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

REPRODUCTION

The first key reason big fish matter centres on the quantity and quality of their eggs. Bruce Tufts points to walleye as an example, noting how a 12-pound female produces far more eggs than three four-pound females combined.

Not only do these big fish produce more eggs, he adds, but the eggs are also supremely bigger and much more vibrant, with greater fat content and higher nutritional quality. This ensures the larvae that hatch have a much better chance of survival, especially during the first winter starvation period under the ice—one of the most perilous stages of life for a wild fish in Canada. They’ll also have a much better chance of being recruited into the population and producing strong year classes.

“What it means is that as big female fish get older, their contribution of quality eggs is exponential in the population,” Tufts says. “And so those big fish are really important. The paradox is that we have traditionally removed them from the population.”

Their own reproduction aside, BOFFFFs also show smaller, younger walleye the ropes when it comes time for them to spawn for the very first time. Namely, they’ll follow the more experienced adults to the best windswept cobble shorelines, shoals and current-exposed areas, learning where to lay their eggs.

“Walleye tend to congregate in schools at different times of the year, and spawning is one of those physiological requirements the fish have to go through,” says biologist Dominic Baccante, who worked in the Ontario government’s Walleye Research Unit. “For young walleye just coming into maturity, they start to get the pheromones and cues that tell them that they should be looking for spawning grounds. So, they follow the older mature fish.”