Overview

Distribution

Global Range: (20,000-200,000 square km (about 8000-80,000 square miles)) Historically this subspecies occurred in the Yellowstone River drainage in Montana and Wyoming and in the Snake River drainage in Wyoming, Idaho, Utah, Nevada, and probably Washington (Gresswell 2009). About 99 perent of the historically occupied stream habitats were in Wyoming, Idaho, and Montana (May et al. 2007).

Native to the Snake River system above Shoshone Falls (except for waters between Jackson Lake and Palisades Reservoir) and Yellowstone River drainage downstream to the Tongue River; also native to the Goose Creek drainage in Nevada and the Raft River drainage in northwestern Utah (extirpated in the latter area) (Behnke 2002). Lakes with large populations include Yellowstone Lake and Henry's Lake; the latter population is slightly hybridized (Behnke 1992). In the upper Snake River drainage and in tributaries of the Yellowstone River downstream from Yellowstone Park, this subspecies has been largely replaced by non-native and/or hybrid trout (Behnke 1992, 2002). Over the past several decades, millions have been stocked outside the native range, especially in the native range of the westslope cutthroat trout (Behnke 1992).

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endemic to a single nation

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National Distribution

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

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Ecology

Habitat

Montana Valley and Foothill Grasslands Habitat

This taxon can be found in the Montana valley and foothill grasslands ecoregions, along with some other North American ecoregions. This ecoregion occupies high valleys and foothill regions in the central Rocky Mountains of Montana in the USA and Alberta, Canada. The ecoregion the uppermost flatland reaches of the Missouri River drainage involving part of the Yellowstone River basin, and extends into the Clark Fork-Bitterroot drainage of the Columbia River system. The ecoregion, consisting of three chief disjunctive units, also extends marginally into a small portion of northern Wyoming. Having moderate vertebrate species richness, 321 different vertebrate taxa have been recorded here.

The dominant vegetation type of this ecoregion consists chiefly of wheatgrass (Agropyron spp.) and fescue (Festuca spp.). Certain valleys, notably the upper Madison, Ruby, and Red Rock drainages of southwestern Montana, are distinguished by extensive sagebrush (Artemisia spp.) communities as well. This is a reflection of semi-arid conditions caused by pronounced rain shadow effects and high elevation. Thus, near the Continental Divide in southwestern Montana, the ecoregion closely resembles the nearby Snake/Columbia shrub steppe.

A number of mammalian species are found in the ecoregion, including: American Pika (Ochotona princeps), a herbivore preferring talus habitat; Bighorn Sheep (Ovis canadensis), Black-tailed Prairie Dog (Cynomys ludovicianus), who live in underground towns that may occupy vast areas; Brown Bear (Ursos arctos); Hoary Marmot (Marmota caligata), a species who selects treeless meadows and talus as habitat; and the Northern River Otter (Lontra canadensis), a species that can tolerate fresh or brackish water and builds its den in the disused burrows of other animals.

There are six distinct anuran species that can be found in the Montana valleys and foothills grasslands, including: Canadian Toad (Anaxyrus hemiophrys); Western Toad (Anaxyrus boreas); Northern Leopard Frog (Lithobates pipiens); Plains Spadefoot Toad (Spea bombifrons); Columbia Spotted Frog (Rana luteiventris), an anuran that typically breeds in shallow quiet ponds; and the Boreal Chorus Frog (Pseudacris maculata).

Exactly two amphibian taxa occurr in the ecoregion: Long-toed Salamander (Ambystoma macrodactylum), a species who prefers lentic waters and spends most of its life hidden under bark or soil; Tiger Salamander (Ambystoma tigrinum).

Reptilian species within the ecoregion are: Milk Snake (Lampropeltis triangulum), an adaptable taxon that can be found on rocky slopes, prairie and near streambeds; Painted Turtle (Chrysemys picta); Western Plains Garter Snake (Thamnophis radix), a taxon that can hibernate in the burrows of rodents or crayfish or even hibernate underwater; Yellow-bellied Racer (Coluber constrictor); Spiny Softshell Turtle (Apalone spinifera); Western Terrestrial Garter Snake (Thamnophis elegans); Rubber Boa (Charina bottae); Western Skink (Plestiodon skiltonianus); and the Western Rattlesnake (Crotalis viridis).

The ecoregion supports endemic and relict fisheries: Westslope Cutthroat Trout (Oncorhynchus clarki lewisi), Yellowstone Cutthroat Trout (Oncorhynchus clarkii bouvieri), and fluvial Arctic Grayling (Thymallus arcticus), a relict species from past glaciation.

