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



Compared to the other species with which it occurs in sympatry, the copper redhorse has the longest lifespan, is the most fecund species and reaches the largest size. Compared to its congeners, the copper redhorse spawns later and takes the longest to reach sexual maturity.


The copper redhorse lives for at least 30 years (de Lafontaine et al. 2002a) and reaches a considerable size. The size (total length) of spawners is generally greater than 500 mm (Mongeau et al. 1986, 1992), although according to Jenkins (1970), males can reproduce once they reach 475 mm. Both sexes reach sexual maturity at the beginning of the 10th year; hence, the reproductive lifespan appears to be at least 20 years. In 12 females captured in 1984 in the Chambly Basin that varied from 547 to 690 mm in total length, fecundity ranged from 34 900 to 111 860 eggs. The fecundity of a 2 kg female is approximately 32 750 eggs (Mongeau et al. 1986, 1992). The weight of female spawners correlates positively with the number of eggs produced and with the diameter of the eggs released (Branchaud and Gendron 1993, Branchaud et al. 1995, Mongeau et al. 1986, 1992). Generally, a sex ratio in favour of the males is observed at reproduction sites, which suggests that they travel to the spawning areas before the females (Branchaud et al. 1993, 1995) or that they are more active (Pierre Dumont, biologist with the Société de la faune et des parcs du Québec, pers. comm.). As has been reported in other Moxostoma, copper redhorse leap out of the water during the reproduction period. This behaviour has been observed at or near spawning sites and is used as an indicator of reproduction activity (Dumont et al. 1997, Vachon and Chagnon 2004).

Spawning begins around the last week of June and can continue until the first week of July, at which time the water temperature ranges from 18 to 26ºC. Spawning likely occurs at night (Boulet et al. 1995, Dumont et al. 1997, La Haye et al. 1992, Mongeau et al. 1986, 1992).

The eggs, which range in diameter from 2.81 to 3.42 mm, are non-adhesive and orangey-yellow in colour. At a constant temperature of 20ºC, hatching occurs after 89 to 127 degree-days, peaking at around 108 to 110 degree-days, which represents 4.5 to 6.5 days of incubation. At hatching, the yolk sac larvae measure 9.09 mm on average. At the start of exogenous feeding, at which time resorption of the yolk sac is practically completed, the average size of the larvae is 13.11 mm. This important stage generally occurs 15 days after fertilization. Emergence of the larvae (beginning of swimming behaviour) has been observed 12 to 16 days after fertilization, with peak activity after 15 days (Branchaud and Gendron 1993, Branchaud et al. 1993, 1995).


In the copper redhorse, the growth rate in length and weight is generally higher than that of its congeners. No difference in growth has been observed between the sexes. The females are generally more corpulent than the males. On the basis of the results obtained by back calculation, a copper redhorse measures on average 370, 550 and 670 mm respectively at 5, 10 and 20 years (Mongeau et al. 1986, 1992). To date, the largest specimen captured measured 780 mm (Vachon and Chagnon 2004). The heaviest individual was a 715 mm female weighing 5.55 kg captured in 1994 in the Richelieu River (Branchaud et al. 1995).

In the fall, the average size of young-of-the-year redhorse in the Richelieu River reflects the temporal sequence of spawning of the different species. The growth of young-of-the-year is closely linked to the cumulative number of degree-days above 10ºC during the growing season, which ends at the latest around the end of September, even if the fall is late. The average total length of young-of-the-year copper redhorse captured from September to November ranges from 37.5 to 48.5 mm (average of 41.6 mm). These juveniles are potentially more vulnerable when facing their first winter season since, in the fall, they are smaller than their congeners. For example, at the same period in 1999 and 2001, the average size of young-of-the-year in the other four species was greater than 57 mm. Young-of-the-year shorthead and silver redhorse measured on average between 72 and 83 mm (Vachon 1999ab, 2002).


Several studies have shown an aging of the population, which appears to be attributable to recruitment problems stemming from low reproductive success (Branchaud et al. 1993, 1995, Boulet et al. 1995, 1996, La Haye et al. 1992, Vachon and Chagnon 2004).

