Keywords: Physical environment, Species and food webs, Fishes, Nearshore habitat, Freshwater habitat, Salmonids, Species of concern, Elwha River

Migration patterns have apparently reawakened for the Elwha River's wild steelhead. Studies show that the fish may have retained much of their genetic drive despite 100 years of being trapped behind dams. We continue our series 'Returning home: The Elwha's genetic legacy' with part two of seven. 


The Elwha Ecosystem Restoration Project, including two dam removals from 2011 to 2014, has offered up many surprises. Sediments confined behind the dams for a century washed downstream more rapidly than many experts predicted. Forceful flows carved out new braided channels in the empty reservoirs. The traveling sediment formed new gravel bars downstream. Dynamic forces altered the aquatic ecosystem, while natural vegetation reclaimed the newfound terrestrial habitat, with help from planting crews.

Meanwhile, many observers were amazed by the rapid repopulation of upstream tributaries by young salmonids. NOAA's George Pess talks about hiking into upstream wilderness areas to observe “clouds of juvenile fish that we had not seen before.” Many of these fish were the offspring of migratory salmonids that had gone to sea and were now swimming past the now-vacant dam sites. Genetic studies would later shed light on the ancestry of these surviving salmon stocks.

John McMillan, a longtime salmon researcher who recently took a job as science director with the group Conservation Angler, lives near the Elwha Valley. He has been snorkeling the river for years. In October of 2013, he donned his wetsuit and entered the icy cold waters of Little River, a tributary of the Elwha, for a quick look around.

“That’s when I saw the first summer steelhead to make it past the site of the lower dam,” McMillan said. “I was shocked, because the dam had just been removed. I snapped three photographs. I was so excited that I sprinted back to my truck. That’s when I knew these fish were going to come back.”

A single juvenile steelhead underwater with rocks in the background

Juvenile steelhead. Photo: John McMillan/NOAA (CC BY-NC-ND 2.0)

Looking back to the days of dam construction, steelhead were still spawning in the Elwha River right up to the lower dam, which marked the end of their migration route. But without access to the upper watershed, the number of steelhead going to sea dropped rapidly and continued to decline through the years. From thousands upon thousands of steelhead in the Elwha before dam construction, eventually no more than a few hundred were returning to the five miles of river below the Elwha Dam — and many of those were hatchery fish. For decades, the fate of the would-be migrants trapped above the dams remained uncertain.

Rainbow trout, the non-migratory form of the species, were able to survive above the two dams, but their populations could have been affected by the planting of rainbows and other trout from elsewhere. As dam removal moved toward reality in the 1990s, scientists began to question not only the long-term effects of limited migration all these years but also the historic gene flow. Did the presence of the dams lead to genetic isolation and distinct new populations?

The answer was first revealed in a study of genetic variability among steelhead and rainbow trout sampled at various river locations from 2004 to 2011. The genetic study, led by Gary Winans of NOAA’s Northwest Fisheries Science Center, ended up grouping the steelhead and rainbow trout into three identifiable categories that generally matched the geographic distribution: those found below the lower Elwha Dam, those trapped above the upper Glines Canyon Dam, and those living between the two dams.

Map showing steelhead and rainbow trout sampling in the lower (blue), middle (green), and upper (red) sections of the Elwha River watershed on the Olympic Peninsula of Washington State.

Steelhead and rainbow trout populations and sampling sites in the lower (blue), middle (green), and upper (red) sections of the Elwha River watershed on the Olympic Peninsula of Washington State. Map: Fraik et al. 2021 (CC BY 4.0)

How the three groups fared after dam removal was the subject of a more complex genetic study published last year in the scientific journal Genes. Researchers involved in the study found that the first steelhead to recolonize the upper Elwha were offspring of migrants that spawned below the lower dam, according to lead author Alexandra Fraik, post-doctoral fellow at NOAA’s Northwest Fisheries Science Center. After all, she said, this group had never stopped migrating, unlike the groups trapped above the dams.

After all is said and done, it appears that the genes for restoring both summer and winter runs of steelhead are still intact in the Elwha.

Even so, the number of juvenile steelhead migrating to the ocean after dam removal suggests other factors in play. For example, the genetic signatures of out-migrating steelhead smolts showed a significant parentage from populations living above and between the dams. It appears that the young steelhead may have inherited a genetic proclivity for migration from parents that were non-migrating rainbow trout.

In addition, despite minor but clear differences in genetic makeup, Fraik’s analysis reveals that a high level of genetic diversity was retained in the resident rainbow trout above the dams. Such diversity offers hope for a more rapid recovery for Elwha steelhead.

