In New England, summer is the time when oyster growers are working hard on the farm to get their baby oysters ready for open waters. Summer is also the time when growers are getting the upcoming season's crop ready for sale in the fall. As we discussed in a previous post, different culturing methods can produce totally different oysters, and there are many of them! Growers choose their preferred grow-out method based on a number of factors including their geography, potential predators, town regulations, and climate. We're going to expand on the most common methods because oyster culture terminology can get confusing, but hopefully this will also shed some light on your oysters and how they are spending their summer!
Grow-out methods generally fall into two categories: bottom culture and off-bottom culture. "Bottom" simply means the ocean floor. So, a bottom culture method means the oysters are growing on the ocean bottom, and an off-bottom culture method has oysters growing without touching the bottom. The two categories are not mutually exclusive. Growers may use both methods over the course of an oyster's life to achieve a desired look or yield.
Bottom culturing is the closest method to growing oysters like wild oysters. Although farmed oysters do not set on a surface like wild spat, if spread on the bottom, they have the same grow-out pattern as their native cousins since they are filtering the same water and living on the same bottom that affects their shell color and rigidity.
It goes without saying that each method has its advantages and disadvantages. The main benefit of bottom culturing is the ability to produce robust and hearty shells. There are a number of speculations why that is. Some think the shells are stronger because they absorb minerals from the mud, or because they get more wave action during tidal changes and rough weather. However, the greatest disadvantage, which might outweigh the advantages, is that growers can lose many oysters to mother nature. Oysters may die from suffocating under the bottom, get attacked by predators, or become frozen in ice that takes them out into the ocean. Every oyster lost is one less oyster a grower can sell for income.
Although "off-bottom" sounds pretty straightforward, there's actually a huge variety of off-bottom methods. These methods vary mainly because of the oyster gear a grower decides to use. Growers typically decide their equipment based on the geography of their farm-site and personal preference. For example, if oysters are grown on a beach, off-bottom culturing may be the only viable grow-out method because otherwise, oysters would risk getting buried as the sand shifts with weather.
The main advantage of off-bottom methods is the opposite of bottom culturing's disadvantages. As you will see, oysters are typically enclosed and protected in off-bottom methods, so a grower has the potential to lose less oysters to weather. This means a better overall yield. The disadvantages, though, include more money spent on gear and more work keeping the gear from fouling. Sometimes there is a tendency for oysters to be brittle because they are so pampered, but there are many techniques growers use to strengthen the shell (e.g. tumbling). We won't get into oyster growing techniques... that can be a whole discussion in itself.
Here are some off-bottom methods that are commonly used.
Cages are exactly what they sound like. They house oyster grow-out mesh bags and keep them secure from floating away or touching the bottom. Cages require a pretty stable bottom because they are quite heavy and may sink into the mud if the bottom is too soft. On our farm, we use cages when the oysters are still very young and not ready for bottom-planting. This gives them more protection than the open water and more space to grow than the upweller. Growers may decide to solely use cages as their only grow-out method, but we cage culture and bottom culture our oysters -- an example of how bottom and off-bottom methods are not mutually exclusive.
In rack-and-bag culture, oysters are placed into oyster grow-out bags, then tied to a steel rebar rack. This method is highly dependent on the tidal range of an area. The area would need low enough tides for growers to access the bags as shown above.
As mentioned earlier, different off-bottom methods depend on the gear used, and in tray culture, oysters are grown in oyster grow-out trays. These trays have the same function as oyster grow-out bags and can be stacked to conserve space.
For surface or floating culture, growers can choose from many different types of gear, systems, and equipment, but essentially, all surface culture gear will float on the surface of the water. Surface culture oysters typically never go dry and get a ton of wave action that naturally tumbles them. When fouling on the gear occurs, the gear is flipped so that seaweed and other clinging ocean organisms are exposed to the air. In the picture above, the Orcutt farm in Pleasant Bay uses floating bags. Other popular gear include the OysterGro system and Taylor floats.
In a suspended culture, the oysters are typically suspended from a buoy that floats on the surface of the water. In other words, the oysters are hanging under water and they rise and fall with the tides. The photo above shows the Shigoku farm when it's dry. Now imagine the tide coming in and the buoy rising above the suspension line with the grow-out bags hanging vertically. As the tide goes in and out, the bags are constantly flipped and moving up and down. There are also other suspension systems such as an adjustable long-line where cages, trays or bags hang from a long line that can be hauled up to be tended. Like surface culture oysters, suspended culture oysters are constantly getting wave action.
There is obviously no one way to grow oysters, and many growers use a combination of grow-out methods. The methods we outlined above aren't even comprehensive of all the methods that exist in the world. Different farms are discovering what works for them and their geographies. And like we mentioned in our other post, that's what's exciting about the oyster industry: there is always something new on the horizon.
What kind of cool grow-out methods have you seen used around the world? If you're an oyster grower, what kind of grow-out method do you prefer to use?
If you're interested in learning more about the pros and cons of different gear types, there are a lot of resources online, but this document from Sea Grant and NOAA does a pretty good summary and is a great starting point.