Study Finds 50-Year Generation Gap in Bigmouth Buffalo, Minnesota’s Longest-Living Fish

A recent study in one of Minnesota’s most pristine spawning grounds found a half-century gap between successful clutches, and that number continues to grow.

This is according to a new study on the bigmouth buffalo (Ictiobus cyprinellus) from the University of Minnesota Duluth (UMD), recently published in Scientific reports.

The study was led by Alec Lackmann, Ph.D., an ichthyologist and assistant professor of mathematics and statistics, and Mark Clark, Ph.D., professor of biology, both of UMD’s Swenson College of Science and Engineering.

The bigmouth buffalo is a fish native to Minnesota and known for its longevity. The researchers wanted to learn more about the species, including how it migrates, reproduces, and how often its offspring reach adulthood. For three years, from 2021 to 2023, Lackmann and his team studied the recreational use (bowfishing, spearfishing, angling) of the species and analyzed the migration of bigmouth buffalo in and around Rice Lake National Wildlife Refuge near McGregor, Minnesota.

The results of the study include:

• Discovery of one of the oldest known populations of vertebrates (median age of 79 years in 2024)
• A generation gap of more than 60 years has occurred since the last major recruitment event in this population, again exposing the glaring vulnerability of bigmouth buffalo in Minnesota.
• Confirmation that fish migrate and reproduce successfully, but young do not survive, likely due to the predator challenge they face on their way to adulthood.
• It highlights the unique challenges of bigmouth buffalo management, including highly variable spawning durations from year to year, as well as the need to protect adults as they mature and to invest disproportionately in reproduction.

Lackmann and Clark have studied buffalo before, and their 2019 research went so far as to extend the maximum age of bigmouth buffalo, previously thought to be about 25 years, to over 100 years using improved aging techniques. The team’s subsequent studies of bigmouth buffalo in North Dakota (2021) and Canada (2023) have documented the environmental conditions linked to their sporadic recruitment success, and their team’s 2023 study published in Scientific reports discovered the second genus of animal for which three or more species (buffalofish) have a known lifespan greater than 100 years.

“No one has really studied the spawning phenology of bigmouth buffalo before,” Lackmann said.

During the Rice Lake study, he and his team examined nearly 400 adult fish, measuring each fish’s length and weight, whether it had spawned, its physical characteristics and its age. The researchers concluded that water controls put in place in 1953 were correlated with a reduced likelihood of subsequent generations, and of the 390 fish studied, only one was from a brood year after 1971. The study also found that bigmouth buffalo were successfully breeding, but by mid- to late summer, the young were noticeably absent, likely having succumbed to predation by northern pike and other predators.

“We found that over 95 percent of the current population hatched before the 1960s,” Lackmann said. With such a large gap, it’s surprising that buffalofish have survived for generations. But Lackmann said it speaks to the fish’s amazing characteristics. “This species evolved to have a long lifespan for an adaptive reason: to bridge these long gaps that can occur naturally.”

During the 1970s, the decline of the bigmouth bison was observed in Canada, Minnesota and North Dakota, and it became a protected species in Canada. In the United States, population declines are compounded by recreational bowfishing, lack of fisheries management, and general lack of knowledge.

For Lackmann, this study further underscores the importance of implementing basic fisheries management principles to protect bigmouth buffalo and other native species. Lackmann acknowledges that there are steps underway to protect native fish in Minnesota, such as the No Junk Fish Bill that became law this spring, but he says there is still much to be done in practice. For example, unlimited year-round harvest of bigmouth buffalo remains open throughout Minnesota starting in September 2024.

“Bigmouth buffalo recruitment into this system has been failing for 50 years, even though we know they migrate and spawn every year. It’s completely unprecedented in the animal kingdom, to our knowledge, for a species to survive this long without having another generation,” Lackmann said. “When you add to that the current, unrestricted, unregulated nature of their exploitation that has increased, particularly in the last 10 years with the increase in bowfishing, there is extreme concern for the long-term sustainability of this species.”

In addition to Lackmann and Clark of the University of Minnesota Duluth, the study was conducted in collaboration with the Aitkin County Soil and Water Conservation District, the United States Fish and Wildlife Service and North Dakota State University.