COSEWIC assessment and update status report on the Westslope Cutthroat Trout (British Columbia and Alberta populations) in Canada
- Assessment Summary
- Executive Summary
- Species Information
- Population Sizes and Trends
- Limiting Factors and Threats
- Special Significance of the Species
- Existing Protection or Other Status
- Technical Summary: British ColumbiaPopulation
- Technical Summary: Alberta Population
- Table 4
- Literature Cited
- Biographical Summary of Report Writers
- Authorities Contacted and Personal Communications
While the original distribution of WCT is not known with certainty, its current native range straddles the Continental Divide (Figure 5). West of the Rocky Mountains, this includes the Salmon, Clearwater, Coeur d’Alene, St. Joe, and Spokane river drainages in Idaho, and the Clark Fork and Kootenai (referred to as Kootenay system in British Columbia) drainages in Idaho, and Montana (downstream to the falls on the Pend d’Oreille River near the Washington-Idaho border; Spahr et al. 1991). A further series of disjunct populations extend westward to the Cascades. These include Lake Chelan in Washington, the John Day drainage in Oregon, and the middle-Columbia River tributaries of Methow, Entiat, and Wenatchee rivers in Washington totalling ~72,900 ha (McIntyre and Rieman 1995). These disjunct populations are likely the product of vicariant events associated with catastrophic flood bursts from Glacial Lake Missoula (Behnke 1992), although some may be of hatchery origin (Shepard et al. 2003).
Westslope cutthroat trout are also native above barriers in the upper Kootenay and Columbia drainages, as well as in the extreme headwaters of the South Thompson drainage in British Columbia. A series of isolated populations in the region originally described as ‘mountain cutthroat’ by Dymond (1931) likely represent recent (postglacial) immigration and subsequent fragmentation of WCT populations, as the areas they inhabit only became available upon retreat of the ice sheets from the region (McPhail and Lindsey 1986). On the eastern slopes of the Rocky Mountains, WCT are native to the upper South Saskatchewan River drainage in Alberta (Bow and Oldman rivers), and the upper Missouri River drainage in southern Alberta, northwestern Wyoming, and Montana (including the headwaters of the Judith, Milk and Marias rivers) to approximately 60 km downstream of Great Falls, Montana (Willock 1969; Behnke 1992).
With the exception of lake trout (Salvelinus namaycush), the original distribution of cutthroat trout was likely greater than any other form of North American trout or salmon (Behnke 2002). Most subspecies, however, particularly the interior forms, have undergone dramatic declines in their numbers and distribution since European settlement (some have disappeared from as much as 90% of the native range). Of the 13 non-coastal subspecies tentatively recognized by Behnke (1992), two are apparently extinct as pure populations. The current global distribution of WCT populations has become extremely fragmented and throughout its range in the United States, WCT are believed to currently occupy ~59% of the 91,000 river kilometres historically occupied circa 1800 (Shepard et al. 2003). Recent genetic testing suggested that WCT populations may be genetically unaltered in as little as 8% of this historical range (Shepard et al. 2003). Unfortunately, this may be an optimistic estimate in that the sites used for that study were not chosen randomly, but were believed to represent pure WCT populations.
Figure 5. General distribution of native and introduced WCT in British Columbia. Core area indicates core native range while peripheral area indicates likely native range where WCT occur in disjunct locations. Points on the map include all observation and stocking records (BC Ministry of Environment 2006).
