Manila clams are generally sold live year-round, although some quantities may be frozen whole. These small clams tend to be soft and sweet in taste. Buyers generally recommend avoiding buying clams by the bushel, a common measure used on the East Coast, because the definition of a bushel can vary among suppliers. If buying by the bushel, check to make sure that the shipments are what was paid for. The best Manila clam shelf life and meat yield is in the winter time, which coincides with reduced prices due to lower demand from coastal resorts, according to some buyers. After the clams spawn in the summer, shelf life drops off.
Water quality is monitored by a national shellfish sanitation program. Manila clam aquaculture production is well-managed, according to the Monterey Bay Aquarium.
Clam farms are usually located in protected beaches, inlets, and estuaries that have been registered with a shellfish authority. On the U.S. Pacific coast, Manila clams are farmed from cultured beds that have received a national permit through the U.S. Army Corps of Engineers. In British Columbia, Manila clams are cultured and harvested from wild beds by hand.
Shellfish are filterfeeders so they generally don’t require additional feed beyond seawater. Some farmers may add some algae as feed but clams can actually lower the levels of nitrogen, phosphorous, and other particles in water, effectively cleaning it. As a result, no controls are necessary for effluent from Manila clam farming operations.
Disease, Pathogen and Parasite Interaction
The majority of farming for clams occurs with the native range of individual species of clams, and although the grow-out phase for clams occurs in open systems (coastal areas and estuaries), the risk to wild stocks is therefore considered low. Additionally, there is little chance of escape by juvenile or adult clams since they are usually secured by netting &/or bags.
Escapes and Introduced Species
Although the species is native to Japan, Manila clams have been farmed along the Pacific coast of U.S. and Canada since the 1930s so there are no negative impacts on native ecosystems. Manila clams are farmed at high densities, but these volumes do not surpass what the beaches can handle. However, outside pollution and contamination from bacteria as well as brown tides have forced beach closures, causing farms to close as well. The mesh netting used to deter predators is not considered harmful. Manila clams are usually collected with tongs, rakes, and handheld dredges that don’t harm the seafloor the way large hydraulic dredges used for collecting other clams can, according to the Seafood Choices Alliance and the Monterey Bay Aquarium.