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 in

part by generous grants from the Trout

and Salmon Foundation, the Montana

Trout Foundation, along with additional

individual donations to the Yellowstone

Fishery Fund.
The Yellowstone Lake Crisis:

Confronting a Lake Trout Invasion

A Report to the Director of the

National Park Service

Edited by John D. Varley and Paul Schullery

Yellowstone Center for Resources

National Park Service, Yellowstone National Park, Wyoming

1995
ACKNOWLEDGMENTS

Many people assisted in the preparation of this

report. We are especially grateful to Jack

McIntyre for his assistance and guidance with

many aspects of the material published here, as

well as for his masterful direction of the lake

trout workshop, whose results are summarized

beginning on page 28. Yellowstone Park Superintendent Michael Finley's recognition of the

magnitude of this crisis and his support of the

production of a report of this scope were likewise essential.

The workshop's arrangements and logistics were

managed by Lauryl Mack, NPS. Additional

workshop support was provided by the U.S. Fish

and Wildlife Service Fishery Assistance Office

in Yellowstone, under the Leadership of Lynn

Kaeding, the NPS Yellowstone Center for Resources staff, especially Sue Consolo Murphy

and Stu Coleman, and NPS Resource Management Operations Coordinator Tom Olliff and Resource Management Coordinator Dan Reinhart.

The report by Kaeding et al., beginning on page

4, appears through special arrangement with the

authors, as it is also being published in the

American Fisheries Society journal Fisheries.

Renee Evanoff, NPS, designed the cover, Sarah

Broadbent, NPS, designed the rest of the report.

Additional editorial and other support was provided by Carrie Gray and Lauryl Mack.

More generally, we thank the many other people

who have given their time generously to help

with this crisis: anglers, rangers, fishing guides,

ecologists, fisheries managers, and many members of the public who have shown a special

concern over this situation and have gone out of

their way to volunteer information and support.

Publication of this report was made possible by

a grant from the Montana Trout Foundation.

Additional funds were provided by many individual donations to the Yellowstone Fishery

Fund 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 ................................................................................. 4

by 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 .................................................................... 12

by Paul Schullery and John D. Varley

Socioeconomic Values Associated with the Yellowstone Lake Cutthroat Trout ....................................... 22

by John D. Varley and Paul Schullery

Review and Assessment of Possibilities for Protecting the Cutthroat Trout ........................................... 28

of Yellowstone Lake From Introduced Lake Trout

Proceedings of a workshop and information exchange held in

Gardiner, Montana, February 15-17, 1995

by John D. McIntyre, Workshop Leader

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

by Tom Olliff

Authors and Workshop Participants .......................................................................................... 36
Yellowstone Lake is home of the premier

surviving inland cutthroat trout fishery in North

America. This fishery is threatened with

destruction by illegally introduced lake trout,

which were discovered in 1994. The lake trout

are known to exist in at least four and possibly as

many as six age groups, proof of a relatively

small but reproducing population (Fig. 1). The

older age groups are now able to reproduce, and

the lake trout population will almost certainly

grow rapidly.

The discovery of these non-native lake trout in

Yellowstone Lake caused great alarm among

fisheries biologists throughout the greater

Yellowstone area because of the lake trout’s

reputation for displacing species such as

cutthroat trout in other western lakes. Park

administrators sought to verify the “doomsday”

opinion of local biologists by arranging an

assessment of the situation by United States and

Canadian specialists in population dynamics

and lake trout biology. The experts convened an

information-sharing workshop in February

1995, and concluded that the lake trout

population in Yellowstone Lake is likely to

expand and cause precipitous decline in the

cutthroat trout population. The majority view

was that the cutthroat trout are likely to decline

to 10-20% of present abundance. These

percentages translate to a decline from an

estimated 2.5 million trout of catchable size at

present to 250,000-500,000 at some time in the

foreseeable future.

Except for its strongholds in the upper

Yellowstone River area, the Yellowstone

cutthroat trout is imperiled. Human activities

have already reduced its range to 15% of its

historic distribution. The appearance of lake

trout in Yellowstone Lake has ominous

THE LAKE YELLOWSTONE TROUT CRISIS

EXECUTIVE SUMMARY

Fig. 1. Three age classes of lake trout captured at various

times in Yellowstone Lake in 1994, indicating ongoing

reproduction in the introduced lake trout population. U.S.

Fish and Wildlife Service photo.

implications for the continued viability of the

Yellowstone cutthroat trout as a subspecies.

The predicted decline of Yellowstone cutthroat

trout will destroy the world-famous fisheries in

the lake and its tributaries, including the storied

fishery in the Yellowstone River between the

lake and the Upper Falls; this latter fishery

gained international prominence in the 1970s as

the site of pioneering advances in catch-andrelease fishing, and remains one of the world's

premier destinations for trout fishermen. For

nearly 150 years, the lake itself has developed

its own superlative reputation as a “trout

catchery.” Though a lake trout fishery will

evolve in the lake consonant with the cutthroat

decline, it will be a highly specialized fishery of

interest only to a comparatively few anglers and

will not occur at all on the rivers and streams.

The replacement fishery will in no respect

(ecologically, economically, or socially) replace the fisheries it destroys.

The cutthroat trout decline will also cause

severe disruption in the food supply for two
species listed under the Endangered Species

Act—the threatened grizzly bear and the

endangered bald eagle—and will likewise

affect many species of special concern,

including the white pelican, otter, black bear,

mink, osprey, and loon; an estimated 42 species

of mammals and birds in all. Grizzly bear, white

pelican, and osprey abundance at Yellowstone

Lake, and perhaps other species as well, are all

correlated with the abundance of Yellowstone

Lake cutthroat trout. Because of pronounced

differences in the habits and habitat uses of lake

trout and cutthroat trout, the lake trout will not

serve as a replacement food source for these

affected species of mammals and birds.

In reviewing current fishery technologies,

workshop participants concluded that there is

little prospect that the lake trout can be

eradicated from Yellowstone Lake. However,

scientists from the Great Lakes region offered

some hope that expansion of the lake trout

population might be contained through an

aggressive gill-netting program such as those

used by commercial fishing operations in the

Great Lakes. Following that lead, personnel

from the National Park Service and the U.S.

Fish and Wildlife Service’s Fishery Assistance

Office at the park developed an action plan to

initiate a control program. The program’s

effectiveness depends on an understanding of

where the lake trout populations are located in

each season so that they can be netted without

harming the cutthroat trout population.

Initial efforts will proceed based on knowledge

that in the summer the lake trout generally

inhabit deeper waters than do cutthroat trout.

As understanding of the location and movements of both species is refined, program

effectiveness will be increased. An important

first step is to import Great Lakes technology as

well as to obtain the additional financial

resources and personnel needed to implement

and maintain these emergency measures. There

was a consensus view among the workshop

biologists that only an aggressive lake trout

control program would protect the cutthroat

population and thus the ecological character of

the entire Yellowstone Lake basin.

While the potential ecological losses are

staggering, the potential economic losses can be

summarized as equally immense. The 1994

value of the Yellowstone fisheries above the

great falls, including the lake and its tributaries,

is estimated at slightly more than $36 million.

The cumulative 30-year value of the cutthroat

trout sport fishery, assuming lake trout were

absent, is estimated at more than a billion

dollars ($1,080,000,000). Assuming lake trout

are vigorously controlled, the consonant value

declines to $685 million. If lake trout are not

controlled, the value declines to $439,950,000.

The last value represents a three-decade

economic loss of $640 million, which can be

considered the net economic effect of the illegal

lake trout introduction if no actions are taken to

control the species.

With lake trout control, at an estimated program

cost of $9 million over 30 years, the effects of

lake trout on the cutthroat trout population have

a high probability of being ameliorated. The

benefit-to-cost ratio for the lake trout control

program is a favorable 27:1.

If the effects of lake trout on cutthroat trout are

greater than projected by the experts, and the

Yellowstone cutthroat trout becomes rare or

nearly extinct, the cost of the destruction of all

fish life in the lake and its tributaries (the startfrom-scratch alternative for restoring the native

fishery), and the subsequent reestablishment of

the cutthroat trout population to its former

condition is estimated to be $32-181 million.

The Yellowstone Lake Crisis 3
Abstract: On July 30, 1994, lake trout

(Salvelinus namaycush) were discovered in

Yellowstone Lake, Yellowstone National

Park, Wyoming, the core of the remaining

undisturbed, natural habitat for the native

Yellowstone cutthroat trout (Oncorhynchus

clarki bouvieri). Data from this and other lake

trout caught subsequently by anglers and the

U.S. Fish and Wildlife Service suggest lake

trout have reproduced in Yellowstone Lake

since at least 1989 and now number in the

thousands, perhaps tens of thousands. A highly

piscivorous, nonnative species, lake trout will

probably thrive in Yellowstone Lake and

reduce the lake’s cutthroat trout stocks

substantially unless preventive management

actions are taken.

Yellowstone Lake, Yellowstone National

Park, Wyoming, is the core of the remaining

undisturbed, natural habitat for the native

Yellowstone cutthroat trout (Oncorhynchus

clarki bouvieri) (Varley and Gresswell 1988).

During the past two decades in particular,

fishery managers have used angling regulations

to greatly reduce angler harvest, considered a

principal human threat to the cutthroat trout

stocks of Yellowstone Lake (Gresswell and

Varley 1988). As a result, the stocks have

recovered markedly from past overharvest and,

to many managers, appeared safe from adverse

human activities (Jones et al. 1993).

The perception of Yellowstone Lake as a

secure refuge for Yellowstone cutthroat trout

changed abruptly on July 30, 1994, when a lake

trout (Salvelinus namaycush) was caught from

the 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 Service

rangers. The angler and guide were

interviewed, and the fish, 43 cm long, was

given to park authorities. On August 5, a

second lake trout (42 cm long) was caught

under similar circumstances and given to park

authorities.

A National Park Service press release dated

August 11, 1994, described the discovery of

lake trout in Yellowstone Lake; outlined

ecological consequences that could result from

establishment of this highly piscivorous,

nonnative fish species; and offered a reward for

information leading to the arrest and conviction

of the person or persons responsible for

illegally stocking the fish. Human culpability

was assumed because natural movement of lake

trout into Yellowstone Lake from other park

waters in which they are found was not

possible.

Extensive media coverage of the issue resulted

in additional reports to the U.S. Fish and

Wildlife Service (FWS) (technical advisors to

the National Park Service) of lake trout

captures from Yellowstone Lake. Two

experienced anglers reported the capture on

August 15, 1994, of three “roughly [46 cm] 18-

inch” lake trout from Yellowstone Lake.

Because the anglers believed the odor of fish

might attract bears to their backcountry

campsite, the putative lake trout were killed

and returned to the lake. On August 20, a park

visitor gave park authorities a photograph of

herself holding a lake trout 43 cm long that she

had caught from the lake July 21, 1994, and

subsequently 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 was

caught and kept by one of his clients in 1993.

Two park employees, both experienced

anglers, reported that they caught and returned

to the lake a lake trout in the mid-1980s.

