Earlier this month, researchers from the Michigan Department of Natural Resources (DNR) Marquette Fisheries Research Station documented the oldest known lake trout in the Great Lakes, a 62-year-old female. The fish was collected in the fall of 2023 from Klondike Reef in Lake Superior.

The discovery was made by Dan Traynor, a fisheries technician at the Marquette Fisheries Research Station, while he was processing samples. According to a press release from the MI DNR, Traynor is "one of the few experts on the age assessment of lake trout in North America." The fish, a humper lake trout subspecies, measured 24.7 inches in length and weighed 4.62 pounds. The humper lake trout are slow-growing and primarily feed on invertebrates.

 "Mary Catherine," a humper lake trout subspecies, was born in 1961. 

Age is one of the main variables used for tracking fish population health. The press release notes that "this finding indicates that lake trout indeed live long and prosper in Lake Superior." The fish hatched in 1961 and was nicknamed "Mary Catherine" because "Mary" was one of the most common names for babies born that year. Also in that year, John F. Kennedy was president of the U.S. 

Fish age is determined by counting growth rings on their otoliths, or ear stones, similar to how tree rings are used. As the fish grows, the otolith also grows, leaving a ring for each winter. The otolith is considered the most reliable indicator of age for lake trout.

 Otolith from “Mary Catherine,” showing 62 years of growth.

Lake trout are adapted to live in oligotrophic (low-productivity) ecosystems, such as Lake Superior, which is the deepest of the Great Lakes, with an average depth of 483 feet and an average annual surface temperature of 40 degrees Fahrenheit. The press release explains that "animals and plants that live in extremely unproductive environments with little food and extreme temperatures and weather...take a long time to grow." The typical lifespan for a lake trout in Lake Superior is 25 to 30 years, and the previous record was a 42-year-old fish documented in 1998.

The 62-year-old lake trout was captured during a survey to inventory lake trout subspecies at Klondike Reef and study their reproductive biology. The study, conducted by the MI DNR's Research Vessel Lake Char crew, is part of a larger effort to support lake trout recovery programs in the lower Great Lakes.

 Native lake trout ecotypes (sub-species) in Lake Superior.

In the mid-20th century, lake trout populations in the Great Lakes collapsed due to the sea lamprey and commercial fishing. In response, the United States and Canada formed the Great Lakes Fishery Commission in 1954 to manage fisheries and rehabilitate lake trout.

In 2024, the Lake Superior Committee of the Great Lakes Fishery Commission declared that "Lake Superior lake trout populations had been finally rehabilitated." The press release states that this is "one of the greatest comeback stories in freshwater fisheries management." Collaborative efforts between natural resource agencies to control fishing, suppress sea lamprey, and stock fish were credited with achieving "genetically diverse, self-sustaining, wild populations of Lake Superior lake trout, similar to levels found in the lake prior to the sea lamprey invasion."