Fish retains prehistoric features

The Sturgeon Thunder   A giant among Wisconsin's inland freshwater fishes, the bottom dwelling lake sturgeon is a living fossil - a relic from the Middle Ages of fish evolution. This ancient species made its first appearance about 100 million years ago in the Upper Cretaceous period of the Mesozoic era, just about the time that the dinosaurs made their abrupt exit from Earth's ever-changing stage. Today the lake sturgeon retains many primitive characteristics that have been lost or modified in other modern-day fishes. Research into the mysterious sounds that lake sturgeon produce resumes in April, or whenever the water warms to a temperature conducive for fish spawning, which is the best time to experience sturgeon thunder. In spring, Ron Bruch, a biologist with the Wisconsin Department of Natural Resources, and Chris Bocast, an acoustic ecologist with the UW Sea Grant Institute, will conduct additional biological examinations and collect detailed field recordings of the infrasonic sounds of this ancient fish.
The sturgeon thunder is at a frequency too low for most humans to hear clearly.
For years, those along waters populated by sturgeon reported mysterious sounds and vibrations, apparently resulting from the sturgeon’s subsonic sound production. Native-Americans in the Fox and Wolf River watersheds have long associated this thunder with the onset of spring sturgeon spawning runs.
"Based on an underwater-microphone recording and consultation with experts at Cornell University’s Bioacoustic Research Program, we have confirmed the fundamental frequencies produced by sturgeon while spawning are based in the sonic spectrum below human hearing. We’re going back out this spring with more specialized audio and video equipment in order to get validated results for academic publication," Bocast said.
"At one time, Bruch thought the sound was the result of the force of the large fish hitting each other or the water. However, thanks to the interdisciplinary scope of Bruch and Bocast’s research, we can now put sturgeon in the surprising company of whales, elephants and other large creatures whose sonic capabilities reaches into the infrasonic. Of course, sturgeons are fish, not mammals. But fish are beginning to be recognized for their ability to produce wide varieties of sounds using all parts of their bodies."
Bruch and Bocast believe the sturgeon use the sound to time gamete release, enabling reproductive success in Wisconsin’s fast-flowing rivers. The sturgeon sound itself is characteristic of sounds produced by other fishes using their swim bladder, which this spring’s study may validate.
Lake sturgeon migrate to their annual spawning grounds generally between mid April and early May, preferring to spawn in shallow, rocky areas along river banks. Sturgeon spawning is dependent on water temperature and flow. Optimum lake sturgeon spawning temperatures range from 52 to 58 degrees F. Sturgeon can often be seen doing pre-spawn porpoising at the preferred spawning sites. As conditions become more favorable, the fish will move into shore to spawn.