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Tidal Powered Nursery Systems for Clam Aquaculture in Georgia Alan Thomas Shierling Todd Recicar Joe Lambrix Nelson Eller & Randal Walker

1UGA Marine Extension Service, Shellfish Research Lab 2UGA Marine Extension Service, Advisory Services, 20 Science Circle, Savannah, GA 31411-1011 715 Street, Brunswick, GA 31520 Tel: (912) 598-2348; Fax: (912) 598-2399; Tel (912) 264-7268; Fax: (912) 264-7310; Website: www.uga.edu/mariculture Website: www.marsci.uga.edu/ext/marex.html

MARINE EXTENSION BULLETIN NO NOVEMBER

ACKNOWLEDGEMENTS ABSTRACT

Financial support for the construction of three upwelling systems The hard clam, Mercenaria mercenaria aquaculture industry is a was provided by the Georgia Department of Natural . small-scale operation in Georgia. There is no commercial hatchery We wish to thank Mr. Robert Baldwin of McClellanville, South in the state, and therefore growers must import seed from hatch- Carolina and Mr. Perry Hall of St. Helena Island, South Carolina for eries in South Carolina and Florida. Imported seed must be certi- allowing us to visit and observe their tidal-powered upwellers. We fied as free of pathogens by the Georgia Department of Natural would also like to acknowledge Mike Townsend, Revis Barrow, Resources. Prior to the planting season, seed shortage is often an Tommy Brown and Alvin Floyd for their assistance in constructing issue for our growers. Typically, Georgia growers purchase seed at and testing our systems. Special thanks are given to G. Davidson a size of 8mm or larger. Clams smaller than this require a nursery and C. Ingram of the Georgia Grant College Program for their facility prior to field planting. Predators can be excluded from a editing and graphics expertise. nursery facility and seed clams have sufficient to ensure rapid growth. This can be quite labor intensive, and often mortality rates are high, however, the benefit is that smaller seed are in ready supply and are inexpensive. We examined the use of tidal-pow- ered upwelling culture systems for the nursery grow-out of hard clam seed in the tidal creeks of coastal Georgia. We detailed the construction, cost, advantages, and the operation and mainte- nance of these systems. We also conducted growth trials over the course of a one year period. It is hoped that the use of tidal upwellers will lead to an increase in clam production for the state.

TABLE OF CONTENTS

Title Page 1 Fig. 11 Temperature (ºC), dissolved oxygen (mg/l), salinity (ppt) Acknowledgements 2 and (secchi disk depth in cm) recorded for the Abstract 2 study area between October 2001 and April 2002. 18 Introduction 4 Fig. 12 Mean wet weight of seed clams (N=200) between Upweller Construction 4 October 2001 and April 2002. In December the seed Advantages of the Tidal Powered was graded and sorted into two size classes. 19 Upwelling System 6 Fig. 13 Mean shell length (± standard error) of seed clams Site Selection 7 (N=60) between October 2001 and April 2002. In December Upweller Operation & Maintenance 7 the seed was graded and sorted into two size classes. 20 Experimental Seed Growth & Survival 7 Fig. 14 Photos illustrating the growth of the clam seed from an References 25 initial 1-mm size (A), to 8+mm (B) over the winter Appendix 26-43 months. Out of an original 250,000 clams an extraordinary 246,000 were estimated to have survived (C). 21 TABLES Fig. 15 Temperature (ºC), dissolved oxygen (mg/l), salinity (ppt) and turbidity (secchi disk depth in cm) recorded for the Table 1. Sample seed prices (2001) taken by averaging prices study area between April 2001 and July 2002. 22 at four commercial hatcheries. 6 Fig. 16 Mean wet weight of seed clams (N=200) between April 2002 and July 2002. 23 FIGURES Fig. 17 Mean shell length (± standard error) of seed clams (N=60) between April 2002 and July 2002. 24 Fig. 1 Upweller design from Baldwin et al. (1995). 5 Fig. 2 Base structure of the bottom of the upweller. 7 Fig. 3 Base structure covered with 3/4” plywood. 8 Fig. 4 Base structure with details of the side construction. 9 Fig. 5 Details of side post construction. 10 Fig. 6 Design for construction of the top structure of the upweller. 11 Fig. 7 Design of the decking on the top of the upweller. 12 Fig. 8 Structural assembly of the base, sidewall, and top for the upweller. 13 Fig. 9 Top structure with swing gates in funnel. 14 Fig. 10 Final assemblage of the upweller. 15

Georgia’s strong tidal currents can be beneficial by providing the INTRODUCTION required to run an upweller system.

