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Scandinavians like to eat caviar made from lake herring eggs. Lake herring comes from Lake Superior. Scientists say the growing export market around this fish combined with mild winters are putting its population at risk. Peter Payette of Interlochen Public Radio reports.
PETER PAYETTE, BYLINE: There wasn't a lot of demand for lake herring until a few years ago. Craig Hoopman says it used to be fed to Mink and used as fertilizer.
CRAIG HOOPMAN: It was just real cheap product that the fisherman would go, and you could make a fairly decent living.
PAYETTE: Hoopman is a commercial fisherman in Wisconsin who fishes around the Apostle Islands. He says about eight years ago, Scandinavians started buying lake herring eggs, or roe, in big quantities. That's because the silvery little fish sometimes called Cisco is similar to one found in northern Europe needed to make a popular caviar.
HOOPMAN: Now the numbers are - we get really good money for our roe. It's shipped to Estonia or Sweden, so it's kind of a really small niche.
PAYETTE: But it's just that niche that worries some marine scientists.
Mark Vinson directs research on the R/V Kiyi for the U.S. Geological Survey. Vinson says this fishery is enormous, and the Apostle Islands are the most prolific breeding grounds. He says in November, a third of the adult herring in this lake will leave the deep water and head to the west end to spawn.
MARK VINSON: Some the order of 60 million fish that are coming into the western arm of Lake Superior in the fall to spawn. And 60 million fish is a lot of fish.
PAYETTE: This fish is a key link in the food web of Lake Superior. For instance, whitefish, the most popular seafood in the Great Lakes, depend on herring eggs to get through the winter.
VINSON: Those eggs provide food for other fish, and then those young fish come off, which are then eaten by other fish.
PAYETTE: The problem is that not many young fish have been hatching and surviving in recent years.
VINSON: Christmas morning, see what's there.
PAYETTE: It's been more than a decade since they saw large numbers of young lake herring. And while this year was decent, some years they find almost no young fish at all. Vincent says explaining why lake herring reproduce so sporadically is the holy grail of fish science up here.
VINSON: There hasn't been anyone who's really solved it, like, put their finger on it and says this is the reason that recruitment is so variable.
PAYETTE: They do know that ice plays a key role. While ice cover on Lake Superior doesn't guarantee a bumper crop of young lake herring, it doesn't seem to happen without it. Commercial fishers around the Apostle Islands are allowed to catch as many lake herring as they want. But earlier this year, the Great Lakes Fishery Commission urged Wisconsin and some Indian tribes to limit the harvest. The request specifically mentions lake trout, another commercial fish that's been stocked for decades in Lake Superior. The trout depend on lake herring for food. Terry Margenau at the Wisconsin Department of Natural Resources agrees there's a problem.
TERRY MARGENAU: What's going on right now we don't think could go on for long without seeing some impacts.
PAYETTE: One of Margenau's biologists put it more bluntly at a conference in March. He used the word collapse to describe what might happen to the lake herring fishery. But Margenau remains optimistic that Wisconsin and the tribes can agree to limit their catches and give the fish a better chance to reproduce this November. For NPR News, I'm Peter Payette.
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