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Recovery Strategy for the Rocky Mountain Sculpin (Cottus sp.), Eastslope populations, in Canada

3. Description of the species and its needs

Recovery efforts should be based on a sound understanding of the species, including its biology, ecology, and the environmental conditions under which it exists. The following sections describe the environmental setting of the St. Mary and Milk river watersheds, what is known about the Rocky Mountain Sculpin, and what can be inferred from other closely related species.

3.1 Environmental setting

In order to fully understand the implications of the information in the following pages, it is important to understand the context around which the St. Mary and Milk river watersheds are managed through international agreement. The agreement discussed below does not likely negatively affect recovery of the Rocky Mountain Sculpin, Eastslope populations, since the population and distribution objective is one of maintenance and protection of self-sustaining populations. However, it does potentially inhibit the types and scale of activities that could occur within the watersheds of the St. Mary and Milk rivers.

The St Mary and Milk river watersheds are shared between Canada and the United States (U.S.) and as such, they are subject to provisions in the Boundary Waters Treaty of 1909 (the Treaty) between Canada and the United States. The Treaty is administered by a binational organization called the International Joint Commission (IJC) (International St. Mary-Milk Rivers Administrative Measures Task Force [ISMMRAMTF] 2006; see also Dolan 2007; Halliday and Faveri 2007a,b; Rood 2007). The IJC has appointed members by both Canadian and American governments and the Treaty itself provides the principles and mechanisms to resolve disputes concerning shared waters. Both the Milk and St. Mary river watersheds were historically, and are currently intensively managed for agricultural purposes (largely irrigation of crops).

In 1921, an order was made by the IJC, defining the apportionment of the waters in the St. Mary and Milk river watersheds. The context of the apportionment is best considered temporally regarding the irrigation season (April 1 to October 31 annually) and the non-irrigation season (November 1 to March 31). It was agreed that, for the purposes of irrigation and power, both Canada and the U.S. would treat the management of water in the Milk and St. Mary rivers as one stream for the benefit of both countries. Generally, it was resolved that during the irrigation season Canada is entitled to three fourths of the water in the St. Mary River and the U.S. is entitled to one fourth. Whereas in the Milk River, Canada is entitled to one fourth of the water and the U.S. is entitled to three fourths of the water. During the non-irrigation season both countries are to share the flows of both rivers equally. In addition it was agreed that the channel of the Milk River may be used at the convenience of the U.S. for conveyance of water from western Montana to reservoirs in eastern Montana. There are numerous rules and caveats to this water use (e.g. timing and baseline volume of flow, shared tributaries, record keeping etc.) and reference to the Treaty and 1921 Order should be made for more specific information (International Joint Commission Order 1921).

To supply additional water to irrigators in Milk River watershed, a large canal and siphon was constructed to divert water from the St. Mary River in northwestern Montana via the “St. Mary Canal” into the North Milk River (ISMMRAMTF 2006) and subsequently the mainstem Milk River. This water flows eastward in the mainstem Milk River through southern Alberta before entering northeastern Montana, where it is used for irrigation. Canada has limited access to waters in the Milk River that are diverted from the St. Mary River, as per the Treaty and 1921 Order, Canada must let much of the diverted water pass into the U.S. for their use.

Over the past two decades, the St. Mary Canal has transported an average volume of about 2.08 x 108 m3 of water annually into the North Milk River (U.S. Bureau of Reclamation 2004). At present, the operating capacity of the St. Mary Canal is about 18.4 m3/s (<650 cfs), which is significantly less than its original design capacity of about 24 m3/s. These lower flows and overall volume of water are issues for Montana and they hope to replace or rehabilitate the aging canal infrastructure and thereby return the canal to its original capacity of 24 m3/s (K. Miller, pers. comm. April 2010; see also Alberta Environment 2004; U.S. Bureau of Reclamation 2004). This increased capacity would likely only be used during the period of peak runoff each year. However, its use will lead to a surge of flow in the North Milk and Milk rivers in June. Studies are planned to examine the effects of higher flows on erosion in Canadian reaches of both rivers. Sites of particular interest for restoration and/or protection are located at Hilmer Bridge, north of Del Bonita on the North Milk River, and at Goldsprings Park and Weir Bridge on the Milk River.

In summary, the waters in the Milk and St. Mary rivers are intensively managed for irrigation use both in Canada and the U.S. The approach to the management of water in the Milk River watershed and St. Mary River is essentially that water (it varies but about 18.4 m3/s) is diverted from the St. Mary River into the North Milk River commencing by April 1 (or earlier) in any given year. The natural winter flows in the Milk River are generally very low at this time (could be <1 m3/s) so the increase in flows is significant, rising up to 15 m3/s or more in a relatively short period of time. These higher flows continue in the Milk River until September or October when the flows are reduced to natural or close to natural flows as the end of the irrigation season approaches. Both rivers have low winter flows; however, the Milk River watershed flows in the winter are natural flows whereas the flows in the St. Mary River are managed via storage facilities in Montana (Sherburne Reservoir and St. Mary Lake).

3.1.1 St. Mary River

Both the St. Mary and Milk river watersheds originate in Montana along the eastern slopes of the Rocky Mountains and flow north and northeast, respectively, into Alberta (Figure 1) (ISMMRAMTF 2006). The St. Mary River flows into the Oldman River near Lethbridge, Alberta, and eventually to Hudson’s Bay via the South Saskatchewan River, Saskatchewan River, Lake Winnipeg, and Nelson River. The North Milk River flows about 90 km through southern Alberta before its confluence with the Milk River, which continues east parallel to the international boundary for another 235 km before crossing back into the U.S. The Milk River is a tributary of the Missouri River and eventually drains into the Gulf of Mexico via the Mississippi River. Both the St. Mary and Milk river watersheds include lowlands that are viable for agriculture, particularly when irrigated.

