After two years of testing, Alaska Department of Fish and Game managers have decided to move the sonar site used to count the Kenai River’s king salmon runs.
Currently, Fish and Game uses a king salmon sonar site at river mile 8.6 to estimate abundance and manage the two runs of king salmon during the season. However, the site has been problematic. It is still within the tidally influenced area of the river and doesn’t fully ensonify the area.
In addition, managers have had to apply a expansion factor to fish counts generated from the site to account for fish that were swimming behind the sonar transducers.
A site at River Mile 13.7 — near the upper end of Falling in Hole — has been in development since 2011 and managers will transition to managing the king salmon runs inseason from that site.
“It’s something we’ve been wanting to do for the last four years,” said Fish and Game Sportfish Division Area Management Biologist Robert Begich. “We get the best information we can about the run (at the new site).”
Before moving to the new site, Begich said staff wanted to see how the area performed under several conditions, including a year of high pink salmon numbers like 2014 when millions of the fish swarmed the site which had the potential to obscure counts of king salmon. In addition, the sonar was tested in high and low water conditions.
The new site has several features that attracted managers, including bank-to-bank coverage of the river which will ensure that fish cannot swim behind the sonar and avoid being counted.
Researchers use five ARIS — a newer generation of the DIDSON sonar — to collect data at the site, compared to the two used at the lower river site.
Anglers in boats will still have to move carefully through the river at both sites as Fish and Game will continue its netting program at the lower river site.
Staff gillnet the river on a schedule designed to help biologists estimate the species of fish that pass the sonar.
“It’s better to have it where it is now,” Begich said of the netting program. “It’s directly comparable to the existing escapement goal the way that we do it now.”
Fish and Game will save about $100,000 by shutting down the lower river site, Begich said, though cost was not a primary motivator in the decision to shutter the site.
“The question became, how long are we going to do this to get the same answer we have now?” Begich said. “We’ve operated, done the side-by-side thing at two different sites for two years. What more can we gain by doing it another couple of years?”
The upriver site is scheduled to be operational on May 16.
Reach Rashah McChesney at firstname.lastname@example.org.