LEWISTON – Fisheries managers for the Idaho Department of Fish and Game are beginning to get a clearer picture of last fall’s alarmingly low return of wild B-run steelhead.
It will still be months, however, before the analysis, which includes genetic testing, is completed.
Window counts at Snake and Columbia river dams indicate fewer than 500 wild B-run steelhead bound for the Snake River returned to the Columbia River. But those counts are estimates, and there are ways in which they can be misleading.
Fisheries workers who count fish that swim up the ladders at Snake and Columbia river dams use length criteria to determine whether a steelhead belongs to the A- or B-run group. Those longer than 78 centimeters, or 30.7 inches, are classified as belonging to the B-run. Members of the B-run generally spend two years in the ocean and spawn in the Clearwater basin, Middle Fork of the Salmon River and South Fork of the Salmon River. Those not produced at hatcheries are listed as threatened under the Endangered Species Act.
The tally of steelhead longer than 30.7 inches gives fisheries manages little more than a ballpark estimate of the strength of the B-run. That is because some members of the A-run can spend more than one year in the ocean and grow to B-run size. Members of the B-run can also spend just one year in the ocean and return before they meet the size criteria. In years when ocean conditions are poor, as they have been since about 2015, some fish that spend two years at sea don’t grow large enough to meet the criteria.
To be more certain of B-run populations, fisheries agencies partner to trap and sample a small percentage of the steelhead passing the dams. There they take genetic samples to determine where the fish are from and whether they are wild.
But even that is an estimation, because the biologists don’t sample all fish. Instead, they sample a portion of them and apply a formula to estimate the size of the run.
In recent years, the Idaho Department of Fish and Game and the Nez Perce Tribe have worked together to place passive integrated transponder, or PIT, tag detectors at the mouths of wild B-run rivers. The tags are rice-sized devises implanted in fish when they are trapped at the dams.
Brett Bowersox, a research biologist for the Idaho Department of Fish and Game at Lewiston, said based on the detection of the tags at places like the Lochsa and Selway rivers, the department believes the true number of wild B-run steelhead that returned to Idaho last fall was larger than the number counted at the dams.
“Looking at the data we do have in hand, I’m comfortable at saying the estimate of wild B-run in Clearwater (River basin) streams is over 1,000 fish,” Bowersox said.
That number doesn’t include fish that returned to tributaries of the Salmon River.
It is also is an estimate, because only a portion of the run was implanted with PIT tags. The tribe and state used a formula to expand the run. Bowersox said the agencies are running genetic tests on the fish that were tagged to make sure they are all wild fish and not hatchery steelhead that did not have their adipose fins clipped.
Bowersox said of the tagged fish detected entering Clearwater River tributaries, only 18 percent met the 78-centimeter criterion.
“So these fish are still wild fish from B-run populations, but because of the diversity of steelhead life history we saw more one-ocean fish than usual in these populations and also some of the two-ocean fish in these pops, and these areas were not meeting that length criteria they use down at the dams in the windows in the ladders to estimate B-run fish,” Bowersox said.
He said even though the wild B-run was likely larger than what dam counts would indicate, the numbers are still concerning.
“That is still a low number, but it’s much better based on what we saw in window counts,” he said. “There is no way getting around last year was a low abundance year. We are certainly glad to see there were more fish out there than the window counts would have suggested, and we have seen low abundance years similar to this in the past then the populations bounce back in pretty quick fashion.”
The 2018 catch and release steelhead season is open on the Clearwater River. Fisheries officials are expecting about 79,000 A-run steelhead, including 22,400 wild steelhead and 56,600 hatchery steelhead, to return to Lower Granite Dam this summer. The B-run forecast calls for a return of about 17,080 of the big fish to return at least as far as Lower Granite Dam, including 2,380 wild fish and 14,700 hatchery steelhead.
If it comes in as forecast, the steelhead run would be an improvement over the last two years, the lowest on record, but it would still be considered a low return year.
“We are forecasting a better return than last year, but it’s still a relatively low return than we have been getting since about 2,000,” said Alan Byrne of the Idaho Department of Fish and Game at Boise.
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