Tagged trout returned
Nine tagged rainbow trout have been returned this spring to a Minnesota Department of Natural Resources fisheries research biologist at French River who is studying the fish.
That brings the total to 14 returned since last spring when Molly Negus began her study.
Negus surgically implanted computer-chip capsules in 76 Kamloops and steelhead rainbow trout and then released the fish in Lake Superior. The capsules recorded information about water temperatures and depth wherever the fish traveled. Anglers were offered a $50 reward to return the fish to the DNR with capsules intact.
Four Kamloops rainbows and five steelhead bearing capsules have been returned by anglers or captured by the DNR at its French River and Knife River traps this spring, Negus said.
"It started out gangbusters," she said. "I was getting one a day for the first week."
Then returns dropped off. Still, returns are about what Negus expected.
"Hopefully, we'll see some more this summer," she said. "Optimistically, that's what I'd like to think."
The capsules have a two-year life, so they'll continue recording information until next spring. And they will continue to carry the data after that.
Two fish bearing the dorsal tag didn't actually contain the capsules, Negus said. She suspects the fish somehow worked the capsules into their digestive systems and expelled them. That has happened with other rainbow trout in studies, she said.
Negus was able to surgically remove capsules from two returned steelhead and release the fish alive in Lake Superior.
Data downloaded from the returned capsules indicate that Kamloops and steelhead spend time in similar waters, Negus said. The data showed that the fish spent most of their time within 15 feet of the surface, making occasional dives as deep as 150 feet. But those dives were brief, lasting less than half an hour.
"Probably the most unfortunate part is that we don't have a specific geographic location for these fish," said Don Schreiner, DNR Lake Superior Area fisheries supervisor at French River. "We don't really know where they are. At 15 feet, is the fish close to shore near the bottom or out in the middle 15 feet down from the top?"
Finding fish in shallow water during the summer isn't unusual, he said.
"They're probably up there feeding on bugs," Schreiner said.
Both Negus and Schreiner said the water temperature information from the returned capsules will help in the DNR's bioenergetic modeling. In that modeling, researchers try to determine how much food it takes to grow fish of a specific size, and water temperature plays an important part in that.
One capsule has been returned four times since last spring, Negus said. Each time it has been returned, Negus has sent it out with another rainbow. It came back two times in Kamloops rainbows last spring and summer, once in a steelhead, and again this spring in a Kamloops rainbow.
This is the first year of the four-year study.