Canadian range– British Columbia population
The native range of westslope cutthroat in Canada is centred on the upper Kootenay River drainage in British Columbia (Figure 6) and includes all its major tributaries (the White, Lussier, Wild Horse, St. Mary, Bull, and Elk rivers as well as Findlay, Skookumchuk, and Mather creeks). They are also native to the Moyie River system (flowing south of Cranbrook, BC to join the Kootenai River in Idaho) and the Goat River system (which joins the Kootenay River near Creston, BC). To the southeast, WCT are present throughout the headwaters of the upper Flathead River, which flows south out of the province into Flathead Lake before joining the Clark Fork River drainage near Plains, Montana. The area is recognized as an important stronghold for native WCT in Montana and is home to some of the last genetically pure populations in the US (Liknes and Graham 1988; Deeds et al. 1999; Montana Wilderness Association, 2003, Hitt et al. 2003). Disjunct populations of WCT are known to inhabit headwater streams and lakes of the upper Columbia, near Revelstoke, BC, as well as tributaries of the South Thompson River (specifically the Shuswap system). These include Yard, Crazy and Frog creeks, which are tributaries of the Eagle River and Mabel Lake, and some small lakes on Mt. Griffin (all in the South Thompson system); as well as Frog, Isaac, and Kirkup creeks near Revelstoke, and Six Mile and Lasca creeks, which flow into the west arm of Kootenay Lake (all in the Columbia system) [Carl et al. 1967]. They may have been native to the Kicking Horse River drainage near Field, BC (Columbia basin), having gained access to the area through headwater transfer with the upper Kootenay River (Mayhood 1995, 2000).
Canadian range – Albertapopulation
In Alberta, the native range of WCT was likely limited to the Bow and Oldman drainages of the South Saskatchewan River and possibly the headwaters of the Milk River on the eastern slopes of the Rocky Mountains (Sisley 1911; Prince et al. 1912; Willock 1969). In the Bow drainage, WCT were originally found from the extreme headwaters above Bow Lake in Banff National Park, downstream to the plains below Calgary and in all of its major tributaries: the Spray, Cascade, Kananaskis, Ghost, Elbow, and Highwood rivers as well as Jumpingpound and Fish creeks (Prince and McGuire 1912; Behnke 1992, Mayhood 2000). Today, populations in the Bow drainage are generally small and restricted to the extreme headwaters of a few major tributaries and upper mainstem, occupying less than 5% of the native range outside Banff National Park (Mayhood 1995; Figure 7). They are now present in the Bow River only above Lake Louise, in the extreme headwaters of the Spray and Cascade rivers, in three small tributaries of the Kananaskis River, the upper reaches of the Ghost River and a few small tributaries of the Ghost River, and in the upper parts of five tributaries of the Elbow River (Mayhood 1995, Mayhood 2000). There appear to be populations in the Highwood River above the Forest Reserve boundary and in a few, short, highly isolated tributary reaches. The Jumpingpound Creek population is similarly present above the Forest Reserve boundary (Mayhood 2000).
Figure 6. Current distribution of native and introduced WCT inAlberta. Dark circles indicate point observations (Alberta Sustainable Resource Development, 2004).
Figure 7. Summary of levels of hybridization in selectedAlbertadrainages (modified from Janowicz 2004).
In the Oldman River drainage, WCT were present from the headwaters falls below Cache Creek downstream to the plains and in all the Oldman River’s major tributaries: the Livingstone, Crowsnest, Castle, and Belly rivers, as well as Willow Creek (Mayhood 2000). Westslope cutthroat trout still occupy most of the native range in the upper Oldman basin, but are no longer found in the mainstem east of the mountain front and most of its accessible tributaries (Radford 1977; Mayhood et al. 1997). Although populations in the upper Oldman, Livingstone and Castle River basins appear to be reasonably large, populations in the St. Mary and Belly drainages appear small and are not common. The Milk River, which flows north into Alberta from Montana before turning south to join the Missouri River, is one of only a few Canadian tributaries of the Missouri River. Although WCT were collected there historically (e.g., Willock 1969), their current status is unknown and no recent records of WCT in the Milk River have been found.
Introduced populations in Canada
Westslope cutthroat trout have been widely introduced both within and outside of their original native range. Most stocking has been done to enhance or replace extirpated native populations, or to seed naturally fishless areas. To date, such activities in Canada have focused mainly on providing or enhancing recreational angling opportunities rather than on rebuilding populations. Rarely have cutthroat trout become naturalized much beyond the original distribution (Behnke 1992). Introductions were made from non-local source populations and in some cases; WCT X RBT hybrid populations have been knowingly propagated. The scope and nature of these introductions can make it difficult to assess the status of wild populations, as such introductions often serve to obscure trends in native production and may, in fact, further contribute to the decline of native populations (e.g., Scribner et al. 2001; Docker et al. 2003; See LIMITING FACTORS).
