconsin 54847

Jim Vashro, Montana Department Fish, Wildlifeand Parks, Kalispell, Montana 59901

USFWS Fisheries Assistance Office,YellowstoneLynn Kaeding, Project LeaderDan Carty, Fishery BiologistDan Mahoney, Fishery BiologistGlenn Boltz, Fishery Biologist

National Park Service, YellowstoneJohn Varley, Director, Yellowstone Center for

ResourcesSue Consolo Murphy, Resource Management

SpecialistDan Reinhart, Resource Management Coordina-

torLauryl Mack, Secretary

the yellowstone lake crisis: confronting a lake trout invasion › yell › planyourvisit › upload...

Documents