Progress report for ONE22-423
Project Information
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.
- 2.2: Distribute quahogs for stock enhancement.
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 (see Previous Work section for more detail). 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.
Cooperators
- - Producer
- - Producer
Research
Objective 1: Test multiple intertidal quahog grow out techniques to determine best practices.
- Objective 1.1 Deploy intertidal experiments: We will test two types of 4mm mesh bags; ADPI oyster bags and 4’x4’ soft clam bags. Both ADPI and soft clam bags will be put in two different tidal heights (low and mid) to test the impact of dry time to prevent biofouling. For the more rigid ADPI bags we will also use two different sediment treatments, bags prefilled with sediment from the surrounding flats, and bags that have no sediment added. Finally, we will test two different overwintering strategies, leaving bags in the intertidal zone and moving bags to subtidal oyster cages. At the beginning of the next growing season, bags that were moved to oyster cages will be placed back on the flat. This is a total of 12 treatments which will each have three replicates. All treatments will be stocked with quahogs ranging from 4-6 mm in shell length. We will use a stocking density of 400 quahogs/bag for ADPI bags (6.5 quahogs per cubic inch) and 1,000 quahogs/bag for soft bags (2.3 quahogs per square inch). Quahog seed size and stocking densities are based off of standard techniques used in the south Atlantic. We could use higher stocking densities when the seed is smaller and transfer to additional bags as it grows; however, we have elected to reduce handling time by starting with lower densities.
- Objective 1.2 Monitoring quahog growth and survival: Quahog growth and survival will be measured three times throughout each growing season. In the first year, we will only measure twice; when intertidal experiments are deployed, and just before they get moved for overwintering. In subsequent years, quahogs will be measured after overwintering to gauge overwinter survival (~April), mid growing season (~July), and late fall (~November) at the end of the growing season before overwintering. Growth is not expected to occur from December-March when water temperatures fall below 5-6°C (Stanley 1985). Survival will be determined from 100 randomly sampled quahogs. Empty shells (i.e., dead quahogs) will be used to calculate percent mortality. Total loss (mortality + loss due to handling) will be calculated as the difference between the initial and final live individuals per bag. Growth will be measured from 50 randomly sampled quahogs from each bag during each sampling event. The effect of treatment on growth and survival will be analyzed using Generalized Linear Models in R. Growth rates will also be used to determine the length of time from seeding to harvesting.
- Objective 1.3 Measuring environmental variables: Onset temperature and water level loggers will be deployed at each site recording hourly temperature and water level measurements. Water level will be used as a proxy to determine exposure time for each tidal height treatment. We will determine if temperature or exposure time correlates with growth or survival and will use these results to inform site selection parameters.
Objective 2 Harvest and/or distribute for stock enhancement and quantify production costs:
- 2.1 Harvest farmed product: All quahogs used in experiments are the property of the respective farm or town partner. For the purposes of producing a farmed quahog product, the ideal size range is 38-45 mm shell length and we estimate it will take 2-4 growing seasons to reach this size (Kramer, 2018; McMahan, 2021). Eros Oyster is also a wholesale dealer of farmed shellfish products and has readily available distribution channels for the experimental quahogs. We will track the number of quahogs sold and the price received to inform farm-scale production costs. We will also consider all gear costs, quahog seed costs, maintenance costs, and any additional time/effort associated with farming quahogs for each method in order to determine overall production costs.
- 2.2 Distribute quahogs for stock enhancement: For the purposes of producing quahogs for municipal stock enhancement, the ideal size range is 20-25 mm shell length, at which point the quahogs are less susceptible to predation by green crabs (Kraeuter and Castagna, 2001). We estimate it will take 2 growing seasons for quahogs to reach this size, at which point they will be removed from the bag experiments and distributed in redetermined stock enhancement areas by the Brunswick Marine Resources Committee and local harvesters. We will track the number of quahogs distributed and compare production costs of this method to other commonly used methods for stock enhancement grow out, such as upwellers or floating subtidal trays.
Objective 3: Conduct outreach to share findings and grow industry knowledge:
- 3.1 Outreach through existing networks and partnerships: We are currently engaged in or leading 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. We will disseminate results of this project through these various networks through presentations, webinars, and one-on-one communication with industry stakeholders. Finally, we will aim to present our findings at a regional conference such as the Northeast Aquaculture Conference and Exposition or the Regional Association of Research in the Gulf of Maine.
- 3.2 Field demonstration: We will host two field demonstrations at Eros Oyster, each targeting up to 10 interested farmers or shellfish harvesters who will be able to see the gear and growing techniques first hand, ask questions, and provide input for the continued development of intertidal quahog aquaculture.
- 3.2 Outreach through social media, newsletter articles, Manomet’s website, and traditional news media. We will feature project updates and disseminate results through Manomet’s website, quarterly newsletter, facebook (@Manomet), and instagram (@manometfisheries) accounts. We will also look for opportunities to highlight this work through traditional news media outlets, such as the Bangor Daily News, The Portland Press Herald, Maine Public, and Aquaculture North America.
We experienced significant delays in getting the project started in 2022 due to permitting issues. The Maine Department of Marine Resources Aquaculture Division has been short staffed recently, leading to longer than normal wait times in getting Limited Purpose Aquaculture (LPA) applications processed. We did eventually secure the LPA for Eros Oyster in Georgetown, but are still waiting for the permit to begin work in Brunswick. Because the timing of receiving the Georgetown permit pushed us into the very end of the growing season for quahogs (i.e., November), we opted to deploy a pared-down version of our original experimental design, to reduce the chance of losing all of our seed stock if the temperatures were too cold for the quahogs to acclimate and bury. We ended up deploying 3 ADPI bags and 1 soft clam bag to test whether or not the gear would be impacted by sea ice (a major question we hope to answer). We put 400 quahog seed into each bag to collect preliminary data on overwintering mortality before executing the full experiments. We did measure a subset of the quahogs in each bag, so we will be able to detect changes in growth; however, we think it is very unlikely any growth will occur as water temperatures were already below the threshold where growth is known to occur when the quahogs were deployed. Due to the permitting delays and issues with seasonal timing of experiments, we aim to deploy the full experiments in both Georgetown and Brunswick in the spring of 2023. We will assess how the quahogs and gear deployed in Georgetown faired over the winter and will make any necessary adjustments based on those results.
In April of 2023, we assessed how the pared-down experiment survived the winter at Eros Oyster in Georgetown. By deploying the pared-down experiment at Eros in fall of 2022, we hoped to see how gear would be impacted by winter conditions. We found that all four bags (3 ADPI and 1 soft bag) were not disturbed by sea ice over the winter. While we didn’t quantify mortality from this pared-down experiment, visual observations did not indicate any mass mortality events. This was a positive indication that at least in Georgetown, quahogs could survive winter conditions in this gear. In addition to looking at gear placement, we also learned many valuable lessons about handling these bags through the pared-down experiment. These insights will help us learn how to be more efficient in working with these bags in the intertidal. We successfully received the LPA license for Brunswick and in April and May, deployed the full experiments (6 ADPI bags, 6 soft bags). Stocking density depended on bag type and site as bags were stocked to give ~100 quahogs/ft2 at the final grow out size (20-25mm in Brunswick and 38-45mm at Eros; Table 1). We measured the initial size of the quahog seed that was put into the bags to understand growth rates over the growing season. In October, we returned to the sites to look at growth rates. Major rain events over the summer caused the loss of two ADPI bags in Brunswick, but none of the soft-bags were impacted. At Eros, there were no gear issues during the growing season. At both sites, we saw significant growth in both bags, but quahogs in both gear types in Brunswick had higher growth rates than those at Eros (T tests, p <0.05 for all comparisons; Figure 1). In Brunswick, the quahogs had grown to our target size of 20-25mm and were spread on flats previously identified as priority areas for shellfish restoration. In Brunswick, we deployed a new cohort of quahogs in soft bags to understand survival and gear retention over the winter which will be assessed in spring of 2024. At Eros, all quahogs and bags were returned to the intertidal site and we will check overwintering success in the spring of 2024.
|
|
Maquoit Bay |
Eros Oyster |
|
ADPI Bags |
~3500 quahogs |
~1000 quahogs |
|
Soft Bags |
~1400 quahogs |
~400 quahogs |
Table 1. Stocking densities of quahogs at each site for different gear types. Stocking densities were set to give ~100 quahogs / ft2 at their target growth size.
Brunswick, average shell length was 22.9 ± 0.18mm, big enough to withstand most green crab predation and clams were spread on flats identified for wild shellfish stock enhancement.
Education & Outreach Activities and Participation Summary
Participation Summary:
We have incorporated outreach as an objective in our Plan of Work (see Objective 3), including engagement with stakeholders through existing networks and partnerships, conference presentations, field demonstrations, and social and traditional media platforms. In addition to the detailed approach outlined above, the project will also greatly benefit from the participation of the Brunswick Marine Resource Committee and 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. Brunswick has 78 commercial shellfish harvesters who stand to benefit from this project, many of whom will be directly involved in deploying and monitoring experiments. We also plan to engage with the Georgetown Shellfish Committee and local harvesters who have expressed interest in this project. Dr. McMahan is a member of the Georgetown Shellfish Committee and can therefore engage directly with harvesters at monthly meetings. Finally, Eros Oyster has outlined additional outreach in their letter of support, including conducting farm tours open to the public and also specifically targeting restaurant owners and staff.
January 2023 Progress Report: We have not begun conducting education and outreach at this stage of the project. We have had several consultations with partner farmers, as well as 2 field days at Eros Oyster to deploy preliminary (pared-down) experiments.
January 2024 Progress Report: We have worked with two oyster farmers in the deployment and measurement of the quahogs, as well as with municipal partners in Brunswick. Two municipal clam harvesters from Brunswick were involved in the measuring and sorting of quahog seed that was used in the experiments. We spent 3 field days both at both Eros Oyster and in Brunswick to deploy the experiments and check growth in the fall. We presented preliminary results at the Northeast Aquaculture Conference and Exposition and hope to share this information at the Maine Fishermen’s Forum in February and the National Shellfisheries Conference in March. Field days in Brunswick were shared on social media channels for Manomet and the town of Brunswick.