Action concertée sur les semis de coquille Saint-Jacques en Europe (1993-1996)

Faced with the decline of scallop {Pecten maximus) fisheries and high costs of ongrowing in suspension, scallop seabed cultivation appeared to be the most suitable technique for European conditions. A three-year European Concerted Action supported by European Union and Norway (associated country) joined together four teams involved in scallop seedings : - IFREMER Brest / laboratory Molluscs, in Brittany (France), a national institute of ocean research (co-ordinator of the Concerted Action) ; - Connemara Shellfish Co-op, in Connemara, County of Galway (Ireland), a fishermen's co-operative ; - Seafish Ardtoe, in Scotland (United Kingdom), an institute provided by the fishing industry ; - Institute of Marine Research, in Bergen (Norway), a national institute of research. Underwater observations were made possible by the important diving team (8 to 10 people) set up by the group, and its video equipment (up to 4 underwater remote video cameras including one in a submarine robot). Three common field works with divers and video, could be carried out. They first required the setting up of a common diving code of practice including the different national regulations. They also enabled the comparison of various underwater sampling methods. These common field works studied : - the recessing behaviour and vitality of juvenile scallops at seeding in Autumn, according to three sizes of juveniles (Brest, France, 1993) ; which pointed out the need of recovery for re-seeded scallops ; - the impact of placing crab traps around the perimeter of plots seeded with juvenile scallops, on the survival of the scallops (Connemara, Ireland, 1994) ; which gave significant effect results with the smaller scallops (30-35 mm) ; - the effect of placing an alternative prey (mussels) together in the seeding area of juvenile scallops, on the survival of the scallops (Ardtoe, Scotland, 1995) ; which gave some preliminary results with weak mussels only (after aerial exposure in the sun). Concurrently, four table meetings were planned for preparation of the field works, as far as for active discussions about the know-how and bottlenecks in seabed cultivation. These meetings facilitated the gathering of up-to-date informations about scallop culture in Europe and in the most important producing countries (Japan, Canada, New-Zealand). In France, scallop seedings now provide one-third to one-half of the local scallop fishery in Brest Bay (90 boats). In Ireland, seedings to enhance the natural scallop fisheries are continuing in two areas and a private company harvested 8 tonnes of bottom cultured scallops in 1996. In the United Kingdom, the granting of the first commercial Several Fishery Orders in February 1993 (giving a legal ownership of the natural or seeded stock of a defined seabed area) increased the interest of scallop farms to turn from suspending techniques to bottom cultivation. In Norway, a governmental report, on the long term strategy of the Norwegian aquaculture, proposed the scallop Pecten maximus, along with the Atlantic halibut as main species for aquaculture development. The Concerted Action identified and analysed 3 factors to improve scallop seabed cultivation : - the fitness of the seeding sites (biological and socio-economical factors) ; - the fitness of juvenile scallops (size and vitality) ; - the fitness of practices, especially in order to avoid prédation. Sites : Scallop seabed cultivation is an extensive aquaculture (sea ranching) requiring broad coastal areas. Criteria of choice for seeding sites, either biological and socio-economical, could be listed and ranked. The abundance of predators, especially crabs, is an important criteria in the choice of a seeding site. In addition, rights to access and to exploit such coastal areas appeared different within European countries, all regulations being unsuited to vast areas under coastal management by professional groups. Juveniles : Fitness of the juvenile scallops comprises two elements, their size and their vitality. Convenient size could range from 20 to 60 mm and was determined in each area according to local constraints in sites and in spat supply. The vitality of animals was identified as an important factor, but was marginally studied in the Concerted Action (some biochemistry in the French field work, 1993), failing to have a satisfactory diagnostic tool. The perfecting of a simple test could enable profitable comparisons in future works. Practices : At present, seeding practices in sea ranching concern only the choice of the seeding season, of the seeding size of animals and of the seeding density ; in future, they would benefit from regarding also the animal acclimatization in order to restore or improve their vitality and the site preparation aiming to decrease the predator density (potting) or activity upon scallops (alternative prey). Faced with increasing numbers of aquaculture S.M.E. or fishery professional organisations involved in scallop seabed cultivation in Europe, the national Research and Development authorities have more or less involved themselves in scallop studies and coastal management. However this needs long term programmes, demanding basic research (physiology), experiments in the wild (diving observations), in an environment which remains poorly known (need of ecology) and poorly regulated (need of law).