Want tto hear a spooky story? I recently witnessed a scene which may rival anything you’ll see in a movie or haunted house this month.
It began with a surgical technician setting up the operating room in an improvised field hospital. She laid sterile instruments out while Bach’s Toccata and Fugue in d-minor played in the background.
Meanwhile, the O.R. nurse recorded vital stats. When finished, he transferred the patient to the operating table, where the anesthesiologist waited with an improvised system for maintaining the patient’s oxygen level.
The surgeon picked up a scalpel and began his work. He made a small cutaneous incision, through which he inserted a device that will help him track the patient’s location for the next several years. Then he closed the site with three stitches and sent the patient to the recovery chamber.
The team quickly performed similar procedures two more times. It took mere minutes. All three patients soon went on their way, apparently healthy and none the wiser. As they left, the surgeon switched on a machine to confirm the tracking devices were working—like something from a twisted sci-fi tale.
It all happened just as I described. Although, I should note the patients were fish. And the organ music was only in my head.
This was the first step of a fisheries management tool called acoustic telemetry. The “tracking devices” are transmitters which send signature pings out into the water every few minutes. Those sound pulses are then picked up by receivers positioned up and down the river.
Over time, the data collected shows how much—or little—an individual fish roams throughout the river system. With enough fish carrying transmitters, fishery professionals can learn an awful lot.
I met Minnesota River fisheries specialist Tony Sindt and his team at the public access south of Fairfax, where he hoped to get transmitters into some walleyes, channel cats, and gar that recent morning. The boat went up and down the river a short distance, and soon returned with those first surgery subjects.
After they swam away, I hopped in to observe the search for more target species. In the process, I got to witness the collection method: electrofishing. Sounds sinister, but it’s actually pretty tame.
Two arms are lowered in front of the boat. Dangling from those arms are several anodes, which send a mild electric current through the water. Stunned fish immediately come to the surface where netters stand waiting for desired species to appear. Once out of the electric field, fish recover quickly and disappear again into the swirling butterscotch waters.
It sounds like acoustic telemetry has been in use on the Minnesota River for not quite ten years now (longer on the Mississippi and St. Croix). Sindt said it began with species like shovelnose sturgeon and paddlefish, which are known to move up and down rivers quite a bit.
More recently, he expanded to include other fish with migratory tendencies. Knowledge of things like their movement patterns and habitat use in the Minnesota is relatively limited, and data is needed before we begin to understand what fish are doing in the river and why it matters.
“Like, is there some key reach that’s critical for spawning for walleyes, or other species? And then, how much are they moving back and forth between other rivers? And do fishing regulations on different rivers make sense if fish are moving back and forth? Things like that,” explained Sindt.
To date, around 225 fish have been implanted with transmitters in the Minnesota River. In total, there are 21 receivers throughout the main stem and a few major tributaries.
Getting transmitters into fish this year has been difficult due to persistent flood conditions. Even the day I accompanied him, Sindt said the river was three or four feet higher than he would have liked. As a result, he ultimately wasn’t able to find as many specimens as he’d hoped.
One bright spot this year, however, was that a higher flow allowed Sindt to get his electrofishing boat into the Blue Earth. He was glad to get transmitters into around 20 fish that already show an affinity for that river.
That work was important in documenting the way fish use the Blue Earth after a century of being cut off by a dam. The DNR also recently installed new acoustic receivers upstream from the dam site: two in the Blue Earth and one in the Watonwan River.
“As soon as the Rapidan Dam failure happened, we made a priority to get those three receivers in the river upstream. Because we wanted to be able to detect any fish, whether it was something we tagged in the Blue Earth or Minnesota or farther downstream,” explained Sindt.
While no fish have been detected yet by those new receivers, he expects that to change after restoration work at the dam site is done and fish passage becomes easier.
At this point, the use of acoustic telemetry in the Minnesota River won’t necessarily have an end date. Sindt said tagged fish tend to provide different information from year to year. And as always, the more data, the better.
“They’re responding to river conditions and migratory cues like big rain events and flood pulses,” he said. “So, having data across years and river systems is valuable for getting a more comprehensive understanding of those movement patterns.”
What’s more, findings will not be confined to the hundreds of miles of the Minnesota River and its tributaries. The wider network of receivers has detected fish moving between the Minnesota and other major rivers, namely the St. Croix and Mississippi.
One gar tagged this summer at Land of Memories Park apparently swam downstream and “all over Pool 2” of the Mississippi.
Then it went up through a lock and dam, up the St. Croix, and was detected near the mouth of the Kinnickinnic River.
“That caught me by surprise…that gar are moving all over the place, when I just assumed they hung out here in a hole and ate shiners all summer long,” laughed Sindt.
Surprising? Yes, and not at all spooky.
Roy Heilman is an outdoorsman, writer, and ethnic Minnesotan. His adventures take him all over the map, but he’s always home at neveragoosechase.com.