Just how old is that fish?

Remember the big largemouth I wrote about a few weeks ago which Darren Marcine caught during the final bass tournament of the year on Lake of the Woods?
It was a monster fish that ended up weighing in at seven pounds, 10 oz.—the largest bass that’s ever been weighed in a bass tournament in Sunset Country.
Before releasing that fish (which swam away nice and happy by the way), Josh Peacock, a local tournament angler and biologist from Kenora, took a scale and dorsal spine sample from the fish so it could be aged.
The aging of fish in Ontario actually is done in Dryden by fisheries aging specialist Susan Mann. After graduating from the University of Guelph with a degree in wildlife biology, she received additional training in moose and bear tooth aging.
Eventually, Mann was asked if she would consider aging fish structures on a permanent basis since the Ministry of Natural Resources was having trouble finding reliable aging consultants to do the work.
So that’s how she ended up with this unique—and cool—job.
“We receive a variety of bony structures taken from a large number of fish species from MNR units all across the province,” Mann explained, noting these bony structures include scales, bones, dorsal spines, pectoral fin rays, and otoliths.
The most commonly-aged structure is the otolith, a small bone in the fish’s ear. Different techniques are used for preparing each structure and after they are prepared, they can be aged under a microscope.
Aging fish structures is a lot like counting the rings on a tree stump. In fish structures, counting one ring to the next ring is considered one calender year.
Ages then are recorded and submitted to biologists to use for statistical analysis.
Mann has found reason to age all species of fish in Ontario but walleye, pike, smallmouth bass, lake trout, and lake whitefish are the most common. She also has aged invasive rainbow smelt and round goby in some samples, as well.
These are significant because in some bodies of water, they have altered the traditional forage for many fish.
Some of her more interesting finds include a 46-cm lake whitefish from Lake Simcoe in southern Ontario that was an astounding 56 years old. The oldest lake trout she’s aged from Sunset Country came from a small unnamed lake south of Eagle Lake that weighed around 22 pounds and was found to be 47 years of age.
That means this lake trout grew at a rate of less than a half-pound per year!
Remember that when you consider keeping a large trout this winter, if you keep a 20-pound fish, it will take more than 40 years to replace that fish!
Mann further explained the age structure of a population of fish gives biologists information about growth, reproduction, and overall population health of lakes. This information, in turn, can be used to predict what changes in regulations will do to fish populations and help manage these populations effectively.
In the coming months, Mann expects to age around 25,000 age structure samples gathered from the 2009 field season as part of a long-term program for monitoring the health of Ontario’s lakes, called the Broadscale Monitoring Program.
Having the interest I do in bass, I had to ask Mann if she could provide some interesting facts about the age characteristics of bass in Sunset Country.
“When bass are young, their bodies grow quite fast, but when they reach sexual maturity, this growth slows down so more energy can be directed at gonad growth,” she replied. “This change in growth can be seen in the bony structures like scales and spines that we look at under a microscope.”
A very interesting fact Mann included was that when we have an unseasonably cold summer, like we have the past two years, the amount of growth laid down in a bony structure is considerably less than the growth during a regular warm summer, meaning that when it’s cold like this year, bass (and most fish for that matter) do not grow as fast.
Finally, the results you’ve all been waiting for: how old was Marcine’s monster bass from Lake of the Woods? Mann aged that bass at 15 years, meaning it was born in 1994.
I was 11 years old at the time and getting ready to fish my second KBI tournament with my dad. Pretty neat stuff!

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