The stocking of rainbow trout, other sub-species of cutthroat trout and rainbow trout x cutthroat trout hybrids into native WCT habitat has resulted in hybridization and introgression in some native WCT populations. Such populations should not be included in the count of remaining pure WCT populations but should instead be evaluated as a threat for the purposes of this document (see also Assessed Populations and Limiting Factors and Threats sections). The Canadian native range of rainbow trout only overlaps that of WCT in the Upper Columbia, South Thompson and Lower Kootenay (most upstream extent of range is to between Libby and Troy in Montana where Kootenai Falls prevented further upstream movement). No rainbow trout occurred in the Flathead or Upper Kootenay systems naturally (Benhke 1992), which is the core of WCT native range in Canada. However, RT have been stocked into a number of WCT-containing waterbodies in this region (e.g., see Table 2 for BC DU).
The following section identifies systems stocked with WCT both within and outside the native range of WCT in Canada.
Many naturally fishless systems in southeastern BC have probably been stocked with WCT since the 1920s. These include high elevation headwater lakes and streams, as well as small lakes near urban centres. In addition, WCT have been stocked into a variety of lakes, streams and rivers likely already containing native WCT populations. Within the native range of WCT, a total of 301 streams or lakes have been reportedly stocked with WCT at least once since 1923 (BC stocking records, Fisheries Inventory Summary system (FISS) http://srmwww.gov.bc.cba/fish/fiss/index.html, summarized in Table 2). Unfortunately, it is impossible to determine for many of these waterbodies which ones originally contained native WCT populations prior to stocking. It is also very likely that introduction of WCT into new waterbodies prior to record keeping occurred since early settlers were known to move fish around through the southeastern BC region in hopes of establishing fishable populations.
1 Three waterbodies stocked >5 times with RT (incl. Kikomun Cr=13, Horseshoe L.=70, Tamarack L.=75x)
2 Five waterbodies stocked >5 times with RT (incl. Kootenay L.=67, Slocan R.=34, Slocan L.=51, Meadow Cr.=27, Lamb Cr.=10)
3 One waterbody stocked > 5 times with RT (incl. Salmo R.=25)
4 Six watebodies stocked > 5 times with RT (including, U. Arrow L.=32, L. Arrow L.=49, Columbia River=21, Cedar L.=60x, Halfway L.=25, Lillian L. = 78.
5 One waterbody stocked with RT >5 times (incl. Eagle Cr.=12)
6 No waterbodies stocked more than 5 times with CCT except Angus Cr. in U. Kootenay stocked 8 times)
There have also been a number of WCT introductions into lakes and streams outside of the native range including the lower Fraser River basin, the Okanagan/Kettle/Similkameen basin, coastal systems and the Peace basin. For example, there have been introductions to the tributary systems of the Similkameen River including the Ashnola River, Ladyslipper Lake, Quinesco Lake, Lake of the Woods and Pyramid lake in Cathedral Park. Limited stocking has occurred at two sites in the coastal Bella Coola River system (Blue and Octopus lakes) but was discontinued in 1995 (Mike Ramsay, BC Ministry of Environment, Williams Lake, BC, personal communication 2003). Approximately 70 such waterbodies outside of the native range of WCT have been stocked at least once.
Early stocking records do not consistently list the origin of the hatchery stocks used for these introductions. In at least one case (Seton River), the cutthroat stocked was of coastal origin from the Cowichan River on Vancouver Island. A variety known as ‘Cranbrook Trout’ (an intentionally crossed RBT X WCT hybrid produced by the Cranbrook Hatchery), was stocked throughout Alberta and to a more limited extent in British Columbia until 1964 when the hatchery closed. Other WCT X RBT hybrid stocks (Monroe and Rosebud) were also introduced for a period (1923 -1945) into small lakes and creeks in the upper Kootenay River drainage. Since 1971, all stocked WCT have been derived from Connor Lakes broodstock, considered to be pure WCT from within the native range of the DU (E. Taylor, Department of Zoology University of B.C., Vancouver, B.C.; personal communication 2006; Taylor et al. 2003), and these fish have been mainly stocked within the native range of the DU.
