COSEWIC Assessment and Status Report on the Western Silvery Minnow in Canada 2001
Table of Contents
COSEWIC status reports are working documents used in assigning the status of wildlife species suspected of being at risk. This report may be cited as follows:
Please note: Persons wishing to cite data in the report should refer to the report (and cite the author(s)); persons wishing to cite the COSEWIC status will refer to the assessment (and cite COSEWIC). A production note will be provided if additional information on the status report history is required.
COSEWIC 2001. COSEWIC assessment and status report on the Western Silvery Minnow Hybognathus argyritis in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. vii + 14 pp. (www.sararegistry.gc.ca/default_e.cfm)
Previous reports:
Houston, J.J.P. 1997. COSEWIC status report on the western silvery minnow Hybognathus argyritis in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. 14 pp.
Production note:
This publication includes the 1997 report by Houston and an addendum prepared in 2001.
Please note the status recommended in the Section "Evaluation and Recommended Status" of the report may differ from the latest status assigned to the species by COSEWIC.
Également disponible en français sous le titre Évaluation et Rapport de situation du COSEPAC sur le méné d’argent de l’Ouest (Hybognathus argyritis) au Canada.
Cover illustration:
Western Silvery Minnow -- provided by the author.
©Her Majesty the Queen in Right of Canada 2004
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ISBN 0-662-38275-7
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Assessment Summary
| Assessment Summary – November 2001 | |
| Common name | Western Silvery Minnow |
Scientific name |
Hybognathus argyritis |
| Status | Threatened |
| Reason for designation | This species is known in Canada from two rivers in Alberta, one of which flows through short-grass prairie that is subject to continuous erosion leading to increased siltation. |
| Occurrence | Alberta |
| Status history | Designated Special Concern in April 1997. Status re-examined and designated Threatened in November 2001. Last assessment based on an existing status report with an addendum |
Executive Summary
Description
The average size of the Western Silvery Minnow (Hybognathus argyritis) is approximately 76 mm in length with a maximum length of 125 mm. The body is elongate, moderately compressed laterally and has a stout caudal peduncle. The head is short, bluntly triangular with a moderately large eye; the snout is rounded and overhangs the mouth which is subterminal. There is one dorsal fin with eight rays originating slightly in advance of the origin of the pelvic fins which have eight rays, but sometimes seven. The caudal fin is forked; the anal fin originates behind the posterior margin of the depressed dorsal and usually has eight rays, sometimes nine; the pectoral fins are relatively short with 15 or 16 rays.
Small nuptial tubercles may be found on the head, back, sides, and on the fins of breeding individuals (sparse on females, more numerous on males). Both sexes are silvery in colour, hence the common name, with a broad, slaty mid-dorsal stripe. During spawning the males are light yellow along the sides and the lower fins.
Distribution
This is a species of the backwaters of large plains streams found in the Mississippi River basin from the mouth of the Ohio River north to the Missouri Basin and the Milk River in Montana.
In Canada, the Western Silvery minnow is found only in southern Alberta where it is known from the south Saskatchewan River and seven sites on the Milk River.
Population Sizes and Trends
The species is known only from presence and absence data from one collection on the South Saskatchewan River and seven sites on the Milk River in southeastern Alberta. The species was first collected in Alberta from the Milk River in 1961 and subsequent collections between 1971 and 1976 verified its presence at a further six sites along the Milk River, but no further collections have been made from the south Saskatchewan River. The number of specimens collected at each site varied from one to 26 and one site was visited in 1974 and again in 1976, 26 specimens were taken in 1974 and 2 in 1976, apparently the species has not been looked for since. There is no information available to establish population sizes or trends. The species may have been more abundant in upper reaches of the Milk River prior to 1900. Increased turbidity resulting from channelling of irrigation water into the Milk River in the early 1900s may have caused a decline in the population numbers of the species in its Alberta range. The recovery of the river and its vegetation following cessation of this practice has permitted repopulation well into Alberta.
Habitat
There is very little information available on the habitat requirements of the species and none from Canada. The ideal habitat of the species is probably quiet waters rich in phytoplankton as in the U.S. It is a plains species, usually found in the backwaters and pools of larger, northern plains steams where the gravelly, sand, muck or debris covered bottom is not covered by silt. Spawning only occurs where the rate of bottom siltation is low.
General Biology
The biology and ecology of this species have not been studied, but are probably similar to other species of Hybognathus. In Canadian waters, it is believed that the species spawns in May, although no observations have been published.
The diet of the silvery minnows appears to consist of diatoms, algae, and bottom ooze. The pharyngeal papillae found in all species of the Genus may be an accessory filtering system (to the gill arches) adapted for herbivory.
Limiting Factors
Hybognathus argyritis is sensitive to turbidity and siltation which are likely causes of population declines in Missouri and Ohio.
