Science Advisory Report 2011/022
Assessment of Softshell Clam Stocks in Quebec’s Coastal Waters in 2010
- Softshell clams are present along most of Quebec’s shoreline. They are exploited by commercial and recreational harvesters. In recent decades, commercial harvesting has been practised essentially on the Upper North Shore. Commercial harvests have been documented for all shellfish beds since 2002. The quantities that are harvested recreationally, a prized activity by coastal communities, remain unknown.
- Since 2007, landings have primarily been from approved or conditionally approved shellfish beds: Baie des Chevaux, Banc Marie-Marthe, Anse du Colombier and Îlets Jérémie in sub-area 1A, Pointe-aux-Outardes in sub-area 1B and Réserve Pessamit Sud in sub-area 1C, as well as three harvesting areas for depuration (limited status): Baie des Grandes Bergeronnes, Baie des Escoumins and Rivière Blanche.
- On the Upper North Shore, clam landings totalled 1,173 t in 2000 and have declined since. They totalled 176 t in 2008, 190 t in 2009 and 56 t in 2010. The harvesting effort dropped from 11,585 vendor-days in 2002 to 1,942 vendor-days in 2009, an 83% drop. The effort was even lower in 2010 due to the closure of two clam processing plants on the Upper North Shore.
- Approved shellfish beds on the Upper North Shore generally showed low catches per unit effort (CPUEs) between 2006 and 2008 compared to 2002-2005. Since 2009, CPUEs have increased somewhat, except for Réserve Pessamit Sud where the 2010 CPUE was the lowest of the series. However, there is some uncertainty on the interpretation of the CPUE in recent years due in part to the inaccurate assessment of the number of harvesters involved in the unit effort (vendor-day).
- The size structures of landed clams vary from area to another. From 2008 to 2010, the median size varied between 52 and 78 mm on the main exploited beds. However, the proportion of clams of sub-legal size (<51 mm) often exceeds 15%.
- The survey conducted in 2010 on the Reserve Pessamit Sud bed indicates a decrease in legal-size clam density and biomass of about 35% and sub-legal size clam density of 57% compared with the 2005 survey. The decline in commercial CPUE observed at this clam bed likely reflects a population decrease. It is recommended, annually, to harvest less than 10% of the commercial biomass to ensure the sustainability of these beds.
- Since the last assessment in 2007, landings and harvesting effort have decreased. The drop in effort could be due to a resource decline or to socio-economic factors. The CPUEs from 2006 to 2008 were among the weakest. The proportion of sub-legal size clams in the landings is sometimes high suggesting a low abundance of legal size clams on certain beds. Despite the low harvesting effort in recent years, there has been no noticeable improvement in the status of the resource
- To protect the reproductive potential of each clam bed, it is recommended to enforce the minimum legal size and limit harvesting effort on the Upper North Shore at a level not exceeding the 2007-2009 average. To mitigate incidental mortality caused by harvesting, it is recommended to close the fishery when the air temperature is at or below 0° C. In addition, better knowledge of recreational harvesting is needed to better assess its impact on the resource.
This Science Advisory Report is from the Fisheries and Oceans Canada, Canadian Science Advisory Secretariat, regional advisory meeting of January 25, 2011 on the Assessment of Quebec Inshore Waters Softshell Clam Stocks. Additional publications from this process will be posted as they become available on the DFO Science Advisory Schedule.
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