TOGA’s Oyster Growth and Longevity Study
as of July 2013
We are now close to concluding our final counts and measurements of the Growth and Longevity Study’s four different oyster strains. This study consisted of two Triploid (sterile) oyster strains (LOLA & DEBY) and two Diploid (fertile) oyster strains (LOLA & DEBY). The volunteers counted and measured their oysters three times a year. We started this out as a 3 year study; predicting that as the timeline for a 3 inch market size average (based on the native wild growth data). Incredibly, some strains achieved the 3 inch size in 7 – 8 months! And surprisingly, fifteen months after deployment, most sites had achieved or surpassed the 3 inch market size with very low mortality rates. So we had to rethink our study plans with the unexpected results of these special, genetically selected, commercial strains spawned by VIMS.
With our market size goal met we decided to study what makes one site outperform others in growth. We know the water flow around the oysters plays a big part in development, as well as food source and salinity. While salinity can be checked very simply, food source and water flows are not easily monitored. Some high growth volunteers checked their water flow at their dock during incoming and outgoing tides and we are currently looking over that data. Another item researched was Google mapping sites to see the different characteristics and how they might influence growth. We will touch on the interesting results with a summary of the study soon after its conclusion.
It was collectively decided (even though our goal of 3 inch averages came early) to push on and review the other segment of the study a little more: the mortality rate of these study oysters. We experienced very little mortality in the first year; with less than 10% overall average. As the second winter came and went we saw some expected increase in loss. But the biggest surge in mortality happened in early summer; especially in the lower salinity sites, probably due to the heavy spring rains. Still the numbers are pretty respectable compared to the oysters available ten years ago.
With 2013 July’s reports (a month shy of two years of our G&L study) we haven’t seen the huge jumps in length as was experienced in the first year. Many now average 4.5 inches. Instead, what we see is the girth (thickness or cupping) of some of these oysters steadily increasing. These results lead us to another question. Since we are comparing Triploid versus Diploid (with slightly different growth rates) which oyster in November carries the most weight and by how much?
It wouldn’t be fair to do this experiment in summer months as the Triploid retains all its weight (being sterile) and the Diploid loses a lot of body mass due to spawning. But in November the Diploid should have regained most of its weight. So for another study within a study, we have selected sites where volunteers are going to donate six oysters so we can measure meat yield. If you eat your oysters in the winter months, is there a huge advantage to growing Triploids over Diploids in meat yields? Is the difference of meat produced by the Triploid so considerable that it outweighs (as some gardeners advocate) growing Diploids for spawning and passing their seed along to help in some repopulation?
With 52 volunteers between the G&L Four strains oyster study and the other T & T (Triploid versus Triploid study) we have learned a lot. But we also have as many questions as we have answers.
All fun stuff! Through communicating with our volunteers we learned about plastic Aussie cages and the excessive fouling than occurs with them versus the wire cage Vic Spain developed (wire downunder). Fouling was different at different sites at different times. And some plastic Aussie cages failed due to rapid growth of oysters. We got reports of heavy barnacle strikes, sea grapes, sponges, oyster strike, many kinds of different algae and growth. Also received stories of small crabs getting into cages, becoming big crabs devouring study oysters. Plus many strange creatures VIMS helped us identify. And much, much more has been shared. After November’s count when all data is in, we will prepare a final report of growth, meat weight, mortality rates and finally the disclosure of the different strains for all to see.
Our sincere appreciation goes out to our Growth and Longevity volunteers for all the hard work. We surely couldn’t have amassed all this data and accomplish this significant oyster study without you.
Stay tune for the final G&L results and possible upcoming studies performed by TOGA volunteers.
Brian Wood/ Lynton Land