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Provisional Evaluation of the Status of Westslope Cutthroat Trout in Canada David W. Mayhood Freshwater Research Limited 1213 - 20 Street N.W., Calgary, AB, T2N 2K5, Canada [email protected] ABSTRACT I surveyed existing publications, reports, historical documents, and selected agency files, conducted field surveys, and interviewed reliable observers knowledgeable about selected waters to determine the native and present distribution of westslope cutthroat trout (Oncorhynchus clarki lewisi) in Canada. I evaluated this information in the light of existing knowledge of potential threats to arrive at provisional determinations of risk status. In British Columbia, westslope cutthroats once occupied: the mainstem of the upper Kootenay River and its major tributaries below impassable barriers; certain Columbia River headwaters; and some small, disjunct headwaters, mostly above barrier falls in the lower Kootenay, Columbia, and South Thompson drainages. Most of the apparently genetically pure native stocks still extant in several upper Kootenay tributaries are vulnerable to hybridization with, or replacement by, accessible nonnative salmonids now widespread in that drainage. The population and genetic status of most British Columbia stocks, including many introduced populations, remains undocumented. In Alberta, westslope cutthroats once occupied the mainstems of the Bow and Oldman rivers and their major tributaries below impassable barriers, downstream far into the plains. Except in the upper Oldman and Castle river basins, native stocks are now rare in Alberta, existing only in short reaches of a few isolated headwaters. Genetically pure native stocks are endangered due to their limited and highly fragmented distribution, continued exposure to introgressive hybridization, probable competition from introduced salmonids, continued habitat damage and loss, inadequate legislation and enforcement, and continued exposure to overfishing of some small populations. Already- introgressed stocks are more common, but are threatened for the same reasons. The numerous introduced populations are vulnerable. All but a few are small, isolated, originate from a single stock, and may lack the genetic resources to adapt to future environmental change. Population and genetic surveys are urgently required throughout the Canadian range. Key words: Alberta, Columbia River, Kootenay River, already been declared extinct (Campbell 1997). Oncorhynchus clarki lewisi, westslope cutthroat trout. These statistics touch only on the surface of the problem. Many North American fishes at risk are not yet officially rec- The present wave of human-induced extinction of plants and ognized as such. The westslope cutthroat trout animals, comparable in magnitude to the great natural ex- (Oncorhynchus clarki lewisi) is an example (Behnke 1992, tinctions in the fossil record (Reid and Miller 1989) has not American Wildlands et al. 1998). This subspecies—native to spared the fishes of North America (Ono et al. 1983). Three southeastern British Columbia, southwestern Alberta, west- genera, 27 species, and 13 subspecies have gone extinct in ern Montana, northern Idaho, and small parts of Wyoming, the last century on this continent (Miller et al. 1989). As of Oregon, and Washington—has only recently been proposed 1990, 292 fish species, or 28% of the North American fauna for listing under the United States Endangered Species Act. in fresh water, were in various categories of risk: indetermi- According to extensive evidence cited by the petitioners nate, rare, vulnerable, endangered, or extinct (Williams and (American Wildlands et al. 1998), westslope cutthroats oc- Miller 1990). A total of 364 North American freshwater fish- cupy just 19% of their native range, are represented by viable es are deemed to warrant protection because of their rarity populations in 8% of the native range, and are abundant in (Williams et al. 1989). Presently in Canada, 57 species, sub- just 2% of that range in Montana. In Idaho, viable popula- species, and special populations of freshwater fishes are offi- tions remain in 36% of the native range, and are strong in cially recognized as either in some category of risk or have just 11% of that range. Native populations on the periphery L. M. Darling, editor. 