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NW Fishletter #385, Sept. 4, 2018

[4] More Small Fish Led To Undercount Of Idaho's Prized Steelhead Last Year

Biologists say last year's wild B-run steelhead count appeared exceptionally low because the return to Snake River upper tributaries included a large fraction of unexpectedly small fish.

Only 452 were thought to have passed Lower Granite Dam, the lowest number since counting of these fish began in 1987. But now it seems the numbers of these prized steelhead returning home to spawn were actually two-to-four times higher.

For fishing advocates and salmon recovery groups, last year's reported low returns were devastating.

"Extinction is alive and much too well in central Idaho," Save Our wild Salmon wrote. Idaho Rivers United published a guest article headlined, "On the Edge: wild Clearwater B-run steelhead teeter on the precipice."

The Conservation Angler wrote, "Idaho, still famous for potatoes, used to be famous for big wild steelhead. How big? The biggest in the lower 48 states." The article noted that last year's return, compared to the early 1960s, declined by 99.9 percent.

Some called for a ban on steelhead fishing, while others concluded that breaching the four lower Snake River dams is the only solution--Lower Granite, one of the four, is in southeastern Washington.

Now, Idaho Department of Fish and Game biologists say that while the numbers are still low, between 1,000 and 2,000 actually returned. The reason needs explanation about B-run fish and how they're counted.

One of the main characteristics of a B-run fish is size. Generally, they're 30.5 inches or larger, and that's how fish-counters at the dams distinguish them from A-run steelhead. They usually spend two years in the ocean instead of one.

But the real distinguishing feature, according to IDFG fisheries biologist Brett Bowersox, is that they return to the Clearwater basin, and to the Middle Fork or South Fork of the Salmon River.

Last year, the B-run stocks were vastly undercounted. Bowersox told NW Fishletter that's because the return included unusually small fish, which he said is part of a trend in Snake River steelhead. Biologists are documenting smaller-sized steelhead in hatchery stocks, for which they have collected data for many years.

He noted "there's a similar trend with steelhead in the Lochsa River," which are also B-run fish, although that's based on "a shorter data set." This smaller size "seems to be a part of the equation of what's going on."

It's not only steelhead in the Snake River that are getting smaller.

Michael Milstein, spokesman for NOAA Fisheries in Seattle, said researchers have also documented that the average size of Chinook--known as the "king of salmon"--is shrinking, all the way from California to Alaska.

Based on data from wild and hatchery populations of Chinook over the last four decades across the northeast Pacific Ocean, a study published Feb. 27 in the journal Fish and Fisheries found both are becoming smaller and younger throughout most of the Pacific coast.

"While it remains to be explored whether these trends are caused by changes in climate, fishing practices or species interaction such as predation, our qualitative review of the potential causes of demographic change suggests that selective removal of large fish has likely contributed to the apparent widespread declines in average body sizes," the study stated.

"The trend of smaller fish is important, and disconcerting," Milstein said in an email.

In interviews with NW Fishletter, Gregory Ruggerone, a research scientist at Natural Resources Consultants, Inc., and a member of the Independent Scientific Review Panel, has also suggested that increasing numbers of wild and hatchery pink salmon throughout the Pacific could be significantly affecting other salmon species, including the growth and survival of steelhead; and on sockeye, Chinook, coho and chum salmon.

Another study, published in the May 2012 issue of Fisheries Oceanography, looked at the summer diets of steelhead in the north Pacific Ocean and Gulf of Alaska and concluded that "interannual variations in climate, abundance of squid, and density-dependent interactions with highly-abundant stocks of pink salmon were identified as potential key drivers of steelhead productivity in these ecosystems."

Regardless of the reasons for the smaller B-run steelhead, Bowersox said, while last year's B-run steelhead return of between 1,000 and 2,000 fish wasn't great, it wasn't catastrophic either.

The error at counting windows happened because fish-counters determine those they believe to be Idaho's wild B-run by size. A-run steelhead are generally smaller than 30.5 inches long, and B-run fish are generally larger. But not last year.

Bowersox said the window counts are preliminary, and final numbers are still awaiting analysis from DNA collected this spring. When steelhead make their way through Lower Granite Dam's fish ladders, biologists trap some of the wild fish, measure them, scrape off a few scales for DNA analysis, and tag them before releasing them. Those fish are then detected when swimming into their tributaries. In-stream detectors this spring showed that between 1,000 and 2,000 wild steelhead spawned in Idaho's B-run streams, he said.

Although much attention is paid to the B-run fish, IDFG does not manage the wild A-run and B-run steelhead differently, Bowersox said. Both are threatened under the Endangered Species Act, and the B-run's longer length is a general characteristic.

"The fact of the matter is, there are fish that return to the Lochsa and Selway [rivers] that in general are a little older and larger than the fish that return to the lower Clearwater or lower Salmon," Bowersox said. "But there's a lot of diversity and variation in these populations that makes the terms A-run and B-run misleading."

That diversity means some B-run fish are smaller than 30.5 inches and spend only one year in the ocean, and some that spent two years in the ocean didn't grow to 30.5 inches because they didn't find enough food. Last year, in particular, there were more small B-run steelhead than usual--only 18 percent of the steelhead detected entering the B-run streams were larger than 30.5 inches, Bowersox said.

Biologists will have a more specific number for last year's B-run when genetic analysis is complete, he said. "We're very confident that it's better than what the window counts showed us. And that's good, but there's no way getting around that last year was a bad year."

This year's B-run steelhead are starting to show up at Bonneville Dam, Bowersox said, and it's too early to predict either the size or the numbers in Idaho's still-famous steelhead run. -K.C. Mehaffey

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NW Fishletter is produced by NewsData LLC.
Publisher/Editor-in-Chief: Mark Ohrenschall, Editor: K.C. Mehaffey
Phone: (206) 285-4848 Fax: (206) 281-8035

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