Livestock Impacts on Bull Trout

The bull trout, a char, is listed under the Endangered Species Act as threatened in the lower 48 states.  It has been extirpated from about 60 percent of its natural range. Worse, like many native salmonids, it is primarily found in headwater streams with little connectivity to larger river systems. The bull trout is a top apex predator, and as a result not abundant wherever it is found. Bull trout can reach weights of 30 pounds or more.

Livestock production is one of the most widespread activities on western lands, and thus has the potential to negatively impact bull trout where the two activities overlap. Unfortunately the FWS has given short shift to the potential impacts of livestock production upon bull trout.

Livestock production includes more than just grazing of vegetation. Production of irrigated forage like hay requires storage reservoirs created by dams, as well as dewatering from ground water pumping or removal from existing stream flows. Many of these impacts also alter competition between other fish species. For instance heating of water favors the exotic brook trout over native bull trout. All of these impacts to fisheries, particularly fish habitat, are well documented.[i][ii] In particular, fragmentation of larger bull trout populations poses a serious threat to bull trout persistence.[iii]

The historical range of bull trout includes major river basins in the Pacific Northwest like the McCloud River in northern California, the Klamath drainage in Oregon and California and Jarbidge River in Idaho/Nevada as well as throughout the Columbia River drainage which includes the Deschutes, John Day, Malheur, Grand Ronde, Imnaha River, and other rivers in eastern Oregon,such western Montana Rivers as the  Bitterroot, Flathead, Blackfoot, Swan, Clark Fork, as well as Idaho streams like the Salmon River, Lost River, Little Lost River, Lemhi River, Boise River and Clearwater River. The fish is also found east of the Continental Divide in Montana in the headwaters of the St. Mary’s River near Glacier National Park.

All of the above mentioned streams and others not listed, have livestock production along their banks and could impact bull trout. Furthermore, compared to other sources of impacts, livestock can affect bull trout in many ways from effects on habitat quality such as riparian areas to reduction of water removed from streams for irrigation.


Bull trout require what is sometimes termed the Four C’s:  cold water, connected habitat, clean water, and complex habitat. Many bull trout populations are migratory, living much of the year in larger water bodies and rivers, then migrating significant distances to spawn in headwater streams. For instance, bull trout in Montana’s Flathead Lake migrate up tributary rivers like the North Fork of the Flathead to spawn in streams in Montana’s Glacier National Park. Habitat complexity means deep pools, overhanging vegetation, and large logs in the stream. All of these habitat complexity measures are frequently compromised by livestock production, as will be explained below.

There are a number of ways that livestock production can negatively impact bull trout. It is a well established fact that livestock tend to linger near streams and creeks where they obtain water, and graze on the lush riparian vegetation found there. Even a small number of livestock can have significant harmful effects on riparian zones.[iv] [v] This includes bank trampling which can widen stream channels. The shallower stream channels that result allows water to heat up (bull trout require cold water), and also make it easier for predators to capture bull trout, particularly smaller fish.

Cattle use of streams has been documented to impact spawning redds. In one study in Idaho, researchers reported that cattle trampled between 12-78% of simulated redds in one experiment. [vi] In general, it was found that cattle trampling was a major cause of egg loss. [vii]

Cattle damage to riparian areas by removal of vegetation such as willows and overhanging vegetation can also favor invasion from exotic species like brook trout. Cattle damage larger trees like cottonwood by consumption of cottonwood seedlings which can reduce in-stream log structure as old “historic” cottonwoods die, but are not replaced.[viii] Studies reveal that bull trout can usually out-compete brook trout if water is cold and if habitat complexity (i.e. amount of logs, overhanging vegetation, etc.) is intact.[ix]

Cattle and sheep use of riparian areas is also a source of nutrient enrichment from feces which can negatively impact water quality.


Livestock impacts are not just limited to riparian areas. Grazing of uplands can compact soils reducing water infiltration (thus soil moisture storage), and reduce vegetation cover allowing more sedimentation and sheet erosion of soils which ultimately winds up in streams. [x]


The biggest use of water in most of the arid West is for hay and other livestock forage production. Irrigation affects bull trout in many ways. Dams are often constructed on large and small waterways alike, fragmenting habitat and precluding the up and downstream movement of bull trout. Many bull trout populations are migratory. Barriers created by dams, and irrigation withdrawals have significantly impacted migratory populations, leading to collapse of many of these fish populations. [xi]

Not only do dams prevent upstream migration, but irrigation has other impacts as well–many small bull trout are diverted into irrigation canals where they perish.

Irrigation withdrawals also affects water temperature leading to shallower water which in turn heats up quicker and may make the existing and remaining stream water unsuitable for the cold-water-loving bull trout. This is particularly troubling since predicted climate change is likely to increase water temperatures across the region making some waters unsuitable for bull trout.[xii]

Irrigation withdrawals directly from streams and/or due to ground water pumping also affect stream-side riparian vegetation.[xiii] Withdrawals reduce the sub-surface flow of water into surrounding soils, reducing riparian vegetation, which in turn reduces habitat complexity and insects and other food that may fall from streamside vegetation. Withdrawals expose fish to greater predation, particularly from avian predators like kingfishers and eagles.

