To ensure the most efficient growth of oysters, you will need to do three things:
You can best accomplish all of these objectives by periodically pulling your garden up onto the dock or shore and letting it dry out. Shading your garden by tying it up under a dock can also help reduce fouling. If you have a Taylor float, you can also consider making a simple, lightweight cover to reduce direct sunlight. The following expands on steps you can take to optimize the growth and survival of your oysters.
Control of Fouling Organisms
The best way to control fouling organisms is to periodically pull your garden out of the water and let it dry out (a process called "desiccation"). Keep your cages or float out for only three or four hours if they are in direct sunlight. This is long enough to kill most unwanted organisms and will not harm your oysters. On cloudy and cool or rainy days, you can leave them out for up to 24 hours. Experience will be your best guide in determining how often to clean your garden. Each site is different, so each garden will require a different desiccation schedule. On average, oyster gardens usually need to be desiccated about once every two weeks during warm months. If you notice a buildup of algae, or if you see flatworms, you may need to clean the garden more frequently; if your garden appears clean and free of predators, you may not need to clean it as often. Remember: freezing air temperatures can kill oysters. Do not remove your garden from the water if the air temperature is at or below freezing. (Oyster gardens should not need to be cleaned in the winter months, except for occasional shaking or moving around of the oysters to dislodge any sediment).
To lighten the Taylor float enough so that you can pull it out of the water for cleaning or desiccation, it may be easiest to reach down and remove most of the oysters first. You can do this either from the dock, or by approaching the float in a dinghy, or even by wading out to the float. Place the oysters you remove in a bushel basket or bucket on the dock. Once you have removed most of the oysters, the float should be light enough to pull up onto the dock. Also keep this strategy in mind when it comes time to return your oysters for planting. Oyster cages should be light enough to be pulled up onto the dock without removing oysters first.
Because of unusually rapid growth, or neglect, you may get to a point where you actually need to scrub your garden with a hard-bristle brush, paint scraper or garden hoe. A high-pressure hose may also be helpful for cleaning the cages or float (use a low setting). You do not have to scrub fouling organisms off the oysters themselves, unless growth is so heavy that it could impede the oysters from opening to feed. Just clean organisms from the garden structure to allow for maximum water flow around your oysters. Remember, it really pays to keep ahead of this unwanted growth - just ask anyone who has spent a Saturday scraping barnacles with a garden hoe!
Cleaning Your Garden
The structure of your oyster garden, and the oyster shells themselves, can trap sediment, which can result in decreased water flow and hence slower growth of oysters. In addition, the filtering activity of oysters will remove suspended algae and sediment from the water. The sediment particles are released as "pseudofeces," and, along with waste products, are deposited into the garden. Because build-up of these particles can also restrict water flow to oysters and result in anoxic (lack of oxygen) conditions, keeping your garden clean is vital.
The best way to clean these particles from cages is to either rinse them with a garden hose (fresh water will not hurt oysters), or pull the line rapidly up and down to rinse them in bay water. Do this as often as possible - at least once every two weeks is best. In fact, it is a great idea to tug up and down on the lines to your garden every time you walk down your dock. Encourage friends and family members to pull them up, look at them, shake them, rinse them - the more the better!
If you're not careful, oysters can grow into the wire mesh of your cages. Unfortunately, removing ingrown oysters usually results in their destruction. To prevent this situation, move the oysters around in your garden often. Gently shaking or tumbling oyster cages works well. Taylor floats can be lifted at one end so the oysters all move to the low end; the oysters can then be rearranged to balance the float. If the float is too heavy to lift, try spreading them around in the float using a garden hoe or long-handled shovel.
When cleaning your garden, do not remove any dead oysters. They will need to be counted when collecting data; in addition, the shells will also provide habitat, both in your garden and when the oysters are ultimately planted on a reef.
Controlling Oyster Predators
The structure of your oyster garden will help to exclude many predatory organisms that would normally eat your oysters. Several species of crabs, fish and other animals may feed on oysters at different stages in their life cycle. The wire mesh of your garden will limit most of the major problems with predation with one exception, the oyster flatworm, Stylochus ellipticus. Flatworms can have a devastating impact on young oysters, spreading via a planktonic larval form, that can easily slip into any garden. They reproduce throughout the summer in Maryland, and one of their favorite foods is oyster spat. A heavy flatworm infestation could result in over 90 percent mortality of your spat in a couple of weeks.
Therefore it is important that you monitor your cages regularly for flatworm presence. Fortunately, flatworms can be controlled via desiccation, so a regular schedule of desiccation to control other fouling is also likely to control flatworm populations. You will see many species of worms in your garden which are harmless. Any organisms that look like normal worms (that is, long, thin, often segmented worms) will not harm your oysters. Flatworms are disk-shaped, generally smaller and thinner than a quarter, and usually grayish or flesh colored. If you see many flatworms on your oysters, consider going to a more regular schedule of desiccation preceded by hosing down with fresh water.
Blue crabs should be removed from your garden whenever they are noticed. While blue crabs should not cause major moralities in your garden, a confined blue crab will eat what is available to it, and in most cases this will be your oysters. Removing any blue crabs when you see them should alleviate the potential problem. You may see many small, brown mud crabs in your garden - these are not harmful to your oysters.
It is not likely that most other oyster predators will cause problems in your garden. One advantage to spat-on-shell is that they are generally more predator-resistant than cultchless oysters. The shell to which they are attached acts as protection for the spat until they reach a size where predation is more difficult.
This page was last modified October 17, 2012
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