The Milk River flows through short grass prairie habitat which is subject to continuous erosion producing a high rate of silt deposition. Activity such as channelling or overgrazing could increase the already high rate of siltation and lead to extirpation of the species from its Canadian range.
Protection
In the U.S. the species is considered of Special Concern in Wyoming.
In Canada the fish are not subject to any protected status and could not qualify for general protection under Habitat Sections of the Fisheries Act (not commercial species). In Alberta, where the species is considered to be of special concern, general protection could be afforded if required under provincial wildlife and endangered species legislation.
Conclusions
The Western Silvery Minnow has a very limited Canadian range and distribution and is considered a species of special concern in Alberta. It requires clear, weedy habitat free of turbidity, pollution or habitat degradation. The species has obviously been in Alberta for some time, and has been overlooked or perhaps misidentified as the Brassy Minnow until recently. It may be that the species has a refuge here, but industrial, urban and agricultural activity may result in habitat degradation as has occurred for so many species with similar habitat requirements in the northern U.S.
The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) determines the national status of wild species, subspecies, varieties, and nationally significant populations that are considered to be at risk in Canada. Designations are made on all native species for the following taxonomic groups: mammals, birds, reptiles, amphibians, fish, lepidopterans, molluscs, vascular plants, lichens, and mosses.
COSEWIC comprises representatives from each provincial and territorial government wildlife agency, four federal agencies (Canadian Wildlife Service, Parks Canada Agency, Department of Fisheries and Oceans, and the Federal Biosystematic Partnership), three nonjurisdictional members and the co-chairs of the species specialist groups. The committee meets to consider status reports on candidate species.
The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) was created in 1977 as a result of a recommendation at the Federal-Provincial Wildlife Conference held in 1976. It arose from the need for a single, official, scientifically sound, national listing of wildlife species at risk. In 1978, COSEWIC designated its first species and produced its first list of Canadian species at risk. Species designated at meetings of the full committee are added to the list.
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Environment Environnement Canada Canada Canadian Wildlife Service canadien |
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| The Canadian Wildlife Service, Environment Canada, provides full administrative and financial support to the COSEWIC Secretariat. | ||
SPECIES INFORMATION
Introduction
The Western Silvery Minnow, Hybognathus argyritis Girard, 1856, is a small cyprinid (average length » 7.6 cm) of the American mid-west in the Missouri River basin. In Canada, the species is known only from the Milk River and South Saskatchewan river systems in Alberta (Scott and Crossman 1973; Nelson and Paetz 1970, 1992), although Scott and Crossman (1973) give its Canadian range as including southern Manitoba based on one collection from a tributary of the Souris River. However, this citation is in error as the Manitoba specimens, which were catalogued in the Royal Ontario Museum (ROM) collection, were actually verified by E. Holm (ROM) in 1982 as the Brassy Minnow, Hybognathus hankinsoni, a sympatric species (K.W. Stewart, Department of Zoology, University of Manitoba, Winnipeg, Manitoba; personal communication).
This synopsis is a result of a request from officials of Alberta Natural Resources to have the species considered by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC), for possible status determination.
Systematic Note
The genus Hybognathus contains seven species in North America, three of which are found in Canada, i.e., the Western Silvery Minnow, the Eastern Silvery Minnow, Hybognathus regius, and the Brassy Minnow, (Robins et al. 1991; Schmidt 1994). Live specimens of Hybognathus argyritis can be distinguished from the sympatric Brassy Minnow by a pointed dorsal fin and silvery colour (Scott and Crossman 1973; Nelson and Paetz 1992), the possession of four scales between the lateral line and the pelvic fins, a thin black line along side of the body partly over the dark lateral band, and five to 12 radiating grooves on scales lateroventral to the dorsal fin (McAllister and Coad 1974). Hybognathus regius is confined to the Atlantic drainage and is found in Canada only in southwestern Quebec and southeastern Ontario (see Scott and Crossman 1973; Lee 1980). Hybognathus nuchalis, the Mississippi, or Central (Pflieger 1980a), Silvery Minnow occurs in the Mississippi basin and adjacent Gulf slope.
Fishes of this genus are characterized by elongate intestines coiled on the right side, a black peritoneum, and subterminal mouths with crescent-shaped lower jaws, (Scott and Crossman 1973; Page and Burr 1991), and origin of dorsal fin anterior to origin of pelvic fins (McAllister and Coad 1974). Three additional morphological characters that support the monophyly of the genus are the longate anterior processes of the urohyal; enlarged epibranchials; and, organization of pharyngeal papillae (Schmidt 1994).
