2685 22 Gulf Fisheries Centre Moncton, N.B.

In suspended blue mussel (Mytilus edulis) culture, the link between sock spacingand mussel performance on a longline system has never been experimentallydemonstrated. Therefore, the objective of this trial was to compare productivity ofmussel socks spaced (sock spacing treatments [Tx]) 10 cm, 20 cm, 40 cm, 60 cm and 80cm apart on a longline. A large-scale experiment was conducted in distinct leases ofTracadie Bay, PEI over a one-year production cycle. Shell growth and survival of premarketmussels were positively associated with higher sock spacing treatments, whilecondition index displayed no temporal and spatial relations to sock spacing treatments.In two of the four experimental sites, results showed significantly greater growth andsurvival levels on mussel socks spaced 80 cm apart (i.e. Tx 80) at the end of theproduction cycle. Shell growth increased by 8% (3.4 mm) and 7% (3.4 mm), whilesurvival was 42% (233 mussels/m) and 18% (87 mussels/m) higher when comparing lowdensity levels (Tx 80) to high density levels (Tx 10) of cultured mussels. When allmanagement strategies (i.e. socking density and seed size) were kept constant, theassociation between sock spacing treatments and productivity were non-significant. Thesignificant differences between sock spacing treatments at two of the four sites may bedue to high initial socking density and smaller seed size. Sites displaying significantassociations were respectively characterized by having 58% and 47% more mussels permeter, while seed mussels were 46% and 23% smaller. Dense aggregation of bivalves atthe farm level and inside mussel socks may lead to intra-specific competition betweenindividuals as food demand at the local scale may exceed food supply and ultimatelylimit growth. Food levels at the local scale were not measured during this study, but aredocumented to be highly variable temporally and spatially within this growing area