The effect of environmental factors, depth and position on the growth and mortality of raft-cultured blue mussels ( Mytilus edulis L.)

One-year-old rope grown blue mussels (Mytilus edulis L.) were grown in experimental lantern nets at two depths (2 and 6 m below the surface) in two different positions (inflow and outflow) off a raft in Loch Etive on the west coast of Scotland. Shell and tissue growth, and mortality were recorded. Water temperature, salinity and food availability were also monitored over the experimental period. There were no significant differences in the length, live weight, wet meat weight, dry meat weight and ash-free dry meat weight between depths (P > 0.05). However, position had a significant effect on these parameters as mussels located at the inflow of the raft differed significantly from those at the outflow of the raft (P < 0.05). Particulate organic matter (POM) and chlorophyll a (Ch a) were significantly higher at the inflow than the outflow of the raft (P < 0.05), but depth had no effect on POM and Ch a (P > 0.05). The results show that food concentration was higher in the inflow of the raft than the outflow. In the light of these results, recommendations for better management of Scottish raft mussel cultivation are discussed.