Along with Hybognathus regius, the Western Silvery Minnow was formerly treated as a synonym of Hybognathus nuchalis, the Central Silvery Minnow, (Pflieger 1980a,b). Scott and Crossman (1973) treated them as subspecies, namely Hybognathus nuchalis nuchalis in the west and Hybognathus nuchalis regius in the east. Pflieger (1971) recommended that Hybognathus nuchalis, Hybognathus argyritis and Hybognathus regius be considered distinct species based on the differences in the shape of the basioccipital process and this has been accepted by the American Fisheries Society (Robins et al. 1991). However, Nelson and Paetz (1992) noted a wide range of variation in Milk River specimens and concluded that a more detailed study of the character and its relation to the significance of Hybognathus taxonomy is needed. Other recent systematic studies of the genus (Hlohowskyj et al. 1989; Schmidt 1994) concluded that Hybognathus argyritis was morphologically similar to Hybognathus regius, but could be also distinguished from Hybognathus regius and Hybognathus nuchalis by differences in the pharyngeal papillae that form a pharyngeal filtering apparatus in Hybognathus.
Description
The average size of the Western Silvery Minnow (Figure 1) is approximately 76 mm total length (T.L.) with a maximum length of 125 mm T.L. (Pflieger 1980b; Scott and Crossman 1973). Maximum length in Alberta is 10 cm fork length (Nelson and Paetz 1992). The body is elongate, moderately compressed laterally and has a stout caudal peduncle. The head is short, bluntly triangular with a moderately large eye; the snout is rounded and overhangs the mouth which is subterminal. The pharyngeal teeth (0, 4-4, 0) are not hooked and have a distinct grinding surface. There is one dorsal fin with eight rays originating slightly in advance of the origin of the pelvic fins which have eight rays, but sometimes seven. The caudal fin is forked; the anal fin originates behind the posterior margin of the depressed dorsal and usually has eight rays, sometimes nine [eight in Alberta (Nelson and Paetz 1992)]; the pectoral fins are relatively short with 15 or 16 rays. The scales are cycloid with eight to 11 long radii; there is a complete lateral line of 38 to 49 scales [36 to 40 in Alberta specimens (Nelson and Paetz 1992)]. The peritoneum is black and the elongate intestine is coiled on the right side; vertebrae number 36 to 38 (see Scott and Crossman 1973; Trautman 1957), but 39 to 41 in Alberta specimens (Nelson and Paetz 1992).
Small nuptial tubercles may be found on the head, back, sides, and on the fins of breeding individuals (sparse on females, more numerous on males). Both sexes are silvery in colour, hence the common name, with a broad, slaty mid-dorsal stripe. Alberta specimens are brownish-yellow dorsally and silver laterally, no lateral band is obvious, but dusky spots may be present (Nelson and Paetz 1992). During spawning the males are light yellow along the sides and the lower fins (Scott and Crossman 1973; Trautman 1957).
DISTRIBUTION
This is a species of the backwaters of large plains streams found in the Mississippi River basin (Figure 2) from the mouth of the Ohio River north to the Missouri Basin and the Milk River in Montana (Pflieger 1980).
Figure 2. North American distribution of the western silvery minnow,Hybognathus argyritis, (after Scott and Crossman 1973; Pflieger 1980).
In Canada, the Western Silvery Minnow is found only in southern Alberta (Figure 3) where it is known from the South Saskatchewan River and seven sites on the Milk River [Pflieger 1980; Scott and Crossman 1973; ROM and UAMZ (University of Alberta Museum of Zoology, Edmonton, Alberta) Collections). It was first collected in Alberta from the Milk River in 1961 (UAMZ 5320), but the first published records were those of Willock (1968) also taken from the Milk River. Henderson and Peter (1969) also report on one specimen 93 mm S.L. taken from the South Saskatchewan River in 1963. They (Henderson and Peter 1969) suggested that the species had invaded the South Saskatchewan River from the Missouri system. No recent collections of the species have been made from the South Saskatchewan River (Nelson and Paetz 1992).
PROTECTION
In the U.S. the species is considered of Special Concern in Wyoming (Johnson (1987).
In Canada the fish are not subject to any protected status and could not qualify for general protection under Habitat Sections of the Fisheries Act (not commercial species). General protection could be afforded if required under Alberta provincial wildlife legislation. The species is considered of special concern in Alberta (Johnson 1987).
POPULATION SIZES AND TRENDS
The species is known only from presence and absence data from one collection on the South Saskatchewan River and seven sites on the Milk River in southeastern Alberta. The species was first collected in Alberta from the Milk River in 1961 (UAMZ 5320) and subsequent collections between 1971 and 1976 verified its presence at a further six sites along the Milk River (UAMZ 2846, 3335, 3234, 3241, 3244, 3548.1, 3838.1). The number of specimens collected at each site varied from one to 26 and one site was visited in 1974 (UAMZ 3548.1) and again in 1976 (UAMZ 3838.1), 26 specimens were taken in 1974 and 2 in 1976, apparently it has not been looked for since. The only known record from the South Saskatchewan River is that reported by Henderson and Peter (1969) and it has not been found there since. Nelson and Paetz (1992) indicate the need for further specimens from the South Saskatchewan River before recognition of its establishment there.