The age structure of the population cannot be clearly demonstrated since the sample size examined is insufficient. However, the shift in size distribution profiles toward higher values over the last 30 to 40 years is obvious and statistically significant (Figure 6). Furthermore, virtually no age‑2+ juveniles have been captured for the past 30 years (Vachon and Chagnon 2004). The last two specimens in the 100 to 150 mm size range were captured in 1974 in the Richelieu River (Mongeau et al. 1986). In the spring of 2003, the average size of the copper redhorse captured in the Lavaltrie sector was 646 mm; 90% of the specimens measured 620 mm or more (Chagnon 2003). The individuals captured in the fish ladder (Richelieu River) in 2002 and 2003 were over 600 mm in length (Fleury and Desrochers 2003, 2004).

Monitoring of the recruitment of young-of-the-year redhorse carried out in September 1998, 1999 and 2001 in the Richelieu River showed that the relative abundance of the copper redhorse compared to its congeners is less than or equal to 0.35%. A single young-of-the-year was captured each year (Vachon 1999ab, 2002). In 1997, despite much more intensive fishing efforts which covered a larger sector of the Richelieu River, the results were scarcely any better; the relative abundance of young-of-the-year copper redhorse was 0.63% (Vachon 1999a). The survival rate of young-of-the-year is not known. However, the hypothesis that these juveniles are more vulnerable during their first winter cannot be ruled out (Vachon 1999a).

Given the very low reproductive success observed in the copper redhorse, the recruitment rate is clearly insufficient to offset natural mortality. This situation is increasingly alarming given the fact that the population is aging. In fact, the capture of spawners could eventually be very difficult and constitute a major obstacle to the success of artificial reproduction (Branchaud et al. 1995).


A study of the contamination profiles of seven copper redhorse aged 9 to 33 that died accidentally in the tailrace of the Saint-Ours dam reveals that the level of contamination of the liver, gonads and muscle tissue by bioaccumulative substances (mercury, trace metals, PCB congeners, dioxins and furans) is comparable or sometimes even lower than that recorded in other younger catostomids of the Yamaska basin and the Richelieu River. The concentrations found are lower than those recognized as harmful to reproduction or as affecting egg and fry survival (from Lafontaine et al. 2002).

Figure 6: Size Frequency Distribution of Copper Redhorse in the St. Lawrence River and the Richelieu River from 1942 to 2001

Figure 6: Size frequency distribution of copper redhorse in the St. Lawrence River and the Richelieu River from 1942 to 2001 (adapted from Vachon and Chagnon 2004).

Adapted from Vachon and Chagnon 2004.

However, these results do not rule out the possibility that other contaminants which do not accumulate in the organism, such as certain pesticides, are disrupting reproductive processes. On the basis of the observations made during artificial reproduction experiments, it appears that, even if the growth and initial development of the gonads take place normally, difficulties arise, particularly in the females, during the later stages of maturation as well as when the gametes are released. None of the females captured at the peak reproductive period released eggs under gentle abdominal pressure and only very few males expressed milt (Branchaud and Gendron 1993, Branchaud et al. 1993, 1995). The hypothesis that these physiological disorders are of toxicological origin was then examined by Gendron and Branchaud (1997). These authors concluded that it is probable that metabolites of alkylphenol polyethoxylates (APEs) impair final gamete maturation in the copper redhorse (endocrine disruptors), while atrazine as well as other pesticides (e.g., diazinon and carbofuran) may confuse the olfactory system of spawners, which would affect the perception of pheromones, substances that help synchronize gamete maturation as well as spawning behaviour in both sexes. Given the presence of these contaminants in the Richelieu River, particularly during the copper redhorse reproduction period, the hypothesis is plausible (Gendron and Branchaud 1997). Andrée Gendron and David Marcogliese, of the Centre Saint-Laurent, are currently testing certain aspects of this hypothesis.

In juveniles, the only information available is from experiments with marking techniques. The marking of copper redhorse with oxytetracycline has not proven as effective as desired (Beaulieu 1996, Branchaud et al.1995, Turgeon 1995). A study is currently under way to assess the permanence of freeze branding. To date, the technique appears promising. Nine days after the marking of juveniles produced in 1994 and reared at the Tadoussac fish station, the marks were clearly visible and no mortality had been observed (Morin 1999). The experiment was continued in order to assess the long-term permanence of the mark and the effects of the technique on the growth and survival of the specimens. According to observations made in 2003, the identification rate is clearly higher if the contact time is six seconds, rather than three. In addition, no effects were observed on the growth of the individuals (FAPAQ and Biodome, unpubl. data).