The St. Mary River has a total drainage area of about 3600 km2, of which about 2400 km2 is in Alberta (ISMMRAMTF 2006). The river rises at Gunsight Lake in Montana’s Glacier National Park and flows northeast about 65 km through St. Mary and Lower St. Mary lakes before crossing the international border. Close to the outlet (approximately 1 km) of St. Mary Lake in Montana there is Swiftcurrent Creek. This creek has been dammed to create Sherburne Reservoir. The creek has been channelized such that it no longer discharges into the St. Mary River but rather flows into lower St. Mary Lake which then discharges into the St. Mary River. The St. Mary River then meanders north about 55 km through mainly shrub-grassland to the St. Mary Reservoir in Alberta. In the U.S., the drainage basin receives about 1200 mm of precipitation on average annually, mostly as snow (ISMMRAMTF 2006). Within Alberta the average annual precipitation in this drainage ranges from 470 mm in the Foothills Fescue Natural Subregion in the south to 394 mm in the Mixedgrass Natural Subregion in the north (Natural Regions Committee 2006).

Flow in the St. Mary River is maintained during the summer by melt water from the high elevations of Glacier National Park (ISMMRAMTF 2006). At the international border, the average monthly flow is <6 m3/s from December through March (WSC 2008c). Flow usually increases abruptly in the spring to peak in June at 73.0 m3/s on average. It then decreases abruptly over the summer and gradually over the fall. Winter flow is sustained by ground-water base flow. Land use practices that may impair fish habitat do not appear significant in the St. Mary River drainage in either Montana (Mogen and Kaeding 2005a) or Alberta.

Lee Creek is a small tributary stream of the St. Mary River (Mogen and Kaeding 2005b). The creek originates in Montana as snow melt and flows north 13 km before crossing the international border. It then meanders 64 km through the mostly shrub-grassland habitat of southern Alberta before entering the St. Mary River, near the town of Cardston, upstream from the St. Mary Reservoir. The average monthly flow in Lee Creek at Cardston rarely exceeds 1 m3/s from August through February (WSC 2008a). Flow increases over the spring to peak in June at a mean of 5.8 m3/s and then declines abruptly back to the seasonal low flow values by August. Timber is harvested from parts of the Lee Creek drainage on the Blackfeet Reservation in Montana, and along its Tough Creek tributary in Alberta (Mogen and Kaeding 2005b; T. Clayton, pers. comm. 2008).

3.1.2 Milk River

The Milk River is a northern tributary of the Missouri-Mississippi Basin, with a 6500 km2 watershed. It flows north from Montana into Alberta, eastward through the southern portion of the province, and then south back into Montana. The average annual flow entering Alberta is 1.06 x 108 m3 and leaving Alberta is 1.67 x 108 m3. The Town of Milk River is one of the few communities in the Milk River watershed.

As the Milk River in Alberta flows east from the Montana Border, it crosses the Foothills Fescue, Mixedgrass, and Dry Mixedgrass subregions of the Grassland Natural Region (Natural Regions Committee 2006; Milk River Watershed Council Canada 2008). It flows within the confines of a defined valley with limited road access. The surrounding land is semi-arid, short grass prairie that is used primarily for cattle grazing. The river is shallow and turbid, with dynamic hydraulic conditions and lacks higher aquatic plants due to the highly mobile stream bed (D. Watkinson, pers. comm. 2006). Rainfall in the Milk River basin averages only 333 mm annually, 72% of which falls during the growing season (Natural Regions Committee 2006). Periods of high runoff occur briefly in late March and April due to snowmelt and in June and July due to intensive, localized rain storms (McLean and Beckstead 1980).

The Milk River has been severely impacted by changes in its seasonal flow regimes. Water diverted from the St. Mary River in Montana augments flows in the Alberta portion of the Milk River from late March or early April through late September or mid-October (ISMMRAMTF 2006). Under natural pre-diversion conditions summer flows in Canada ranged from 1 to 2 m3/s in the North Milk River to between 2 and 10 m3/s at the Milk River’s eastern crossing of the international border (McLean and Beckstead 1980). Since the diversion, flows in the Milk River at the Town of Milk River have ranged from 10 to 20 m3/s from May to September, and have averaged 15 m3/s between June and August. The effects of flow augmentation are much greater in the North Milk River, which has a relatively small drainage area (238 km2 at the North Milk River gauge 11AA001), than they are downstream at the eastern crossing of the international border, where the river receives runoff from a much larger area (6800 km2 at gauge 11AA031) (McLean and Beckstead 1980). As the Milk River flows through Alberta the concentration of suspended sediment in the water increases, and with it the turbidity (Spitzer 1988). These levels tend to decline over the augmentation period despite flows that remain fairly constant.

When the diversion of water from the St. Mary River is terminated in late September to mid-October, the river reverts to natural flows for the remainder of the winter season (ISMMRAMTF 2006), albeit within a somewhat modified river channel (McLean and Beckstead 1980; Milk River Watershed Council Canada 2008). Ramping down of the diverted flow occurs over about a week, and flows in the river decline over the next several weeks. The decline is most rapid in upstream reaches of the river. Under severe drought conditions, such as those of 2001-2002, there may be little or no surface flow and the lower Milk River can be reduced to a series of isolated pools until spring, although subsurface flows may continue (K. Miller, pers. comm. 2006). At the Town of Milk River, the average flow rate over the period 1912 to 2006 was <2 m3/s in November and February, and <1 m3/s in December and January (WSC 2008b).

