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Dauvin, J.-C., Basuyaux, O., & Spagnol, M. (2026). Stock and Catch Assessment of Ruditapes Populations and Awareness-Raising Activities for Recreational Fishers Along the Western Coast of Cotentin (French Coast of English Channel). Journal of Environment and Ecosystems, 1(1), 0003. https://ojs.sgsci.org/journals/jee/article/view/717
Volume 1, Issue 1

Stock and Catch Assessment of Ruditapes Populations and Awareness-Raising Activities for Recreational Fishers Along the Western Coast of Cotentin (French Coast of English Channel)

For several decades, the western coast of Cotentin has been colonized over a length of about 80 km by the Manila clam Ruditapes philippinarum. This species has become established due to the development of clam farms in the Chausey Archipelago. This paper summarizes the main ecological patterns of the clam populations and describes approaches to assess the stocks subject to high pressures caused by recreational and professional harvesting along the western coast of Cotentin (WCC). Ruditapes show low densities (from 0 to 52, but often <10 ind.m-2). An annual one-day survey was carried out in August estimates there to be roughly 6500 fishers present along the WCC. According to the mean clam size (37.5 mm) and mean weight (13.6 g), it is possible to approximate the biomass of the clams living in five identified patches (15% of the total surface occupied by clams on the WCC): 816 t in 2015 and 1142 t in the early 2000s. The estimated biomass of minimum fishable clams (>40 mm for a mean weight of 16.8 g), is assessed at between 648 and 907 t: i.e., 79% of the total biomass. The total annual clam catches by recreational and professional fishers are assessed at 300 t for the years 2000. Awareness-raising actions by a shore mediator have been implemented to inform the public about regulations during fishing activities (100 clams of more than 40 mm per day and per fisher) and have proven very efficient since the beginning of these actions 10 years ago. An experiment of non-fishing carried out on an area of 6 km² for five years failed to identify any interannual difference in terms of abundance and size either inside or outside the reserve. At present, the stock does not appear to be endangered and has supported a considerable fishing effort over several years.

Manila clam Cotentin sampling design fishing effort stock assessment

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Supporting Agencies

  1. Funding: This study was carried out in part of the Framework of the LIFE programme entitled ‘Experimentation pour une gestion concertée et durable de la pêche à pied de loisir’ coordinated by the ‘Agence des Aires Marines Protégées’, 3POC programme (‘Pêche à Pied à la Palourde sur la côte Ouest du Cotentin’) supported by the Normandy Region, and the RS2S programme (‘Reconstitution d’un Stock de bivalves Indicateur de Stocks et Vigie des Havres’) supported by the Seine Normandy Water Agency (AESN). The organizations associated with these programmes are the SMEL (‘Synergie Mer Et Littoral’), the GEMEL (‘Groupe d’Etudes des Milieux Estuariens et Littoraux’), Avril Association, the UMR-CNRS laboratory ‘Morphodynamique continentale et côtière’ of Caen Normandy University, and the UMR-CNRS laboratory LEMAR of West Bretagne University.