Evaluation of Summer Oyster Crassostrea virginica Growth and Survival using Cage Aquaculture in Georgia

Thomas Bliss*, Justin Manley, and Robert Hein
University of Georgia
Marine Extension Service
Shellfish Research Laboratory
20 Ocean Science Circle
Savannah, GA 31411
tbliss@uga.edu

Aquaculture of single oysters (Crassostrea virginica) in Georgia is on the rise and survival during the summer months (May-October) is critical for success.  Current regulations prohibit the use of floating gear so a small scale study was undertaken to evaluate the use of cage aquaculture, which are allowed.  Two type of cages; 2Hx2W bag cages and double stack LowPro's (Chesapeake Bay Oyster Co.) were evaluated along with and four mesh size (4,6,9, and 12mm). Three 2Hx2W bag cages and three double stack LowPro cages were set on bottom in the inter-tidal zone, three 2Hx2W bag cages, anchored and made buyout, were set in the inter-zone, and three double stack LowPro were placed sub-tidally on bottom.  

Oysters used were wild collected spat from summer 2014 and had a mean height of 44.6mm when set out in April 15, 2015. Two hundred and fifty oysters were placed in each bag and each cage received four bags of each mesh size randomly assigned to the top and bottom sections.  Cages are pulled during the first week of each month (May - November) and 28 oysters from each bag were measured to the nearest mm (height, length, and width) to examine growth and all oyster counted for survival. Through July, semi-buyout oysters had the most growth of 12.7mm, followed by sub-tidal, intertidal LowPro and intertidal 2x2 cages with 11.9mm, 11.6mm, and 10.4 mm, respectively.  Survival was similar with semi-buoyant highest with 79% survival followed by intertidal LowPro, sub-tidal, and intertidal 2x2 with 72%, 71%, and 36%, correspondingly.  Intertidal oysters had similar survival 57%-67% among all mesh sizes with 4 mm and 6 mm being the highest at 63% and 67%, respectively.  Sub-tidal  oysters had higher survival in large 9 and 12mm bags with 80%-81%, than small mesh  bags which have 62%-71% survival.

To date, it seems that tidal placement and bag mesh size affect survival and that overall semi-buoyant cages have the best growth and survival during the summer.  This data suggest that single oyster aquaculture is possible in Georgia and that gear selection and placement is critical to success.  The success seen in semi-buoyant cages increases the need to examine the use of floating gear (floating bages, OysterGro) in the state.