Although the evidence in late August 1994

indicated that lake trout were present in

Yellowstone Lake, the origin of the lake trout

population was not clear. Some people

speculated that the lake trout caught by anglers

in 1994 were part of a small group of fish

illegally stocked into the lake as fingerlings

only a few years earlier. Remarkably, a

scenario similar to this was described in a

fictional magazine article (Parks 1991) that had

been brought to the attention of park

authorities. Alternatively, it was possible that

the lake trout caught by anglers had been

produced in the lake from a founding parent

stock that had been present there for many

years.

In late August 1994 the FWS developed a plan

of action that had as its goal the elimination of

lake trout from Yellowstone Lake. This goal is

consistent with National Park Service policy

(NPS 1988) that directs the removal of

nonnative organisms from the park when

feasible, especially when they present threats to

native organisms. Objectives of the plan were

to (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 report

describes and interprets the data collected

under Objectives 1 and 2.

YELLOWSTONE LAKE

AND CUTTHROAT TROUT

Yellowstone Lake lies 2,356 m above mean sea

level in east-central Yellowstone National

Park. The lake has a surface area of 341␣km ̋,

shoreline length of 239 km, mean depth of

48.5 m, and maximum depth of 107 m. A

thermocline forms in July and may persist in

mid-September at a depth of 10-20 m. The

hypolimnion remains well-oxygenated during

stratification. Phytoplankton standing crops

are low and generally dominated by diatoms.

Summer surface temperatures rarely exceed

18°C, and ice covers the lake from midDecember through May or early June (Benson

1961, Knight 1975, Kaplinski 1991).

Yellowstone cutthroat trout and longnose dace

(Rhinichthys cataractae) are the native fishes of

Yellowstone Lake, whereas longnose sucker

(Catostomus catostomus), redside shiner

(Richardsonius balteatus), and lake chub

(Couesius plumbeus) are established, nonnative species. The minnow species inhabit only

warm, vegetated bays and other littoral areas;

cutthroat trout and longnose sucker are found

throughout the lake (Benson 1961).

Yellowstone cutthroat trout are obligate stream

spawners (Varley and Gresswell 1988).

Approximately half of the lake’s 126 tributaries

are known to be used for spawning by cutthroat

trout from Yellowstone Lake. Cutthroat trout

in Yellowstone Lake provide the most popular

sportfishery in Yellowstone National Park

(Jones et al. 1993), as well as food for grizzly

bears, osprey, white pelicans, river otters, and

other animals (Davenport 1974, Swenson

1978, Reinhart and Mattson 1990).

PROCEDURES

Characterizing the Lake Trout Population

Gill nets, set perpendicular to the lake shore in

relatively shallow water in mid-September,

have been used for more than two decades to

monitor trends in cutthroat trout and longnose

sucker populations in Yellowstone Lake (Jones

et al. 1993). That traditional monitoring

program continued in 1994, and its techniques

were also generally used in the search for lake

trout in deeper water during the remainder of

the field season.

The Yellowstone Lake Crisis 5
6 Lake Trout Discovered

Gill nets used routinely are 38 m long, 1.8 m

deep, and have five 7.6-m panels of 19, 25, 32,

38, and 51 mm mesh (bar measure)

monofilament netting. For subsequent

deepwater gill netting, these nets and others

similar in construction but twice as long (i.e.,

two “monitoring” nets attached end-to-end)

were used. Gill nets were set during the day

and retrieved the next morning. Captured fish

were measured to total length and weighed.

Captured lake trout (and those provided by

anglers) were frozen and retained for agegrowth, sexual maturation, and other analyses.

Angling was also used in attempts to capture

lake trout. Downriggers were used to troll a

variety of lures at depths shown by sonar to be

occupied by fish. Shallow trolling often

accompanied deep trolling with downriggers.

Most of the angling effort was expended in lake

regions from which recreational anglers had

captured lake trout.

Locating Potential Lake

Trout Spawning Areas

Visual observation of substrates was used to

locate potential lake trout spawning areas.

Observers in a boat moving slowly along the

lake shoreline, in water 2-7 m deep, recorded

substrate characteristics on topographic maps.

RESULTS

Gillnetting

Altogether, 1,368 Yellowstone cutthroat trout,

630 longnose suckers, and 2 lake trout were

caught in gill nets set in many regions of

Yellowstone Lake (Fig. 1). Catch rates for

cutthroat trout and longnose suckers were

highest in shallow water and declined with

increasing depth (Table 1). Few longnose

suckers were found in water deeper than 30.5

m. Lake trout were caught in nets that had their

shallow end in water about 36.6 m deep.

Range in lengths of individual cutthroat trout

Fig. 1. Locations of traditional gillnet sets (dots) and

deepwater gillnet sets (ovals), and capture locations for

lake 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 in

waters 15.2-30.5 m deep (Fig. 2). Ranges in

lengths were similar for longnose suckers

caught in waters 0-15.2 m and 15.3-30.5 m

deep (Fig. 3). The lake trout caught in gill nets

were 20 and 32 cm long.

Angling

Twenty Yellowstone cutthroat trout (32 -53 cm

long) were caught by angling. Of these, seven

were 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 many

as four lures were fished simultaneously during

the 59 hours spent fishing between September

7 and October 5, 1994.

Analyses of Individual Lake Trout

Analyses of scales revealed that the two lake

trout (43 and 42 cm long) caught by the guided

anglers were five years old, whereas the two
The Yellowstone Lake Crisis 7

Fig. 2. Length-frequency distributions for Yellowstone

cutthroat trout caught in gill nets set in three ranges of

water depth. Water depth is based on the depth of the

shallow end of the gill net.

lake trout (32 and 20 cm long) caught in gill

nets were four and two years old. The fish

therefore were of the 1989, 1990, and 1992

year-classes, respectively (C. R. Bronte,

National Biological Service, Ashland, Wis.,

pers. commun.).

Analyses of gonadal tissue from the two large

lake trout revealed that both fish were male.

However, opinions on stage of reproductive

maturity differed between the two analysts who

examined the histological preparations. Beth

MacConnell (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-stage

spermatogenesis in both specimens. (The

tissue preparations had been considerably

distorted by freezing and thawing that occurred

before tissue fixation.) Kaya also pointed out

that brook trout (Salvelinus fontinalis) at a

similar stage of gonadal development in June

can spawn in October (Henderson 1962).

Potential Spawning Habitat

Visual observation revealed that cobble,

rubble, or boulder substrates occur in many

areas 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-long

gill 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 anglers

in 1994 were approximately 43 cm long and

might have been of one year-class produced in
8 Lake Trout Discovered

1989. If so, these fish recruited into the

sportfishery at age 5, the minimum age of

maturity in wild lake trout (Healey 1978).

Whether the 1989 year-class embodies the first

natural reproduction of lake trout in

Yellowstone Lake is unknown. The presence

of these fish and additional, younger lake trout

suggests that lake trout have reproduced

annually in Yellowstone Lake since at least

1989.

On the basis of a mark-recapture (in gill nets)

experiment that included more than 49,000

marked, adult cutthroat trout, and extrapolation of areal densities of fish caught in purse

seines set at many locations around the lake,

Jones et al. (1980) concluded conservatively

that there were 1-4 million catchable cutthroat

trout (>35 cm long) in Yellowstone Lake in

Fig. 3. Length-frequency distributions for longnose

suckers caught in gill nets set in three ranges of water

depth. Water depth is based on the depth of the shallow

end 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 trout

would be much larger, perhaps by a factor of

three or more. If cutthroat trout are equally

abundant today, and they and lake trout are

similar in their vulnerability to capture in gill

nets, the approximate 1000:1 ratio of these fish

in our gillnet catch suggests that lake trout

number in the thousands, perhaps tens of

thousands, in Yellowstone Lake.

Such numbers of lake trout are too large to be

explained hypothetically by an introduction of

fingerling lake trout a few years ago. Instead,

large numbers and multiple year-classes of lake

trout indicate reproduction in Yellowstone

Lake. When the founding stock of parent lake

trout began to reproduce is unknown, as is the

reproductive history of their progeny. Lake

trout in Yellowstone Lake were unknown to

park authorities prior to 1994 because the

population of catchable-size lake trout was

much smaller, the few anglers who caught lake

trout did not bring the fish or other substantial

evidence to park authorities, and traditional

monitoring programs were designed to sample
The Yellowstone Lake Crisis 9

cutthroat trout in shallow water in early fall

(when lake trout are likely to be in deep water

because the lake has not yet undergone

temperature destratification).

Lake trout are capable of rapid population

increase (Curtis 1990) and are likely to thrive in

Yellowstone Lake unless preventive management actions are taken. Lake temperatures and

water quality are ideal for lake trout, and

substrates ostensibly suitable to lake trout

spawning (areas of cobble and rubble with little

or no fine sediments [Thibodeau and Kelso

1990, Edsall et al. 1992]) occur at many

locations. Reproduction by the 1989 year-class

of lake trout in Yellowstone Lake could rapidly

increase the population.

The extent that the cutthroat trout population of

Yellowstone Lake might be reduced by lake

trout competition or predation is unknown but

potentially substantial. Macroinvertebrate

foods of cutthroat trout and longnose sucker

(Benson 1961, Benson and Bulkley 1963) also

are eaten by young lake trout (Elrod 1983,

Elrod and O’Gorman 1991), and cutthroat trout

and longnose suckers themselves would be

food for juvenile and adult lake trout.

Individual lake trout in Yellowstone Lake grow

slowly, similar to lake trout in nearby (10

highway km) Lewis Lake, where the species

was introduced officially in 1890, and an

abundant population has developed (Jones et al.

1983). This suggests that competition for food

already occurs among lake trout and other fish

species in Yellowstone Lake.

Predation on cutthroat trout by lake trout might

become especially significant in Yellowstone

Lake because, as our data suggest, many

cutthroat trout, including young fish, occupy

deep water, the habitat of lake trout. In

contrast, the other potential prey species,

longnose sucker, occurs primarily in shallow

water.

Introduced lake trout have been implicated in

the extinction of Lahontan cutthroat trout (O. c.

henshawi) in Lake Tahoe (Cordone and Frantz

1966). Benson et al. (1961) stated that

introduced lake trout eliminated native

cutthroat trout in several large, deep lakes in

the Rocky Mountain region but provided no

supportive data. In Heart Lake, Yellowstone

National Park, the native Yellowstone

cutthroat trout may have declined markedly

after lake trout of unknown origin became

established (Dean and Varley 1974). In

Jackson Lake, Wyoming, substantial decline in

the native Yellowstone cutthroat trout

accompanied colonization of the lake by lake

trout (Behnke 1992). Lake trout also have been

shown to eliminate native bull trout (S.

confluentus) in lakes (Donald and Alger 1993).

In Yellowstone Lake, the lake trout is a

potential keystone predator (sensu Paine 1966),

an organism that greatly influences ecosystem

processes as a result of its feeding activity.

