Optimization of Atlantic Sea Scallop (Placopecten magellanicus) Aquaculture in the Gulf of Maine

In the 1960s a Japanese fisherman in Mutsu Bay, wrapped an onion bag around a traditional cedar leaf oyster spat collector allowing larval spat to enter and settle on the collector while preventing juvenile scallops from falling out after settlement. This simple innovation pioneered the global scallop aquaculture industry that is currently worth an estimated $5.8 billion in annual scallop sales. Rapid growth of scallop aquaculture has been seen in China, Japan, Korea, Peru, and Chile following the establishment of successful culture methods. In Japan, national scallop production rose from 5,000 mt in 1969 to over 100,000 mt in 1975; in 2022, Japan reported a net scallop export value of $612 million (¥91.1 billion). Meanwhile, the United States imported $3.73 billion of scallop products in 2022, representing a larger trend in its general seafood deficit, with 75% of seafood imported to the United States. In an effort to alleviate this dependence on foreign imports and capture a portion of the scallop market cap, recent research has been invested into aquaculture of the commercially valuable Atlantic sea scallop (Placopecten magellanicus) in Maine. ` Aquaculture is a rapidly developing industry in Maine, from 2007 to 2017 sales from aquaculture production nearly tripled from $50 million to $137.1 million. Much of this growth, particularly in employment and production volume, can be attributed to shellfish aquaculture (i.e., oysters, mussels, clams, scallops, etc). The Atlantic sea scallop is native to Maine, and a species of high aquaculture opportunity in the region. In 1999, a collaborative effort between the Aomori Prefecture in Japan and Maine resulted in a scallop aquaculture technology transfer partnership that has continued until the present. Multiple trips from industry and researchers operating in Maine in relation to scallop aquaculture have benefitted from this partnership and in 2021, DMR listed aquaculture scallop landings separately from wild-capture scallops at a total landing weight of 369 lbs (167.4 kgs) adductor-only for the first time. Most recently in 2023, production increased to 1,723 lbs (781.5 kgs) representing an almost five-fold increase in production in just two years. While industry growth has been promising, it is important to remember that scallop aquaculture in Maine is an incipient industry. Research into optimization and automation of processes is necessary for long-term success of the industry. Decades of research in Canada from 1980-2000 were similarly promising, and even resulted in several commercial scale operations; however there is little evidence of that industry spreading beyond a small-scale, cottage opportunity today. This dissertation addresses grower concerns identified by Struan Coleman in ‘Developing a bioeconomic framework for scallop culture optimization and product development’ (M.S. Coleman, 2021) highlighting seven key themes: (1) Site Selection, (2) Spat Supply, (3) Biofouling Control, (4) Mechanization (Automation), (5) Biotoxins, (6) End-Market Uncertainty, and (7) Farm Size/Scale. To address site selection, biofouling, mechanization (automation), and farm size/scale, we conducted a two year study of on-farm grow-out. Scallop aquaculture encompasses three broad phases on the farm: (1) nursery culture where settled scallop seed is grown to 3-15mm with very little maintenance required (approximately one year post-settlement), (2) intermediate culture where young scallops are transferred to a lower stocking density (approximately one to two years old) , and (3) grow-out culture where scallops are transferred to their final grow-out system until harvest occurs after up to two years (approximately two to four years old). Shell height measurements were taken from scallops immediately following transfer to intermediate culture until a final harvest period of four years, while tissue weights (adductor, gonad, viscera) were collected during the final year of grow-out (three to four years old). To address earlier concerns of biofouling, mechanization, and farm size/scale, the ear-hanging technique pioneered by the Japanese scallop industry was assessed in comparison to traditional lantern net culture. Ear-hanging is a front-end, automated process whereby scallops are individually pinned onto dropper lines using specialized equipment at the end of intermediate culture. The process requires the purchase of expensive, specialized machinery to assist with the pinning process and biofouling control. Finally, growth data was fitted to an environmentally-explicit, temperature-based model to inform site selection for growers interested in maximizing growth to a range of scallop product markets. Our second analysis was a techno-economic analysis integrating growth modeling from our field study to address biotoxin and end-market uncertainty concerns. Early sea scallop aquaculture research focused on small scallops (<90 >mm) for a whole scallop market. However, the most common product sold in North America is the adductor-only portion of the scallop at larger sizes (>100 mm) by weight. In the adductor-only market, larger adductors (sold in a ‘Count per Pound’ designation) fetch higher prices with the most valuable category referred to as U10 (10 adductors lb-1 or 0.45 kg-1). Whole scallop markets also have to contend with costly and labor intensive biotoxin testing to avoid potentially lethal levels of harmful algal blooms that can cause paralytic shellfish poisoning and amnesic shellfish poisoning. The techno-economic analysis was designed to address adductor-only and whole scallop business models allowing growers to select a variety of market options and circumvent biotoxin testing concerns. Additionally, to engage with growers, the techno-economic assessment was formatted into an application, designed for efficient and straight-forward scenario testing and disseminated to growers. Finally, assessment three considered issues related to spat supply concerns. While collaboration with Japan provided valuable insights into grow-out technology, Japan collects its entire scallop seed supply via wild spat collection at unusually high settlement rates. Wild spat collection for Atlantic sea scallops in Maine is significantly reduced and much less understood than Japanese processes creating a large hurdle for entry to growers. Additionally, Japanese scallop production relies on efficient spat collection to obtain millions of juvenile scallops, which can be culled and sold following the intermediate stage to select only the fastest growing scallops for grow-out and high-value sales. Spat limitation in Maine requires the grow-out of all seed obtained, greatly reducing efficiency at farms which are more likely to be on the scale of hundreds of thousands, than millions of scallops. Collaborative hatchery experiments beginning in 2021 have successfully cultured sea scallops and the final analysis constructed a bioeconomic model for hatchery culture of juvenile sea scallops in order to determine necessary industry demand to ensure supply and price are appropriate to facilitate profitable commercial hatchery operations. This dissertation research progresses scallop aquaculture growth in an attempt to ‘optimize’ the culture of Atlantic sea scallops in Maine following several important themes. The backbone of this research process relies on university-industry research collaboration in order to better focus on key industry concerns vital to informing applied research science in aquaculture. Our process engaged established growers and commercial hatcheries to inform our research goals throughout the studies. Site selection modeling was shifted to an ‘environmentally-explicit’ system designed to be generalizable. Early models of Atlantic sea scallop culture relied on mechanistic (i.e., von Bertalanffy) models that relied on time, however for mutability at specific grower sites, it was important to realize the place of time as a proxy variable. By removing time and basing our response on temperature, our model is capable of predicting changes through time in a system that is projected to be heavily impacted by climate change in the future. Finally, the term ‘Optimal’ was used in an effort to re-define the concept and present a framework for categorizing research into various formats of efficiency. The question of ‘optimal’ harvest strategy is not a simple matter of ear-hanging versus lantern net culture, or hatchery versus wild spat collection of seed but instead a scale based on business design. Optimal is an individual combination of social, biological, and economic concerns related to each specific farming operation. The ultimate goal of this dissertation is to shift aquaculture research practice away from the description of ‘optimal’ which is a specific set of conditions of each business model, and instead to categorize research into social, biological, and economic spheres that growers can assess and combine to determine their individual optimal aquaculture business strategy.

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