Marine clam farming techniques developed in other parts of the Currently, Georgia clam farmers are required to a larger seed United States generally do not well in Georgia. This is be- size than farmers in other states. Experimental planting of clams cause Georgia has the greatest tidal along the eastern less than 6 mm in size utilizing a variety of grow- out techniques United States and Gulf of Mexico coastlines with the exception of has resulted in 100% mortality (Walker & Hurley, 1995). Typically upper coastal . Georgia’s average of 6-7 feet seed are purchased at a size of 8-10 mm and are raised in mesh results in strong tidal currents which preclude local clam farmers bags placed on the river bottom. Once they reach a size of 25 mm, from using common clam growing techniques. In Florida, which they are planted out in bottom plots where they grow until they has an average tidal range of only 1-2 feet, small 2-mm seed clams reach a harvest size of 45 mm. A crop requires approximately 18 are placed in wooden boxes filled with sand (Vaughan & Creswell, months in the field before they reach harvestable size. Acquiring 1989). Boxes are covered with a mesh top which allows to sufficient 25-mm seed from a commercial hatchery is difficult flow through the boxes and excludes predators. These boxes are because they are expensive and usually in short supply. Tidal- then placed on bottoms, where clams are allowed to grow powered clam nurseries offer a solution to this problem. to market size. When growers attempted to use this technology in Georgia, the sand and clam seed were sucked out of the box by strong currents, and the boxes floated to the surface. Other clam UPWELLER CONSTRUCTION farming techniques developed for different areas of the United States and the world have met with a similar fate when subjected to With funds (State Shellfish Lease Revenue) from the Coastal Georgia's and currents. Resources Division of the Georgia Department of Natural Re- sources (GADNR), the University of Georgia's Marine Extension The nursery phase (i.e., between hatchery and field grow-out) of Service adapted tidal-powered clam nursery technology for clam culture is typically the most difficult part to accomplish in an Georgia clam growers. Originally developed in Maine, the model economically feasible manner. At this size it is critical to protect was subsequently used in South Carolina (Baldwin et al., 1995) before the vulnerable seed while providing sufficient food and oxygen for being modified for Georgia. The model’s basic design consists of a growth and survival. Recent research has proven that upwellers floating tank structure with a wide scoop at the end, which directs are the optimal way to culture small shellfish seed through the incoming tidal water up into suspended bins that hold the seed nursery phase (Appleyard & Dealteris, 2002). This technique secured on a screen (Fig. 1). The water moves up through the involves forcing plankton-rich up through a partially seed mass, passes out into a collecting trough above, and exits at the fluidized bed of shellfish seed. Many upwelling designs have been rear of the unit. These systems are anchored in the river and turn developed. Some involve moving water through the system with with the , so the scoop always faces the tidal flow. They also compressed air and electrical devices. Many of these systems are require ample area to rotate with the turning of the tide. Because expensive to purchase and operate. Here in Georgia tidal power of this, they must be moored in open areas so as not to hinder presents an attractive alternative. Instead of being an impediment, boat traffic.

