We asked the Drake brothers for help to build some special racks to enable us to grow oysters on trays at an unusally high height. Len set this at the maximum height where Pacific oysters survive in the wild in this area – about 300 mm above standard rack height. This means that the oysters are out of the water for much longer each day. We reasoned that this would have three effects – firstly it would reduce their exposure to the POMS virus, secondly it would expose them to sunlight and possibly also to higher temperatures, which might be beneficial (UV light can kill viruses, and the heat might be like inducing a fever to help fight an infection) and thirdly it would slow their growth (in France fast growth has been a risk for POMS virus).
Here is the design for our first experiment in the Georges river:
8000 oysters were transferred from the Hawkesbury River and placed in trays on the Georges river on 20th October 2011. These comprised 4000 adult and 4000 spat. These were divided randomly and placed across three leases, half at standard rack height (which we call “low”) and half at a height 300 mm above standard rack height (which we call “high”). We used a standard stocking density of 320 oysters per tray. Each tray is divided into 8 segments, so we put 40 oysters in each segment.
We collected a random sample of oysters from each treatment at the start, and we will re-sample them every 2 weeks (or more often when we need to!).
The 12 different treatments are:
Lease site: A, B, C
Age: adult, spat
Rack height: high, low
There were 640 oysters in two trays in each treatment at the start of the trial (if you do the maths there were 320 spare oysters!)