Dams can also alter natural flow patterns. For instance, more water may be released in summer to accommodate irrigation needs. By the same token, draw downs in winter downstream of dams during water storage periods can expose banks to freezing temperatures and cause mud/sediment to freeze/thaw which increases sediment flow when water is again flowed into the stream. All of these manipulations can degrade bull trout habitat.


Bull trout spawn in the fall and the eggs, and young overwinter in streams that typically have ground water sources. This input of ground water sources can be impacted by livestock grazing. Trampling and compacting of soil around springs, wet meadows and along riparian areas reduces the “sponge” effect of these area and their ultimate contribution to ground water flows in streams. Therefore, cattle use of uplands, particularly the smaller upland streams and other wetlands can potentially impact bull trout survival during winter.


There is a strong correlation between roads and bull trout persistence.[xiv] While logging generates far greater road density, many livestock allotments are reached by roads that often are located immediately next to streams. This has a number of negative impacts. Roads are a well documented source of sedimentation in streams which has some impacts including reduction in deep pools, coverage of spawning beds, and reduction in water clarity which can affect insects hence food for young bull trout.[xv]  Road construction can also diminishes the amount of streamside vegetation which can also harm fish.


Livestock production has many negative impacts on bull trout where the two overlap. Throughout much of its natural range, livestock production is likely the major impact on bull trout by altering riparian and stream habitat, changing water temperatures, altering habitat complexity, contributing to stream sedimentation, and by dam/reservoir storage for irrigation and dewatering for irrigation.


[i] Knapp, R. A., and K. Matthews. 1996. Livestock grazing,

golden trout, and streams in the Golden Trout Wilderness,

California: impacts and management implications.

North American Journal of Fisheries Management


[ii] Platts, W. S. 1991. Livestock grazing. Pages 389–424 in W.

  1. Meehan, editor. Influences of forest and rangeland

management on salmonid fishes and their habitats.

American Fisheries Society, Special Publication 19,

Bethesda, Maryland.


q 1999 by the Ecological Society of America


[iv] Platts, W. S. 1991. Livestock grazing. Pages 389–424 in W.

  1. Meehan, editor. Influences of forest and rangeland

management on salmonid fishes and their habitats.

American Fisheries Society, Special Publication 19,

Bethesda, Maryland.

[v] Hall, F. C., and L. Bryant. 1995. Herbaceous stubble height as

a warning of impending cattle grazing damage to riparian

areas. U.S. Forest Service General Technical Report


[vi] JIM S. GREGORY and BART L. GAMETT Cattle Trampling of Simulated Bull Trout Redds North American Journal of Fisheries Management 29:361–366, 2009

[vii] Douglas P. Peterson, Bruce E. Rieman, Michael K. Young, and James A. Brammer. 2010.Modeling predicts that redd trampling by cattle may contribute to population declines of native trout. Ecological Applications. 20:954–966.



[x] Joy Belsky and Dana Blumenthal. 1997. Effects of livestock grazing on stand dynamics and soils of upland forests in the West. Conservation Biology Pages 315-327.Vol. 11 No. 2.

[xi] Nelson, M.L., McMahon, T.E., and Thurow, R.F. 2002. Decline of the migratory form in

bull charr, Salvelinus confluentus, and implications for conservation. Environmental

Biology of Fishes 64(1-3): 321-332.




q 1999 by the Ecological Society of America


[xv] Platts, W.S., Torquemada, R.J., Mchenry, M.L., and Graham, C.K. 1989. Changes in

salmon spawning and rearing habitat from increased delivery of fine sediment to the

South Fork Salmon River, Idaho. Transactions of the American Fisheries Society 118(3):




  1. Logan Avatar

    I read the abstract of your 6th reference and that information alone is incredible. I may have to purchase access to read the full article. Surely the findings of that report carry over to spawning grounds for cutthroat trout as well.

  2. Gary Humbard Avatar
    Gary Humbard

    This information is from the bull trout draft recovery plan. “Based on our most recent status review (USFWS 2008a), historic habitat loss and fragmentation, interaction with nonnative species, and fish passage issues are widely regarded as the most significant threat factors affecting bull trout”. The plan included dozens of threats, but did not implicate livestock grazing as a major threat, so it’s interesting why the author chose this particular issue.

  3. Ed Loosli Avatar
    Ed Loosli

    Gee Gary, do you think the USFWS is ignoring scientific evidence of negative livestock grazing impacts to the bull-trout for political reasons?? The same political reasons that the USFWS is ignoring the well documented negative impacts of livestock grazing on sage-brush habitat and the greater sage-grouse…The same political reasons favoring of the private livestock industry that is falsely saying the gray wolf has “recovered” as a species, and that the grizzly bear is also “recovered” in the Greater Yellowstone region. Let’s face it, Dan Ashe, Director of the USFWS is in lock-step with the livestock industry in the West, and until he leaves, and the current Interior Secretary leaves, nothing really can be expected for a science driven USFWS.

  4. rork Avatar

    In Frank Church, we always wondered if decline of salmon species wasn’t helping, since bull trout seem like smolt eating machines.


George Wuerthner is an ecologist and writer who has published 38 books on various topics related to environmental and natural history. He has visited over 400 designated wilderness areas and over 200 national park units.

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George Wuerthner