The Atlantic Jackknife, aka the Razor Clam (Ensis directus) is getting more attention in recent years, as a potential aquaculture species. They are tasty and versatile, but since they are difficult to capture, and usually accessibly only during very low tides, they can be hard to find in the marketplace. Those who have attempted to dig a razor will attest to the fact that move surprisingly fast, and can burrow very deeply into the sediment. It takes a quick but gentle hand with the clam rake, to get to one and to pull one from its burrow, because the foot will hold on very strongly - a razor clam likes to stay home! Oddly enough however, razor clams will often come up to the surface and emerge halfway or more, if a small amount of salt is sprinkled on the razor clams' burrow, at low tide. Click here for a video from Maine Sea Grant, showing salting for razor clams.
Below is a photo of an adult razor clam in the spawning table, with the foot extended. The muscular foot can change shape rapidly, from pointed to clubbed; helping to dig, to anchor, or to push up from the sediment.
Biology and Predators
Razor clams occur naturally in the Western Atlantic, from Labrador through South Carolina. They prefer sandy substrates in the lower intertidal and immediate subtidal zone, although they will occur to some extend in mud and gravel. Sexes are separate, and eggs are fertilized externally during spawning, which is often in June. Available data indicate fairly rapid growth for the species in favorable conditions, and quite rapid in the hatchery and nursery; from 0.5mm/day in the early stages, and upwards of 0.3mm/day in growout cages. Predators of the razor clam include a variety of shorebirds, the green crab (Carcinas maenas), moon snail (Euspira heros) and the milky ribbon worm (Cerebratulus lacteus).
The market for razor clams in the Northeast is sporadic, but there are indications that the market could be grown, if a steady supply of product were available. Work by Leavitt and others (see below) indicated that there is both a live and a processed market, and that the minimum size for the live market was generally above 3 inches, though 4 inches is preferred. Given the growth rates cited in publications and recent work, it appears likely that a market-size product is attainable in two growing seasons, here in the Northeast. Prices generally range from $2.50 to $6.00 per pound to the producer.
To date, production attempts have focused on two or three main methods, bottom seeding in plots with a mesh predator screen over the top, a screened-in enclosure to keep the razor clams confined and protected, and sediment-filled containers, placed on the bottom, and with predator screening. Like soft-shell and hard clams, razor clams need to be in sediment for good growth - they undergo stress when exposed, and they also expend too much energy via the adductor muscle, in trying to keep the valves of the shell closed. Since razors can swim and can excavate burrows up to a half-meter below the sediment, keeping them protected and contained is an issue. The links below will provide readers with a sense of the equipment used in prior experiments.
Disease and Health
To date, no diseases specific to E. directus have been identified, and no specific human health risks have been identified, although like other bivalves, razor clams are filter feeders, and can accumulate biotoxins from harmful algal blooms.
NRAC Project - 2011
In 2011, the Northeast Regional Aquaculture Center funded a project entitled: Optimization of Hatchery and Culture Technology for Razor Clams". Hatchery work will be conducted in early 2012, at the University of Maine's Darling Marine Center, in Walpole, Maine, at the Blount Hatchery of Roger Williams University in Bristol, Rhode Island, and the Aquacultural Research Corporation, in Dennis, MA. The goal is to refine and improve hatchery production, and to produce 1 million razor clam seed. It is expected that the seed produced from the project will serve as the basis for growout trials with industry participants in both states. Collaborators on that project include Paul Rawson (University of Maine, School of Marine Sciences), Dale Leavitt (Roger Williams University), Diane Murphy (Cape Cod Cooperative Extension, and Woods Hole Sea Grant), Michael Devin (UMaine Darling Marine Center) and Dana Morse (Maine Sea Grant, Univ. of Maine Cooperative Extension).
A workshop was held at the Darling Marine Center on May 2, 2012 to discuss the project, and to hear from growers and others about how best to proceed, if the hatchery phase is successful. Some of the presentations are available from that meeting, including:
Dale Leavitt on basic razor clam information (3.2 MB, pdf format)
Notes from that meeting can be downloaded HERE (pdf format 86 kb)
Project Update, November 2, 2012
The razor clams at the Darling Center were placed into sand-filled, shallow trays, and placed in flow-through conditions. The trays were divided into those filled with unsterilized sand, and those for which the sand had been autoclaved. Over the last couple of months, it's been evident that many of the clams have survived, because of the holes observed at the sediment surface, and some clams that have swum up into the tank and settled back to the bottom. That said, we have not had a check on size or numbers, because the clams have been so small, they'd be likely to break during handling. Today we checked on two of the trays and found that they were filled with juveniles, and looking good. Average size has not been calculated yet, but eyeball estimate figures to be about 10-12 mm.
Project Update: July 16, 2012
The hatchery work at the Darling Center and ARC continues to move right along, with some pretty great success. Below is a photo from Dale Leavitt of some of the juveniles, and a video courtesy of Diane Murphy, of the young ones growing like crazy over at ARC..
...and here's the video of the little swimmers at ARC..it's a biggish file, so please be patient!
Project Update: June 28, 2012
So far today, a very successful controlled spawn at the Darling Center.
PROJECT UPDATE: June 12, 2012
Well now....after an unexpected spawn of the broodstock razors, the hatchery crew (Mick Devin - Hatchery Manager, Molly Flanagan and Chauncey Devin), did some fancy footwork to save the fertilized eggs and to get them into larval culture. After 12 days or so of watching the tanks do well, they gathered sediment from location where the broodstock were captured, and deployed small trays containing the sediment into the larval tanks. Then more waiting. Early indications showed nothing but dead post-set, but algal counts always decreased, indicating that something was grazing on the feed being added. Earlier this week, they observed a couple of live post-set, but then today saw a very nice sample of happy, fat, active little razor clams...which made everyone's day. Great work by the hatchery team!
Below, left to right: Chauncey Devin, Molly Flanagan, Mick Devin
Below: a group of five juvenile razor clams - gills clearly visible and bellies full of food
Click HERE for a video of razor clam juveniles under the microscope, (best in iTunes) and
click HERE for a second brief video.
Still June 12, 2012... More good news..
Diane Murphy reports that Dick Kraus and his staff at Aquaculture Research Corporation in Dennis, MA, has also been successful, and that their larvae are just shy of 1mm to date. Looks like a win so far on both ends!
Below is a very nice photo of one of the juveniles, and
HERE is a video: both the video and the photo are courtesy of Diane at Cape Cod Cooperative Extension, and Woods Hole Sea Grant.
For more reading, click on the following links
- A Fact Sheet on Razor Clams (Northeast Regional Aquaculture Center #217, by Dale Leavitt)
- Final Report to NRAC, by Bill Burt, et al., 2005: "An industry directed feasibility study of the razor clam (Ensis directus) as a candidate for intertidal and shallow subtidal culture in the northeastern U.S."
- PDF summary of a Power Point slide show by Dale Leavitt, summarizing the NRAC razor clam project from 2005