Some areas of the Milk River experience protracted periods with little or no surface flow during the non-irrigation period (K. Miller, pers. comm.). Upstream from its confluence with the North Milk River to the Montana Border, surface flow in the Milk River occasionally dries up from July or August until March. The Milk River mainstem east of Aden Bridge dries up less frequently, perhaps on the order of every 15 or 20 years; most recently in 1988 and 2001.

3.2 Species description

The Rocky Mountain Sculpin is a bottom-dwelling fish characterized by a large head, heavy body that tapers towards the tail, and no air bladder (Figure 2). Fish with a total length (TL from tip of snout to tip of tail) of up to 114 mm have been caught in the North Milk River (R.L.&L. Environmental Services Ltd. 2002).

Figure 2. Rocky Mountain Sculpin

Rocky Mountain Sculpin (see long description below).

Photo credit D. Watkinson, Fisheries and Oceans Canada (DFO), Winnipeg.

Description of Figure 2

The Rocky Mountain Sculpin has a green, brown and black mottled colouration and pattern. The dorsal fin extends from the front third of the fish back to the caudal or tail fin. The pectoral or side fins are as large as the body height.

The taxonomic identity of the Rocky Mountain Sculpin is becoming clearer. Sculpins in the St. Mary and Milk river watersheds belong to an undescribed species of the genus Cottus that is widespread in the upper Missouri River system (Taylor and Gow 2008; D. Neely, pers. comm. 2008). Recent morphological and molecular genetic analyses by Taylor and Gow (2008) and Neely (pers. comm.) have demonstrated that a separate population of the same species occupies portions of the Flathead River system in British Columbia, and that these fish are not Cottus bairdi punctulatus as suggested by Troffe (1999) and in the Alberta status report (Alberta Sustainable Resource Development [ASRD] 2004). These analyses also support the distinction of the Rocky Mountain Sculpin from Shorthead Sculpin (C. confusus), Columbia Mottled Sculpin (C. bairdi hubbsi), and other sculpin species in western North America (Committee on the Status of Endangered Wildlife in Canada [COSEWIC] 2005; Taylor and Gow 2008; see also Peden et al. 1989). Efforts are underway to resolve the taxonomy of the western sculpin complex by analyzing samples from Alberta, British Columbia, and Montana (D. Neely, pers. comm.).

3.3 Population and distribution context

3.3.1 Distribution

The Rocky Mountain Sculpin is only found in North America. It occurs in the upper Missouri system from Alberta (i.e., the Milk River) south to southern Montana (in the mainstem to at least Great Falls), and probably the Bighorn system of Wyoming (D. Neely, pers. comm.). It also occurs in Alberta’s St. Mary River, which is a headwater tributary of the Nelson River watershed, and in the lower 24 km of British Columbia’s Flathead River and associated tributaries, which are part of the Columbia River watershed (Peden and Hughes 1984; D. Neely, pers. comm.).

Within Alberta, the Rocky Mountain Sculpin distribution appears to be limited to the St. Mary River system above the St. Mary Reservoir, and the upper Milk and North Milk rivers. It is the only sculpin that occurs in these waters (ASRD 2004). The species’ current distribution has likely been determined by postglacial dispersal and preference for cooler upstream waters (ASRD 2004; Fullerton et al. 2004). Its distribution may have expanded when the St. Mary Canal was constructed in 1917, as the canal enabled fish to move downstream from the St. Mary River into the Alberta portion of the North Milk and Milk rivers (Willock 1969).

The sculpin’s Alberta distribution in the St. Mary River watershed appears to be limited to the lower 35 km of Lee Creek, the lower 500 m of Aetna Creek, and the St. Mary River upstream of the St. Mary Reservoir (Paetz 1993; R.L.&L. Environmental Services Ltd. 2002; COSEWIC 2005; D. Watkinson, unpubl. data). Whether the species inhabited lower reaches of the St. Mary River prior to construction of the reservoir is unknown. However, the abrupt decline in the species’ abundance beginning at the reservoir, suggests that it may have been extirpated from the reservoir, and possibly from areas downstream. As such the St. Mary Reservoir likely represents a major obstacle to downstream dispersal of sculpins in the St. Mary River. The reservoir has very steep banks and almost no littoral zone (English 1977).

Rocky Mountain Sculpin occur in the North Milk River from the Alberta/Montana border downstream to its confluence with the Milk River, and within the Milk River downstream to within 85 km of the border (Willock 1969; Clayton and Ash 1980; R.L.&L. Environmental Services Ltd. 1987, 2002; Paetz 1993; ASRD 2004; COSEWIC 2005; T. Clayton and D. Watkinson, unpubl. data). Tributary use has not been observed as most tributaries of the North Milk and Milk rivers are ephemeral (T. Clayton, pers. comm. 2007). Since the species was first reported in the Milk River in the 1960s (Willock 1969), records of its occurrence have been extended downstream at least 130 km from the North Milk River well into the mainstem Milk River and past the Town of Milk river (Clayton and Ash 1980). Whether this a real change in distribution or a sampling artifact is unknown.

3.3.2 Population size and trends

An overall population estimate is not available for the Rocky Mountain Sculpin in Alberta, but the species is abundant in the St. Mary River upstream from the St. Mary Reservoir; in the lower 13 km of Lee Creek; in the North Milk River; and in the Milk River from Deer Creek upstream to the North Milk River confluence (Paetz 1993; R.L.&L. Environmental Services Ltd. 1987, 2002; P.&E. Environmental Consultants Ltd. 2002; D. Watkinson, unpubl. data).

The sculpin’s abundance is fairly even throughout its Alberta range in the St. Mary River and in the lower reaches of Lee Creek (R.L.&L. Environmental Services Ltd. 2002; D. Watkinson, unpubl. data). From 2006 to 2009, electrofishing of 2787 habitat quadrates in the St. Mary River found an average abundance of 0.62 fish/m2 in habitats shallower than 1 m (D. Watkinson, unpubl. data). Prorating these values over the area of suitable habitat from the U.S. border to the St. Mary Reservoir suggests that this reach of river supports a population of 750 000 Rocky Mountain Sculpins.

