How Mother Nature replenishes fish in spring is an annual wonder

The recipe for good fishing starts with eggs, and Mother Nature is cooking like crazy this time of year.

From north to south and east to west, the spring spawn in underway in Minnesota. And what a spawn it is.

"More than 90 percent of the fish that anglers catch in Minnesota are the result of natural reproduction," said Henry Drewes, Minnesota Department of Natural Resources regional fisheries manager in Bemidji. "All of the state's bluegills, crappie and bass are wild fish. That's true of northern pike, too, except for some stocking in the far south. More than 80 percent of the state's walleyes are the result of in-lake spawning, and so are upward of half of the muskellunge."

Billions of fish hatch this time of year as part of a seasonal sequence that has evolved over thousands of years. For game species, this annual replenishment begins with the northern pike, a species that starts to spawn while ice still covers lakes. Next come the muskellunge. As waters warm and days grow longer, walleye, perch, bass, crappie and bluegill follow suit, and largely in that order. Suckers and other prey species spawn in spring, too.

"The beauty of the spawning sequence is that newly hatched predators always have newly hatched prey to feed upon," said Drewes. "Little northerns find even littler perch and walleye to eat. Little bass find even littler bluegill. Nature devised a way for each species to sustain itself, and it's pretty darn cool."

Though Mother Nature serves up fresh batches of fish each year, the numbers vary greatly depending on water temperature. Walleye, for example, rarely flourish when an early warm spell is followed by extended cold. That type of weather pattern retards zooplankton production, the microscopic organisms that mosquito-sized fish depend on after they have absorbed their yolk sac. Still, one year's bust is often followed by another year's boom as late springs typically result in stronger walleye year classes.

"The spawning season is always special," Drewes said. "Walleyes are running in the rivers, anglers are chasing crappies in the shallows, and giant sturgeon are being caught on the Rainy River. It's all good. It's nature doing its seasonal thing, and we all get to be part of it."

Unlike most Minnesota fish species, the bluegill spawn lasts a long time. Some bluegills spawn in May when water temperatures hit about 60 degrees. Others don't spawn until early July when water can be 80 degrees. This is called asynchronous spawning, which is nature's way of ensuring a good year class of fish will be produced because the spawn is so drawn out.

Smallmouth bass have high "nest fidelity," meaning they often return to their same preferred spawning site year after year. Eric Altena, DNR fisheries supervisor in Little Falls, Minn., said a bass that his staff tracked in the Mississippi River traveled upstream 18 miles to spawn in the same spot as the year before. Female smallmouth bass often lay eggs in several nests rather than one as way of increasing the odds that one of these male-protected nests will produce a good hatch.

An excellent walleye hatch occurred last spring in Lake Pepin, the huge Mississippi River pool downstream from Red Wing. This happened because three key conditions aligned:

• Cool August weather in 2017, which enhanced egg production in females that would spawn the following spring;

• The number of walleye age 4 or older was relatively low, which enhanced recruitment;

"Rarely do all three conditions come together," said Nick Schlesser, DNR large lake specialist. "This strong year class of fish will reach legal size in late summer of 2020."

Anglers who fish shallow bays for crappie shortly after ice-out often mistakenly think the fish are spawning. In fact, crappies move from deep water into warmer dark-bottomed bays to stimulate gonad growth. Spawning comes later. Crappie spawning success in northern Minnesota is often exceptionally good or exceptionally poor, leading to boom and bust year classes of crappie. For anglers, there is a boom-and-bust cycle, too. The best crappie fishing occurs about five years after a huge year class has hatched. These "hot bites" are when localized fishing pressure peaks.

The giant of all Minnesota fish, the lake sturgeon is the midst of a remarkable recovery, especially in the northwest. The recovery is due, in part, to removing or modifying lowhead dams on rivers so sturgeon can reach preferred spawning sites. Over the past 20 years, dozens of dams have been removed or modified in the northwest. Today, lake sturgeon from the Breckenridge, Minn., area are known to travel in the Red River of the north all the way to Canada's Lake Winnipeg, a distance of more than 500 river miles.

C.B. Bylander is a freelance writer. He lives near Baxter, Minn.