COSEWIC Assessment and Update Status Report on the Copper Redhorse in Canada
- Assessment Summary
- Executive Summary
- COSEWIC History, Mandate, Membership and Definitions
- Lists of Figures and Tables
- Species Information
- Population Sizes and Trends
- Limiting Factors and Threats
- Special Significance of the Species
- Existing Protection or Other Status
- Technical Summary
- Acknowledgements and Information Sources
- Biographical Summary of Report Writer, Authorities Contacted, and Collections Examined
The copper redhorse (Moxostoma hubbsi) is one of seven species of the genus Moxostoma (family Catostomidae) occurring in Canada. Its discovery has been attributed to Vianney Legendre in 1942 (Legendre 1942), but it appears to have been first described by Pierre Fortin in 1866 as an already known species of the genus Moxostoma.
The species occurs nowhere in the world except Canada. Its extremely small range, which is restricted to a few rivers in the lowlands of southwestern Quebec, has contracted significantly in the past few decades. Confirmed populations currently exist in the St. Lawrence and Richelieu rivers. Rivière des Mille Îles likely supports a remnant population.
The copper redhorse occurs primarily in medium-sized rivers where water temperatures exceed 20°C in summer. Spawning occurs in riffle areas where the current is moderate to slow and the depth ranges between 0.75 and 2 m, over fine to coarse gravel and cobble substrate. Like its congeners, young-of-the-year copper redhorse spend their first growing season in shallow shoreline areas no more than 1.5 m deep, characterized by gentle slopes, vegetation, a very slow current and fine substrate (mix of clay-silt and sand). To date, there are only two known spawning grounds (Chambly archipelago and the channel downstream from the Saint-Ours dam) and a nursery area (Saint-Marc-sur-Richelieu) has been identified in the Richelieu River. Very recently, the presence of copper redhorse has again been reported in the Lavaltrie-Contrecoeur sector of the St. Lawrence River. The reasons for its presence in this stretch of the river in the spring and early summer (pre-spawning congregation, spawning or migration route) and fall (wintering grounds) could not be determined. High quality copper redhorse habitat is in decline. Its apparent extirpation from the Yamaska and Noire rivers is closely linked to environmental degradation.
By comparison with the other redhorse species with which it occurs in sympatry, the copper redhorse has the longest lifespan (over 30 years), is the most fecund and reaches the largest size (over 70 cm). Its spawning period is later than that of its congeners, occurring from late June to early July, when water temperatures range from 18 to 26°C. The species also reaches sexual maturity later than its congeners (at about 10 years). The copper redhorse feeds almost exclusively on molluscs, which it crushes with its very robust pharyngeal apparatus and molariform teeth.
Population Sizes and Trends
Archaeological excavations provide evidence that the species was more abundant at various times in the past. Since the mid-1980s, its abundance relative to the other species in the genus has declined significantly. The population is aging and recruitment is extremely low. Compared to its congeners, the relative abundance of young-of-the-year copper redhorse in the Richelieu River, the only river in which spawning is confirmed, is 0.35% or less. The upward shift in size distribution values in the past 30 to 40 years is significant. There have been virtually no catches of juveniles aged 2+ years in the last 30 years. The total number of mature individuals appears to be several thousand at the most.
Limiting Factors and Threats
A number of biological characteristics of the copper redhorse, such as its longevity, late age of sexual maturity, late spawning activities and specialized diet, make it unique among its congeners. However, they also contribute, in some respects, to making it more vulnerable. Since the waters inhabited by the copper redhorse are located in the most densely populated areas of Quebec, anthropogenic factors come into play. The nature of those factors cannot, however, be determined with certainty and act in combination. The degradation and fragmentation of its habitat and its low spawning success are believed to be key reasons for its decline. Contamination, siltation, eutrophication, introductions of non-native species, dam construction (which impedes the free passage of fish) and the disturbance of spawners on spawning sites all constitute possible factors in the species’ decline.
Special Significance of the Species
The significance of the copper redhorse is not limited to scientific and ecological considerations. It extends to social values, sustainable development and biodiversity conservation. In some respects, the species is an indicator of the impact of human activity on the ecosystems of southern Quebec. Public interest in the species is not only strong but continues to grow.
As in the case of other fish species, the copper redhorse and its habitat receive a level of protection under the federal Fisheries Act, the Quebec Act Respecting the Conservation and Development of Wildlife and Environment Quality Act. However, because these statutes were considered inadequate for ensuring the preservation of the species, additional measures have been taken, such as amendments to the sport fishing regulations in a number of sectors used by the copper redhorse and the creation of the Pierre-Étienne-Fortin Wildlife Preserve at Chambly in October 2002. The objective of the wildlife preserve is to protect the integrity of the largest spawning site and prevent disturbances of spawners and encroachment on spawning sites during the spawning period. The copper redhorse was designated threatened in 1987 by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC). In April 1999, it was designated threatened under the Quebec Act Respecting Threatened or Vulnerable Species. This is the most critical status that can be applied to a species under Quebec legislation and is used when the loss of the species is feared. Currently, the survival of the species hinges essentially on protection and reintroduction efforts.
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