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Habitat Type: Freshwater

Comments: Habitat includes rivers, creeks, beaver ponds, and large lakes; optimum water temperature generally may be 4.5-15.5 C, but tolerance of much warmer temperatures probably occurred historically in larger rivers (now mostly extirpated), and warm-water populations occur currently in some geothermally heated streams, though the fishes there may rely on thermal refugia (see Gresswell 1995).

Resident populations generally spawn within their home range in lotic systems; they may migrate to some degree but do not enter tributary streams; after emergence, fry may move upstream or downstream or remain near the redd (Gresswell 1995).

Fluvial populations migrate from larger streams into tributaries to spawn; juveniles may emigrate as fry or spend 1-3 years in natal tributaries before returning to the mainstem (Gresswell 1995).

Adfluvial populations live in lakes and ascend inlets or descend outlets to spawn; young may move into the lake shortly after emergence, or they may remain in their natal stream for one or more years if the habitat is suitable; spawners may remain in breeding habitat about 1-3 weeks or up to many months (Gresswell 1995). Fry generally use areas of low water velocity. In Yellowstone Lake, juveniles apparently are primarily pelagic.

Spawning streams generally are perennial with groundwater and snow-fed water sources and a gradient usually less than 3 percent; some spawning in intermittent streams does occur (Gresswell 1995). Spawning sites generally have gravel 12-85 mm in diameter, a water depth of about 9-30 cm, and a water velocity of 14-73 cm/sec (see Gresswell 1995). Spawning occurs usually in the natal stream.

See Gresswell (1995) for further details on habitat.

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Migration

Non-Migrant: Yes. At least some populations of this species do not make significant seasonal migrations. Juvenile dispersal is not considered a migration.

Locally Migrant: Yes. At least some populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: No. No populations of this species make annual migrations of over 200 km.

Resident, or migrates short distances between breeding and nonbreeding habitats.

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Trophic Strategy

Comments: Yellowstone cutthroat trout apear to feed on fishes more so than does the westslope cutthroat (Behnke 1992). They are highly piscivorous in some lacustrine habitats but feed opportunistically on zooplankton, larger crustaceans, and aquatic insects in other situations, including some lakes (Gresswell 1995).

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Population Biology

Number of Occurrences

Note: For many non-migratory species, occurrences are roughly equivalent to populations.

Estimated Number of Occurrences: 81 - 300

Comments: This species is represented by a large number of occurrences (subpopulations) and locations (as defined by IUCN). May et al. (2007) identified a total of 383 separate conservation populations. A high percentage of the conservation populations were identified as "core" conservation entities reflecting an unaltered genetic condition.

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Global Abundance

>1,000,000 individuals

Comments: Total adult population size is uncertain but apparently exceeds 1,000,000 (see May et al. 2007).

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General Ecology

Predators include white pelicans, bald eagles, and grizzly bears. Introduced longnose sucker, redside shiner, and lake chub have had no detectable effect on the cutthroat population in Yellowstone Lake (see Behnke 1992 and Gresswell 1995). In Yellowstone Lake, tapeworm infection is common and there is evidence that human infection from eating infected fishes is possible (see Gresswell [1995] for further information on parasites and diseases).

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Life History and Behavior

Cyclicity

Comments: Active feeding may occur at water temperatures as low as 0-4 C (Gresswell 1995).

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Reproduction

Spawner abundance generally increases as water temperature rises and discharge decreases from spring runoff peak; spawning occurs generally between March and August, with migrations beginning when temperatures approach 5 C and peaking at 10-20 C (varies with location) (see Gresswell 1995). Spawning often peaks in June in many areas. Eggs hatch generally in 25-49 days, and juveniles emerge from the gravel 2 weeks later (see Gresswell 1995). Age of spawners varies geographically; youngest spawners generally are 3-5 years old. Average age of spawners in a Yellowstone Lake tributary increased from 3.9 years to 5.6 years after mortality due to angling was reduced; the increase was due mainly to an increase in the number of repeat spawners (see Behnke 1992). Growth rate generally increases as elevation decreases (Gresswell 1995). In different populations, maximum age varies from about 8 to 11 years. Repeat spawning, in consecutive or alternate years, is common, though it may be infrequent where angler harvest is relatively high (Gresswell 1995).

