At Hurricane Island this summer, we are working on setting up research on scallop growth rates using three different culture techniques.

Photo: Alex Griffith (HICSL)

Lantern nets are a traditional Japanese method of growing scallops that is currently widespread in the Gulf of Maine. The nets look like an accordion, and serves as an apartment building of sorts, with ten levels for scallops. These nets are suspended from floats or lines off the bottom, limiting damage from bottom strikes and predation. However, their location close to the surface means fouling by algae and organisms like tunicates that prefer to feed higher in the water colum, which dramatically reduces water flow to the scallops. Further, high densities of scallops can effect growth rates through food competition and "knifing," wherein scallops can pinch or cut other scallops with their open shells.

Bottom cages are less common in the Gulf of Maine, but have a similar concept to lantern nets. Cages hold six mesh "bags," and these cages are weighted to sit on the bottom. Biofouling is still an issue with these cages and bags, but they do not seem to foul as quickly as lantern nets. They do require more materials, take up more space, and are overall more expensive than other options. Much like lantern nets, high densities can lead to lower growth rates. The picture above shows a bottom cage off of Hurricane island viewed from the top; here you see two bags of scallops, and beneath each are two more for a total of six bags.

Photo: Portland Press Herald

Ear-hanging is relatively new for the Gulf of Maine, but is now quite widespread in Japan and is a favored method. Scallops are not placed in a net or cage; instead, a hole is drilled through the "ear" of the scallop, and the scallop is then threaded onto a plastic hanger attached to a strand of rope. This plastic hanger is hooked, so a scallop will not fall off. This method limits the amount of gear needed, and thus is cheaper and easier to clean. Scallops do not touch neighbors, and so are free to grow unconstrained by space or food competition. Further, they spend more time with their shell opening and closing while the feed, excercizing the edible adductor muscle and accelerating growth. However, drilling these holes in scallop ears are incredibly time-consuming by hand, and machines that automate the process are tens of thousands of dollars. Ear-hanging scallops are also less protected from predators and the elements. Mortality can thus be high after a heavy storm, especially if the lines are not far enough from the bottom. 

Certain methods may yield larger scallops, but the cost per scallop to the farmer may be more expensive compared to other methods, and so it is not the only factor when selecting culture techniques. We are hoping to continue taking monthly data on growth rates this summer and in following summers, with the goal of demonstrating which methods provide optimal growth.

Adult scallop, 3 years. Note eyes on rim of mantle

Juvenile scallop (less than a centimeter), less than a year. Collected using spat bags off of Muscle Ridge

Madison and I spend a lot of time counting and measuring scallops!