There is no information available to establish population sizes or trends. The species appears to be native to the Alberta fauna and has, no doubt, been there for some time, previously going unnoticed or perhaps misidentified as the Brassy Minnow as it was first described as Hybognathus argyritis by C.P. Girard is 1856 from specimens collected from the Milk River in Montana (Nelson and Paetz 1992). Willock (1968) hypothesized that the species may have been more abundant in upper reaches of the Milk River prior to 1900. Increased turbidity resulting from channelling of irrigation water into the Milk River in the early 1900s may have caused a decline in the population numbers of the species in its Alberta range. The recovery of the river and its vegetation following cessation of this practice has permitted repopulation well into Alberta (Willock 1968).
Willock (1968) provided a hypothesis of the probable history of its occurrence in Alberta and in the Hudson Bay Watershed (South Saskatchewan River). Following deglaciation temporary links existed between the Hudson Bay and Missouri systems and movement in the Missouri system was not difficult. Hybognathus argyritis appears to have moved north from a Missouri Refugium (Crossman and McAllister 1985).
Willock (1968) attributed its loss from extensive areas in the U.S. to increased turbidity and the disappearance of aquatic vegetation and organic debris due to siltation. Apparently it is still abundant where found in the U.S. (Pflieger 1980).
There is very little information available on the habitat requirements of the species and none from Canada. Willock (1968) indicated that the ideal habitat of the species is probably quiet waters rich in phytoplankton as suggested by Trautman (1957) for the Silvery Minnows of Ohio. It is a plains species, usually found in the backwaters and pools of larger, northern plains steams (Pflieger 1980). Although sympatric with the Plains Minnow, Hybognathus placitus, in the Missouri basin, and the Central Silvery Minnow in the Mississippi basin (Figure 4), it occupies a different niche as the Plains Minnow occupies the open channels of the streams (Gilbert 1980) and can tolerate more turbid waters (Gilbert 1980; Hlohowskyj et al. 1989). The Central Silvery Minnow also occupies the backwaters and pools, but usually in smaller streams than those where the Western Silvery Minnow may be found (Pflieger 1980a,b), and is less tolerant of turbid conditions than either of the other two species (Hlohowskyj et al. 1989).
Figure 4. Approximate distributions of Hybognathus argyritis, amarus, nuchalis, placitus and regius. The solid line outlines the range of the Plains Minnow and the dashed line and shaded area are Western Silvery Minnow (modified from Gilbert 1980; Lee 1980; Pflieger 1980 a, b).
Trautman (1957) indicated that both the Western and Eastern Silvery Minnows were most abundant in areas of little or no current, where the waters are rich in phytoplankton and the gravelly, sand, muck or debris covered bottom are not covered by silt. He (Trautman 1957) also found that spawning only occurs where the rate of bottom siltation is low.
Like the Central and Eastern Silvery Minnows spawning probably occurs in heavily vegetated backwaters in slower moving reaches of the streams (Scott and Crossman 1973; Ramshaw and Mandrak 1995).
The young of the Eastern Silvery Minnow appear in small schools along the shore in the emergent vegetation about two weeks post-hatch (Raney 1939).
HABITAT
There is very little information available on the habitat requirements of the species and none from Canada. Willock (1968) indicated that the ideal habitat of the species is probably quiet waters rich in phytoplankton as suggested by Trautman (1957) for the Silvery Minnows of Ohio. It is a plains species, usually found in the backwaters and pools of larger, northern plains steams (Pflieger 1980). Although sympatric with the Plains Minnow, Hybognathus placitus, in the Missouri basin, and the Central Silvery Minnow in the Mississippi basin (Figure 4), it occupies a different niche as the Plains Minnow occupies the open channels of the streams (Gilbert 1980) and can tolerate more turbid waters (Gilbert 1980; Hlohowskyj et al. 1989). The Central Silvery Minnow also occupies the backwaters and pools, but usually in smaller streams than those where the Western Silvery Minnow may be found (Pflieger 1980a,b), and is less tolerant of turbid conditions than either of the other two species (Hlohowskyj et al. 1989).
Figure 4. Approximate distributions of Hybognathus argyritis, amarus, nuchalis, placitus and regius. The solid line outlines the range of the Plains Minnow and the dashed line and shaded area are Western Silvery Minnow (modified from Gilbert 1980; Lee 1980; Pflieger 1980 a, b).
Trautman (1957) indicated that both the Western and Eastern Silvery Minnows were most abundant in areas of little or no current, where the waters are rich in phytoplankton and the gravelly, sand, muck or debris covered bottom are not covered by silt. He (Trautman 1957) also found that spawning only occurs where the rate of bottom siltation is low.
