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.
|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.