Study: Some Saginaw Bay walleyes are wanderers
Saginaw, Mich. — When considering Saginaw Bay walleyes, fisheries managers just might have to think of them more like salmon, or steelhead trout, or lake trout.
Not stay-at-home members of the perch family, that is, but wanderers eager to take their shows on the Great Lakes road.
Dave Fielder, research biologist at the DNR’s Alpena Fisheries Research Station, told the Natural Resources Commission at its March meeting here that early findings of an electronic tagging study show that the bay’s burgeoning population of walleyes move more frequently and more dramatically than previously thought.
The ongoing work, entitled “Spatial Ecology, Movement and Mortality of Walleye,” is a cooperative effort of the Michigan DNR, Ohio DNR, Great Lakes Fishery Commission, U.S. Geological Survey, and Carleton University.
One-half of Saginaw Bay’s walleyes, the study found, leave the Lake Huron bay in whose tributaries they’re born, to travel as far as the Straits of Mackinac at one end of the big lake, and the outer shoreline of the Thumb at the other.
In the study, a total of 465 walleyes – 200 from the Tittabawassee River in 2011 and 65 more from it in 2012, and 200 from the Maumee River in the Lake Erie watershed – were captured on spring spawning runs. They were surgically fitted with radio-telemetry transmitters, each emitting a radio signal in a frequency unique to it.
Ready to receive those signals from as far as a mile away were hydrophones, receivers about the size of large soda bottles, stationed in various locations, mainly near shorelines through whose shallows walleyes were thought to migrate.
Two arrays of hydrophones stretched across the mouth of Saginaw Bay (the double line to determine direction of movement), another across Thunder Bay at Alpena. In all, about 160 receivers were placed in Lake Huron, ready to track walleye movement.
“We knew some walleyes migrate out of Saginaw Bay,” Fielder told the commissioners. “But one-half of walleyes in Saginaw Bay out-migrate, a bigger share than we thought. Fifty-eight percent passed the first line of receivers, 51 percent the second.”
Most out-migration took place by early June, “earlier than we thought,” Fielder added. Fish return to Saginaw Bay and its tributaries such as the Saginaw and Tittabawassee rivers in winter.
Fielder used a PowerPoint presentation to trace the migrations of four specific walleyes. One sped to northern Lake Huron, one to Oscoda, one to the Thumb shoreline, and one stayed in the bay. Each returned to inner Saginaw Bay come winter. And the next year, Fielder said of a surprise, each one went back to the same place it did before.
Why the migration? Fielder said biologists don’t yet know if it reflects the abundance of fish, water temps, changes in the prey base, or a combination.
“In some respects they’re more like salmon, steelhead, or lake trout than (exhibiting) what we normally think of as walleye behavior,” Fielder said.
The study, he said, “is challenging a lot of what we know about walleyes.
“It kind of leaves us with more questions than answers,” he said, adding that researchers will continue sifting more than 1 million bits of data for more answers.