Summary of Ground-Breaking Study on Fate of Stocked Walleye Fingerlings

New Research Documents Movement and Survival of Large, Fall-Stocked Walleye Fingerlings

By Dave Neuswanger, AFS-Certified Fisheries Scientist
President and Fisheries Program Leader, Quiet Lakes Improvement Association
February 20, 2020

Wisconsin fishery managers have learned that stocking 6- to 8-inch walleyes in early fall usually results in higher percent survival than the less expensive, decades-old practice of stocking 1- to 2-inch fish in late spring. Hatchery reared 6- to 8-inch walleyes stocked in the fall are often termed “extended growth” or EG fingerlings. They typically cost $1.50 to $2.00 per fish produced and delivered. Since 2011, the Wisconsin DNR and Quiet Lakes Improvement Association have spent a conservatively estimated $136,686 stocking 91,124 EG walleye fingerlings into Teal, Lost Land, and Ghost lakes in Sawyer County, Wisconsin. WDNR provided 93% of the funding for these fish, and the agency is dedicating significant resources to evaluate the outcome, financed largely by Federal Aid in Sport Fish Restoration. Fishery biologists believe EG fingerlings are less vulnerable to starvation and predation than small fingerlings, which cost only $.02 each to produce and stock. But in lakes with abundant largemouth bass (predators on and competitors with walleyes), EG fingerlings may be the only option for stocking walleyes with a reasonable chance of survival to adulthood.

Researchers at Iowa State University teamed up recently with the Iowa DNR to complete a first-of-its-kind study aimed at learning exactly what happens to EG walleyes in the first six months after stocking. A scientific article based on their 2017-2018 study was accepted for publication in the North American Journal of Fisheries Management in November of 2019. With this review, I will summarize the new Iowa study and discuss its implications for walleye management in the Quiet Lakes. Readers who wish to judge the rigor and applicability of this study for themselves are welcome to click on the PDF below and read this excellent paper in its entirety.

Iowa EG Walleye Telemetry Study by Weber et al. 2019

Past studies aimed at comparing post-stocking survival of small versus large walleye fingerlings have employed various marking techniques, including clipping fins, staining the ear bones of small fish with fluorescent dye, and implanting larger fish with tiny chips like those used to ID pets. All of these methods have limitations, and none of them allow researchers to accurately estimate immediate post-stocking movement, habitat use, daily survival, or cause of death. In the Iowa lakes study, stocked EG walleyes were implanted with radio transmitters and tracked by telemetry. This study removes some of the mystery and provides useful insights into the behavior and short-term survival of stocked EG walleyes. The findings have implications that could influence management practices on the Quiet Lakes for years to come.

One might legitimately ask whether the three Iowa study lakes were similar enough in size, character, and fish species assemblage to allow application of study results to Teal, Lost Land, and Ghost lakes in northwestern Wisconsin (aka “The Quiet Lakes”). I believe they were. Areas of the two man-made Iowa impoundments (somewhat similar to Wisconsin flowages) were 692 and 813 acres; and one natural lake in NW Iowa was 1,836 acres. Teal and Lost Land lakes fall within that range, though Ghost Lake is smaller at 384 acres. Two of the Iowa study lakes were relatively shallow and very weedy (similar to our Quiet Lakes). One of the Iowa study lakes had few weeds and lacked submersed woody cover, offering few places for small fish to hide and providing an interesting learning opportunity. All three study lakes had largemouth bass, adult walleyes, and muskellunge as potential predators (also similar to our Quiet Lakes), though only one of the Iowa lakes had northern pike, which are common in Lost Land and present in Teal.

