Back on the Mississippi

By: Aaron Von Eschen and Jeff Lockington

walleyeA female lake sturgeon collected during walleye spawning Photo credit: TJ Turner

Warming weather in the spring triggered staff at Genoa National Fish Hatchery to deploy walleye nets in an annual effort to collect walleye and sauger eggs for the upcoming production year. Roughly 50 hoop nets were set in late March to begin collecting ripe females. It did not take long to determine the staff had set nets just in time as walleyes were beginning to spawn. Generally the staff spawns walleye across an approximate three week period in early to mid-April as female walleye begin to ripen and eggs begin to flow. Usually there is no waiting for the male walleye to get ready as they are eager and willing. Spring rains and snow melt helped the staff this year collect walleyes as the increased flow pushed walleye closer to the river banks where nets were set. This was a welcome relief after last year’s low water made it difficult to find the fish. Water temperature was a different story however, instead of a gradual increase, the water temps fluctuated up and down and triggered spawning ready females to turn on and off and made it slow for females being held to ripen up and release eggs. This can present a difficult challenge as unripe females are being held; male walleyes can “dry up” toward the end of the season meaning less milt is produced making it difficult to fertilize eggs that are collected later in the season. A daily trip usually consisted of getting on the river right away and lifting nets. It takes staff about 3-4 hours depending on weather conditions to hoist all 50 nets and check them for walleye and clear by catch. The most exciting part of a day of walleye spawning can be when an unusual species shows up in the nets. This year staff caught a female lake sturgeon that weighed an estimated 60+ pounds. By catch mostly consists of yellow perch, white bass, and freshwater drum so seeing a big lake sturgeon was a bit of a surprise for staff members. Once all the nets were checked, staff headed to the live box to check females being held there to determine if they were ripe and ripe females collected that day were spawned. Eggs were stripped from females into a stainless dish and once completed the females were immediately released back into the river. Males are then used to fertilize the eggs. Well water is then used to activate the sperm and stirred for one to two minutes. A mixture of bentonite clay and well water is then added to the bucket to ensure that eggs to do no clump and stick together, this could result in suffocation of the eggs. After two minutes in the clay mixture eggs are then rinsed with well water and placed into a larger bucket containing an iodine mixture to ensure they are disinfected before returning the hatchery.

Once at the hatchery eggs are rinsed of the disinfectant and placed into hatching jars. The following day, after the eggs have water hardened, they are then enumerated to determine how many eggs were collected. This process is repeated each day during the spawn until wild fish have completed spawning at which point the nets are collected and returned to the hatchery to be mended and repaired and used again the next year. All said and done just shy of 600 walleyes were spawned with almost 200 of them being females. Approximately 25 million eggs were collected this year, with good spawning success staff was able to ship excess eggs to state and tribal partners while still meeting the stations production requests for stocking and future freshwater mussel hosts and allowing for over 2.2 million hatched fry to be returned to the Mississippi River. Walleye are the host fish for the black sandshell mussel, an endangered species or a species of concern for several states. In an effort to supplement existing populations or reintroduce black sandshell mussels to various state waters, the walleye are a key species at Genoa NFH.

 

 

 

 


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