Cumulative effects of human activities on bull trout (Salvelinus confluentus) in the upper Flathead drainage, Montana

587. 55 HEADWATERS HYDROLOGY

June ^it%eha American Water Resources Association 1989

____________ E if Is U

OTHLKTIVE EFFECTS OP HOWRN ACTIVITIES CN
BOLL TROOT (Salvelinus confluentufl) IN THE UPPER FLATHEAD DRAINAGE, MONTANA

John Fraley, Tom Weaver and Jim Vashro

ABSTRACT: We reviewed the potential cumulative effects of human activities on bull
trout in the Flathead Lake and River system of northwest Montana. Bull trout are the
largest fish native to the Flathead drainage, attaining a length of up to one meter
and a weight of 10 kg. This species migrates from Flathead Lake up to 250 km
upstream to spawn in cold headwater tributaries with groundwater upwelling and clean
gravels. Spawning and rearing habitats are limited and vulnerable to damage by
deposition of fine sediments. Potential threats to bull trout habitat and
populations include timber harvest, road building, mining, residential and
agricultural development, hydropower construction and operation, harvest of fish by
anglers, and non-native fish species. Management and mitigation options include
application of best management practices and riparian guidelines for logging, habitat
protection and improvement, improved fish passage to blocked areas, fishing
regulations and integrative management of fish populations. Because of reduction in
habitat, continued potential for habitat degradation, and limited options for
management, the bull trout population is vulnerable and should be closely monitored
to detect signs of decline.

KEY TERMS: Migratory bull trout; spawning and rearing habitat; land management;
sediment deposition; hydropower development; fisheries management and mitigation

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The bull trout is the largest fish native to the Flathead drainage, attaining a
length of up to one meter and a weight of up to 10 kg. The bull trout of inland
waters is a separate species from the smaller, coastal Dolly Varden (Cavenderr 1978) .
Most bull trout in the Flathead system are migratory, growing to maturity in Flathead
Lake and migrating up to 250 km through the river system and into tributaries to
spawn (Fraley and Shepard, 1989, Fraley, 1989). Juvenile fish remain in tributaries
from one to three years before migrating to the lake. Most bull trout in the North
and Middle forks of the Flathead River mature in Flathead Lake.

Bull trout spawn in September and October, selecting low-gradient mountain
streams with cold, clean water, beds of clean gravel, and areas of upwelling
groundwater necessary for successful egg incubation (Fraley and Shepard, 1989).
Hiding cover such as logs and undercut banks is required for adult spawners. These
strict requirements make good spawning and incubaticon habitat limited and valuable.

Montana Department of Fish, Wildlife and Parks, Box 67, Kalispell, MT 59903.

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Suitable habitat for rearing juvenile bull trout is also limited. Young bull trout
require cold-water tributaries with good cover (rocks and woody debris) and,
W relatively little streambed sediment. Most juvenile bull trout are found in Flathead
tributaries with average summer afternoon temperatures below 15 C.

Considerable research and management activities have been directed toward bull
trout in the Flathead Basin (Fraley and Shepard, 1989) . In cooperation with the USDA
Forest Service, the Montana Department of Fish, Wildlife and Parks (MDFWP) has
monitored effects of timber management on spawning and rearing habitat and fish
populations in the upper drainage (Weaver and Fraley, 1988, Shepard et. al., 1984,
USDA Forest Service, 1988) . Monitoring activities have been coordinated with the
Flathead Basin Commission's water quality monitoring program (Flathead Basin
Commission, 1988) . The trophy fishery for bull trout has been controlled by strict
catch limits and by closing major spawning tributaries to angling.

Bull trout are listed as a Class B Species of Special Concern by MDFWP, which
means they occur in limited habitat and numbers in Montana. The Flathead bull trout
are one of the more significant populations in North America and their elimination
would mean at least a moderate loss to the gene pool of the species (Bolton, 1980).
Bull trout are very sensitive to environmental (disturbance. In this paper we examine
the potential cumulative effects on bull trout caused by limited spawning and rearing
habitat, the effects of land management activities, and increasing human population
in the basin. We also consider measures to protect and enhance the bull trout
population in the upper Flathead drainage.

