Final report for ONE22-423
Project Information
The Gulf of Maine is experiencing rapid climate-driven environmental change that threatens the livelihoods of thousands of Mainers resulting in the need for marine resource diversification to adapt to this change and promote economic resilience for Maine’s coastal communities. Manomet, in partnership with Eros Oyster Farm and the Brunswick Marine Resource Committee, tested the viability of intertidal quahog culture techniques in Maine for shellfish farming (target shell length 38-45mm) and stock enhancement activities (target shell length 20-25mm) using untreated soft clam bags, soft clam bags coated with a latex dip and ADPI oyster bags. Overall, we found success growing quahogs in the intertidal and saw the highest growth in untreated soft clam bags which also required the least labor. At both sites, quahogs grown in the soft clam bags were significantly larger when compared to those grown in hard bags (Kruskal-Wallace test, p=8e-05 for Maquoit Bay, p=5.4e-05 for Eros) and quahogs grown in the untreated soft bags were larger than those grown in soft bags coated in a latex dip (Kruskal-Wallace test, p=6.1e-11 for Eros, p=0.092 for Maquoit Bay). While we were unable to grow quahogs to market size at Eros Oyster in the timeline of this project, we were successful in reaching the target size suitable for stock enhancement in Maquoit Bay and saw high overwintering gear retention and survival. More work is needed to determine the time needed for quahogs to grow to market size and this could be highly variable depending on local site conditions (i.e., warmer temperatures and higher chlorophyll concentrations promote faster growth). Through field demonstrations, presentations at local, regional and national meetings, published media, and in-depth conversations with industry, we shared this work with over 30 shellfish harvesters and farmers. This engagement reinforces the need for diversification strategies and the opportunity to build off our initial findings to determine impact of site selection, stocking densities and nursery systems to maximize growth and survival, efficiency and profitability.
This project seeks to test a new method of intertidal quahog aquaculture in Maine. Our specific objectives are:
Objective 1: Test multiple intertidal quahog grow out techniques to determine best practices.
- 1.1: Deploy intertidal experiments.
- 1.2: Monitor quahog growth and survival.
- 1.3: Measure environmental variables.
Objective 2: Harvest and/or distribute for stock enhancement and quantify production costs.
- 2.1: Harvest farmed product (shell length 38-45mm).
- 2.2: Distribute quahogs for stock enhancement (shell length 20-25mm).
Objective 3: Conduct outreach to share findings and grow industry knowledge
- 3.1: Outreach through existing networks and partnerships.
- 3.2: Field demonstrations.
- 3.3: Outreach through social media, newsletter articles, Manomet’s website, and traditional news media.
If successful, this will be an opportunity for sea farmers to expand their operations and diversify their crops, as well as a method for supporting municipal shellfish wild stock enhancement activities.
The Gulf of Maine is experiencing rapid climate-driven environmental change that threatens the livelihoods of thousands of Mainers. Simultaneously, the diversity of Maine’s fisheries resources is at an all-time low (Steneck et al. 2011). The marine economy is over 75% dependent on the American lobster, which is showing signs of decline in the southern Gulf of Maine (Wahle et al. 2013). Marine resource diversification is essential for adapting to a rapidly changing ecosystem and ultimately promoting economic resilience for Maine’s coastal communities.
Shellfish aquaculture provides an opportunity for diversification, and has rapidly expanded in Maine in the past decade (MDMR 2020). New and underutilized shellfish species, such as quahogs (Mercenaria mercenaria), present an opportunity to further expand Maine’s farmed shellfish products and provide a high-quality source of protein for consumers. Simultaneously, landings of quahogs from the wild harvest fishery have more than doubled in the past five years in southern and midcoast Maine as waters have warmed, and their value has increased 35% (MDMR 2021b). As the economic importance of wild quahogs has grown, many municipal shellfish programs have expanded wild stock enhancement efforts, purchasing quahog seed from hatcheries and growing it to a size that can be planted in the mudflats.