Like the Central and Eastern Silvery Minnows spawning probably occurs in heavily vegetated backwaters in slower moving reaches of the streams (Scott and Crossman 1973; Ramshaw and Mandrak 1995).
The young of the Eastern Silvery Minnow appear in small schools along the shore in the emergent vegetation about two weeks post-hatch (Raney 1939).
GENERAL BIOLOGY
General
The biology and ecology of this species have not been studied, but are probably similar to other species of Hybognathus (Pflieger 1980b). The following discussion is drawn from information on the Central and Eastern Silvery Minnows and the Plains Minnow after Scott and Crossman (1973), Gilbert (1980) Pflieger (1980a,b), and Ramshaw and Mandrak (1995).
Reproduction
Raney (1939) provided a detailed description of the reproductive biology of the Eastern Silvery Minnow from a study of populations in Cayuga Lake, New York. Spawning took place in about 0.3 m of water in late April and early May in heavily vegetated backwaters in slower moving reaches of the streams. Eddy and Underhill (1974) reported that Hybognathus nuchalis (= argyritis) spawns in May and June in Montana. The eggs were about 1 mm in diameter, non-adhesive and egg number varied with female size, varying from 2000 in a 60 mm female to 6600 in a 90 mm female. The eggs hatched in six to seven days with the water temperature varying between 13.3°C and 20.5°C. When propagated in ponds, the Eastern Silvery Minnow reached maturity and spawned at age two, and spawned again the following year (Raney 1942).
In Canadian waters, it is believed that the species spawns in May, although no observations have been published (Scott and Crossman 1973). The Central Silvery Minnow appears to have a similar reproductive biology (Forbes and Richardson (1920). Spawning in the Plains Minnow is protracted from April to August (Gilbert 1980) and there is evidence to suggest that the same may be the case for the Eastern Silvery Minnow (Scott and Crossman 1973).
Growth
Newly hatched larvae of the Eastern Silvery Minnow measured 6 mm T.L. and were 38 mm T.L. by July and about 51 mm by August. Females appear to spawn at one year of age at about 50 to 55 mm S.L., but males probably do not spawn until their second year (Raney 1939). Larval stages have been described and illustrated by Mansueti and Hardy (1967).
Species Movement
The Eastern Silvery Minnow migrates to spawning grounds in large schools. In Raney (1939) noted that this migration reached its peak in April in New York. Gascon and Leggett (1977) found large postspawning congregations of the Eastern Silvery Minnow in early summer in Quebec.
Diet
The diet of the Eastern Silvery Minnow consists of diatoms, algae, and bottom ooze (Raney 1939; Eddy and Underhill 1974). The Central Silvery Minnow apparently has a similar diet (Pflieger 1989a) as does the Plains Minnow and probably all species of Hybognathus (Gilbert 1980). The pharyngeal papillae found in all species of the Genus may be an accessory filtering system (to the gill arches) adapted for herbivory (Hlohowskyj et al. (1989).
Gascon and Leggett (1977) outlined the diet of the Eastern Silvery Minnow in Lac Memphrémagog, Quebec. The diet of 0+ fish changed from cladocerans (82% by volume), rotifers (8.4%) and chironomids (7%) to organic detritus (95%) and cladocerans (3%), as the average fork length (F.L.) increased from 32 mm to 44 mm. Individuals greater than 40 mm F.L. fed almost exclusively on organic detritus, except in June when 46% of their diet was cladocerans.
Parasites
Three species of trematodes, one protozoan, and the larval form of the cestode, Ligula intestinalis, have been listed as parasites of silvery minnows in North America (Hoffman 1967).
LIMITING FACTORS
Hybognathus nuchalis is sensitive to turbidity and siltation (McAllister and Coad 1974) which are likely causes of population declines in Missouri and Ohio (Pflieger 1971, Trautman 1957). Hlohowskyj et al. (1989) suggested that the finer, densely crowded pharyngeal papillae of the Central Silvery Minnow may be related to this. The Rio Grande Silvery Minnow, Hybognathus amarus, (restricted to the Rio Grande drainage) and the Plains Minnow, [sympatric with the Central Silvery Minnow in the Mississippi basin (Figure 3)] are often found in turbid habitats. These species have shorter, less crowded papillae and appear to be well-adapted to silty environments (Hlohowskyj et al. 1989).
The Western and Eastern Silvery minnows possess pharyngeal papillae intermediate to those in Hybognathus nuchalis, and the Rio Grande and Plains minnows (Hlohowskyj et al. 1989), and are thought to be less sensitive to turbidity and siltation than the Central Silvery Minnow. Massé and Mongeau (1976), for example, relate a decrease in abundance of Hybognathus regius (and other fishes) to increased turbidity and siltation resulting from ship-induced wave action in the St. Lawrence River at Montreal. The Western Silvery Minnow and the Plains Minnow usually occupy different habitats, the former being found in backwaters and pools of larger plains streams (Pflieger 1980), and the latter in open, shallow river channels (Gilbert 1980).