2000. Proceedings of a Conference on the Biology and Management of Species and Habitats at Risk, Kamloops, B.C., 15 - 19 Feb.,1999. Volume Two. B.C. Ministry of Environment, Lands and Parks, Victoria, B.C. and University College of the Cariboo, Kamloops, B.C. 520pp. 579 MAYHOOD of the native distribution in Wyoming, Oregon, and stream to the plains well below the city of Calgary, and from Washington have been similarly devastated. Most U.S. stocks the headwaters to the mouths of its major tributaries: the have hybridized introgressively with other black-spotted Spray, Cascade, Kananaskis, Ghost, Elbow, and Highwood trouts, especially rainbow trout (O. mykiss) and Yellowstone rivers, and Jumpingpound Creek (Prince et al. 1912, cutthroat trout (O. c. bouvieri). Mayhood 1995). In the Oldman drainage the subspecies was As yet there has been no comprehensive assessment of native from the falls in the headwaters below Cache Creek, the status of this fish in Canada. Recently, cutthroat trout downstream far out onto the plains, and from the headwaters were recognized as being at high risk with regard to forestry to the mouths of the major Oldman tributaries: the considerations in British Columbia, and research on the Livingstone, Crowsnest, Castle, and Belly rivers, and Willow species was recommended as a high priority (Haas 1998). Creek. Cutthroats were excluded from almost all high moun- The westslope subspecies is not included on the Red or Blue tain lakes, most of which were formed in hanging valleys and lists in British Columbia (Cannings and Ptolemy 1998) or cirques by waterfalls and steep torrential reaches on the Alberta, and is not presently being considered for listing in glacially steepened sides of the main valleys. Accordingly, the Canada (Campbell 1997). I assessed the status of westslope westslope cutthroat as a native trout in Alberta was primarily cutthroat trout in parts of Alberta and British Columbia a fish of mainstem rivers and their accessible tributaries, (Mayhood 1995, Mayhood et al. 1997a, 1998), but these which were mostly at low elevations. There are numerous analyses considered only parts of the range, or considered historical records indicating that these trout were abundant the whole range at a scale too coarse to support a reasonable throughout most of the native range in Alberta. overall assessment of conservation status. This paper sum- marizes the status of westslope cutthroat trout within its na- Present Status of Native Stocks tive range in this country. The assessment is provisional Westslope cutthroat now occupy considerably less than 5% until up-to-date population surveys, and surveys of the true of the native range in the Bow drainage, being restricted to extent of hybridization using reliable biochemical genetic the extreme headwaters of a few of the major tributaries and techniques, are completed throughout the Canadian range. the upper mainstem (Mayhood 1995). More specifically, westslope cutthroat trout are now absent from the Bow mainstem below Lake Louise; from all but the headwaters of METHODS the Spray River; from all but the extreme headwaters of the I reviewed and surveyed existing information in historical Cascade River; from the Kananaskis River mainstem and all documents, technical publications and reports, agency files, but 3 of its small tributaries; from all but the upper reaches and, in some cases, interviewed people with reliable first- and small upper tributaries of the Ghost River; from the hand knowledge of certain local waters. Principal sources of Elbow River and all but the upper parts of 5 tributaries above information have been listed elsewhere (Mayhood 1995, the Forest Reserve boundary (1 population is known to be in Mayhood et al. 1997a, 1998). The survey was substantially decline; J. Stelfox, Alberta Fish and Wildlife, pers. comm.); more complete in Alberta than in British Columbia. This ma- from the Highwood River below the Forest Reserve boundary terial was supplemented with my own direct field observa- and from all but short, highly isolated reaches of a few tribu- tions of westslope cutthroats during my work in the Alberta taries; and from Jumpingpound Creek below the Forest portion of the native range from 1972 to the present. The Reserve boundary. Most remaining Bow drainage popula- number of data sources reviewed is too large to provide a tions within the native range are tiny and isolated. comprehensive analysis in this paper, and only a brief In the Oldman River drainage westslope cutthroats still overview is supplied here. occupy most of the native range in the upper Oldman basin, but have been lost from native waters in the mainstem east of the mountain front and most of its fish-accessible tribu- STOCK CHANGES AND PRESENT STATUS taries (Radford 1977a, Fitch 1977–80, Mayhood et al. ALBERTA 1997a). Most remaining populations within the native range Native Stocks in the upper Oldman, Livingstone, and Castle river basins Westslope cutthroat trout originally occupied the Bow and appear to be reasonably large. Cutthroat trout are uncom- Oldman river drainages and accessible tributaries (i.e., below mon to rare in the St. Mary and Belly drainages (including waterfalls and other impassable barriers), and may have ex-