Surprises abound in Bays de Noc study of walleyes

Escanaba, Mich. — Results of a DNR study of walleyes in the Upper Peninsula’s Bays de Noc has revealed naturally reproduced fish are contributing more to the population than stocking efforts.

DNR officials launched a study in 2004 to measure the contributions of hatchery and naturally reproduced walleyes in both Little Bay de Noc and Big Bay de Noc by marking all stocked fish with oxytetracycline, which is included with their food in the hatchery and later shows up in their bones.

Between 2005 and 2009, DNR fisheries biologists stocked approximately 832,000 OTC-marked walleye fingerlings in Little Bay de Noc, and about 1,017,000 in Big Bay de Noc, then used fine gill nets and electrofishing to sample the juvenile population each fall.

“This gives us the first quantitative measure of how stocked fish are contributing versus natural reproduction,” Troy Zorn, DNR research biologist out of Marquette, told Michigan Outdoor News. “We’ve never been able to put a number on the natural reproduction.”

The percentage of naturally produced walleyes over the course of the study registered at 76 percent in Little Bay de Noc, and 62 percent in Big Bay de Noc, Zorn said, meaning more than half of the walleyes collected were produced in the lake.

There were other interesting findings.

DNR officials stocked walleyes in Little Bay de Noc in 2004, 2006, and 2008, and in Big Bay de Noc in 2005 and 2009, but no walleyes were stocked in 2007 due to concerns about spreading viral hemorrhagic septicemia, a deadly fish virus. Over the course of the study, DNR biologists collected a total of 2,194 walleye fingerlings from Little Bay de Noc and 763 from Big Bay de Noc.

“We found, looking at the years when we stocked fish compared to the years we didn’t … you couldn’t tell the difference,” Zorn said. “It’s unclear as to whether the stocked fish are really contributing to the fishery.”

Data showed no relationship between stocking and angler harvest in Big Bay de Noc and only a tiny correlation in Little Bay de Noc, he said.

Zorn said he suspects stocked fish in the Big Bay likely are eaten close to shore or migrate off shore.

“We’re still trying to figure out what’s going on,” he said.

DNR officials said the data will be used to inform future management decisions, but will have no immediate impact on walleye stocking in the bays. Jessica Mistak, the DNR’s northern Lake Michigan fisheries supervisor, said some local anglers were concerned the high rate of natural reproduction could lead to stocking cuts.

“It’s been since the ‘70s we’ve been trying to rebuild the bays,” for walleye, Mistak said. “We’re not walking away from managing the bays or walleyes, and we’re not walking away from stocking walleyes.”

The lack of a correlation between stocking and angler harvest may be misleading, because angler effort also has decreased, Mistak said. DNR officials believe stocked walleyes  are contributing to the system, but the data clearly show naturally reproduced walleyes make up the bulk of the population, she said.

“We do know anecdotally that fishing has declined from creel clerks interviewing anglers … which presumably means less fish being harvested,” Mistak said.

DNR officials will continue to use a stocking plan developed two years ago in a collaborative effort between the DNR, local anglers, and others. That plan takes into account the estimated number of adult walleyes, angler catch rates, age one and age two natural reproduction, forage fish levels, and other factors, Zorn said.

“We’ve developed a walleye strategy on Little Bay de Noc … and our stocking decisions for the little bay will be guided by what’s happening in the lake,” he said.

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