Figure 3. Alberta distribution of the Rocky Mountain Sculpin showing key habitat features.

Map showing species occurence andsampling location (see long description below).

Distribution records are from the ASRD Fisheries and Wildlife Management Information System as of May 2010.

Description of Figure 3

Figure 3 is a map showing the species occurrence and sampling location in the St. Mary and Milk river. The majority of species occurrence is in the upper reaches of the St Mary River and in the mid to upper reaches of the Milk River within Alberta. Included for the mid to upper reaches of the Milk and North Milk river are habitat features describing reach breaks, stream gradient and substrate composition.

Within the Milk River the abundance of Rocky Mountain Sculpin appears to decline progressively downstream from the North Milk River until it is absent near the Pinhorn Ranch. Despite severe drought conditions in 2001, this sculpin remained one of the most abundant fish species in some sections of the Milk River in 2002 (P.&E. Environmental Consultants Ltd. 2002). The species is typically more numerous in samples taken during October and November than July and August, but this is likely an artifact of the higher flow and turbidity encountered during the summer (T. Clayton, pers. comm. 2008). Rocky Mountain Sculpin are present in the Milk River upstream from the confluence with the North Milk River (D. Watkinson, unpubl. data), but the species’ abundance there is likely limited by low flow conditions that occur periodically and can extend from late summer through to spring. The potential for fish from the St. Mary River to move downstream via the canal into the Milk River watershed is a complicating factor in determining population sizes and trends in abundance for both populations. Elsewhere, the Flathead River in British Columbia may support a substantial population of Rocky Mountain Sculpin (Peden and Hughes 1984). No information is available on the sizes or trends of populations in the United States.

3.3.3 Nationally significant populations

The Rocky Mountain Sculpin has no direct commercial economic importance but it does have intrinsic value as a contributor to Canada’s biodiversity. Because of its preference for cool waters and clean substrates this fish may serve as a bio-monitor of environmental conditions in the rivers it inhabits (ASRD 2004).

3.4 Needs of the Rocky Mountain sculpin

3.4.1 Biology and life history

Information on the biology and life history of the Rocky Mountain Sculpin in Alberta is available from studies of the St. Mary River by Roberts (1988) and the North Milk and Milk rivers by R.L.&L. Environmental Services Ltd. (2002), and from ongoing work on both watersheds by T. Clayton, Alberta Sustainable Resource Development (ASRD) and D. Watkinson, Fisheries and Oceans Canada (DFO). Where gaps remain, information from other sculpin populations that inhabit similar habitats has been cited. This includes, in particular, work on Rocky Mountain Sculpins that inhabit the West Gallatin River tributary of the Missouri River in southwestern Montana (Bailey 1952) and the Flathead River of British Columbia (Hughes and Peden 1984; Peden et al. 1989). It may also include information from closely related Shorthead Sculpin (Cottus confusus) and Mottled sculpin (Cottus bairdii).


Rocky Mountain Sculpins in the North Milk River can grow to at least 114 mm TL (R.L.&L. Environmental Services Ltd. 2002). Newly hatched young in Montana ranged from 5.8 to 8.1 mm TL, and began feeding at about 9 mm (Bailey 1952). Sculpins in the Flathead River of BC averaged 19.2 mm total length (TL) by mid-September of their first summer (young-of-the-year, age 0+) and ranged from 36 to 43 mm TL by the end of their second summer (age 1+)(McPhail 2007). Most males were sexually mature by their third summer (age 2+), and most females by their fourth summer (age 3+). Young-of-the-year in the St. Mary and Milk river watersheds appear to grow faster, attaining lengths of 30 to 40 mm TL by the end of their first summer (age 0+) (Hughes and Peden 1984; Roberts 1988; D. Watkinson, unpubl. data). This difference does not appear to be the result of mistaking age 1+ fish for young-of-the-year as suggested by McPhail (2007). The smallest mature female examined from the St. Mary or Milk river watersheds was 52.3 mm TL (Roberts 1988).


Gravid female Rocky Mountain Sculpin have been observed in the St. Mary River of Alberta in mid-May at a water temperature of 7.5 °C (Roberts 1988). At the same time, males in the Lee Creek tributary were guarding eggs in 15°C water. Spawning by sculpins in southwest Montana has been documented in June at water temperatures ranging from 7.8 to 12.8°C (Bailey 1952).

Fecundity is directly related to size, and ranges from 100 to about 750 eggs per female in the St. Mary and Milk river watershed populations (Roberts 1988; D. Watkinson, unpubl. data). Rocky Mountain Sculpin in the St. Mary River seldom exceed 87 mm TL, so their egg counts are typically less than 400. Little else is known about the reproduction of these fish in Alberta.

Based on studies in southwestern Montana, some male sculpins are likely polygamous, having multiple mates (Bailey 1952). They construct nests under rocks or sometimes on aquatic vegetation, wood, or debris. Breeding males are dark with a yellow-orange margin on the first dorsal fin (McPhail 2007). More than one female may be attracted to lay a cluster of adhesive eggs on the underside of the nest rock, and a single nest was found to have 1884 eggs (Bailey 1952). In the nest, the pale yellow to orange-yellow eggs are about 2.5 mm in diameter. After spawning, the male fans the developing eggs for several weeks to keep them silt-free. The incubation period is temperature dependent. Based on observations of spawning and hatching dates the incubation in the West Gallatin River was 21 to 28 days, at afternoon water temperatures that ranged from 7.8 to 17.2°C. Eggs taken artificially and held at temperatures between 8.9 and 10.0°C, began hatching 30 days after fertilization and continued for another 10 days. Absorption of the egg sac takes about two weeks (Bailey 1952). Longevity and spawning periodicity are unknown, but a male sculpin collected in Howell Creek, BC was in its seventh growing season (age 6+) (McPhail 2007), and Shorthead Sculpins in Idaho (Gasser et al. 1981) spawn annually following maturity. Genetic studies of Mottled Sculpin suggest that only a small proportion of the potential breeders in a sculpin population may breed successfully in a given year (Fiumera et al. 2002).

