While harvest regulations for walleyes have generally been based on estimates of abundance, this study suggests that the ability of a lake to sustain harvest depends more on its productivity.
October 29, 2023
By Steve Quinn
This article was excerpted from the June 2021 Bits & Pieces column.
In recent decades, Wisconsin fishery biologists and managers have noted the declining quality of walleye fishing in many lakes, despite what appears to be low exploitation levels, generally less than 15 percent. Benchmarks for sustainable harvest have been considered to be about 35 percent there. Regulations have remained rather stable statewide and in the “Ceded Territory,” where Ojibwe tribal members also spear walleyes, bag limits have been adjusted accordingly.
Researchers recently investigated walleye abundance, growth, and harvest over 28 years on 179 walleye lakes there.* Lead author Holly Embke reports that their analysis suggests that 40 percent of walleye fisheries are overharvested, which is ten times higher than the estimates state managers currently use. She adds that the main reason for this “hidden harvest” is that managers have for the last 30 years focused on fish abundance instead of fishery productivity when calculating harvest limits. The early limits worked for many years, they noted, but production in many lakes has declined by about 35 percent, likely associated with climate change and invasive species.
“One way to describe this situation is the analogy of a bank account,” Embke says. “Abundance represents the number of dollars in your account, while production is like the interest you earn on that principle amount. If you withdraw more from your account than interest adds, your savings shrink. After a few years of such withdrawals, your balance has shrunk considerably.”
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The team used data that had been collected by Wisconsin and tribal biologists to calculate how walleye biomass had changed over the 28-year period. Comparisons of walleye production to harvest revealed that overharvest was far higher than had been believed, and fishing had suffered in many lakes as a result. More productive lakes, however, remained strong fisheries with robust populations that could handle present harvest levels. Lakes within a region demonstrated great variation in their productivity, they found.
They concluded that, “these results highlight the urgent need for improved governance, assessment, and regulation of recreational fisheries in the face of rapid environmental change. The climate is different from what it was in the 1980s and it isn’t going back. That means walleye habitat is decreasing and, on average, walleye stocks can’t handle the harvest levels they have seen in recent decades.” The good news is that frequently collected fishery data can be used to determine production in order to better understand the resilience of different populations and to craft regulations that match it more closely.
*Embke, H. S., A. L. Rypel, S. R. Carpenter, G. G. Sass, D. Ogle, and T. Cichosz. 2019. Production dynamics reveal hidden overharvest of inland recreational fisheries. Proc. Natl. Acad. Sci. 116(49):24676-24681.
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