Shad horde could threaten Columbia River salmon and rainbow trout restoration efforts

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The salmon and rainbow trout of the Columbia River Basin might have another growing challenge: a horde of American Shad.

In recent years, non-native shad migrating past the Bonneville Dam into the Lower Columbia River has far outnumbered the total number of salmon and rainbow trout counted at the dam, according to a recent report presented to Northwest Power and Conservation Council.

“We’re starting to see shad at several times the numbers of salmon and rainbow trout,” said John Epifanio, lead author of the report. “Shad is the dominant species which now seems to pass over the dam.”

However, less is known about how the shad boom could affect native salmon and rainbow trout runs, Epifanio said.

This uncertainty is the reason why an independent scientific advisory committee wanted to alert policy makers to the growing number of shads. Much remains to be learned about their effects on the ecosystem, Epifanio said.

For example, he said, little is known about whether shads compete for the same food as salmon or if they might eat young salmon. Additionally, little is known about what mammals or birds might eat from shad.

The bigger question is whether shad might be contributing to the decline of salmon and rainbow trout or whether shad might just profit from the lack of salmon, Epifanio said.

In recent years, the non-native American shad migrating past Bonneville Dam outnumbered the total salmon and rainbow trout.

Smithsonian Environmental Research Center / Flickr Creative Commons

“At the intestinal level, with millions of adult fish moving up the river, how can they not have an impact on the ecosystem? he said.

Although shad is not native to the Pacific Northwest ecosystem, bony fish have been in the area for over a century.

Shad first visited the West Coast in the 1800s from the East Coast, Epifanio said. By the 1890s, they had been seen in the Columbia, he said.

The number of shads remained low until the construction of the Bonneville dam, the most upstream dam.

“All of a sudden it made it easier for the shad to move up the river, and we started counting these things as well,” Epifanio said.

With the hydroelectric system allowing the shad to swim upstream, their numbers began to slowly increase, he said.

In addition, Epifanio said, the shad enjoys ideal conditions, including slower water flow, warmer water temperatures caused by climate change and recent patterns of ocean warming near the sea. rating.

Since the 1960s, the number of shads has increased by about 5% each year, according to the report. In some years, shad made up over 90% of the fish counted in dams in the lower Columbia River.

“There is no real sign that the uptrend is leveling off,” Epifanio said.

The trend could mean that shad has become the predominant migratory fish in the Columbia River, according to the report.

Even with so many fish, consumers on the west coast aren’t used to the bone-and-fat shad, he said.

“There is often a prospect that all we have to do is stand them out from the crowd,” he said.

Right now, that wouldn’t work with shad, he said, because there is simply no consumer demand for them.

In addition, salmon and rainbow trout are often entangled as bycatch in the nets that catch shad, he said.

“You have to be careful not to go for a too simple solution that may not really work,” Epifanio said.

To learn more about American Shad, researchers at the Pacific Northwest National Laboratory develop a small fish tag it could help to study juvenile fish.

In addition, the developers of Whooshh innovations, also known as the salmon cannon, suggested a scanning system in the wake of Whooshh Innovations, technology could keep shad under dams.

In a Darwinian turn, while the American shad appears to have adapted successfully to the west coast, the native shad is rapidly declining throughout the east coast, Epifanio said.

“It’s a fascinating case study of how a species has adapted to a new environment,” said Epifanio. “If we can understand this, it has broader implications for other species of fish in other contexts.”


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