Hybridization can occur between Rocky Mountain Sculpin and Slimy Sculpin (Cottus cognatus). It has been documented in an area of the Flathead River below a hydroelectric dam where the release of hypolimnetic water has altered thermal regimes and habitat structure (Zimmerman and Wooten 1981; see also Taylor and Gow 2008).

Ecological role

Sculpins forage at night and eat mostly bottom-dwelling invertebrates. Young-of-the-year sculpins in southwestern Montana feed mainly on midge larvae (Bailey 1952). As the fry grow, the larvae of other bottom dwelling aquatic insects are added to their diet. During the open water period adult Rocky Mountain Sculpins in the St. Mary and Milk river watersheds eat primarily midge larvae (Order Diptera, Family Chironomidae) and caddisfly nymphs (O. Trichoptera) (D. Watkinson, unpubl. data). They also eat mayfly nymphs (O. Ephemeroptera), nematodes (Phylum Nematoda), invertebrate eggs, Trout-perch (Percopsis omiscomaycus), molluscs (Ph. Mollusca), amphipods (O. Amphipoda), water mites (Sub-Order Hydracarina), beetles (O. Coleoptera), and crane fly larvae (F. Tipulidae). Other taxa that have been reported from the adult diet include the molluscs Physa sp. and Pisidium sp., and two fish species, Longnose Dace (Rhinichthys cataractae) and Rainbow Trout (Oncorhynchus mykiss) (Bailey 1952; Paetz 1993; Hughes and Peden 1984; ASRD 2004). Adults will eat fry and eggs of their own species (Bailey 1952).

Rocky Mountain Sculpins in Alberta may be quite sedentary. The estimated home range of sculpins in a small Montana stream was less than 46 m of longitudinal stream channel, with maximum observed dispersal upstream of 180 m and downstream of 153 m (McCleave 1964; see also Bailey 1952). During 1 hour observation periods both small (<50 mm TL) and large (≥ 55 mm TL) Mottled Sculpins in a small Appalachian stream moved within an area less than 0.50 m2 (Freeman and Stouder 1989). Movement data from both studies should be interpreted with caution as the studies were limited in both geographical scope and methodology.

Eighteen fish species, including the Rocky Mountain Sculpin, have been documented in Canadian reaches of the St. Mary River watershed upstream of the St. Mary Dam (T. Clayton, pers. comm. 2007). The dam is a barrier to upstream fish movement. All of these fish species have distributions that overlap that of the Rocky Mountain Sculpin. Walleye (Sander vitreus) that were introduced to the St. Mary Reservoir have become established (Clements 1973). There may be introduced species in the U.S. reaches of the St. Mary River, upstream, that have not been found in Canadian reaches of the river.

Twenty-three fish species, including the Rocky Mountain Sculpin, have been documented in the Milk River mainstem and tributaries in Canada. Nineteen of these species occur within this sculpin’s range in the Milk River.

The recent identification of Trout-perch, Yellow Perch (Perca flavescens), Walleye, and Lake Whitefish (Coregonus clupeaformis) in the Milk River watershed by the MULTISAR (Multi-Species at Risk) Program, a basin-wide terrestrial and aquatic species identification and stewardship program, suggests that fish may be immigrating from Montana or that introductions may be occurring (T. Clayton, pers. comm. 2007). Bull Trout (Salvelinus confluentus) and Pearl Dace (Margariscus margarita) have been entrained in the St. Mary Canal (Mogen and Kaeding 2002), but have not been reported from the Milk River in Canada. [Note: the Lake Chub (Couesius plumbeus), which is common in both rivers but was not identified among the entrained species, is sometimes misidentified as Pearl Dace.] Slimy Sculpin reported by Wells (1977) from the Milk River were probably misidentified Rocky Mountain Sculpin (Roberts 1988).

Competition of the Rocky Mountain Sculpin with other fish species has not been documented in Alberta. Rocky Mountain Sculpin in the Flathead River of British Columbia occupy habitats downstream from those occupied by Slimy Sculpin, with little overlap in their distributions (Hughes and Peden 1984). Likewise, there is no distributional overlap of Rocky Mountain Sculpin with the Spoonhead Sculpin (Cottus ricei), which occurs in the Belly, Waterton, Oldman and Castle rivers, in Willow Creek, and in the St. Mary River below the St. Mary Reservoir (T. Clayton, pers. comm. 2007).

Predation of Rocky Mountain Sculpin in the Milk and St. Mary river watersheds by other fish species has not been documented. Sauger, Walleye, Northern Pike (Esox lucius), and Burbot (Lota lota) likely predate various life stages of Rocky Mountain Sculpin, while eggs and larvae may be consumed opportunistically by other fish species. Garter snakes (Thamnophis sp.) have been observed eating Rocky Mountain Sculpin (D. Watkinson, pers. comm.).