Among the ecosystem processes likely to be

affected by lake trout is energy flow from the

aquatic to the terrestrial ecosystem. Today,

this energy transfer includes Yellowstone

cutthroat trout eaten by grizzly bears, white

pelicans, river otters, ospreys, and other

terrestrial animals. Because cutthroat trout

spawn in tributaries and use other shallowwater habitats during other times of the year in

Yellowstone Lake, they are vulnerable to such

predation. In contrast, the habits of lake trout

make them almost entirely unavailable to

terrestrial predators.

ACKNOWLEDGMENTS

D. L. Mahony (FWS), N. Rowe, and

numerous National Park Service personnel

assisted in data collection. We thank R. E.

Gresswell, J. D. McIntyre, and J. D. Varley

for their constructive reviews of a draft of this

report.
10 Lake Trout Discovered

LITERATURE CITED

Behnke, R. J. 1992. Native trout of western

North America. Am. Fish. Soc. Mono.

Benson, N. G. 1961. Limnology of

Yellowstone Lake in relation to the

cutthroat trout. U.S. Fish Wildl. Serv.,

Res. Rep. 56.

_____, J. R. Greeley, M. I. Huish, and J. H.

Kuehn. 1961. Status of management of

natural lakes. Trans. Am. Fish. Soc.

90:218-224.

_____, and R. V. Bulkley. 1963. Equilibrium

yield and management of cutthroat trout in

Yellowstone Lake. U.S. Fish Wildl. Serv.,

Res. Rep. 62.

Cordone, A. J., and T. C. Frantz. 1966. The

Lake Tahoe sport fishery. Calif. Fish

Game 52(4):240-274.

Curtis, G. L. 1990. Recovery of an offshore

lake trout population in eastern Lake

Superior, USA and Canada. J. Gt. Lakes

Res. 16(2):279-287.

Davenport, M. B. 1974. Piscivorous avifauna

on Yellowstone Lake, Yellowstone National Park. Master Sci. Thesis. Montana

State Univ., Bozeman.

Dean, J. L., and J. D. Varley. 1974.

Yellowstone fishery investigations. U.S.

Fish Wildl. Serv., Yellowstone National

Park.

Donald, D. B., and D. J. Alger. 1993.

Geographic distribution, species displacement, and niche overlap for lake trout and

bull 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. Surficial

substrates and bathymetry of five historical

lake trout spawning reefs in nearshore

waters of the Great Lakes. Gt. Lakes Fish.

Comm. Tech. Rep. 58:1-53.

Elrod, J. H. 1983. Seasonal food of juvenile

lake 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 Ontario

in relation to abundance and size of prey

fishes, 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 on

the cutthroat trout of Yellowstone Lake.

Am. Fish. Soc. Sym. 4:45-52.

Healey, M. C. 1978. The dynamics of

exploited lake trout populations and

implications for management. J. Wildl.

Manage. 42(2):307-328.

Henderson, N. E. 1962. The annual cycle in

the 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 program

in Yellowstone National Park. U.S. Fish

Wildl. Serv., Yellowstone National Park.

_____, P. E. Bigelow, R. E. Gresswell, L. D.

Lentsch, and R. A. Valdez. 1983. Fishery

and aquatic management program in

Yellowstone National Park. U.S. Fish

Wildl. Serv., Yellowstone National Park.

_____, Boltz, D. G. Carty, L. R. Kaeding, D.

L. Mahony, and T. Olliff. 1993. Fishery

and aquatic management program in

Yellowstone National Park. U.S. Fish

Wildl. Serv., Yellowstone National Park.

Kaplinski, M. A. 1991. Geomorphology and

geology of Yellowstone Lake, Yellowstone

National Park, Wyoming. Master Sci.

thesis. Northern Ariz. Univ., Flagstaff.

Knight, J. C. 1975. The limnology of the West

Thumb of Yellowstone Lake, Yellowstone

National 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 and

species diversity. Am. Nat. 100(910):65-

75.
The Yellowstone Lake Crisis 11

Parks, G. 1991. Fish story. Grays Sporting

Journal. Summer :64-70.

Reinhart, D. P., and D. J. Mattson. 1990.

Bear use of cutthroat trout spawning

streams in Yellowstone National Park. Int.

Conf. Bear Res. Manage. 8:343-350.

Swenson, J. E. 1978. Prey and foraging

behavior 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 in

Yellowstone Lake. Experimental gillnetting

conducted by the U.S. Fish and Wildlife Service

has yielded several hundred additional lake trout

from 7 inches up to 32 inches (12.5 lbs.)

National Park Service staff received angler

reports of nearly 100 additional lake trout, most

caught by anglers from the lake shore. Most of

these fish were in the 16-19 inch size range, with

several ranging up to 23 inches. Lake trout were

comparatively common along the shore and in

surface waters until the middle of July when they

moved to deep water.

Both the numbers and the distribution of these

lake trout serve to strengthen the prevailing

opinion that the situation is grave and alarming.

It is now clear that there are many lake trout of

a variety of age classes in the lake, and that one

or more age class is capable of spawning. It is

likewise clear that the fish are distributed

throughout the lake, as these fish were caught

in 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 in

the Great Lakes. Can. Tech. Rep. Fish.

Aquat. Sci. 1739:1-20.

Varley, J. D., and R. E. Gresswell. 1988.

Ecology, status, and management of

Yellowstone cutthroat trout. Am. Fish.

Soc. Sym. 4:13-24.
Yellowstone Lake is the last great refuge of the

once widespread Yellowstone cutthroat trout,

Oncorhynchus clarki bouvieri. Though heavily

exploited by recreational and commercial

fishing between 1890 and 1970, recent changes

in fishing regulations have restored robust

numbers and population structure (Gresswell

and Varley 1988). Yellowstone Lake and its

tributaries and outlet stream have become

world-renowned as examples of intensively

used yet healthy fisheries (Varley and Schullery

1983), and the potential effects of an illegally

introduced population of lake trout, Salvelinus

namaycush, therefore causes considerable

anxiety among managers, scientists, and the

public.

All the roles played by cutthroat trout in the

lake’s ecosystem have not been examined, but

many have, and the accumulated information

allows cautious predictions of the consequences

of a collapse of the cutthroat trout population.

For example, we know there are 42 species of

mammals and birds that are known or suspected

of using cutthroat trout for food in the

Yellowstone Lake area (Table 1). These

mammals and birds take all ages of fish, in all

parts of the lake and in the tributary streams.

Their predation on living trout is best known

(e.g., osprey) but the consumption of carcasses

of migratory salmonids, particularly in spawning streams, has been shown to be ecologically

significant (Cederholm et al. 1989). This

consumption, or scavenging, is apparently quite

complex, and may reach quite far into the

terrestrial food chain.

We cannot look into the future and say that any

of these bird or mammal species would

themselves be extirpated as a consequence of

the collapse of cutthroat trout population, but

knowing the importance of the native trout to

these species, we must assume that some of

them would be seriously diminished, if not

imperiled.

Ecologists have noted the extraordinary

precision of resource partitioning among

predators on the Yellowstone Lake cutthroat

trout (Davenport 1974, Varley and Schullery

1983). The many avian and mammalian

predators who depend wholly or in part upon

this resource are surprisingly specialized in the

size of the fish they take, with the result that fish

of all ages are subjected to predation, and are

therefore of importance to some or several

predators. Thus any alteration of the age

structure of the trout population will begin to

have effects on some predators before it affects

others, but eventually, as the trout population

declines, all predators will be affected.

A LAST STRONGHOLD OF YELLOWSTONE

CUTTHROAT TROUT AT RISK

When white settlers first began colonizing the

western United States there were probably 14

subspecies of cutthroat trout (Onchorhynchus

clarki spp.) in various levels of abundance

(Behnke 1979). After several centuries of

civilized “progress,” two subspecies are extinct

and eight of the remaining groups are listed by

the American Fisheries Society (1989) as

endangered, threatened, or of special concern.

In this sad history of neglect and extermination,

the preservation of two subspecies, the coastal

cutthroat trout (O. clarki clarki), and Yellowstone cutthroat trout (O. clarki bouvieri), gave

the 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 trout

as a food source in the Yellowstone Lake drainage.

Species Known Suspected

Mammals:

Water shrew Sorex palustris X

Masked shrew Sorex cinereus X

Dusky shrew Sorex monticolus X

Deer mouse Perimyscus maniculatus X

Red squirrel Tamiasciurus hudsonicus X

Uinta chipmunk Tamias umbrinus X

Flying squirrel Glaucomys sabrinus X

Muskrat Ondatra zibethicus X

Ermine Mustela erminea X

Longtailed weasel Mustela frenata X

Mink Mustela vison X

Marten Martes americana X

Striped skunk Mephitis mephitis X

Otter Lutra canadensis X

Wolverine Gulo gulo X

Badger Taxidea taxus X

Coyote Canis latrans X

Bobcat Lynx rufus X

Cougar Felis concolor X

Black bear Ursus americanus X

Grizzly Bear Ursus horribilus X

Raccoon Procyon sp. X

Birds:

White pelican Pelecanus occidentalis X

Common merganser Mergus merganser X

Blue heron Ardea herodias X

California gull Larus californicus X

Eared grebe Podiceps caspicus X

Loon Gavia immer X

Caspian tern Hydroprogne caspia X

Barrows goldeneye Bucephala islandica X

Bufflehead Bucephala albeola X

Dble. crest. cormorant Phalacrocorax auritus X

Western grebe Aechmophorus occidentalis X

Redtailed hawk Buteo jamaicensus X

Bald eagle Haliaeetus leucocephalus X

Osprey Pandion haliaetus X

Belted kingfisher Megaceryle alcyon X

Dipper Cinclus mexicanus X

Gray Jay Perisoreus canadensis X

Stellers jay Cyanocitta stellari X

Crow Corvus brachyrhynchos X

Raven Corvus corax X

The Yellowstone Lake Crisis 13
14 Cutthroat Trout and the Yellowstone Lake Ecosystem

91% of the remaining range of the Yellowstone

cutthroat trout is located in Yellowstone

National Park, and practically all of that is in the

Yellowstone Lake and River (Fig. 1, Varley and

Gresswell 1988). The report by McIntyre (this

volume) now causes us considerable concern

for the fate of these cutthroat trout in their last

major stronghold.

This subspecies is worthy of preservation in its

own right; it is part of the planet’s biodiversity.

But there are many other reasons for preserving

this trout population. The cutthroat trout is a

celebrity among the trout family (e.g., Trotter

1987) due to its popularity with sport fishermen.

As an all-around sport fish it has few peers: it

grows to a fairly large average size, is highly

vulnerable to sport fishing, even by novice

anglers, and it has high susceptibility to

repeated catches when released (Varley 1984,

Gresswell and Liss 1995). Cutthroat trout, more

than any other trout species, is the archetype of

western trout fishing. These traits are also the

reasons that it is so vulnerable to overexploitation

and the main reason so many of the cutthroat

subspecies are declining.

All of this is very important, of course, but the

Yellowstone cutthroat trout is also important in

the fabric of something very much larger: the

ecosystem in which it lives. It is this dimension

we explore here.