While one might think that 100 years of isolation above the dams might significantly reduce genetic diversity, that period is just 25-30 generations for steelhead, Fraik noted. In contrast, the tributary of the Elwha called Little River contains a 10-foot natural waterfall on its south fork. The waterfall is considered an impassible blockage to adult steelhead, because of a too-shallow “jump pool” needed for the powerful fish to propel themselves to such heights.

 “Although the dams were present for over 100 years, our results suggest that populations divided by dams were not as diverged as those separated by natural barriers,” states the article published in January 2021.

The large historic population of steelhead before the dams were constructed could be another factor contributing to the high genetic diversity seen in the rainbow trout trapped above the dams, said Fraik, who has studied the dramatic loss of genetic diversity in small populations — including the critically endangered Tasmanian devil of Southern Australia.

 “I think this shows the importance of population size in predicting how a species will respond to big environmental changes,” said Fraik, noting that larger populations tend to harbor greater genetic diversity. “The thing that I found most surprising was how quickly these populations responded (following dam removal).”

Of particular interest in the Elwha are specific genes, discovered in recent years, that govern steelhead behavior. One influential gene, called GREB1L, plays a strong role in determining the time of year that migrating steelhead return to the rivers to spawn. Research in numerous river systems has shown that a genetic variant of GREB1L is associated with an early return of steelhead. These “summer” steelhead generally travel farther upstream than later-arriving “winter” steelhead.

In the Elwha just before dam removal, only a handful of steelhead were showing up during the early time period, from May through October, and most appeared to be strays from other rivers, according to McMillan.

The data show a general increase in adult steelhead moving upstream, from a total of less than 400 in 2013 to nearly 2,300 in 2021, with an increasing percentage of wild versus hatchery steelhead.

“For two years prior to dam removal, I snorkeled the lower Elwha from the dam to the river mouth on a weekly basis,” he said. “I never saw more than three adult summer-run steelhead in the lower Elwha. Plus, one or two of the fish were fin-clipped, so they were hatchery fish from another system, as the Elwha hatchery wasn’t releasing summer runs at that time.”

The life-history strategy of summer steelhead calls on them to wait in the river — often far upstream — for up to six months before spawning. Being trapped below the dams, as they were for a century, increased their risk of death from elevated temperature, predation and other threats. Winter steelhead, which begin arriving in January, don’t wait so long before they are ready to spawn.

During studies after dam removal, Fraik and her fellow researchers were able to sample only seven summer steelhead, resulting in some uncertainty. Nevertheless, they found the GREB1L variant, suggesting a powerful association with early run timing in the Elwha. They also found that steelhead swimming farther upstream were more likely to have this early-migration gene when compared to those in lower reaches.

The researchers also retested genetic samples of rainbow trout collected upstream before dam removal. Sure enough, the GREB1L gene was found in the descendants of fish trapped above the dams. After all is said and done, it appears that the genes for restoring both summer and winter runs of steelhead are still intact in the Elwha.

Counting steelhead in the Elwha has been a challenge at times because of high turbidity, not only from sediment unleashed by dam removal but also from spring snowmelt. To avoid the need for visibility, researchers are now using sophisticated sonar equipment to record the movement of steelhead and estimate the number of migrants.

The data show a general increase in adult steelhead moving upstream, from a total of less than 400 in 2013 to nearly 2,300 in 2021, with an increasing percentage of wild versus hatchery steelhead.

Because the Fraik study on genetic makeup was conducted so soon after dam removal, these results may represent only the first pages of an unfinished book. Future generations of summer steelhead are likely to move farther upstream into the nooks and crannies of an extensive watershed, where researchers will be challenged to find them. Some of the best data on the growing steelhead population is likely to come from improved techniques using smolt traps to count the out-migration along with sonar arrays to count the returning adults.

Up next: Will the mighty spring Chinook rise again?

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View of the Elwha River above the site of the former Glines Canyon Dam in 2021. Photo: Sylvia Kantor

Following dam removal, migratory salmon have been free to swim into the upper Elwha River for the first time in 100 years. Their actual behaviors and reproductive success may well be driven by changes in their genetic makeup. Our seven-part series 'Returning home' examines how the fish are doing and whether the Elwha's genetic legacy remains intact. 

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Two fish swimming underwater with rocks below them.

Our series 'Returning home: The Elwha's genetic legacy' continues with a look at the possible return of spring Chinook to the upper portions of the Elwha River. We bring you part three of seven.

More stories next week!


About the author: Christopher Dunagan is a senior writer at the Puget Sound Institute.

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