C

STUDY AREA

The Flathead Lake and River system is a headwater drainage *>£ the Columbia River
Basin (Figure 1). Flathead Lake has a surface area of 476 km and a mean depth of
over 30 m. The Flathead River enters the north end of the lake. The South, Middle
and North forks drain areas of the Great Bear and Bob Marshall wilderness, Glacier
National park and managed Flathead National Forest Lands. The upper North Fork
drains southern British Columbia. The Swan River enters Flathead Lake near the mouth
of the Flathead River. More than half of Flathead Lake and the lower river system
are within the Confederated Salish and Kootenai Indian Reservation.

Bull trout from Flathead Lake originally spawned in tributaries of all forks of
the Flathead and the Swan River. Hungry Horse Dam was cxanstructed in 1954 and
blocked all migration into the South Fork Flathead River. Bigfork Dam was
cxmstructed in 1902 and has blocked most migration into the Swan River. Kerr Dam was
constructed on the outlet of Flathead Lake in 1938 and blocked all upstream movement
of bull trout from the lower Flathead and Clark Fork systems.

RESULTS AND DISCUSSION

Potential Threats to the Bull Trout Population

Timber harvest activities . —Major management activities on forested land in the
drainage are timber harvest and associated road construction. In the Swan drainage,
Shepard et al. (1984) and Leathe and Enk (1985) found a significant relationship
(jT- 0.56, P < .01) between road development, stream gradient and stream substrate
score, a transect method which estimates available clean or unembedded rearing

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habitat in streams. Also, the percentage of stream substrate materials less than
6.35 mm iru diameter was significantly correlated to road development and stream
gradient (r - 0.49, P < .01) (Leathe and Enk, 1985). These relationships indicate
that road building associated with timber harvest can cause increased fine materials
to be deposited in the streambed.

I \ { STUDY
\ '■J AREA

CANADA

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USA

BOUNDARY

UPPER VL

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FLATHEAD

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RIVER

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BASIN

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BIG FORK

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FLATHEAD
LAKE

KERR
DAM

Figure 1. The Upper Flathead Drainage

Fine materials deposited in streambed gravels reduce survival to emergence of
incubating fcull trout embryos. Average survival to emergence of incubating bull
trout embryos in Coal Creek (a tributary of the North Fork Flathead) fell from over
60 percent in gravels with 30 percent fine materials, to zero percent in gravels with
44 percent fine nwterials (Weaver and White, 1985). Clearly, excessive fine
materials deposited in spawning areas could greatly reduce fry production.

Rearing habitat for juvenile bull trout in tributaries is also harmed by
deposited sediments. Juvenile bull trout densities in tributaries of the Swan River
were significantly correlated to the percentage of streambed materials less than 6.35
mm (r - 0.33, P < 0.01) and substrate score (r ■ 0.40, P < 0.01) (Shepard et al., -
1984, Leathe and Enk, 1985). These fjjidings indicate that land management activities
that deliver fine materials to the stream could significantly reduce the instream
habitat for juvenile bull trout.

Mining. — Mining and associated timber removal and road construction have the
potential to eliminate bull trout stocks spawning in a particular tributary. A

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recent case illustrating this potential threat was an International Joint Commission
study on the proposed Cabin Creek coal mine in the Cabin and Howell creek drainages
in Canada (International Joint (Amission, 1988). As proposed, the open pit coal
mine would eliminate ten percent of the migratory bull trout spawning stock in
Flathead Lake because of the loss of Howell Creek as a spawning site (Biological
Resources Committee, 1987). The spawning and rearing habitat in Howell Creek would
be destroyed by increased toxic cceipounds of nitrogen in the groundwater, reduction
of groundwater flow, sedimentation from land clearing, and stream channel changes.
Mining activities could be especially damaging because bull trout require streams
with a steady flow of groundwater for successful spawning and survival of incubating
embryos.

Residential, and agricultural development. — Over 73,000 people (1980 census) live
in the Flathead Basin. As the population increases, more domestic sewage will enter
the drainage. Increased agricultural use of fertilizer in the Flathead Valley could
increase nutrient levels in the river. These factors could combine to lower water
quality in Flathead Lake, where bull trout grow to maturity. Reduced water quality
could favor more tolerant nongame fish and introduced fish species.

