The main objective of this paper is to show that a wellmanaged lake sturgeon Acipenser fulvescens population can support a high and sustainable commercial catch, even in the Great Lakes drainage where the species has nowadays become rare. In a 350-km long un-fragmented stretch of the lower St Lawrence River located between Montreal and downstream Quebec City, with declared annual catches of 150 tonnes, the lake sturgeon population was considered overexploited by a governmental scientific committee in 1987 on the basis of high annual mortality rates (17-25% for age groups 14-31), unbalanced age structure, deficit of reproductive potential and commercial catch yields well over 1.5 kg ka )1 . A first management plan implemented in 1987 failed to reduce the catch and provide more protection to the spawning stock. During the 1990s, the declared catch of the 76 commercial fishermen kept increasing over 200 tonnes. The age at the recruitment of the 20-cm-mesh gill-nets shifted towards older fish, indicating a decrease in the numbers of younger fish. In the population, sub-adult abundance decreased by 60%, as well as the year-class strength and the abundance of the females on the largest known spawning ground. In 2000, a stronger management plan was then enforced in order to adapt the total catch to the potential of the resource. The commercial catch was reduced by 60% in 3 years and an individual codebar plastic tag and a code-bar weight declaration coupon were established to control its application. The fishing season was also shortened. Ten years later, we are confident in maintaining the actual commercial fishery because the commercial catch is now much lower (80 tonnes) and is more effectively controlled, the abundance of juvenile lake sturgeon increased throughout the St Lawrence River and the regular yearly production of cohorts has been demonstrated. Restrictive management measures, close supervision of landings combined with periodic monitoring of the population are key elements in managing this long-lived species. We also emphasize the importance of preventing any further fragmentation of this portion of 350 km of fluvial habitat as well as to maintain habitat quality to ensure the sustainability of this fishery.

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The study of distribution and dispersal of invasive fishes is challenging during the early stages of invasion. Quantification of trace elements incorporated into fish hard parts represents an innovative technique for this task. Otolith chemistry has been used to describe fish stock structure, migratory behaviour and to support the management of several species. We used otolith chemistry to study the dispersal and population structure of Tench (Tinca tinca), an invader in the St Lawrence River. Tench movements throughout the invaded portion of the system were reconstructed using a Random Forests Algorithm. The results showed that, despite the presumed limited dispersal capacity of the species, Tench are capable of extensive migratory movements (up to 250 km). The variability in migratory patterns among individuals, including both short- and long-distance movements, supports a stratified diffusion. Such a strategy may explain the successful invasion of Tench in the St Lawrence River ecosystem. Our study represent a flexible framework for the study of Tench ecology in its invaded and native range, as well as for other freshwater invasive fishes.

Fishes are among the most threatened taxa in Canada with over 70 species, subspecies, and (or) designatable units presently listed for protection under the Species at Risk Act (SARA). Protecting these species requires a diverse set of strategies based on the best-available data and information. One approach identified under SARA and in Canadian federal recovery strategies for improving the status of SARA-listed fishes is species reintroduction, which involves the release of individuals into areas from which they have been extirpated with the goal of re-establishing self-sustaining populations. The success of reintroduction relies on a comprehensive understanding of species ecology and life history, with considerations around population genetics and genomics. However, SARA-listed species are some of the most poorly known species in Canada due to their rarity and relative lack of research investment prior to the enactment of SARA. As a result, SARA-listed species have the most to lose if reintroduction activities are not carefully researched, planned, and executed. Therefore, the purpose of this review is to present an accessible summary on the state of reintroduction science for SARA-listed fishes in Canada with the hope of motivating future research to support reintroduction activities. We focus our review on 14 SARA-listed freshwater or anadromous fishes identified as candidates for reintroduction in federal recovery strategies. We follow the species-specific summaries with guidance on how basic research questions in population ecology, habitat science, and threat science provide a critical foundation for addressing knowledge gaps in reintroduction science. Subsequently, we identify the importance of genetic and genomic techniques for informing future research on the reintroduction of SARA-listed species. We conclude with recommendations for active, experimental approaches for moving reintroduction efforts forward to recover Canadian fishes.