Both quahog aquaculture and quahog stock enhancement have been slow to advance in Maine due to several barriers that have limited economic viability. However, the general outlook from shellfish farmers and harvesters remains positive, with many eager to continue experimenting with culture techniques, including a growing interest in intertidal quahog aquaculture. The intertidal zone has historically been used by municipal shellfish committees for stock enhancement of the soft-shell clam fishery (Miller, 2021), but recently there has been increased interest from farmers and harvesters in growing quahogs in this space. Historically, potential conflicts between landowners (riparian landowners own the intertidal zone to the low water mark in the state of Maine) and harvesters has limited the growth of aquaculture in this area. However, the majority of quahog aquaculture in the U.S. occurs in the sediments of the intertidal or shallow subtidal zone (Kraeuter and Castagna, 2001), making this a logical area to explore next steps in advancing quahog aquaculture techniques in Maine. Furthermore, there may actually be a lower barrier to entry for intertidal aquaculture as it does not require access to a boat and the increased infrastructure costs of setting up moorings and anchoring systems that is required for subtidal aquaculture.
This proposal aims to test the viability of intertidal quahog growing techniques in Maine for both shellfish farming and stock enhancement activities. Determining viable pathways for culturing quahogs in the intertidal zone will benefit existing and potential new shellfish farmers looking to diversify their crops, as well as shellfish harvesters who are increasingly dependent on the wild quahog resource. We believe that this project can provide an example for how intertidal aquaculture can be thoughtfully conducted in a way that minimizes conflict with other users of the intertidal zone. For example, one of our partner farms, Eros Oyster, is also the riparian landowner of the land adjacent to the intertidal area where the work will be conducted, eliminating potential landowner conflict (although we recognize that this will not always be the case, and further work on identifying ‘low conflict’ zones for intertidal aquaculture is likely needed). Currently, there is no active wild shellfish harvesting in this area, and both Eros Oyster and Manomet have received verbal confirmation from local shellfish harvesters and managers that they are supportive of the project and eager to monitor the success of this growing method for their own potential farming interests. Furthermore, our second partnership is with the Brunswick Marine Resource Committee, the body responsible for managing the town’s wild shellfish fishery. As we explore techniques to culture quahogs in the intertidal zone, we believe it is imperative to have wild shellfish harvesters at the table to benefit from the potential of using these techniques for stock enhancement, as well as to reduce conflicts surrounding the use of intertidal space.
This project contributes to SARE’s outcome statement by continuing to develop diversification strategies for sea farmers who will benefit from additional products and increased resilience to disease and pests. The project also aims to strengthen resources for local shellfish harvesters, who are being disproportionately impacted by climate change and have been historically marginalized in the fisheries sector, which has been particularly evident in the lack of resources allocated for research and management of the wild harvest fishery. Quahog farming could provide an accessible and economically viable way for shellfish harvesters to diversify their resources. Ultimately, intertidal quahog farming has the potential to benefit both shellfish farming and wild harvest industries, promoting sustainability and resilience for coastal communities and contributing to the livelihoods of sea farmers and shellfish harvesters.
Citation List
Kraeuter JN & Castagna M. (2001). Biology of the Hard Clam (Developments in Aquaculture and Fisheries Science, Vol. 31). Elsevier.
MDMR (Maine Department of Marine Resources). (2020). Harvest of farm-raised American oysters in Maine. Maine Department of Marine Resources. Retrieved March 8, 2022, from https://www.maine.gov/dmr/aquaculture/data/documents/AmericanOyster2020.pdf
MDMR (Maine Department of Marine Resources). (2021b). State of Maine Northern Quahog (Hard Clam) Landings. Commercial Maine Landings. Retrieved March 30, 2022, from https://www.maine.gov/dmr/commercial-fishing/landings/documents/HardClam.graph.pdf
Stenck RS, Hughes TP, Cinner JE, Adger WN, Arnold SN, Berkes F, Boudreau SA, Brown K, Folke C, Gunderson L, Olsson P, Scheffer M, Stephenson E, Walker B, Wilson J, & Worm B. (2011). Creation of a Gilded Trap by the High Economic Value of the Maine Lobster Fishery. Conservation Biology, 25(5), 904–912. https://doi.org/10.1111/j.1523-1739.2011.01717.x
Miller MF. (2021). The Human Dimensions of Aquaculture Development in Maine Including a Governance Perspective. Electronic Theses and Dissertations 3419. University of Maine. https://digitalcommons.library.umaine.edu/etd/3419
Wahle, R. A., Brown, C., & Hovel, K. (2013). The Geography and Body-Size Dependence of Top-Down Forcing in New England’s Lobster-Groundfish Interaction. Bulletin of Marine Science, 89(1), 189–212. https://doi.org/10.5343/bms.2011.1131
Cooperators
- - Producer
- - Producer
Research
We experienced significant delays in getting the project started in 2022 due to permitting issues. The Maine Department of Marine Resources Aquaculture Division was short staffed at the time, leading to longer than normal wait times in getting Limited Purpose Aquaculture (LPA) applications processed. We did not secure LPA’s until the very end of the growing season for quahogs. Due to this delay, we were unable to deploy the experiments as planned in September of 2022. We opted to deploy a pared-down version of the original experimental design at Eros Oyster in November, 2022 to reduce the chance of losing all of our seed stock if the temperatures were too cold for the quahogs to acclimate and bury. Three ADPI bags and 1 soft clam bag were put in two intertidal zone heights (high and low) on November 7 with 400 quahogs in each bag. The rest of the seed was overwintered in sunk oyster cages at Eros Oyster Farm and on the Brunswick Marine Resource Committee Municipal LPA in Middle Bay. While this was not the full experiment, it allowed us to see if bags would stay in place over the winter.
