Koronis (main lake)

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How deep is Koronis (main lake)?

What kind of fish can you catch in Koronis (main lake)?

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What aquatic invasive species are found in Koronis (main lake)?

A targeted survey of Tullibee (Cisco) in Lake Koronis was conducted during mid-late November of 2023 at four lake survey special gillnet stations. A targeted survey is generally used for sampling a specific kind of fish or time of year (i.e. spawning season, fall season, etc.) unlike a standard survey which samples a wider range of fish species during the summer months using standard methodology (i.e. standard time of year, set sampling stations, taking water clarity readings and oxygen/temperature profiles, etc.) and gears (i.e. lake survey gillnets, trapnets and possibly spring electrofishing for Largemouth Bass).

Koronis is a large (2,968 acres), and deep (132 feet maximum) lake located in Stearns and Meeker Counties. Koronis is currently infested with invasive species such as Curly-leaf Pondweed, Starry Stonewort and Zebra Mussels. A standard survey (summer gillnets and trapnets) of Koronis was last conducted during mid/late July of 2022. A fall electrofishing survey was conducted on October 4, 2023 to evaluate young of year "YOY" (fingerling sized) Walleye abundance in Koronis.

Tullibee were believed to be initially introduced into Koronis and Green Lake during the 1880's. Green is the only other Spicer Area lake with a self-sustaining Tullibee population. Tullibee spawn in 3-6 feet of water over bottom substrates consisting of large rock during late November to early December when the water temperature reaches 41 degrees Fahrenheit "F" or less. Spawning substrates in both Green and Koronis during recent years have been covered by periphyton/filamentous algae except in shallow (<1 foot) windswept shoal areas. Increased phosphorus inputs or availability often result in greater blue-green and filamentous algae blooms. Climate changes (e.g. warmer temperatures, additional growing days, increased storm/runoff activity, etc.) coupled with continued nutrient inputs and Zebra Mussel impacts may be negatively affecting Tullibee natural reproduction and recruitment success in these lakes due to degrading spawning habitat and increasing numbers of warm water fish species (e.g. Rock Bass, Pumpkinseed, Smallmouth Bass, Largemouth Bass, etc.) which prey upon Tullibee eggs, fry or fingerlings.

Adult Tullibee are susceptible to summerkill in Koronis if oxygen levels drop (<2 ppm) in the cooler deeper areas (<74 F) of the lake for an extended time (1-3 weeks) during late July to early August. Young Tullibee can tolerate warmer water temperatures than adult Tullibee. A minor summerkill of adult Tullibee occurred in Koronis during 2010, but none was reported in Green. Low dissolved oxygen (<2 ppm) levels were present at depths where preferred adult Tullibee water temperatures (<74 F) occurred for a short time period on Green in the 2010 late summer. A major summerkill of Tullibee occurred in Koronis during 2011, but only a minor kill occurred in Green during the 2011 summer. Drought conditions and extremely high air temperatures were the norm for the Spicer Area during July and early August of 2012. There were no apparent summerkills in Green or Koronis during 2012, but adult numbers were so low that summerkill events may not have been recognizable, especially due to the large numbers of pelicans living on Lake Koronis' islands. A narrow band (1-3 feet) of marginal water temperatures (<74 F) and dissolved oxygen levels (1-3 ppm) was present in depths of 25-30 feet in Green during late July and early August of 2012. Dissolved oxygen levels and water temperatures in Green were at potential summerkill levels of 2 ppm and 74 F on both July 30th and August 9th of 2012. Summer temperature and oxygen conditions were more conducive for Tullibee survival during 2013-2019 for both Koronis and Green. The month of June had warmer air temperatures (up to 90 F) and drier (< 2 inches of rain) than normal conditions during 2020-2022. July air temperatures were near or below normal during those same years. The 2023 summer was warmer and drier than normal especially for June, but no tullibee summerkills were observed in Green or Koronis. Adequate water temperatures and dissolved oxygen levels were present from 17 feet depth (73 F, 6 ppm) to 20 feet depth (70 F, 4 ppm) for tullibee survival on July 28, 2023.

