Our objective was to compare movements and biological statistics of lake sturgeon (Acipenser fulvescens) populations from two fluvial lakes on the St. Lawrence River, Lac Saint-Louis and Lac Saint-Pierre, which are main commercial fishing sectors, and from Lac des Deux Montagnes on the Ottawa River. Sturgeon can move freely among these three lakes. Lac des Deux Montagnes sturgeon differ from the other groups by their higher degree of sedentariness, slower growth, and lower condition factor. Lac Saint-Louis and Lac Saint-Pierre sturgeon are also sedentary, but some movement between the two lakes was observed. Sturgeon tagged on the Rivière des Prairies and Rivière L'Assomption spawning grounds, located in the central part of the study area, and also on pre- and post-spawning concentration sites, were recaptured throughout the St. Lawrence River, from Lac Saint-Louis to Lac Saint-Pierre. Length, weight, and age composition of the commercial catch, growth, and total mortality varied between Lac Saint-Louis and Lac Saint-Pierre. Higher commercial exploitation rates in the latter could be responsible for some differences. The management implications of these results are discussed.

The copper redhorse, Moxostoma hubbsi (Legendre), which was discovered in 1942, is a threatened and endemic fish species of the lowlands around Montréal (Quebec). A survey of historical data, an investigation of the preserved specimens, and a comparison of selected biological characteristics of the five Quebec Moxostoma species living in sympatry in the Richelieu River show that this redhorse has a unique combination of life history characteristics. Compared with the other redhorses, it is among the most long-lived (more than 20 years), has the highest growth rate and fecundity, and is the latest spawner, its reproduction probably taking place at the end of June or at the beginning of July. The copper redhorse shows a high degree of specialization in the use of alimentary resources and feeds almost exclusively upon molluscs. The comparison of the stomach contents of the different species living in sympatry shows little diet overlap. This may be due to the specialization of their pharyngeal apparatus and to a certain degree of spatial segregation. Similar to its congeners, the copper redhorse shows a predilection for lowland rivers of medium size characterized by abrupt banks and uniformly deep channels (4–7 m) flowing over a solid clay, sand, or gravel bottom. The most populated sections of river have rather slow currents; they are interspersed by sections of rapids suitable for spawning. In the St. Lawrence system, the range of the copper redhorse is much more restricted than that of other redhorses, and this species appears much more vulnerable to habitat degradation.