Hands-on, high-tech methods combine at salmon weir

One fish, two fish

Posted: Sunday, September 10, 2006

Beneath the lacy shadows of deciduous trees, Hidden Creek tinkles like a wind chime as its ankle- to knee-deep water tumbles over a bed of gravel and rocks. But when Gary Fandrei followed the length of the creek downstream from where it ducks under Skilak Lake Loop Road on Sept. 1, he was greeted by a very uncreek-like sound.

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  Approximately 6,900 fish captured at a fish wheel on the Kenai River were tagged this year using a passive integrative transponder, or PIT tag. The tag, about the size of a dill seed, is injected into the cheek plate of each fish using a hypodermic needle. Photo by Patrice Kohl

The metal bars of a weir clinked in their sockets as more than 100 salmon pushed and jumped at the weir like dogs in a kennel.

The weir acts like a fence, holding the salmon on its downstream side until they can be counted and released to continue their journey upstream to spawn in Hidden Lake.

Hidden Lake sockeye have been counted at the weir for nearly three decades, but this year the weir is also part of a broader project to help the Alaska Department of Fish and Game get an estimate of how many sockeye salmon are returning to the Kenai River, said Fandrei, who is executive director at the Cook Inlet Aquaculture Association.


Sockeye salmon throw themselves against a weir in Hidden Creek while Cook Inlet Aquaculture Association Executive Director Gary Fandrei prepares to open the weir to release and count them.

Photo by Patrice Kohl

The “mark and recapture” project begins downstream on the Kenai River where sockeye are caught and receive a tag, also known as a passive integrative transponder, or PIT tag. The fish are caught at a Fish and Game fish wheel at the department’s sonar station at mile 19 of the Kenai River. The tag is injected into the salmon’s cheek plate using a hypodermic needle.

Fish carrying the tiny tag, about the size of dill seed, can then be detected and logged by electronic readers installed at the Hidden Creek and Russian River weirs, Fandrei explained as he prepared to open a section of the Hidden Creek weir and count salmon Sept. 1.

Fandrei stood ready at the opening in the weir with a silver counter cupped in his hand. As the fish began pushing their way through the opening in the weir, Fandrei’s extended hand bobbed in the air, marking each fish with a push of a button on the counter.

Some of the fish that pass through the weir carry battle scars received further downstream. Faint ring-like scars circle the bodies of fish that managed to squeeze through gillnets, and small flesh tears mark salmon that pulled free of anglers’ hooks. Others take hooks with them, carrying them all the way from the Kenai River to Hidden Creek.


Trent Dodson, a Cook Inlet Aquaculture Association biologist, plucks a scale from a sockeye salmon. Biologists can use the scale to determine how many years the fish spent in freshwater and how many it spent in saltwater before it returned to Hidden Creek to spawn.

Photo by Patrice Kohl

“Yesterday, behind the weir, we probably picked up 20 hooks,” Fandrei said, pointing to a tree near the creek where he and two other people visiting the weir had deposited the hooks a day earlier. “They’re carrying them up and then they drop off.”

As he counted, Fandrei noted another deformity that salmon sometimes suffer after an encounter with fishermen.

Just upstream of the weir a sockeye swam weakly, moving neither forward or backward in the creek. From nearly head to tail the salmon’s body was covered in milky white patches, like a rock covered in lichens.

“This fish with the fungus all over his head was here yesterday,” Fandrei said, pointing to the fish. “I don’t think he’s going to make it. I think he’s going to tire out and end up against the weir and die. I give him credit for making it this far.”


Fandrei checks a data logger at the Hidden Creek weir to see how many tagged fish have been detected swimming past the weir.

Photo by Patrice Kohl

Although salmon might get infected with fungus without having encountered a fisherman, their risk of becoming infected is greater after a fisherman has handled them, particularly if the fisherman does not handle the fish carefully, he said.

The mucus-like slime that covers a fish protects the fish from infections, and handling can remove the protective slime, increasing a fish’s risk of acquiring an infection, Fandrei explained.

After about 15 to 20 minutes, the fish that had been pushing at the bars of the Hidden Creek weir made their way upstream and Fandrei reclosed it.

Fandrei looked down at the silver counter, which read 101, and then walked over to the data logger on the creek bank to see if the electronic reader had detected any tags among the fish he counted.

The electronic reader on the weir will count fish carrying tags, but the majority of the fish that swim by are untagged.

By counting all of the fish that swim by the weir visually and then checking the electronic reader to see how many of the fish were tagged, the CIAA can tell Fish and Game what percentage of the fish were tagged. The department can use that information to produce an estimate of how many fish have entered the Kenai River.

