Wisconsin Department of Natural Resources's Brad Ray holds the lake trout that they've been referring to as "Old Fish."  Photo courtesy of Brad Ray/Wisconsin Department of Natural Resources

By Danielle Kaeding of Wisconsin Public Radio

Wisconsin Department of Natural Resources biologists say a lake trout caught this month near the Apostle Islands of Lake Superior is the oldest they’ve found there in recent history.

The fish was snagged Nov. 2 in the Gull Island Refuge as part of the agency’s fall lake trout assessment, said Brad Ray, senior fisheries biologist on Lake Superior. Ray said it’s the eighth time they’ve tagged the fish in four decades.

"It’s been out at large for 36 years since we originally tagged it. At that time, it was at least 10 or 12," he said. "It could have been much older than that … That makes it at least 46, if not 48, and it could even be over 50."

Ray said to double that number to get an idea of how old it would be in human years — so this fish, dubbed "Old Fish," could be 100 years old in human years.

The trout’s age was determined by its size when it was first caught in 1981. At that time, the fish was 27.3 inches.

Ray said Lake Superior is home to fish that can live to a ripe old age, including herring and sturgeon. Sturgeon reach sexual maturity around 25 and live up to 100 years old in human years. Lake trout reach sexual maturity when they’re 7 to 8 years old.

Ray said it’s likely the roughly half-century old fish has spawned seven generations of lake trout. The fish has likely been swimming around the Apostle Islands of Lake Superior since Richard Nixon was president, according to the DNR.

Ray said the agency’s previous record for the oldest lake trout caught there was 43 years old. The oldest lake trout ever recorded was 70 years old, according to the U.S. Fish and Wildlife Service.

"It’s definitely a rarity to see an old fish, and it just really shows the importance of the refuge system to protect those fish to limit the harvest," he said. "That fish probably lived most of its life in the refuge, because in 36 years it only grew 8 inches, which is pretty slow growth."

Ray said the lake trout was 35.5 inches, but biologists didn’t have time to weigh it because they sampled 419 other fish that day. The only way to truly know the trout’s age is to harvest it, Ray said. However, the fish was tagged and released back into the refuge to live out its long life.