Research Document 2020/055

Assessment of Softshell Clam (Mya arenaria) Stocks of Québec’s Inshore Waters in 2019 – Methodology and Results

By Brulotte, S.

Abstract

The softshell clam (Mya arenaria) is found all along Québec’s coastlines, where it is harvested recreationally and commercially. Since 2008, harvesting has been performed exclusively with hand tools. For management purposes, Québec’s coastal areas are divided into shellfish harvest areas in three main regions: the North Shore, Gaspé–Lower St. Lawrence, and the Îles-de-la-Madeleine. Recreational harvesting is carried out in all three regions, while commercial harvesting is limited to the Upper North Shore and the Îles-de-la-Madeleine. Commercial landings on the Îles-de-la-Madeleine have been small (< 3 t) for a number of years, and the current commercial fishery is limited almost exclusively to the Upper North Shore.

Commercial landings on the Upper North Shore reached a peak in 2000, at 1,173 t, and then declined rapidly, with average landings of 26 t recorded in 2017–2019. Total allowable catches (TACs) are not fully utilized owing to the low fishing effort. Commercial landings come mainly from 10 shellfish harvest areas. Since 2017, the average size of landed clams has ranged between 65 mm and 74 mm in the six areas sampled, with sub-legal size clams (< 51 m) making up only a very small proportion of landings.

In all, 23 shellfish harvest areas on the Upper North Shore were surveyed from 2016 to 2019; eight of these had been previously covered in surveys from 2002 to 2014. Commercial density (i.e., the density of legal-size clams) increased substantially in five of these eight areas. However, the current area of some of these beds is much smaller than that measured in surveys from 1967 to 1977. Indicators used for assessing softshell clam stocks in the shellfish areas surveyed in 2016–2019 include harvestable area, density of 20–50 mm clams, density of legal-size clams (≥ 51 mm) and commercial biomass.

In order to protect the reproductive potential of each shellfish harvest area, it is recommended that the exploitation rate be limited to a maximum of 5% of the commercial biomass. However, at a 5% exploitation rate, certain shellfish areas could be more vulnerable to a loss of reproductive potential. Therefore, it is suggested that this rate be adjusted downward for shellfish areas with a harvestable area of less than 0.05 km² and an average density of sub-legal size clams (20–50 mm) of less than 15 clams/m². The suggested exploitation rates apply to all removals (from both commercial and recreational harvests).

Research Document 2020/055 (PDF, 2,795 KB)

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