Expanding sustainable shellfish aquaculture: Optimizing growth and survival in a bay scallop nursery system

View the project final report

• 2016 annual report

Commodities

• Animals: fish

Practices

• Animal Production: general animal production

The bay scallop (Argopecten irradians), an Atlantic marine bivalve found in coastal New England waters, which has historically supported a significant fishery. However, since the 1980’s the commercial fishery has been in decline due to losses in nursery habitat (eelgrass beds), overfishing and coastal water quality degradation. Bay scallops are a high value, sustainable product which require very similar growing techniques to shellfish that are currently cultured, such as oysters and clams. Shellfish farmers throughout New England are seek complementary species to grow in order to diversify risk and increase revenue. Additionally, expanding shellfish aquaculture will provide excellent ecosystem benefits by increasing water clarity and reducing impacts of eutrophication. However, bay scallop culture techniques are still rudimentary, and efficiency could be significantly improved if further investigations were done on new technology and aquaculture methods. In 2015, Ward Aquafarms constructed a pilot-scale nursery system utilizing a unique floating downweller design which significantly improved growth and survival as compared to existing bay scallop nursery systems. We propose to investigate differences in growth, survival, and food availability in relation to flow rates, initial stocking densities and mesh sizes. The results of the proposed project will allow Ward Aquafarms, in conjunction with Cape Cod Cooperative Extension to make recommendations to farmers and resource managers throughout New England on how best to farm bay scallops to expand jobs for shellfish farmers while promoting sustainable farming techniques.

Proposed solution

What is the best way to grow bay scallop seed from the hatchery (0.75 mm) to a size ready for growout (20 mm) with the fastest growth rate and the highest survival?

1. In order to maximize bay scallop nursery growth and survival, we will evaluate four different stocking densities over the entire nursery phase, in order to compare flow rates, growth, survival and food depletion in a floating downweller system.

This objective will be achieved by comparing four different stocking densities, over four different mesh sizes throughout the nursery phase of the bay scallop production cycle. As the scallops grow, every 14 days we will calculate flow rates and nutrient availability, and evaluate these variables with respect to growth and survival.

2. All results and techniques must be made public so all shellfish farmers in the northeast region can begin to grow bay scallops on their farms as well.

We will communicate all findings to the wider aquaculture community by utilizing farmer workshops, online web sources, and conferences to make findings readily available to farmers who would like to grow bay scallops.

Background information

In bay scallop aquaculture, maximizing growth in the intermediate nursery stage in year one is essential for getting an economically viable product to market (Milke et al., 2006). Bay scallop seed is currently available from several hatcheries in the northeastern United States, though intermediate nursery systems to grow the seed from the size supplied by the hatchery (0.75 mm) to a viable growout size (20 mm) are inefficient in terms of labor, growth rates, survival, accessibility and stocking densities (Lefcheck et al., 2014; Leverone et al., 2010). Land based downweller and raceway systems as well oyster FLUPSY’s, have been tried to produce bay scallops with limited success, reducing the economic viability of growing bay scallops commercially in New England (Karney et al., 2010; MacKenzie, 2009). Land based raceways and downwellers are labor and cost intensive as intermediate nursery options, and are nutrient limited compared to floating systems (Magnensen et al., 2010; Milke et al., 2006). The advent of the floating upweller, such as the FLUPSY, revolutionized oyster aquaculture in and led to the success of the industry today. However the FLUPSY was not designed for bay scallops, which need room to spread out and which can swim and easily escape out of the system (Mackenzie, 2009).

In 2014, Ward Aquafarms acquired bay scallops for the first time and the bay scallops were put in a standard oyster FLUPSY, stocked in 4 silos, each measuring 2 feet by 2 feet wide and 2.5 feet tall. The main feature differentiating bay scallops from other shellfish is that most shellfish species are completely sedentary (oysters, clams, etc.), while bay scallops can swim freely in search of best flow and place to attach. Since the upweller moved water up and out of the silos, the bay scallops were prone to swim with the flow of the upweller, and escape out of the silo. Mesh could be placed on the outflow to prevent escapement, but that led to a significant decrease in flow, reducing food and nutrient availability. The silos were also a single layer, which forced the scallops to be piled on top of each other. The scallops on top had better access to nutrients, and grew faster than the scallops underneath, which resulted in overcrowding and stunted growth. The scallops on top grew at a rate of 0.29 mm/day compared to 0.04 mm/day for the scallops underneath which did not have sufficient access to food or space.

