Coho in spawning colors move past a deconstructed dam in the Dredge Lakes area this week.
Coho habitat destroyed by beaver dam dismantler
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 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.
This is a nice reminder from Juneau that beavers help salmon and people who rip out beaver dams hurt salmon. (Just in time for the salmonid conference, and I hope everyone attending reads it.) If I had my way every person in the hemisphere would read it, and probably a few in Scotland.
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,” said Schneider. “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.”
I want a beaver patrol! How do we get a beaver patrol? My guess is that this is the off shoot of the group of folks started by Bob Armstrong who dismantled dams in Mendenhall Glacier State Park so that the rangers wouldn’t have to exterminate to control flooding. He made sure that Mike Callahan came out and did a field assessment for them. The Tongass forest isn’t that far away, so I’m guessing these groups are related.
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.
If we learn anything about beavers and salmon it will happen in Alaska first, where there are four species of salmon in massive supply and the entire economy hinges on their life cycle. That’s where Michael Pollock started his research and where people really started to see that beavers make the difference to population numbers. People in Alaska are really really smart about beavers. Maybe I should move there.
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.”
Sigh. Never mind.
