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COSEWIC Assessment and Update Status Report on the Copper Redhorse in Canada

Limiting Factors and Threats

Several characteristics of copper redhorse biology, such as the fact that it reaches sexual maturity at a relatively late age (around 10 years), its specialized diet and its late spawning activities, which contribute to increasing the risks of exposure to contaminants and to producing young-of-the-year that are smaller in the fall than its congeners, constitute factors which increase its vulnerability. Furthermore, according to Parent and Schmirl (1995), the biological characteristics of the copper redhorse are most similar to the general profile of the species most at risk of extinction, identified on the basis of 51 characteristics of threatened (n=29) or non-threatened (n=88) species.

Since the watercourses inhabited by the copper redhorse are located in the most densely populated areas of Quebec, anthropogenic factors are undoubtedly endangering the species. However, the causes of its decline cannot be determined with certainty. The species appears most likely to be the victim of a combination of factors. Habitat degradation and fragmentation, as well as low reproductive success, appear to be key elements in explaining its decline (Gendron and Branchaud 1997, Mongeau et al. 1986, 1988, 1992, Scott and Crossman 1973, Vachon 2003b).

The species’ habitat is fragmented by the construction of dams, notably the Saint-Ours dam on the Richelieu River, which obstructs the free passage of spawners to the most important and promising of the two known spawning areas, namely in the archipelago of the Chambly Basin (Dumont et al. 1997). Although various structures were built at Saint-Ours from the 1850s onward to facilitate navigation as far as Chambly, until 1969 these structures did not completely obstruct the free passage of fish because a fish ladder had been installed. In addition, the dam, which at the time was built of rock caissons, was often partially destroyed or even carried away by spring floods. The passage of fish was most likely possible, albeit reduced. However, during the last major reconstruction of the dam, begun in 1967 and completed in 1969, the dam was raised and did not include any kind of structure to allow fish to bypass it (Dumont et al. 1997). It was not until the spring of 2001 that a multispecies fish ladder (Vianney-Legendre fish ladder) was installed at the Saint-Ours dam. A five-year monitoring program is currently under way with the aim of optimizing its operation. Although the use of the fish ladder by copper redhorse could not be confirmed in its first year of operation (Groupe conseil GENIVAR 2002), individuals were captured in it in 2002 (n=4) and 2003 (n=4) (Fleury and Desrochers 2003, 2004). At Chambly, a dam was first built in 1896 for the production of electricity. This dam was replaced in 1963-1964 (Blaquière and Auclair 1974). It was only quite recently that an eel ladder was installed at the site, but the dam is still impassible for other species. Other dams located in the water bodies inhabited by the copper redhorse prevent the passage of fish: the Sainte-Pie and Emileville dams in the Noire River, the T‑D‑Bouchard dam at Saint-Hyacinthe in the Yamaska River and the Des Moulins dam in the Rivière des Mille Îles at Terrebonne (Figure 5). Although, the Des Moulins dam only partially impedes the passage of fish, their movements are nonetheless reduced (Gravel and Dubé 1980).

The acceleration of erosion (siltation) and increased turbidity resulting from agricultural activities, deforestation and urbanization also appear to affect the copper redhorse. These processes are threatening the integrity of aquatic ecosystems by degrading the habitat and disturbing the entire food chain, including molluscs, an essential food source for the copper redhorse. The central and lower portions of the Yamaska River are particularly affected by siltation and the increase in turbidity. In the basins of the Richelieu and Yamaska rivers, certain maxima recorded (turbidity and suspended solids) are sufficient to adversely affect populations of aquatic invertebrates, particularly if these conditions persist (Vachon 2003b). Most fish in the family Catostomidae, specifically those in the genus Moxostoma, are extremely sensitive to high levels of pollution, siltation and turbidity (Vachon 2003b). Moreover, in Karr’s index of biotic integrity (IBI) (1981), the number and species composition of individuals belonging to the family Catostomidae is one of the 12 descriptors used. More recent studies show that changes in the structure of the Catostomidae community reflect the biological integrity of the ecosystem (Emery et al. 1999). In several cases, the history of the constriction of the range of several members of this family since the beginning of the century has coincided with the deterioration of biotic integrity (Jenkins and Burkhead 1994, Scott and Crossman 1973, Trautman 1981). The copper redhorse presents biological characteristics and ecological requirements (reproduction and feeding patterns) similar to those of other species known to be most affected by habitat degradation, siltation and increased turbidity (Vachon 2003b).

