Science Advisory Report  2010/069

Assessment of Habitat Quality and Habitat Use by the Striped Bass (Morone saxatilis) Population of the St. Lawrence Estuary, Quebec

Summary

• Prior to its disappearance in the late 1960s, the Striped Bass population of the St. Lawrence Estuary spent its entire life cycle in the area between Lake Saint-Pierre and Rivière-du-Loup. Since its reintroduction, starting in 2002, Striped Bass have been captured mostly in the same sector. 
• The spawning, incubation and larval stage sites have never been located. In 2008, juvenile Striped Bass were captured even though no stocking of this age group had occurred that year, which confirmed that these habitats were still present in the St. Lawrence River and Estuary.
• Prior to the disappearance of the Striped Bass, the first catches of juveniles (age 0+) started at Neuville in July, then gradually at sites downstream up to Rivière-Ouelle in late August. Since the reintroduction, juveniles have been caught in eel traps in September and October in the area from La Pocatière to Kamouraska, 96% of the catches were made in Anse Sainte-Anne and 4% downstream from this area.
• Immature and mature Striped Bass do not appear to be associated with a particular habitat, but they rather move based on the distribution and abundance of their prey. Variations in the longitudinal distribution of individuals based on age and time of year were recorded prior to the species’ disappearance. Immature striped Bass were concentrated in the upper estuary, while Striped Bass aged 3+ and older could be found further upstream in winter and downstream in the summer.
• Before the population’s disappearance, aggregations of adult size Striped Bass were observed in Lake Saint-Pierre in the winter. Since the reintroduction, many adult-sized Striped Bass have been observed in the spring in the warm water plume of the Gentilly-2 nuclear generating station in Gentilly and in the Rivière-du-Sud basin at Montmagny.
• Several anthropogenic threats could disrupt or destroy the habitat characteristics of Striped Bass. Dredging, changes to the shoreline, the plume of warm water produced by the Gentilly-2 nuclear generating station along with its management measures, the presence of contaminants, vessel traffic, the development or expansion of commercial or industrial ports, the development of underwater generators, disturbance caused by fishermen in concentration areas and the emergence of new exotic species are some examples.
• The identification and characterization of habitats used by the different development stages are necessary, with priority given to spawning, incubation and larval stage areas, habitats used by juveniles, concentration areas for mature individuals in spring and winter concentration areas.
• Data analysis of the extinct and the reintroduced population has helped identify important habitats for each development stage. Further studies on the reintroduced population are needed to locate these habitats and determine which should be designated as critical habitat. However, at this stage, it is clear that Anse Sainte-Anne at La Pocatière is an important habitat for juveniles in late summer and measures should be implemented to protect this habitat.

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