Table 1. Fish species that occur in Canada in the St. Mary River upstream of the St. Mary Dam and/or in the North Milk and Milk rivers, with ranges that overlap (Y) or do not overlap (N) with the Rocky Mountain Sculpin (Nelson and Paetz 1992; T. Clayton and D. Watkinson, unpubl. data). Dashes indicate species that have not been reported.
Common NameScientific NameSt. Mary River/Lee CreekMilk River Watershed
Brassy MinnowHybognathus hankinsoni-----Y
Brook SticklebackCulaea inconstansYY
Bull TroutSalvelinus confluentusY-----
BurbotLota lotaYY
Cutthroat TroutOncorhynchus clarkii-----Footnote aY
Cutthroat Trout x Rainbow Trout hybridOncorhynchus clarkii x Oncorhynchus mykissY-----
Rocky Mountain SculpinCottus sp.NANA
Fathead MinnowPimephales promelasYY
Flathead ChubPlatygobio gracilis-----Y
Iowa DarterEtheostoma exile-----N
Lake ChubCouesius plumbeusYY
Lake WhitefishCoregonus clupeaformisYY
Longnose DaceRhinichthys cataractaeYY
Longnose SuckerCatostomus catostomusYY
Mountain SuckerCatostomus platyrhynchusYY
Mountain WhitefishProsopium williamsoniYY
Northern PikeEsox luciusYY
Northern Redbelly DaceChrosomus eos-----N
Rainbow TroutOncorhynchus mykissY-----
SaugerSander canadensis-----Y
Spottail ShinerNotropis hudsoniusY-----
StonecatNoturus flavus-----Y
Trout-perchPercopsis omiscomaycusYY
WalleyeSander vitreusYY
White SuckerCatostomus commersoniiYY
Western Silvery MinnowHybognathus argyritis-----Y
Yellow PerchPerca flavescens-----N


Footnote A

Genetically pure cutthroat trout may no longer exist in the St. Mary River.

Return to footnote a

3.4.2 Habitat

Habitat preferences

In Alberta, Rocky Mountain Sculpin are associated with cool, clear headwaters (Willock 1969). They tend to be more common in silt-free rocky substrates near stream margins with low to moderate water velocities than in mid-stream areas where velocities are higher (Paetz 1993) (Figure 4). However, as their presence in both the St. Mary and Milk river watersheds suggests, the Rocky Mountain Sculpin is tolerant of periods of suspended sediments during high flows. In rivers or creeks where rocky cover is absent, such as near the Cardston (Lee creek), these fish may use emergent or riparian vegetation for cover.

Figure 4. Rocky Mountain Sculpin on gravel substrate

Rocky Mountain Sculpin (see long description below).

Photo credit T. Clayton, Alberta Sustainable Resource Development, Lethbridge.

Description of Figure 4

Figure 4 is a photo of several large and small size Rocky Mountain Sculpin inhabiting clean pebble and cobble rocky substrate. The fish appear to be resting on the bottom substrate.

The distribution of Rocky Mountain Sculpin in the St. Mary and Milk river watersheds is strongly correlated with stream gradient and substrate type (Clayton and Ash 1980; R.L.&L. Environmental Services Ltd. 2002; D. Watkinson, unpubl. data). During June through October these fish frequented shallow runs and riffles that contained gravel, cobble, or boulders. Areas with moderate to high velocities (0.1-1.8 m/s), shallow water (0.1-1.0 m), and mainly gravel and cobble substrates with thin silt cover (0.0-0.02 m) were preferred (R.L.&L. Environmental Services Ltd. 2002; D. Watkinson, unpubl. data). Young-of-the-year and adults occupied habitat with similar ranges in flow velocity (<1.5 m/s), depth, and substrate but proportionately more young-of-the-year occupied shallower areas with lower water velocities, and silt substrates (D. Watkinson, unpubl. data). The larger fish showed a slight preference for substrates with more interstitial spaces (i.e., less embeddedness).

Rocky Mountain Sculpins occupy habitat with water temperatures up to 23.6°C, basic pH in the typical range of 8.0 to 8.6, conductivity of 100 to 920 (μS/cm), turbidity of 0.34 to 10.3 NTU--but typically less than 3.5 NTU, and dissolved oxygen levels of at least 7.4 mg/L (R.L.&L. Environmental Services Ltd. 2002). Turbidity was seldom sufficient to provide visual cover. In the Milk River, there is an abrupt change in gradient at the confluence with Deer Creek (Clayton and Ash 1980). Rocky Mountain Sculpins were common upstream of this confluence, where the stream gradient ranges from 1.3 to 7 m/km (0.13% to 0.70%), and absent downstream where the gradient is about 0.65 m/km (0.065%) (Clayton and Ash 1980). They were as common at creek mouths as in the river itself (Willock 1969).

Habitat use by specific life stages is not well known. Adults in the Flathead River were abundant in summer at similar water depths and velocities as those used by sculpins in the St. Mary and Milk river watersheds (McPhail 2007). During the day they sheltered in the substrate and at night emerged to forage along river edges in the shallows (<30 cm) where there was little surface current (<0.1 m/s). A September movement by larger males in the Flathead River to areas with faster surface velocities (>0.6 m/s), coupled with their association with large rocks and boulders, and spawning colouration suggest that breeding territories may be established in the autumn (McPhail 2007). During the winter, fish in the West Gallatin River of southwestern Montana lived in water with temperatures ranging from 0 to 2.2°C (Bailey 1952). In the spring, water depth at their nests was over 30 cm, and surface water velocities ranged from 0 to 1.4 m/s. The nests were typically located under rocks that were 12 to 38 cm in diameter.

Juveniles in the Flathead River occupy similar habitats to those used by the adults but are usually found closer to shore in shallower and quieter water (McPhail 2007). This distribution may be a response to predation by and competition with adults in the deeper, faster waters rather than a habitat preference, since both small and large fish prefer deep microhabitat (Freeman and Stouder 1989). Juvenile Rocky Mountain Sculpins can be abundant in silty, low gradient areas of the Milk River (D. Watkinson, unpubl. data) where they may stir up silt to provide cover (Bailey 1952; Willock 1969).