Trautman (1957) indicated that both the Western and Eastern Silvery Minnows were intolerant of silt and turbidity and felt that increased turbidity was responsible for the extirpation of the Eastern Silvery Minnow in Ohio.
The Milk River flows through short grass prairie habitat which is subject to continuous erosion producing a high rate of silt deposition. Activity such as channelling or overgrazing could increase the already high rate of siltation and lead to extirpation of the species from its Canadian range (Willock 1968.
SPECIAL SIGNIFICANCE OF THE SPECIES
The Western Silvery Minnow is probably an important forage species where abundant, but in the northern parts of the range it may be too rare to be of significance. In the U.S. it may have some value as a bait fish (Eddy and Underhill 1974), but in Canada it is not commonly used as a bait fish as it does not survive well in a bucket (Scott and Crossman 1973).
The recent appearance in Canada and its distribution and habitat requirements are of interest to science in relation to the zoogeographic history and distribution of species subsequent to the Wisconsin Period of glaciation.
EVALUATION
The Western Silvery Minnow has a very limited Canadian range and distribution and is considered a species of special concern in Alberta. It appears that the species may be less sensitive to siltation and turbidity than the Central Silvery Minnow, but like the Eastern Silvery minnow probably requires clear, weedy habitat free of turbidity, pollution or habitat degradation. The species has obviously been in Alberta for some time, and has been overlooked, or perhaps misidentified as the Brassy Minnow until recently. It may be that the species has a refuge here, but industrial, urban and agricultural activity may result in habitat degradation as has occurred for so many species with similar habitat requirements in the northern U.S. Given the restricted range and apparent rarity of the Western Silvery Minnow in Canada the species should be considered as Vulnerable.
ACKNOWLEDGEMENTS
The author would like to thank R. Campbell, Subcommittee Chairman of the COSEWIC Fish and Marine Mammals Subcommittee for helpful comments and advice in preparing this report. Thanks also to E.J. Crossman and E. Holm of the Royal Ontario Museum for provision of ROM collection records and for their critical review and comments. Financial support was provided by World Wildlife Fund (Canada) and the Department of Fisheries and Oceans.
LITERATURE CITED
Crossman, E.J., and D.E. McAllister. 1985. Zoogeography of freshwater fishes of the Hudson Bay drainage, Ungava Bay and the Arctic Archipelago. Pages 54-101 in The Zoogeography of North American freshwater fishes. Edited by C.H. Hocutt and E.O. Wiley. John Wiley and Sons, New York, New York.
Eddy, S., and J.C. Underhill. 1974. Northern fishes. University of Minnesota Press, Minneapolis, Minnesota.
Forbes, S.A., and R.E. Richardson. 1920. The fishes of Illinois. Illinois Natural History Survey 3: 1-357.
Gascon, D., and W.C. Leggett. 1977. Distribution, abundance, and resource utilization of littoral zone fishes in response to a nutrient/production gradient in Lake Memphremagog. Journal of Fisheries Research Board of Canada. 34: 1105-1117.
Gilbert, C.R. 1980. Hybognathus placidus Girard, Plains minnow. Page 178 in Atlas of North American freshwater fishes. Edited by D.S. Lee, C.R. Gilbert, C.H. Hocutt, R.E. Jenkins, D.E. McAllister, and J.R. Stauffer Jr. North Carolina State Museum of Natural History, North Carolina Biological Survey Publication 1980-12.
Henderson, N.E., and R.E. Peter. 1969. Distribution of fishes of southern Alberta. Journal of the Fisheries Research Board of Canada 26(2): 325-338.
Hlohowskyj, C.P., M.M. Coburn, and T.M. Cavender. 1989. Comparison of a pharyngeal filtering apparatus in seven species of the herbivorous cyprinid genus Hybognathus (Pisces:Cyprinidae). Copeia 1989: 172-183.
Hoffman, G.L. 1967. Parasites of North American freshwater fishes. University of California Press, Los Angeles, California.
Johnson, J.E. 1987. Protected fishes of the United States and Canada. American Fisheries Society, Bethesda, Maryland.
Lee, D.S. 1980. Hybognathus regius Girard, Western silvery minnow. Page 179 in Atlas of North American freshwater fishes. Edited by D.S. Lee, C.R. Gilbert, C.H. Hocutt, R.E. Jenkins, D.E. McAllister, and J.R. Stauffer Jr. North Carolina
State Museum of Natural History, North Carolina Biological Survey Publication 1980-12.
