Research Document 2023/035
Results of soft-shell clam (Mya arenaria) surveys from 2016 to 2020 on the Upper North Shore and update of surveys from 2001 to 2014 in Quebec
By Brulotte, S.
Abstract
Soft-shell clam (Mya arenaria) is found throughout Quebec’s coastline. Quebec’s coastal zone is divided into shellfish areas, which are grouped into three major regions: the North Shore, Gaspé–Lower St. Lawrence and the Magdalen Islands. Clam beds in 28 shellfish areas on the Upper North Shore were surveyed from 2016 to 2020. The results—including the area of the beds, density (number/m2) and yield (g/m2) of sub-legal-size (20-50 mm) and legal-size (≥ 51 mm) clams, harvestable area, biomass of clams ≥ 51 mm, size structure, sediment grain size and associated species counts—are provided for all those surveys. In addition, an update of the results of surveys from 2001 to 2014 is provided.
Shellfish beds varie from 0.004 km2 (Batture aux Gibiers Est) to 5.99 km2 (Pointe-aux-Outardes Ouest). The preferred habitat of soft‑shell clams is a mixture of mud and sand sediments in varying proportions. The average density of clams 20-50 mm varies greatly from one bed to another, from 0 (Batture aux Gibiers Est) to 277 clams/m2 (Anse du Colombier). The average densities of clams ≥ 51 mm ranged from 2 (Pointe aux Vaches) to 79 clams/m2 (Rivière Blanche). Values greater than 45 clams/m2 were observed in Rivière Blanche, Îlets Jérémie and Réserve Pessamit Sud. Such values were never obtained during previous surveys from 2001 to 2014 in Quebec.
Within each shellfish area, the harvestable area is delineated by a minimum of three contiguous stations with a density of legal-size clams ≥ 16 clams/m2, based on the premise that harvesters target locations with sufficient density of clams. With this premise, four shellfish areas do not have a harvestable area, whereas others have harvestable areas between 0.03 km2 (Batture à Théophile) and 2.37 km2 (Pointe-aux-Outardes Ouest). The mean density of clams ≥ 51 mm over the harvestable area varies from 17 clams/m2 (Batture à Théophile) to 98 clams/m2 (Rivière Blanche). The average yield of clams ≥ 51 mm varies from 338 g/m2 (Batture à Théophile) to 2,843 g/m2 (Rivière Blanche). The highest harvestable biomasses were obtained in Pointe-aux-Outardes Ouest and Réserve Pessamit Sud.
These results were compared with those of previous surveys conducted on the same beds. In general, the densities of clams ≥ 51 mm are similar or higher to those in the surveys from 2002 to 2014. However, comparison with surveys conducted from 1967 to 1970 shows that recent densities are lower for several areas.
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