Science Advisory Repor. 2010/072

Advice relevant to the identification of critical habitat for copper redhorse (Moxostoma hubbsi)

Summary

• Copper redhorse distribution is limited to Canada, more specifically to the south-western part of Quebec and the species forms a single population.The copper redhorse occurs in the St. Lawrence River between Lake Saint-Louis and Lake Saint-Pierre, and in the Richelieu, Mille-Îles and Des Prairies rivers, as well as in the downstream portions of the St. François and Acadie rivers.Its presence is now uncertain and even unlikely in the Yamaska and Noire rivers.
• The only two known spawning sites for copper redhorse are located in the Richelieu River, in the archipelago of the Chambly rapids and the downstream reach of the Saint-Ours dam. The size of these spawning grounds is likely sufficient to support the needs of a recovered population of 4,000 spawners.Other sites could potentially meet the requirements of copper redhorse spawning, but the presence of reproductive activities has never been clearly demonstrated.
• The Richelieu River is the only river where copper redhorse larvae have been observed.Littoral grass beds in the Richelieu River has been identified as playing a key role in fry rearing (growth, food and shelter) and also represent an important habitat for juveniles and adults.The littoral zone of 0-4 meters deep throughout the Richelieu River up to the Chambly basin and around the Islands are the preferred habitat of young redhorse and adults that frequent the Richelieu or use it a.a migration corridor.Knowledge about the sub-adult habitat remains incomplete.
• The size of potential habitat as a feeding and adult growth area does not appear to be a limiting factor to achieving the recovery target in the St. Lawrence River (between Beauharnois and Trois-Rivières).However, the habitat size currently used in the river between Montreal and Sorel, appears more limited.
• The copper redhorse is a migratory species and free access between different habitats that provide critical roles for their life cycle should be maintained.
• Considering that the offer in terms of habitat may be limited by its quality, any measure aimed at improving habitat quality should be put forward, both in the Richelieu River and in the St. Lawrence.Given the major role that grass beds play in the survival and recovery of copper redhorse at different stages of life, and considering the vulnerability of these habitats to environmental degradation, actions must be undertaken quickly in order t.ensure their protection.

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