Fig Upweller design from Baldwin et al ()

We modified this design, so that it would better suit conditions in construct and operate. Since it is powered by tides, it has no Georgia. Our upweller has two scoops, one on each end of the or costs, and it is also environmentally friendly. It can be system. This allows the nursery system to be anchored in small anchored in a stationary position in small tidal creeks, or it can be tidal creeks so that it remains stationary. It can also be attached attached to exiting pilings or docks, such as those found in alongside exiting pilings or docks, such as those found in marinas. marinas. It does not require a special permit or lights. The upweller Figures 2-10 illustrate the construction of our upweller design. Further can also hold a large number of seed in a small space where they drawings and a detailed material list and cost estimate are pro- can be inspected easily. The floating dock provides extra vided as an appendix. The estimated cost per unit in 2003 is $2,998. It workspace for the operation and maintenance of the system. By requires approximately 160 man-hours to construct the system. attaching lockable doors over the central tank area, the seed can be protected from theft, vandalism and predation by otters and ADVANTAGES OF THE TIDAL minks. The system is also mobile and can be moved to another location if conditions become unfavorable. Because it is capable POWERED UPWELLING SYSTEM of raising seed from a size of 1 mm, the problem of limited seed availability is reduced. Finally, 1 mm-clam seed is less expensive There are many advantages to using this type of upwelling system than 8-mm seed (Table 1), and therefore offers growers the in Georgia. First of all, the system is relatively inexpensive to potential to increase their production levels.

Table Sample seed prices () taken by averaging prices at four commercial hatcheries

Mesh Size Clam size Clams/liter $ per

       

Figure Base structure of the bottom of the upweller

 Figure Base structure covered with /” plywood

Figure Base structure with details of the side construction

Figure Details of side post construction

Figure Design for construction of the top structure of the upweller

Figure  Design of the decking on the top of the upweller

Figure Structural assembly of the base sidewall and top for the upweller

Figure Top structure with swing gates in tunnel

Figure Final assemblage of the upweller

SITE SELECTION gently, immerse them in freshwater, and allow to air dry. It is advisable to have replacement bins to use while the other bins are going through a cleaning cycle. In the summer months, when Selecting a suitable site to deploy the upweller is critical. In terms fouling organisms are abundant, cleaning is required once per of , the maximum growth will occur where the week. In winter, once per month should suffice. Once a year the salinity ranges from 25-35‰, the temperature from 20-28ºC /68 upweller should be removed from the water entirely for a compre- 82ºF, and where dissolved oxygen levels are greater than 4mg/L hensive cleaning. The best time for this is during the warmest (Ansell, 1968; Eversole, 1987; Chesapeake Bay Program, 1987; Lorio summer months just after the clams have been planted in the & Malone, 1995). Any deviation from the optimal salinity range field. can reduce the clams’ tolerance for high temperatures. Conversely, optimal temperatures enhance the clams’ tolerance to unfavor- All shellfish do not grow at the same rate. To ensure the highest able salinities. The upwelling system requires a water current of at survival and growth rates, it helps to periodically sort and grade least 0.5 knots to open the doors inside the scoop ends. However, the seed into similar size classes. Slow-growing seed will do much a faster current speed is desirable. The current should not be so better if separated from the more competitive larger clams fast that causes the seed to bounce on the bin screens, which (Baldwin et al., 1995). Additionally, the larger seed should be placed reduces their ability to filter plankton, and thus inhibits growth into a bin with a larger mesh screen bottom, which allows greater rates. In Georgia, soft muddy substrates predominate. In order to water flow to the seed. The number of bins should be increased reduce the amount of siltation in the upweller system, a depth of whenever the seed size doubles. Growers should pay close atten- 10-15 feet at low water is advisable. Finally, it is wise to choose a tion to this before initially stocking the upweller (e.g., if two bins site away from intense wave action, boat , agricultural are initially filled, by the time they have reached planting size a runoff and frequent boat traffic. total of eight bins will be filled). UPWELLER OPERATION EXPERIMENTAL SEED & MAINTENANCE GROWTH & SURVIVAL

