As in the first phase of the demonstration project, oysters were also cultured at the UF experimental lease off Cedar Key in the second phase. On June 7, 2017, diploid and triploid oyster seed were stocked into 14 mm mesh Vexar bags at a density of 150 per bag. The effects of float design (type and bag placement) on oyster production and fouling control were further tested in these field trials. See the June 2017 news article for more information on gear types and management practices evaluated. In addition, two commercially available, biocide-free antifouling coatings were applied to some of the oyster bags. To document growth and survival during the culture period on a bimonthly basis, two replicate bags from each of the treatments, a total of 20 bags, were sampled on July 26, with the remaining two replicate bags sampled on September 12. During each sample period, 50 oysters from each replicate bag were measured for shell dimensions (height, length, width) and weighed (total or whole weight). Live and dead oysters in each bag were counted to determine survival. Diploid (2N) and triploid (3N) oysters were photographed to document their appearance at the time of sampling. Results from each sample period follow.
Five long lines holding 40 experimental bags supported by different float designs at the UF experimental lease in the Dog Island Aquaculture Use Zone off Cedar Key.
July 2017 Sample Period (10 months post-spawn, 7 weeks growout)
After 7 weeks of growout in 14 mm mesh bags, shell height (SH) of triploid oysters (avg 56 mm) was greater than diploid oysters (avg 47 mm). Similarly, triploid oysters (avg 35 grams, total weight, TW) weighed more than diploid oysters (19 grams). However, average survival of diploid (92%) and triploid (94%) oysters was similar. Oysters cultured in bags supported by different floats (4.5” square versus bullet) and placement (square floats attached to sides of bags versus top of bags) were also sampled. Regardless of ploidy type, oysters in bags supported with square floats attached to the top of bags were larger and heavier (2N avg – 49 mm SH, 23 g TW; 3N avg – 59 mm SH, 40 g TW) than oysters in bags supported by square floats on the sides of bags (2N avg – 46 mm SH, 17 g TW; 3N avg – 54 mm SH, 32 g TW) and oysters in bags supported by bullet floats (2N avg – 46 mm SH, 17 g TW; 3N avg – 56 mm SH, 32 g TW). Survival of triploid oysters (91-94%) was similar across float designs, whereas the lowest and highest survivals obtained in this sample period were of diploid oysters in bags supported by square floats placed on top of bags (88%) and in bags supported by square floats placed on sides of bags (97%). Antifouling coatings did not seem to influence oyster production at this time.
Diploid (2N) and triploid (3N) oyster growth (shell height, top left; total weight, top right) and survival (bottom) in bags supported by different float designs after seven weeks in growout, where B = Bullet floats, SS = Square floats placed on Sides of bags, and ST = Square floats placed on Tops of bags.
An oyster bag with a biocide-free antifouling coating (left), and oyster bags with square floats attached to sides after seven weeks of growout.
September 2017 Sample Period (12 months post-spawn, 14 weeks growout)
After 14 weeks of growout in 14 mm bags, shell height of triploid oysters (avg 68 mm) continued to exceed that of diploid oysters (avg 53 mm). Likewise, total weight of triploid oysters (avg 82 g) was greater than and doubled that of diploid oysters (avg 40 g). As was seen in the first sample period, average survival was similar in diploid (83%) and triploid oysters (84%). However, mortalities of 9-10% occurred between the first and second sample periods. With respect to float design, both diploid and triploid oysters in bags supported with square floats attached to the top of bags were slightly larger (2N avg – 56 mm SH, 3 N avg – 73 mm SH) than oysters in bags supported by square floats on the sides of bags (2N avg – 51 mm SH, 3N avg – 71 mm SH) and oysters in bags supported by bullet floats (2N avg – 52 mm SH, 3N avg – 68 mm SH). Note that triploid oysters were reaching 75 mm (3 inches) in size after 14 weeks of growout. Weight of oysters was variable across the float design treatments. The heaviest oysters (3N avg – 94 grams) and lightest oysters (2N avg – 31 grams) were in bags supported with square floats attached to the sides of the bags. Survival of oysters was similar across the float design treatments. Interestingly, triploid oysters cultured in bags without an antifouling coating were larger (72 mm SH) and heavier (91 grams), than those cultured in bags with antifouling coatings (coating A – 68 mm SH, 79 g TW; coating B – 66 mm SH, 75 g TW); survival of triploid oysters did not seem to be affected by coating treatments.
Diploid (2N) and triploid (3N) oyster growth (shell height, top left; total weight, top right) and survival (bottom) in bags supported by different float designs after 14 weeks in growout, where B = Bullet floats, SS = Square floats placed on Sides of bags, and ST = Square floats placed on Tops of bags.
Biofouling of both oysters and bags was apparent in this sample period. Barnacles were the prevalent organism found on oysters regardless of ploidy type or float design. The Dog Island lease location is a high salinity site with monthly averages of 29 ppt obtained in June and 32 ppt in July. Salinity data was not available in August. All bags with floats attached to the sides, regardless if square or bullet shaped, were flipped weekly. In June, bags with floats attached to the top of bags were flipped weekly and aerial dried for about six hours prior to being flipped back into the water. Beginning in July because of the higher air temperatures, these bags were flipped late in the afternoon, allowed to aerial dry overnight, and then flipped back in the morning, for about 16-18 hours of drying. Nonetheless, these methods were not adequate in controlling the successive barnacle sets that occurred at this site during the summer months. There were apparent differences in the amount of biofouling found on the bags with different float designs. Bags with floats attached to the top had more fouling, particularly barnacles, and were much heavier than bags with floats attached to the sides.
Samples of oysters after 14 weeks in 14 mm Vexar bags supported with different float types and placement on bags.
Vexar oyster bags supported with different float types and placement on bags after 14 weeks of culture at the UF experimental lease off Cedar Key.