OTHER FISHES

For the past 10,000 years or so, only the

longnose dace (Rhinichthys cataractae) shared

Yellowstone Lake with the native cutthroat

(Varley and Schullery 1983). As a result of the

activities of modern humans, the Yellowstone

cutthroat trout now share Yellowstone Lake

with several other introduced fish species:

redside shiners (Richardsonius balteatus),

longnose sucker (Catostomus catostomus

griseus), lake chub (Couseus plumbeus), and

most recently, lake trout (Salvelinus namaycush).

Fig. 1. Probable past (pre-1880s) and present

distributions of native Yellowstone cutthroat trout (light

shading). Dark shading in Wyoming is the probable

distribution 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 survival

of the native cutthroat trout did not appear to be

affected by the nonindigenous newcomers. In

fact, cutthroat trout are occasionally known to

feed heavily on some of these fish (Brown

1974). The effects of a collapse of the cutthroat

trout population on these other species is not

known, nor is the effect of lake trout predation

on these species predictable. We can speculate

that lake trout might prey heavily on the sucker

because both are hypolimnetic (deep-dwelling,

bottom-oriented) species, but all age and size

groups of all species (including cutthroat trout)

would be potentially vulnerable to lake trout

Montana

Wyoming

Idaho

Utah

Montana

Wyoming

Idaho

Utah

Past

Present
The Yellowstone Lake Crisis 15

predation, depending upon their preferred

habitats.

BIRDS

We know or suspect that a minimum of 20 bird

species in the Yellowstone Lake ecosystem

(Table 1) have evolved using the cutthroat trout

as a primary or significant source of food. The

species diversity is as complex as it is

fascinating. The stream-dwelling dipper

(Cinclus mexicanus), for instance, is an efficient

predator of trout fry as they emerge from the

gravel and migrate lakeward. Based on this fact,

we can speculate about the effect no cutthroat

spawners, or greatly diminished spawning

activity, might have on this species. What

follows are short case histories of the bird

species we have the most knowledge of, and the

potential effects of the lake trout disruption.

The bald eagle (Haleaeetus leucocephalus) is

widely thought of as a predominantly fisheating species, but studies in Yellowstone show

that only about 25% of its diet is fish (Davenport

1974, Swenson et al. 1986), and only about half

of the fish it eats are trout (Davenport 1974).

This does not mean that trout are unimportant to

the bald eagle, of course; its status over the past

several decades has often been precarious, and

any change or reduction in its food base,

especially protein- and fat-rich fish, could be

critically significant. As well, some of its other

prey, especially waterfowl, are themselves in

part dependent upon fish, and so in effect the

eagle’s reliance on fish is higher than might

appear from an examination only of its

immediate prey. Davenport (1974) estimated

that the daily consumption of fish per bald eagle

was 0.09 lb. per day. Lake trout are not expected

to be vulnerable to bald eagle predation.

The osprey (Pandion haliaetus) lives almost

entirely on fish, and most of the fish are trout

(Fig. 2). Yellowstone Lake and River host

numerous breeding pairs of ospreys. Swenson

(1978) found that 93% of the fish bones

identified near osprey nests were from trout, and

the rest were from Longnose suckers. Longnose

suckers may have been overrepresented in this

sample because their bones are heavier and

more likely to endure and be found. Swenson

(1978) also determined these birds selectively

preyed on cutthroat trout about 11 inches in

length. Davenport (1974) estimated that

ospreys averaged 0.88 lb. of fish per day on

Yellowstone Lake. Because they live at a far

greater depth than cutthroat trout, lake trout will

hardly ever be available to ospreys. After

several decades of struggle, osprey are doing

relatively well in Yellowstone National Park

(Fig. 3), but past experience indicates their

susceptibility to stress.

White pelicans (Pelecanus occidentalis) are

among the most-studied species of animals in

Yellowstone National Park (Fig. 4, Diem and

Condon 1967). The nesting colony in

Yellowstone is the only known colony in an

American national park, and is the highest

elevation colony known anywhere (Fig. 5). In

1994, a record 739 white pelican nests were

initiated on the Molly Islands, but nesting

success was low (T. McEneaney, NPS, pers.

commun., 1995). In 1922, Ward estimated that

virtually all of the pelican diet in Yellowstone

Lake was trout, but since then the introduction

Fig. 2. Osprey are obligate fish-eaters in Yellowstone

Lake. NPS photo.
16 Cutthroat Trout and the Yellowstone Lake Ecosystem

several recent studies that indicate that white

pelicans consume 2 to 4 pounds of fish per day.

Davenport (1974) estimated that 72% of the diet

of great blue herons (Ardea herodias) around

Yellowstone Lake was trout, and that they

consumed an estimated 1.93 lb. of food each per

day. While the population of herons is

relatively small (several dozen) the birds

average about 1,000 “heron-use days” in the

course of the summer season. Unlike many

species of fish-eating animals, but like the

pelicans, herons take fish of many sizes, from 2

to 16 inches in length. Lake trout are not

expected to be vulnerable to herons.

The common merganser (Mergus merganser),

though not as large or glamorous as the abovenamed species, may in some years actually

consume more fish than any of them because the

population is fairly large (400-800 birds, 62,000

use-days) and they spend a long season on the

lake (Davenport 1974). Davenport (1974)

estimated that mergansers averaged 1.0 lb. of

trout 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 evolution

of ecosystem management in America’s National Parks. University of Arizona Press, Tucson.

and proliferation of the longnose sucker has

probably shifted the percentage of nonsalmonids consumed to some extent. Pelicans

fish in shallow water for trout and suckers

between 6 and 16 inches, and it is unlikely lake

trout will be vulnerable in this way to the birds

in 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 its

cutthroat trout, in W. L. Halvorson, and G. E. Davis, eds.,

The evolution of ecosystem management in America’s

National Parks. University of Arizona Press,Tucson.

30 -

25 -

20 -

15 -

10 -

5 -

0 -—

----

—

----

—

----

—

----

—

----

—

----

—

1924 1965 1970 1975 1980 1985 1990

Yellowstone Lake

Shoreline

Frank Island

Number of Breeding Osprey Pairs

DDT Banned in Greater Yellowstone Ecosystem

DDT Banned in USA

Trout

Restoration

Campsite Closures Near Nests

Island 

Closures

Number of White Pelicans Fledged

700 -

600 -

500 -

400 -

300 -

200 -

100 -

0 -

Human Disturbance on Molly Islands

Pelican Pop. Control

Year

Trout Restoration

Boat Disturbance

Permitted Near Islands

Islands Free of 

Human Impacts

DDT Banned in USA

—-

-------- —---------

 —-

-------- —--------- —--------- —--------- —--------- —--------- —--------- —--------- —

1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 
The Yellowstone Lake Crisis 17

According to Davenport’s (1974) estimate of

trout consumption in 1973 and 1974, the

California gull (Larus californicus), whose

population was estimated between 1,400 and

2,000 (160,000 bird-days use) and whose diet is

50% trout, consumed as much trout as did

pelicans. The eared grebe (Podiceps caspicus),

whose numbers ranged from 2,500 to 3,000

(100,000 bird-days use) depended entirely upon

trout for its diet, and consumed 0.31 lb. per day.

The common loon (Gavia immer) and the

caspian tern (Hydroprogne caspia), occur in

smaller numbers (15 and 35, respectively) but

both 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 eat

trout include the Barrow’s goldeneye (Bucephala

islandica), bufflehead (Bucephala albeola), and

belted kingfisher (Megaceryle alcyon). None of

the above species are expected to utilize lake

trout because of the fish’s deep water habits.

Double-crested cormorants (Phalacrocorax

auritus) are another prominent fish-eater on

Yellowstone Lake (Fig. 6). Cormorants

apparently consume few trout, and may not

have inhabited the lake at all until after the

introduction of longnose suckers (Davenport

1974). If cormorants are profundal predators, as

a diet of suckers suggests, they may consume

lake trout in Yellowstone Lake. It is not known

if the presence of lake trout, who will

themselves prey on longnose suckers, will

enhance or decrease cormorant population size.

All of the above species of birds, with the

possible exception of the cormorant, prey on

fish within a few feet of the surface of

Yellowstone Lake, along the lake shoreline, or

in 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 monitored

since the late 1800s. NPS photo.
18 Cutthroat Trout and the Yellowstone Lake Ecosystem

Schullery 1991), it is assumed that prior to the

creation of Yellowstone National Park, grizzly

bears (Ursus arctos) preyed heavily on

spawning cutthroat trout in the tributary streams

of Yellowstone Lake. During the extended

period of open-pit garbage dumps in Yellowstone (roughly 1890-1970), when increasing

numbers of bears devoted much of their

attention to feeding at these concentrated food

sources, relatively few reports were made of

bears feeding on these spawning runs, a notable

exception being bears that discovered easy

concentrations of fish at spawner collection

weirs operated by hatchery managers. By the

1960s, when the first ecological study of

Yellowstone grizzly bears was undertaken, the

Yellowstone Lake cutthroat trout population

was severely depressed and garbage feeding by

bears was at its height (Schullery 1992). The

Craighead research team observed no feeding

by grizzly bears on spawning trout in the 1960s

(J. Craighead, pers. commun., 1984).

In the late 1960s, a general overhaul of park

fishing regulations allowed the cutthroat trout

population to begin a rapid recovery, with

concurrent increase in grizzly bear activity

along spawning streams (Fig. 7). Yellowstone

Lake has 124 tributaries, at least 59 of which are

known to have cutthroat trout spawning runs.

Surveys in 1974 and 1975 revealed bear activity

on 17 streams, and clear evidence of bear fishing

on 11 (Hoskins 1975). Surveys in 1985-1987

revealed that 93% of the streams now had

evidence of bear activity, and 61% “had

conclusive evidence of bear fishing” (Fig. 8,

Reinhart and Mattson 1990). An estimated

minimum of 44 bears used these spawning runs

in 1987 (Reinhart and Mattson 1990), and

sometimes this use was substantial; Yellowstone Grizzly Foundation researchers observed

an adult female grizzly bear maintain an average

harvest 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 few

aquatic bird species on Yellowstone Lake that may not be

be adversely affected by the collapse of the cutthroat trout

population. NPS photo.

and outlet stream. Cutthroat trout, who prefer

these same habitats, are thus vulnerable to this

predation. Lake trout spend almost all of their

lives at depths too great to be reached by these

predators. In the event of a collapse of the

cutthroat trout population and an increase in the

lake trout population, the lake trout are not

expected to provide a replacement prey.

MAMMALS

With the exception of grizzly bears, the use of

cutthroat trout by mammals has not received the

amount of study attention birds have received;

yet a surprising number of mammal species—

22—are known or suspected of using cutthroat

trout as a primary or significant food item

(Table 1). For species like otters there is little

doubt of the potential impact of lake trout.

Observers on Yellowstone Lake have reported

they seem to be able to catch cutthroat trout at

will. The deep-dwelling lake trout will certainly

be less available and accommodating. What

follows are short discussions and some

speculation on the effect of lake trout on our

best-known mammal species.

