MORE AND BIGGER WALLEYES

If you're a walleye, does it make any difference if you are born in an even-numbered year or an odd-numbered year? I know it sounds like a ridiculous question, but it's not. In fact, from a young-of-the-year walleye's perspective, the year in which it is born can have the most profound affect on its well-being. The one between living and dying.

That is what two good friends and former colleagues, Ontario Natural Resources biologists, Bev Ritchie and Peter Colby discovered when they compared the historical strength of walleye year classes. In fact, they found that walleye born in even-numbered years are far more likely to survive and grow into adulthood than their brothers and sisters hatched in odd-numbered years.

And, what, you might wonder is the cause of these superior year class strengths? Is it warmer water temperatures, higher water levels, lunar phases, better oxygen concentrations or perhaps just plain luck? Nope, it is none of those things.

Amazingly, what causes even-numbered year classes to be exceptionally strong, while odd-numbered year classes lag behind, is a simple burrowing bug that lives in the muck bottom of most walleye waters. It's the mayfly Hexagenia limbata, the darling of trout fly fishermen.

What the OMNR fisheries scientists discovered is that this large mayfly's lifespan is stretched over two years, as opposed to one year for most other mayflies. The majority of that time it lives as a nymph in the bottom of our walleye lakes before it finally emerges, in the very last days of its life, as the familiar and strikingly handsome adult.

Peter and Bev discovered that the Hex hatch is far more pronounced in even-numbered years, when so many nymphs are available in the spring and summer that the insects act as massive buffer forage which reduces cannibalism by and predation on young walleyes.

The biologists call this a bi-annual "pulse production" of mayflies, but the degree of "thump" is only truly appreciated when you realize that in the spring of even-numbered years over 120 nymphs can be crawling around each square metre of lake bottom. That puts the total population of tasty nymphs, which are virtually 100 percent protein, in the billions, if not trillions of insects in large walleye lakes. In odd-numbered years, however, the density of nymphs is reduced by a factor of four.

Peter and Bev, thus concluded, "that walleye, northern pike, and yellow perch consumed H.limbata nymphs from January to June, prior to emergence and that H. limbata occurred more frequently in walleye, northern pike, and yellow perch stomachs in even-numbered years. As a result of this increased availability of H. limbata, forage fish, including young walleyes, were less important food items (in terms of occurrence) for walleyes, northern pike, and yellow perch in the spring and early summer when young-of-the-year walleyes and yellow perch were pelagic and vulnerable to predation."

Just as amazing, the researchers also believe that the huge crops of H. limbata account for the higher fecundity of larger walleye which lay greater numbers of eggs in the spring of even-numbered years. That is great news for walleye anglers everywhere, who can now be excused for scratching their heads and wondering how they can adjust their calendars, so that every year ends with an even number.

Gord Pyzer, Fishing Editor

Outdoor Canada Magazine

October 2022