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Conservation

Conservation Status

National NatureServe Conservation Status

United States

Rounded National Status Rank: N4 - Apparently Secure

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NatureServe Conservation Status

Rounded Global Status Rank: T4 - Apparently Secure

Reasons: In determining that petitioned listing of Yellowstone cutthroat trout is not warranted, USFWS (2006) reported the following: At least 195 extant conservation populations of this subspecies collectively occupy 10,220 km (6,352 mi) of stream and lake habitat in Idaho, Montana, Wyoming, Utah, and Nevada. Those 195 populations are distributed among 35 component watersheds in the Snake and Yellowstone River basins. Of those 195 conservation populations, about 133 were considered likely to qualify as potential ''core conservation populations'' comprising nonintrogressed Yellowstone cutthroat trout (99 percent genetic purity standard). If, after further genetic testing the existence of approximately 133 core conservation populations is verified, then those populations would include about 3,009 km (1,870 mi) of habitat encompassing about 29 percent of the existing range of conservation populations of Yellowstone cutthroat trout. Although the distribution of Yellowstone cutthroat trout has been reduced from historical levels and existing populations face threats in several areas of the historic range, USFWS found that the magnitude and imminence of those threats do not compromise the continued existence of the subspecies within the foreseeable future (defined as 20-30 years). Many former threats to Yellowstone cutthroat trout, such as those posed by excessive harvest by anglers or the ongoing stocking of nonnative fishes, are no longer factors that threaten the continued existence of Yellowstone cutthroat trout.

Subsequent analyses (May et al. 2007) confirmed the existence of a large number of conservation populations occupying several thousand of stream kilometers, but concluded that this subspecies depends on continual conservation action.

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Global Short Term Trend: Relatively stable (=10% change)

Comments: Recent trends appear to be stable or upward, with a few notable exceptions (i.e., Yellowstone Lake, Teton River) (USFWS 2006).

Global Long Term Trend: Decline of 70-80%

Comments: Anthropogenic activities have resulted in a substantial reduction in the historical distribution of this subspecies, and many unique local populations have been extirpated (Gresswell 2009). Distribution has declined perhaps by more than 50% over the past 200 years; much of that loss is believed to have occurred in the late 19th and early 20th century (see USFWS 2006).

Yellowstone cutthroat populations are broadly distributed and many remain robust in headwater streams, but migratory populations in large rivers and lakes have declined substantially (May et al. 2007). May et al. (2007) estimated that currently occupied (conservation and sportfishing populations) habitat was 7,527 miles (12,043 kilometers) (43 percent of historical habitat).

Gresswell (2009) concluded that "Currently, this subspecies occupies approximately 27 percent of its historical range, and it appears that the proportion of the range that supports healthy, secure core conservation populations (genetically unaltered and suspected genetically unaltered) is low. Core populations are currently found on 10 percent of the historical range, or 35 percent of the currently occupied range. Only four populations (24 km of stream habitat) exist where non-indigenous salmonids do not occur. Given the array of potential factors that are negatively affecting Yellowstone cutthroat trout populations, persistence of core populations is not certain."

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Threats

Degree of Threat: High - medium

Comments: Although management actions initiated in the past several decades appeared to stabilize, and occasionally improve, the probability of persistence of the Yellowstone cutthroat trout, recent events, including the introduction of non-indigenous lake trout in Yellowstone Lake, the spread of Myxobolus cerebralis (the causative agent of whirling disease), and extended drought in the Intermountain West have resulted in population declines in many areas (Gresswell 2009).

Gresswell (2009) summarized primary threats as follows: "Primary threats to the persistence of Yellowstone cutthroat trout include (1) non-indigenous species, (2) habitat degradation (e.g., surface water diversions, grazing, mineral extraction, timber harvest, and road building), and (3) global climate change. Many of these threats are geographically ubiquitous, and when systems have been exposed to such threats, restoring altered environments to previous conditions is often impossible. Although each of these threats can be significant alone, in combination, the probability of negative consequences increases substantially. Furthermore, the decline and disappearance of individual populations or assemblages have led to increasing isolation and fragmentation of remaining groups, a fact that increases their susceptibility to the demographic influences of disturbance (both human and stochastic) and genetic factors."

Climate change may ultimately be the greatest threat to the persistence of Yellowstone cutthroat trout because it will exacerbate current negative effects of non-indigenous aquatic species and habitat degradation. (Gresswell 2009).

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Management

Restoration Potential: Restoration can be difficult and expensive once native cutthroat populations have been replaced by and/or have hybridized with non-native salmonids.

Management Requirements: Primary management concerns include preventing the establishment of non-native fishes in waters occupied by native cutthroat trout. Once cutthroat trout have been replaced by another salmonid, the situation generally is irreversible without human intervention (Moyle and Vondracek, cited by Gresswell 1995). Elimination/curtailment of trout stocking in streams by state agencies has been helpful in maintaining the genetic integrity of Yellowstone cutthroat trout populations. In the 1980s, chemical treatment of Arnica Creek, a tributary of Yellowstone Lake, apparently was successful in eliminating illegally introduced brook trout (see Behnke 1992), but such removals are expensive and difficult to achieve (Gresswell 1995). Genetic restoration of introgressed populations is needed in some areas.

