Drumming Fish in Lake Mendota
by John Magnuson
Not only birds, frogs, and cicadas make sounds. The name, freshwater drum, gives away the fact that this fish produces sounds like the rapid taping of a drum (ta,ta,ta,ta). Some are a lower pitch that others and they occur in bursts about 5 seconds long. Hans Schneider, studying at the University of Wisconsin-Madison, with an underwater microphone in May 1959, made this recording from Lake Winnebago.
Freshwater drum are one of about 38 fish species living in the lake; they are moderately abundant as are the white sucker, Eurasian carp, rockbass, and catfishes. While common around the state especially in large rivers, freshwater drum were not found in Lake Mendota until after 1930 when they were stocked during fish rescue operations from the shrinking backwaters of the Mississippi during the droughts of the dust bowl. The freshwater drum is the only strictly freshwater species in a diverse family of 160 species of marine fishes called the drum or Sciaenidae.
The drumming occurs in the spring and early summer starting at 10 or so in the morning; this musical fish occurs in Lake Mendota off the Preserve shoreline. Only the males drum and the sounds are thought to be a part of courtship behavior. The males have a unique set of muscles and tendons attached to the inner walls of the body cavity and extend over the top of the gas bladder. The rapid contraction of these causes a drumming sound to come from the bladder. The gas bladder typically serves as an organ to help fishes achieve weightlessness in water; in drums it also serves as a gas filled drum.
Perhaps going along with its sound production, the freshwater drum has a uniquely large “otolith” located in the inner ear used in hearing. A large drum has an ivory-colored otolith as large as a quarter or so in diameter and is up to about a quarter inch thick. As a boy I would occasionally carry one of these around in my pocket. They also have growth rings that can be used to determine how old the drum is and how fast it has grown. Otoliths from large drum have been found in Indian middens in the floors of caves along the Mississippi indicating that the freshwater drum was in the diet of early Native Americans; they also used drum otoliths for trading and adornment. Another unique feature of the freshwater drum is that its lateral line along the side of the body extends all the way to the very tip of its tail. The lateral line, a distance touch receptor, also may be related to perception of low frequency drumming.
There are drummers in Lake Mendota, not only on Union Terrace. These piscine drummers are a part of the diversity of life in the waters along the Lakeshore Preserve.