McAllister, D.E., and B.W. Coad. 1974. Fishes of Canada's National Capital Region. Fisheries Research Board of Canada Miscellaneous Special Publication No. 24. Ottawa, Ontario.
Mansueti, A.J., and J.D. Hardy Jr. 1967. Development of fishes of the Chesapeake Bay Region. Par I. National Research Institute, University of Maryland, Baltimore Maryland.
Massé, G. and J.-R. Mongeau. 1976. Influence de la navigation maritime sur la repartition geographique et l'abondance relative des poissons du Fleuve Saint Laurent, entre Longeuil et Sorel. Service de l'Amenagement de La Faune. Ministère du Tourisme de La Chasse et de La Pêche. Montreal, Québec.
Nelson, J.S., and M.J. Paetz. 1970. The fishes of Alberta. University of Alberta Press, Edmonton, Alberta.
Nelson, J.S., and M.J. Paetz. 1992. The fishes of Alberta. Second Edition. University of Alberta Press, Edmonton, Alberta.
Page, L.M., and B.M. Burr. 1991. A field guide to freshwater fishes, North America: North of Mexico. Houghton Mifflin Company. Boston, Massacheusetts.
Pflieger, W.L. 1971. A distributional study of Missouri fishes. University of Kansas Museum of Natural History Publication. 20: 225-570.
Pflieger, W.L. 1980a. Hybognathus nuchalis Agassiz, Central silvery minnow. Page 177 in Atlas of North American freshwater fishes. Edited by D.S. Lee, C.R. Gilbert, C.H. Hocutt, R.E. Jenkins, D.E. McAllister, and J.R. Stauffer Jr. North Carolina State Museum of Natural History, North Carolina Biological Survey Publication 1980-12.
Pflieger, W.L. 1980b. Hybognathus argyritis Girard, Western silvery minnow. Page 174 in Atlas of North American freshwater fishes. Edited by D.S. Lee, C.R. Gilbert, C.H. Hocutt, R.E. Jenkins, D.E. McAllister, and J.R. Stauffer Jr. North Carolina State Museum of Natural History, North Carolina Biological Survey Publication 1980-12.
Ramshaw, W.H., and N.E. Mandrak. 1997. Status of the Eastern Silvery Minnow, Hybognathus regius, in Canada. Report to the Committee on the Status of Endangered Wildlife in Canada (COSEWIC). Canadian Wildlife Service, Ottawa, Ontario K1A 0H3.
Raney, E.C. 1939. The breeding habits of the Eastern Silvery Minnow, Hybognathus regius Girard. The American Midland Naturalist 21: 674-680.
Raney, E.C. 1942. Propagation of the Silvery Minnow (Hybognathus regius Girard) in ponds. Transactions American Fisheries Society 71: 215-218.
Robins, R.C., R.M. Bailey, C.E. Bond, J.R. Brooker, E.A. Lachner, R.N. Lea, and W.B. Scott. 1991. Common and scientific names of fishes from the United States and Canada. Fifth Edition. American Fisheries Society Special Publication 20. Bethesda, Maryland.
Schmidt, T.R. 1994. Phylogenetic relationships of the genus Hybognathus (Teleostei: Cyprinidae). Copeia 1994: 622-630.
Scott, W.B., and E.J. Crossman. 1973. Freshwater fishes of Canada. Fisheries Research Board of Canada Bulletin 184.
Trautman, M.B. 1957. The fishes of Ohio. Ohio State University Press, Columbus, Ohio.
Willock, T.A. 1968. New Alberta records of the silvery and brassy minnows, stonecat and sauger, with a preliminary list of fishes of the Milk River in Alberta. Canadian Field-Naturalist 82(1): 18-23.
THE AUTHOR
Jim Houston has been the Environmental Advisor of the Canadian Section of the International Joint Commission (IJC) since June, 1986. Before coming to the IJC, Mr. Houston worked with the Department of Fisheries in Ottawa and Burlington from 1982 to 1986 where he served in a number of capacities, including assessing northern and inland fisheries.
After receiving his B.Sc. in Marine Biology from the University of Guelph, Ontario, Mr. Houston consulted on a number of projects for the Department of Fisheries and Oceans and World Wildlife Fund Canada. He has authored or co-authored over a dozen papers on the status of fish and marine mammals in Canada. Recently, he became a fellow member in an international group which has demonstrated skills for leadership in environment and development.
COSEWIC Status Report
Alberta, Environment, Fisheries and Wildlife Management Division initiated studies to assess the distribution and relative abundance of "Species at Risk" in accordance with the National Accord for the Protection of "Species at Risk". Three fish species of concern were identified in the St Mary and Milk river drainages, one of these being the western silvery minnow, Hybognathus argyritis. Summer and fall collection programs were conducted in August (10 sites on the Milk River, six on the St Mary River and four on Lee Creek; and October (18 sites on the Milk river and two on the St. Mary River) 2000. Only two specimens were taken from the Milk River (0.1 % of species composition). Apparently a concomitant US study on the Milk River between the International Border to the Fresno Reservoir in Montana found that the western silvery minnow constituted 5.86 % of species composition in that section of the river (RL&L 2001a).
