Coho habitat destroyed by beaver dam dismantler

Coho in spawning colors move past a deconstructed dam in the Dredge Lakes area this week.

Last summer was a great year for coho salmon returns to Dredge Creek. Unfortunately, salmon redds in the creek below Dredge Lake have been negatively impacted by someone it appears was trying to help them, says the Beaver Patrol.


The “Beaver Patrol” is a group of volunteer Juneau naturalists and concerned citizens who have been working in the Dredge Creek and Dredge Lake area — U.S. Forest Service Land — for about five years. They and the Forest Service manage the dams and have improved salmon habitat in the stream, said member Chuck Caldwell.

Another factor helping Dredge Creek’s coho rearing? Beavers.

In late October of last year, the Beaver Patrol became aware that someone was destroying the dams in Dredge Creek between the holding pond and Dredge Lake.

Caldwell had taken note of three different redds — nests of pebbles where salmon deposit their eggs — just above a beaver dam. A fourth was outside the main channel and needed a nearby dam to maintain its water depth. The destruction of the dam lowered the water and this winter that area froze, he said.

“He was tearing (the dams) out once or twice a week. Clearly he just hated beavers. He also wanted to dig in the stream to make a nice, deep channel. He dug through two of the redds,” Caldwell said.

The digging and the dismantling of the dams destroyed all the salmon redds he had observed in that area, Caldwell said.

In the first half of November, Beaver Patrol member Jos Bakker ran into and confronted the man when he was in the process of destroying a dam. The man doesn’t appear to have come back after that, but the damage was already done, Caldwell said.

Tongass Fisheries Biologist Pete Schneider said he’d be reluctant to draw conclusions about the overall health of the stream’s salmon population based on those actions, especially as Dredge Creek is impacted by humans regularly.

“If I caught a person doing that, it would be a perfect opportunity to educate them on what may or may not happen,” he said.

The Beaver Patrol emphasizes beavers’ positive impact on salmon rearing.

“If you look back a couple of decades, people used to think that if you got the dams out, the fish could move back easier,” Caldwell said. “That’s not the limiting factor in the coho population. The limiting factor is having a habitat the juvenile cohos can live in.”

“By and large, it’s a safe bet that beaver dams do provide excellent coho rearing habitat,” Schneider said. “They can cause major problems for adult cohos to access fish habitat, and that’s probably what gets most folks in the public tempted to tear out dams. It has to be a fine balance, like anything else ... In a normal setting, you would have these major flood events on occasion. It would rearrange them and keep them in check. You’re not going to get that in Dredge. On top of that, there are not normal predator levels that you would find in a normal wild setting.”

Dams’ impact on adult salmon in a setting like Dredge is something about which the Beaver Patrol and the Forest Service are not in complete agreement. Member Mary Willson says 90 percent of the time beavers are actually helpful to coho populations. Schneider disagrees.

This doesn’t prevent them from working together; Schneider emphasized the importance of the Forest Service’s partnerships with volunteers like the Beaver Patrol.

“If it wasn’t for groups like that, it would be a lot harder for us to do our jobs,” he said.

Something they do agree on: Even when dams are at a level at which they may impact adult salmon, that’s no reason to rip one out.

That’s where people like Beaver Patrol member and Cub Scout leader Scott Miller come in.

Miller is leader of Mendenhall River Community School Cub Scout Den 1, Pack 7. He and the cub scouts, also Beaver Patrol members, have been helping to open fish passage in the upper dams above Dredge Lake for the last five years.

Some of the redds in that area may have fared better, as the dams weren’t destroyed, Caldwell said.

Miller said he’s seen coho clear a six-foot dam when the water is high. “They definitely can jump if they can get a deep enough pool below,” he said.

In a careful process, Miller and the scouts sometimes notch the dams to increase water flow and help salmon passage. Sediment from the dams has to be carefully handled so that it doesn’t wash down and cover the redds.

“In fall, when fish show up, we go up every day,” Miller said. “We got quite a few (around 100) coho up to the upper branch of the stream this year…. It is an active spawning ground that is being restored slowly and somewhat naturally.”

When he and the cub scouts notch the dens, they use specific techniques and tools to ensure muddy debris doesn’t end up covering redds.

Beaver management does require a balance, Miller said.

It’s one of those interesting situations,” he said. “It’s true that habitat is being created, but at the same time, beavers are very destructive.”

In areas where beavers might create an aesthetic issue, the patrol has put a cloth around the trees that will keep the beavers from gnawing them, Miller said.

“We do clear culverts and try to prevent trails from flooding, but only the minimal amount that’s necessary. We don’t walk in the stream beds, so we don’t kill next year’s, two years, or three years down the road the new crop that might be coming back,” he said. “It’s a pretty unique place, but we do have some challenges. One of them is having people aware it’s being actively managed.”

Willson said Dredge Creek has two families of beavers, one upstream and one downstream. (Her most recent census was after the destruction of the dams, none of which were lodges.)

Right now the Mendenhall Glacier area is supporting about all it can handle, she said. If and when the population increases, she expects the young beavers would relocate.

• Contact Outdoors reporter Mary Catharine Martin at


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