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Study shows Snake River steelhead anglers more likely to catch hatchery than wild fish; catch-and-release mortality is low

A University of Idaho study indicates anglers catch wild steelhead at a lower rate than hatchery steelhead.  (Eric Barker/Tribune)
A University of Idaho study indicates anglers catch wild steelhead at a lower rate than hatchery steelhead. (Eric Barker/Tribune)
By Eric Barker Lewiston Tribune

LEWISTON – Anglers are more likely to catch hatchery than wild steelhead in the Snake River Basin, according to a study by a University of Idaho graduate student.

The student, guided by a professor with the Idaho Cooperative Fish and Wildlife Research Unit, documented catch-and-release mortality rates to be less than the 5% level assumed by state and federal fisheries officials. Both findings could help fisheries managers justify sometimes controversial recreational fishing seasons that target hatchery fish but also involve the handling of protected wild steelhead.

“Overall hatchery fish encounter rates are in fact greater than wild fish encounter rates, and we saw that pretty consistently across both spawn years,” said graduate student Will Lubenau, who recently defended his master’s thesis based on the work. “It’s about 20% higher on average.”

Lubenau spent two years tracking steelhead on the Snake River and its tributaries. In a cooperative study that involved the Idaho Department of Fish and Game, UI and the U.S. Geological Survey, Lubenau placed visible tags on both wild and hatchery adult steelhead intercepted at Lower Granite Dam or caught by him and UI professor Michael Quist on the Clearwater River. Anglers who subsequently caught tagged fish were asked to remove and report the tags, some of which carried rewards of as much as $200.

The fish also were implanted with tiny passive integrated transponder tags that can be detected by PIT tag readers placed at the mouths of spawning tributaries, at hatchery facilities and at downstream dams.

The combination of tags allowed Lubenau and Quist to track the study fish and determine how many were documented to have been caught or not caught, and how many from each group were later detected entering spawning streams, hatcheries or attempting to pass Snake or Columbia river dams on a bid to return to the ocean after spawning.

The researchers also were able to calculate a mortality rate for caught-and-released fish by comparing the later detection rate of fish known to have been caught with fish that were not documented to be caught.

Lubenau said during the 2019-20 season about 30% of the wild steelhead in the study were caught at least once and 57% of the hatchery fish were caught. In the 2020-21 season, 37% of wild fish and 52% of hatchery fish were documented to have been caught. Across both years, about 35% of the wild fish and 53% of hatchery fish were encountered by anglers.

He documented a catch-and-release mortality rate of about 3.8%. When he looked at the mortality rate just for fish with reward tags, he found a mortality rate of 3.9%.

Quist said the work gives Idaho Fish and Game biologists a better idea of more accurate wild fish encounter rates. The agency now assumes wild and hatchery steelhead are caught at the same rate.

Wild steelhead in the Snake River Basin are listed as threatened under the Endangered Species Act and anglers who catch them while fishing for hatchery steelhead are required to release them. State fisheries agencies must obtain federal permits to ensure their fisheries don’t further harm imperiled species. Throughout the Northwest, state fisheries agencies assume 5% of the wild steelhead that are caught and released die from the encounters.

The study showed the 5% assumption is close and likely appropriately conservative. It also illustrated the assumed encounter rate of wild fish is substantially higher than what is happening. Work by a former UI graduate student, Stacey Feeken, suggested wild fish likely are caught at a lower rate. Feeken tracked hatchery and wild steelhead in an earlier study, as well as where anglers concentrate their fishing efforts, and showed wild and hatchery fish often occupy different stretches of river, and anglers concentrate their efforts in areas with more hatchery fish.

Lubenau’s study built on Feeken’s work, and Quist said the results are good news for anglers, wild fish and fisheries managers.

“It’s relevant for conservation of wild fish and it’s also relevant for the recreational fishery, so it’s good news in all ways, truthfully, because it shows the impact rate – how many wild fish are handled by anglers and ultimately die as result of the fishery – is going to be fairly trivial,” he said.

The study found some fish are caught more than once, about 31 across both years. But those twice-caught fish had nearly identical post-catch detection rates as fish documented to have been caught one time.

“Those fates are essentially the same, 70% versus 71%, which is going to suggest that multiple captures – first of all, they don’t occur that often in the basin, and when they do occur, they seem to survive being encountered multiple times pretty well,” Lubenau said. “It just doesn’t seem to be a huge concern.”

Brett Bowersox, a Fish and Game fisheries biologist at Lewiston, said the results aren’t likely to prompt the agency to make any changes to how it manages steelhead fishing seasons in the short term.

“It illustrates the management scheme or the way we are calculating the impact of the fishery has been conservative,” he said. “That is the correct side of that equation we want to be on, of managing conservatively when it comes to a valuable wild fish resource and a valuable recreation fishery.”

Lance Hebdon, chief of fisheries for the Idaho Department of Fish and Game at Boise, said the study results may prompt the agency to look at how it calculates wild fish encounter rates, but he would like to see it repeated. He noted the work was done during a period of low steelhead abundance.

“The last five years we have been operating on fairly low wild runs and low hatchery runs,” he said. “It would be good to repeat this when the runs bounce back.”

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