Multi-Species Marine Traps
Used Aquaculture & Processing Machinery
Fukui's Monthly News Letter
Culturing clams with ADPI bags
There is growing interest in North America in the farming of
shellfish such as clams and quahogs. A variety of husbandry methods
can be used, depending on the specifics of the site. The majority,
however, tend to be labour intensive.
The method now most widely used consists of planting seeds on
intertidal flats, which are then covered with predation netting for
protection form crabs. At harvest time, the netting is removed and
cleaned for later use, if possible. The clams are harvested in the
traditional way using a clam hoe/rake. Reseeding is then done and
the process starts over again.
While that method works, it's hardly
ideal. The labour portion of the business is quite high and, for
very large sites, can be a problem. Further, the predation threat
is not always solved with netting because over time there is the
possibility that the crabs will find a way underneath it, or, by
chance, the net may get damaged.
So, the question is: how can we reduce labour cost and increase
yield for this valuable shellfish? Dr. Joth Davis, who runs his own
shellfish company, Baywater Inc., as well as working for Taylor
United Hatchery near Quilcene, WA, has developed a culture method
for Manila clams that answers the question.
The method relies on the use of ADPI CBC-1 bags. While the site
specifics have to be considered shellfish growers on the East Coast
may want to look closely at this approach. Baywater Inc., which is
located on Bainbridge Island, WA, has successfully practiced it for
the last eight years.
ADPI Bags for Clam Grow Out
Cage, bag, or box
Whether you call it a cage, bag, or box, the ADPI CBC-1 is
36" x 16" x 4 ½" with a 3/8" square mesh.
The Baywater site is on Thorndyke Bay on the Hood Canal. Clam culture
is able to be done on the intertidal beach because the tidelands are
largely sandy-silt. There is no natural set of clams, so the
operation relies on hatchery seed. Relatively productive water in
the spring though fall allow the company to practice both clam and
oyster culture (rack and bag) at this intertidal site.
The basics of the culture method as described by Dr. Davis, are as
1. ADPI bags are obtained, which must be assembled into
the box shape, using stainless hog rings (5) to seal one end of the
bag. The area of the bag is approximately 4.5 square feet. The
folded bag depth is generally about 4".
2. A rectangular stainless steel frame is fabricated,
with dimensions slightly larger than the size of the folded bag.
It is pressed into the sand at the spot selected for the grow-out
bag, similar to pressing a cookie cutter into dough. The sides of
the frame enable the sand to be removed, while preventing the
sides of the excavation from caving in while the depression is
being dug. The sand being dug out is placed into the open end
of the bag, which is sitting upright nearby.
3. When enough sand has been removed, the bag is pinned
shut using three stainless steel hitch pins, and, full of sand, is
rolled into the depression. If the depression has been properly
prepared, the top of the bag will extend above the level of the
substrate by about ¾".
4. The frame is removed from around the deployed bag,
and the process is repeated.
5. The bag is seeded by sprinkling Manila Clam seed,
which is 1/4" - 3/8" over the exposed top. Even with the tidal flow,
the seed quickly digs into the substrate and tends to stay put
unless windy weather is at hand.
It should be noted that clam seed larger that the 3/8" mesh is added
to the bag just prior to closing it up and rolling it into the
6. Stocking densities are going to be site specific, but
the Baywater people use approximately 400 clams per bag on their
site. That will yield about 18-20 lbs. of clams per bag. They have
tried stocking bags with as many as 600 clams, but the shellfish
did not grow nearly as quickly.
7. The rate of growth to market size, which is about
1.5" shell height, is about 2.0 to 2.5 years, depending upon when
bags are started.
8. A good worker can deploy between 12-15 bags per hour.
Since Baywater pays by the bag ($1 each), a worker can make good
money deploying bags over a tidal cycle. A typical tidal cycle
will last about five hours, and at this rate 60-75 bags can be
deployed daily per worker.
9. Bag retrieval is very efficient with about the same
amount of time required to remove and harvest as it was to deploy.
The bags are lifted slightly from the bottom, where they are
shifted back and forth several times to remove as much silt as
possible. The clipped end is opened and the clams and remaining
silt are dumped into a harvest basket.
The following numbers are based on a per acre basis, and assume that
the basic infrastructure for a shellfish farm are already in place.
These figures reflect Baywater's approximate labour and materials
costs associated with putting the project in the ground.
Cost of Production
ADPI Bags (2000): $7000
Bag Preparation: $1000
Bag Deployment: $2000
Seed costs (1,000,000): $4500
Nursery Costs (100 bags): $1000
Harvest Costs $2000
Total Costs $17,500 / acre
This cost structure breaks down to about $9 per bag. Obviously, the
second cycles does not include the costs associated with procuring
and preparing bags, so the second cycle costs about $5 per bag to
deploy with added seed.
At a stocking density of 400 clams per bag, Baywater realized little
mortality and harvest between 18-20 pounds per bag. On a per acre
basis, this represents between 36,000 - 40,000 pounds of clams per
acre per harvest (2000 bags).
There can be some problems with this culture method, such as the
sanding in of bags during the winter and early spring.
As a general rule, if you see significant ripple marks on the sand
at your site from wind and tide based circulation, you will not be
able to conduct clam culture because the bags will be sanded in over
a relatively short time.
You must be attentive to the husbandry of the culture method and
physically lift up the bags so that the entire outline of the bag
surface is free of the sand (at least with short-siphoned Manila
There is also the time constraint of working the low tide time
needed to deploy bags. There is never enough time to get the work
done, the major caveat of shellfish culture generally.
As you can probably see by now, using this method could save a lot
of labour, especially on the harvest end. And, predation from crabs
Joth Davis and I discussed some other methods of deployment and
harvesting that are worth developing, however neither one of us
are aware of anybody who has actually worked them as of yet:
1. It may be possible to lay pre-seeded cages out like patio slabs
over a large area of bottom and then, using a pump, discharge water
and silt over the top of them. The silt would drift though the
mesh of the cage. Normal tidal flow will eventually flush the balance of the sandy silt substrate into the cages.
2. It may be possible, depending on the type of bottom,
to gang a number of pre-seeded cages together in a grid type format
so that they may be gently dragged across the site. The movement
will allow silt and sand to settle inside the cage as a substrate.
Harvesting would involve the simplicity of pulling the grid
though the water column to clear the sand and then to open the
bags for collection at the surface.
Both the above husbandry methods could be tested very inexpensively
in a variety of site conditions.
Joth Davis, Ph.D. can be contacted at Baywater, Inc., 15425 Smoland
Lane, Bainbridge, Island, WA. USA 98110, or through my office.
Contact Don Bishop at:
Fukui North America
PO Box 669
110-B Bonnechere St.W.
Eganville, Ontario K0J 1T0
**NEW**Tel: 613-559-0075 or 613-628-5266
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