Although most land in the upper basin is public, some residential development
exists and is ongoing along some tributaries used by spawning bull trout in the North
and Middle Fork drainages. Domestic sewage from this development and stream channel
changes caused by building in the floodplain (where most private land is located)
could reduce habitat quality in some tributaries.

HYdropower development. — Hungry Horse and Bigfork dams have reduced by nearly 50
percent the spawning and rearing habitat available to bull trout in Flathead Lake
(Figure 1) . loss of nearly half of the available stream habitat probably reduced the
population of bull trout in Flathead Lake by a proportional amount.
The construction of Hungry Horse Dam resulted in an estimated loss of 4,000 adult
™ bull trout in Flathead Lake (Fraley et al., 1989). Current operations of Hungry
Horse Dam, which affect flow and temperature, may be affecting bull trout rearing and
movements in the Flathead River below the South Fork.

This major loss of spawning and rearing habitat is largely Irreplaceable.
Migratory bull trout must now rely on only half of their former habitat, making them
more susceptible to environmental degradation in the remainder of the drainage. Loss
of the South Fork and Swan River stocks could have reduced genetic diversity in the
Flathead Lake population.

Harvest of bull trout by anglers. — Because of the restricted distribution of
bull trout spawning in the Flathead Basin and the limited size of the annual spawning
run, harvest of mature fish by anglers in both the lake and river could have a
dramatic effect on the population. We estimate that only 3,000 to 5,000 bull trout
from Flathead Lake escape harvest and successfully spawn in tributaries each year.
Based on harvest and escapement figures in 1981, anglers may have taken up to 40
percent of the adult bull trout that entered the river system. Any increase in
fishing pressure and harvest could reduce the spawning population, cause a loss of
juvenile production, and reduce the population in Flathead Lake.

The segment of the population most vulnerable to overharvest is the upper river
stocks . These fish can be seen in the clear headwater streams and must pass anglers
along the river system to reach spawning areas. Mostly because of this
vulnerability, MDFWP lowered the creel limit in the lake and river from two to one
fish in 1982. A creel survey in 1987 in the North Fork estimated that harvest was
only half that estimated in 1981, although spawning populations did not increase
consistently after the limit was reduced. The British Columbia Ministry of the
Environment reduced the creel limit to one fish in the Canadian portion of the North
Fork in 1983.

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Bull trout are protected from legal angling once they reach many of the
tributaries in which they spawn. MDFWP closed most of the important spawning streams
to angling in the early 1960s, and Glacier Park closed important streams within park
boundaries in the 1970s. In 1983, the B.C. Ministry of the Environment closed to,
angling all North Pork tributaries in Canada used by spawning bull trout. Illegal
harvest of bull trout in tributaries has long been recognized as a serious management
problem. Large bull trout in small tributaries are easily snagged, and lack of
enforcement personnel has made it difficult to reduce poaching in remote areas.

Introduction of non-native fish. — Bull trout coexist with 23 other species of
fish in Flathead Lake, only ten of which are native. Introduced species, such as
lake trout, may compete with bull trout for food and space and may prey on young bull
trout entering Flathead Lake. Kokanee, yellow perch and lake whitefish, as food
items, may provide an advantage for bull trout. In addition, brook trout occupy some
tributary streams and could compete and interbreed with bull trout. It is not
possible to estimate the overall effect on bull trout by these Introduced fish
species. Because of these concerns, MDFWP has adopted a policy of not planting non-
native species where they will compete with native fish stocks in northwest Montana.
The use of non-native fish in private ponds is similarly controlled. New fish
species could be introduced only after completion of an environmental assessment
showing no probable adverse effects.

Populations of non-native opossum shrimp (Mysis relicta) in Flathead Lake have
increased greatly since they became established (from tributary drift) in 1981
(Beattie et al., 1988, Bukantis and Bukantis, 1987). These organisms eat Daphnia
thorata, and they have contributed to the recent decline in zooplankton and kokanee
in Flathead Lake. Young bull trout have been shown to eat Mysi3 in Idaho lakes, so
bull trout in Flathead Lake may benefit by using Mysis as a food item. However,
Mysis may also benefit the lake trout population which could have a negative effect
w on bull trout. Finally, Mysis could cause large-scale changes in the trophic
structure of Flathead Lake that could affect bull trout.