In 2015 Ward Aquafarms designed a custom floating downweller to more efficiently grow bay scallops and overcome the nursery challenges presented using the FLUPSY. The downweller pumps water laterally into 6 constructed silos (3’W x 3’L x 4’H); 3 on each side of a central trough. Each silo has a 4” opening at the top to allow water to enter with an attached 36” downpipe to pull water from below the waterline to avoid contaminants on the water surface. Each silo drains into the central trough through a 3”H x 36”L gap at the bottom of the silo, with a 3/4 hp pump attached to the middle of the central trough, yielding approximately 150 gal/min per silo. By pumping water down through the silos, instead of up like the FLUPSY, the scallops cannot swim out of the system. Each silo accommodates up to 6, 3’W x 3’L x 4”H trays stocked with scallops. Each silo now has six mesh trays instead of one mesh bottom, increasing the surface area to 324ft² compared to the FLUPSY’s 32ft².

Preliminary results suggest that the new design gave sufficient surface area for a large number of scallops to grow from the size from the hatchery through 20 mm, when they were ready to be put into growout gear. The scallops in the downweller grew at 0.34 mm/day, 0.39 mm/day, and 0.29 mm/day (each two week period, respectively) for the six weeks preceding being moved out into growout gear. We know the poor growth and survival that resulted from utilizing a FLUPSY in 2014, and preliminary data from the downweller in 2015 indicates that it may be a viable nursery system. However, there are many parts of the nursery downweller which must be investigated to increase the efficiency of the system, which is the purpose of the proposed project. Optimizing survival and growth in the nursery phase would significantly increase the viability of bay scallop aquaculture, which will benefit both farmers as well as ecosystems throughout the Northeast.

Methods

For this project, the first step is to construct a second downweller at Ward Aquafarms, with dimensions identical to the downweller used in 2015. This is due to the fact that the downweller has 6 silos, with 3 on either side; and in order to compare stocking densities throughout the nursery stage, we will need a minimum of 3 silos per treatment in order to get an average and compare treatments statistically. If we only use the downweller from 2015, that will mean 3 silos on the left and 3 silos on the right, meaning only comparing 2 densities at a time. Additionally, as the shellfish grow, we will need to lower the densities and increase the number of trays in order to continue to compare the impact of density and mesh size. Therefore, in order to keep the densities equal as the shellfish grow, we will need to remove some shellfish from the system, thereby wasting the bay scallop seed as it is dumped outside of the nursery system. By constructing a second downweller, we will be able to compare 4 densites and flow rates at a time, and instead of dumping the bay scallop seed, we will be able to keep it growing, while determining the optimal stocking rate and growth methods over the entire nursery period. Any additional scallops at the end of the project period will be either given for free to farmers on Cape Cod for their own growout, or given free to the town of Falmouth, MA for bay scallop restoration purposes.

Briefly, the constructed downweller will be the same footprint as a standard oyster FLUPSY (8’W x 20’L), and therefore could be utilized in an identical manner as a FLUPSY for new scallop farmers. Farmers have prior knowledge of where to place a FLUPSY at their farm, how to use it, and therefore that knowledge would facilitate an easy transition to bay scallop farming as well. The downweller pumps water laterally into 6 constructed silos (3’W x 3’L x 4’H); 3 on each side of a central trough (1’W x 9’L x 5’H). Each silo has a 4” opening at the top to allow water to enter with an attached 36” downpipe to pull water from below the waterline to avoid contaminants on the water surface. Each silo drains into the central trough through a 3”H x 36”L gap at the bottom of the silo, with a 3/4 hp pump attached to the middle of the central trough, yielding approximately 150 gal/min per silo. Each silo accommodates up to 6, 3’W x 3’L x 4”H trays stocked with scallops. Each tray can be lined with different sizes of mesh, depending on what size the bay scallops are. By pumping water down through the silos, instead of up like the FLUPSY, the scallops cannot swim out of the system. Each silo now has six mesh trays instead of one mesh bottom, increasing the surface area to 324ft² compared to the FLUPSY’s 32ft².

