Two good-sized steelhead are seen in a net in this file photo.

Last year’s Idaho steelhead run received a lot of attention for the wrong reason. It was a low run year, and Fish and Game biologists did not initially see as many fish back as they would have liked, but they were pleasantly surprised in the spring.

The wild run of large fish known as “B-runs” destined for the upper Clearwater, Middle Fork and South Fork of the Salmon rivers received even more attention because of a very low return based on window counts at dams as steelhead migrated up the Columbia and Snake rivers. The low return focused the attention and concerns of fisheries managers and anglers alike. But data from last fall suggested the return of wild B-runs wasn’t as low as window counts estimated and information gathered during spring in spawning streams confirmed it.

The actual spawners in wild B-run drainages exceeded a thousand fish despite dam counts showing less than 500. Wild steelhead are divided into two categories — A-run and B-run — based on length, which is useful for managing Columbia River fisheries, but a bit misleading when those fish return to Idaho streams. In general, B-run fish are older and larger than A-run fish, and B-runs start their spawning migration from the ocean later in the fall than A-runs. There is a lot of variation in Idaho’s steelhead populations and what we see in the wild does not always perfectly align with those simple categories.

Lower Granite Dam on the Snake River is the last of eight dams steelhead cross prior to entering Idaho waters. People counting fish at the dam’s fish ladder classify B-run steelhead as those longer than 30.5 inches. Based strictly on fish size at Lower Granite window counts last fall, there were 452 B-runs, which was the lowest estimate since counts started in 1987.

Idaho Fish and Game personnel, along with federal NOAA fisheries staff, trap wild steelhead as they pass through Lower Granite Dam’s fish ladders. Personnel tag the fish, measure their lengths, take samples for genetics and scrape off scales that determine how old each fish is. Tiny electronic tags are inserted into the fish, which are then detected upstream when the tagged steelhead swim into spawning tributaries. The age, length and genetic data from steelhead tagged at the dam can be identified within a specific spawning population, giving fisheries managers a better understanding of the biology of the fish. Based on the tag detections over the last nine years, biologists know not all fish destined for the B-run rivers and streams are longer than 30.5 inches. Some are smaller, and spent only one year in the ocean, while some fish that spent two years in the ocean still don’t grow to 30.5 inches if they did not find enough food.

Biologists saw a larger percentage of smaller steelhead returning to these B-run streams during spring. Only 18 percent of the steelhead swimming past the detectors in B-run streams were longer than 30.5 inches. So, those fish were not identified as B-runs in the window counts at the dam. Only after the spawning season could Fish and Game account for that difference based on detections of fish at the instream detectors, so biologists were able to estimate that 1,000 to 2,000 wild steelhead spawned in Idaho’s B-run streams during spring.

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