In the Iowa study, 15 radio-tagged walleye fingerlings averaging 9.3 inches in length were stocked along with large numbers of unmarked fish into each of the three study lakes. (EG walleyes stocked into the Quiet Lakes since fall 2011 have averaged only 6.8 inches.) Stocking occurred in late October of 2017 when lake water temperatures ranged between 40F and 56F. The 45 Iowa study fish were tracked frequently from the day after stocking until ice-up, under safe winter ice, and from ice-out until late May of 2018 shortly before transmitter battery life expired. Lake depth at each observed location was recorded, but it was not possible to know if the radio-tagged fish were near the bottom or suspended above the lake bed.

Results were illuminating. Researchers recorded a grand total of 527 radio-tagged walleye detections in the three Iowa study lakes. By the time the study ended in late May of 2018, cumulative survival of radio-tagged fish was an astonishingly high 76%. Frequent tracking early in the study revealed that most mortality occurred within the first 20 days post-stocking. Fish confirmed as dead had averaged 8.8 inches long at time of stocking, a full 0.5 inch shorter than the 9.3-inch fish that survived or whose fate was unknown. Because even this relatively small difference in length-at-stocking resulted in a statistically significant difference in survival, we probably cannot assume that EG walleyes stocked into the Quiet Lakes at a mean length of only 6.8 inches (2.5 inches smaller) have survived from fall to spring at the high 76% rate documented in these Iowa lakes. Unpublished data on one of the Iowa study lakes (East Okoboji) suggests that predation has been a significant source of post-stocking mortality for EG walleyes, and that seems likely in our Quiet Lakes as well.

Most radio-tagged walleyes dispersed quickly and did not remain in the shallows near shore after stocking. Average water depth at detection locations was 8 feet throughout the study period, including times of ice cover. The deeper the lake, the greater the mean depth at time of detection. The most revealing result, however, was the relatively short distance that tagged fish traveled from points of release over the 8-month study period, especially in the two shallow, weedy study lakes that were similar to our Quiet Lakes. Combining all three study lakes, average dispersal (linear distance traveled) from points of release was less than 0.6 mile, and maximum dispersal was only 1.0 mile. Most dispersal occurred within two weeks after stocking. Average home range for fish with three or more detections was only 96 acres. Dispersal was significantly lower in the two shallow, weedy study lakes than in the deep lake largely devoid of cover. EG walleyes stocked into the deeper study lake dispersed throughout the lake and clustered around hotspots of sparse cover.

Implications for the Quiet Lakes: This excellent article left me with three take-home points to share with members of the Quiet Lakes Improvement Association:

1) The bigger the fall-stocked walleye fingerlings, the more likely it is that they will survive until spring. It is highly unlikely that survival of 6.8-inch fish stocked into our Quiet Lakes is anywhere near as high as the 76% first-winter survival reported for the 9.3-inch fish stocked into these Iowa study lakes.

2) Dispersal of EG walleyes from points of release is surprisingly slow during the first cold-water period after stocking. This might allow predators to eventually sense and exploit a concentration of available prey in areas where stocked EG fingerlings tend to congregate (in submersed weeds and wood within a half mile of points of release). In our larger lakes like Teal and Lost Land, we might want to establish more than one stocking location in proximity to escape cover (submersed aquatic plants or woody cover), thereby minimizing predation on stocked fish and increasing the amount of suitable-size prey available to each stocked fish.

3) Where near-shore woody cover is lacking, dropping densely branched trees in the water along our shorelines might provide incentive for stocked EG walleyes to disperse further at shallower depths in pursuit of quality escape cover that is rarely used by larger predators during cold-water periods.

We owe thanks for this important work to the researchers at Iowa State University, to biologists with the Iowa Department of Natural Resources, and to U.S. Fish and Wildlife Service administrators who select worthwhile projects to allocate Federal Aid in Sport Fish Restoration funds collected as excise taxes on fishing tackle and marine fuel. For that significant source of funding for fishery management and research, we can thank late Senator Malcom Wallop (R – Wyoming) and retired Senator John Breaux (D – Louisiana) for leading the bipartisan expansion of the 1950 Dingell-Johnson Act in 1984.