Though the historical record is sketchy due to

the shortage of observers and changing patterns

of human use (Skinner 1927, Whittlesey 1988,
The Yellowstone Lake Crisis 19

Fig. 7. Percent of Yellowstone Lake tributary streams

fished 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 cutthroat

trout, in W. L. Halvorson, and G. E. Davis, eds., The

evolution of ecosystem management in America’s

National Parks. University of Arizona Press, Tucson.

Fig. 8. Grizzly bear fishing Flat Mountain Arm Creek

during cutthroat trout spawning run. NPS photo.

(Streubel 1989), and has been a commonly

observed denizen of the lake since the park’s

earliest history. As predators in Yellowstone

Lake, they are trout specialists but are also

thought to eat longnose suckers. It is not known

whether a shift of biomass in the lake from

cutthroat to lake trout will have an effect on

otters, but given the observed vulnerability of

the cutthroat trout to otters, we suspect the shift

will be negative.

The above-described birds and mammals are

the best-known consumers of Yellowstone

cutthroat trout, because we have research data in

hand on them. But there are many more species

who are known or assumed (either from local

anecdotal information or from the scientific

literature) to use these fish (Table 1). In all,

some 42 species of birds and mammals are

known or suspected to depend on the

Yellowstone cutthroat trout to some extent. The

list could undoubtedly be extended with the

inclusion of reptiles, amphibians, invertebrates,

bacteria, and fungi. It is obvious from the above

discussion and from Table 1 that the

Yellowstone cutthroat trout is the central, or

keystone, species in the Yellowstone Lake

ecosystem, and that its decline or disappearance

would have disastrous consequences for much

of the remaining animal life.

Black bears (Ursus americanus) also fish these

spawning streams, though they are not

observed as often as are grizzly bears. Most use

of spawning runs has been by grizzly bears, but

Reinhart and Mattson (1990) noted that “black

bear use of streams was also increasingly

common, progressing from the east shore to the

west shore.” The presence of grizzly bears on a

stream apparently deterred black bears from

fishing more.

Gunther (1995) noted that “cutthroat trout are an

important, high quality food source for grizzly

bears that have home ranges adjacent to

Yellowstone Lake. Unlike cutthroat trout, lake

trout do not move up tributary streams to spawn,

but spawn within the lake at depths making

them unavailable to many terrestrial predators

such as grizzly bears.” It is not possible to

quantify the effects of this loss of an important

nutritional source with much precision, but

those effects will obviously be substantial.

Unlike the bears, the river otter (Lutra

canadensis) is “almost entirely carnivorous”

* **

**

**

* Estimated Use

Confirmed Use

1953–1970 1974–1975 1985–1987

100

75

50

25

0

Percent of Streams Fished by Grizzly Bears
20 Cutthroat Trout and the Yellowstone Lake Ecosystem

LITERATURE CITED

American Fisheries Society. 1989. Fishes of

North America, endangered, threatened, or

of special concern. Fisheries 14(6):2-38.

Behnke, R. 1979. The native trouts of the

genus Salmo of western North America.

Report to the U.S. Fish and Wildlife

Service, Denver, Colo.

Brown, R. R. 1974. The predation of cutthroat

trout on redside shiners in Pelican Creek.

Pages 124-131 in U.S. Fish and Wildlife

Service, Division of Planning and Assistance, Annual Project Report Yellowstone

Fishery Investigations, Yellowstone National 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 coho

salmon (Onchorhynchus kisutch) carcasses

in spawning streams. Can. Jour. of Fish. and

Aquatic Sci. 46(8):1347-1355.

Davenport, M. B. 1974. Piscivorous avifauna

on Yellowstone Lake, Yellowstone National Park. Yellowstone National Park,

U.S. Fish and Wildlife Service internal rep.

62pp.

Diem, K. L., and D. D. Condon. 1967. Banding

studies of water birds on the Molly Islands

Yellowstone Lake, Wyoming. Yellowstone

Library and Museum Association, Yellowstone National Park. 41pp.

Gresswell, R. E., and J. D. Varley. 1988.

Effects of a century of human influence on

the cutthroat trout of Yellowstone Lake.

Am. Fish. Soc. Symp. 4:45-52.

Gresswell, R. E., and W. J. Liss. 1995. Values

associated with management of Yellowstone cutthroat trout in Yellowstone

National Park. Cons. Biol. 9(1):159-165.

Gunther, K. A. 1995. Grizzly bears and

cutthroat trout: potential impacts of the

introduction of non-native lake trout to

Yellowstone Lake. Bear Management

Office, Yellowstone National Park, Information Paper No. BMO-8. 3pp.

Hoskins, W. P. 1975. Yellowstone Lake

tributary survey project. U.S.D.I. Interagency Grizzly Bear Study Team, Yellowstone National Park, unpubl. rep. 10pp.

Kaeding, L. R., D. G. Carty, D. L. Mahony, G.

Boltz, and S. M. Anderson. 1995. Fishery

and aquatic management program in

Yellowstone National Park. U.S. Fish and

Wildlife Service, Yellowstone National

Park, Tech. Rep. for 1994. 38pp.

Reinhart, D. P., and D. J. Mattson. 1990. Bear

use of cutthroat trout spawning streams in

Yellowstone National Park. Int. Conf. Bear

Res. 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 furbearing animals of Yellowstone Park.

Roosevelt Wildl. Bull. 4(2):163-282.

Streubel, D. 1989. Small mammals of the Yellowstone ecosystem. Roberts Rinehart,

Boulder. 152pp.

Swenson, J. 1978. Prey and foraging behavior

of ospreys on Yellowstone Lake, Wyoming.

J. Wildl. Manage. 42(1):87-90.

_____, K. L. Alt, and R. L. Eng. 1986. Ecology

of bald eagles in the greater Yellowstone

ecosystem. Wildl. Monogr. No. 95, 1-46.

Trotter, P. 1987. Cutthroat: Native trout of the

west. Colorado Associated University

Press, Boulder. 219pp.

Varley, J. D. 1984. The use of restrictive

regulations in managing wild salmonids in

Yellowstone National Park, with particular

reference to cutthroat trout, Salmo clarki.

Pages 145-156 in J. M. Walton, and D. B.

Houston, eds. Proceedings of the Olympic

wild fish conference, Mar. 23-25, 1983, Port

Angeles, Wash.
The Yellowstone Lake Crisis 21

_____, and R. E. Gresswell. 1988. Ecology,

status, and management of the Yellowstone

cutthroat trout. Am. Fish. Soc. Symp. 4:13-

24.

_____, and P. Schullery. 1983. Freshwater

wilderness: Yellowstone fishes and their

world. Yellowstone Library and Museum

Association, Yellowstone National Park.

132pp.

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

Yellowstone National Park, unpubl. rep.

25pp.

Whittlesey, L. H. 1988. Yellowstone place

names. 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 dimensions of fish and wildlife in our country is a

relatively young discipline, even for sport species harvested or otherwise of great interest to

people, but especially when applied to

nonconsumptive activities such as wildlife viewing or hearing. We know, for example, that

wildlife observation is “the single most important activity” for 94% of Yellowstone National

Park visitors (Duffield 1992), eclipsing even the

storied geysers. From this information, we

can conclude that wildlife viewing is socially

valuable. A dollar valuation for this enormously

important activity, however, has never been established. Though fish viewing has seldom been

held in the same esteem as wildlife observation, the social significance of a robust population of nonharvested cutthroat trout recently

became obvious to park managers. In recent

years, cutthroat trout viewing at Fishing Bridge

and 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 particularly surprising is that in Yellowstone National

Park, an area famous for its trout fishing, the

nonconsumptive fish viewing public exceeds the

total number of anglers (Fig. 2).

SOCIAL AND

ECONOMIC VALUES

Fish and wildlife are recognized as having several types of economic values besides those associated with their direct consumption (e.g.,

hunting, trapping, or fishing harvest). These

values include use value, which is how much

an individual is willing to pay to enjoy wildlife,

either firsthand, or through some media; option

value, which is how much an individual is willing to pay just to ensure that the wildlife exists

in case the individual some day may choose to

go view it; existence value, which is how much

Fig. 1. LeHardys Rapids, where cutthroat trout are

frequently visible during their spawning run, has become

a significant visitor attraction emphasizing a

nonconsumptive use of the fishery. NPS photo.

an individual is willing to pay just to know that

an animal continues to thrive in the wild; and

bequest value, which is how much an individual

is willing to pay to know that an animal will

survive for the enjoyment of future generations

(Swanson et al. 1994). Except for wolf recovery, whose future regional net economic impact is on the order of $43 million a year

(Duffield 1992), these values have not up to now

been computed for any species in the Yellowstone Lake ecosystem, but are quite high in other

nature reserves (Swanson et al. 1994).

Though wolf recovery analyses and data from

other reserves may by suggestive, or even compelling, nontraditional economic values remain

poorly considered and frequently neglected,

merely because they have not been as well quantified as have many other types of resources.

For example, if the existence value of the grizzly bear to all Americans and all other people

with a concern for wildlife were to be calculated, it would at least seriously compete with

the better-known values of many other traditionally recognized resources, and in fact might
exceed them. An example given by Duffield et

al. (1987) concluded that stream fisheries in

Montana compared favorably economically with

marketed resources such as timber, coal, or grazing. The current plight of the Yellowstone Lake

cutthroat trout, with its consequences for many

other species of wildlife, is an excellent example

of why more analyses of these values are needed.

Until now, no attempt has been made to estimate at least some of the lost spiritual, scientific, or recreational values should the Yellowstone Lake cutthroat trout population be reduced

or destroyed.

SIGNIFICANCE OF THE

YELLOWSTONE LAKE ECOSYSTEM

Yellowstone Lake, the waters tributary to it,

and its outlet downstream to the Upper Yellowstone Falls are the most popular and heavily

used fisheries in the park (Fig. 3), together supporting more than 264,000 cutthroat trout

“catches” annually and almost 50% of the total

parkwide fishing interest. Yellowstone Lake

has more than 100 tributary streams and a halfdozen lakes in its immediate watershed within

the park boundary. It must be emphasized that

fish populations and fishing in the tributary

streams (e.g., Pelican Creek, Upper Yellowstone River) and in the world-famous section of

the Yellowstone River between Fishing Bridge

and the Upper Yellowstone Falls will be as severely affected by lake trout as will Yellowstone Lake.

In 1994, 237,700 angler days were reported on

all parkwide waters, and 78,169 (33% of the

parkwide total) of those were spent on Yellowstone Lake (Kaeding et al. 1995). Extrapolating from data and interpretations for the Yellowstone Lake ecosystem presented in Varley

et al. (1976) and the 1994 sport fishery data

from Kaeding et al. (1995), we estimate the

1994 use on the Yellowstone River between the

falls and the lake at 33,500 (14%) angler days,

and the lakes and streams flowing into Yellowstone Lake at 3,400 (1.4%) angler days. Thus,

we can estimate about 115,069 angler days,

which in the past have been totally supported

by cutthroat trout, to be in some way jeopardized by the advent of lake trout in this ecosystem.