In the spring of 2016, 575,000 bay scallops will be purchased from Muscongus Bay Aquaculture (Bremen, ME) at a size of 0.75 mm. The bay scallop seed will be stocked into all twelve silos, with one tray per silo (3’W x 3’L x 4”H), initially lined with 0.75 mm mesh. The four different stocking densities throughout the trial will be maintained at the following ratios: 8:4:2:1. For example, to start, 3 silos will be stocked at 100,000 scallops/tray (11,111/ ft²), 3 silos at 50,000 scallops/tray (5,555/ ft²), 3 silos at 25,000 scallops/tray (2,700/ ft²) and 3 silos at 12,500 scallops/tray (1,388/ ft²). We will maintain the scallops at the same stocking density ratios throughout the entire nursery period, and therefore we will be able to collect equivalent food depletion information for all size ranges. As the shellfish grow, they will be graded every 14 days to reduce densities and increase mesh size and number of trays. Three of the silos will be stocked at the values noted in Table 1 (maximum stocking density), with 3 silos stocked at 50% of the maximum density, 3 silos stocked at 25% of the maximum density and 3 silos stocked at 12.5% of the maximum density, to maintain the 8:4:2:1 stocking ratio. Once scallops reach a size of 20 mm, they will be moved out of the nursery for the growout phase.

Before stocking the silos with scallops, we will measure entering and exiting flow rates using a flow meter (Sierra InnovaSonic Flow Rate Meter). Once base flow rates have been recorded, the trays with scallops will be placed into each silo. We will then measure entering and exiting flow for each silo immediately after tray placement, and once a week for the entire nursery period (June 1 – September 1) after initial stocking to assess reduction in flow with increasing mesh and scallop size. We will also assess food availability and depletion under different stocking densities and tray configurations by measuring Chl a, and phaeopigment levels at the water entrance and exit of each silo each week at the same sampling time point (Beagle Bioproducts Inc.).

Every 14 days, all trays will be removed from each silo and all scallops will be graded on a given mesh size (3 mm, 4 mm, 6 mm, 9 mm, 12 mm and 16 mm), which is increased each grading period. Every 14 days a subsample (20 individuals) will be taken from each tray in each silo, and measured using a caliper by the research technician, and both live and dead scallops will be enumerated for survival analysis. The research technician will compare growth, survival, flow rates and food reduction assess differences in growth and survival as they relate to the four different stocking densities. All results will be compared with either a one-way or two-way ANOVA, as appropriate.

Timetable

Daniel Ward (farm owner) and Harrison Tobi (research assistant), will construct a floating downweller system in the April-May of 2016. Once the downweller has been completed, it will be placed in Fiddler’s Cove Marina (North Falmouth, MA). In June of 2016, 575,000 bay scallops will be purchased from Muscongus Bay Aquaculture (Bremen, ME) at a size of 0.75 mm by Dr. Ward. Before stocking, Mr. Tobi will measure Chl a and phaeopigment as well as water flow rate, entering and exiting each silo without trays present. Mr. Tobi and Dr. Ward will then put tray with scallops into all twelve silos at the following densities: 3 silos at 100,000 scallops/tray (11,111/ ft²), 3 silos at 50,000 scallops/tray (5,555/ ft²), 3 silos at 25,000 scallops/tray (2,700/ ft²) and 3 silos at 12,500 scallops/tray (1,388/ ft²).

Every 7 days from June-September, Mr. Tobi will measure water flow, Chl a and phaeopigment entering and exiting each silo. In week two (and every 14 days thereafter for the entire nursery period: June – September), Dr. Ward and Mr. Tobi will first grade each silo on the appropriate mesh (3 mm) and collect a subsample (20 individuals) from each tray in each silo. Dr. Ward and Mr. Tobi will count all live and dead scallops, and measure a subsample using a caliper. In weeks four, six, eight, ten and twelve, Harrison Tobi will repeat the grading and sampling procedures performed in week two, each time increasing grading mesh size to 4 mm, 6 mm, 9 mm, 12 mm, then 16 mm.

