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The Ririe reservoir is full of Kokanee, but don’t expect anything too large

Living the Wild Life

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Photos: Bill Schiess | EastIdahoNews.com

RIRIE – During the gillnetting survey in 2018, each net averaged 89 Kokanee per net per night, while this year the numbers had dropped to 50 kokes but the size was considerably larger.

“We set out three nets in the lower part of the reservoir, four in the middle and three in the upper portion,” said John Henkel, an Idaho Fish and Game fishery biologist says. “Every net produced some Kokanee, but the larger ones were in the lower area from the dam up to the restroom near the power line that crosses the reservoir. The middle area had more kokanee per net, but they were smaller and the least were in the upper area near Blacktail.”

A piece of interesting data shows the three nets in the lower area produced Kokanee between 15 to 17 inches, which was about 10 percent of the catch while catching only one perch. Meanwhile in the middle section, perch outnumbered the kokanee, and in the upper section, perch dominated the fish taken in the nets. During the three days of netting, no walleye were captured.

“We took the temperature each night to find the thermocline and then would set the middle of the net where we would find the 54 degree temperature where most of the Kokanee should be,” said Heckel. “The thermocline varied a little, but most of the time it was about 25 feet below the surface in the lower section, and at 15 feet in both the middle and upper sections.”

During the summer, the sunlight increases the plankton growth and the thermocline is more pronounced because of it. The thermocline can change quickly due to wind, water depth and sunlight. Cloudy days during the summer can inhibit the development of plankton, causing the fish to have to scatter to find food. In the fall, the Kokanee have a tendency to spread out as the thermocline falls apart causing the Kokanee to sometimes go deeper during the winter.

“The larger fish could be a result of more food available with fewer Kokanee in Ririe,” said Henkel. “This year we are catching the 2017 plant of 320,000 and we caught a lot of immature fish over 12 inches, meaning they have another year and could be very large during the winter and next summer. We won’t have the age data available until this fall.”

Historically, the Kokanee in Ririe do not reproduce naturally and most of the 2017 plant will die after spawning this fall, leaving the 2018 plant of 263,000 for the winter and next summer. In May, the Fish and Game increased the stocking back up to 320,000 for 2019.

“We really don’t know why the fishing was so poor last winter and early this spring, but we are encouraged by the size of some of the Kokanee,” said Heckel. “The fishermen appear to be happy with the larger fish, so we will probably keep the stocking rate as it is now and also keep the limit of 15 per day. The Kokanee are put in Ririe for the fishermen to enjoy.”

Since the gillnetting, the fishing for the Kokanee has slowed back down again and most schools have appeared to drop down to 35 to 60 feet below the surface almost requiring fishermen to use down riggers to get down to them. It will be interesting to see what the fishing will be like late this fall and winter.

By the way, fishing for perch is good, even in the lower area of the reservoir. But to get them, you have to fish next to the flooded willows and rocks where you will also find trout and bass.

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