The capture of several copper redhorse a short time before spawning at the tailrace of the Saint-Ours dam during various field studies (Branchaud and Gendron 1993, Branchaud et al. 1993, 1995, Boulet et al. 1995, 1996, Dumont et al. 1997, La Haye and Clermont 1997) and records of the presence of the species in the fish ladder in 2002 and 2003 (Fleury and Desrochers 2003, 2004) clearly show that the species forms pre-spawning aggregations.

The recurrent presence of copper redhorse in the Lavaltrie-Contrecœur sector (St. Lawrence River) during the months of April and May, followed by a drop in numbers thereafter also suggests that individuals congregate and undertake spring migrations to spawning sites. The reasons for its presence in this section of the St. Lawrence in the spring and early summer (pre-spawning aggregations, spawning or migration route) have so far not been conclusively determined (Vachon and Chagnon 2004). Interannual comparisons of captures and recapture results also show that the Lavaltrie-Contrecoeur sector appears to be an important congregation site or even an over-wintering area for the species (Vachon and Chagnon 2004).

The capture of several adult redhorse, including one copper redhorse and one river redhorse off the left bank of Jeannotte Island (Richelieu River) in early June 1998 (Vachon 1999a) also supports the hypothesis of pre-spawning migrations. Jeannotte Island is located approximately 21 km downstream of the Chambly Basin and approximately 24 km upstream of the Saint-Ours dam. These two specimens were already in the sector upstream of the Saint-Ours dam, since at that time there was no fish ladder. If they were migrating to a spawning area, it was that located in the Chambly rapids (Vachon and Chagnon 2004). The nature and concentration of certain contaminants found in the tissues of copper redhorse from the tailrace of Saint-Ours also support this hypothesis. Contaminants more typically associated with the St. Lawrence River such as cadmium, mirex and PCB congener 77 were detected in their tissue (de Lafontaine et al. 2002a).

The juveniles are dispersed simply by drifting of the larvae after hatching. The larvae are distributed along the river. Unfed fry and juveniles subsequently remain associated with the grass beds near the shore during their first growing season and at least at the beginning of the second. In the fall, particularly when the water temperature is less than 12ºC, the young-of-the-year move away from the shores and head toward deeper water (Vachon 1999a). These observations appear to agree with those obtained during experiments on the behaviour of juvenile stages of redhorse conducted in 1996, which show that at fall temperatures (7.5°C), young-of-the-year copper redhorse exhibit a clear preference for coarser substrates, while such behaviour was not observed at temperatures of 21°C (Branchaud and Fortin 1998).

Diet and Interspecific Interactions

In adults, the diet is specialized and consists almost exclusively of molluscs (more than 90% by number). In the streams of the St. Lawrence Plain, several other species feed on molluscs, including the river redhorse, but not exclusively (Mongeau et al. 1986, 1992). Indeed, the particular configuration of its pharyngeal apparatus is well adapted to crushing (Eastman 1977, Jenkins 1970, Mongeau et al. 1986).

There is very little overlap between the diet of the copper redhorse and that of the other species. The taxa most frequently encountered in the digestive tracts of copper redhorse are Unionidae, Sphaeriidae and Amnicolidae, in its entire range (Mongeau et al. 1986, 1992). An examination of non-animal substances found in the digestive tracts of redhorse suggests that there is a spatial segregation between the species when they feed. Copper and greater redhorse feed on hard bottoms, river redhorse on gravely bottoms, while shorthead and silver redhorse appear to feed in or near grass beds. The species most likely to be associated with the copper redhorse are the Carp (Cyprinus carpio), the river redhorse and the silver redhorse (Mongeau et al. 1992).

Conversely, in young-of-the-year and age-1 individuals captured in the spring, there was little difference in diet between the species, despite the fact that at this period of ontogenesis, the morphology of the copper redhorse’s pharyngeal apparatus is already distinctive and can be used to distinguish it from its congeners. In juvenile copper redhorse, whose total length ranges from 36.0 to 53.5 mm, more than 50% (by number) of prey are microcrustaceans (Cladocera: Chydoridae; Copepoda: Harpacticoida). Worms (Nematoda) and algae (Desmidiae) also occupy an important place and chironomid larvae are also frequently ingested (Vachon 1999a).