In autumn, young-of-the-year in the Flathead River were associated with sand and detritus substrates in quiet water areas such as pools, root-wads, back-channels, and shallow embayment’s (McPhail 2007).

Habitat availability

Limited information is available for specific habitat types in the Milk River watershed and their use by Rocky Mountain Sculpin. In November 1979, sculpins were found overwintering at most sites surveyed on the North Milk River from 14 to 80 km upstream of the confluence with the Milk River, and on the Milk River from near the Alberta/Montana border downstream to Verdigris Coulee (Clayton and Ash 1980). Sculpins were not found further downstream on the Milk River, at the Deer Creek Bridge or at a site 12 km upstream from the border. The highest numbers were generally caught at sites on the North Milk River. Overwintering habitat may not be limiting for Rocky Mountain Sculpin populations in the Milk River watershed under normal winter flow conditions (R.L.&L. Environmental Services Ltd. 2002). The availability of this habitat type during periods of drought is less certain. Droughts are not an infrequent occurrence in the Milk River watershed and species that occur there may be adapted to such conditions. Little is known about overwintering habitat in the St. Mary River. Low flow conditions also occur in the St. Mary River, but are not as pronounced, with surface flow occurring uninterrupted year-round.

Spawning and rearing habitat are not likely to be limiting for Rocky Mountain Sculpins in the Milk River watershed, since flow augmentation provides a continuous source of fresh, cool water (R.L.&L. Environmental Services Ltd. 2002). Changes to the current flow regime related to the St. Mary Diversion could affect the availability of these habitat types in the Milk River watershed but would be less likely to affect the St. Mary River. Lee Creek would not be affected by changes to the St. Mary diversion.

Ongoing habitat studies have found Rocky Mountain Sculpin to be common and widely distributed in the St. Mary River, from the International Border to the Highway 5 crossing (D. Watkinson, unpubl. data). Fish use of the various habitat types is currently being documented for specific life stages of the Rocky Mountain Sculpin.

Habitat trends and limitations

Completion of the St. Mary Canal in the United States in 1917 (ISMMRAMTF 2006), and of the St. Mary Dam and Reservoir in Alberta in 1951 (Gilpin 2000), significantly altered the hydraulic conditions of both the St. Mary and Milk river watersheds and thereby the availability of sculpin habitat. Flow diversion from the St. Mary River has increased seasonal flows in the North Milk and Milk rivers while reducing flows in the St. Mary River. Given the relative size of the systems, the effects have been more pronounced in the North Milk and Milk rivers, where flow has increased tenfold (McLean and Beckstead 1980). Construction of the St. Mary dam and reservoir replaced lotic (riverine) habitats with lentic (lake) habitats that are unsuitable for the Rocky Mountain Sculpin. Sculpin have not been reported from the impoundment or downstream, where they may have been extirpated by habitat degradation and fragmentation. The effects of flow diversion on upstream reaches of the St. Mary River are less pronounced and have not been
for Rocky Mountain Sculpin habitat. Lee Creek is currently unaffected by flow regulation and any flow diversion is local.

Since 1917, the general character of the North Milk and Milk rivers has remained essentially unchanged although channel widening, increased cut-off activity and higher sediment yield have been documented (McLean and Beckstead 1980). The effects are most prominent in the smaller channel of the North Milk River, where the flood frequency has doubled and the magnitude of the flood flows has increased dramatically since diversion. Flow augmentation continues to erode river banks and reduce fine-sediment bottom habitats in the Milk River (McLean and Beckstead 1980).

Habitat availability in the North Milk and Milk rivers varies from year to year depending on flow, particularly when it is not being augmented during late summer, fall, and winter. There is the potential for Alberta to consider water storage in the Milk River in Canada and feasibility work has been completed (and would have to consulted with the U.S.). However, there are currently no plans to construct a reservoir on the Milk River in Canada and the impact of such a development has not been assessed. Given that reservoirs are not suitable habitat for the Rocky Mountain Sculpin, some adverse effects on the species should be anticipated if a reservoir is built on either system. In addition, should restoration to the St. Mary Canal occur and flows increase from 18.4 m3/s to 24.1 m3/s, changes to sculpin habitat in both the St. Mary and North Milk and Milk rivers are likely (Alberta Environment 2004; U.S. Bureau of Reclamation 2004).

Habitat protection

The Rocky Mountain Sculpin, Eastslope populations, is afforded varying degrees of direct or indirect habitat protection through existing statutes and programs.

Federally, the Fisheries Act (R.S.C. 1985, c. F-14) prohibits any work or undertaking that results in the harmful alteration, disruption or destruction of fish habitat except as authorized by the Minister (S. 35). Subsection 36(3) of the Fisheries Act protects aquatic health by prohibiting the deposit of deleterious substances into waters frequented by fish (i.e. fish habitat). The Canadian Environmental Protection Act (S.C. 1999, c. 33) contributes to sustainable development and protects people and the environment through pollution prevention. The Canadian Environmental Assessment Act (S.C. 1992, c.37) ensures that certain federal regulatory actions including proposed alterations, disruptions, or destruction of fish habitat are subjected to an environmental review process. The Species at Risk Act (S.C. 2002, c.29) prohibits the killing, harming, harassing, capturing or taking individuals of wildlife species listed as extirpated, endangered or threatened (s.32(1)). Section 58 ensures that the critical habitat of listed species at risk is legally protected either by way of a prohibition, under SARA, against the destruction of critical habitat, or by provisions in, or measures under, Species at Risk Act (SARA) or other Acts of Parliament.

