Growing seed clams is a labor-intensive process that begins in January when soft-shell clam broodstock are collected from local flats. Hatchery staff culture algae (single-celled plants, or phytoplankton), and feed the algae to clam broodstock for approximately two months before inducing them to spawn. The larval (swimming) clams that result are microscopic. For their first two weeks of their life, the larval clams live in large circular tanks where they grow from 1/600th of an inch to 1/50th of an inch, or a little bit smaller than a grain of sand.
Clam-rearing requires that marine phytoplankton (microalagae) be reared at DEI.
Mass quantities of cultured phytoplankton in these 25-gallon fiberglass containers are required to feed millions of clam seedlings.
Clam broodstock are held in the facility for several months prior to spawning. We use a thermal shock technique to induce clams to spawn. This involves keeping the clams at 10-15oC (50-60oF) for several weeks prior to shocking them with with 23-24oC (73-75oF) seawater.
Here, a male clam has been induced to spawn using the thermal shock technique.
A soft-shell clam pediveliger (ca. 14-days old). This is a swimming clam larvae, and is approximately 180-microns, or nearly 1/125th of an inch.
Tank at DEI used for rearing soft-shell clam larvae.
The tiny clams are then transferred to trays with fine mesh screening and floated on the surface of water-filled rectangular "set" tanks. (The tanks are referred to as set tanks because the clams which have been swimming in the water "settle" out to land on the surface of the screens that have been placed in the set tanks.) From that point on, the animals feed on cultured algae that hatchery staff grow in large, 25- and 50-gallon fiberglass tanks that surround the periphery of the hatchery building.
Hatchery-reared soft-shell clam seed at DEI resting on window screening.
Cleanliness is critical to the survival of tiny clams, and hatchery workers drain and refill the set tanks every other day, spraying off the clams and moving them to increasingly larger screens as they grow. When the clams attain a size of two millimeters in length, hatchery staff use a graduated cylinder to measure out 15,000 to 20,000 animals, which are placed in trays constructed of wood and window screening. Each tray receives a handful of periwinkles before being moved to a nearby ocean nursery site.
Seed clams being prepared for floating nursery trays. A handful of periwinkles is added to each side of the tray, and these help keep the window screen meshes clear of fouling macroalgae and other debris that would reduce water flow to the clam seed.
There the trays float on the surface of the water until November, which is the end of the clams’ natural growth cycle. During this time, the periwinkles act as marine vacuum cleaners and help keep the screens free of fouling material. By the end of the growing season, the juvenile clams are 1/4 to1/2-inch in length.
Floating trays with black plastic covers to keep seagulls from poking through the mesh and preying on the growing clams inside the tray.
Soft-shell clam seed have grown from 2.5 mm to 12-15 mm from June to late October.
Close-up of soft-shell clam seed in late fall prior to overwintering.
Although the clams are large enough to seed, staff return them to our Black Duck Cove facility rather than expose them to winter mortality on the flats. The seed clams are transferred from the trays into mesh bags, which are stacked into modified lobster traps and submerged in circulating seawater until Spring.
Off-loading nursery trays at DEI during November 2010.
Bags of clams inside overwintering cages at DEI. These will be submerged in running seawater from November until the following April/May.
The following spring, clams are stocked onto flats in communities that are interested in enhancing their flats with cultured clam seedlings.
A spring seeding on flats in Hampton, New Hampshire. Nets (1/4-inch aperture) are used to deter predators such as green crabs.