Introduced lake trout need to be controlled in Yellowstone Lake. Gillnetting or some combination of gillnetting and trapping may be the most effective management actions (Kaeding et al. 1996).

Habitat protection is important, as is enhancement, such as modifying culverts to facilitate fish movement (see Gresswell [1995] for suggestions and references). Other needed management actions include reductions in water diversions, improved riparian management, continued use of angling restrictions (Gresswell 1995).

Management Research Needs: Identify large-scale habitat factors that influence distribution, dispersal, and recolonization so that the effects of current land-use activites and anticipated global climate change can be evaluated (Gresswell 1995). Determine whether life history variation has a genetic basis (Gresswell 1995). Examine life history characteristics in relatively undisturbed populations (Gresswell 1995). Assess the indirect effects of angling, such as redd trampling and bank erosion (Gresswell 1995).

Biological Research Needs: See Gresswell (2009).

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Needs: Protect populations from introductions of non-native salmonids and from excessive harvest. Protect populations in various habitats throughout the range, including multiple representatives of all life history forms.

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Relevance to Humans and Ecosystems

Benefits

Economic Uses

Comments: This is a popular game fish that has been widely stocked in much of the West; different stocks vary in their productivity when stocked in non-native waters (Behnke 1992).

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Risks

Stewardship Overview: Yellowstone Cutthroat Trout Interagency Coordination Group maintains status information, promotes conservation actions, and gathers scientific information appropriate for conserving Yellowstone cutthroat trout (Gresswell 2009).

Persistence of this subspecies will require vigilance and continual conservation action; human intervention will be necessary to bring about the changes required to reduce or eliminate the challenges facing Yellowstone cuttheroat trout (May et al. 2007).

Gresswell (2009) summarized management of this subspecies as follows (abbreviated from original):

Yellowstone cutthroat trout populations are managed as sport fish in the states and national parks. Beyond this basic management strategy, a hierarchical classification for conserving the genetic integrity of cutthroat trout has been developed. Individual groups have been defined as (1) core conservation populations that have not been genetically altered; (2) conservation populations that may be slightly introgressed but have attributes worthy of conservation; and (3) populations managed primarily for their recreational fishery value.

Currently there are two basic management strategies. One strategy focuses on preventing risks associated with non-indigenous species (e.g., introgression, disease, predation, and competition) by isolating populations of Yellowstone cutthroat trout. The second strategy concentrates on connecting occupied habitats to preserve metapopulation function and multiple life-history strategies. In addition, numerous projects are addressing habitat restoration or non-indigenous species removal at a local scale.

A coordinated conservation effort was initiated in 2000 with a Memorandum of Understanding among fish management agencies from the five states where Yellowstone cutthroat trout were historically present (Montana, Idaho, Wyoming, Nevada and Utah) and two federal land management agencies (USDA Forest Service and National Park Service) in the area. The goals of the effort were "to ensure the persistence of Yellowstone cutthroat trout within the historical range" and "to preserve genetic integrity and provide adequate numbers and populations to provide for the protection and maintenance of intrinsic and recreational values" of the subspecies. The objectives included (1) identification of existing populations; (2) protection and enhancement of conservation populations; (3) restoration of extirpated populations; (4) public outreach; (5) data sharing; (6) coordination among agencies; and (7) solutions to common problems and threats. Native American tribes with management responsibility for Yellowstone cutthroat trout have developed similar management and conservation actions. Management activities include population restoration and expansion, and habitat restoration (e.g., riparian fencing, instream habitat improvement, diversion modification, riparian planting, and stream bank stabilization).

Conservation of the subspecies may benefit from a hierarchical approach that includes (1) protection of the strongest core conservation populations; (2) enhancement by reconnecting and replicating the core populations whenever possible; and (3) restoration of populations when practical.

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Names and Taxonomy

Taxonomy

Comments: Introductions have led to hybridization with westslope cutthroat trout and rainbow trout. Hybrids between this subspecies and rainbow trout may not be detectable using morphological/meristic traits alone (e.g., see Kruse et al. 1996). Forbes and Allendorf (1991) found that mitochondrial genotypes had no detectable effects on meristic traits in interbreeding trouts of the subspecies lewisi (westslope) and bouvieri (Yellowstone), which exhibit substantial genetic divergence.

Management actions in the first half of the 1900s, largely in the Yellowstone Lake system, led to the potential mixing of up to 68 historically distinct genetic entities (Gresswell 1995).

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