Diversified & Profitable: Overcoming Challenges of Winter Mortality in Bay Scallop Culturing to Meet Increasing Demand Left by Wild Fishery Decline

Progress report for FNE23-070

Project Type: Farmer
Funds awarded in 2023: $12,042.00
Projected End Date: 05/31/2024
Grant Recipient: Aquidneck Island Oyster Company
Region: Northeast
State: Rhode Island
Project Leader:
Dan Torre
Aquidneck Island Oyster Company
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Project Information

Project Objectives:

This project seeks to identify methods to remove bottlenecks in growing a highly demanded but under-cultured species that has been subject to overfishing and habitat loss. This study aims to elucidate techniques to optimize the two most important life cycle stages of bay scallop culturing including, nursery and overwintering. Two specific objectives are proposed:

  1. Evaluate nursery techniques to identify the best scalable method of producing marketable, single season, in-shell bay scallops.
  2. Assess winter strategies to provide guidance to growers on the best methods to maximize survivability of bay scallop overwinter, taking into account environmental variability, gear types, and stocking densities.


Previous centuries boasted a robust and lucrative bay scallop (Argopecten irradians) fishery, which has since been periled with large scale and widespread population declines (MacKenzie 2008, Verkamp et al. 2022). Habitat loss (Gallager et al. 1989, Goldberg et al. 2000, Tettelbach et al. 2002, Fonseca & Uhrin 2009, Verkamp et al. 2022) and overharvesting (Oreska et al. 2017) have largely contributed to these declines and collapse of a once staple fishery in many regions. Even more recent declines of an already deflated industry are evident. Bay scallop landings in 2020 and 2021 averaged only 3 percent of those in 2017 and 2018 in the Peconic (Winzelberg 2022).

The demand for bay scallops in the restaurant and wholesale industry is not being met due to wild harvest limitations (Barber and Davis 1997, Blake and Shumway 2006, Mackenzie 2008a, 2008b, Tobi and Ward 2019). Shellfish aquaculture has been demonstrated as an avenue to fill voids in the market left by wild fishery shortcomings in the past, and even help to reestablish a more sustainable approach to wild harvest fisheries (Dewey et. al 2011). Still, bay scallop culture is often overlooked by aquaculturists because of bottlenecks at different stages of the growing cycles. Knowledge of optimizing bay scallop cultivation is still limited (Mackenzie 2008a, 2008b, Tobi and Ward 2019), however, it has been demonstrated that bay scallops can be reared as a single season crop as a potentially valuable diversification and startup crop for shellfish farmers.


Bay scallop rearing is met with two bottlenecks which typically deter or impact growers. The first and largest bottleneck that limits success is excessive overwinter mortality during growout (Leavit et al. 2010).  The second bottleneck is seed availability and timing from hatcheries. Bay scallop seed is often spawned as an afterthought to oysters once orders are filled, and thus is provided to growers late in the growing season further limiting overwinter survivability. Overwinter culturing strategies for bay scallops have not been studied in depth. For in-shell marketability, bay scallops need to be large enough to be utilized while being free of undesirable biofouling.


In order to promote bay scallop culture as a lucrative and scalable diversification crop, research is needed to either optimize nursery techniques to facilitate a single season in shell crop or overcome hurdles in winter survivability. The study proposed will look at both ends to maximize nursery growth to aim for a year one crop, as well as evaluate methods to mitigate overwintering mortality. Strategies to optimize growth and survivability of bay scallops, including research to evaluate gear that’s readily available for oyster growers at both nursery and winter stages, will help to advise future growers the most efficient techniques to employ.

Impacts of results

Results from this study will elucidate methods to remove bottlenecks in growing a coveted but under-cultured species that has been subject to overfishing and habitat loss. Growth and mortality data from this study will provide guidance to farmers, nursery operations, hatcheries, and FSA. Growers will be better suited to make equipment decisions based on their environment, and hatcheries will be enlightened on the best time to produce seed for growers. Additionally farmers will have the information needed to add a diversification crop that will make their revenue stream more robust.

Distinguish from other work

Previous work in bay scallop culture has helped to identify pitfalls and increase productivity, however overwintering is still a dealbreaker for many growers. Bypassing large scale mortality in the winter by altering culturing techniques and/or by having marketable stock before winter would make bay scallops a much more appealing crop for many growers. This study aims to illuminate solutions to these bottlenecks to facilitate a more robust and profitable crop for shellfish growers.


Click linked name(s) to expand/collapse or show everyone's info
  • Azure Cygler
  • Cameron Ennis
  • Robert Rheault
  • Eric Scherer
  • Kim Tetreault - Technical Advisor


Materials and methods:

Stage 1 Evaluation of Nursery Culture --To evaluate best practices for nursery culture of bay scallops, knowledge accumulated from previous studies will be leveraged while testing some novel techniques. Three nursery culture techniques will be studied, to evaluate growth rates, survivability, operation costs and labor per unit. 

Raceway—Raceways are a commonly used land-based nursery system. Ambient water will be pumped using a variable speed 3/4hp iceeater pump to flow through the raceways which hold seed and use 0.5mm mesh catch sieves on the output to eliminate loss. Flow rates will be monitored and altered to make sure animals are properly fed without causing too much turbulence. Daily visual inspection will be conducted on the raceway which will identify if animals are stocked at proper densities. Typically scallops will attach to the tanks and detach only when food becomes limited. When this happens, the operator will either increase flow, or reduce stocking densities. Raceways will be drained and cleaned weekly and are typically energy intensive due to pumping water at grade. Energy costs will be monitored via meter.

