Let the lunkers go: New science explains why big fish matter so much

NUTRITION

A similar situation occurs as smaller fish mature and begin to seek out a heftier diet. “The behavioral side of things is very important,” says Baccante. “That’s why we’ve always promoted the idea of maintaining a balanced fish population in terms of age groups. Those older walleye have a lot of learned behaviour in regards of where feeding and spawning grounds are located.”

We often forget that younger eight-, 10- and 12-inch fish such as walleye, bass, trout, pike and muskies are prone to predation and therefore go about their early life in ways quite different from the BOFFFFs that optimize their daily routines. The smaller, less mature fish typically hide in the weeds and around cover, venturing out into more open-water areas only when they’ve grown bigger and older.

Amazingly, that’s why our favourite spots for big walleye, bass, lake trout, northern pike and muskies tend to hold only big fish, observes Tufts. I can certainly attest to that. On my home waters of Lake of the Woods, I’ve accumulated a handful of muskie locations where I’ve only caught big fish over the course of 47 years of intense fishing.

“If a big fish is removed from a spot, and you catch another fish off that spot, even a year or two later, it’s often also a big fish,” says Tufts. In particular, he says research has shown big fish will occupy the best spawning areas, as well as the prime spots offering the most food and energy reserves. “If you remove a fish, even experimentally, another big fish will take its place. It’s something that evolution has fine-tuned over millions of years.”

Older walleye have learned where the best feeding and spawning grounds are located

Baccante agrees, noting how big, old, fat, fertile, female walleye will vacate spring spawning areas much earlier than smaller, younger fish, and much sooner than many anglers realize. They’ll retreat to deeper, cooler, main-lake structures—underwater points, deep rock piles and shoals—where they can optimize their growth, control their metabolic rate and produce more eggs by marauding on schools of super-nutritious pelagic ciscoes.

In explaining the unique behaviour of big walleye, he refers to fellow biologist Peter Colby, his former colleague at the Walleye Research Unit. Colby wrote Synopsis of Biological Data on the Walleye for the UN’s Food and Agriculture Organization, looking at the growth traits of walleye in lakes with and without ciscoes. He found that once the predators finally reach an appropriate size, they start feeding on the outrageously nutritious silvery prey, and their growth rate skyrockets off the charts.

“It’s based on energetic behaviour and rules,” says Baccante. “They take advantage of the more nutritious food, because they’re not going to get a lot of nutrition from the shallow littoral [shoreline] zone yet.” Instead, he says, the larger ciscoes out in deeper water are much more beneficial to the larger females. “Walleye will go towards where these prey fish are schooling. It outlines the importance of maintaining a balanced population with these older mature fish.” 

COD CONUNDRUM The cod fishery on the Grand Banks of Newfoundland and Labrador was once one of the greatest living biomasses the world has ever seen. The schools were so thick, early seafarers had difficulty scooping up water because their buckets became so full of big fish. As we know, the East Coast cod population collapsed in the late 1900s after centuries of relentless commercial overfishing, and it has not bounced back. And as fisheries biologist Bruce Tufts observes, the cod population now lacks critically important big, old, fat, fertile, female fish, and without them, it will be difficult to recover.