The U.S. Fish and Wildlife Service annual reports for the past several decades have quantified extremely high levels of angler satisfaction

with the fishing experiences produced by the

Yellowstone Lake ecosystem. For example,

in 1994, more than two-thirds of all anglers

landed one or more cutthroat trout per outing,

and those fish averaged more than 15 inches in

length. Seventy-eight percent of the anglers

responding to questionnaires reported satisfaction with their angling experience (Kaeding et

al. 1995). Most fishermen and fishing writers

speak of these kinds of angling adventures in

superlatives.

There are accepted ways to derive an economic

value for sport fisheries and we have done that

here to underscore the importance of exactly

what is at risk in the Yellowstone Lake ecosystem. To a great extent we have followed the

method and calculations of Duffield et al. (1987),

a part of which is known as a regional Travel

Cost Model (TCM). The TCM approach is recommended by both the Water Resources Council (1979, 1983) and the U.S. Department of

the Interior (1986) as a preferred technique. Another 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 outlet

of Yellowstone Lake. NPS photo.

The Yellowtone Lake Crisis 23
24 Socioeconomic Values

wild trout fishery with a hatchery-supported fishery would cost $281,200 annually. He further

estimated, based on actual hatchery production

costs, that each wild cutthroat trout was worth

$72.63 over the span of its projected three-year

catchable life. Varley (1984) concluded that to

recreate a fishery supported solely by hatchery

fish equal to the Yellowstone River could not

likely be done because the costs per fish were

too high for any public agency to bear, or for

anglers to tolerate paying for.

No specific economic analysis has been conducted of angler benefits or expenditures on the

Yellowstone River, but calculations have been

made for similar, close-by waters in the state of

Montana and Wyoming. The economic data

generated from fisheries in the two states are

fairly comparable. For the sake of simplicity

and relevance to the present, we have used

Montana’s figures. The 1987 study by Duffield

et al. calculated total recreational value per day

for many Montana waters. Based on a reported

travel cost of $.36 per mile, the statewide average for all stream fisheries was $135.38, but

the data on the “blue-ribbon” Yellowstone River

in Montana was higher, amounting to $276.74.

Using the 1994 estimate of use on the Yellowstone River downstream from Fishing Bridge

of 33,500 angler days, and Montana’s calculation for their portion of the Yellowstone, yields

a 1994 value of $9,270,800 for this portion of

the Yellowstone River.

It is worth noting that among all Montana

streams, those nearest Yellowstone National

Park (Upper Yellowstone, Upper Yellowstone

tributaries, Madison, Madison tributaries) had

the highest values per day in the state.

Yet another significant measure of economic

value of fisheries is angler expenditure per outing. Duffield et al. (1987) calculated that total

angler expenditure per day for Montana residents on streams was $29.45. For nonresidents

the daily expenditure on streams was $153.61.

Yellowstone Park fishermen are essentially all

which can be additive to those figures derived

from the TCM. Both techniques, according to

Duffield et al. (1987) “are the appropriate values to use in benefit/cost analysis or where economic efficiency decisions are being made.” A

third model (Varley 1984) focuses on the cost

of replacing or duplicating a wild fishery resource in “avoided fish hatchery costs.” Because the calculations from the above models

are based on inflated dollars, all dollar figures

presented in this report have been converted to

1994 U.S. dollars using the Consumer Price

Index (U.S. Bureau of Labor Statistics).

THE YELLOWSTONE RIVER BETWEEN

FISHING BRIDGE AND UPPER

YELLOWSTONE FALLS

This portion of the Yellowstone River arguably

has more fame than any other trout stream in

the Rocky Mountains (Fig. 4). Because this

section of river is largely populated by cutthroat

trout from Yellowstone Lake, the fortunes of

the river are closely tied to the viability and

health of the stock in the lake. Varley (1984)

examined the 8.9 mile section of the Yellowstone River between Fishing Bridge and the Upper Falls, and concluded that to reproduce this

Fig. 3. The cutthroat trout population of the Yellowstone

River (between Fishing Bridge and the Upper Falls) is

threatened by the lake trout invasion, because these

cutthroats spend the winter in the lake and are therefore

vulnerable to predation. This river fishery is world-famous

as the site of pioneering work in special regulations, and

would be severely reduced in quality if the lake trout thrive

in Yellowstone Lake. NPS photo.
The Yellowtone Lake Crisis 25

nonresidents in terms of their expenditures and

so the angler expenditure for the Yellowstone

River equates to $5,145,900.

YELLOWSTONE LAKE TRIBUTARY

STREAMS AND LAKES

The rivers, streams and lakes tributary to Yellowstone Lake are often cited by fishermen and

writers as notable fisheries in their own right.

Well-known streams such as the Upper Yellowstone River (above the lake), Thorofare Creek,

Pelican Creek, plus literally dozens of others,

and lakes such as Alder, Trail, Riddle and Sylvan, are expected to be seriously affected by

the introduction of lake trout in Yellowstone

Lake. Almost all of these fisheries are significantly tied to the fortunes of the cutthroat trout

of Yellowstone Lake, mostly because of the annual spawning migrations from the “mother

lake,” and the resultant redistribution of trout

biomass. Using the economic factors detailed

above, plus the Duffield et al. (1987) figures

for lakes in the “Madison [River] Area” near

Yellowstone Park, we estimate the total recreational value per day for these fisheries to be on

the order of $809,700.

In terms of the average nonresident angler expenditure per day, an additional $365,300 can

be added to the annual value of the fisheries

associated with the lakes and streams tributary

to Yellowstone Lake.

YELLOWSTONE LAKE FISHERY

The Yellowstone Lake fishery has been considered peerless since it was discovered by modern anglers in the middle of the last century.

Since its popularity with Euroamericans began,

literally tens of millions of cutthroat trout have

been harvested, although catch-and release regulations in recent years have reduced that harvest to fewer than 100,000 annually (Fig. 5).

We have estimated the value of the Yellowstone

Lake 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 Fishing

Bridge and the Upper Falls has a calculated recreational value of about $72.00.

NPS photo.
26 Socioeconomic Values

Yellowstone River catch-and-release section on

the value of each catchable cutthroat trout, and

the estimate quoted in McIntyre et al. (this volume) on the number of catchable trout in the

lake to compute an average “catchable stock.”

Thus, the estimate of 2.5 million catchable cutthroat trout in the lake with a nominal value of

$72.63 per fish yields a value of $181,575,000

for the current catchable stock in terms of “replacement or duplication value” and “avoided

fish hatchery costs.”

Using the Montana valuation figures (Duffield

et al. 1987) for total recreational value, we

project that the 1994 estimates of 78,169 angler

days spent on Yellowstone Lake, and a value of

$194.74 per angler day, yield an estimated value

of $15,222,600 for that year. Using the figures

calculated by Duffield et al. (1987) for average

nonresident expenditure on quality lakes near

Yellowstone Park an additional figure of

$5,257,600 can be estimated.

ECONOMIC VALUE OF THE

YELLOWSTONE LAKE ECOSYSTEM

Based upon the above figures for the Yellowstone River, Yellowstone Lake, and the tributaries to the lake, summed to a grand total, we

conservatively estimate that the nominal one year

(1994) economic value of the sport fisheries in

the Yellowstone Lake ecosystem is $36,021,900.

The effect of lake trout on the Yellowstone Lake

ecosystem has been projected out over a 30-year

horizon, so given the following assumptions,

we can project the economic effect over the next

three decades. We assume 1) no lake trout control is implemented, and 2) the demise of the

cutthroat trout occurs as predicted by McIntyre

et al. (this report). We falso factored in the

expectation that during the decline of cutthroat

trout, lake trout will offer a replacement sport

fishery at least on par with the Lewis Lake lake

trout fishery in the park. Given these assumptions, we project that in 30 years (2024) the

Yellowstone Lake ecosystem sport fisheries will

decline from the 1994 value of $36,000,000 to

an annual value of $8,492,300.

Consequently, the cumulative 30-year value of

the cutthroat trout sport fishery assuming the

introduction of lake trout had not occurred is

estimated at more than a billion dollars

($1,080,000,000). The consonant value assuming lake trout populations are vigorously controlled and do not exceed 20-30% of the trout

biomass in the lake is $685,000,000. If no significant lake trout control is carried out and their

population approaches 70-80% of the trout biomass, the 30-year value of the sport fishery is

expected to decline to $439,950,000. This last

scenario represents a three decade economic erosion of $640 million, which we consider the

long-term net economic effect of the introduction of lake trout if park managers fail to take

action.

Further, if the surge of lake trout is greater than

proje and the decline in cutthroat trout is worse

than expected, and this results in the cutthroat

trout population becoming extinct or nearly so

at the end of 30 years, we estimate that the total

ecological restoration of the cutthroat trout in

Yellowstone Lake, its outlet stream, and its

tributaries, would have a one-time cost of a minimum of $31,250,000, or a multiple year “replacement-in-kind” of $181,575,000. If the cutthroat decline was severe enough, the subspecies may warrant listing under the Endangered

Fig. 5. Yellowstone Lake is the west’s premier cutthroat

trout lake fishery, which has a calculated annual

recreational value of more than $15 million.

NPS photo.
The Yellowtone Lake Crisis 27

Species Act, which would increase the restoration costs cited above.

By any measure it is obvious that saving the

native ecosystem would be the desired course

of action on both biological and economic

grounds. Elsewhere in this volume, a lake trout

control program is presented that uses a combination of sport angler exploitation and intensive, large-scale gillnetting and trapping to significantly suppress their population. This type

of program, which would have to be carried

out indefinitely (assuming no technological

breakthroughs occur), would cost approximately

$300,000 per year (30 years = $9,000,000).

Thus, the lake trout control program and preservation of as much of the cutthroat trout fishery as possible would result in a highly favorable benefit:cost ratio of 27:1.

Through this brief presentation of social and economic dimensions of lake trout invasion, we

have attempted to add a useful perspective on

some of the values at risk. Though we were

only able to speculate about option, existence,

and bequest values, it is clear to us they would

be substantial if those figures were available.

However, by any measure the angler-use projections, while partially presumptive, demonstrate a resource of extraordinary scope, quality, and value. The fishery at risk is held in

great esteem by the public and is very valuable

to the local and regional economy. The Yellowstone Lake cutthroat trout population fits the

definition of extraordinary significance: in their

own right because they are now an imperiled

subspecies, for the fishing experience they provide, on behalf of the charismatic wildlife species they feed, for the scientific laboratory they

are a part of, and for the economic bonanza

they provide the region.

LITERATURE CITED

Duffield, J., J. Loomis, and R. Brooks. 1987. The net

economic value of fishing in Montana. Montana Department of Fish, Wildlife and Parks.

Duffield, J. 1992. An economic analysis of wolf recovery in Yellowstone: park visitor attitudes and values.

Page 31-87 in Wolves for Yellowstone? A report to

the 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 associated with Management of Yellowstone Cutthroat Trout

in 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 aquatic

management program in Yellowstone National Park.

