Progress report for FNE23-052
Project Information
1) This project aimed to test whether bay scallops could be grown in rapidly-warming Maine waters. Our approach used techniques that were developed to grow bay scallops in their traditional range and techniques used to grow sea scallops locally. Success will be gauged by growth rates and survivorship from planting in July 2023 until harvest in December 2024
2) This work aimed to address biofouling and handling issues associated with lantern nets (the most successful grow-out gear used in other trials), by building a raft that allows scallops to stay submerged while portions of nets are air-dried. Fouling species on nets were compared to those seen elsewhere on the farm.
Most Maine seafarms operate as monocultures, leaving farmers vulnerable to pests, pathogens and changing environmental conditions, as well as swings in demand. By adding a crop with different environmental and spatial needs, farmers could address this vulnerability without displacing their primary crop, potentially increasing yield without expanding their footprint on the landscape.
The floating subtidal oyster farms most common in the region use just the top few feet of the water column. Lantern net culture (growing shellfish in hanging tiered nets) offers farmers an opportunity to grow shellfish in deeper waters in their existing lease footprints. This middle section of the water column is sheltered from major wave action and sees much less sedimentation than the ocean floor. This position is ideal for scallops, which are sensitive to both turbulence and smothering.
Two species of scallops are present in the northern Gulf of Maine. Sea scallops (Placopecten magellanicus) are endemic and widespread. Bay scallops (Argopecten irradians) are a more southerly species that is slowly encroaching as waters warm. In Maine, much active research focuses on sea scallop aquaculture. This project will focus on growing bay scallops in part as a climate adaptation strategy in region with some of the fastest warming waters on the planet.
Bay scallops are a commercially important species that demands a high price- particularly from the wild populations in southern New England (with Nantucket bay scallops fetching a price as much as 50% higher than local Maine sea scallops during the applicant’s time working in fish markets). These wild populations are under stress from habitat loss and fishing pressure and are only available during a short harvest season (Nov. 1 through March 31 in MA, the closest wild fishery). A successful aquaculture crop could help take pressure off of this population and expand availability into other parts of the year. Live bay scallops can be sold on the half-shell market, offering oyster growers a secondary product to sell to their existing networks of distributors.
Previous work saw some success in lantern net culture- with sea scallops locally, and with bay scallops in other locales. Crop loss due to biofouling and difficulty handling nets and are cited as problems in this work. Unlike oyster cages, lantern nets stay submerged. Biofouling organisms (most problematically colonial tunicates and sea vases) can rapidly smother and weigh lantern nets down, causing crop mortality and making lifting/handling difficult or dangerous for the farmer.
To deter fouling organisms, net drying rafts were built for this project. This raft was used to periodically hold lantern nets horizontally at the surface of the water with half exposed top the air, killing pests above the water line. The dryer kept sensitive scallops submerged, reducing handling stress. Nets were rotated to insure each surface is dried. Drying offered an effective strategy to clean nets without the noise or energy use of pressure washing.
Cooperators
- - Technical Advisor
Research
One millimeter shell-length scallop seed was acquired from a hatchery (Muscongus Bay Aquaculture) on July 13 2023. Seed was stocked in soft spat bags with a 0.5mm mesh for initial nursery phase using a stocking density of 10000/bag cited in NRAC bulletin #215-2010. Mesh was stretched into a frame using segments of garden hose and bags were sealed with zip ties
Spat bags were loaded into lantern nets (one bag per tier) and were suspended from a floating longline at Winnegance Oyster Farm in 27’ of water (mean high tide depth).
During this initial nursery phase, scallops were checked weekly determine timing of movement to a larger mesh size (0.75mm) to minimize loss to sifting and handling. Scallops were large enough to be moved into 0.75mm mesh spat bags without loss after one month of growth.
Scallops remained in .75mm spat bags until early November (when the smallest individuals were of a sufficient size for grading). Seed was graded in an onboard water bath using rigid mesh sieves and shell lengths were recorded. Seed was split between three lantern nets that stayed at the surface through the winter. Equipment was not be handled from Dec to March (when the farm is not operating), but the lantern nets were checked for storm damage before the resumption of farm operations in April.
In the spring observation of shell lengths and mortality resumed. Scallops were stocked at a density that initially covered 33% of lantern net tiers to prevent overcrowding mortality (cited in personal communications by several sea scallop growers- 75 individuals/tier in this case).
Lantern nets were dried on a specially designed raft to prevent biofouling. Each net was be dried no more than once every two weeks to ensure adequate feeding of scallops. Fouling species and prevalence were noted.
In October and December of 2024, the cumulative number of scallops reaching a minimum market size of 50mm were noted. Scallops for the trial were sold to local seafood dealers to gauge their market value.
Seawater temperatures were recorded on our existing loggers.
The field trial and data collection ended in December 2024. Data analysis is ongoing- with preliminary results shown below
Growth
In the first four months on the farm, scallops grew between 6 and 40 times their initial length (1mm). On average scallops were 22.3mm during November measurements.
Growth continued at a high rate through 2024- with the majority of surviving scallops reaching a marketable size by Oct (15 month)
Mortality:
Mortality between stocking the farm until September was <1%. By Nov 4 mortality had reached 8%. Mortality was largely seen when mussel fouling was present.
Overwintering mortality was substantial though cause was unclear. Lantern nets were heavily fouled by two distinct cohorts of mussels. The farm was also hit by six storm-force weather events (70mph+ wind) during off season months). Winter temperatures were much warmer than typical- which may have helped survivorship.
Fouling:
Fouling patterns were exceptionally unusual in 2023. The farm saw four separate waves of fouling from mussels, each far larger and quicker onset than anything else witnessed in the farm's 9.5 years of operation. Despite this challenge, scallops fared relatively well. Though both lantern nets and the exteriors of spat bags saw colonization by mussels, the interior of bags stayed comparatively clean. This was observed in both .5mm bags and .75mm bags and contributed to the decision to delay transfer out of these bags until late fall. Fouling by other species was light and was largely made up of coral-like bryozoans and skeleton shrimp.
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Heavy mussel fouling continued through the winter- with two distinct age classes settling onto all equipment. Once scallops were transferred to from spat bags directly into lantern nets in the spring, fouling was significantly easier to control. Periodic drying on the custom rafts prevented most fouling from forming and what little fouling occurred (in the form of red algae and feathery bryozoans) was easily mitigated. New mussel fouling was not an issue in the 2024 growing season anywhere on the farm. Heavy fouling from several species of tunicates (sea squirts/sea vases) was noted on the farm in 2024 from Aug-Nov 2024. The regularly dried lantern nets in the scallop trial were not affected.
Data analysis is ongoing. Conclusions will appear in our final report.
Education & Outreach Activities and Participation Summary
Participation Summary:
In Nov 2023, I attended a workshop aimed at aquaculturists and researchers working in the region. I discussed the project during several roundtables, and consulted with staff from a conservation non-profit that is attempting to grow bay scallops. The workshop had ~50 attendees- most of whom were exposed to this project
In July 2024 we gave 11 tours at our open farm day. During the tours 30 people had hands on experience of gear and techniques.
A presentation of this project's preliminary results was given at the Maine Aquaculture Research, Development & Education Summit. 35 people were in attendance. The audience was polled and 15 of these identified as growers, 15 identified as researchers, and 10 identified as managers (groups overlapped).
The project was also presented to the PI's shellfish cooperative - reaching 11 additional farmers.
Infographics are in development for social media outreach prior to the final report.
