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Clam Farming Components
(66 KB) The components of clam farming can be viewed as occurring in three biological or cultural stages - production of small seed in a hatchery, growing of larger seed for final planting in either or both a land-based and field nursery, and growout to a marketable size on an open-water lease. Hatchery Clam 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 large capital investment in coastal property, buildings, equipment and skilled labor. For these reasons most growers prefer to purchase seed from a hatchery. There are about 15 hatcheries operating in Florida, ranging from small backyard operations to commercial-sized facilities. In the hatchery, adult clams are induced to spawn by manipulation of water temperatures. Brood stocks are selected for reddish striated markings on the shells, referred to as “notata”, to distinguish the clams as farm-raised versus product harvested from wild stocks. Once spawned, fertilized eggs and resulting free-swimming larval stages are reared under controlled conditions in large cylindrical tanks filled with filtered, sterilized seawater. Cultured phytoplankton, or microalgaes, are fed at increasing densities during the 10 to 14-day larval culture phase. After which, the 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 still microscopic and vulnerable to fluctuating environmental conditions. Thus they are maintained in the hatchery for another 30 to 60 days in down-wellers until they reach about 1 mm in size. Nursery The land-based nursery component serves as an intermediate step 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 on the lease for growout. Nursery systems built on the land usually consist of wellers and raceways. A weller system consists of open-ended cylinders suspended in a water reservoir. Seawater circulates through the seed mass, which is supported 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, or naturally occurring phytoplankton, and oxygen to the clam seed. Many growers are attracted to the nursery option since seed costs are lower and, at times, smaller seed are more available. Further, the systems can be constructed rather inexpensively and maintained on a part-time basis. Depending on water temperatures, 1-2 mm seed require from 6 to 12 weeks to reach 5-6 mm in shell length, the minimum size planted in the field. Currently, over 90 land-based nursery facilities are operating statewide. In addition, these systems can be novel. Floating wellers, or FLUPSYs, are employed at specific sites, usually marinas. Growout Clams are primarily 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 pollution. The FL Department of Agriculture and Consumer Services administers the aquaculture lease program and monitors coastal waters for shellfish harvesting classifications. The lease is good for a 10-year term and is renewable and transferable. The lessee pays an initial application fee and a nominal annual rental fee thereafter. In addition, the leaseholder must plant a minimum of 100,000 clam seed per acre annually to fulfill their agreement with the state. There are currently about 450 clam growout businesses located throughout the state operating on over 1,700 acres of state-owned lands dedicated to shellfish leases. Since clams are bottom-dwelling animals, growout systems are designed to place the clam 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. Most growers in the state use a soft tray which is made of a polyester mesh material in the form of a bag. The bag is staked to the bottom using a variety of materials, such as PVC pipe or fence post wire. Bags are typically “belted” together in units of 5 to 10 and planted in rows on the lease. Naturally occurring sediments provided by tidal actions and currents serve as the bottom substrate. When harvested, only the product and bag are removed from the bottom. A winch operated from the boat is used to assist in harvesting the bags. The bag culture method usually involves a 2-step process. The first step entails field nursing seed of a size of 5-6 mm, or 1/4”, in shell length in a small mesh bag. Typically, about 10,000 seed are planted in a 3-4 mm mesh bag with the dimensions of 4’ by 4’. When the seed reach a minimum size of 12-15 mm, or 1/2”, usually after 3 to 6 months, they are transferred to the final bag size which ranges from 9 to 12 mm in mesh size. The larger seed are stocked at a lower density of 800 to 1,200 per bag, or at a rate of 50-75 per square foot. A crop of littleneck-sized clams, which are 1” in shell width, can be grown within 10-18 months depending on season planted. Phenomenal production of clams in Florida is attributed to subtropical waters and high natural productivity allowing for almost year-round growing conditions. Crop times exceed 2 years in the mid-Atlantic states and 3 years in the northeastern states. Survival rates are specific not only to planting methods and experience, but also predator abundance. Additional cover netting, such as galvanized wire, placed over the bags is required in some areas. Crabs, snails, rays, fish, and humans are among the many predators that attribute to mortalities. Once clams are harvested, they are delivered by the grower to a certified shellfish wholesaler. There are over 55 clam wholesalers in the state. 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 are used in transporting product to marketplaces throughout the state and nation.
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For website comments or problems, please contact the Webmaster. Last updated March 24, 2005
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