U.S. Fish and Wildlife Service, Yellowstone National

Park, Tech. Rep. for 1994. 38pp.

Swanson, C. S., D. W. McCollum, and M. Maj. 1994.

Insights into the economic value of grizzly bears in

the Yellowstone recovery zone. Int. Conf. Bear Res.

and Manage. 9(1):575-582.

U.S. Bureau of Labor Statistics. 1995. Consumer Price

Index, 1970-1994. Washington, D.C. 1p.

Varley, J. D. 1983. The use of restrictive regulations in

managing wild salmonids in Yellowstone National

Park, with particular reference to cutthroat trout.

Pages 145-156 in J. M. Walton and D. B. Houston,

eds. Proceedings of the Olympic Wild Fish Conference, 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, fishery and aquatic program, Yellowstone Park. U.S.

Fish and Wildlife Service, Yellowstone Park, tech.

report. 148pp.

U.S. Department of the Interior. 1986 Natural Resource

damage assessments: final rule. 43 CFR Part 11,

Federal Register 51(148), Aug. 1, 1986.

U.S. Water Resources Council. 1979. Procedures for

evaluation of national economic development (NED)

benefits and costs in water resources planning. Final

Rule, Federal Register 44(242), Dec. 14, 1979.

U.S. Water Resources Council. 1983. Economic and environmental principles and guidelines for water and

related 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 IN

GARDINER, MONTANA, FEBRUARY 15-17, 1995

BY JOHN D. MCINTYRE, WORKSHOP LEADER

Chairman), Reginald Reisenbichler (Seattle,

Washington), Bruce Rieman (Boise, Idaho),

James Selgeby (Ashland, Wisconsin), and

James Vashro (Kalispell, Montana). Additional

information was provided by David Donald

(Regina, Saskatchewan) and Robert Behnke

(Ft. Collins, Colorado), who were unable to

attend the meeting.

The team was directed to an exploration of the

available information concerning fish community dynamics in Yellowstone Lake and in other

lakes where lake trout have been introduced.

Based on these discussions and on their

personal experience and background, each

member judged the likelihood that lake trout

can be eliminated from Yellowstone Lake, the

likelihood that the lake trout population can be

controlled, and the expected percent loss in the

cutthroat trout population with and without

suppression of lake trout. Team members were

also asked to identify potentially useful

management methods and to judge the potential

effectiveness of each. Finally, they were asked

to describe information needed to address the

problem and to monitor the result of actions that

may be taken by the National Park Service

(NPS).

PROGNOSIS

The team concluded there is only a slight chance

that lake trout can be eliminated from

Yellowstone Lake (Fig. 1A), but they all judged

there to be at least a 50% chance that substantial

INTRODUCTION

Lake trout (Salvelinus namaycush) were

captured in Yellowstone Lake, Yellowstone

National Park in 1994. Lake trout are not

indigenous to the lake and their predatory habits

are perceived to be a threat to the native

Yellowstone cutthroat trout (Oncorhynchus

clarki bouvieri) and to all other aquatic and

terrestrial species that depend on the presence of

a robust population of cutthroat trout. As part of

an action plan to address the problem,

administrators of Yellowstone National Park

convened a team of scientists to help

characterize the threat to the cutthroat trout and

to identify and judge the potential effectiveness

of management actions to reduce that threat.

The team met in Gardiner, Montana, in

February 1995. Members were selected so that

as a whole the team had demonstrated capacity

for objective analysis and broad experience

with cutthroat trout, lake trout, population

biology, management techniques, and management strategies. This is a report of their findings

and judgments.

PARTICIPANTS AND PROCEEDINGS

Participants included Frederick Binkowski

(Milwaukee, Wisconsin), Theodore Bjornn

(Moscow, Idaho), Jon Erickson (Jackson,

Wyoming), Robert Gresswell (Corvallis, Oregon), Michael Healey (Vancouver, British

Columbia), Leo Marnell (Glacier National

Park, Montana), John McIntyre (Boise, Idaho,
control of lake trout population’s expansion was

feasible (Fig. 1B).

If the lake trout population is not suppressed,

most participants judged the loss of cutthroat

trout from present levels would equal or exceed

50% within the next 20 years (Fig. 2A). They

judged that suppression of the lake trout

population 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 of

cutthroat trout would be reduced by 70% or

more within 100 years (Fig. 2C). The

expectation of loss in 100 years with lake trout

suppression was variable, but five of eight

respondents judged that it may be possible to

limit the loss of cutthroat trout to 10-20% of

present levels (Fig. 2D).

It is not a foregone conclusion that lake trout

population will cause a catastrophe for the

cutthroat trout. One participant concluded that

even with no suppression of lake trout, cutthroat

trout are likely to be reduced only by 20% in the

Fig. 1. Frequency distributions of estimated probabilities that lake trout can

be eliminated from Yellowstone Lake (A), and that lake trout abundance can

be effectively controlled in Yellowstone Lake (B).

short term (Fig. 2A) or the long term (Fig. 2C).

Most concluded otherwise, however, and

judged that protection of a robust population of

cutthroat trout may require aggressive action on

the part of NPS managers to suppress lake trout.

Suppression of the lake trout population was

judged possible, and the cutthroat trout

population remaining within 100 years may be 2

to 4 times as large as is likely if the lake trout are

not suppressed.

POSSIBLE CONTROL METHODS

The following methods for suppressing the lake

trout population were identified by the team or

were otherwise brought to its attention. Options

that received no more than a 0.5 chance of

success by half or more of the team members are

described first. Methods judged likely to be

more effective are described second.

Status Quo Angling

Present angling regulations include killing any

captured lake trout and reporting the catch to

park authorities. Most team members judged

that the present sport fishery of Yellowstone

A

B

Probability of Success

Probability of Success

Frequency Frequency

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 —

———————————

———————————

The Yellowstone Lake Crisis 29
30 Review and Assessment of Possibilities

Lake had less than a 50% chance of effectively

limiting the lake trout population. The present

open season, no-limit regulations for lake trout

will continue to raise public awareness and

provide an additional monitoring tool.

Killing Lake Trout Embryos

This proposal included covering spawning

areas with polyethylene sheeting, or with

screens to collect and subsequently destroy

spawn, killing developing embryos with

toxicants or smothering (e.g., sand), use of

mechanical removal methods (e.g., suction

dredge), or use of concussion to destroy

embryos. Locating and covering all of the

potential spawning areas did not seem to be a

viable strategy for Yellowstone Lake. The

majority of the team judged there to be less than

a 30% chance that any of these alternatives is a

viable method for suppressing lake trout in

Yellowstone Lake.

Provide Cover for Juvenile Cutthroat Trout

The proposal was to construct artificial cover

near the outlet of major spawning tributaries to

protect cutthroat trout fry as they enter the lake.

None of the participants judged this tool as

having a chance for success of even 20%. The

additional cover was thought to be as likely to

provide cover for waiting predators, including

lake trout, as well as for migrating cutthroat

trout fry.

Release Sterile Sea Lampreys

in Yellowstone Lake

Discussion of this proposal included an

acknowledgment that there is no source of

sterile sea lamprey. Further, there is concern

that use of such a tool cannot be applied without

causing additional risk to cutthroat trout and

other endemic species. No participant gave this

proposal more than a 10% chance for successful

control of lake trout at the present time.

Attract Lake Trout to Sound or Chemicals

Experimental evidence exists that fish can be

attracted to sound and to chemicals (including

pheromones), captured, and removed. Given

Fig. 2. Frequency distributions of estimates of reduction of cutthroat trout in

Yellowstone Lake within 20 years if lake trout are not suppressed (A), within

20 years if lake trout are suppressed (B), within 100 years if lake trout are

not suppressed (C), and within 100 years if lake trout are suppressed (D).
The Yellowstone Lake Crisis 31

the absence of evidence that large numbers of

lake trout could be attracted from substantial

distances, the team judged that there was no

more than a 30% chance of success with sound

or chemical attractants.

Trap-net

More than half the team members judged the use

of trap-nets to have at least a 40% chance of

successfully suppressing the lake trout population. The main disadvantage of the method is

high expense of operation.

Long-line Fishing

Nine participants judged that long-line fisheries

would have only between 10 and 30% chance of

success in controlling lake trout abundance.

One participant judged long-line fishing to have

a 60% chance for success. Disadvantages of the

method include the need for use of cut-baits, and

this technique is more labor intensive than

netting and trapping techniques.

Use of Divers or Remotely

Operated Vehicles to Kill Lake Trout

These methods offer little hope for success in

killing large numbers of lake trout. No

respondent judged that even a 30% chance for

success exists.

Supplementation of

Cutthroat Trout Population

Increasing the number of cutthroat trout in

Yellowstone Lake by stocking hatchery-reared

cutthroat trout was viewed as only contributing

to an even greater food supply for lake trout. No

respondent judged supplementation to have

more than a 20% chance of reducing the

perceived risk to the cutthroat trout population

in Yellowstone Lake.

Stocking “Buffer Species”

The general conclusion was that the effects of

adding new species to the lake community were

too unpredictable. Most team members judged

this proposition to have only a 10% chance of

successfully diverting the lake trout’s dietary

habits and reducing risk for cutthroat trout.

Use of Chemical Toxicants

There was no support for use of chemical

treatment of Yellowstone Lake to eliminate the

lake trout. Disadvantages include the nonselectivity of potential chemicals and the

infeasibility of treating such a large lake.

Use of “Judas Fish”

The proposal was to obtain and sterilize male

lake trout from Lewis Lake. These males would

then be fitted with radio or ultrasonic

transmitters and released in Yellowstone Lake

where they would help to locate the spawning

grounds. The team judged that such ventures

might be useful but should begin with fish

captured from Yellowstone Lake.

Use of Sterile Male Lake Trout

The proposal was to stock large numbers of

sterile males according to protocols developed

for insect pest control. The ensuing discussion

generally discounted the proposal because the

needed technology for fish has not been

developed.

The following methods were judged to have at

least a 50% chance of being successful in

reducing lake trout abundance by more than half

of the respondents.

Directed Angling (Fig. 3A)

This option included use of anglers experienced

in catching lake trout. Cut bait, echo location,

ice fishing, and other approaches known to be

effective in catching lake trout would be used.

Lake-wide Gillgetting (Fig. 3B)

Commercial fisheries in the Great Lakes can

effectively harvest and depress targeted stocks

of lake trout. Locations and movements of lake

trout tend to be predictable, thus making the fish
32 Review and Assessment of Possibilities

vulnerable to such fishing. Removal of large

fish is an effective means of limiting lake trout

reproduction because they do not mature until

attaining a body length of 15 to 18 inches. Net

fisheries should be able to avoid cutthroat trout

for the most part by fishing when lake trout and

cutthroat trout are separated by depth, and

where together, by targeting lake trout that are

larger than cutthroat trout.

Capture on Spawning Grounds (Fig. 3C)

This method includes location of lake trout

spawning grounds through use of radio or

ultrasonic tagging, and use of intensive netting

or other techniques to capture or destroy the

congregated fish.

