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Clam Farming 101
Hatchery
Nursery
Growout
Harvest
Hatchery Nursery
Growout Harvest
The Components of Clam Farming From the hatchery to your plate Clam farming consists of the following biological or cultural stages: Production of small seed in a hatchery
 Rearing of larger seed for field planting in a nursery
 Growout on an open water lease to a marketable size
 Clams are harvested and processed for markets nationwide.
HatcheryClam culture begins in the hatchery with the production of seed. While hatchery techniques are well defined, they are fairly complex. In addition, a hatchery operation requires a capital investment in property, facilities, equipment, and skilled labor. For these reasons, most growers prefer to purchase seed from a hatchery. There are 8-10 hatcheries in the state, ranging from small backyard operations to commercial-sized facilities, which provide almost a half billion seed annually. In the hatchery, adult clams, or broodstock, are induced to spawn by manipulation of water temperatures. Fertilized eggs and resulting free-swimming larval stages are reared under controlled conditions in large tanks filled with filtered, sterilized seawater. Cultured marine phytoplankton, or microalgae, are fed at increasing densities during the 10 to 14-day larval culture phase. After which, pediveliger larvae begin to settle out of the water column, or metamorphose. Even though a true shell is formed at this time, post-set seed are microscopic and vulnerable to fluctuating environmental conditions. They are maintained in the hatchery for another 30 to 45 days in downwellers until they reach about 1 mm in size.
Nursery This component serves as an intermediate stage and provides the small clam seed produced in a hatchery with an adequate food supply and protection from predators until they are ready to be planted for growout. Nursery systems built on land usually consist of wellers or raceways. A weller system consists of open-ended cylinders placed in a water reservoir. Seawater circulates through the seed mass, which is suspended on a screen at the bottom of the cylinder. The direction of the water flow defines whether the system is referred to as a downweller or upweller. Raceways consist of shallow tanks or trays with salt water pumped from an adjacent source providing a horizontal flow as opposed to a vertical flow in the wellers. The water flow provides food (naturally occurring phytoplankton) and oxygen to the seed. Many growers are attracted to the nursery option as seed costs are lower and, at times, smaller seed are more available. Further, the systems can be constructed inexpensively and maintained on a part-time basis. Depending on water temperatures, 1-2 mm seed require from 6-12 weeks to reach 5-6 mm in shell length, the minimum size planted in the field. About 40 nursery facilities are located statewide. These systems can be novel, such as floating upwellers or FLUPYS, which are employed at specific sites, usually at marinas.
Hard clams are grown on estuarine or coastal submerged lands leased from the State of Florida. Successful clam farming requires good water quality, free of bacteriological and industrial contamination. Since clams are bottom-dwelling animals, growout systems are designed to place the seed in a bottom substrate and provide protection from predators. The system must allow substantial water flow to provide both oxygen and natural food, or phytoplankton, for growth. Many growers in the state use the soft bag, which is made of a polyester mesh material. The bag is staked to the bottom using a variety of materials. Bags are typically “belted” together in units of 5 to 10 and planted in rows on the lease. The bag culture method is a two-step process. The first step involves nursing of the seed in the field. Typically, about 10-15,000 seed are planted in a 4 mm mesh bag with the dimensions of 4 feet by 4 feet. When the seed reach a size of 12-15 mm (1/2 inch), usually after 3 to 6 months, they are transferred to the final bag size, which may range from 9 to 12 mm in mesh size. The larger seed are stocked at a lower density with rates varying from 800 to 1,400 per bag. Additional cover netting placed over the bags is required in some growing areas. Growout
A crop of littleneck-size clams, which are one inch in shell width, can be grown within 12-18 months depending on water temperatures and food. Survival rates are specific not only to planting methods and experience but also predator abundance and environmental (for example, salinity) conditions. Crabs, snails, rays, fish, and humans are among the many predators that contribute to mortalities. Another culture method, traditionally used in the Northeast, is now used by growers on the east and southwest Florida coasts. The bottom plant method places a single layer of cover netting over the broadcasted seed.
Harvest Naturally occurring sediments provided by tidal action and currents, as well as the digging activity of the clams, buries the bags on the lease bottom. During the harvest of clams, farmers get into the water and first remove the cover nets. Then the mesh bags full of clams are wrestled out of the sediment and removed from the bottom. A winch or roller rig operated from the boat sometimes assists in harvesting the heavy bags. Harvesting takes place most days of the week and in some of the best and worst weather imaginable. Whether it is raining, freezing cold or perfectly tropical, Florida clam farmers go out on their leases, get in the water and harvest the clams by hand. Bad weather, hyperthermia and stingray stings are just a few of the hazards of the job. Once clams are harvested, they are delivered by the grower to a nearby certified shellfish wholesaler. At the wholesaler’s processing plant, clams are prepared for market by washing, sorting, grading by size, counting, packaging, and tagging. Clams are generally sold live, or as shellstock, and refrigerated trucks or commercial air carriers are used to transport them to marketplaces around the state and nation.

About this Site

 

The website was developed by the University of Florida IFAS Shellfish Aquaculture Extension Program, in partnership with the Florida shellfish aquaculture industry, in an effort to promote cultured clams as an environmentally friendly and sustainable seafood product.

 

Ada Lang, Designer-At-Large, created this website using Adobe  Muse.

Funding Funding for the website was provided by the Florida Department of Agriculture and Consumer Services, Division of Aquaculture through the 2014-15 Florida Aquaculture Program (contract #00094300). Continued support is provided through the Cedar Key Aquaculture Association.
Acknowledgments Photography for the website provided by Sean Dowie, Ada Lang, Robert Seidler, University of Florida IFAS Communications, Carlton Ward, Jr., and Eric Zamora. The Florida Department of Agriculture and Consumer Services, Bureau of Seafood and Aquaculture Marketing provided the photos of cooked clams and recipes.