Minnesota fisheries managers are concerned about the long term health of the lake herring fishery in Lake Superior.
Biologists worry not enough young herring are surviving to sustain the fishery, while at the same time demand for the fish has spiked.
Minnesota's 25 or so commercial fishermen who ply the waters off the North Shore have caught a lot fewer cisco in recent years. The herring, or cisco, fishery is always unpredictable, said Steve Dahl, a commercial fisherman who works out of the Knife River marina on the North Shore of Lake Superior.
The last few falls have been tough for Dahl, whose nets have yielded fewer herring at a crucial time of year.
Fishermen like Dahl can earn up to half their annual income just in the month of November, when herring congregate along the shore to spawn.
This year was different, though.
"November was really good, one of the better ones I've had," he said. "Towards the end I sort of got overwhelmed, it was just too much."
Despite Dahl's success this November, the herring catch has fallen recently.
In 2011 and 2012, Minnesota commercial fisherman harvested more than 350,000 pounds of cisco each year. But the last two years, that's dropped below 250,000 pounds.
"I think there's general agreement at least on the western arm of Superior that the population is not in a healthy state," said Minnesota DNR fisheries chief Don Pereira.
Cisco, Pereira said, are vital to both whitefish and lake trout, which eat herring, or herring eggs, to survive.
"They're critical for moving energy from the lower food web up to the top predators," he said. "So if lake trout, don't have an adequate replacement, it's questionable as to how stable the now successful lake trout restoration will be in the future if we can't bring lake herring up to healthy levels."
The fragile cisco population has led Minnesota fisheries managers to impose conservative limits on fishermen. In Wisconsin, though, there hasn't been any cisco limit.
Over the past decade or so there's been a huge surge in demand for cisco, particularly the eggs, which are used to make a kind of caviar that's a Scandinavian delicacy.
In Wisconsin waters, mainly around the rich fishing grounds surrounding the Apostle Islands, the annual cisco harvest has tripled since the early 2000s, to one and a half million pounds last year.
After pressure from Minnesota and others, Wisconsin for the first time put a limit on its cisco harvest this fall. But that limit — 1.5 million pounds — is the same as what was harvested last year.
"We do not want to limit our commercial fishermen if there doesn't appear to be a scientific need to do so," said Terry Margenau, fisheries supervisor for Lake Superior for the Wisconsin DNR. "Having said that, this rule is designed to be reassessed every three years ... to make sure we're still where we want to be."
Biologists around Lake Superior have recommended limiting the cisco harvest to between 10 and 15 percent of the estimated total biomass of cisco.
Wisconsin set its quota at about 7.5 percent, leaving an additional 7.5 percent to the Red Cliff and Bad River Bands of Lake Superior Chippewa, which have commercial fishing rights on Lake Superior. Minnesota sets its harvest more conservatively.
Cory Goldsworthy, the Lake Superior area fisheries supervisor for the Minnesota DNR, said the department sets its limits every year at an estimated 10 percent of the total biomass of cisco.
The Great Lakes Fishery Commission, which coordinates management among states, tribes and Canadian provinces, will be evaluating whether Wisconsin's plan is sustainable.
But the herring population in Lake Superior is getting squeezed on two sides. In addition to more fishing pressure — and more predation from a recovered lake trout population — not as many young herring are surviving past one year.
That's coincided with major climactic changes on Lake Superior since 1998, said Mark Vinson, a fisheries biologist with the U.S. Geological Survey in Ashland, Wis.
"We've had less ice cover, we've had earlier spring warming and higher summer surface temperatures," he said. Recently, there's been a strong correlation between years of low ice on Lake Superior and poor recruitment years for cisco, Vinson said.
"There's probably only one or two years over the last 40 where we've had low ice and good recruitment," he said. It's still too early to draw a definitive link between climate change and lake herring survival, Vinson said. He's currently conducting additional research to look at impacts of warming and less ice cover on herring at different life stages.
At the far northeastern tip of Minnesota, the Grand Portage Band of Lake Superior Chippewa took its own steps this year to protect the herring fishery.
The tribe cut the harvest in the water it manages off the shore of its reservation in half from about 60,000 pounds to 30,000 pounds.
Commercial fishermen were upset, said tribal biologist Seth Moore. It's a significant portion of their livelihood.
"But we felt it was important to take a leadership role in helping to manage a sustainable fishery for the lake," Moore said, "as an example to the state of Wisconsin and the tribes in Wisconsin that are harvesting at a high level."