Conclusions

Based on these results, the team concluded that

use of mechanical removal methods, either

gillnetting or some combination of gillnetting

and trapping is likely to provide the greatest

success in controlling lake trout abundance.

Initial control measures can be initiated in 1995

field season along with an experimental

gillnetting program for obtaining the information needed to improve the effectiveness of the

program. Adaptive management strategies to

incorporate new information and understanding

on a continuing basis. Some of the reviewed

methods or other ideas may become useful in

the future, either by themselves or in

combination with other methods.

Control of the lake trout population is likely to

require a perpetual effort. In the short term, the

lake trout population is expected to continue

expanding limited by the effectiveness of the

control effort. In the long term, the lake trout

population presumably will tend to stabilize at a

level also dictated by the effectiveness of the

control program. The effort (including costs

and other resources) needed to control the lake

trout population at that level can then be

estimated. A carefully developed and managed

lake trout control program can provide the

information needed to evaluate its success.

INFORMATION NEEDS

The team concluded that most information

needed to implement an effective program can

be 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

Probability of Success

Frequency 3 —

2 —

1 —

0 ——

———————————

Frequency

Frequency

3 —

2 —

1 —

0 —

3 —

2 —

1 —

0 ——

———————————

————————————

Probability of Success 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

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Probability of Success

B

C
The Yellowstone Lake Crisis 33

experimental gillnetting program for lake trout

and refining the existing monitoring program

for cutthroat trout. Elaborate and expensive

new program elements are not needed over and

above the gillnetting program. Primary

information needs are data to assess the status

(abundance indices and distribution in space

and time) of the lake trout and to monitor

impacts on Yellowstone cutthroat trout.

Accurate information to assess abundance

trends of cutthroat trout is most important.

Present gill-netting, creel census, and census

methods in spawning streams need to be refined

to enable cohort and catch-curve analyses.

Extensive surveys of spawning streams combined with intensive investigation of three

spawning streams in separate locations around

the lake would help to improve the present

database. Information needed to monitor lake

trout abundance and to develop their population

dynamics (age-determination, mortality, recruitment, spawning dynamics, diet) and

growth rates was considered the next most

important task.

Appropriate locations and time periods for the

most effective removal of lake trout without

further harming cutthroat trout are unknowns.

Accordingly, adaptive management must be

seen as an integral component of the lake trout

control program.

Depth distribution may be the most appropriate

criterion for separating cutthroat trout and lake

trout because considerable overlap in their size

distributions is expected in Yellowstone Lake.

Almost no cutthroat trout are found at depths

greater than 30 m, and lake trout may prefer

depths near 40-60 m. These criteria can be used

to begin a control program, and target depths

can be verified from netting, tagging, and radio

tracking. Captured lake trout might be fitted

with radio tags to facilitate locating the

spawning grounds. As information comes

available to show the most effective sizes,

locations, and seasons for use of nets, an

increasingly aggressive program can be

developed to control lake trout abundance.

Additional information to assess the source and

reproductive success of the lake trout in

Yellowstone Lake, to describe the genetic

structure of the cutthroat trout metapopulation,

and to partition sources of cutthroat trout

mortality were also identified as important for

understanding the dynamics of the system, but

not as critical to the immediate need as the

information described earlier.

SUMMARY

1. Although there is a slight chance that lake

trout will not threaten the Yellowstone Lake

cutthroat trout, chances are high that lake trout

cannot be eliminated and will seriously reduce

the cutthroat trout population in Yellowstone

Lake.

2. The probability that lake trout abundance can

be limited by initiating an aggressive control

program using mechanical means of removal is

high, but there is little chance that lake trout can

be eliminated. Consequently, a long-term

commitment is required to maintain control lake

trout abundance.

3. The cutthroat trout population is likely to be

reduced whether or not the lake trout are

suppressed, but suppression of lake trout may

reduce the expected loss of cutthroat trout by

50% or more.

4. Most information needed to increase the

effectiveness of initial control measures can be

obtained from the control program itself. Some

modification of the present monitoring program

is required to enable detection of changes in the

cutthroat trout population.
INTRODUCTION

In the absence of complete knowledge of the

behavior and habits of lake trout in Yellowstone

Lake, we intend to develop a program for

limiting their expansion based on available

knowledge coupled with careful monitoring and

application of adaptive management strategies.

Control will begin by gillnetting at depths

where cutthroat trout do not occur, and

secondarily by experimental gillnetting designed primarily to gain information on lake

trout distribution in space and time. Monitoring

provides the basis for assessing the success or

failure of alternative management actions and

provides the basis for making real-time

adjustments needed to help reduce deleterious

effects in the cutthroat trout population.

Our long-term goal is to develop and maintain a

program for controlling lake trout abundance

that will limit the loss of cutthroat trout to less

than 20% of present levels. Proposed levels of

effort may be initially too conservative or

excessive, but rigorous application of adaptive

management will enable us to make appropriate

adjustments as the program develops in

subsequent years.

We identify the fact that additional resources are

needed if our present fishery program is to

remain intact. We have, however, elevated the

perceived crises caused by the lake trout to our

most important problem for fishery investigations. If we cannot successfully secure the

additional funding required for this effort, we

will redirect existing resources for aquatic

ecosystem 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 new

funding to finance the 1995 experimental

program.

2. We will take action to secure a permanent

addition of $300,000/year to base funding for

the fishery program to maintain the control

program.

3. Present monitoring efforts for cutthroat trout

were designed only to detect long-term changes

in the population and must be supplemented to

attain the desired result. The cutthroat trout

population needs to be monitored at a level of

rigor that will provide the statistical sensitivity

needed to detect changes in abundance in a

timely manner. Consequently, we will expand

spawning ground surveys to all important

spawning streams, and increase the intensive

monitoring presently conducted only at Clear

Creek to three runs by including two additional

tributaries.

4. We want to prevent existing lake trout from

attaining spawning size. We will accordingly

move aggressively to remove as many lake trout

from deep water as time and personnel permit.

5. We will develop a suitable index for

monitoring lake trout abundance in Yellowstone Lake. Data from Objectives (4) and (6)

will help to attain this objective.

6. We will improve our effectiveness in

removing lake trout. This objective requires

that we develop an understanding of lake trout
The Yellowstone Lake Crisis 35

OBJECTIVES FOR 1997

1. We will maintain an expanded spawning

ground survey on all important spawning

streams, and intensively monitor runs in three

important tributaries.

2. We will continue efforts to prevent as many

lake trout as we can from attaining spawning

size by gillnetting in deep water and other

locations where it is shown from work in 1995

Objective (5) and 1996 Objective (4) that lake

trout can be captured without harming cutthroat

trout. We will continue to develop a suitable

index for monitoring lake trout abundance in

Yellowstone Lake.

3. We will continue to improve our effectiveness in removing lake trout via an experimental

gill-netting program designed to assess where

and when lake trout can be effectively captured

without harming cutthroat trout. The objective

includes description of lake trout age-structure,

mortality, recruitment, and behavior.

4. To the extent that by 1997 adaptive

management has enabled us to redirect

resources and personnel to some additional

endeavors, we will initiate studies to locate

spawning locations and to assess spawning

success for lake trout, to describe the structure

of the cutthroat trout metapopulation, and to

partition the sources of mortality for cutthroat

trout.

population dynamics. An experimental gillnetting program will be initiated to begin an

assessment of where and when lake trout can be

effectively captured without harming cutthroat

trout. We will use the data obtained here and in

(4) to describe age-structure, mortality, recruitment, and behavior of lake trout.

OBJECTIVES FOR 1996

1. We will attempt to secure permanent funds

(estimated at $300,000/year) added to our base

funding to maintain the control program.

2. We will maintain an expanded spawning

ground survey on all important spawning

streams, and intensively monitor runs in three

important tributaries.

3. We will continue preventing as many lake

trout as we can from attaining spawning size by

gillnetting in deep water and other locations

where it is shown from work in 1995 Objective

(5) that lake trout can be captured without

harming cutthroat trout. We will continue work

and analysis to develop a suitable index for

monitoring lake trout abundance in Yellowstone Lake.

4. We will continue to improve our effectiveness in removing lake trout via an experimental

gill-netting program designed to assess where

and when lake trout can be effectively captured

without harming cutthroat trout. The objective

includes 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, WY

82190

Daniel G. Carty, U.S. Fish and Wildlife Service,

Yellowstone Fishery Assistance Office, P.O.

Box 184, Yellowstone National Park, WY

82190

Lynn R. Kaeding, U.S. Fish and Wildlife Service, Yellowstone Fishery Assistance Office,

P.O. Box 184, Yellowstone National Park, WY

82190

John D. McIntyre, U.S. Forest Service (retired)

P.O. Box 1651 Boise, Idaho 83701

Tom Olliff, National Park Service, Division of

Resource Management and Visitor Protection,

P.O. Box 168, Yellowstone National Park, WY

82190

Paul Schullery, National Park Service, Yellowstone Center for Resources, P.O. Box 168, Yellowstone National Park, WY 82190

John D. Varley, National Park Service, Yellowstone Center for Resources, P.O. Box 168, Yellowstone National Park, WY 82190

WORKSHOP PARTICIPANTS OR ATTENDEES

Workshop Members

Bob Behnke, Department of Fish and Wildlife

Biology, Colorado State University, Fort

Collins, Colorado 80523 (participated through

e-mail).

Fred Binkowski, Center for Great Lakes Studies, 600 East Greenfield Ave, University of

Wisconsin, Milwaukee, Wisconsin 53204

Ted Bjornn, National Biological Service, Idaho

Cooperative Fish and Wildlife Research Unit,

University of Idaho, Moscow, Idaho 83844-

1136

Jon Erikson, Wyoming Game and Fish Department (retired), P. O. Box 1054 Jackson, Wyoming 83001

Bob Gresswell, U.S. Forest Service, Pacific

Northwest Forest Sciences Lab, 3200

Jefferson Way, Corvallis, Oregon 97331

Mike Healey, West Water Research Center, University of British Columbia 1933 West Mall,

Vancouver, British Columbia Canada V6T 1Z2

Leo Marnell, National Biological Service, Glacier 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 Forest Sciences Lab, 316 E. Myrtle Street, Boise,

Idaho 83702

Reg Reisenbichler, National Biological Service

Laboratory, Building 204, Naval Station, Seattle Washington 98115

James Selgeby, National Biological Service,

Ashland Field Station, Route 1 Box 24, Iron

River, Wisconsin 54847

Jim Vashro, Montana Department Fish, Wildlife

and Parks, Kalispell, Montana 59901

USFWS Fisheries Assistance Office,

Yellowstone

Lynn Kaeding, Project Leader

Dan Carty, Fishery Biologist

Dan Mahoney, Fishery Biologist

Glenn Boltz, Fishery Biologist

National Park Service, Yellowstone

John Varley, Director, Yellowstone Center for

Resources

Sue Consolo Murphy, Resource Management

Specialist

Dan Reinhart, Resource Management Coordinator

Lauryl Mack, Secretary