ANR-832, New Oct 1993. By Richard K. Wallace, Extension Marine Specialist, Auburn Marine Extension and Research Center, Auburn University.

Oysters In Alabama

Oyster landings in Alabama have averaged a million pounds per year since the 1880s. However, large fluctuations occur on a year-to-year basis. For example, 1982 was a relatively good year with landings of 1.5 million pounds. The next year landings were only 336,000 pounds. The worst sustained decline occurred from 1985 to 1989 when landings went from 1.3 million pounds to 9,500 pounds. By 1992 landings had rebounded to 1.2 million pounds with a dockside value of $1.7 million and the total contribution to the economy was estimated to be about $6 million.

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Biology

Oysters spawn from April through October if the water temperature is 72°F or higher and salinity is above six parts per thousand (ppt). Eggs and sperm are released into the water at fertilization. Females release anywhere from 70 million to 170 million eggs. The fertilized eggs develop into a free-swimming larval stage in about 24 hours. After several weeks, the developing shell on the larvae becomes too heavy for swimming and the larvae settle to the bottom. The larval oysters require a clean hard bottom for attachment and can actually move about on the bottom seeking a good substrate. If good bottom is found, the larvae secrete fluid that cements them permanently to the bottom. Larvae settling out in soft mud or other unsuitable areas usually do not survive. Once settled, the developing oysters can become sexually mature within a month and then contribute to another generation of oysters in a very short time. Interestingly, oysters sometimes change sex after spawning. In particular, young males often become egg-producing females.

Oysters eat by filtering food from the surrounding water through their gills. Under ideal conditions an oyster can pump 5 gallons of water an hour through its filtering apparatus. Alabama oysters reach harvestable size (3 inches) in about 24 to 30 months.

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The Environment

Oysters are bound to one spot after they settle and are at the mercy of the water brought to them by currents and tides. When the water is too fresh (less than 10 ppt salinity) for long periods, oysters die. On the other hand, when salinity is high, oysters are likely to be devastated by oyster drills (a snail), crabs, and a tiny parasite called dermo. Oyster drills alone are capable of killing 85 percent of the young oysters on a reef. Furthermore, oysters can be smothered by sand and silt from dredging operations or extremely heavy storms.

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Management

Oyster management can be divided into two areas of concern--public health and conservation. The Alabama Department of Public Health and the Department of Conservation and Natural Resources (DCNR) monitor the waters around oyster reefs. They close the reefs to harvesting when bacterial counts indicate that disease-causing organisms are above acceptable levels. These closures generally coincide with high river flow in winter and early spring, which carries increased sewage into the lower Bay. Bacteria and other pollutants are a particular problem for oysters because they are filter feeders and can concentrate harmful substances in their body tissues. Generally, these pollutants do not harm the oysters but make them unfit to eat, especially raw.

The Marine Resources Division of the DCNR conserves oysters by requiring licenses, enforcing a size limit of 3 inches, and allowing only hand or oyster tong harvest on public reefs. The Marine Resources Division also plants clam shell to provide new substrate for oyster larvae to settle on and grow. Large amounts of clam shell were planted after the oyster beds were devastated by Hurricane Frederic and after the spring floods in 1983. Approximately 10,000 more acres can be planted with shell if funds become available.

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Oyster Measures

Unlike many other foods, oysters are harvested, processed, and sold on the basis of volume rather than weight. Oyster harvesters catch tubs, sacks, and barrels of oysters. Oyster shuckers are paid by the gallon for meat shucked, and consumers buy sacks of whole oysters and gallons, half-gallons, or pints of oyster meat.

The following are the approximate relationships among the different measures. A bushel basket or a tub equals one sack; four sacks equal one barrel. An average sack yields about six pints of oyster meat, depending on the time of year. If oysters are packed four sacks to a barrel, then a sack should weigh about 60 pounds.

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The Future

Oysters are a valuable natural resource in Alabama. The industry provides jobs and a large economic benefit to the state. Like all marine resources, oysters depend on good water quality for continued use by man. Good water quality can be maintained by preserving wetlands, by careful planning of dredging activities, and by controlling pollution both in Mobile Bay and in the tributaries that feed the Bay.