Home » News » It’s Sockeye Smolt-Out Time at Tustumena Lake

It’s Sockeye Smolt-Out Time at Tustumena Lake

Each year, CIAA conducts “smolt out” counts at Kasilof River of juvenile sockeye on their way out of Tustumena Lake toward Cook Inlet.

by | May 19, 2022

A raft crew prepares the sockeye smolt trat at Tustumenta Lake.
It is all hands on deck for the deployment of the inclined-trap in Kasilof River this year. Using a motorized raft to guide the trap, staff floated the raft down river from the boat launch to install it in the river. Lisa Ka’aihue / CIAA

At 25 miles long, Tustumena Lake is the largest freshwater lake on the Kenai Peninsula. The milky, silty waters are a clue that this glacially-fed lake is quite chilly. And here’s a surprising fact: It is also very deep — deeper, in fact, than any point in Cook Inlet. Tustumena Lake is home to many species of anadromous fish. These are species of fish that migrate from freshwater to saltwater and back during their life cycles. Sockeye salmon is the lake’s most abundant run. It’s prized by commercial, sport, and personal use fishermen who harvest them in the Kasilof River and Cook Inlet. To help evaluate the run and provide data for fisheries predictions, the Cook Inlet Aquaculture Association (CIAA) has started its 23rd year of counting the millions of Tustumena sockeye smolt leaving the lake via the Kasilof River system.

How CIAA Counts Tustumena Lake Sockeye Smolt

A sockeye smolt from Tustumenta Lake.
A representative Tustumena smolt seen in the trap. Breanna Smart / CIAA

During routine smolt counting, CIAA places a smolt trap across a small outlet to capture smolt and count them. Due to the width of the Kasilof River, CIAA installs an inclined-plane trap near the river’s confluence with Crooked Creek. An anchored system of pontoons supports the five-foot wide trap. Water flows up the incline and pours down a series of live boxes that capture the smolt.

On counting days, a team of two CIAA fisheries technicians travel out to the trap via a small boat. They then spend the night counting and releasing the smolt that typically migrate at night to avoid predators. The technicians also collect a portion of the smolt using nonlethal procedures to determine age, weight, and length. After sampling the fish, we release them back into the Kasilof River.

Marking Sockeye Smolt With Gold

Sockeye smolt temporarily marked with gold-colored dye.
CIAA temporarily dyes a portion of the smolt for a mark-recapture study. Ronnie Minter / CIAA

The trap cannot capture every smolt swimming down the wide Kasilof River. That’s why we use a mark-recapture method to estimate the total population. About once a week, the technicians collect 1,000 sockeye smolt from the trap. We then hold the smolt briefly in a large tank, where we mark them with a temporary, harmless gold-colored dye.

We then transport the dyed smolt up river and release them. Our technicians count the gold-colored fish recaptured in the trap to help determine the total out-migration of sockeye smolt from Tustumena Lake.

“This is one of the first weirs we set up every season, as the lead biologist on this project, I always look forward to getting the trap in safely as it means the field season is underway. Our crews are always eager to get out in the field, there is nothing quite like counting those first salmon smolt that make their way into the trap,” says CIAA biologist Emily Heale.

How the State Uses Smolt-Out Counts

The top of the inclined-plan trap with smolt in the live boxes.
The top of the inclined-plan trap with smolt in the live boxes. The water runs swift down the Kasilof River. Ronnie Minter / CIAA

The Alaska Department of Fish and Game reviews the smolt-out information collected by CIAA. Fisheries managers use this data along with adult counts the state collects via sonar in the Kasilof River to make adult return predictions and set harvest limits.

Due to cost and safety considerations, we are investigating alternatives to using the inclined-plane trap in the future. Recently, CIAA entered into a cooperative agreement for ADF&G to perform two years of hydroacoustic and townet surveys on Tustumena Lake. These surveys take only a few days during the fall season to complete, in the relative isolation of Tustumena Lake.

Once these two years of surveys are complete we will decide whether we can get enough information about the juvenile sockeye population to help generate adult return statistics.

It may be less costly to use the survey methods, but it is definitely less risky than putting the inclined-plane trap in the swift, glacial Kasilof River. This process requires extra caution when installing, operating, and removing the trap each year. We worked with Kasilof River sports fishermen to find a trap location that ensures our ability to collect robust data, while also trying to stay somewhat away from the many recreational boats that go down the river in pursuit of kings and sockeyes.

To ensure recreational boaters know about the trap we have signs posted at the boat launch, on the trap, on both banks of the Kasilof River near the trap, and just upstream from the trap. Although we may end inclined-plane trap operations in the future, we intend to keep helping fisheries managers make informed decisions regarding Kasilof River sockeye salmon harvesting opportunities.

See the Season’s Smolt Counts

You can stay up to date on the Tustumena sockeye smolt out by following in-season counts on our website.

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