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Species at Risk Act - Legal Listing Consultation Workbook, Copper redhorse

Background information on copper redhorse

Statut :endangered

Last COSEWIC assessment :  november 2004

2.1 Description of the species

Copper redhorse (Moxostoma hubbsi, Legendre, 1942) is one of seven species of the genus Moxostoma (Catostomidae family) occurring in Canada. The metallic appearance of its scales is the reason for its name. In this family, there are three other species living in the same area: the silver redhorse (M. anisurum), the shorthead redhorse (M. macrolepiotum), and the river redhorse (M. carinatum).

2.2 Distribution of the species

The species occurs nowhere in the world except Canada, and its range is restricted to a few rivers in the lowlands of south-western Quebec. It is the only vertebrate that is found only in Quebec. Since 1942, the year it was discovered, it has been observed only in certain sections of the Richelieu, Yamaska, Noire and Mille Îles rivers, at the mouth of the Maskinongé River, and in a few reaches of the St. Lawrence River, between Vaudreuil and the downstream area of Lake Saint-Pierre. Its current distribution is limited to certain locations in the Richelieu River, to a short reach of the St. Lawrence, and possibly a residual aggregation in the Mille Îles River.

2.3 Copper redhorse biology

The copper redhorse has several biological features that distinguish it from its congeners, such as longevity (more than 30 years) and considerable size. 

2.3.1 Breeding and spawning

They reach sexual maturity at an older age (about 10 years) and spawn later in the season than its congeners. High female fecundity is another one of its features. The breeding period occurs at the end of June and beginning of July. So far, two breeding grounds have been identified, both in the Richelieu River, at several kilometres from each other: one upstream, in the archipelago of the Chambly rapids, and the other in the lower reach of the Saint-Ours dam.

2.3.2 Movements and migration

Younger redhorses have a different predilection site than adults. Younger redhorses are found in shallow water near the shoreline. They remain there at least until the beginning of their second year. The section of the Richelieu River that includes the Jeannotte and the Cerfs islands is a significant rearing area. Summering and wintering areas for adults and young redhorses two years and older are still unknown. It is possible however that adults winter in the reaches of the Lavaltrie-Contrecoeur river corridor.

2.3.3 Diet

Over 90% of the copper redhorse diet is made up of small molluscs. Their pharyngeal apparatus is well adapted to crushing this small shell prey. This type of diet is unique to this species of fish in North America.

2.3.4  Population size

Since the discovery of the copper redhorse in 1942, less than 800 individuals have been identified. Despite the tagging made in the Richelieu River in the 1990s, no tagged fish has ever been recaptured. It is therefore impossible to estimate the number of individuals. Currently, the only estimate available concerns the Lavaltrie-Contrecoeur aggregation. This group numbers around 100 individuals. There have been almost no captures of juvenile redhorses of two years and older over the last 30 years. These observations show how serious the issue of recruitment is.

2.3.5 Habitat

Some studies have described in a general way the streams where the copper redhorse can be found. They inhabit medium-sized rivers, with steep banks, a maximum depth of 4 to 7 m, a hard bottom, generally composed of gravel, sand and clay. Current is moderate and summer water temperatures are higher than 23°C. Areas with rapids are conducive to breeding. The two known spawning grounds (archipelago of the Chambly rapids and the Saint-Ours dam) have the following characteristics in common: riffle areas, with a moderate to slow current and depths ranging from 0.75 to 2 m; bottoms made up of different size gravel, rocks and fragments of bedrock partly submerged in the clay.

In 1998, an aggregation of copper redhorses was rediscovered in the Lavaltrie-Contrecoeur sector of the St. Lawrence River. This reach of the river could be a spring or fall gathering area or even a wintering area. It could not be shown that this area was a spawning ground. Contrary to adults who avoid shallower areas with dense vegetation, young-of-the-year and one-year olds prefer them. The significant rearing site, located in the Jeannotte and Cerfs islands area, is characterized by a current and a soft slope, and by a homogeneous substrate made up of a mix of fin clay-silt particles and sand. The fry of the year prefer to gather in shallow areas (1.5 m) with vegetation.

2.4 Why has COSEWIC designated the copper redhorse as an endangered species?

Here are the reasons for the COSEWIC copper redhorse designation:

  • Global distribution of the species limited to a few streams in the St. Lawrence plain;
  • Rare in its distribution range and numbers in decline;
  • Weak numbers: total population estimated at a few thousand individuals at the most;
  • Particular biological characteristics: specialized diet species, and late sexual maturity and spawning periods;
  • Habitat degradation and fragmentation;
  • Introduction of potentially competing species;
  • Aging population and low recruitment;
  • Breeding difficulty in natural environment.