Management and Mitigation Options

Management options that will prevent harmful effects, or mitigate existing
effects on bull trout or their habitat include: 1) Application of Best Management
Practices (BMP's) and riparian guidelines during timber harvest; 2) Stream habitat
protection efforts; 3) improving fish passage to blocked areas; 4) special
management designations such as wild and scenic and wilderness; 5) habitat
enhancement in tributaries; and 6) Integrative Management of fish populations.

BMP.' s and riparian , guidelines . —Application of BMP's greatly reduces damage to
stream habitat during timber harvest operations (Environmental Quality Council,
1988). BMP guidelines address road planning and location, design, drainages from
road surfaces, road construction, and maintenance. BMP's also include guidelines for
timber harvesting, streamside management, slash treatment, stream crossings, winter
logging, and hazardous substances.

In a recent BMP Audit, the Environmental Quality Council (1988) reports that the
most commonly reported violations were iradequate road drainage facilities,
inadequate erosion control from skidding, excessive logging disturbance in the
streamside management zone, and improper management of logging slash. The Council
listed various options, including a forest practices act, to promote the use of BMP's
in Montana. Strict BMP application would reduce the delivery of sediments to
important bull trout spawning and rearing areas.

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The Flathead National Forest has included riparian guidelines for all management
activities, including timber harvest, in their forest plan (USDA Forest Service,
1985) . These guidelines apply to all classified riparian areas and serve to
emphasize protection of fish and wildlife habitat. Specific management standards
were also developed to protect important bull trout spawning and rearing habitat in
the basin. These standards will be amended to reflect new information from ongoing
research and monitoring efforts.

Streambed protection laws. — The county soil and water conservation districts are
responsible for administering the Natural Streambed and Land Preservation Act, which
is designed to protect stream habitat on private lands. The Montana Department of
Fish, Wildlife and Parks cooperates with the conservation districts to inspect
proposed projects which could affect a stream channel. MDFWP administers the Stream
Protection Act, which is designed to protect stream channels on government land.
Approximately 100 projects are reviewed each year. Efforts by MDFWP and the
conservation district have been effective in protecting bull trout habitat in the
basin.

Improved fish passage. — With modifications and/or redesign^ the inoperative fish
ladder at Bigfork Dam could allow bull trout access to 1813 km of drainage area in
the Swan system (Fraley et al., 1989). Tributaries in the Swan drainage where brook
trout have become established could be chemically rehabilitated and planted with bull
trout to establish migratory bull trout runs. Screens placed across the diversion
channel at the damsite diversion channel would minimize mortality of juveniles and
adults moving downstream.

Other opportunities for improving fish passage past natural and man-made
barriers exist in the upper drainage. For example, bull trout spawned in Tunnel
Creek in the Middle Fork drainage before road cxjnstruction and a large culvert
blocked the system to migratory fish.

Special management designations. — Special designations of river corridors and
land areas are an option to protect stream habitat. Currently, over 1.5 million
acres of the upper watershed lie in Glacier National Park and the Bob Marshall-Great
Bear Wilderness complex. Also, much of the upper North and Middle Fork drainage is
included in the wild and scenic rivers system. Many of the major spawning areas for
bull trout in the Middle fork drainage already are protected by these designations.-
Further proposals for wilderness and wild and scenic designations could protect
additional bull trout spawning and rearing habitat from degradation.

Habitat enhancement in tributaries. — The Flathead National Forest and MDFWP
began an experimental habitat enhancement program on Coal Creek in 1988 (Weaver and
Fraley, 1988). Workers felled trees into the stream channel at strategic areas to
provide additional cover for juvenile bull trout rearing in several stream sections.
Control sections were established to gauge the effect of the habitat treatments.
These efforts should increase populations of young bull trout in these sections if
rearing habitat is a limiting factor. If successful, these efforts could be expanded
to more tributaries in the basin to increase rearing capacity and recruitment of
young bull trout to Flathead Lake.

Integrative management of fish populations. — Managers could increase populations
of bull trout in the Flathead Lake-River system by reducing non-native species,
reducing angler harvest on bull trout and increasing limits on competing species, or
by stocking hatchery-reared juvenile bull trout in tributaries or directly into the
lake. Brook trout could be removed from seme tributaries in the Swan and Middle Fork
drainages to reduce competition with rearing bull trout. Removing brook trout from
these tributaries also would reduce the chance of hybridization with bull trout.