Objective 1: Test multiple intertidal quahog grow out techniques to determine best practices.
- Objective 1.1 Deploy intertidal experiments: Intertidal quahog experiments were conducted at Eros Oyster in Robinhood Cove, Georgetown, ME and with the Brunswick Marine Resource Committee in Maquoit Bay, Brunswick, ME using two types of 4 mm mesh bags: ADPI oyster bags and 4x4 ft soft clam bags. In Maquoit Bay, bags were put into the intertidal on 4/14/23 and at Eros Oyster on 6/6/23. Quahogs used in the experiment had been grown in nursery gear the previous summer and overwintered in sunk oyster cages. Quahogs were sorted before being placed into the experimental gear and were large enough to retain on a 4mm mesh screen. At each site, we deployed six soft and six ADPI bags. We tested two types of soft bags, untreated bags and coated bags that had been dipped in a latex net dip. The purpose of the latex net dip was to see if the coated bags performed better than the normal, untreated bags. This gave us a total of three experimental treatments. Soft bag treatments had three replicates and the ADPI bag treatment had six replicates. At Eros Oyster, stocking density was 400 quahogs/bag for ADPI bags and 1,000 quahogs/bag for soft bags while in Maquoit Bay the stocking density was 1400 quahogs/bag for ADPI bags and 3500 quahogs/bag for soft bags. Stocking densities were based on standard techniques used in the south Atlantic and to give an appropriate density at the target harvest size without requiring thinning during the project timeline (Table 1). At Eros Oyster, bags were placed below the mean low water (MLW) line, while in Maquoit Bay, they were slightly above MLW. Bag placement was random and not grouped by treatment (Figure 1). To deploy the ADPI bags, a slight depression was made in the mud, the bag was placed in the depression and mud was spread over the edges of the bag to hold it in place. A 4ft piece of rebar was attached to one side of the soft clam bags which helped keep the bags in place and the edges of the soft bags were lightly pushed into the mud. ADPI bags are heavier and therefore did not need rebar for added weight.
- Objective 1.2 Monitoring quahog growth and survival: Quahog growth and mortality was assessed three times after deployment: Fall 2023, Spring 2024 and Fall 2024. At sampling events during the experimental period, 50 quahogs were randomly selected from one bag from each experimental treatment. At the final sampling event for each site (Spring 2024 in Maquoit Bay and Fall 2024 at Eros,) 50 quahogs were measured from every bag. Shell length was measured to the nearest millimeter and a total weight for all 50 quahogs was recorded to the nearest gram. Weight measurements were not used in the growth analysis due to the difficulty of accurately measuring the weight of small, wet quahog seed. Overwinter mortality was assessed in the Spring of 2024 by counting the number of quahogs exhibiting prior season growth that were no longer alive. Average quahog shell length was calculated for each site and treatment at each sampling date. Shell length data was tested for normality using the Shapiro-Wilk test and was not normally distributed, therefore the Kruskal-Wallace test was used to test the influence of bag type on shell length at each site using the ‘stats’ package in R (R Core Team 2024).
