Arctic surfclams, Mactromeris polynyma, are a $100 million fishery in Atlantic Canada and Quebec. This valuable species grows in the Gulf of Maine, but commercial quantities don’t exist in Maine waters.
As seawater has warmed and predation has increased, coastal communities in Maine have lost thousands of jobs in the soft-shell clam industry. To help mitigate these losses, the Downeast Institute has been experimenting with the culture and grow-out of Arctic surf clams. Our goal is to create new economic opportunities, especially in eastern Maine where median household income is nearly 20% lower, and unemployment over 50% higher, than the statewide averages.
Downeast Institute (DEI) scientists have mastered the hatchery and nursery phases of Arctic surf clam production. Since 2015, DEI has investigated methods to culture seed and then grow it to sizes between 1.5-2-inches, developing a novel shellfish product, smaller than wild-caught, to introduce to the market.
Cultured juveniles and adults are able to survive and grow in the lower intertidal in eastern Maine where seawater temperatures are relatively cool, but require predator protection to grow to size. DEI has developed a grow-out unit which protects Arctic surfclam seed from green crabs, resulting in > 95% survival of cultured seed (8-13 mm SL) with relatively fast growth rates in the lower intertidal in 2-3 years.
Building upon that development, DEI’s third phase of Arctic surf clam research will further demonstrate intertidal Arctic surfclam farming techniques, with clammers and other entrepreneurs, in a comparative study in two eastern Maine communities. The experiments explore the interactive effects of stocking density, size of grow-out unit, and predator-deterrence on growth and survival of cultured Arctic surfclam seed.
By the end of this phase, we will better understand what size unit is best for growing Arctic surfclams to a marketable size, and how many clams should be planted in the growout unit.
Hatchery Production of Arctic Surf clams
All Arctic surf clams used in this research were cultured at DEI in the previous year. They are grown to a size of 10-15 mm shell length for planting in the field for these experiments.
Year 1 (2021) Field Research
Cove locations for the grow-out sites were chosen by clammers. Field trials commenced in the spring in the lower intertidal (area of the mudflat exposed 0-1 hours before low tide) of each cove.
During the first year we evaluates at each of the two study sites how the following factors affect the growth and survival of cultured Arctic surf clam seed, as well as how these factors interact:
- Stocking density (25, 50, or 100 clams per sq. ft.);
- Predator deterrent top frame thickness (1- vs. 2-inch);
- Size of growout unit (2-sq. ft. 4-sq. ft.).
The grow-out units are 4-inch deep wooden boxes. They are anchored onto the sediment surface with laths. A piece of PetScreen® mesh (aperture = 1.9 mm x 0.7 mm) is affixed to the bottom of each box. This size aperture allows seawater to drain from the boxes at low tide while deterring infaunal predators such as crabs and milky ribbon worms. Boxes contain terrestrial sand to avoid marine sediments that could contain small predators such as worms and crabs.
Year I Results:
Results of the 2021 Arctic surfclam work are contained in this report.
Year II Research:
In the second year we will evaluate the effect of growout unit size (4-, 8-, 16- vs. 32-ft. sq.) on survival and growth of Arctic surfclams.
Northeast Sustainable Agriculture Research & Education (SARE) through the Research for Novel Approaches Program provided funding for this research.