Improving the efficiency of wild Pecten maximus spat collection: potential effects of spat bag design and of species temporarily settling in spat bags

The single and combined effects of external bag size and external bag mesh size upon the collection and retention of wild King Scallop spat (Pecten maximus L.), other scallop species (Aequipecten opercularis) and other animal groups were investigated in a collection area off the west coast of Scotland. Collection was assessed after 5 weeks and at harvest (after 20 weeks). After 5 weeks, 90% of collected animals consisted of scallops (P. maximus and A. opercularis), Mytilus edulis (Mollusca: Bivalvia) and Lacuna vincta (Mollusca: Gastropoda). One-way analysis of variance on count data obtained after 5 weeks showed that the larger bag and mesh size treatments had collected significantly greater numbers of scallop spat when numbers collected were compared to the quantity of material used for each treatment (P<0.05). This was partly attributed to significantly greater numbers of L. vincta crawling juveniles temporarily recruiting in the smaller bag and mesh treatments (P<0.05). Similar trends of spat abundance in treatment bags were observed at harvest, although all treatments had scallop spat retention efficiencies of less than 12%. The importance of the structural design of spat bags for spat collection and the effects of incidentally collected non-predatory species upon the collection of scallop spat are discussed.