Tidal Powered Upwelling Nursery Systems for Clam Aquaculture in Georgia Alan Power Thomas Shierling Todd Recicar Joe Lambrix Nelson Eller & Randal Walker 1UGA Marine Extension Service, Shellfish Research Lab 2UGA Marine Extension Service, Advisory Services, 20 Ocean Science Circle, Savannah, GA 31411-1011 715 Bay 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 Resources. 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 Sea 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 food 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 turbidity (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 energy required to run an upweller system. Marine clam farming techniques developed in other parts of the Currently, Georgia clam farmers are required to plant a larger seed United States generally do not work well in Georgia. This is be- size than farmers in other states. Experimental planting of clams cause Georgia has the greatest tidal amplitude 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 Maine. Georgia’s average tidal range 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 water 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 lagoon 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 tides 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 mass secured on a screen (Fig. 1). The water moves up through the involves forcing plankton-rich seawater 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 tide, 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 fuel Georgia. Our upweller has two scoops, one on each end of the or electricity 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.