Hard clams are available year-round, with an increased supply during warmer months. These clams have a mild flavor that is sweet and briny. Hard clams are sold fresh live and as shucked meat, frozen shucked meat, frozen on the half-shell, canned, and in value-added products such as sauces and soups. Hard clams have a longer shelf life than soft shell clams. Hard shells should be tightly closed when bought in the shell, and any open live shells should snap shut when tapped or put in cold water. Live clams should not smell bad. Since a “bushel” definition varies among suppliers, buyers recommend getting clams by the piece or by the pound instead. Most hard clams are named according to their size.
Key sustainability sourcing notes for hard clams based on landings data from 2013-2016 and the most recent 2015 (wild-caught from U.S.) and 2018 (farm-raised) Seafood Watch assessment are as follows:
~100% of U.S. hard clam landings meet a Seafood Watch "Best Choice (green)" rating
Landings by U.S. state are: ~50% Virginia, ~30% New York, ~10% Rhode Island and Massachusetts each
Overall U.S. landings increased ~25% from 2013 to 2016, but the New England region decreased ~10%
Total U.S. farms for hard clams in 2013 is 278, down ~35% from 2005, but sales increased ~10% over the same time
2013 U.S. farm counts for hard clams include: Florida-119, New Jersey-37, Massachusetts-33, Connecticut-16, South Carolina-8, and Washington-4
Comparing total sales for wild and farmed U.S. hard clams for 2013 shows ~55% farm-raised and ~45% wild-caught.
Hard clams are bivalve mollusks that have a two-part thick, hinged shell. Both halves of their shell are of a relative size and are triangular in shape. The outside of their thick shells ranges from gray to white in color, with concentric growth lines. The inside of the shell is white with areas of violet color. Hard clams contain a foot, along with a set of siphons, used for respiration and gathering food. Adults are sessile, meaning they stay in one place, but they will burrow into sediment using their foot.
Hard clams have slow growth rates. The species usually measures between three and five inches. This species lives from 12-20 years on average but can live for up to 40 years. Spawning occurs from late spring into fall, when water temperatures are between 68 and 73 degrees Fahrenheit. Females can produce close to five million eggs during spawning events and release them into the water column where they are fertilized by sperm that the male clams have released. Free-swimming larvae hatch from the fertilized eggs over the next one to two weeks. During this time, larva will grow a foot which is used to find a surface to settle on. Once they find a suitable surface, they will anchor themselves and metamorphose into juveniles, developing gills, siphons, and a digestive system.
Hard clams will extend their siphons out from their shell in order to feed. The siphons draw in water, which is then passed through the gills where plankton is filtered out for food. The unused water and particles are ejected back out into the water. Hard clams are sufficient filter feeders - a large adult quahog can filter almost a gallon of water per hour. Adult clams have many natural predators including marine birds, rays, and crabs.
The native range for hard clams extends from the Gulf of St. Lawrence down along the East Coast of the United States to Florida into the Gulf of Mexico to Texas. They have subsequently been introduced to the West Coast of the United States, Puerto Rico, the United Kingdom, France, Holland, Belgium, and Taiwan. Hard clams primarily occur in shallow, estuarine environments between the intertidal zone to 49 feet (15 meters) deep. Adults are sessile and will burrow below the surface to 15 centimeters deep – leaving only their siphons exposed to feed. They are found in all sediment types, although they prefer burrowing in sediments made up of sand and mud, with some coarse material. They can also be found near oyster reefs and in seagrass beds. Hard clams can tolerate a range of salinities and temperatures but must inhabit areas with adequate water circulation where water movement brings in food, maintains water quality, and removes excess waste from the environment.
Hard clams provide numerous ecosystem benefits by removing excess algae, organic matter, and nutrients from their environment – culminating in improved water quality. Hard clam beds help stabilize coastal sediments ultimately minimizing the impact of storm surges. Additionally, clam beds and farms can provide habitat for a variety of marine species.
Science & Management
The Milford Laboratory at the Northeast Fisheries Science Center (NEFSC) is focusing on ways to enhance growth and survival of shellfish in hatchery settings. The scientific studies the center conducts help to inform management strategies for the sustainable expansion of aquaculture operations. In addition, the NEFSC is using technological advances to investigate how improvements can be made to hatchery operations while decreasing impacts on the environment at the same time. The center is also trialing certain dietary supplements to see if they can alleviate responses to common stressors in hatcheries.