Seed should be purchased and placed into the upweller bins In Georgia, clam grow fastest in spring and fall and slowest during early in the growing season. Once in place, the seed should be the winter months. Summer growth rates fall somewhere in inspected visually for the presence of predators (crabs) as regu- between. The upweller was placed in a tidal creek in McIntosh larly as possible. Fouling organisms (e.g., sea grapes) should be County, Georgia at a depth of about 20 ft. The water was sampled removed regularly from the system (upweller bottom and sides, regularly for turbidity with a secchi disk, dissolved oxygen with a bin mesh, and weed screen), because they compete for food and probe, temperature with a thermometer and salinity with a also will restrict the flow of water to the seed. The best cleaning refractometer (Fig. 11). The upweller was stocked with 250,000 1- technique for the delicate bin mesh bottoms is to brush them mm seed. Every two weeks, three sets of 200 clams were randomly

selected and weighed to determine mean wet weight (Fig. 12). On upweller during . Mortalities may have been reduced each occasion, 60 clams were also randomly selected and their somewhat by stocking the upweller bins less densely. shell length measured (longest possible measurement, i.e., ante- rior-posterior) under a dissecting scope. Six months later in April Based on these experiments it is not recommended that clams 2002, the survival rate was 98% with 66% (estimated by volumetric remain in the upweller systems in the warmest summer months. displacement) of the clams averaging 8.43 mm (± 0.16 S.E.) and If this upweller system can be used to successfully raise two 33% averaging 7.55 mm (± 0.10) (Fig. 13). Figure 14 illustrates the batches of seed per year in coastal Georgia, then we recommend growth and survival from the experiment’s initiation to its termina- purchasing seed and stocking the upweller in early-mid Septem- tion. Although growth was slow over these winter months, the ber, and again in mid-late March. experiment showed that clams could be grown successfully in the upweller at this time of the year with high survival rates.

The experiment was started again in April 2002, when another batch of 250,000 1-mm seed were placed into the upweller. Water quality (Fig. 15), mean wet weight (Fig. 16), and shell length (Fig. 17) were again monitored as before. Growth was much more rapid at this time of year with clams reaching a planting size in half the time it took over the winter months. However, the clams’ survival rate was very low with approximately 67,000 (26.4%) remaining at the end of July 2002. In May approximately 230,000 clams were alive, but this number was dramatically reduced to 83,000 in June. Several stressor factors may have contributed to the high mortali- ties observed during June including higher water temperature, which climbed to 28ºC in June. Water temperature peaked at 30ºC in July 2002. Dissolved oxygen levels were consistently low throughout this experimental period. They fell below the recom- mended level of 5mg/L, dropping from 3.72 to 2.4 mg/L between May and June 2002. In a 48-hour period prior to the June sam- pling date, approximately five inches of fell. This resulted in a much reduced salinity, down from 32 ppt in April and May to 20ppt. In addition, predatory crabs, fouling organisms, and bacte- ria were much more abundant in the growing bins at this time of year. A combination of these effects is likely responsible for the high mortality rate. Effects probably were intensified in the

 Temperature (C) DO (mg/l) Salinity (ppt) Turbidity (inches)

60

50

40

30

20

10

0 4-Oct-01 4-Nov-01 4-Dec-01 4-Jan-02 4-Feb-02 4-Mar-02 4-Apr-02

Fig Temperature (ºC) dissolved oxygen (mg/l) salinity (ppt) and turbidity (secchi disk depth in cm) recorded for the study area between October and April

35

30

25

20

15

Wet Weight (g) 200 Clams 10

5

0 04-Oct-01 18-Oct-01 01-Nov-01 15-Nov-01 29-Nov-01 13-Dec-01 27-Dec-01 10-Jan-02 24-Jan-02 07-Feb-02 21-Feb-02 07-Mar-02 21-Mar-02 04-Apr-02 18-Apr-02

Fig Mean wet weight of seed clams (N) between October and April In December the seed was graded and sorted into two size classes

9

8

7

6

5

4

3 Mean Shell Length (mm) ± Standard Error Mean Shell Length (mm) ± 2

1 4-Oct- 18-Oct- 1-Nov- 15-Nov- 29-Nov- 13-Dec- 27-Dec- 10-Jan- 24-Jan- 7-Feb- 21-Feb- 7-Mar- 21-Mar- 4-Apr- 18-Apr- 2001 2001 2001 2001 2001 2001 2001 2002 2002 2002 2002 2002 2002 2002 2002 Date