In Flathead Lake, lake trout are a competitor with bull trout for food and
space. Increased angling limits on lake trout could allow an increase in numbers
and/or growth of bull trout in the lake. More restrictive limits (shorter season,

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partial closure) on bull trout in the river system during the spawning migration
would increase escapement to tributaries. Also, additional tributaries used by
spawning bull trout in the Middle Fork drainage could be closed to angling for bull
trout.

A bull trout stocking program is a promising management option for enhancing tha
recreational fishery in Flathead lake. Bull trout use a variety of lake and river
habitats, and they are opportunistic feeders (they eat whitefish, perch and Mygjs,).
Bull trout could be cultured in hatcheries and released into Flathead Lake to
increase bull trout populations in the Flathead system. Hatchery fish could
compensate for part of the loss of bull trout spawning and rearing areas caused by
the construction of Hungry Horse and Bigfork dams. Two major methods are available
to culture bull trout: taking eggs from wild fish and incubating the eggs in a
hatchery, or developing a captive brood stock of mature fish that would remain in the
hatchery.

A large hatchery program for bull trout would require careful planning and
evaluation of culture methods. Several years would be required to determine the
feasibility of raising young fish to two or three years of age for release into
tributaries or Flathead Lake to simulate the natural life cycle. Managers have had
limited success in increasing populations of bull trout by striking hatchery
juveniles in the Arrow Lakes system (Peter Brown, British Columbia Ministry of the
Environment, pers. comtn. ) . Five years would be required to develop and determine the
feasibility of captive brood stock. A large bull trout stocking program could alter
the genetics and size of wild bull trout in Flathead Lake.

These and other fisheries management options are now being considered in a five-
year plan for fisheries co-management for the Flathead system being developed by the
Confederated Salish and Kootenai Tribes and Montana Department of Fish, Wildlife and
Parks (1988).

CONCLtEICtS

Virtually all human activities in the upper Flathead watershed have affected (or
could affect) bull trout or their habitat negatively (Table 1). Many of these
activities (timber harvest, road building, residential development, hydropower
operation, poaching) to seme degree continue to affect the bull trout population and
habitat. Hydropower construction blocked nearly half of the original upstream range
and all of the downstream range of adult bull trout in Flathead Lake. This major
restriction of habitat availability and diversity reduced the population in the lake
and probably resulted in increased sensitivity of the population to further
environmental disturbance. Cumulative effects can be more than simply additive; loss
of habitat in one tributary could reduce the overall spawning stock, making other
stocks more vulnerable to overharvest.

The bull trout population has been relatively stable since monitoring began in
1979 (Fraley and Shepard, 1989). However, we have no index of the historical
population level. The present population could be near a threshold where continued
omilative negative effects on habitat or adults could lead to a steep decline. A
major information need for better management is an analysis of limiting factors for
each bull trout life stage.

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Table 1. Cumulative effects of human activities on bull trout
in the upper Flathead watershed.

W*^

i | Life Stage | Direction/ 1
Activity | Potential Effects 1 Affected 1 of Effect 1 Ml tIaetion/'Manaaement Options

Mining | Increased sediment, I embryo. | — | restrict fining activ1t1e« 1n critical drainages
| groundwater contamination | juvenile | |
| channel changes 1 1 1

Timber harvestl increased sediment, 1 embryo. | -- | restrict activities in sediment delivery areas,
road building | channel changes I juvenile | I follow BMP and riparian guidelines, enforce

| | | streaabed protection laws

Residential | lower water quality 1 embryo, | 1 strictly enforce water quality and streambed
and agricul- | end harm physical | juvenile, | | protection laws
tural I habitat 1 adult 1 1

Hydropower | block spawning »1gra- | adult, I I Improve fish passage, plant hatchery fish for
development | tions, change rearing | juvenile | | compensation, maintain minimum flow*
and operation | habitat below dams | | 1

Sport fishing/I remove maturing fish | adult | 1 reduce catch limits or seasons, close tribu-
poaching 1 from the population | | 1 taries to angling. Increase enforcement

Introduction | genetic hybridization, | juvenile, | 1 impose liberal catch limit* on non-natwes,
of non-native | competition, change 1n | aduLt | or | poisoning of tributary fish
fish and | food supply in Flathead | 1 + 1 populations, restrict new species
invertebrates | Lake 1 1 1 introductions