“We know the percentage of fish that are tagged, they know how many are tagged, they can then use the number tagged and that percentage and get a total estimate of the population,” Fandrei said. “That’s the basis behind it.”


Approximately 6,900 fish captured at a fish wheel on the Kenai River were tagged this year using a passive integrative transponder, or PIT tag. The tag, about the size of a dill seed, is injected into the cheek plate of each fish using a hypodermic needle.

Photo by Patrice Kohl

Say, for example, that Fish and Game tag 10,000 late-run sockeye in the Kenai River and learn 1 percent of the sockeye counted at the Hidden and Russian River weirs are found carrying those tags. Assuming that the percentage of tagged sockeye is the same for the Kenai River drainage system as a whole, Fish and Game can then estimate that 1 million late-run sockeye entered the Kenai River.

This is the quick and dirty explanation of how the sockeye run estimate is reached using the tags. There are additional factors Fish and Game considers when reaching its final estimate, but this relates the basic idea behind how the project works.

Among the 101 fish Fandrei counted Sept. 1, one marked fish, carrying tag 161000749960, was detected. Fandrei said he did not know when that particular fish was tagged, but a record of when each of the project’s fish are tagged is available at Fish and Game. A call to Fish and Game a couple of days later revealed that the fish had been tagged at Kenai River mile 19 on Aug. 20, 13 days before it swam past the Hidden Creek weir.

Using the fish wheel at river mile 19, Fish and Game captured, tagged and released 6,900 fish from July 1 to Aug. 24, 215 of which also received radio tags enabling biologists to track their progress more regularly.


A sockeye salmon swimming above the weir was found covered with fungus. Fish become vulnerable to fungus infections when fishermen do not handle them carefully and wipe away a protective slime found on the outside of the fish.

Photo by Patrice Kohl

The radio tags, about the size of a fourth of a hot dog, were inserted into the salmons’ stomachs and give biologists a better idea of where sockeye salmon are going to spawn. The Kenai River drainage area includes many creeks and lakes, and by tracking the radio-tagged fish, Fish and Game can get a better idea of which are most heavily used by sockeye entering the Kenai River, said Tim McKinley, a research biologist for Fish and Game.

CIAA began counting fish at the Hidden Creek weir July 8 and detected their first tagged fish Aug. 1, Fandrei said.

Soon after Fandrei finished counting Sept. 1, CIAA biologist Trent Dodson arrived to help measure, weigh and take scale samples from sockeyes as more slowly congregated at the base of the weir.

Fandrei spotted one and scooped it into a landing net. The fish was hung from a scale using the net and weighed in at 5.7 pounds. Once Dodson jotted down the weight and sex — male — Fandrei transferred the fish to a shallow wooden trough, where the fish was measured from its eye to the fork in its tail.

Fandrei measured the fish at 19.5 inches, Dodson recorded the length and then descended, armed with tweezers, to where Fandrei was holding the fish.

Dodson swiftly plucked a scale and placed it on a wallet-sized card before Fandrei returned the fish to the creek.

Using the scale, biologists can determine the salmon’s age and how many years of its life it spent in fresh water and how many it spent in saltwater.

“You’ll get these rings,” Fandrei explained, drawing an illustration of a fish scale. “Each one of these rings is not an annual growth, but you’ll look for where the rings are close together and far apart. Because they grow slow in the winter and fast in the summer. The other thing that happens is that when they hit saltwater they start growing real fast so you’ll see this big spurt of growth.”

Sockeye returning to Hidden Lake typically spend one year in freshwater then two years in the ocean before they return to spawn. In comparison, typically larger Skilak Lake sockeye usually spend two years in freshwater and three years in the ocean before swimming up the Kenai River to spawn in Skilak Lake.

As Fandrei and Dodson continued to record measurements and collect scales from sockeye, the conversation turned to the fungus-infected fish swimming above the weir.

“In honor of Gary, I always call them cheeseheads,” Dodson said, referring to Fandrei, who moved to Alaska from Wisconsin.

When called for an update on Friday, Fandrei said that he and Dodson where still counting fish at the weir. But based on the preliminary data they had collected so far, he said that among the approximately 38,500 fish that had been counted, about 208 tags had been detected.

McKinley, with Fish and Game, said the department initiated the project to “ground-truth,” or test the accuracy of, the Kenai River sonar counter.

With something as valuable as sockeye salmon are to the peninsula, it’s important to get the best possible abundance estimate, he said.

“So much of the economy around here, with the commercial fishing, recreational fishing and dipnetting, is based on how many fish come into the river,” he said. “And it’s good business to evaluate and reevaluate the program that we have here.”

Patrice Kohl can be reached at patrice.kohl@peninsulaclarion.com.

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