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Group tests fish trap in Columbia above Cathlamet

Outlawed gear effective at reducing bycatch mortality


December 21, 2017

Pound nets or fish traps used to capture large numbers of salmon were outlawed on the Columbia River in 1936, over 80 years ago, largely due to massive harvests of salmon and steelhead when using the gear. So why has a Northwest nonprofit been testing the fish traps just upstream of Cathlamet for the last two years?

That’s because the fish traps are more selective than commercial gillnets and, according to 2016 and 2017 testing, result in an immediate survival rate for released fall chinook salmon of over 99 percent. The more selective method of fishing is a way to better protect and release wild fish during harvest, while retaining hatchery fish.

That’s a far cry from beach and purse seines, also being tested by lower Columbia River commercial fishers, where long-term mortality (from net to spawning grounds) can reach nearly 50 percent, according to Adrian Tuohy, biologist and project manager testing the nets for the Wild Fish Conservancy.

Tuohy said that in the first year (2016) they targeted fall chinook and coho salmon to test whether the gear would catch what he calls “commercially viable quantities” of salmon while also minimizing the immediate mortality of the fish

“Results from the 30-day test fishing period suggest that commercial salmon traps may work well as stock-selective fishing tools: during the test period, over 2,100 salmonids were captured and released with an immediate survival rate of 99.58 percent,” the 2016 assessment of the test said.

Tuohy reviewed the first two years of testing at the Northwest Power and Conservation Council’s meeting in Portland on Dec. 13.

Tuohy said that they are also investigating long-term and cumulative post-release survival through a tag, release, and recapture procedure that will count surviving fish from the point of return at Cathlamet to McNary Dam.

Regulations on commercial gillnetting, considered by many to be a non-selective method of harvesting hatchery fish due to the bycatch of salmon and steelhead listed under the federal Endangered Species Act, are requiring a change in the commercial industry toward finding ways to selectively and safely harvest fish.

As a result of legislation, the Washington and Oregon fish and wildlife commissions in 2013 adopted harvest reform policies designed to promote conservation of salmon and steelhead, prioritize recreational salmon fishing in the lower Columbia River, and transition gillnet fisheries into off-channel or select areas.

The policy also called for increasing hatchery releases in these areas, while expanding commercial fishing opportunities through the use of alternative fishing gear.

Yet, after nearly seven years since harvest reform, alternative gear assessed in the lower Columbia River have all resulted in high cumulative mortality (a combination of point of release mortality and long-term mortality as fish swim to spawning grounds) in the range of 35 to 70 percent.

Tangle nets, along with beach and purse seines have also been tested, all resulting in higher mortality than pound nets. Immediate mortality of tangle nets has been estimated at 20 percent, while beach and purse seine immediate mortality is about 1 percent, a respectable rate that outperforms tangle nets. However, cumulative mortality rates for beach and purse seines have been estimated at 10 to 50 percent for chinook and 22 to 41 percent for coho salmon.

Researchers used old blue prints of traps used more than 80 years ago to design the one they use in the Cathlamet Channel. The trap is a series of pilings and nets starting at the high water mark on shore and continuing out into deeper water. Fish are passively funneled from the shore to what is called the “lead,” which is perpendicular to the shore, through a maze of net walls and compartments.

“The first of these compartments, the ‘heart’, is positioned at the outside end of the lead and is V-shaped, with the apex pointing upstream. Fish are naturally guided by the shape of the heart and their desire to move upstream through the apex of the V-shaped compartment to what is known as the ‘tunnel,’” the report says. “The tunnel is conical in shape with a wide entrance and a very narrow outlet; it guides fish further upstream to the ‘pot’ and tends to prevent most fish from returning backward to the heart. Once in the pot—a rectangular compartment that can be blocked at both the upstream and downstream ends—salmon are effectively entrapped. The pot acts as a holding pen for fish that are removed from the containment ‘spiller’.”

After fishing for 30 days from Aug. 25 to Sept. 29, 2016, the pound net captured 2,144 salmonids and 2,135 of those were released unharmed or 99.58 percent of the catch.

The pound net outperformed both beach and purse seines on daily catch, with over 70 fish, while beach seine daily catch was about 45 and purse seine catch about 15 fish.

In 2017, fishing from Aug. 26 to Sept. 29, catch skyrocketed with 7,129 fish trapped and a mean daily catch of 215 fish, Tuohy said.

The highest percentage of the catch was coho, with chinook a close second, followed by steelhead. Post release survival for chinook was 99.6 percent and 94 percent for steelhead.

Tuohy concluded that fish traps are efficient, have a high post release survival and are a viable alternative for the commercial fishery.

There is still work to do. Make the gear legal, for one, but also figure out how commercial fishers can use a fish trap and make it profitable. After all, gillnetters are single person businesses and a fish trap would require something like a co-op for the gillnetters to participate.

For 2018, Tuohy said the project will focus on spring chinook and shad. It’s a way to reduce the impact of the invasive fish, he said of the shad, but would require the development of new markets.


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