Every year several million walleye eggs are taken from fish in North Dakota and raised at the hatchery. When the walleye are about two inches long they are released into waters throughout the state. In 2020 however, a limited number of newly hatched walleye remained at the hatchery.

The walleyes, now about 10 inches long, are healthy and growing rapidly in one of the hatchery’s indoor raceways. They’ll remain there until two years old as part of a program that is not only new for the hatchery, but a first for the nation.

“Idaho asked us to take on this project and see if it could be done. It’s never been done anywhere else before with walleye. It’s something new,” said Rob Holm, hatchery project leader.

What is it?

Destined to be “super” walleyes, these young fish will be kept in a hatchery environment until reaching two years of age.

Simply put, these walleyes will have their chromosome make-up altered through an additive to the feed they are consuming. Male walleyes normally carrying X and Y chromosomes will then have YY chromosomes, meaning they will always pass a Y chromosome on to a female, thus insuring an all male hatch.

“A male will then, essentially, be a female. It’s just got the wrong parts,” explained Holm. “It doesn’t change the genetic make-up of the fish. They are still a male. Eventually they will turn a wild population to all males and there won’t be any more walleyes produced.”

Why the heck do that?

It is a tool biologists have developed, successfully, to remove certain species of fish from a body of water where they are not wanted. For example, Idaho raised “super” brook trout and released them into water where brook trout, which were not native to the waterway, overtook the previous realm of cutthroat trout.

Several years after releasing “super” brook trout containing all male chromosomes, the population of cutthroat trout began increasing, which is what exactly anglers and biologists had hoped would happen.

While walleyes are a favorite of fishermen in North Dakota, there are places where they are not very popular at all. Some of those places are in Idaho where they have taken over long-time trout fisheries.

“Walleyes are not native in Idaho. Anglers took it upon themselves to introduce walleyes,” explained Holm. “In particular, they are looking at cutthroat trout and the high number of walleyes feeding on them. There’s some serious competition there.”

So, if all proceeds as planned, “super” walleyes raised at the Garrison Dam National Fish Hatchery will be shipped to Idaho, released into waters where walleyes are threatening the native population of cutthroat trout and, over a period of several years, turn the walleye population into all males. With reproduction impossible, the walleyes eventually will be eradicated and the cutthroat will be free to flourish.

Holm is looking beyond the “super” walleye program, wondering about other possible applications of managing unwanted species in the years to come.

“Asian carp would be one but what about common carp?” said Holm. “They were introduced by the Fish and Wildlife Service in the 30’s and 40’s, brought over from Europe. Now there’s places that want them eradicated and this might be an opportunity for the future.”