Throughout the entire nursery period (June-September) Dr. Ward, in conjunction with Mr. Tobi will then analyze the flow, food (Chl a and phaeopigment), survival and growth data for differences in growth and survival at each 2 week time point throughout the nursery cycle. We will then analyze the results for each 2 week sampling period statistically using either an one-way ANOVA (size or survival analysis), or a two-way ANOVA (size or survival vs. flow or available food resources) as appropriate for each sampling period. Once scallops reach 20 mm in size (August-September), they will be moved out by Ward Aquafarms staff into growout cages in Buzzard’s Bay for the growout phase.

Outreach plan

Following the conclusion of the nursery phase in September, Dr. Ward and Mr. Tobi will work with Josh Reitsma (technical advisor) ,who is an extension agent at Cape Cod Cooperative Extension and Woods Hole Sea Grant, to communicate the results to the broader northeastern aquaculture industry. We will most effectively communicate the results to farmers in the region through an extension bulletin, and relevant information will be included in their regular aquaculture education course. We will communicate to farmers outside Cape Cod by presenting the results at the Northeast Aquaculture Conference and Expo, which is attended by farmers, regulators, extension agents and scientists throughout the Northeast region.

Cape Cod Cooperative Extension (CCCE) is the education department for Barnstable County, and has been assisting with the editing and outreach component of this project. The Fisheries and Aquaculture Specialist for CCCE and Woods Hole Sea Grant, Josh Reitsma, has suggested several methods by which the results of this project could be made known to farmers in Cape Cod specifically. Dr. Ward will present the results at farmer workshops held by CCCE, and the MA Aquaculture Association, and he will put together the results into an information sheet which can be posted on the CCCE and Woods Hole Sea Grant websites for farmers to access. Dr. Ward will also present the results at the Northeast Aquaculture Conference and Expo, which will be held in December 2016. He will also be a guest speaker for the CCCE 8-week course, held every other year in Cape Cod. Dr. Ward will communicate all results from the project with the other farmers in the area which all operate in Buzzard’s Bay with similar culture conditions to the proposed site, and help them incorporate what was learned from this project into their farm.

Bibliography

Karney, R., Surier, A., and Leavitt, D. 2010. Nursery culture of the bay scallop. Northeast Regional Aquaculture Center.

Lapointe, G. 2013. Overview of the aquaculture sector in New England. Northeast Regional Ocean Council.

Leavitt, D. and Karney, R. 2010. Grow-out culture of the bay scallop. Northeast Regional Aquaculture Center.

Lefcheck, J.S., van Montfrans, J., Orth R.J., Schmitt, E.L., Duffy, J.E., and Luckenbach, M.W. 2014. Epifaunal invertebrates as predators of juvenile bay scallops (Argopecten irradians). Journal of Experimental Marine Biology and Ecology. 454: 18-25.

Leverone, J.R., Geiger, S.P., Stephenson, S.P., and Arnold, W.S. 2010. Increase in bay scallop (Argopecten irradians) populations following releases of competent larvae in two west Florida Estuaries. Journal of Shellfish Research. 29, 2: 395-406.

MacKenzie, Jr., C.L. 2008. History of the Bay Scallop, Argopecten irradians, Fisheries and Habitats in eastern North America, Massachusetts through northeastern Mexico. Marine Fisheries Review, 70, 3-4: 1-5.

Mackenzie, Jr., C.L. 2009. Small-scale commercial culturing of northern bay scallops, Argopecten irradians irradians, in Atlantic United States and Canada. Marine Fisheries Review. 71, 3: 46-49.

Magnesen, T., Egra, S.R., and Christophersen, G. 2010. Growth of scallop spat in raceway nursery during autumn conditions in Western Norwegian coastal waters. Journal of Shellfish Research. 29, 1:45-54.

Milke, L.M., Bricelj, V.M., and Parrish, C.C. 2006. Comparison of early life history stages of the bay scallop, Argopecten irradians: Effects of microalgal diets on growth and biochemical composition. Aquaculture. 260: 272-289.

Reitsma, J., Hollingsworth, C., Murphy, D.C., and Buttner, J.K. 2012. Aquaculture situation and outlook report 2012: Massachusetts. Northeast Regional Aquaculture Center.

Rhodes, E., Garrison, R., Morse, D., Getchis, T., and Macfarlane, S. 2005. Expanding Shellfish Culture in the NRAC Region – Constraints to existing industry expansion and an analysis of the economic feasibility of new, small-scale oyster culture businesses. Northeast Regional Ocean Council.