In the 2000 study (RL&L 2001) the species was collected at only one of the 18 sites sampled in the lower Milk River. The site were the fish were found was close to sites where it had previously been captured (Willock 1969; Clayton and Ash 1980; RL&L 1987), but it was not found at other sites where it had previously been collected on the Milk River. Water levels were extremely low and the lost River (a tributary to the Milk River) was dry, but this is a small intermittent stream and not always available as habitat.
Twenty sites were sampled on the Milk River between 18 and 24 October 2001 and 27 western silvery minnows were taken from the lowermost sections of the river with a CPUE of 1.97 fish/100m2 (RL&L 2001b). Water levels were extremely low due to drought and drw down for irrigation and urban supply (Figure 1) and the fish were concentrated in the remaining pools.
The record of a specimen from the South Saskatchewan River (Henderson and Peter 1969) is spurious and still needs to be verified.
Western silvery minnow are usually captured only in mainstream areas of the river with low siltation (Willock 1969). Overwintering may be limited in some years by low water, but is probably possible in the lower reaches of the river (RL&L 1987) a long as water levels are sufficiently high. Suitable feeding and rearing habitat also seems to be available in lower sections of the river, yet few western silvery minnows have been collected (RL&L 2001a). Oher factors such as low winter water flows, high suspended sediment levels, high siltation, low winter dissolved oxygen and limited availability of refugia are probably the limiting factors.
DISTRIBUTION
AB
Extent of occurrence: < 500 km2
Area of occupancy: < 100 km2
POPULATION INFORMATION
Total number of individuals in the Canadian population: Unknown, but not relatively abundant
Number of mature individuals in Canada (N): Unknown
Generation time: 2 years
Population trend: Unknown
Rate of population decline:
Number of sub-populations: 2
Is the population fragmented? Yes
number of individuals in each sub-population : Not known
number of extant sites: 2
number of historic sites from which species has been extirpated:
Does the species undergo fluctuations?
Fluctuations in?
RESCUE POTENTIAL
Does species exist outside Canada? YES
Is immigration known or possible? Possible from populations in MT
Would immigrants survive in Canada? YES
Is suitable habitat available for immigrants? YES - but range extensions are limited by water quality and habitat availability
THREATS
Increased siltation from channeling and/or overgrazing and fluctuation in water levels due to impoundments and water draw down for irrigation and urban use. Periods of drought reduce the river to a trickle and siltation has all but eliminated channels from the river bed. If water levels are not sufficiently restored over the winter months there is the possibility of many or all fish being lost due to oxygen deprivation.
EXISTING STATUS
Nature Conservancy Ranks: Global - G4; National: US - N4 , Canada - N3N4; Regional: IL - S2, IA - S1, KS - S2, MO - S2, MN - S4S5, NE - S5, ND - S?, SD - S5, WY - S2, AB - S1
Prior COSEWIC designation- Vulnerable 1997
Clayton, T.D. and G.R. Ash. 1980. A fisheries overview study of the Milk River Basin. Prepared for Alberta Environment Planning division, Edmonton, Alberta. 93 pp. + App.
Henderson, N.E. and R.E. Peter. 1969. Distribution of fishes of southern Alberta. 3. Fish. Res. Board Can. 26:325-338.
Houston, J. 1998. Status of the Western Silvery Minnow, Hybognathus argyritis, in Canada. Canadian Field-Naturalist 122(1):147-153.
Nelson, J.S. and M.J. Paetz. 1992. The fishes of Alberta. The University of Alberta Press, Edmonton, Alberta. 437p.
RL&L Environmental Services Ltd. 1987.An inventory of aquatic habitats and fish resources in the Milk River, Alberta. Prepared for Alberta Environment, Planning Division, Edmonton, Alberta. 80 p. + App.
RL&L Environmental Services Ltd. 2001a. Fish species at risk in the Milk and St. Mary Drainages. Prepared for Alberta Environment Natural Resources Service, Edmonton, Alberta. 53 pp. + 3App.
RL&L Environmental Services Ltd. 2001b. Fish species at risk in the Milk and St. Mary Drainages. Progess Report - Fall Session November 2001. Prepared for Alberta Environment Natural Resources Service, Edmonton, Alberta. 5 pp.
Willock, T.A. 1968. New Alberta records of the silvery and brassy minnows, stonecat and sauger, with a preliminary list of fishes of the Milk River in Alberta. Canadian Field-Naturalist 82:18-23.
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