The walleye population in the lower St. Louis River is down to about half what it was 25 years ago and the number of walleye harvested in 2015 was more than the annual production of new fish - a trend that could diminish the fishery if it continues.

That was the report given last week by fisheries biologists from the Minnesota and Wisconsin departments of natural resources to a meeting of the Twin Ports Walleye Association, a local anglers group.

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The report was based on an intensive 2015 effort to determine an accurate walleye population for the system. That effort included traditional net surveys as well as capturing, tagging and releasing some 6,400 walleyes and then documenting when and where those fish were caught by anglers over two years.

The study found the St. Louis River estuary and western Lake Superior hold an estimated 46,862 walleye. That's down from about 76,000 estimated in 1981 and is well under the historic estimates of 80,000 to 90,000 fish made by local fisheries experts in years between. It's less than half the nearly 100,000-walleye estimate from a different survey technique in 1995.

"It's clear that in 2015 the population is lower than in 1981,'' said Paul Piszcek, fisheries biologist for the Wisconsin DNR who oversees the popular fishery.

The 2015 survey also found that anglers caught and kept more walleye than are produced in a single year on the river/lake system, with harvest hitting up to 106 percent of production. That level of harvest would be unsustainable in the long run, eventually removing much of the walleye breeding stock. The system produced about 20,500 pounds of new walleye biomass in 2015, but anglers caught and kept nearly 21,000 pounds, just over one-fifth of the total walleye biomass in the system.

"We're at this level that we've deemed is at the maximum,'' Piszcek said of the walleye harvest. When asked if that harvest level would be alarming if it continued, Piszcek responded "absolutely."

"That has to come down, in my opinion,'' he said.

Trend unclear

But the biologists were quick to say they don't know if 2015 was part of an unsustainable trend or simply one year of higher than normal harvest.

"What we know is that we need more data points, more years,'' Piszcek, said noting biologists are preparing for another major walleye survey and population estimate in 2020, which should help show if there is a trend.

The report concluded the lower number of total walleye was likely due to fewer new fish coming into the system due to poor survival of newly hatched fish before 2011. But Piszcek and Minnesota DNR fisheries biologist Jeremy Pinkerton said there was good news in recent years that may not have shown up in 2015 survey results.

Walleye spawning success in 2012 and 2013, and the survival of small walleyes those years, was ''off the charts'' good. And those little walleye are now approaching both spawning age and catching size. Biologists and anglers are hoping those fish will show a healthier total population in 2020 and be numerous enough that new fish outweigh the annual harvest by then.

The lower St. Louis River/western Lake Superior fishery is jointly managed by Wisconsin and Minnesota and tribal agencies.

Members of the walleye association said the fact that the river/lake system holds only half the fish it used too isn't surprising. Many said they've been seeing a steady decline in walleye numbers for a decade.

Where a team of association members in the 1990s and 2000s might have caught 80-100 walleyes in a day, they noted, now it's more like 30-40. That's still good compared to many lakes and rivers, but not up to the St. Louis River's previous standards.

Reams of association data from catch-and-release tournaments held on the river also show a trend of declining numbers and size of walleyes, said Brandyn Kachinske, president of the group.

"I'm alarmed by that number (46,862 total walleye). It seems like it's not really enough,'' Andrew Frielund, a walleye association member and avid angler, told the biologists. "But you didn't have to show us these numbers. We've known it's been down for a decade."

No changes proposed - yet

The report suggested more frequent monitoring but stopped short recommending any intensive stocking or regulation changes, such as the number or size of walleyes that anglers can keep. The river currently has a very conservative, two-fish daily limit, and anglers must throw back any walleye under 15 inches.

But anglers can keep any fish over 15 inches, and association members said they are seeing too many other anglers keeping too many big fish, especially during ice fishing season when large, spawning-size female walleye enter the harbor from the lake to stage before laying eggs.

The two fish over 15 inches limit "doesn't protect big fish,''' Jarrid Houston, an association member, local guide and fishing columnist for the News Tribune, told biologists at the meeting.

Piszcek and Pinkerton said their agencies are discussing potential regulation options that might help bolster the river/lake system's overall walleye population. Regulation changes could be part of new management plans that both states currently are developing for the river/lake system. So far no specific new rules have been proposed.

"We're at the point of talking about what we should be doing going forward,'' Piszczek said.

Asked whether a slot limit might help lower the overall harvest and protect the population, Pinkerton said "that's something we're looking into." Many lakes and rivers have slot limits that require anglers to keep only fish between certain lengths, or throw back all fish between certain lengths.

Association members generally support a new regulation that would limit or stop anglers from keeping large, spawning size walleyes - those over 22 inches long. Others want Wisconsin to drop the Lake Superior walleye limit from five fish daily to two, the same as the river, especially considering big walleyes spend more time in the lake. No one seemed to know why anglers who leave the harbor to fish in the lake have been allowed to keep more than twice as many fish from the same population.

"They are the same fish, they come from the same place," Kachinske noted. Minnesota's Lake Superior walleye limit is two, the same as in the river.

Other trends

The report also showed some interesting facts about the massive walleye fishery that sprawls from the Fond du Lac dam through the estuary, the Duluth-Superior harbor and well into Lake Superior:

• For a whopping 91 percent of spawning-size (larger) walleye surveyed, more than half their food consisted of species from Lake Superior, a strong hint that big walleye spend much of their time in the lake. Biologists measured stable isotopes to determine exactly what type of food the fish had consumed (Lake Superior smelt vs. river shiners, for instance.) They found small walleye spend most of their time in the river and medium-size fish split their time about evenly. Some people have suggested that the number of big walleye caught on the river is going down because the big fish are spending more time in Lake Superior than in past years, especially since the 2012 flood that radically changed the lower river.

• Walleye tagged while spawning in the river were caught as far away as the Keweenaw Peninsula in Michigan, more than 250 miles away. Most are caught in the Spirit Lake and lower harbor area of the estuary, however, with another segment caught along the South Shore from the Superior Entry to about the Brule River.

• The system has an unusually diverse size range of female walleye that are spawning, from about 17-32 inches long. That's a sign of a healthy fishery, biologists said, and "really encouraging" for the long-term population.

• An older, less precise formula to measure fish populations shows and even steeper decline in the walleye population. That formula, which has a very large margin of error, showed the St. Louis River walleye population at about 55,000 fish in 1980, spiking to 90,000 fish by 1990, peaking at nearly 100,000 walleye in 1995 and then declining to 89,000 in 2002 with 46,862 in 2015. Biologists said the spike was probably due to the river being cleaned up by modern sewage treatment and the downward trend likely started when anglers returned to the cleaner river and caught and kept many walleyes.