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

Population Sizes and Trends

Despite the tagging of numerous specimens with spaghetti tags or microchips in the Richelieu River in the 1990s, none has ever been recaptured. It is therefore impossible to estimate the number of individuals in this river.

Since the discovery of the species, fewer than 800 copper redhorse of all ages have been captured. Currently, the only estimate available concerns the Lavaltrie-Contrecoeur population and is based on information obtained from commercial fishers in the fall of 2000. At that time, at most a few hundred individuals (generally fewer than 500) were circulating in the sector. The limits of the confidence interval at 95% of these estimates, which are based on only a few recaptures, vary, depending on the method used, from about 40 to fewer than 1650 individuals in almost all cases (Vachon and Chagnon 2004). The possibility that the individuals in the Richelieu River and those in the St. Lawrence River represent two genetically distinct populations is not ruled out given the fact that the Saint-Ours dam appears to have contributed to isolating them. In fact, this dam has constituted an obstacle to the free passage of fish for 150 years and has been an impassable obstacle for 30 years (Dumont et al. 1997). The hypothesis is currently under study.

In terms of relative abundance compared to its congeners, it is clear that the copper redhorse was formerly more abundant at various periods of history and prehistory. Archeological digs at the site of Mandeville, on the west shore of the Richelieu River (Iroquois occupation between 1450 and 1550 AD), and the site of the Jacob Wirtele inn at Place Royale in Old Montreal (early 19th century), show that copper redhorse represented respectively 16.7% and 9.1% of identified redhorse (Courtemanche and Elliott 1985, Ostéothèque de Montréal inc. 1984, Michelle Courtemanche, pers. comm.). These results are significantly higher than the proportions of 2% to 3% reported during the fish surveys of the waters of the Montreal area between 1963 and 1985 (Mongeau et al. 1986), and higher than the figure of 0.04% recorded at the fish ladder in the spring of 2003 (Fleury and Desrochers 2004). Copper redhorse bones have also been found at other locations, including Laprairie (BiFi-23), dating back to the French occupation of the area in the late 17th and early 18th centuries, Place Jacques Cartier in Montreal (BjFj-44) (Michelle Courtemanche, pers. comm.), and the archaeological site at Station 4 at Pointe-du-Buisson (BhFl-1, 920-940 AD) located on the south shore of the St. Lawrence River, at its mouth in Lake Saint-Louis (Courtemanche 2003).