66 MARCH 2017 • WORLD AQUACULTURE • WWW.WAS.ORG is working to develop best grow-out methods for single oysters. Previous work by Moroney and Walker (1999) found that placing oysters on the bottom during the recruitment period reduced the amount of fouling, but the labor required to keep bags from silting in and suffocating oysters is time consuming. Therefore, we evaluated the use of oyster cages and how they performed in Georgia, specifically during the warmer months (April-October) that place the most stress on oysters. We evaluated the field performance of approved gear (2×2 cages, and Low Pro cages) within the intertidal and sub-tidal zone to determine utility for oyster aquaculture. The effect of grow-out bags with different mesh size on oyster growth and survival was also evaluated. To examine the affect of cages and bag mesh size, we set out 11,760 diploid oysters that were 2-mm spat in July 2014. Oysters had a mean height of 45 mm and were randomly selected and stocked at 245 per grow-out bag. Four mesh sizes were evaluated (4, 6, 9, and 12 mm) and four bags of each mesh size were placed into each cage. We set out 12 cages, nine 2×2 bottom cages and three Low Pro cages. In the intertidal zone, at approximately -0.3 m mean lower low water (MLLW), three 2×2 cages were set on the bottom, three 2×2 cages modified with a large buoy and anchored to allow cages to move off the bottom by ~1m at high tide and rest on the bottom at low tide, and three Low Pro cages were set out (Fig. 2). Three 2×2 cages were set on bottom in the sub-tidal zone at a depth greater than 3 m at MLLW. All cages were manufactured by the Chesapeake Bay Oyster Co., and were deployed on 15 April 2015. After two weeks, oysters were measured and dead oysters Shellfish growers in Georgia want to diversify shellfish aquaculture, currently dominated by hard clam Mercenaria mercenaria, to include eastern oysters Crassostrea virginica. Oyster harvesting has been a way of life in Georgia for over 100 years and, from the early to mid-1900s, supported a robust canning industry. Since the end of the oyster canning industry, the commercial oyster harvest in Georgia has focused on the bulk collection of wild oyster clusters intended for traditional local markets and oyster roasts. Georgia has a short coastline of approximately 160 km that is defined by several ocean inlet systems and expansive salt marshes. Georgia is a prime area for oyster aquaculture because coastal ecosystems are intact with excellent water quality and high primary productivity. Currently one of the greatest limitations to industry expansion is availability of hatchery-produced oyster spat. The demand for single oysters continues to grow throughout the US, specifically in the southern US from North Carolina to Texas, and this has prompted the industry in Georgia to push for sustainable oyster aquaculture. The price for high-quality raw-bar grade oysters continues to rise nationally as a result of a decreasing supply and growth in the consumer market (Brake et al. 2003, Jacobsen 2007). Increased consumer demand for “boutique” (50-mm) oysters and a sub-tropical climate provides a great opportunity for shellfish growers in Georgia to enter the market as significant producers of single premium oysters. To help facilitate oyster aquaculture, the University of Georgia Marine Extension and Georgia Sea Grant is providing oyster spat from its hatchery on Skidaway Island (Fig. 1) in Savannah, GA, and Evaluation of Cage Aquaculture on Growth and Survival of Eastern Oysters in Georgia Thomas H. Bliss, Justin Manley and Rob Hein FIGURE 1. Study site on Skidaway Island, Chatham County, GA. FIGURE 2. Intertidal cages at low tide in the Skidaway River. (Photo: UGA Marine Extension Georgia Sea Grant)
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