Study traces salmon stocks

Biologists document genetics of setnet king harvest

A genetic analysis of chinook salmon caught in the Upper Cook Inlet east side setnet fishery showed more than 25 percent of the harvest typically attributed to the Kenai River actually returning to the Kasilof River.

The new information means estimates of the percentage of the late run Kenai River harvested by the setnet fishery — usually between 17-19 percent according a Fish and Game researcher — will drop.

More than 2,300 samples were collected between 2010, 2011 and 2012. However, because the setnet fishery was closed for most of the 2012 fishing season to protect Kenai River king salmon, that year was excluded from the final data.

“The department typically doesn’t release data sets of this kind without three years of data,” said Pat Shields, area biologist with the Alaska Department of Fish and Game. “But in this case there’s so much interest ... you can’t go anywhere without someone talking about king salmon, they decided they would release this.”

Shields said consistency between the two years — less than a 10 percent difference between the Kenai and Kasilof River portions of the commercial king salmon harvest — probably helped researchers decide to release the data.

According to the report, in 2010, 64.7 percent of the kings harvested were traced to the Kenai River and its tributaries, while 33.1 percent were traced to the Kasilof. In 2011 72.7 percent were traced to the Kenai and 26.7 percent to the Kasilof.

“In the scientific world in fisheries, that’s pretty ... consistent data,” Shields said.

According to the report, the data should be considered preliminary until more years can be added to the analysis.

The salmon were traced into one of five statistical areas: the Northwest Cook Inlet; Kenai Tributaries; Kenai Mainstem; Kasilof Mainstem; and the Coastal South Kenai Peninsula.

The bulk of salmon were traced to the Kenai and Kasilof rivers. The combined contribution of all other areas did not exceed 2.4 percent in both years according to the report.

Tissue samples collected from processors that received fish from multiple statistical areas were excluded from the analysis as was data from poor quality DNA samples according to the report.

The final analysis included 715 genetic samples between 2010 and 2011.

Shields said the genetic data will help researchers determine how stock composition data should be interpreted and help the committee that is currently calculating a new DIDSON-based escapement goal for Kenai River kings.

“So we have a commercial fishery out there that catches kings, prior to this year we’ve considered all of those kings in the commercial fishery to be Kenai River kings, every single one of them,” Shields said. “People used to come to us and say, ‘You know they’re not all Kenai,’ and we’d tell them, ‘Yes, but we don’t have any reliable way right now of determing that.’ ... This is the first time that we have some data that says alright this is the stock composition of the harvest.”

An average of the percentage of chinook caught that belong to each river will be taken and applied to previous years’ setnet harvest data, Shields said.

While the data is fairly consistent between the two years analyzed, and researchers will continue to add samples to their analysis in coming years, Shields said he expected there would be people who did not have confidence in the report.

“There are people that would tell you that the genetics data has some error built into it, it’s not perfect,” Shields said. “It’s the best data we have right now.”

Rashah McChesney can be reached at rashah.mcchesney@peninsulaclarion.com.

Genetics Report

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