Zebra Mussels were first observed in Koronis in 2022. It is unknown the extent Zebra Mussels will affect Tullibee and their corresponding forage base. Koronis was open to public gillnetting for Tullibee in the fall prior to the early 1980's but was closed due to low numbers and high incidental catch rate of other species such as Northern Pike and Walleye. Until recently, Green was the only lake in the Spicer Area open to the public for fall gillnetting of Tullibee during late November or early December from the late 1980's to 2011. Green Lake has been closed for Tullibee gillnetting since 2012 due to the low numbers sampled in recent years. Tullibee are an important forage fish for trophy northern pike in both Koronis and Green.

Tullibee eggs were collected using a 300 foot gillnet (2.25-2.5 bar mesh) on November 18, 2022 at Lake Koronis for a doctoral research project. A total of 88 tullibee were captured in the overnight gillnet set. Approximately 2 quarts were stripped from 15 females and fertilized with 30 plus males on Koronis. One third of these eggs were immediately shipped to the University of Ohio-Miami. The remaining eggs were incubated in Muskellunge jars at the New London Hatchery for several weeks at 40 F river water and later shipped to the same research facility. The objective of the study was to evaluate the effects of UV light on cisco egg hatching and fry survival. The hatch rate was moderately successful. Local tullibee propagation (incubation, hatching and rearing to fryling stage) is possible at the New London Hatchery if using a recirculation system and a dry diet regime until fish can be stocked in the spring following ice out.

Tullibee were present (0.20 fish/gillnet, 17.44 inches average length) in the 2022 Koronis summer survey. Moderate numbers of Tullibee were caught in 2019 (1.80 fish/gillnet, 14.17 inches average length). Tullibee were not present in the 2017 summer standard survey. The Tullibee historical average catch rate is 1.08 fish/gillnet for Koronis.

Tullibee numbers were low in 2023 November survey (5.00 fish/gillnet, 16.41 inches). Moderate numbers of Tullibee were captured in Koronis during 2019 (27.50 fish/gillnet, 15.75 inches) and 2015 (19.67 fish fish/gillnet, 14.17 inches), but low numbers in 2017 (10.33 fish/gillnet, 14.41 inches). The highest recorded tullibee catch was 119.83 fish/gillnet on Koronis during 1996. Low tullibee numbers (4.00 fish/gillnet, 10.78 inches) were also caught in Green Lake during 2023. The November Tullibee historical average catch rate and average length are 28.52 fish/gillnet and 15.16 inches for Koronis. Tullibee growth rates were excellent for ages 1-8 in the 2023 November survey gillnet catches. The 2017 and 2015 year classes each comprised 35% of the 2023 November Tullibee survey catch. The inconsistency of Tullibee natural reproduction and inadequate adult Tullibee numbers on the spawning grounds as sampled by the DNR is not a good indication for the long term sustainability of the Tullibee populations in Green and Koronis. Hopefully, consecutive cool summers will continue to occur periodically, which may result in a good hatch, recruitment and survival of Tullibee to maintain a long-term population in Koronis.

Improving and maintaining good water quality in Koronis is the key for Tullibee numbers to survive and flourish. Tullibee propagation is an option for maintaining a viable population. Other sampling methodology such as fall electrofishing and summer vertical gillnetting may better sample Tullibee populations in Green and Koronis. Public fall gillnetting season will probably be postponed until the adult population rebounds to adequate levels. Current fish management activities on Koronis include monitoring the fish population on a periodic basis, assisting aquatic plant management and enforcement personnel with invasive species monitoring and education, protecting aquatic vegetation through the permit process, participating in local watershed initiatives, and stocking various fish species as warranted. The Koronis fishery will be sampled in the 2024 summer for all fish species. Tullibee will be sampled by vertical gillnetting and hydroacoustic methods in June of 2024, and November gillnetting in 2025 for both Green and Koronis.

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