Lobsters feeding on mussels in multitrophic aquaculture

The mussel farmers’ harvests need not always end when they have plucked the last of the mollusks from the lines. Under the mussel lines may await another harvest, this time, of a higher value crop.

            The concept is to grow-out adult American lobsters in benthic cages beneath the mussel lines. The lobsters would feed on mussels dropping off the lines.

            Yes, the multitrophic operation could be this simple.

            The lobsters would grow and, at the same time, contribute to the environmental clean-up by eating moribund mussels as well. (See side-bar.)

            Growth, however, could still be improved.

            This multitrophic project was the topic of a poster entitled “Use of Mussel Farms for On-growth of American Lobster, Homarus americanus,” by Iain J. McGaw and Guoqiang Wang of the Department of Ocean Sciences at Memorial University in Newfoundland, Canada. The abstract was submitted to Aquaculture 2016, which was held in February in Las Vegas.

            The focus was on determining “if lobsters can be maintained for prolonged periods in cages and survive and grow larger by feeding on mussels dropping off of culture lines “ and determining “ if lobsters can be incorporated into a multitrophic aquaculture operation as a means of removing moribund mussels that might otherwise stagnate on the seabed.”

            “This project showed that although lobsters can be stored in benthic cages in the field for up to six 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,” the abstract cited.

            The study was conducted for six months in mussel (Mytilus edulis) farms in Newfoundland, and monitored effects of biotic and abiotic factors on the molting, growth rates and serum protein concentrations in both the field and the lab.

            With the exception of the high survival rate, the performance of lobsters in benthic cages fell low compared to their lab counterparts.

            “Although survival rates were high under mussel lines (> 95%), the molting rate was relatively low (13%) and analysis of serum protein concentration showed they were in a poorer condition than fed lobsters in lab experiments,”  notes the abstract.

            “In the laboratory, 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, molting was highest at 15̊C and survival lowest at 5̊C, and lobsters fed a mixed versus a mussel-only diet were healthier. In a separate lab experiment, lobsters that were fed twice weekly grew larger than those fed once per month.”

            Low temperature and infrequent food input were identified as the most probable causes for low molting rate and overall quality of the caged lobsters.

            Molting rate is very important for lobsters because they grow continuously throughout their life cycle. The more frequent they molt, the bigger they get.

— Ruby Gonzalez