In rearing ponds, chironomid larvae and pupae as well as cyclopoid copepods were the main organisms consumed by very early juvenile stages of copper redhorse (TL=13.0 to 22.1 mm) (Branchaud et al. 1995). In the laboratory, older copper redhorse juveniles (average size 108.4 mm) fed on zebra mussels (Dreissena polymorpha) less than 8 mm in length (Branchaud and Gendron 1993).


Natural Environment

Given its sensitivity to pollution and siltation, the fact that individuals congregate at certain times of the year and its extremely small range, the species is particularly vulnerable to any natural disasters that could affect its habitat in any way. Any disturbances which might affect mollusc populations could also adversely affect the copper redhorse, since it feeds almost exclusively on this type of prey.

Artificial Reproduction and Rearing

Numerous studies have made it possible to develop artificial reproduction and rearing techniques. Efforts to reproduce the species artificially have been successful, but hormonal induction had to be used (Branchaud and Gendron 1993, Branchaud et al. 1993, 1995). In these studies, spawners were held for several days in tanks. A few adult specimens were also held for several months or even a few years in aquariums. However, spawners must be handled very carefully since they exhibit severe stress reactions when captured (Branchaud and Gendron 1993). Holding adults in long-term captivity has, however, proven difficult. Most of the specimens die (Dumont et al. 1997, Pierre Dumont, biologist with the Société de la faune et des parcs du Québec, pers. comm.).

In 1994, juveniles were reared in a semi-closed system at the Tadoussac hatchery as well as in a small experimental pond (Branchaud et al. 1995, Turgeon 1995). The survival rate of the larvae was approximately 23% in the fertilized pond and 87% at the Tadoussac hatchery. The larvae and juveniles feed on both artificial and natural foods (Branchaud and Gendron 1993, Branchaud et al. 1993, 1995, Turgeon 1995). Although the rearing experiments in 1994 were encouraging, some adjustments had to be made given the low growth rate (average length of 22.8 mm after 91 days of rearing) and the high prevalence of scoliosis observed in the individuals produced in a semi-closed system at Tadoussac. In 1995 and 1996, rearing in fertilized ponds at the Baldwin Mills hatchery was recommended. The improvement of rearing techniques made it possible to produce larger advanced fry in the fall (average size 42 mm) and the deformation problems were corrected (Branchaud and Fortin 1998, Dumont et al. 1997, Pierre Dumont, biologist with the Société de la faune et des parcs du Québec, pers. comm.).

Following these studies, some 100 000 fry were stocked, on an experimental basis, in the Richelieu River in the fall of 1994, 1995 and 1996. The survival of the specimens stocked in the fall of 1994 is very improbable since they were very small in size (average: 22.8 mm) and in poor condition (thin). In 1995, some 40 000 fertilized eggs were released in the Chambly rapids, 35 000 unfed fry were raised at Baldwin Mills and approximately 21 000 larger advanced fry (average: 42 mm) were stocked in the Richelieu River in the fall (Branchaud et al. 1995, Branchaud and Fortin 1998, Dumont et al. 1997, Pierre Dumont, biologist with the Société de la faune et des parcs du Québec, pers. comm.). With the exception of one specimen captured in 1997, the origin of which is unknown (Vachon 1999a), no copper redhorse likely to have been stocked has been found (Boulet et al. 1995). However, this absence of recaptures cannot be interpreted as a failure since it is often difficult to monitor small fish returned to their natural environment. In fact, their dispersal greatly reduces the chances of recapture (Boulet et al. 1995). The implementation of a copper redhorse breeding and reintroduction plan is now one of the actions considered a priority by the Comité d’intervention. To this end, an artificial breeding plan has just been drafted (Bernatchez 2004) and implementation will begin this year. The preliminary results of a study on the genetic characterization of copper redhorse populations show that genetic variability is still high in the populations from the Lavaltrie-Contrecoeur sector (St. Lawrence River) and those caught downstream from the Saint-Ours dam (Richelieu River). Because the analyzed tissue samples come largely from larger, older individuals, this study underscores the urgency of artificial breeding and rearing of the species in order to preserve its genetic diversity (Lippé et al. 2004).