– Hatchery –

Soft-Shell Clams


To purchase clams that are ready to be seeded (larger than 2mm), you should order cultured soft-shell clam (Mya arenaria) juveniles in the late winter for planting in the following spring (15 months in advance). This is the only way we can be sure to have an adequate supply of seed on hand for you.

If you are interested in ordering small clams up to 2 mm (for growing in an upweller or floating nursery trays), these can be shipped to you between May and June the same year you order them. Due to winter mortality, we advise against planting clams in the fall and recommend they be overwintered in flow-through seawater until planting the following spring.

Seed clam prices are based on size, as larger clams require more care and handling by DEI staff.

Contact Kyle at 207-259-5048 or e-mail: kyle.pepperman@downeastinstitute.org with questions or to place an order.

For Delivery Inside Maine

Size (mm) Size (in) Price per 1,000
1 mm 0.04 in $5.30
1.5 mm 0.06 in $8.00
2 mm 0.07 in $10.15
5-7.9 .20-.31 $19.00
>8 mm >.32 $25.00

For Delivery Outside Maine

Size (mm) Size (in) Price per 1,000
1 mm 0.04 in $5.30
1.5 mm 0.06 in $8.00
2 mm 0.07 in $10.15
5-7.9 .20-.31 $24.00
>8 mm >.32 $30.00

*Size is shell-length.

Clam Pick Up and Planting

You are encouraged to pick up your clams sometime in April, but prior to May 1. After May 1 we cannot guarantee that your order will be filled. Planting clams during April or May ensures that the animals will reach their maximum shell length by the time growth ceases in the fall.

For more information on increasing clam survival in the clam flats and hatchery culture, check out DEI’s Manual on the Culture and Grow-Out of Soft-Shell Clams: A Practical Guide for Growing Clams in the Intertidal.

Transplant Permit Required in Maine

For Maine communities and individuals ordering DEI soft-shell clam seed, remember that you will need to obtain a transplant permit from the Maine Department of Marine Resources.  Please follow this link to find a transplant/relay permit application and instructions, as well as contact information for the area biologists in your region.


Growing seed clams is a labor-intensive process that begins in January when we collect soft-shell clam broodstock from local flats. Hatchery staff grow algae (single-celled plants, or phytoplankton) to feed clam broodstock for approximately two months before inducing them to spawn. The newly born larval clams swim in the water and are microscopic. For their first two weeks of life, the larval clams live in conical 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.

A variety of microalgae is also used to feed clam larvae and juveniles.

The first step in growing algae at the hatchery begins with stock culture in small 125 mm flasks.
Cultured phytoplankton, required to feed millions of clam seedlings, is then held in algal tubes (25-gallon fiberglass containers).
Clam broodstock are held in the facility for several months prior to spawning. We use a thermal shock technique to mimic nature and induce clams to spawn. This involves keeping the clams at 10-15oC (50-60oF) for several weeks prior to bathing them with 23-24oC (73-75oF) seawater.
Here, a male clam has been induced to spawn.
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.

The tiny clams are then transferred to trays with fine mesh screening which float in large rectangular “set” tanks filled with seawater. From that point on, the animals feed on the cultured algae grown in the hatchery.

Hatchery-reared soft-shell clam seed resting on window screening at DEI.
Tank used for raising soft-shell clam larvae.
Hatchery Manager Kyle Pepperman and intern Miranda Furnani watch for signs of mussel spawning.

Cleanliness is critical to the survival of tiny clams, and hatchery workers drain, clean, 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 grow to two millimeters in length, hatchery staff use a graduated cylinder to measure out 15,000 to 20,000 animals and place them in trays constructed of wood and window screening. Each tray receives a handful of periwinkles to prevent fouling before being moved to a nearby ocean nursery site.  Alternately, clams may be moved to an upweller during their nursery phase.

Seed clams being prepared for floating nursery trays. A handful of periwinkles is added to each side of the tray.These help keep the window screen meshes clear of fouling macroalgae and other debris that would reduce water flow to the clam seed.

The trays float on the surface of the water until November, which is the end of the clams’ natural growth cycle. By the end of the growing season, the juvenile clams are 1/4 (6.35 mm) to 1/2-inch (12.7 mm)  in length.

An upweller used for growing shellfish.
Floating trays with black plastic covers 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 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.
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 seed.

A spring seeding on flats in Hampton, New Hampshire. Nets (1/4-inch aperture) are used to deter predators such as green crabs.A spring seeding on flats in Hampton, New Hampshire. Nets (1/4-inch aperture) are used to deter predators such as green crabs.

All proceeds from shellfish seed sales helps support DEI’s nonprofit mission.

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