There is no doubt that the stocking of rainbow trout and other cutthroat trout subspecies has affected the genetic integrity of WCT populations in BC. In recent years, almost all rainbow trout stocking within the native range of WCT has been limited to releases into small lakes. Furthermore, a significant portion of these fish are triploid and/or all female stocks. However, the degree to which these lakes are considered ‘closed’ is uncertain, and over 100 water bodies have been stocked since 2000. Furthermore, reproductively viable juvenile Gerrard strain rainbow trout were stocked multiple times into a tributary of Kookanusa Reservoir from 1986 to 1998 (FISS stocking records). During this period, the Montana government also stocked large numbers of reproductively viable rainbow trout from Murray Springs Hatchery into the reservoir. These fish would have access to all connected tributaries and outlets of the reservoir.
In Alberta, WCT have been widely introduced in several major drainages, both within and outside of the original native range, most commonly into previously fishless headwater lakes located above impassable barriers. They have been introduced into several streams in the Oldman and Bow river systems (Mayhood 2000) and into many naturally fishless lakes in Waterton Lakes National Park (Landry et al. 2000). In the upper North Saskatchewan River, a system in which they did not naturally occur (Sisley 1911; Prince et al. 1912), they have been stocked into small headwater lakes above the Clearwater junction and the upper half of Brazeau River (Lake of the Falls, Landslide Lake and some tributaries of the Nordegg River). Recently, they have been introduced into the Bighorn River and Ram River above David Thompson Canyon, to the Athabasca River, Mowitch Creek (Jasper National Park), and into tributaries of the Peace River (Smoky, Wapiti, Simonette, Little Smoky, Pine and the Narraway watersheds) (Nelson and Paetz 1992). While transplanted WCT in Alberta are widespread, individual populations appear to be small and localized with the exception of the Ram River population in the North Saskatchewan River drainage (Mayhood 2000). Populations stocked outside of the natural range are not included in the assessment.
Again, it is often difficult to trace the origin of these introduced stocks. Many of the early introductions were made with eggs and fry imported from the United States (particularly in Waterton Lakes National Park). For several years, eggs were taken from a native population in the Spray Lakes (AB), but when that population was no longer available, fish were obtained from a variety of sources including coastal cutthroat trout stock from Washington State, and a Yellowstone cutthroat trout variety from the Cranbrook hatchery in BC (Ward 1974).
The majority of recent (since 1998) WCT stocking in Alberta has come from Job Lake, a high elevation lake in the North Saskatchewan River basin. Approximately 2‑300,000 WCT eggs are taken from Job Lake every other year to the Sam Livingstone Hatchery for rearing and later planted as fingerlings into various lakes and streams in Alberta (Carl and Stelfox 1989). An average of about 124,000 fish were stocked out every other year from 1988 – 2004 (Alberta Fisheries Management system 2005). Job Lake was barren of fish until 1965 when it was stocked with WCT from Marvel Lake (Banff National Park; McAllister et al. 1981). These fish originally came from a single population native to the Spray Lakes that has since been extirpated due to the construction of the Spray Lakes Reservoir (Ward 1974, Mayhood 2000). The Job Lake hatchery stock, is considered wild stock from within the native range; however, most plantings have been done in lakes, and rarely in streams and rivers (J. Stelfox, Alberta Sustainable Resource Development, personal communication, 2004).
It is certainly true that past introductions have affected the genetic integrity of pure populations. However, there are no instances in Alberta in the past eight years where rainbow trout have been introduced into waters where pure westslope cutthroat trout are still present. In all cases where rainbow trout continue to be stocked in Alberta, there is no longer a pure cutthroat trout population present and a self-sustaining population of rainbow trout has been established from past introduction, but the damage has already been done (Stelfox, pers. comm. 2006).
As indicated above populations outside of the native range are not included in the assessment, and given the uncertainty of the purity of source stocks, neither are introductions or augmentations within the native range. The only steams remaining within the native range in Alberta that still are thought to contain pure populations of what are considered to be pure WCT are those listed in Table 3.
- Date Modified: