Testing the Efficacy of a Hybrid Floating Bag and Bottom Planting Method to Grow Oysters

Coastal states have seen an enormous opportunity for oyster aquaculture in underutilized waters and have worked to capitalize on these opportunities. Our farm, as well as other farmers in our community, use intensive subtidal bottom cages to farm oysters. This gear is used from seed through harvest to grow oysters and protect them from cownose ray predation. Cownose ray predation has a large impact on the shellfish industry, costing farmers time and money to protect oyster crops. However, the gear used to mitigate cownose ray issues has its own issues in terms of cost and labor. To address these issues, we intend to create a hybrid method of growing oysters using a temporal combination of off-bottom floating gear and bottom planting oysters. Off-bottom floating bags would grow out the oysters from Spring through Fall, then the oysters will be bottom planted in the early Fall (after cownose rays migrate out of the area) to then be harvested in the following Spring (before cownose rays migrate back for the Summer). We will evaluate whether this method can produce a marketable oyster in less than 16 months. The three main obstacles we plan to address with this method are cost (i.e., gear and labor), marketability, and survivorship (i.e., overwintering, predator avoidance).

Using bottom cages in oyster farming from seed to harvest requires significant capital, as well as intensive labor to maintain and winterize. The advancement of selective oyster breeding has given oyster growers access to fast-growing oyster seed, allowing growers in the Barnegat Bay and surrounding areas to harvest oysters in under 18 months. However, as oysters grow and require more gear, the costs become a significant barrier for start-up operations and for the profitability of existing operations. To reduce stocking density, the splitting of bags is necessary as the oysters grow, which involves the laborious tasks of tumbling and grading the oysters by size and putting them into new bags. This process forces growers to constantly purchase new bag materials or risk degradation of quality and the smothering of oysters. The prevention of biofouling organisms that collect on gear and oysters is another laborious aspect of our current gear system. It involves lifting the cages and pulling out the bags to be exposed at low tide. In this drying position, the racks and bags often fall due to wind and boat wakes, increasing labor needed to collect the fallen bags off the bottom and rearrange the racks. Winterizing our current gear is also extremely laborious because the gear must be moved to a deeper protected bay, or numerous oysters would be lost. 

The use of a floating bag system could reduce physical labor and increase productivity and profitability. In terms of biofouling prevention, the bags can simply be turned over when needed to expose the accumulated biomass to air. The float-bag system will naturally tumble the oysters, where tumbling in general prunes the oysters' outer growth and contributes to better shape and shell density. Once the oysters are bottom-planted following the float-bag growing season, the oysters can continue to grow to market size without manipulation or labor needed to winterize. The oysters can then be harvested off the bottom in late spring. Bottom planting oysters is an appealing method because not only does it require less labor and gear expenses, but we have observed on our farm that oysters grown on the bottom (accidentally dropped and picked up in later seasons) appear to be cleaner and have improved aesthetics (see Image 1). Oysters, if given sufficient space, will grow an appealing round shell and a deep cup, contributing to a greater aesthetic and better meat to shell ratios. Oysters grown directly on the bottom also tend to naturally exclude the biofouling that is typical in the water column, further reducing labor and improving marketability.

The methods of our proposed solution will improve farm productivity, reduce farming costs, and increase net farm profitability. Our methods could contribute to an improved quality of life for farmers and employees not only involved in the Barnegat Bay Oyster Collective, but oyster farmers in the entire northeastern region, by cultivating oysters without such costly and time-consuming methods. Finally, oyster farming is a naturally sustainable farming practice, where oysters filter the surrounding water just by feeding. Therefore, creating more productive oyster farming techniques will undoubtedly contribute to the enhancement of water quality. Attached is a letter from other farmers in our New Jersey growing community that support and have an interest in the funding of our proposed solution. 

The practice of bottom planting oysters over the winter season and harvesting them off the bay bottom by hand is a known practice in New England, but it is not applied southward due to cownose ray predation issues. On an oyster farm based in Massachusetts, oysters are grown out in cages and are then planted on the bayfloor in the Fall (Tompkins, 2017). We’d like to adopt this bottom planting method in combination with a floating bag method in our community because it is expected to be less costly and labor-intensive than our current growing methods and could very well create a more marketable product. 

Fisher et al. (2011) conducted a study in Virginia pertaining to cownose ray predation relative to bivalve ontogeny. It was shown that cownose ray predation on shellfish is limited by shell size and density and is related to the gape size and bite force of the ray. If an oyster was too large or required too much force to be broken by the ray, the oyster was discarded. It was suggested that farmed oysters should have some measure of protection until they reach a shell depth of 22-24 mm or are strong enough to withstand a force of 1,400 Newtons. This gives our study guidance because it shows that growing oysters to a certain size before bottom planting would provide some defense against cownose ray predation. Our oysters would be well above the 22-24 mm shell depth before bottom planting and should therefore not be affected by lingering cownose rays in the area before or after their migration.

Thomas et al. (2019) evaluated the effect of aquaculture gear on the growth and shape of oysters during a “finishing period” in the Chesapeake Bay. Submarket sized oysters had been grown-out in subtidal bottom cages and were then transferred to four different gear types over a four-month “finishing” period to evaluate how shell shape and product quality were affected. The four gear treatments assessed were: floating bags, a rack and bag system, a bottom cage placed in the intertidal zone, and the control treatment of oysters remaining in a subtidal bottom cage. Overall, it was found that the floating bag treatment produced the largest gains in growth and shell shape improvement, indicating that this system may be a valuable method of finishing oysters over a relatively short period. This is similar to our proposed study due to the evaluation of a combination of two different growing methods. Our project would build on this by using an opposite method of first growing out the oysters in the floating bags and then bottom planting them.

In New Brunswick, Canada, Mallet et al. (2013) had compared the growth performance of horizontal rope-grown oysters and floating bag grown oysters. The results had shown that after one growing season, shell growth was 60% higher and weight gain was nearly double in the rope-grown oysters. The floating bag-grown oysters were found to have grown less due to crowding and competition for food in the water column. The rope-grown oysters in this study analogize to the bottom planted oysters in our proposed study, where the oysters would not be confined in equipment and expected to be able to grow better in the open instead of being crowded in floating bags for their entire growing span. This study shows that just using floating bags would not be optimal for oyster growth, and therefore the transfer of oysters to a more spread-out growing area with less competition from other oysters would be optimal for getting the oysters to market size.

Our project will also build on a study that is currently taking place on our oyster farm with Rutgers Haskin Shellfish Research Laboratory (RHSRL), funded through the NOAA Sea Grant project that is looking to optimize oyster seed strains that will grow well in high-salinity environments. With our proposed study looking to optimize the grow-out and gear methods of oyster farming, the results of our study could be combined with the results of the RHSRL findings, leading to a revelation of sustainable oyster farming using optimal seed strains and farming methods in our community. The results of this project would be impactful for farmers in our community, especially entry-level farmers because it would provide an outline to start up a sustainable and cost-effective oyster farm. This would be helpful because although NJ allocates great resources to industry development, there is not many advisories for technical help with starting an oyster farm. If funded, practical guidance would be offered to interested individuals.