V .. Negative effect on growth and/or abundance
+ Positive effective on growth and/or abuncance

The most likely opportunities for increasing the populations are: (1) a
successful hatchery program to supply young fish for recruitment into Flathead Lake,
and (2) opening blocked areas to increase rearing habitat. Management efforts, such
as habitat protection and improvement and regulations probably will not increase the
population significantly, but will preserve quality rearing and spawning habitat.
The population should be closely monitored through redd counts and estimates o£
juvenile abundance to detect any signs of decline of spawning or rearing fish in
important tributaries. Also, managers should continue to monitor the quality of
spawning and rearing habitat by measuring substrate composition and substrate score.

AO^NCWLEICGMENTS

Michael Enk, Flathead National Forest, Bigfork, reviewed the manuscript and made
helpful suggestions.

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IJTERATURE CITED

Beattie, W.B., P. Clancey and R. Zubik, 1988. Effects of the Operation of Kerr and
Hungry Horse Dams on the Reproductive Success of Kokanee in the Flathead System.
Montana Department of Fish, Wildlife and Parks, Kalispell, MT, 89 pp.

Biological Resources Committee, 1987. Predicted Impacts of the Proposed Sage Creek
Coal Limited Mine on the Aquatic and Riparian Resources of the Flathead River
Basin, British Columbia and Montana. Report to the Flathead River International
Study Board, 352 pp.

Bukantis, R. and J. Bukantis, 1987. Mandibles. Montana Outdoors 18(4):15-17, 26.

Cavender, T.M., 1978. Taxonomy and Distribution of the Bull Trout (Salvelinus
confluentus) From the American Northwest. California Fish and Game 64:139-174.

Fjivironmental Quality Council, 1988. Report for House Joint Resolution 49, Forest
Practices and Watershed Effects. EQC, Helena, MT, 95 pp.

Flathead Basin Commission, 1988. Biennial Report, 1986-1988. Flathead Basin
Commission, Helena, MT, 85 pp.

Fraley, J., 1989. Travelin' Fish. Montana Outdoors 20(2): 32-37.

Fraley, J., B. Marotz, J. Decker-Hess, W. Beattie and R. Zubik, 1989. Mitigation,
Compensation and Future Protection for Fish Populations Affected by Hydropower
Development in the Upper Columbia System, Montana, USA. Regulated Rivers 3: In
Press.

Fraley, J. and B. Shepard, 1989. Life History, Ecology and Population Status of
Migratory Bull Trout in the Flathead Lake and River System, Montana. Northwest
Science 63:In Press.

Holton, G. , 1980. The Riddle of Existence: Fishes of "Special Concern". Montana
Outdoors ll(l):2-6,26.

International Joint Commission, 1988. Impacts of a Proposed Coal Mine in the
Flathead River Basin. IJC, Washington, D.C., 26 pp.

Leathe, S.A. and M.D. Enk, 1985. Cumulative Effects of Microhydro Development on the
Fisheries of the Swan River Drainage, Montana. Volume I, Summary Report.
Montana Department of Fish, Wildlife and Parks, Kalispell, MT, 114 pp.

Montana Department of Fish, Wildlife and Parks, Confederated Salish and Kootenai
Tribes, 1988. Draft Upper Flathead System Fisheries Management Plan. MDFWP,
Kalispell, MT; CSKT, Pablo, MT, 59 pp.

Shepard, B., S. Leathe, T.M. Weaver and M. Enk, 1984. Monitoring Levels of Fine
Sediment Within Tributaries to Flathead Lake, and Impacts of Fine Sediment on
Bull Trout Recruitment. 11 pp. in Wild Trout III, American Fisheries Society
Symposium.

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USEA Forest Service, 1985. Flathead Forest Plan, Flathead National Forest,
^r Kalispell, MP, 559 pp.

Weaver, T.M. and J.J. Fraley, 1988. Coal Creek Fisheries Monitoring Study No. VI and
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Parks, 29 pp.

Weaver, T.M. and R.G. White, 1985. Coal Creek Monitoring Study No. III. Montana
Cooperative Fisheries Research Unit, Bozeman, MT, 94 pp.

W-

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