- Objective 1.3 Measuring environmental variables: Onset temperature and water level loggers were deployed at each site to record thirty minute temperature and water level measurements. The water level loggers did not function well inside the bags with sediment deposition and did not result in any usable data. Thirty minute temperature data was collected from each site throughout the project.
Objective 2 Harvest and/or distribute for stock enhancement and quantify production costs:
Production costs were recorded for each site including gear and labor requirements. Production costs and growth results were reviewed with partners at each site to determine overall viability for growing market size and stock enhancement size quahogs.
Objective 3: Conduct outreach to share findings and grow industry knowledge:
See Results
Objective 1
Pilot Project
All bags deployed in the pilot project (6 ADPI and 2 soft bags) were not disturbed by sea ice or storm conditions over the winter. While we didn’t quantify mortality from this pared-down experiment, visual observations did not indicate any mass mortality events. This positive indication suggests that at least in Georgetown, quahogs could survive winter conditions in this gear. While not what we originally intended, the pilot experiment from November 2022 to May 2023 allowed us to assess how the quahogs and gear fared over the winter and gave us an opportunity to make adjustments before deploying the full experiment. A major lesson learned was that it is not feasible to pre-fill the ADPI bags with sediment. They become too heavy and unwieldy to work with and instead need to use bags with the quahogs inside and passively allow sediment to accumulate with time. This necessitates an earlier planting date in the fall to allow enough time for sediment to accumulate and quahogs to adequately bury before temperatures drop below 40℉ and they become dormant. We also found that at Eros Oyster, the upper tidal height was less suitable for this work as the sediment was coarser, making it harder to anchor the gear resulting in only one tidal height tested for the full experiment.
Gear Usability
Throughout the project, we did not encounter any gear issues at Eros Oyster with either the soft bags or ADPI bags; all bags stayed in place for the entire project period. In Maquoit Bay, we lost two ADPI bags in the spring of 2023, three weeks after the bags were deployed during a period of high rains. This excess flow dislodged the bags and they were later found in a channel with high freshwater runoff. All the quahogs in both bags were dead. All bags in both locations stayed in place over the winter, but in the spring of 2024 during a late season storm, a soft clam bag in Maquoit Bay was dislodged and carried a short distance. This bag was recovered with live quahogs. A concern for this gear was the potential of ice buildup to pick up and move bags in the intertidal. We did not encounter this issue, although this is site specific and dependent on winter conditions. Eros Oyster is located in a protected cove while Maquoit Bay is more exposed. It is important to note that severe coastal storms in January of 2024 caused unprecedented damage and storm surges across Maine, however, the bags were not impacted by these events. Site selection is a key component to any aquaculture operation, and when considering the use of bags in the intertidal, a protected area with less ice buildup is beneficial.
The ease of working both styles of bags was another key component of this project. It was quickly evident that ADPI bags were not a suitable gear type for this type of work. As sediment accumulates in the bags, the bags become heavy and cumbersome, increasing labor requirements. As a result, we do not recommend using hard, ADPI style bags as an intertidal quahog grow out method. Due to the flat design, soft bags did not accumulate as much sediment inside the bag and weigh less once removed from the intertidal. Additionally, the deployment of soft bags requires less labor as the soft bags are placed on top of the mud and the attached rebar keeps them anchored in place rather than digging a depression in the mud for the ADPI bags.
Quahog Growth & Environmental Variables
Growth was impacted both by site and bag type. By the end of the first growing season (fall 2023), quahogs in Maquoit Bay were visibly larger than those at Eros. Quahogs reached the target size in Maquoit Bay and were distributed before the end of the project period so we can not directly compare final sizes between sites. Since the seed used at each site came from separate cohorts and experienced different conditions and stress events during the nursery stage (seed used in the Eros experiments was in worse condition than seed used in Maquoit Bay) we did not do any statistical comparisons between sites. However, observations showed that quahogs were larger in Maquoit Bay than in Robinhood Cove on multiple sampling events. Maquoit Bay is a warmer system than Robinhood Cove, likely leading to faster growth rates. While the maximum and minimum temperatures recorded at both sites were similar, 32.9˚C and -2.3˚C in Maquoit Bay and 31.9˚C and -2.1˚C in Robinhood Cove, the average temperature over the 2023 growing season (June through September) was almost 5 degrees warmer in Maquoit Bay (21.6˚C for Maquoit Bay, 16.8˚C for Robinhood Cove). Food availability may also have differed between sites, although this is not something we measured.
