AKELEY, MINN. – Friday is Earth Day, and few people study the Earth as closely as ­Dallas Hudson.

A phenologist by vocation and avocation, Hudson, 51, an employee of the U.S. Geological Survey, years ago began to detail his observations about the ever-changing seasons and their effects on plants and animals.

Elm and red maple trees, for example, are just now flowering near his northern ­Minnesota home, while spring peepers and tree frogs are singing and white-throated sparrows and yellow-rumped warblers are migrating.

Additionally, marsh marigolds, hepaticas and coltsfoot are blossoming, while variegated meadowhawks — a type of dragonfly — are passing through en route to points north.

The research by Dallas Hudson and some of his assistants from Bemidji State has underscored how fragile north pike and other fish populations are. Hudson received a permit from the Department of Natural Resources to net.

“For some time, I would notice these and other changes that occur with the seasons,” Hudson said, “but I didn’t write them down. Finally, I started a journal to document what I saw. Today, I guess you’d call it an obsession.”

Prepared anew this spring to detail seasonal changes, Hudson a few days ago fired up a small outboard motor that hung from the transom of a well-used johnboat. He and two assistants, both students at Bemidji State University, were headed onto a 160-acre lake to check nets they had set to catch bluegills, crappies, northern pike, largemouth bass and other fish.

One of four property owners on the lake, Hudson has been researching the small body of water since 2009, when he was given a permit by the Minnesota Department of Natural Resources to set nets in it.

Their intent is to document the growth in size and number of the lake’s fish, particularly its northern pike and bluegills.

“At one time this was a great fishing lake,” Hudson said. “But it was essentially fished out. Too many fishermen taking too many fish.”

Hudson was himself a pro-harvest angler for many years. As a kid growing up in Akeley, his favorite after-school wintertime activity was trudging onto ice-covered 11th Crow Wing Lake to fish for walleyes and to spear northern pike.

His catches were plentiful, and the fish he caught or speared ended up in his ­family’s freezer.

Ten thousands times over, or more, other Minnesotans of Hudson’s generation, and multiple generations previous to it, similarly caught and kept fish, many of them big.

That Minnesota lakes and rivers in many cases no longer yield such slabs is widely acknowledged by anglers as well as the DNR.

The state smallmouth bass record, for instance, was set in 1948 (8 pounds), the same year the bluegill record was established (2 pounds, 13 ounces). Meanwhile, the northern pike record was set in 1949 (45 pounds, 12 ounces), the walleye record was caught in 1979 (17 pounds, 8 ounces) and the sauger record was set in 1988 (6 pounds, 2 ounces).

“I think it’s pretty obvious we’ve overfished most of our lakes for some species,” ­Hudson said. “In many lakes, what we’ve got now are stunted bluegills and hammer-handle (small) northerns.”

DNR officials agree, and a movement has been afoot in the agency for more than a year to significantly change the way northern pike in ­particular are managed.

A proposal now on the floors of both chambers of the Legislature would establish three northern pike management zones in the state: one in the northeast, another generally in the north-central, and one in the south. Under the plan, harvest strategies would vary in each region. One goal, particularly in the north-central area, would be to reduce the number of small northern pike inhabiting lakes there.

DNR fisheries chief Don Pereira calls northern pike management one of Minnesota’s greatest resource ­challenges.

“In some of our lakes, there just aren’t that many northern pike larger than 22 inches,” Pereira said. “If the new zone management plan works, there will be more northerns in the ‘sweet spot’ range of 26 to 29 inches, which is the size more anglers prefer.”

Focusing on pikes

A goal when the research began was to determine whether a population of small bluegills could be increased in average size if these fish were subjected only to a limited harvest. That appears to be true, as the bluegill in this photo indicates.

As the late comedian Rodney Dangerfield would put it, northern pike get no respect.

Their mouths are toothy and their skin slimy. And cleaning them requires a series of “Y” bones to be excised from along side their backbones.

Yet, on the plus side, they can strike an angler’s bait viciously, providing, in many cases, a better fight than the state’s most exalted species, the walleye.

And properly prepared, a northern pike’s firm, white meat provides excellent table fare.

More important, pike might play key roles in determining the abundance and size of a lake’s other fish, perhaps particularly its bluegills and ­crappies.

To determine whether and how quickly larger northern pike could be returned to Hudson’s study lake, he and the three other lakeshore owners agreed in 2009 to limit angling access to the lake and to require anyone fishing it to return all caught northern pike to the lake.

Meanwhile, only a limited harvest of bluegills and crappies would be allowed.

“If someone fishing the lake wants to keep a meal of panfish occasionally, that’s fine,” Hudson said. “But all bluegills over 9 inches are released.”

To track responses by the lake’s northern pike, Hudson and others helping in the study attach numbered tags to each fish that is netted. Each northern pike is also measured and weighed so its growth rate can be determined when it’s caught again.

Hudson and others also occasionally fish the lake in winter with tip-ups and minnows to determine the ­susceptibility of northern pike to angling.

Results are startling. Some northerns have been caught by anglers more than 20 times — a statistic, Hudson said, that confirms the vulnerability to angling of this aggressive ­species.

“Of the 97 northerns we caught by angling two winters ago,” Hudson said, “only seven hadn’t been caught before. The remaining 90 we had caught a combined 431 times.”

Given that northern pike in Hudson’s study lake require nine years to grow to 30 inches, careful harvest of the species would seem to be warranted.

The challenge for the DNR is to produce those larger fish in widely varied lake types without limiting harvest as severely as Hudson does on his study lake.

A previous DNR proposal, in fact, to protect northern pike statewide from 24 to 40 inches was roundly rejected by anglers.

Thus the three-zone option, which the DNR believes, combined with continued special harvest regulations on some lakes, will give Minnesota the best opportunity to produce a broader size spectrum of these fish.

Size limits in the zones would vary significantly. In the southern zone, for example, no harvest of northerns smaller than 24 inches would be allowed, whereas in the north-central zone, up to 10 northern pike would be allowed, two larger than 26 inches, with pike 22 to 26 inches protected.

Even stricter harvest regulations would yield more large pike faster, Hudson believes, and perhaps bigger panfish, too. But he conceded such rules might meet angler ­resistance.

Meanwhile, on the runup to Earth Day, changes were afoot in northern Minnesota.

Blue-winged teal, scaup and ring-necked ducks were touching down on Hudson’s study lake.

“And male leopard frogs are calling,” he said. “Looking for mates.’’