DULUTH 鈥� A small, native fish in Lake Superior is having a population explosion, great news for the big lake鈥檚 ecosystem but maybe a mixed blessing for anglers.
The lake鈥檚 population of cisco, sometimes called lake herring, have rebounded with a massive group of young fish coming up through the system.
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鈥淔rom what we鈥檙e seeing so far, this is the biggest year class we鈥檝e ever seen,鈥� said Cory Goldsworthy, Lake Superior fisheries supervisor for the Minnesota Department of Natural Resources.
The News Tribune first reported the cisco boom last fall after DNR test netting showed higher numbers of young fish. But DNR biologists were waiting for spring trawling data from the U.S. Geological Survey to confirm their hunch. Those results are now in, and cisco are indeed booming.
鈥淭hey (USGS) have been doing this since 1978 and the only other year that was near this big was 1984, but it looks like this one will be bigger,鈥� Goldsworthy said.
Cisco are an important prey fish for larger predator fish like lake trout. In recent years, Lake Superior hasn't had as many prey fish for larger predator fish to eat.
鈥淎 boom in cisco is great news for the whole ecosystem,鈥� Goldsworthy said.
More cisco than smelt
In fact, cisco are now the most numerous fish in Lake Superior, according to USGS estimates, surpassing even invasive rainbow smelt.
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鈥淭hat's the first time in our lifetime that鈥檚 ever happened,鈥� Goldsworthy said.
The current explosion of cisco were spawned in fall 2021 and hatched early in 2022, are now up to 6 inches long and they already are showing up in the stomachs of lake trout and other bigger fish.
鈥淪ome of the charter captains are telling us the lake trout stomachs are just gorged with cisco,鈥� Goldsworthy said. 鈥淭hat's what we expected.鈥�
The abundance of food may already be making Lake Superior trout and salmon fatter than usual. Anecdotal reports of much larger than usual coho and Chinook salmon and lake trout are coming in from anglers around the Twin Ports. And the steelhead rainbow trout captured by the DNR in the Knife River this spring were longer and fatter than previous years.
鈥淲e might normally see a couple of steelhead 30 inches long and 10 pounds, but this year we had numerous ones that big,鈥� Goldsworthy said.
The one possible downside is that so many baitfish roaming the lake may make big fish less likely to chase an angler's spoon or plug being trolled nearby. They may be too full to bite. (So far this season it's not the case 鈥� fishing has been very good.)
鈥淲e might see that for a year or two until the cisco get too big. But the fish they (anglers) do catch will be bigger,鈥� Goldsworthy said.
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Eventually, the cisco will grow to about 16 inches long 鈥� too big for most trout and salmon to eat. But they will then be available for commercial netters to capture, both for their tasty filets and their valuable roe sold as a substitute for caviar to European markets. There are about 25 DNR-licensed commercial netters on the North Shore along with several tribal netters.
鈥淲e should see quotas going up (for netters) by 2025 or 2026. 鈥� And because cisco can live to 25 or 30 years or more, this should be great news for the (commercial) cisco harvest for many years into the future,鈥� Goldsworthy said.
Cold water, not necessarily ice, may be key factor
Biologists had connected winters with extensive ice cover to great spawning success for cisco. But now they may be shifting to water temperature as opposed to ice as the most critical factor. The winters of 2021-22 and 2022-23 had average ice cover or less, Goldsworthy said, but had very cold, late springs. Those cold-water temperatures appear to have boosted cisco production.
Cisco had been in decline for several decades on the big lake, charting down as water temperatures charted up with climate change, with poor reproduction and dwindling numbers in general.
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