Tracking Northern Pike in Green Bay

CFL grad student, Dan Oele, is trying to see if pike return to their “birthplace” to spawn or if any ol’ tributary will do. Thanks to funding from the Great Lakes Restoration Initiative, Oele is out in Green Bay working on an answer. Watch (or read) below:

GREEN BAY — It’s the second day of April and Dan Oele is cruising the tributaries of Green Bay on the hunt for northern pike.
“I always come down here to see if I can see any fish staging to come up but it doesn’t really look like it.”

Dan Oele checks a hoop net for pike

This would normally be a good time to spot adult pike as they head inland from Lake Michigan for the shallow wetlands, streams and even road culverts where they spawn. But, this year, Oele’s not spotting many pike in the tea-colored water. For many of the fish, the spawning run is already done.
“It’s a pretty wild spring.,” Oele says. “The warm temperatures really bumped up all the fish migrations, the spring migrants. From walleye, sturgeon, suckers, northern pike are at least four weeks ahead of schedule and its all water temperature related. That really hot spell in mid-March started things really early.”
Oele is a graduate student in Pete McIntyre’s lab at the Center for Limnology at the University of Wisconsin-Madison. He’s working on a masters’ degree thesis exploring the nature of pike migrations.
“The core question,” he says, “is ‘Are northern pike returning to the same areas they were born in to spawn every year?’ That is, do they show natal site fidelity? And the way we’re answering that question is through otolith microchemistry.”
Joseph Brooks displays two otoliths taken from a northern pike

Otoliths, tiny disks of calcium carbonate often called “ear stones,” sit near a fish’s brain and help it detect sounds and vibrations, as well as orient itself in its 3-D underwater world. For researchers, otoliths are indispensible recorders of a fish’s life history. Not only do they have growth rings, much like trees, but they take in trace elements of the surrounding habitat as they grow. Since the water chemistry of an inland stream is different from a Great Lake, these changes show up in all fish, including the pike Oele studies.
“So a young fish is born in a tributary, stays there for a little while, migrates back out to Green Bay or Lake Michigan to grow up and mature. And when it’s mature enough to spawn going back into a tributary, we can detect those subtle changes in the otolith chemistry.”
Oele and Brooks record data on a pike taken from one of their nets

In several tributaries around Green Bay, Oele has set up hoop nets that allow pike to swim upstream to spawn and then corral them as they head back downstream. On this particular day, only one net turns up a pike. Oele and his field assistant, Joe Brooks, remove the pike from the net and take a series of size and weight measurements as well as scale samples and fin clippings. They then remove the otoliths.
Oele needs to catch ten fish in each of his nets to have enough evidence to take back to the lab. Once there, he can analyze the chemical make-up of each otolith to try to reveal if pike should join the ranks of fish like salmonids and suckers that return to their birthplace to spawn or, if pike simply head inland in the spring and use any suitable habitat to lay their eggs.
“Apart from being a really cool science experiment,” Oele says, “this has some really strong management implications. And that is, if pike are going back to the same areas to spawn, if you’re going to create a new wetland or habitat for pike to spawn, you’re going to have to seed it somehow with young fish that will imprint on that water body and in that way they’ll find it. And, if the opposite is true, and these fish are just cruising the coast of Green Bay and waiting for the water temperatures to get warm and clue in on that, you can reasonably expect to build a pristine wetland habitat and just leave it be and the fish will find it on their own.”
The answer to his question, Oele says, might one day help fisheries managers better protect future populations of one of Wisconsin’s biggest, and most popular, sport fish.
Oele displays the lone catch of the day. The unseasonably warm March weather drove an extremely early spawning season this year