Last month, the Alaska Department of Fish and Game and U.S. Fish and Wildlife Service wrapped up fieldwork for phase one of a project that tags coho salmon and traces their movement via radio signals. Scientists want to better understand their spatial distribution, including where they’re swimming, how they’re getting there and where they’re spawning.
Ken Gates is a senior fish biologist with U.S. Fish and Wildlife. He says the method of tracking, known as radio telemetry, is a common practice among biologists.
“Knowing where fish are through this technology can help us prioritize where we spend our money,” he said.
Gates says the project informs scientists on how the Kenai River’s fishery is being used and what enhancement efforts, like fish passage culverts, are needed in the future.
“One of the biggest take homes for me would be the future of where this project could lead,” said Johnna Elkins, a fishery biologist with the Alaska Department of Fish and Game. She ran the project’s day to day operations in the field.
Since fieldwork began in 2022, the agencies have jointly tagged about 1,300 coho on the Kenai River between the Kenai River Bridge in Soldotna and Bear Creek, about a mile downstream of the Funny River confluence. The tags themselves are small, programmed to emit signals 24 hours a day for 240 days. They’re inserted into the coho’s stomach through the mouth with an antenna that sticks out.
During the late summer and early fall months, scientists were on the river every day of the week netting and tagging coho. Gates, who wasn’t in the field, says the team also tracked the tagged coho twice a week by boat, air or foot.
“We have to physically go out weekly to track these fish with radio receivers that decode the radio frequency that’s coming out of the tag," Gates said. "We have specialized equipment that is tuned for a certain frequency range.”
Scientists say some of the radio tags were tracked to coho that later died, or had been fileted. The tags had a phone number labeled on them in case an angler found one. They say this season, about 30 of the nearly 450 deployed were called in.
Although there’s been some less comprehensive studies that have tracked the movement of Kenai River coho, scientists say there are still a lot of unknowns about their behavior. So far, new data from this sample size dispelled a myth that coho runs can happen in early winter. The team didn’t catch much after mid-October.
Gates says the team also found that tributary spawning coho entered the river before those that spawned in the mainstem.
“The Kenai River, for whatever reason, has a lot of uniqueness to it compared to other watersheds throughout the state," Gates said. "The streamlife of certain species, of coho in particular, we’re talking months that these fish will remain in fresh water before they actually start spawning.”
While the study’s sample size is small, scientists say the tagging project is allowing them to better estimate the population size of coho in the Kenai River watershed.
“The collaborative work has been great, I think it’s awesome working with multi-agencies to improve fisheries," Elkins said. "And also, just develop future projects about coho.”
If funding is approved, phase two of the project would tag Kenai River coho to confirm their genetic baseline from phase one data. Scientists would also add known populations of coho in the watershed to a database.