We grow oysters in two different ways, we have the wild spat fall from oysters in the river and we buy in oyster seed which is commercially grown oyster spat and comes in a variety of sizes.
Shall we start with wild oysters?
Oysters are both male and female and they will release the oyster spat, baby oysters into the water where they will float around for a while and then sink to the oyster beds or river bed. We put crushed shell on to the oysters beds at spat fall time so that the oyster spat has something to grab onto so it's not washed away by the tide. You can tell a wild oyster as when it is fully grown you will see a stone or a piece of shell at the heel of the oyster, this is the thing that they oyster spat grabbed onto when it first fell to the oyster bed. Another benefit to the oyster growing this way, is that the piece of shell or stone will give the oyster an element of protection from predators when it's small and vulnerable.
Oysters grown from seed
Calling it oyster seed makes it sound like something you would plant in the ground, water and watch it grow. Instead it's just a way for us to differentiate between the wild oyster spat and the oyster spat we buy in. We buy different size oyster seed, the smaller it is the cheaper it is but the percentage that will die is greater. You can get seed as small if not smaller than your little finger nail, the seed that we buy the most of is the size of a one pound and two pound coin. These oysters go to our oyster nursery for a short while before they go onto the oyster beds
Our oyster nursery
The oyster nursery is a number of floating rafts that we keep in a deep part of the river thats most protected from the strong easterly winds we get at the fishery. It has to be deep to keep the oyster seed submerged in the water at all states of the tide. This means that the oysters are in the water the whole time so they can focus on growing and they are subjected to fewer temperature changes from the tidal height changes. It also means that the oysters are more protected from predators to give them the best chance of survival as this is the time the oysters are most vulnerable.
We check the oysters regularly to ensure that the rafts haven't got clogged up with seaweed and mud and that the water is flowing through the oysters as the tide pushes it up and down the river. We also check the how much the oysters are growing and whether it's time to put them out on the oyster beds. Typically the oyster seed will only be in the oyster nursery for a few months, sometimes a little longer depending on the water temperature.
The oyster beds
Once the oyster seed has grown too big for predators we take it to our oyster beds in another part of the river. The oysters are spread over the beds, floating down through the water until they land on the shell that has been put on the layings. The oysters stay on the beds for about two, three or four years depending on how much they grow each year and what size oyster we want. It's really tempting to bring in all the oysters once they reach the smallest grade, but we need to keep some in the river to grow on from an A to a AA or even a AAA, the largest oyster we sell.
We regularly check the oyster beds, at very low water we can walk along the beds to make sure that everything is growing as it should. The oysters sometimes grow too closely together so we need to spread them further apart, but that's the only real intervention the whole time the oysters are growing in the river.
As I mentioned we can walk along the oyster beds, this leads to an important point about our oysters. The oyster beds are inter-tidal meaning that they are covered by water at high tide and exposed at low tide, this creates a stronger oyster as it has to remain tightly closed for a period of time each day when it's out of the water. When the oysters are sold and packed out of the tanks, they have spent years strengthening the muscles that hold the shell closed so it can remain closed for longer and keep the oyster fresher for longer. It also means that the oyster is exposed to a variety of temperatures at low water, so if it's a hot summers day the oyster will spend a proportion of that day basking in the sun and the heat of the day before being cooled down by the incoming tide. It creates a resilient and strong oyster, they are pretty incredible really.