Overall, quahogs grew best in the untreated soft clam bags (Figure 2). Quahogs grown in the soft bags were significantly larger than those grown in hard bags (Kruskal-Wallace test, p=8e-05 for Maquoit Bay, p=5.4e-05 for Eros). Quahogs grown in the untreated soft bags were also significantly larger than those grown in soft bags coated in a latex dip. At Eros, quahogs grown in the untreated soft bags were significantly larger than those grown in the soft coated bags but in Maquoit Bay, quahogs were slightly larger in soft untreated bags but there was no significant difference to the soft coated bags (Kruskal-Wallace test, p=6.1e-11 for Eros, p=0.092 for Maquoit Bay). Since the soft coated bags did not outperform the untreated soft bags, we do not recommend pursuing the coated nets at this time as it requires additional steps for bag preparation increasing expenses.
Seed Challenges & Mortality
Due to the permitting delays and having to overwinter seed in sunk oyster cages, we faced significant challenges with seed condition. At Eros Oyster, we had extremely high seed mortality over the winter. When selecting seed to use in the experiment, we had low volume of live seed and its condition was not ideal. This led to mortality being a difficult metric to measure as much of the seed originally put in the bags was already dead. Seed used in the Maquoit Bay experiment was in better condition than that used at Eros. Determining mortality of the smallest quahogs in the field experiments was not feasible.
At Eros, overwintering mortality in the ADPI bags was 18% and in the soft clam bags it was 8%. In Maquoit Bay, quahogs in the ADPI bags experienced very high mortality (80%) but mortality in the soft bags was 5%. This overwintering mortality comes from the second winter as experiments were not deployed until spring of 2023. Testing overwintering mortality during the first winter is an important area for future work as overwintering survival could vary based on size.
Green crab predation was another concern during this experiment. The use of bags may prevent predation from larger crabs but there is no way to prevent crabs from settling into the bags. We saw a higher presence of green crabs inside the bags at Eros Oyster, with three of nine bags containing multiple green crabs. In Maquoit Bay, only one bag contained a green crab. However, even in the bags with green crabs, there was still high quahog survival.
Objective 2:
Distribution for stock enhancement: All quahogs grown for stock enhancement purposes reached their target size range (20-25mm shell length) by fall 2023 after one growing season in the intertidal bags. However, because we wanted to gauge overwintering suitability of gear and survival of quahogs, they were left onsite until spring of 2024 when they were distributed on intertidal flats as part of a conservation effort undertaken by the Brunswick Marine Resources Committee. While we are unable to compare direct costs to other stock enhancement opportunities, we believe that this is a less expensive method of growth due to low gear costs and limited labor requirements (Table 2). Additional costs required in this project were the utilization of an airboat to reach the site, however this could be mitigated by different site selection. Labor required to fill the bags and deploy on site was completed during one low tide (~6 labor hours). After deployment, the quahogs were left undisturbed until the end of the season when they were spread on the flats. This method requires significantly less labor than floating nursery tray systems or floating upweller systems. In 2024, the Brunswick Marine Resource Program experimented with growing quahog seed for stock enhancement in an upweller and estimated the cost to be $30,000, requiring site labor several days every week throughout the summer growing season.
Market distribution:
Due to slow growth rates at Eros Oyster Farm, none of the quahogs were large enough for market (38-45mm shell length) by the end of the 2024 growing season. This prevented us from conducting a product cost assessment. However, gear costs for this method are fairly low and required minimal labor (Table 2). We intentionally designed the experiment to limit labor costs by using a stocking density appropriate to the final target size for each site to eliminate the need to grade and split quahogs. In a commercial setting, these practices would likely be altered requiring more labor throughout the growing season. In prior work that tested subtidal quahog grow out methods, a significant amount of labor was required to control biofouling which was not required in this setup as daily exposure during low tides and accumulation of sediment controlled most biofouling.
