In May 2023, an angler in Sheboygan reeled in a Salvelinus namaycush – commonly known as a lake trout. Though trout and salmon are frequently pulled from Lake Michigan, the specific lake trout had a unique story to tell, thanks to a coded wire tag implanted in its snout.
The code written on the tag revealed that the trout was 39 years old, marking it the Great Lakes Mass Marking Program’s oldest coded wire-tagged lake trout on record. The 16-pound fish hatched in 1984 before its stocking into Lake Michigan on July 12, 1985.
But according to the program’s supervisory fish biologist, Matthew Kornis, it’s just the tip of the iceberg for what looms below the lake’s rippling surface.
“I have no doubt that there’s 40-year-old fish swimming out there in Lake Michigan,” Kornis said.
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To uncover a fish of 39 years, a certain order has to fall into place, beginning with the program’s marking operation. Under its supervision, a lake trout’s lifespan is bookended with the implantation and removal of a coded wire tag.
The Great Lakes Mass Marking program implants the wire tags in hatcheries, where fish begin their journey to populate the lake. The stocking process includes trout and salmon, which are stuck with tags to keep track of their population.
For fish that go through the tagging process, the journey is as short as it is thrilling – fed through channels of sorters and slides before the tag, just a millimeter long, is implanted into the snout.
“My kids love [seeing it] because they’re like, ‘The fish go down the water slide,’” Kornis said. “And that’s kind of what’s happening.”
Within the snout of the fish, the tag is stuck just behind its nostrils and in front of its eyes, nestling into a ball of cartilage that hugs the tag in place as the years go by – in one case, 39 of them.
The process takes place as part of the AutoFish system, which sorts and tags fish under the oversight of a few crew members. Prior to the mechanical setup, the process was done manually, involving removal from water, sedation and the careful precision of the human hand to place a tag within the fish.
The modernized, automated operation, which takes place in a trailer, allows the fish to stay submerged the entire time. Up to 8,000 fish are tagged per hour. After its development in the late 1990s, the system came to Wisconsin with the installation of the Great Lakes Mass Marking Program in 2010.
The machinery, which also places fin clips on salmon, features its own quality control, as cameras and magnets register the placement of markers as the fish pass through.
While some tags can miss the cartilage, including cases where the fish enters the machine upside-down and gets tagged in the tongue, the system picks up the misfires. Though a few inevitably fall out of place, the tag loss rate stabilizes at around 98% after 100 days, meaning that nearly all fish released from the hatchery keep their tags for good.
Parallel to the implantation process is the one where the tag is removed, which happens when the fish is caught after swimming out its years in the lake.
“Our program was initiated with the tagging in the hatcheries,” Kornis said. “But all that tagging doesn’t do you very much if you don’t have data on those fish when they return.”
They read the tags offsite, so it wasn’t until well after the original angling that the 39-year old trout’s story was known. The lake trout was stored for a few months before its tag and story were finally pulled out.
The process of reading the tag is a puzzle. Once removed from a freezer, the snout of the fish is cut in half, after which a magnet hovers over each side to determine which one holds the marker. The process repeats itself like an everlasting fraction until the remaining section is small enough to uncover the 1-millimeter tag.
Upon reading the tag under a microscope, the number is stocked into a spreadsheet, which is then referenced to determine the fish’s origins.
However, due to the 39-year-old trout’s age, the tag read a bit differently than most. The modern tags have a set of six numbers. Before the turn of the century, though, the coding was binary, so this fish’s marker revealed a set of dots and spaces once put under a microscope.
While in one case, the tag revealed an age of almost two scores, the Mass Marking Program continues to tag, oversee and log the fish that inhabit the Great Lakes. As the implanted millimeter of wire carries the story of its own trout or salmon, so it awaits the chance to share it, giving a glimpse into the world below the surface.
