Science Advisory Report  2013/040

Recovery Potential Assessment for the Atlantic Sturgeon, St. Lawrence population

Summary

• The Atlantic Sturgeon, St. Lawrence population, is mainly found in the St. Lawrence River, downstream of Trois-Rivières and on into the Estuary and Gulf of St. Lawrence.
• The abundance of Atlantic Sturgeon, St. Lawrence population, has never been formally established. The current size is unknown. Based on data regarding spawning sturgeon collected in a study on the life cycle of Atlantic Sturgeon in the St. Lawrence between 1997 and 2000, Dadswell (2006) estimated the population of mature adults to be between 500 and 1,000 individuals. This was based on released fish (tagged and recaptured). However, since the data used to calculate abundance were not intended for this type of study, these results should be used with caution.
• The absence of an analytical model prevents us from accurately estimating the size of the minimum viable population (MVP) for the Atlantic Sturgeon in the St. Lawrence River. However, the results of various studies on the MVP indicate that an MVP of between 5,000 and 6,000 Atlantic Sturgeon adults would ensure the survival of the species for 500 years.
• Due to the existing uncertainties about demographic parameters required for modelling, no long-term projection has been made. However, based on an estimate of the abundance of the first cohort, which fully avoided being fished (19 years) (variation between 300 and 700) and by applying the natural mortality (M) rate found in the literature for different populations of sturgeon (variation between 0.05 and 0.09), it is possible to project abundance for each year and estimate the size of the population. Depending on various parameters, we obtain values ranging between 1,597 and 7,723 mature Atlantic Sturgeon after about 40 years if we consider that some individuals survive to 60.
• Six areas of adult concentration were identified, including four in the river estuary (between Trois-Rivières and Quebec) and two in the middle estuary (downstream of Île d'Orléans). Three of the four areas in the river estuary have been identified as potential spawning grounds (Richelieu Rapids, mouth of the Chaudière River, Saint-Antoine-de-Tilly), while the other three areas seem to be best suited for resting and feeding (Saint-Charles River estuary, Traverse du Milieu Channel, the north channel between Sault-au-Cochon and Petite-Rivière-Saint-François).
• The transition zone between fresh water and salt water in the St. Lawrence estuary is home to groups of benthic prey preferred by the Atlantic Sturgeon and is an important habitat for the breeding and feeding of juveniles. The extent of this habitat, strongly associated with the brackish water transition zone, was estimated at 76 km² and includes two main areas where juveniles are concentrated, between the towns of Saint-Jean (Île d'Orleans) and Cap-Saint-Ignace.
• Potential threats to the Atlantic Sturgeon, St. Lawrence population, are mainly associated with commercial fishing and the degradation and loss of preferred habitat. Dredging constitutes a major threat, especially in juvenile feeding areas. Acquiring new knowledge about the habitat of the Atlantic Sturgeon, particularly the precise location of spawning grounds, and the impact of certain threats is essential before appropriate mitigation measures can be implemented.

This Science Advisory Report is from the February 21, 2012 meeting on the recovery potential assessment of Atlantic Sturgeon (Acipenser oxyrinchus), St. Lawrence population. Additional publications from this meeting will be posted as they become available on the DFO Science Advisory Schedule.

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