Potential use of Mussel farms as Multitrophic on-growth sites for American lobster, Homarus americanus (Milne Edwards)

Abstract

Mussel (Mytilus edulis) farms in Newfoundland, Canada were investigated as potential sites to hold adult lobsters Homarus americanus in inshore benthic cages. The goals of this project were to determine if lobsters can be maintained for prolonged periods in cages and survive and grow by feeding on mussels dropping-off culture lines. The effects of biotic and abiotic factors on the moulting, growth rates and serum protein concentrations were monitored at regular intervals in both the field and the lab over 6 months. Although survival rates were high under mussel lines, the moulting rate was low and analysis of serum protein concentration showed they were in a poorer condition than fed lobsters in lab experiments. In the laboratory diet type, temperature, feeding frequency and compartment size were manipulated to determine possible factors influencing survival and growth of the lobsters in the field. In the lab, moulting was highest at 15°C and survival lowest at 5oC; lobsters fed a mixed versus a mussel only diet were healthier. In a separate lab experiment, lobsters that were fed twice weekly attained a larger size at post-moult than those fed once per month. However, feeding frequency did not affect survival or the number of animals moulting. The lab experiments suggested that the combination of low temperature and infrequent food input was the cause of the low moulting rate and overall quality of the lobsters in the field. This project showed although lobsters can be stored in benthic cages in the field for up to 6 months, relying on mussel drop-off alone is limited, and lobsters may need supplemental feeding in order to produce a larger, higher quality product for market. Initial results also suggest the promise of incorporating lobsters into a multitrophic aquaculture system as a means to remove moribund mussels underneath culture lines.