Ocean acidification causes a number of changes in seawater chemistry that can ultimately harm a variety of species, including hard clams. NOAA’s Ocean Acidification Program is currently investigating the impacts of ocean acidification on shellfish survival, growth, and physiology as well as working to develop new technology for ocean acidification monitoring systems to help increase our understanding of long-term changes in ocean chemistry.
Numerous local, state, and federal agencies are involved to some degree in the permitting process and regulation of hard clam aquaculture in the United States. While there is no national oversight agency for aquaculture in the US, there are extensive regulations in place regarding predator controls, therapeutant use, and disease management. Permitting varies by location with numerous federal agencies providing some degree of oversight. These include:
The United States Department of Agriculture (USDA) – which is responsible for coordinating national aquaculture policy and providing the industry with research, information, and extension services;
The Environmental Protection Agency (EPA) – which regulates waste discharge from aquaculture facilities;
The Fisheries and Wildlife Service (FWS) – which regulates the introduction and transport of fish; and,
The Food and Drug Administration (FDA) – the FDA’s Center for Veterinary Medicine is responsible for approving and monitoring the use of drugs and medicated feeds used in the aquaculture industry.
Additionally, the National Oceanic and Atmospheric Administration (NOAA), the US Coast Guard, the Bureau of Ocean Energy Management (BOEM), and the US Army Corps of Engineers are involved in the permitting and management of hard clam aquaculture. Regulations shellfish farms must adhere to include the Magnuson Stevens Fishery Conservation and Management Act, the Endangered Species Act, the Clean Water Act, and the National Environmental Policy Act.
Wild hard clams are managed at the state-level generally through measures such as gear restrictions, fishing seasons, and size limits. Each state has its own specific regulations which usually include some variation of the aforementioned management measures. For instance:
Massachusetts manages its hard clam fishery in partnership with local municipalities. Generally, it is the responsibility of municipalities to issue permits and administer licensing fees, coordinate spatial management, and establish gear restrictions. The only statewide regulation is a minimum size limit of one-inch thickness.
Rhode Island manages its hard clam fishery by implementing possession limits, fishing licenses, and seasons. Possession limits vary depending on the location, but generally range from three to twelve bushels a day. Hard clams are managed spatially within established management areas where clams can be legally harvested. Additionally, clams are harvested in a rotational manner allowing the area to recover post-harvest. Rhode Island conducts clam relays – transporting hard clams to specific areas to ensure optimal growth and reproduction based on environmental conditions and to avoid pollution. Rhode Island also conducts yearly stock surveys.
New York manages its hard clam fishery in partnership with local municipalities. Statewide regulations include gear restrictions and a minimum size limit of one-inch thickness. Commercial harvesters must have a New York State Digger permit. Some municipalities have conducted stock surveys and have developed spawner sanctuaries that are off-limits to harvesting. These sanctuaries aim to help increase spawning success rates for hard clams.
North Carolina manages hard clams through harvest and size limits. Additionally, North Carolina has established seasonal and area restrictions as well as relay programs.
While some states conduct stock surveys, most do not have current individual stock assessments which are needed to ensure the long-term health of hard clam fisheries.
Hard clams, also known as littlenecks, Northern quahogs, cherrystones, chowder clams and topnecks, are a fecund species that don’t move much throughout their lives. Since they are concentrated in beds, they are vulnerable to fishing pressure. Hard clams are found along the Atlantic coast and Gulf of Mexico in intertidal waters. Although they are not listed as overfished by international bodies, their abundance in some areas has declined to low levels compared with historical levels. The overall population is considered unknown.
Habitat impacts (Wild)
Hard clams are primarily gathered using tongs and rakes. Hand rakes have less of an impact on the seagrass beds where the clams are harvested than mechanized rakes or small dredges. Overall the gear impact is considered moderate since heavy raking can have a long-lasting effect on aquatic vegetation. Since clams are filter feeders, they can improve water quality where they grow.
Bycatch in the hard clam fisheries is very low because the fishery is highly selective and the gear is designed to lower the likelihood of catching undersized clams.
The hard clam commercial fishery has some management measures depending on the area that include area closures and local data collection. The entire fishery lacks adequate data monitoring, though. While the hard clam fishery’s capacity has declined over time, this has been attributed to lower commercial profitability and declining availability rather than a direct consequence of management action.