Schiess: Walleyes rare in Ririe Reservoir

For the last three years you can always bank on two things happening the last week of October – the ghosts and goblins come out and the Idaho Department of Fish and Game checks on the population of walleyes in Ririe Reservoir. After the illegal introduction of these predatory fish was discovered in 2008, the Fish and Game have been trying to monitor their population growth to determine how to manage the lake.

Using volunteers to help with the process, the Fish and Game sets out six nets on three consecutive nights in three areas of the reservoir. The first night of netting was done in the upper end near Willow Creek and no walleyes were captured. On the second night six walleye were captured in the middle section of the impoundment, with five caught on the third night on the lower section near the dam.

The nets are gathered each morning for the fish to be removed from the nets; sorted by specie and weighed and measured. It is a tedious four to six hour job for the volunteers from BYU-I, citizens from the Master Naturalists, techs from the Fish and Game and even a high school student, Tyson Siddoway, from Idaho Falls High School for his senior project.

“There were 13 caught last year and 11 caught this year with the largest being about five pounds,” Jon Flinders, a regional fishery biologist for the Idaho Falls office, said. “Walleye are more active at night and they cannot see the nets as well to avoid them, and that is why we set them at night and pull them in the morning.”

It appears that the population is very small, but they grow rapidly with all the food available, but most of them captured this year were between 12 to 14 inches with the largest at 22 inches.

“We are only picking up one or two in some nets each night,” Flinders said, and there are no indications that the population is large enough for them to travel in schools.”

When asked why there were no walleye taken in the nets on the upper third of the reservoir where fishermen targeting them usually fish, Flinders thought it might be because of the dirty water caused by ash from the Henry Creek fire. Being a fish that hunts by sight, they may move to the areas where the water is clear for their hunting.”

During the past ice fishing season and this summer, fishermen fishing the reservoir were interviewed about their success and recommendations of what species they would like to see the reservoir managed for. About half of those questioned desired kokanee salmon while a lower percent desired walleye.

“You cannot have both a walleye and a kokanee fishery together,” Flinders explained. “Walleye are the top predator in the fish chain and they would destroy the kokanee and rainbow populations at Ririe.

While the gill netting indicated the population of walleye are remaining consistently low, the process also showed other specie populations are doing well. In the 2015 netting operation only 27 kokanee were harvested ranging from six to 13 inches. This year 124 kokanee were captured, slightly larger than last year, which caused Flinders to speculate that there will be “a higher abundance of kokanee in the fishery heading into the winter compared to last year.”

The most numerous specie at Ririe continues to be the yellow perch. On the first day of trapping this year, of the 1,300 fish taken, 950 of them were perch ranging from four to 10 inches. Rainbow trout, small-mouth bass, chubs and suckers were also taken.

With the ratio of fish species in Ririe, fishermen targeting walleye could expect to catch one walleye for every 2,000 other fish. Ririe is not a walleye fishery and the Fish and Game are hoping it remains that way.

“If the population of walleye increases greatly we would have to stop the stocking of kokanee and rainbows, because we would just be feeding the predators,” Flinders summarized.

It will continue to be interesting to monitor the make-up of the fish population on this reservoir.