Seattle, WA--This story about the wild salmon of the Pacific
Northwest Coast has all the elements of a best-selling thriller: It involves an
endangered species, politics, big business, and some pretty awesome technology.
In recent years, fewer and fewer native Chinook and Coho salmon have been
returning to places like Washington's Columbia River Basin to spawn. Marking
hatchery fish by clipping the adipose fin on the salmon's back has long been
considered the best way to build up dwindling native stocks, as it gives
fishermen a quick means of differentiating between wild and hatchery salmon. In
fact, Washington state adopted a new policy in 1998 that requires fishermen to
release any salmon that have an intact adipose fin.
Until now, such a man-date would have been ludicrous. The chore of removing
the fins of some 132 million hatchery, which must be completed within a
90-day-window, is cost-prohibitive. It takes 12 seconds just to mark one fish by
hand.
What a fish tale! Enter Stratos Product Development Group, a
technology-driven engineering/design firm whose president stumbled onto the
scene through a chance meeting while on--where else?--a fishing trip. Although
the firm's work typically involves more conventional products like printers and
computers, engineers rose to the challenge of developing an automated system
capable of clipping the fins of two fish per second. The machine also inserts a
1.5 mm-long, magnetized tag into the nose of the fish to help biologists track
salmon migration patterns.
"During the early part of the project we were basically on a fishing
expedition, because we had never designed anything like this before," says Mark
Tempel, a mechanical engineer who headed up the development. "Biologists who
study salmon were helpful in pointing out what keeps fish happy--they like dark,
enclosed areas and moving water, for example. But they couldn't tell us what
would happen if a fish bottomed out at the end of a gravity feed system or how
much clamping force a fish could take without getting hurt. Building a test bed
to study these unpredictable behaviors really helped us out."
Automation is not typically flexible. But, incredibly, Stratos' automated
tagging and marking system compensates not only for the vagaries of individual
fish behavior (anesthesia was not an option), but it also accommodates seven
fish-size classifications (ranging from 62- to 142-mm long). The fact that other
parameters such as fish height, width, and location of the adipose fin vary
according to length added even more complexity to the engineering effort.
The machine consists of three major components: a staging system,
gating/gravity feed system, and holding system. The patented staging system is
basically a holding tank that orients the fish for head-first, upright induction
into the gating system.
The tank's V-shaped exit slot is a dark color and unlit, for example. Since a
swimming fish is automatically oriented in the correct position to enter the
gates downstream, designers arranged to pump water from the bottom near the exit
of the tank. Only a slight current results, guaranteeing that only fish that are
swimming enter the slot while still ensuring a steady flow of water through the
exit.
Because of the taper in their tail, fish can overlap as they enter into the
inclined gating system. So the first gate singulates the fish and then
accelerates and guides them into the holding system. The two sets of gates are
positioned a fish-length apart and electronically-actuated. Like flippers on a
pinball machine, they open and close based on signals received from a series of
IR emitter/detector pairs sensing the presence or absence of a fish. Software
developed by Stratos calibrates a baseline level for each sensor pair and
filters out any noise caused by the water turbulence.
Downstream of the gates is the gravity feed system, which has an additional
drop in elevation. Combined with the water flowing out of the gate system, this
helps to accelerate the fish so it will bottom out in the holding system's
headmold.
The holding system was one of the most challenging aspects of the project,
and one of several parts of the design for which a patent has been applied for.
It consists of two pairs of foam-lined clamping plates to hold the fish in
place, a stainless-steel mechanical cutter, and an imaging system to verify fish
orientation and fin removal.
"The one question we kept going back to was, 'How are we going to clamp the
fish in a controlled way?' Because if we couldn't do that, we couldn't do the
design," says Tempel.
He ultimately hit on the idea of controlling the clamping force using
contoured plates and foam density. The plates, which vary in size depending on
the grade of fish, are lined with a Neoprene polymer with a compression
deflection of 25% at 2-5 psi. "That results in a force on the fish, depending on
size, of between 2 and 7.5 psi, which compares to a water pressure of 4.3 psi at
10 ft," says Tempel.
Developing an optical system to locate the adipose fin and then verify that
it has been clipped was no easy task. "A wet environment with turbulent water,
where a single drop can act as a reflector, is not a great place for an imaging
system. Plus, the fins have varying degrees of translucency," says Tempel.
Adding water diverters, pushing the fish's belly up to aid viewing, and
taking advantage of a known-image background all helped. Engineers also
developed their own software algorithms for the PC-based system, which allows
the image capture and processing cycle to be accomplished in less than 150 ms.
Feedback from locations such as the Green River Hatchery near Auburn, WA,
that have been using the system has been extremely positive: The machine is
performing at better than 98% accuracy and with a fish mortality rate of less
than 1%, the machine is actually more gentle on the fish than manual
marking.
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To achieve a throughput of two fish per second, each automated tagging
and marking system consists of four parallel units, identical to the one
shown above. This design allows different grades of fish (shown at
1/8-inch scale in this article) to be processed at the same
time. |
Additional details…Contact Stratos Product Development Group, LLC, 2025
First Ave. PH-B, Seattle, WA 98121; (206) 448-1388
Mark Tempel is a senior mechanical design engineer at Stratos Product
Development Group LLC. He holds a B.S. in mechanical engineering from Washington
State University. In his 15-year career, he has concentrated on mechanism design
and electro-mechanical packaging for a wide variety of products, including
marine sonar and radar, medical devices, and consumer electronics. Richard Dolf,
John Havard, and Dave Hemin were also on the Stratos design team.The Washington
Department of Fish and Wildlife (through monies provided by the Bonneville Power
Administration) funded the development of the automated tagging and marking
system.
Other Applications
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Fish sorting
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Fish inoculation
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