At the provincial level, Alberta’s Wildlife Act (R.S.A. 2000, c.W-10) requires that the Minister responsible for that Act establish an Endangered Species Conservation Committee that will advise the Minister on endangered species and make recommendations to the Minister with respect to (among other things) organisms that should be established as endangered species and the preparation and adoption of recovery plans under that legislation. The Environmental Protection and Enhancement Act (R.S.A. 2000, c.E-12) protects land, water, and air by requiring those operating or proposing developments to meet their environmental responsibilities. The Alberta Public Lands Act (R.S.A. 2000, c.P-40) enables the designation of different types of Crown land use including agricultural, oil and gas and other resource uses. The Alberta Water Act (Chapter/Regulation: R.S.A. 2000, c.W-3) focuses on managing and protecting the province’s water, and regulates the allocation of water resources.

Under the “Water for Life” strategy, Alberta supports the formation of Watershed Planning and Advisory Councils and the development of Watershed Management Plans. These plans identify watershed strategies and may influence Government of Alberta policy regarding water use. The needs of fish can be considered in the development of these plans but aquatic protection is only part of their purpose. The Milk River Watershed Council of Canada completed a State of the Watershed Report and a basin Management Plan is underway. The Oldman Watershed Council provides advice on water management in the St. Mary River watershed (S. Petry, pers. comm. 2007).

At writing, 56% of the land bordering the North Milk and Milk rivers was publicly owned; the rest was held privately (T. Clayton, pers. comm. 2006). Only 11% of the public and 14% of the private lands had conservation plans (plans created in part by landowners/users to protect the agricultural way of life and the environment) associated with them that included riparian protection. The remaining land was used mainly for grazing, or for small areas of municipal development (e.g., Town of Milk River). Six percent of the public land along the river was designated as park land, for public use and access during the summer but with restrictions on development. Much of the lands bordering Lee Creek (79%) and the St. Mary River (75%) were held privately (T. Clayton, pers. comm. 2007). The rest was publicly owned or part of the Blood Reserve. The proportion of these lands with conservation plans that include riparian protection is unknown.

Municipal approval is required for shoreline development on any municipal environmental easements. Some other initiatives or agencies that make recommendations affecting water quality and/or water flows, management of shorelines, and other aspects of watershed conservation include: Agriculture Canada, Alberta Agriculture, Alberta Environment, Alberta Health and Wellness, Alberta Riparian Habitat Management Society (Cows and Fish), Ducks Unlimited, Environment Canada, Environmental Farm Planning, Fisheries and Oceans Canada, Health Canada, MULTISAR, Nature Conservancy, and Operation Grassland Community.

3.4.3 Residence of the Rocky Mountain sculpin

In southern Alberta, Rocky Mountain Sculpin generally spawn between May and June when water temperatures reach 7-13°C (Bailey 1952; Watkinson, Unpubl. data). Male sculpin construct nests on the underside of rocks, aquatic vegetation, wood or debris in which a female(s) may deposit clusters of adhesive pale yellow to orange eggs (see Sec. 3.4.1). When a male constructs a nest it will remain at the nest for up to several weeks, beginning prior to egg deposition by a female, and continuing during incubation and early embryo life stages (Peden 2000; Bailey 1952). The male will actively fan the nest post egg deposition to keep the eggs free of silt and may protect the eggs and fry from predators. It is possible that the male stays at the nest until the yolk sac is reabsorbed.

The Species at Risk Act defines a residence as “a dwelling place, such as a den, nest or other similar area or place, that is occupied or habitually occupied by one or more individuals during all or part of their life cycles, including breeding, rearing, staging, wintering, feeding or hibernating”.

The nests created and used by Rocky Mountain Sculpin for spawning demonstrate that there is significant investment in creating and maintaining the nest by sculpin. Thus, nests are considered to be the residence of this fish. The residence is limited to the nest itself and the spawning time period during which the male sculpin maintains the nest structure. This time frame also corresponds to the period of time when eggs, alevins or fry are present in the nest.

Sculpin are largely sedentary and relatively uniform in distribution in Alberta streams where they exist, so nests can likely occur at any location in a stream channel where appropriate structure exists. It is thought that much of the spawning that occurs in the St Mary and Milk river watersheds occurs on the underside of rocks, boulders or debris since usable riparian and instream vegetation is largely absent due to the dynamic and erosive nature of the watersheds. There is likely more opportunity for sculpin spawning to occur on riparian or instream vegetation or woody debris in Lee Creek.

3.4.4 Limiting factors

Too little is known of the Rocky Mountain Sculpin’s physiology or ability to adapt to different conditions to identify all factors that might limit population survival and maintenance. However, because it is a riverine species that has adapted to survive in cool, clear, running waters changing these conditions will likely have an adverse affect on survival of the species. Flow regulation or increased sedimentation might, for example, cause them to lose their advantage to competitors or increase their vulnerability to predators. Many sculpin species do not survive the transition to lake habitats when their streams are impounded, although the reasons are unclear (Peden 2000).

Although it is somewhat uncertain, Rocky Mountain Sculpin from Montana may have colonized the North Milk and Milk rivers via the St. Mary Canal, and may continue to do so in the future in the event that the Alberta population in the North Milk and Milk rivers was to become extirpated. However, the sedentary habits of closely related sculpin species (Bailey 1952; McCleave 1964; Peden 2000) suggests limited potential for re-colonization of upstream habitats such as Lee Creek or the Milk River upstream of its confluence with the North Milk River. Re-colonization of the St. Mary River from the North Milk River is not feasible given five drop structures (30 m long with 30° slopes) and two inverted siphons that create an impassable barrier to upstream migration (K. Miller, pers. comm. 2007). The apparent absence of this species in the Missouri River system downstream from the Milk River precludes re-colonization from within that watershed (Stash 2001).