Keeping track of the overall health of various fish in the Great Lakes is an endless job. Part of that job involves capturing fish and trying to determine how old they are since the age of fish is a good indicator of the overall well-being of a population.

When researchers with the Michigan Department of Natural Resources (DNR) Marquette Fisheries Research Station caught a lake trout in September of 2023, they didn’t think anything of it. The specimen wasn’t particularly long or heavy, so they ran their normal tests before handing it off to Dan Traynor, who is the lake trout age expert.

Traynor is able to determine the age of a lake trout by analyzing the rings in the otolith. This is a stone of calcium carbonate that is located within the inner ear of fish. As the fish grows, the otolith grows as well, leaving a small ring each winter, not unlike trees.

Counting the rings is able to give a fairly accurate estimate of how old the fish is.

To everyone’s surprise, this trout looked to be 62 years old, making it by far the oldest lake trout ever found in the Great Lakes. Before this fish, the oldest ever found was in its 40’s. Normally, this species of fish lives between 25 and 30 years.

Sadly, running these tests on the fish is typically fatal, and that was the case here. The DNR, however, did honor this record breaking fish by naming it Mary Catherine. Mary was chosen because it was one of the most common names for children in 1961, when it is estimated this fish first hatched.

While it is sad that the fish died, it is a good sign that it had lived so long. The DNR Fisheries research biologist, Shawn Sitar, wrote in a recent bulletin:

“Age is one of the most vital statistics used to assess the health of fish populations. Scientists look at the age distribution in fish populations to measure mortality, growth and longevity. This finding indicates that lake trout indeed live long and prosper in Lake Superior.”

The Great Lakes had gone through some troubling times ecologically in the last 60 years, so the fact that this fish survived may be a good indication that progress is being made to improve the overall ecosystem.

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