Management of the Lake Sturgeon Acipenser fulvescens population in the lower St Lawrence River (Québec, Canada) from the 1910s to the present

Summary The main objective of this paper is to show that a well-managed 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 code-bar 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.