Science can come in handy when it suits your biases. Otherwise — especially in the case of fish and wildlife management — it can be a hassle.

Just ask those who are complaining about the Department of Natural Resources’ recent declaration that anglers this spring and early summer on Mille Lacs can’t keep any walleyes.

None. Nada.

Only beginning on Aug. 16 will anglers on the big lake be able to stow one walleye, and then only if it measures between 21 and 23 inches or is longer than 28 inches.

A little history:

In 1999, the U.S. Supreme Court, ruling in an 1837 treaty case, laid the groundwork for co-management of Mille Lacs fisheries by the Department of Natural Resources and eight Chippewa bands. One result was establishment by the DNR and the bands of annual “safe harvest levels” of Mille Lacs walleyes, with each party taking a portion of the surplus.

The 2024 Mille Lacs harvestable walleye surplus, for example, is 157,500 pounds, with the state’s share (to be taken by sport anglers) set at 91,550 pounds. These amounts are lower than the 2023 Mille Lacs harvestable walleye surplus of 175,000 pounds, with anglers getting 103,000 pounds and the bands awarded the balance.

This year’s reductions — and particularly the DNR’s edict that no angler-caught walleyes can be kept from Mille Lacs in spring and early summer (when fishing is generally productive, compared to the dog days of August) — are being challenged by various anglers and angler groups, who complain the DNR is underestimating the lake’s walleyes and therefore unnecessarily imposing its no-harvest restriction.

Some anglers also say a percentage of Mille Lacs walleyes should be harvested to better balance the number of big and small walleyes in the lake, or so Mille Lacs walleye numbers are better aligned with the lake’s reduced forage base.

My opinion is that DNR fisheries scientists who study Mille Lacs are correct on this one, and any attempt to muscle agency management or the governor’s office to overturn the no-harvest restriction not only constitutes a bad look for anglers, it could backfire and shut the lake down this summer, even to catch-and-release walleye angling.

The reason: Walleyes that are released after being caught are subject to delayed mortality, an estimate of which must be factored into the angler’s portion of Mille Lacs’ harvestable walleye surplus.

. . .

Critics of the DNR’s 2024 Mille Lacs walleye harvest restriction contend:

* The agency is wrong when it says a relatively high number of walleyes were caught by anglers this winter — given that temperate weather shortened the Mille Lacs cold-weather angling season by about a month.

* The DNR’s methods of estimating Mille Lacs walleyes are for various reasons incorrect and result in an undercounting of the fish’s numbers.

Let’s take a look.

The DNR used the same creel measurement methods this winter on Mille Lacs it used in past winters (and summers) to estimate that 3,277 walleyes were caught during the recent cold months.

That’s more than triple the 2023 Mille Lacs harvest of 1,070 walleyes, and higher also than the 2022 winter take of 1,968. But it’s a far cry from the 8,756 harvested in 2020 and the 37,481 harvested in 2012 — estimates made using the same methods, when no one complained.

More important is the harvest rate, a computation that considers the number of fish caught relative to effort.

By that calculation, the recent winter’s Mille Lacs walleye harvest rate was the highest since 2012. Last summer’s harvest rate also was the highest in more than 10 years.

The likely reason: not an overabundance of walleyes, as some online angler-experts tout — “What I can tell you as someone who spends a ton of time actually fishing on Mille Lacs, there’s a bazillion walleyes in there!” — but a shortage of forage fish, primarily juvenile yellow perch but also tullibees. Last summer’s estimate of hatch-of-the-year yellow perch, for example, was the second lowest in the past 10 years.

The same shortage likely caused the high walleye catch rate on Mille Lacs last summer.

Here are other considerations DNR fisheries scientists and managers weighed in considering Mille Lacs walleye angling restrictions this spring and early summer:

* Mille Lacs no longer supports dependably regular strong year classes of walleyes. Abundant now are 2013 and 2017 year classes, with the 2021 and 2022 classes showing promise. But given cannibalism and other factors affecting young Mille Lacs walleyes, a year class isn’t considered “safe” until age 3.

* Mille Lacs is no longer as fertile as it once was. Septic and other effluents flowing into the lake became cleaner beginning in the mid-1990s, and zebra mussels showed up in 2005, with spiny water fleas following in 2009. The lake is clearer as a result, and less fertile, reducing energy available to the lake’s other critters, including walleyes.

* The DNR has no idea how quickly Mille Lacs will warm up this summer. If the state’s early spring morphs into an early, warm summer, walleye release mortality will increase, which must be included in anglers’ estimated harvest. Also unknowable is whether the summer’s weekend weather will be stormy or pleasant. The former restricts angler activity, the latter encourages it.

* The DNR can’t estimate the size of this year’s yellow perch hatch until June. If it’s good, Mille Lacs walleye fishing success likely will decline, which could increase DNR harvest options. If not, continued high harvest rates — and continued restrictions — are likely.

In the end, anglers can choose to believe fish and wildlife management science developed by professionals — or not.

Either way, as a wise fellow once said, “The good thing about science is that it’s true whether or not you believe in it.”