Objective 3:
Outreach through existing networks and partnerships: We used new and existing networks to discuss this work and disseminate the results of this project through presentations, meetings and one-on-one communication with industry stakeholders. We engage in or lead numerous wild harvest and shellfish aquaculture networks and partnerships, including the Casco Bay Regional Shellfish Working Group, Maine Shellfish Learning Network, Maine Shellfish Co-Management Initiative, Maine Shellfish Advisory Council, Downeast Fisheries Partnership, Maine Aquaculture Hub, Aquaculture in Shared Waters, and Maine Sea Grant where conversations about this work occurred during the project timeline as well as dissemination of results. We formally presented our findings at the Brunswick Marine Resources Committee, Maine Fishermen's Forum, Northeast Aquaculture Conference and Exposition, National Shellfisheries Association annual meeting and the Maine Aquaculture Research, Design and Education Summit.
We originally intended to hold two field demonstrations at Eros Oyster targeting up to 10 interested farmers or shellfish harvesters so they could see the gear and growing techniques first hand, ask questions, and provide input for the continued development of intertidal quahog aquaculture. Early on, we realized that rather than bringing farmers to the site, it was easier to meet them wherever they were to discuss the project and future ways to integrate it into their operations. We still held two field demonstration days, one at each Eros Oyster Farm and in Maquoit Bay, but only three farmers or harvesters were present on each day. However, we reached 30 harvesters and farmers through other outreach activities.
We also conducted outreach through Manomet’s website, traditional news media and social media. Maine Public Radio produced a story about this project as well as being featured on Manomet’s website and newsletter. Posts about this work were found on Manomet’s, Town of Brunswick and Eros Oyster instagram feeds.
While widely used in other areas along the eastern seaboard, soft clam bags have not previously been used as a grow out method in Maine and ADPI bags are not used in the intertidal. This project explored the viability of these bag types for growing quahogs in the intertidal in Maine both for growing market and stock enhancement sized quahogs.
Overall, the gear held up well over the winter, did not break down or tear over the course of the field experiments, and did not experience much external fouling (although some settlement of mussels and tunicates did occur inside the bags). There was some movement caused by storms but this could be mitigated with alternate site selection. Determining winter suitability of this gear was a major initial hurdle to overcome, and our results indicate that this gear type is viable in Maine.
This project tested three separate bag types and found the soft uncoated clam bags were the cheapest to purchase, required the least upfront labor, were easier to handle during deployment and were much less heavy and easier to handle during retrieval. Additionally, growth rates were highest when compared to the other two treatments. While more work needs to be done to determine if this is economically feasible, the results of this project suggest that farmers should focus intertidal efforts on soft clam bags.
While we were unsuccessful in growing quahogs to market size, we believe that this method has potential and merits further testing. We were successful in growing quahogs for stock enhancement and see potential for towns to adopt this method as a quahog culture method that requires less upfront cost and ongoing labor than other commonly used methods. Compared to prior work funded by Northeast SARE (ONE19-341) that explored quahog culture in subtidal systems, grow out in soft bags required less labor, had relatively high survival and seems more promising as a method to pursue for quahog culture.
Education & Outreach Activities and Participation Summary
Participation Summary:
Education and outreach was a specific objective in our Plan of Work (Objective 3) which included engagement with stakeholders through existing networks and partnerships, conference presentations, field demonstrations, and social and traditional media platforms. In addition to outreach during the project period, we continue to engage many of the same networks as we distribute final results from this project. A pivot we made from our original objectives was we did not hold specific field demonstration days. Originally, we hoped to have two days that would attract up to 10 farmers to show the experimental design and talk through ways it could be beneficial to them. Early on, we realized that rather than bringing farmers to the site, it was easier to meet them wherever they were to discuss the project and future ways to integrate it into their operations. We still held two field demonstration days, one at each Eros Oyster Farm and in Maquoit Bay, but only three farmers or harvesters were present on each day. To increase the reach of this project, we presented at the Brunswick Marine Resource Committee meeting which had a mixed audience of farmers, shellfish harvesters, industry and community members. This presentation led to two consultations with oyster farmers who were interested in producing quahogs with soft bags, one of whom has applied for a lease with this gear. Maine Public Radio aired a report about this work and it has been featured in Manomet’s quarterly newsletters and in Manomet’s, Town of Brunswick and Eros Oyster instagram feeds. Throughout the project, we had ten field days that engaged farmers at Eros Oyster, town officials and clam harvesters in Brunswick. In addition to the presentation at the Brunswick Marine Resource Committee Meeting, the work was presented in 2024 at the Maine Fishermen's Forum, Northeast Aquaculture Conference and Exposition and the National Shellfisheries Association annual meeting. In 2025 we presented at the Maine Aquaculture Research, Design and Education Summit and will be presenting at the 2025 Maine Fishermen's Forum. We are continuing to look for other areas to share results from the project.