Downweller—Floating downwellers have recently been identified as a successful means to rear bay scallop through the nursery stage. Downweller systems as described in FNE16-861 will be constructed with multiple silos and inserts to house scallops. The system will be fed by a 3/4 hp iceeater pump and monitored to maintain ideal flows. Energy costs will be monitored via meter. Downwellers will be drained and cleaned weekly to maintain proper flow rates by eliminating biofouling from the system. Similar to raceway culture, daily inspection/adjustments will be conducted.

Netron—NetronTM, a plastic mesh material, has been used as a substrate for shellfish setting in different capacities. By culturing the shellfish in ambient water, the necessity for pumping water (as in the other proposed methods) to maintain food and oxygen levels is alleviated, thus reducing energy consumption. Each replicate of this treatment will include 3 feet of Netron mesh folded into thirds, and added to a settling tank where scallops will adhere to the mesh. 3 replicates will be sacrificed to sample baseline conditions (size and number of scallops). Replicates will be placed in ambient water to grow. Animals will be removed only during sampling periods, and each Netron system will only be sampled once. Removing the animals from the media and cleaning them for the final grow out stage could be a potentially laborious endeavor. 

Seed–Seed will be obtained from the Cornell extension program at ~ 1mm following clean pathology report and clearance to import into Rhode Island growing area 4a. Seed will then be split amongst the nursery culture techniques described above and stocked ~5,000 to 10,000 scallops/m2. Several replicates of each nursery technique will ensure sufficient sampling (number of replicates depends on seed availability). During the nursery phase of this experiment, scallops will be removed and graded using the vibratory seed separator biweekly for a total of 4 sampling periods (8 weeks). Following grading, enumeration and recording, random subgroups will be randomly sampled and measured for shell height and total volume. A random sample of 100 animals for each group will be measured to the nearest 0.1 mm using vernier calipers. As scallops outgrow the nursery system (~14mm shell height) they will be removed from the nursery systems and put into final growout stages. Growth rates and mortality rates will be calculated and recorded for different subgroups at each sampling period. Labor required for all aspects of nursery culture will be monitored and recorded for each of the respective nursery techniques to calculate effort/unit to provide guidance on scalability.

Stage 2 Assess Overwintering Strategies—Extreme mortality of submarket product during the winter months accounts for a huge bottleneck in bay scallop culture. To evaluate methods of overwintering scallops, 2 gear types will be tested in 2 environmentally different regions. Additionally, stocking densities will be varied at 3 different levels to test the impact of stocking density on overwinter mortality. Overwintering experiments will start when water temperatures drop to around 50 degrees Fahrenheit, when scallop growth is expected to slow dramatically (Rhodes and Widman 1984).

Site selection— Environmental conditions including, wind, waves, fetch, depth, temperature, salinity, etc all play a vital role in site selection and gear selection for shellfish aquaculture. Particularly for scallops, gear selection is critical and largely influenced by surrounding conditions. To evaluate gear effect on survivability, two differing sites will be used during the overwinter mortality study. The first site is in the Sakonnet River, Portsmouth, RI which has extremely fast flow rates and is subject to great turbulence and wind/wave energy. This site is representative of most open-water leases like those located throughout Narragansett Bay, RI. The second site is in Nanaquaket pond, Tiverton RI which has moderate flow and is largely protected, and thus much less impacted by wind and wave energy. This site is representative of salt-pond or small embayment type leases like those located in Southern RI.

Bottom—Bottom gear is commonly used in rearing different species of shellfish. By securing gear on the bottom of the waterbody, adverse impacts of weather are typically avoided and the shellfish remain unaffected by any turbulence on the surface. Bottom grown shellfish are typically slower growing as opposed to floating. 8-bay bottom cages fit with HDPE bags (14mm aperture) will be used to test designated stocking densities. Cages will be added to a bottom trawl long line to secure them in place and will be marked/accessed by a float line.

Suspended—Suspended gear has been proven to be a highly effective grow out technique for shellfish in a variety of environments, particularly lantern nets. Suspended gear has the benefits of being higher in the water column encouraging faster growth, without extreme exposure to the turbulence that floating gear is subject to. 7-tier lantern poly lantern nets with 14mm apertures will be stocked respectively to test overwintering. Lantern nets will be secured to a longline system with buoys at each of the connections to keep the lanterns afloat. In addition a small section of chain will be added to the bottom of the lantern net array, to keep the net’s vertical and reduce gyration of animals caused by wind/wave turbulence. 

Stocking density–Bay scallops from stage one will be continue growing throughout the summer and then in stage 2 to test gear selection and stocking density effect on overwintering survivability. Medium sized animals (~ 50mm or less) that did not make it to marketable size will be used in this study. Animals will be measured and deployed into respective gear types at low, medium, and high stocking densities in early December. The effect of stocking density on winter mortality will be tested at 3 different treatments, Low (15/ft2), medium (30/ft2) and high(60/ft2) (Leavitt 2010).Several replicates of each treatment will be tested at each site to ensure sampling is sufficient (replicate numbers depend on availability). When waters warm in the spring and growth should be expected (around 50 degrees Fahrenheit), scallops will be pulled out and sampled to measure mortality and meat quality (visual inspection).Statistical analysis–As data becomes ready and is prepared for analysis, one/two-way ANOVA will show whether treatments were statistically significant or not.

Research results and discussion:

2023 progress:

Seed from Cornell was in short supply, and obligations had to be met for town restoration projects before we would receive any seed. Unfortunately we were unable to receive seed from Cornell early in the season. Though we were unable to procure small seed early in the season, which has been a consistent bottleneck in bay scallop production, we were able to get some excess larger seed from a nearby farm. Due to the size of the seed, nursery studies were not conducted. We are currently investigating gear type impacts on overwintering of bay scallops.

Participation Summary
Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.