Pilot-scale Efforts to Demonstrate Commercial Growout Technologies of the Arctic Surfclam in the Marine Intertidal

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Commodities

• Animals: shellfish

Practices

• Animal Production: aquaculture
• Education and Training: demonstration

Maine’s soft-bottom intertidal zone has witnessed a steady decline (75% since 1975) in landings of its iconic soft-shell clam fishery with concomitant job losses from 4,500 clammers to 1,500 today. Clams were ubiquitous from low water to the high tide line; however, as seawater temperatures have increased dramatically since the 1980s, the once-abundant clams now are restricted to thin strips along the upper shore – areas that are out of the reach of many waterborne predators, including the invasive green crab that has seen dramatic increases in population numbers over the same period. Surprisingly, the combination of climate change and lack of sustainable clam management practices has resulted in a tremendous opportunity to create new wealth in the lower intertidal zone. Arctic surfclams, Mactromeris polynyma, occur subtidally in the northwest Atlantic from Rhode Island’s offshore waters to Newfoundland. A $100 million fishery, also known as the red-footed surfclam (“hokkigai”), exists in Atlantic Canada, and is highly-valued as sushi and sashimi in Asian markets and restaurants. While no large, commercial beds occur in the Gulf of Maine, we obtained broodstock with a goal to create a new culture candidate and diversify the shellfish industry by growing individuals to sizes between 38-50 mm SL (shell length) that can be consumed raw on the half-shell, steamed, fried, or broiled, or used in chowders, stews, or even in salads. We worked for five years to close the hatchery and nursery phase of this species for the first time ever. Fieldwork using cultured juveniles demonstrated Mactromeris can grow and survive in the lower intertidal, especially in eastern Maine where seawater temperatures are colder than elsewhere along the coast. Greatest impediments to commercialization are crustacean and bird predators that can shred protective netting and consume >90% of 6-12 mm individuals. Recently, we created a new growout unit that is effective in deterring predators. Field trials (April-Oct 2019) at two intertidal sites using small juveniles examined effects of stocking density in 2-ft² growout units. Mean survival was >95% at both sites with grow rates >15 mm SL. We propose to repeat these pilot-scale trials with clammers from two eastern Maine communities during Year I. Working hand-in-hand with clammers provides the best opportunity to demonstrate growout techniques that will eventually lead to commercialization. Specifically, in Year I together with three clammers from each community we will evaluate effects of stocking density (30, 60, and 90 individuals ft^-2), size of growout unit (2- and 4-ft²), and type of predator deterrence on growth and survival of cultured surfclam juveniles. In Years II and III, we will vary growout unit size from 4- to 32-ft². Clammers will present their findings to their peers at an annual forum for fishers (Years II&III).

Project Objectives

1. To develop and deploy pilot-scale field growout trials in two communities in eastern Maine to produce marketable, cultured Arctic surfclams, and;
2. To demonstrate growout technologies to clammers and other entrepreneurs who earn their income working in the soft-bottom intertidal.

Arctic surfclams are a new culture candidate. We wish to explore with 3 clammers from two eastern Maine communities novel methods to grow cultured seed (10-15 mm SL) to commercial size (40-50 mm SL). Recent field trials have been encouraging (annual survival [> 90%] and growth rates [15-20 mm SL]).  Field trials will test scale-dependent repeatability of these results.