Tapping deep into the potential requires a thorough understanding of optimizing growth and survival in nursery – which are very critical – as well as grow-out and overwintering phases.
Ward and Harrison Tobi, aquaculture and research technician at Ward Aquafarms, investigated this in their study, “Nursery and grow-out strategy optimization in bay scallop Argopecten irradians aquaculture.”
Ward Aquafarms was already farming eastern oysters when it expanded to bay scallop in 2014, initially starting off with a nursery. The first harvest of scallop came two years later.
Downweller vs. upweller
On the premise that growing bivalves shared similar protocols, Ward attempted to grow scallop the way they did with oyster. It didn’t work.
“We started farming eastern oysters, and so we started copying those methods for farming bay scallops, and in almost every instance the techniques had to be modified for the bay scallops. Handling is different, stocking densities are different, gear types are different, and marketing and harvesting methods are different,” Ward tells Hatchery International.
The oyster upwellers, which were initially utilized, created problems that could be traced to scallop physiology. Ward finally had a breakthrough in optimizing survival and growth rate in the nursery stage by utilizing a floating downweller system, which they custom-designed in 2015.
“In our previous work, raising bay scallop seed in floating upweller, like those typically used for commercial oyster farming, had resulted in survival rates lower than 50 percent in the first three months of culturing. Due to the fact that bay scallops can swim – and, when not in an ideal location, will swim to find a new area to attach – upwellers without mesh over the outflow will not effectively retain scallops. Mesh may be placed over the outflow, but clogging can be an issue, and reduced flow requires further reduced densities.
“In the present study, when using floating downweller systems, the mean percent survival was 82.7 percent across all stocking densities for all sampling periods, which is a significant improvement over the replication,” they cited in the study.
The downweller system likewise provides an environment ideal for the physiological and behavioral requirements of the bay scallop, producing large volume of shellfish to a size suitable for grow-out in a short period of time.
Over the past four years of research, they have optimized all of the culture stages from <1 mm shell height through to market size of >50 mm.
Ward has set up their own scallop hatchery, ensuring an adequate supply of seeds and spats. They also sell to other growers.
From one million seeds in 2018, Ward is targeting in 2019 “millions of seeds and live-in shell products in the low hundreds of thousands.”
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Maine sea scallop
In Maine, which is pushing for their farmed sea scallop industry, spats are still sourced from the wild. Coastal Investment Inc. (CEI), a key industry proponent, acknowledges that being able to post a significant growth is tied to having access to hatchery-produced seeds and spats.
“There are a couple of growers in Maine who have been working on spat collection for close to 20 years,” Hugh Cowperthwaite, director for Sustainable Fisheries and Aquaculture Program at CEI, tells Hatchery International.
“As more growers show interest in growing scallops, there is an increasing demand on spat for further grow out. More growers are learning to collect their own spat but not everyone wants to do this. Some growers would prefer the opportunity to purchase spat.”
Hatchery production is the only way a farmed scallop industry can ramp up, Cowperthwaite notes. Basing all farm production models on wild collection is risky, unpredictable and ultimately not sustainable, he adds.
Achieving a critical mass of growers could provide the impetus. “As more growers come online, it would be great if this opportunity could help drive the development of a well-funded hatchery effort for which an industry can be built. Until we have hatchery production of scallop spat, the industry will stay relatively small,” he says.
Several attempts to culture sea scallop in a lab had been done but were not successful. “Scallops are a finicky species that require high attention to detail and little room for error,” Cowperthwaite says.
CEI has been pushing for the state’s farmed sea scallop industry since 2010. “Farm-raised scallops have huge potential and we are seeking to develop high-end niche value markets. Several growers are working on different grow-out methods for different scallop market sizes, all of which could come into play in the next couple of years,” he says.
In February, CEI released Market analysis of Maine farm-raised sea scallops, which indicated a “promising” overall outlook for the state to develop scallop aquaculture.