Researchers capture sounds of the sturgeon

A sturgeon in the Wolf River near Shiocton

SHIOCTON - Sturgeon spearing begins in just a few days on Lake Winnebago and the upriver lakes. But a new scientific approach hopes to shed some light - or sound - on how the prehistoric creatures reproduce.

The sounds of sturgeon spawning on many stretches of the Wolf River are familiar to many. But beneath all the splashing and thrashing, there may be more than meets the ear.

"The first time I heard it, it was scary. Like the hair would go up on the side of your arms. Because you're like oh, what is that?" asked Chris Bocast, University of Wisconsin-Platteville Audio Research Specialist.

Bocast said his research reveals the sound of a sturgeon.

There is rapping. And chirping too.

"We brought these sounds to science, and were able to accurately analyze them," said Bocast.

Bocast spent three seasons in the chilly waters of the Wolf and Embarrass rivers recording the underwater sounds. The groundbreaking research was the foundation for his doctorate in the field.

"What we learned really surprised us. We found out that these sounds were infrasonic. In other words, they were below the level of human hearing," said Bocast.

Bocast says he sifted through more than 40 hours of audio.

"The sounds work as a shock wave, basically. Boom. And that's it. So it's not like whales, where they're bouncing very low frequency sounds off the sea floor, and sending them for hundreds of miles. It's not one of those situations. They only go for a short distance, he said.

Bocast says contours in the river bottom prevent low frequency sounds from traveling more than 15 feet. But high-frequency sounds are more powerful.

"You can hear the hydrodynamic sounds of the pods thrashing for at least 200 feet downstream," he said.

So the big question is why?

"The noises that we've documented are pretty much during spawning season," said Ron Bruch, Department of Natural Resources Bureau of Fisheries Director.

Bruch took part in the research project. He says the fish likely make the sounds through vibrations in their swim bladders. He says males and females make the sounds, perhaps trying to improve the chance of success.

"When these fish are migrating hundreds of miles up the river, there's a lot of different rock piles that they can spawn on. The males have to know where this female is going to be. So they listen for this action, and then they know that there's something taking place that they want to participate in," said Bruch.

And researchers say sturgeon use whiskers to help them hear.

"They're called barbels, and those are common in fish species that are electro-receptive," said Bocast.

Biologists say knowing the sounds can help manage the population.

"So you get a hydrophone out, and if you hear the sound, you know you have spawning fish," said Bruch.

Bocast says he is proud to be part of the project.

"Making an actual scientific discovery was really quite thrilling," he said.

Bocast says his research is far from finished. He plans to be back on the river. This time, he wants to record the sturgeon activity from above the surface.