Fig Mean shell length (± standard error) of seed clams (N) between October and April In December the seed was graded and sorted into two size classes

A C

Fig Photos illustrating the growth of the clam seed from an initial mm size (A) to mm (B) over the winter months Out of an original clams an extraordinary were estimated to have survived (C)

B

Temperature (C) DO mg/L Salinity ppt Turbidity

35

30

25

20

15

10

5

0 Apr-02 May-02 Jun-02 Jul-02

Fig Temperature (ºC) dissolved oxygen (mg/l) salinity (ppt) and turbidity (secchi disk depth in cm) recorded for the study area between April and July

40

35

30

25

20

15 Wet Weight (g) 200 Clams 10

5

0 20-Apr-02 20-May-02 20-Jun-02 20-Jul-02

Fig Mean wet weight of seed clams (N) between April and July

10

9

8

7

6

5

4

3 Mean Shell Length (mm) ± Standard Error Mean Shell Length (mm)

2

1 20-Apr-02 20-May-02 20-Jun-02 20-Jul-02

Fig  Mean shell length (± standard error) of seed clams (N) between April and July

REFERENCES

Ansell, A. D., 1968. The rate of growth of the hard clam Vaughan, D.E. and R.L. Creswell, 1989. Field grow-out tech- Mercenaria mercenaria (L.) through out the geographical niques and technology transfer for the hard clam, range. Conseil Permanent International pour l'Explor- Mercenaria mercenaria. Aquaculture Report Series, ation de la Mer, Journal du Conseil 31(3): 364-409. Florida Department of Agriculture and Consumer Services, Tallahassee, Florida. 42pp. Appleyard, C.L. and J.T. Dealteris, 2002. Growth of the north- ern quahog, Mercenaria mercenaria, in an experimental- Walker, R.L. and D.H. Hurley, 1995. Biological feasibility of scale upweller. Journal of Shellfish Research, 21 (1): 3-12. mesh bag culture of the northern quahog Mercenaria mercenaria (L.) in soft-bottom in coastal Baldwin, R.B., W. Mook, N.H. Hadley, R.J. Rhodes and M.R. of Georgia. The University of Georgia Marine DeVoe, 1995. Construction and operations manual Extension Bulletin No. 16, August 1995. for a tidal-powered upwelling nursery system. South Carolina Sea Grant Consortium, Charleston. 44pp.

Chesapeake Bay Program, 1987. "Habitat Requirements for Chesapeake Bay Living Resources." Chesapeake Bay Living Resources Task Force.

Eversole, A.G., 1987. "Species Profiles: Histories and Envi- ronmental Requirements of Coastal Fishes and Invertebrates (mid-Atlantic): Hard Clam." U.S. Fish and Service Biological Report 82(11.75). U.S. Army Corps of Engineers TR EL-82-4.

Lorio, W.J and S. Malone, 1995. Biology and culture of the northern quahog clam (Mercenaria mercenaria). Southern Regional Aquaculture Center. SRAC publi- cation Number 433.

APPENDIX

TIDAL POWERED UPWELLING SYSTEM CONSTRUCTION DRAWING LIST

DWG = Drawing DWG M-16: Final Assembly DWG B-1: Base Structure Detailed Material List and Cost Estimate DWG B-2: Item #2 From DWG B-1 DWG B-3: Items 1, 3, & 4 From DWG B-1 DWG B-4: Base Structure Plywood DWG S-5: Sidewall Structure DWG S-6: Detail B & Item 8 From DWG S-5 DWG S-7: Items 9 & 10 From DWG S-5 DWG S-8: Sidewall Panel Layout DWG S-9: Item 14 Details From DWG S-8 DWG S-10: Items 11, 12 & 13 From DWG S-8 DWG T-11: Top Deck Structure DWG T-12: Top Structure Decking DWG M-13: General Arrangement-Misc Items DWG M-14: Item 24 From DWG M-13 DWG M-15: Items 19, 20, 21, & 22 From DWG M-13