Building a better fish trap – that’s hands free
May 25, 2016 By Tom Walker
Portland General Electric (PGE) operates a series of dams on the North Fork of the Clackamas River, southeast of Portland, Oregon.
Since the late 1950’s they have built extensive ladders for returning salmonids, as well as considerable infrastructure to get smolts back down stream, including a 7-mile fish pipeline. Fish moved under their own power and a hatchery program supplemented wild stocks.
That was all running smoothly until the late 1990’s when low returns of wild fish prompted a push to create a fish sanctuary.
“There was a budding movement to protect wild fish and one of the ways to do that was to create a sanctuary in the area above the dams where we can remove any hatchery fish,” explains Garth Wyatt, Fisheries Biologist with PGE. The primary goal of the sanctuary was to reduce any ecological or genetic impact of the hatchery program.
“Because our program is located essentially in the mid point of the Clackamas River basin, it gave them a good spot to pull those hatchery fish out,” added Wyatt. And pull them out was exactly what they did.
An old Buckley style trap that had been used as a trap-and-haul facility while the fish ladders were being built was brought back into service. An operator would stand in waist-deep water on the braille floor of the cage-like structure and hand-sort each fish with a net, one species at a time. “In fall the majority of fish are hatchery Chinooks so you may be going through 500 hatchery fish to get to your 50 wild fish (if that is what the truck is taking) and the rest get bumped and jostled,” says Wyatt.
“As the guy who stood at the bottom for several years you really question the stress you are putting on the fish and how you are elevating their pre-spawn mortality just to sort them,” says Wyatt. “I would have tendinitis on an annual basis during the Chinook run.”
That system ran from 1999 to 2013. When the Federal Energy Regulatory Commission renewed the PGE license in 2010 they called for a new sorting facility.
“The regulators challenged us with developing a facility that would sort hatchery from wild fish without physically handling them and without the use of anesthetic,” says Wyatt.
They went looking at other facilities. Some systems were able to use gates to separate fish based on species, but not on rearing type. “I thought we can at least get fish going down a flume,” says Wyatt. “But how do we stop them momentarily to figger out whether or not they have an adipose fin? That is when we came up with the idea for the observation tanks, which are essentially giant aquariums.”
Wyatt started with a sketch and together PGE staff completed the entire design on their own, with MacMillan Engineering planning the concrete structures. It’s sized for their needs and unlike anything Wyatt has seen before.
The sorting facility was built near the up-stream end of the ladder system. Fish are encouraged into a holding pool by cool water sourced from above the dam. When enough fish are collected to sort, the braille floor of the holding pool is raised and that encourages the fish to swim over a false weir into a flume with a gate controlled by an optical eye. As each fish passes through the optical eye, the gate switches position and the fish slide alternately into one of two glass observation tanks. The operator takes a second to ID the fish and taps one of two control panels to flush the fish out of the tank. A pre-programmed button selection sends wild fish back out into the ladder system to continue up-stream to spawn and hatchery fish are diverted to three different holding tanks. An electronic counter keeps track.
The full cost was $5.1 million. Wyatt says they save on operator, trucking and fuel costs and it’s much safer for staff. There isn’t an operator standing on the top of a tank truck as spilled water turns to ice on a freezing November day. And it’s much safer for fish. As they move through the system largely on their own volition, there are fewer injuries and less stress.
“Were pretty thrilled with it. We almost draw straws to see who gets to go work it,” quips Wyatt.
— Tom Walker
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