2.5 What is threatening this species?

2.5.1 Geographical and biological features

Global distribution of the species limited to a few steams in the St. Lawrence plain.

Since 1942, it has been found only in certain sections of the Richelieu, Yamaska, Noire and Mille Îles rivers (a residual aggregation), at the mouth of the Maskinongé River, and in a few reaches of the St. Lawrence River, between Vaudreuil and the downstream area of Lake Saint-Pierre. Currently, aggregations are located in the Richelieu River and a short reach of the St. Lawrence River.

Specialized diet species

The copper redhorse’s pharyngeal apparatus is very specialized and limits its choice of prey. Its diet is almost exclusively limited to small molluscs.

Late sexual maturity and spawning periods

Sexual maturity at an older age (10 years) and a late spawning period (shorter time for growth and smaller fry size facing their first winter) are two factors contributing to the species vulnerability. It has not yet been demonstrated, but it is possible that smaller fry are dying during winter.

Breeding and aging population

Some studies suggest that the species has difficulties breeding in a natural environment (late sexual maturity and spawning periods, restricted diet). The very low recruitment is insufficient to balance out natural mortality. The only two known spawning grounds are the Chambly basin archipelago, downstream from the Chambly rapids, and the one at Saint-Ours. The only confirmed breeding aggregation is in the Richelieu River, at two different sites.

Decreasing distribution range

There is no doubt that man-made activities jeopardize the species. In fact, the copper redhorse streams are located in the most heavily populated areas of Quebec. Other areas within the distribution range could have the necessary characteristics for copper redhorse breeding (Grand Moulin rapids on the Mille Îles River, Dorion and Sainte-Anne-de-Bellevue channels). However, there has been no copper redhorse found at those sites.

2.5.2 Degradation, fragmentation and changes to the habitat 

Among the different theories explaining the decline of the species, the most significant obviously have to do with habitat degradation and fragmentation. The degradation of the quality of streams is caused by, among other things, the excessive input of nutrients and by the increase of the rate of erosion (silting).

Agricultural, foresting and urbanization activities

It is likely that the copper redhorse disappeared from the Yamaska and Noire rivers because of significant problems related to heavy agricultural activities, foresting and to urban development: deoxygenation (eutrophication), silting and turbidity (muddy water). These changes destroy habitat and disrupt the entire food chain; the copper redhorse and its prey, molluscs, are particularly sensitive to this type of aggression. The excessive input of fertilizers in streams causes a blooming of vegetation that attracts carp (Cyprinus carpio), pumpkinseed (Lepomis gibbosus) and newly introduced tench (Tinca tinca). These species compete with copper redhorse and therefore restrict the available habitat for young-of-the-year. For adults, the blooming vegetation works against them because they usually avoid this type of habitat.

The discovery of zebra mussel colonies (Dreissena polymorpha) in the Richelieu River is alarming. This mussel could take over sites that harbour molluscs that are part of the copper redhorse diet. Furthermore, this mussel, which is well known for its ability to concentrate contaminants in its organism, could intoxicate the copper redhorse if it began eating it.

Some contaminants stemming from pesticide use and from water treatment plants effluents could interfere with hormonal signals and prevent males and females from being able to breed. Copper redhorse spawners, eggs and larvae are more exposed to contaminants than their congeners who spawn earlier in the season, because the spawning period coincides with the reduction of the flow in streams and the peak of agricultural pesticide application. These same pollutants are likely to contaminate copper redhorse prey that, by eating them, will also become contaminated.

Water control structures

Many dams were built in the copper redhorse distribution range and restrict its movements. This is the case of the Saint-Ours dam (between 1967 and 2001). Beginning in the spring of 2001, the Vianney-Legendre multi-species migratory fishway at the Saint-Ours dam allowed the copper redhorse to travel to the Chambly basin archipelago several kilometres further upstream. The Yamaska, Noire and Mille Îles rivers are also regulated, and the copper redhorse cannot move freely.

Disturbance

In the Chambly basin archipelago, near the rapids, recreational boaters and vacationers are also visiting the copper redhorse spawning grounds. Human movements on the islands disturb spawners, and in certain areas, eggs are being stepped on. In 2002, in an attempt to protect the copper redhorse habitat, the Pierre-Étienne-Fortin Wildlife Sanctuary was created and regulations were implemented.

2.5.3 Other factors

Lower water levels in the St. Lawrence River could make certain potential spawning areas inaccessible to copper redhorses and restrict their feeding grounds.

Because the copper redhorse was a favourite food in the 19th century, over-fishing could have weakened certain populations.