Dennis Higgs and collaborators analyzed hours of intimate audio recordings of lake trout mating rituals to pinpoint popular spawning grounds in the Great Lakes. The head of the biology department says the study aims to help boost lake trout populations by deterring fishing near confirmed spawning grounds during known mating periods.

“Since the introduction of the sea lamprey, lake trout populations have shrunk, yet they remain a popular recreation fish, so if we can protect them during mating season, their population has a chance to grow,” says Dr. Higgs.

He partnered on the study led by Nick Johnson from the United States Geological Survey in Hammond Bay Michigan, as well as with researchers from the University of Vermont. Dr. Johnson tagged the fish with transponders to find out where they aggregated and Higgs provided underwater microphones — called hydrophones — to record the fish sounds, and offered his skills as a fish sex sounds expert.

“Lots of fish make sounds and being able to identify these sounds is crucial in confirming where fish mate in the wild,” he says. “In this case no one had ever recorded lake trout so Johnson needed my expertise,” he says.

The hydrophones can record long-range high quality sound and be left out in the wild for a month. They were placed off spawning reefs in Lake Huron and Lake Champlain.

“It is great because we can do this all by eavesdropping on the fish and the fish don’t even know we are there, it’s a completely non-invasive technique,” says Higgs. “We were pretty sure the snaps and growls were mating sounds, because they were similar to other species, but this particular species had never been recorded before.”

The researchers also corroborated the sounds recorded in the wild by recording lake trout in a tank in Johnson’s lab.

“This information has helped boost population numbers with other species,” he says. “We aren’t telling people flat-out not to fish, but by using the recordings to show that spawning happens only at night and only during a few weeks in late May and early June, we can ask fishing to be avoided in those areas, during those times.”

To listen to acoustic recordings, go to the Great Lakes Fishery Commission publication on the collaborative study.

Watch a video of the lab tank: