Progress report for FNE23-052
Project Information
1) This project aims to test whether bay scallops can be grown in rapidly-warming Maine waters. Our approach will use techniques that were developed to grow bay scallops in their traditional range to grow sea scallops locally. Success will be gauged by growth rates and survivorship from planting in July 2023 until 16 months of age.
2) This work aims 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 will be recorded and 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, this project will construct a net drying rafts. This raft will be 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 will keep sensitive scallops submerged, reducing handling stress. Nets will be rotated to insure each surface is dried. Drying offers 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 will stay at the surface through the winter) and three oyster cages (that will sit on the seafloor). Equipment will not be handled from Dec to March (when the farm is not operating), but the lantern nets will be checked for storm damage before the resumption of farm operations in April. As of 1/12, lantern nets had survived three major storm-force weather events- with winds gusting over 70 mph.
Starting in the spring scallops will be measured monthly. Measurements will include shell lengths and percent mortality. Stocking density will be thinned to 33% coverage of tiers to prevent overcrowding mortality (cited in personal communications by several sea scallop growers). The number of scallops needed to reach this density will be noted during each sampling period.
Lantern nets will be dried on a specially designed raft to prevent biofouling. Each net will be dried no more than once every two weeks to ensure adequate feeding of scallops. Fouling species and prevalence (% cover) will be noted and compared to fouling species noted on oyster cages, and always-submerged ropes.
In October and November 2024, the cumulative number of scallops reaching a minimum market size of 50mm will be noted.
Seawater temperatures will recorded on our existing loggers.
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.
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.
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.
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