Why the increase in walleye in the Ririe Reservoir?
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The following is a news release from Idaho Fish and Game.
The illegal introduction of walleye into Ririe Reservoir resulted in the establishment of this predatory species and is a concern to fishery managers because of the potential for walleye to negatively impact other fish populations, specifically kokanee and trout. Ririe Reservoir is one of the most popular flatwater angling destinations in the Upper Snake Region.
With a diverse, multi-tiered fishery supported by cold and cool-water fish species, Ririe Reservoir offers something for all anglers. Most anglers target kokanee or yellow perch, but many like to fish for smallmouth bass, rainbow trout or tiger trout. Because of the potential impact walleye can have on fish populations in Ririe Reservoir, they are the focus of monitoring efforts by the Idaho Department of Fish and Game (IDFG) to track changes in fish size, growth and abundance.
Walleye numbers had been stable for a number of years after they were first observed in the reservoir in 2008, however, monitoring efforts in 2023 indicated there was an increase in walleye abundance. Since 2010, IDFG has used a walleye sampling methodology called Fall Walleye Index Netting (FWIN) to monitor relative abundance, size and growth of walleye in Ririe Reservoir. This methodology was developed by fishery managers in Ontario, where walleye are a popular, native sportfish.
In Ririe Reservoir, IDFG conducted FWIN surveys annually from 2010 through 2017. During this time, IDFG captured between zero and 15 walleye each year compared to total sportfish (kokanee, rainbow trout and yellow perch) catches of 300 to 2,000 annually. With such a low number of walleye observed during the FWIN surveys, IDFG changed to performing FWIN surveys every three years instead of annual efforts. walleye catch during FWIN surveys remained low for the next four years with only 11 walleye caught in 2017 and three in 2020. In 2023, IDFG observed an alarming change with 86 walleye captured during FWIN.
With a nearly eight-fold increase in walleye catch during FWIN, IDFG was concerned that the population was at an inflection point and ready to expand exponentially in number and influence on other fish species. Instead of waiting for three years for the next scheduled FWIN, IDFG decided to conduct another FWIN survey in 2024 to gather additional information related to the trend of walleye in Ririe Reservoir. This additional FWIN survey helped provide information to explain why we observed a sudden increase in walleye relative abundance in 2023.
The 2024 FWIN survey suggests the spike in walleye numbers was due to strong year-classes of walleye produced during the drought years of 2021 and 2022. In the 2023 FWIN survey, 73% of the walleye caught hatched in 2021 or 2022 and this percentage increased to 91% of the catch in 2024. The 2024 survey provided insight into how strong the 2023 production year was after two good spawning years for walleye during drought conditions. The 2023 year-class was weak, comprising only 3% of the catch of walleye during the 2024 FWIN survey. This would suggest that the sudden increase in abundance is short-lived and not sustained by high rates of reproduction on an annual basis in Ririe.
It will take time and additional survey effort to better understand how the strong production years of 2021 and 2022 will affect the trend of walleye abundance in Ririe Reservoir. Walleye mature around two to three years of age in Ririe Reservoir, so the coming FWIN surveys will help us understand better if this bump in walleye abundance will result in long term impacts to population numbers. IDFG will continue to monitor walleye relative abundance, growth and survival in coming years to help direct management efforts to maintain the fishery at Ririe Reservoir for kokanee, yellow perch and trout species.
Anglers can help secure these valuable fisheries by harvesting walleye. The following map may help you in your walleye pursuit if you decide to target them on Ririe. This map shows the locations of the gillnets used during Ririe Reservoir FWIN surveys.
IDFG has observed at least one walleye in all 18 net locations throughout our years of FWIN surveys. However, in the map, the locations marked with yellow pins are where walleye were caught each year of the 2023 and 2024 sampling efforts. Of these locations, nets 5, 10, 11 and 13 had the highest combined catch over the last two years, which is the section of Ririe Reservoir that includes the Meadow Creek arm and extends upstream to the Willow Creek arm.
With a relatively small population of walleye in Ririe Reservoir, anglers who catch walleye can play a big role in fisheries management, and we wish you the best of luck in your upcoming fishing trips to Ririe Reservoir.
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