Tongass culverts a barrier to fish passage

Posted: Tuesday, August 01, 2000

JUNEAU (AP) -- Two-thirds of the culverts that let salmon streams cross roads in the Tongass National Forest may be inadequate for fish passage, according to a study released Monday by state and federal agencies.

Scientists have examined about 60 percent of the permanent roads in the forest, which covers most of Alaska's southeastern panhandles, said Lana Shea Flanders, southeast regional supervisor of the Department of Fish and Game's Habitat and Restoration Division.

The remaining roads and culverts are being surveyed this year, and a similar study of temporary roads also is planned.

Of 273 culverts examined on salmon streams, 179 were found inadequate, Flanders said. Some culverts were completely blocked, but some merely run too fast for young fish to move through easily during high water.

Culverts on streams without salmon were even worse, Flanders said. Of 622 such culverts, 85 percent did not allow proper fish passage.

The most common problem was undersized culverts that produce a rush of water too strong for juvenile fish to pass, Flanders said. Many of the culverts were installed many years ago when requirements for fish passage were lower, Flanders said.

''The science and the art of designing culverts to pass fish has been steadily improving through time as we all learn through the mistakes others make,'' Flanders.

Culverts also become clogged by debris, Flanders said. The flow of water from some culverts erodes the stream bed downstream, leaving the culvert mouth perched several inches above the stream -- too far for young fish to jump.

''It's a not a stable environment and the culverts react to the forces on them,'' Flanders said.

Both state and federal law require that culverts be designed to let the weakest fish pass easily, Flanders said.

The study focused on juvenile coho salmon less than 3 inches long, Flanders said.

Flanders said the culverts' impact on salmon populations hasn't been studied, although she said improving fish passage could increase production.

Tom Puchlerz, Forest Supervisor for the Tongass National Forest, said the agency has spent more than $2 million to address the problem in the last couple of years and has $1.5 million budgeted for culvert replacement next year.

The study is a 3-year joint project involving Fish and Game, the Forest Service, the state Department of Environmental Conservation and the U.S. Environmental Protection Agency.

The 1997 Tongass National Forest Plan raised fish passage standards for culverts and other crossing structures such as bridges.


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