Rambunctious Reproduction Overheard Among Great Lakes' Lake Trout

New study peeps on lake trout reproduction; reveals noisy sex may help manage populations

Peeping on the sex lives of others is normally considered taboo, but not when it comes to fish. Researchers are always looking for new information about key species' preferences and behaviors, and insight into fish-spawning rituals is revealing. In the case of lake trout (Salvelinus namaycush)—a species subject to intensive management across the globe—this scientific voyeurism may help fisheries managers gain more insight into better management techniques for this keystone species.

A Commission-funded study led by Dr. Nick Johnson of the U.S. Geological Survey and colleagues at Michigan State University, the University of Windsor, and the University of Vermont, used underwater sound recorders and cameras to spy on spawning lake trout in Lakes Huron and Champlain. It's a first-of-its-kind study for lake trout, and Dr. Johnson found some tantalizing results.

"Many fishes are able to produce and detect sound, and use sounds to communicate during reproduction," explained Dr. Johnson. "During our study, we determined that lake trout mainly make two sounds during spawning—snaps and growls. To our knowledge, this is the first evidence of sound production by a trout or a salmon species."

Researchers set up acoustic telemetry and video both on and off known spawning reefs in Lakes Huron and Champlain. Researchers heard lake trout emit both snaps and growls on spawning reefs, but not on non-spawning reefs, and both sounds were heard more commonly at night than during the day. By analyzing the sound and video recordings, the research team determined lake trout emitted snaps more often during the pre-spawning period and growls more often during spawning. By comparing these sounds to those produced by other sound-producing species, Dr. Johnson and his team postulate that snaps may be produced when trout nip and bite during pre-spawning displays, and growls are produced internally during the spawning period, perhaps by muscles regulating the swim bladder during this physically taxing activity.

Although studying the sounds lake trout make during such seemingly intimate moments may seem a bit bizarre, the research actually has important implications for lake trout management in North America. Lake trout are extraordinarily diverse and support valuable recreational and commercial fisheries. Consequently, lake trout are intensely managed in many areas, including in the Great Lakes, where an extensive stocking program, along with sea lamprey control, has been underway for decades to support restoration.

"Revealing the sounds produced during lake trout reproduction could be beneficial by inspiring new tactics to enhance reproduction where populations are valued," described Dr. Johnson. "For example, underwater microphones could be used to determine where lake trout spawn. Microphones could be cheaper, more effective, and less invasive than traditional approaches used for spawning assessment, such as gill netting."

Another application is to play lake trout spawning sounds underwater to encourage use of artificial or restored spawning habitats. Anyone that has spent an evening out on the town knows that the hottest spots are often the ones that can be heard from down the street. Similarly, lake trout may be drawn to spawning sites by what they hear.

"Research describing the exact source of the sounds – whether they come from males or females – and the use of sounds in finding or selecting mates, and locating or judging spawning sites is needed before application to lake trout management," Dr. Johnson cautioned. "For now, the results are enticing and suggest many possible applications in the future."

Read more Pulse on Science: Project Spotlights

Read more Pulse on Science: Project Spotlights