Photos: Listening for clues to Mille Lacs walleye decline


Researchers want to test a hypothesis that invasive species impact walleye.
1 The Mille Lacs Band of Ojibwe received a nearly $200,000 grant from the U.S. Fish and Wildlife Service to use acoustic telemetry technology to study the walleye population on the popular central Minnesota lake. They launched from Shah-bush-kung Bay public access in Vineland, Minn., on July 13, 2018. 
A small transmitter inserted into the walleye will send data to receivers.
2 A small transmitter inserted into the walleye will send data to receivers that were placed throughout the lake in a grid pattern. 
Sixty-one acoustic receivers attached to a concrete anchor were placed.
3 Sixty-one acoustic receivers attached to a concrete anchor were placed in a grid pattern throughout Lake Mille Lacs to collect data from walleye inserted with a special transmitter. They were placed in various habitats in the lake in depths ranging from 10 to 40 feet deep. 
Aaron Shultz holds a thin green strand that tells anglers a fish is tagged.
4 Aaron Shultz, climate change fisheries biologist with the Great Lakes Indian Fish & Wildlife Commission, holds a thin green strand with a phone number that will let anglers know that the walleye has been implanted with a special transmitter tag. 
Aaron Shultz inserts a transmitter tag into the fish's abdominal cavity.
5 Shultz inserts a small transmitter tag into the fish's abdominal cavity. 
Johnson holds a sedated walleye while Schultz performs the procedure.
6 Intern Brandon Johnson holds a sedated walleye while Schultz performs the surgical procedure to insert a small transmitter tag. The fish is sedated using a machine that sends an electrical pulse to its muscles. 
The procedure to insert the transmitter tag takes only a few minutes.
7 The surgical procedure to insert the transmitter tag in the sedated fish takes only a few minutes. 
This is the first time the technology has been used on inland Minn. lakes.
8 This is the first time the acoustic telemetry technology has been used on a large inland Minnesota lake, although it's been used extensively on the Great Lakes. 
After the walleye are tagged and have recovered, they are released.
9 After the walleye are tagged and have recovered, they are released back into the lake. The tags emit a pinging sound, which is picked up when they are within range of receivers in the lake. Researchers expect to hear from each fish at least once every hour. 
Fish are released back into the lake where their behavior will be tracked.
10 Along with the fish's location, researchers can track the depth and temperature of the water where they spend time throughout the year.