Lake of the Woods walleye

Biologist samples 27 year-old walleye from Lake of the Woods

As part of his annual fisheries assessment on Lake of the Woods, Large Lake Specialist Tom Heinrich collects bony structures from a representative sample of fish. He then uses those structures to assign an age to the fish. The structures that he takes from walleyes are called otoliths, which are commonly referred as “ear bones. ”

The otoliths are cracked in half, charred with fire, and then observed under a microscope. Since walleyes in Lake of the Woods grow slower in winter than in summer, a record of the slow winter growth is apparent in bony structures such as the otolith. Age is determined by counting the alternating periods of slow growth (winter), and fast growth (summer). The principal is very similar to counting the growth rings in a tree to determine it's age.

Among the fish that Heinrich collected last fall (2005) was a walleye that was estimated to be 27 years old. This was the oldest walleye that Tom has "aged" since he started working on Lake of the Woods in 1990. The previous "oldest" walleye was 24 years old.

To put the age of this old walleye into perspective, she was part of the 1979 year class. What were you doing in 1979?

Otolith from 27 year-old walleye
Photo: Otolith from 27 year-old walleye


For more information on the Lake of the Woods fishery, contact area fisheries supervisor Phil Talmage at [email protected].

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