As presented above, the serious difficulties experienced by the copper redhorse in reproducing in the natural environment are most likely associated with toxicological factors which hinder the final maturation of gametes and affect the olfactory abilities of spawners (Gendron and Branchaud 1997). Water contamination by the widespread use of pesticides therefore constitutes an important limiting factor to consider. Because it spawns later (late June and early July) than the other species, the copper redhorse appears to be more exposed to contaminants since this period corresponds to the peak periods of fertilizer application as well as reduced river flows. The 1998 and 1999 surveys show that atrazine is omnipresent in the Richelieu River and that the highest levels generally coincide with the period when spawners congregate or during the copper redhorse spawning period. Some ten other types of pesticides (metoalachlor, 2,4-D, bentazon, etc.) have been detected in the main channel of the Richelieu River during the copper redhorse spawning period. Little is known about the effects of such a combination of contaminants on aquatic organisms (Gendron and Branchaud 1997, Giroux 2000). It is important to recall that the contamination of watercourses probably also affects the populations of molluscs on which the copper redhorse feeds exclusively. In the basins of the Richelieu and Yamaska rivers, the integrity of the benthic communities is considered fair or poor over at least half of their length. This deterioriation of integrity is also directly linked to agricultural, urban and industrial pressures (Piché 1998, Saint-Onge 1999). The negative impact of current agricultural practices on habitats and wildlife, including the copper redhorse, is increasingly recognized (Société de la faune et des parcs du Québec 2002).

The eutrophication of watercourses by the increased use of fertilizers may negatively impact the copper redhorse. The resulting proliferation of aquatic grass beds appears to favour other species, such as Yellow perch (Perca flavescens), Pumpkinseed (Lepomis gibbosus), and Brown bullhead (Ameiurus nebulosus), which prefer this type of habitat. These conditions are also optimal for the Carp (Cyprinuscarpio), a ubiquitous species identified as co-occurring with the copper redhorse and a potential competitor of the Catostomidae (Mongeau et al. 1986, 1992).

The impact of the introduction of the Tench (Tincatinca), now considered established in the Richelieu River in the sector upstream of the Chambly Basin, is unpredictable. Given its high fecundity and its ability to adapt to various environmental conditions, even the most adverse, the dispersal of the Tench in the Richelieu River and the St. Lawrence River could represent an additional threat to the copper redhorse (Dumont et al. 2002, Vachon and Dumont 2000).

Other studies show that the invasion of the Richelieu River by zebra mussels (Dreissena polymorpha) has started and is progressing well. Little is known about the potential impact of this species on the ecosystem of the river, but it is likely to be significant (Cusson and de Lafontaine 1997, de Lafontaine et al. 2002b). The adverse effects of the introduction of zebra mussels on native species of molluscs are well known. Some groups, on which the copper redhorse feeds almost exclusively, specifically pelecypods and gastropods, could be affected (Dermott and Kerec 1997, Stewart and Haynes 1994). Moreover, because zebra mussels have a large capacity to concentrate contaminants (Bruner et al. 1994), the effects of contaminant bioconcentration will have to be studied if the mussels are ingested in large numbers by the copper redhorse. In the laboratory, juvenile copper redhorse have been observed to ingest zebra mussels (Branchaud and Gendron 1993). The evolution of the benthic communities of the Richelieu River in the presence of these mussels is very important given that any change in these communities could adversely affect the copper redhorse (de Lafontaine et al. 2002b, Vachon 2003b).

The declines in St. Lawrence water levels may also constitute an additional threat to the copper redhorse by making potential spawning areas inaccessible and by limiting feeding areas. The phenomenon has been under way for about a decade and is giving rise to serious concerns, not only regarding the copper redhorse, but the entire fish community. It is currently the subject of numerous studies and consultations.

The studies by Branchaud and Jenkins (1999) recently concluded that certain populations may have been severely impacted by overfishing during the 19th century. At the time, the copper redhorse was prized as a food fish and therefore sought after in the markets.

Finally, pleasure craft traffic in the reproduction areas in the Chambly rapids during the copper redhorse spawning and egg incubation period is another factor contributing to endangering the species (Gendron and Branchaud 1997, 1999). The Regulation Respecting the Pierre-Étienne-Fortin Wildlife Preserve (Act Respecting the Conservation and Development of Wildlife, C-61.1, r.3.01.3.3), adopted in November 2003, should improve the situation.