Learning Outcomes
Key areas in which farmers reported changes were in propagation methods of quahogs as well as partnerships with municipal shellfish programs for mutual benefit. This introduced an entirely new gear type to the region that farmers are interested in continuing to experiment with for maximum efficiency. It also opened new doors for conversation between private farms and municipal shellfish programs to think about ways they could work together for shellfish grow out.
Project Outcomes
As a result of this project, the Brunswick Marine Resource Committee believes soft bags are a viable option for growing out seed in a less labor intensive way for stock enhancement of their municipally managed mudflats. They applied and received a second LPA that is permitted for this gear type and could be used as the final grow out stage from nursery gear before seeding on the flats. One farmer who heard about this work through our presentation at the Brunswick Marine Resource Committee Meeting sees a lot of potential in this method for diversifying species grown on his farm and has submitted an intertidal lease application that includes soft bags.
This project intended to explore the feasibility of growing quahogs in the intertidal zone as a way for oyster farmers to diversify their farmed products and for municipal programs to explore other opportunities for stock enhancement. To do this, we utilized gear types that fell into one of the following categories: not currently being used in Maine (soft clam bags) or not being used in the intertidal habitat (ADPI bags). For both gear types, a big concern was whether the gear would survive the winter season and if quahogs would be adequately protected from freezing conditions in the bags. At both sites, winter conditions were not a limiting factor. All of the soft clam bags survived winter conditions and only two of the ADPI bags were displaced. We did not see any evidence of mass winter mortality suggesting that quahogs were able to bury deep enough in the mud to insulate against low temperatures. We successfully grew quahogs to a size appropriate for stock enhancement but not to market size. However, we do not see this as a failure but as an opportunity to think deeper about site selection and to continue to see if growing quahogs to market size is economically feasible. In addition, we learned many valuable lessons about best practices for working with these gear types. At this time, we do not recommend pursuing intertidal culture of quahogs in ADPI bags but see potential for soft clam bags in the Maine aquaculture industry.
This project was not without its challenges, many of which were outside of our control. Permitting delays forced us to delay the start of our work until the spring of 2024. As a result, we had to overwinter seed on oyster farms which resulted in high mortality at one sight and limited our ability to understand a true timeline for how long it would take for seed to go from the nursery system to target size for stock enhancement or market. In addition, the poor quality of seed for our market experiments may have led to slower growth rates. Despite these limitations, we were able to pivot and still explore the use of these gear types in Maine and believe that further testing is warranted for soft clam bags and seems to be the most promising method of quahog culture to build on.
Specific areas for continued testing and commercial use include site selection factors beneficial for quahog growth with low exposure to winter ice and storm conditions. This could include water temperatures, available food source, sediment type and sediment accumulation rates. Based on growth results seen in Maquoit Bay, it’s possible that a market size product could be achieved using these growing techniques, but more research is needed to determine site selection components and time to market size. To make this culture method profitable, stocking density and bag mesh size should also be tested to maximize growth and amount of product grown. We used a low stocking density and a single bag mesh throughout the experiment to minimize labor requirements but increasing stocking density at smaller size classes and splitting quahogs into smaller quantities in larger mesh bags as they grow could increase growth rates. However, a larger mesh size could increase potential for green crab predation. Finally, this culture system does not replace the needed nursery stage for quahog seed after leaving the hatchery. While not in the scope of this project, the nursery stage also warrants further work.
The use of soft clam bags will be most beneficial to aquaculturists who are interested in growing quahogs on their farm or to individuals interested in becoming aquaculturists but are unable to set up an oyster farm. Additionally, this technique may appeal to farmers who already hold an intertidal lease or are interested in intertidal farming. As the soft clam bags do not require any anchor setup for longlines and can be accessed during low tide and do not require a boat, they could have a lower startup cost than other aquaculture farm designs. This is specifically applicable for farmers in the southern and western areas of Maine as waters are warmer and growing conditions are more suitable for quahogs. This region may grow in the future as waters in the Gulf of Maine are likely to continue warming due to climate change.