Washington Hunter
Well-known member
The Associated Press
CORVALLIS, Ore. — A wet winter might seem like good weather for fish, but flooding can pose dangers to aquatic life because of development along rivers, researchers say.
Historic natural river systems were complex, with multiple channels that spread the impact of the flooding and created holding places for migrating and resident fish.
Now dams, development and the transition from forests to pastures and housing tracts have eliminated that complexity from many river systems, said Oregon State University ecologist Stan Gregory.
Development has turned many rivers into single channels that are more like pipes than rivers. And though most adult and juvenile fish can survive those conditions, newly deposited eggs or young fry can be washed downriver, he said. “Historically, steelhead would come back to spawn in the winter over three, four and even five months, depending on the stream,” Gregory said.
But early hatcheries took their eggs from first-arriving fish to ensure their supply, Gregory said, and fish runs began arriving early. The window for returning fish shrank to a couple of months.
“Then the impact of a single flood on the population could be much greater,” he said.
Fortunately, adult fish have proven resilient, Gregory said.
“Steelhead and other native fish have had thousands of years to adapt to flooding,” said Gregory, a professor of fisheries and wildlife.
“Not only can they survive, floods usually improve the habitat by scouring out river bottoms, creating new pools and cleaning out the silt.”
And flooding may even help egg survival in the long term by cleaning out the fine particles from gravel and washing silt downriver, Gregory said. Clean spawning gravel allows for better flow of water over the eggs and supplies oxygen to eggs deposited in gravel redds or spawning depressions.
In studies of trout that live in streams year-round, the number of juveniles rises dramatically in the year after a flood, he said.
After extensive flooding in February 1996, Gregory and his colleagues surveyed cutthroat trout in Mack Creek in the H.J. Andrews Experimental Forest, where they had been conducting studies of trout populations since 1973.
Despite living in a creek that was 3 feet over flood stage, the researchers found 30 percent of the fish stayed in the same 150-yard sections where they were found the year before surviving in a stream that had been a whitewater torrent during the flood.
“In Mack Creek, there were tons of fry in the stream the year after the 1996 flood,” Gregory said. “They were four times as abundant as anything we’d ever seen before.”
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On the Net:
Oregon State University: http://www.orst.edu
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CORVALLIS, Ore. — A wet winter might seem like good weather for fish, but flooding can pose dangers to aquatic life because of development along rivers, researchers say.
Historic natural river systems were complex, with multiple channels that spread the impact of the flooding and created holding places for migrating and resident fish.
Now dams, development and the transition from forests to pastures and housing tracts have eliminated that complexity from many river systems, said Oregon State University ecologist Stan Gregory.
Development has turned many rivers into single channels that are more like pipes than rivers. And though most adult and juvenile fish can survive those conditions, newly deposited eggs or young fry can be washed downriver, he said. “Historically, steelhead would come back to spawn in the winter over three, four and even five months, depending on the stream,” Gregory said.
But early hatcheries took their eggs from first-arriving fish to ensure their supply, Gregory said, and fish runs began arriving early. The window for returning fish shrank to a couple of months.
“Then the impact of a single flood on the population could be much greater,” he said.
Fortunately, adult fish have proven resilient, Gregory said.
“Steelhead and other native fish have had thousands of years to adapt to flooding,” said Gregory, a professor of fisheries and wildlife.
“Not only can they survive, floods usually improve the habitat by scouring out river bottoms, creating new pools and cleaning out the silt.”
And flooding may even help egg survival in the long term by cleaning out the fine particles from gravel and washing silt downriver, Gregory said. Clean spawning gravel allows for better flow of water over the eggs and supplies oxygen to eggs deposited in gravel redds or spawning depressions.
In studies of trout that live in streams year-round, the number of juveniles rises dramatically in the year after a flood, he said.
After extensive flooding in February 1996, Gregory and his colleagues surveyed cutthroat trout in Mack Creek in the H.J. Andrews Experimental Forest, where they had been conducting studies of trout populations since 1973.
Despite living in a creek that was 3 feet over flood stage, the researchers found 30 percent of the fish stayed in the same 150-yard sections where they were found the year before surviving in a stream that had been a whitewater torrent during the flood.
“In Mack Creek, there were tons of fry in the stream the year after the 1996 flood,” Gregory said. “They were four times as abundant as anything we’d ever seen before.”
———
On the Net:
Oregon State University: http://www.orst.edu
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