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Background | Industry Status | Industry Components | Hatchery | Nursery | Growout

Shellfish aquaculture in Florida consists primarily of clam farming. However, along the Panhandle, primarily in Apalachicola, there are several operations culturing the eastern oyster Crassostrea virginica using extensive methods. Shells are planted on state-owned submerged land leases to attract natural oyster spat. There are 500 acres of shellfish cultch leases formerly granted according to Chapter 370 Florida Statutes. In 1999, the Florida Agricultural Statistics Service reported oyster sales valued at $329,000. Results from recent aquaculture surveys conducted by FASS combined oyster production information with other aquatic species.

Background

Clam farming is a relatively new aquaculture industry in the Sunshine State. Attempts to culture clams originated along the east central coast of Florida during the early 1980s. Fluctuating wild clam harvests in the Indian River prompted harvesters to investigate the potential of aquaculture as an alternative supply source to natural stocks. Marine research institutions in the area, in particular Harbor Branch Oceanographic Institute, assisted by adapting culture techniques used in the Northeast to subtropical conditions. At the same time, state-funded educational programs introduced the general public to the prospects of shellfish culture. During the 1990s the industry began developing on the west coast of Florida, primarily through the efforts of job retraining programs. A transition to shellfish aquaculture as an alternative employment opportunity for the fishing industry was the focus of these federally-funded, community-based programs. Over 350 oyster harvesters and net fishers put out of work by increasing regulations and closures were trained in clam culture technologies. In addition, shellfish aquaculture leases were identified, permitted, surveyed and marked, allowing for placement of program graduates onto farm sites in five coastal counties.

Industry Status

Currently, the clam farming industry supports about 350 growout operations on 1,200 acres of state-owned submerged lands, issued under Chapter 253 Florida Statues, off of 11 counties. The naturally warm temperatures and high productivity levels of Florida waters create a superb environment for growing clams. Growth of the northern hard clam Mercenaria mercenaria is almost year round, resulting in a half to a third of the crop time realized in other clam-producing states. In addition, Florida clam growers are able to plant seed year round, enabling them to harvest product continuously. As a result, clam production has increased rapidly over the past 20 years. This is reflected in the results of aquaculture surveys conducted every other year by the Florida Agricultural Statistics Service. Production was reported at 2.4 million clams in 1987 by 13 growers. In 1999, 351 growers reported over 134 million clams produced. Corresponding farm gate, or dockside, sales also increased, with the value in 1999 reported at $16 million. The industry was negatively impacted by the hurricanes of 2004-5 with production in 2005 declining to 92 million clams. In 2007, production information was obtained from a survey of shellfish wholesalers in the state by University of Florida (UF) economists. In that year, 184 million clams were reported to be sold at a farm gate sales value of $19 million. Florida has become a leading producer of cultured clams in the U.S. The 2005 aquaculture census conducted by the U.S. Department of Agriculture ranked Florida second in the nation in hard clam production, but first in the number of small-scale clam farms. 

More importantly, clam farming has brought economic revitalization to many fishery-dependent communities and has allowed its citizens to continue making a living on the water. In addition to the number of growout businesses, there are many spin-off businesses that have developed in support of the clam farming industry. For instance, there are hatcheries operators who produce and rear seed for growers, seamstresses who make clam bags, boat builders who specialize in clam work skiffs, and manufacturers who produce harvesting and processing equipment. Shellfish wholesalers purchase clams from growers, add value, and distribute product to markets throughout the nation. The industry also provides local employment, such as processing plant workers and truck drivers. Thus, the economic impact of this industry is much larger than the dockside sales values. UF economists surveyed wholesalers in 1999 and, again, in 2007 to determine the number and value of clams handled in those years to estimate direct, indirect, and induced impacts. The contribution of cultured clam sales was assessed to be $34 million to the state's economy in 1999 increasing to $53 million in 2007, making clam farming an important agribusiness.

Industry Components
 

The components of clam farming can be viewed as occurring in three biological or cultural stages--production of small seed in a hatchery, rearing of larger seed for field planting in a land-based nursery, and growout on open-water leases to a marketable size.

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 capital investment in property, facilities, equipment, and skilled labor. For these reasons, most growers prefer to purchase seed from a hatchery. There are 10-15 hatcheries in the state, ranging from small backyard operations to commercial-sized facilities, providing 0.5 billion seed annually. In the hatchery, adult clams, or brood stock, 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 phytoplankton, or micro algae, 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 60 days in downwellers until they reach about 1 mm in size.

From left to right:  1) spawning adult clams, 2) larval culture tanks and downweller, 3) algae production, 4) post-set seed clams

Photo Credits:  1, 3, 4) Tom Smoyer (HBOI); 2) Sean Dowie

Nursery:  The 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 for growout. Nursery systems built on land usually consist of wellers and 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. Currently, over 70 land-based nursery facilities are located statewide. These systems can also be novel, such as floating upwellers or FLUPYS, which are employed at specific sites, usually marinas.

From left to right:  1) wellers in tank, 2) raceways, 3) raceways on aquaculture dock, 4) nursed clam seed

Photo Credits:  Leslie Sturmer

Growout:  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. The Florida Department of Agriculture and Consumer Services’ Division of Aquaculture administers the lease program and monitors coastal waters for shellfish harvesting classifications. The lease is for a 10-year term and is renewable and transferable. The lessee pays an initial application fee and an annual rental fee thereafter. In addition, the leaseholder must plant a minimum of 100,000 clam seed per acre per year to fulfill their agreement. 

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. Most 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, 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 action and currents, as well as the digging activity of the clams, allow the bag to become buried in the bottom sediments. When harvested, only the product and mesh bag are removed from the bottom.  A winch or roller rig operated from the boat assists in harvesting the bags.

The bag culture method usually involves a two-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 to 4 mm mesh bag with the dimensions of 4’ by 4’, or 16 ft². 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, a rate of 50-75/ft². A crop of littleneck-sized clams, which are 1” in shell width, can be grown within 10-18 months depending on the season planted. Survival rates are specific not only to planting methods and experience, but also predator abundance. Additional cover netting, such as galvanized wire or plastic netting, placed over the bags is required in some growing areas. Crabs, snails, rays, fish, and humans are among the many predators that contribute to mortalities.

Once clams are harvested, they are delivered by the grower to a 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 are used in transporting product to marketplaces throughout the state and nation.

From left to right:  1) stocking seed in bags, 2) lease area, 3) harvesting clams, 4) washing clams for market

Photo Credits: 1) Leslie Sturmer, 2) DACS Division of Aquaculture, 3) Carlton Ward Jr., LINC, 4) Eric Zamora