Fisheries researchers count bone rings, mend nets as winter nears
ALPENA — In a small building on the lip of the Thunder Bay River, a handful of fishermen spend their winter mending nets and looking through microscopes at tiny pieces of fish bone.
It’s not the most exciting way to spend six months, said Darren Vercnocke, fisheries technician at the Michigan Department of Natural Resources Fisheries Research Station in Alpena.
But the information gathered through tedious study helps keep the Great Lakes great, for both their inhabitants and the humans who live nearby.
From ice thaw to ice formation, the employees of the fisheries station and their vessel, the Tanner, prowl the western rim of Lake Huron, scooping up fish.
Using a trawl net — dragging it behind the boat like a giant sock — or dropping hundreds of feet of gill netting and reeling it back up a day later loaded with fish — the Michigan Department of Natural Resources workers nab fish of all kinds to be weighed, measured, and studied.
The data offers a clear picture of how many fish are in the lake’s waters, how healthy they are, and what they need to thrive.
And healthy fish mean healthy habitats, good water quality, and humans able to enjoy those resources, said David Fielder, fisheries research biologist with the Alpena station.
Fish caught in the holes of the gill net — like a 7,200-foot chain-link fence, anchored four to five feet above the lake’s bottom — are usually sacrificed to provide data to keep other fish healthy. Their meat is given to a local food pantry — no use wasting it, said Jeff Diemond, captain of the Tanner, as he mended nets at the fisheries station on Wednesday.
Wooden drawers with dividers are filled with small envelopes, each holding a bone fragment.
“Every envelope is a fish,” said Vercnocke, rifling through the carefully-marked envelopes.
The drawer isn’t as full as usual this year, as the coronavirus pandemic kept the researchers from their spring survey. In a typical year, the station processes 6,000 fish, examining stomach contents, looking for identifying markings showing where the fish was released, and finding the fish’s age.
Aging a fish requires a microscope, a low-tech makeshift Dremel saw stand, and patience.
Small portions of fish are carefully sliced using rigged-up tools — if they do the job, there’s no point in getting something fancy, Vercnocke said — and examined for annuli — rings left like the markings on a tree trunk, indicating a year’s growth.
A slice of lake trout jaw bone, displayed on Vercnocke’s computer monitor, had 32 annuli — old, for a trout.
Walleye, which live about 15 years, have to be tough, because they hang out in rough neighborhoods — like Saginaw Bay, where, Vercnocke said, everything below water will cut or poke you. In such volatile surroundings, the fish’s dorsal spines, used in self-defense, are strong enough to provide a good cross-section to be aged.
A tiny bone from the inner ear of a whitefish, barely big enough to be grasped between fingertips, can be sliced to show a fish’s age. Even scales, held to a light, show growth rings, though less precisely, Vercnocke said.
Up until a few years ago, fish researchers didn’t use jawbones to age lake trout. Workers at the Alpena fisheries station, frustrated with inaccuracies in other methods, realized jawbones would be a fix. They now get calls from research stations in other countries, asking about the method.
“Fisheries research, right?” said Vercnocke. “That’s our job.”
Once the water temperature drops below 50 degrees, the Tanner will head out for one more survey before winter, this time targeting lake trout and gathering information about contaminants for the U.S. Environmental Protection Agency.
The laborious bending over saws and penciling data provides information used by researchers to make decisions to keep Lake Huron healthy, from adjusting fishing limits or season dates to creating spawning reefs and adjusting yearly fish releases.
The fun part of the year, though, is being out on the lake, hauling in nets, dressing fish, and getting to be a fisherman, said Diemond.
The Alpena native is retiring in spring, after 30 years of watching the changes happening all the time under the lake’s surface as nature adapts to humans’ actions.
It’s been a good job, he said.
“You’re going to pay me to go out fishing? Seriously?” said Diemond, tugging on the brim of his DNR cap with a grin. “OK.”