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How CIAA makes beaver dams better for salmon

Beaver dams can help protect juvenile salmon from natural threats, but they can also block runs. Learn how CIAA helps keep salmon running.

by | August 12, 2022

The pond created by a beaver dam at Shell Creek provides important habitat for juvenile salmon. CIAA

Although beaver dams improve natural habitat for young salmon, sometimes they can get in the way of adults trying to spawn. Salmon have been cruising into our rivers since sometime in May, but many of these fish are just now arriving to their home waters. Salmon have instinctively return to the lakes and streams where they hatched. Those salmon born in our hatcheries also attempt to return to the same streams, lakes, or bays where Cook Inlet Aquaculture Association (CIAA) releases them.

Beaver dams can benefit juvenile salmon by buffering streams against flooding and cleaning up water that passes through them. If returning adult salmon can’t get past a dam, they won’t be able to spawn and produce the next generation of juveniles.

A beaver dam at Shell Creek. CIAA

An aquatic obstacle course

While most of our salmon don’t have trouble finding the Kenai or Susitna rivers, most continue to smaller tributaries and the lakes that feed into them. Many small streams present a challenge to salmon trying to swim up them. During dry years, they may be too shallow. During hot years, they may be too warm for the cold-blooded fish.

Most of the time, though, beavers are trying to dam those streams up. Those big rodents are trying to make ponds to live in and open up their access to surrounding wetlands.

CIAA biologist Andy Wizik notching a dam on Shell Creek. CIAA

How CIAA improves beaver dams

One of the first projects CIAA took on in 1978 was to find ways to reduce the harm beavers can have on salmon habitats without removing the benefits. We tried blocking beavers from a notch in the dam, and we tested different culvert configurations. All of them were no match for the tenacity of beavers.

After a lot of trial and error, CIAA decided on the best way to help salmon get past these barriers. We made a list of dams that were causing problems and made a temporary notch on top to let fish swim up river. Shortly after notching, the beavers patch it back up — but there is another benefit to this method.

Often, the issue with a dam is not the height, because we know that salmon are pretty good jumpers. The problem is the silt that builds up under the dam.

Depending on the creek, there may only be an inch or two of water below the dam. Because it is so shallow, salmon cannot orient themselves upward to get a running start at a jump attempt. Once we notch a dam, a large hole forms beneath it that may allow fish to clear the dam even after the beavers get it fixed.

Beaver dam surveys

We regularly survey several streams with beaver dam issues, as well as other streams in the Cook Inlet region where we hear reports of dams blocking salmon.

In August and September, we send crews out by helicopter to look for stranded salmon. When we find fish impounded behind dams, we first find a safe place to land. We then create a 3- to 5-foot notch in the middle of the dam using hand tools and people power.

Then, the salmon do what they do best: head up stream. Because the dam had trapped them, the salmon are often in a hurry and begin to swim past before we even finish the work.

Helping out the little guys

When many people think of the Susitna or Kenai rivers, we tend to think of one large salmon run. These runs, however, lead to several smaller systems. A Susitna salmon may in reality be a Yentna salmon, which may be a Skwentna salmon, which, in turn, may be a Talachulitna salmon. Once it has made it back to the Talachulitna it may still not be home; it may be headed for Trinity Creek where beaver dams could end its journey to the lake. 

By surveying for and notching beaver dams, CIAA aims to ensure that all of these “minor” salmon stocks remain viable. In doing so, we can make sure we see the greatest diversity in the gene pool and make sure we do not lose the many building blocks that make up the Southcentral Alaska salmon runs.      

Report blocked salmon runs

We are beginning this season’s beaver dam surveys. If you know of a beaver dam that is currently blocking salmon in the Cook Inlet region, please call Andy Wizik.

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