- New study suggests lake sturgeon may live for centuries, with some populations potentially reaching 200 to 400 years old, far beyond previous estimates
- Researchers used 44 years of data from five Great Lakes populations to measure how slowly individual sturgeon grow
- The findings could influence how scientists estimate the ages of other long-lived fish and how fisheries managers approach sturgeon harvest and recovery
Some lake sturgeon may have been swimming through the Great Lakes longer than the United States has existed. In fact, some may have seen the first Europeans arrive in Michigan in the 1600s.
A new study suggests the fish, already known to be among North America’s longest-lived freshwater species, may routinely survive for more than 200 years, some potentially reaching 300 or even 400 years.
Researchers estimated that a 160-centimeter male lake sturgeon could live between 90 and 279 years, depending on the population. For 180-centimeter females, estimated ages ranged from 99 to 427 years.
The study, published in the “Journal of Fish Biology,” used 44 years of data from when sturgeon from five Great Lakes populations were tagged, released and then years later captured again. Rather than trying to determine the exact age of individual fish, researchers used how slowly the fish grew over decades to estimate how long it would take them to reach the largest sizes observed in each population.
The method addresses a problem with traditional aging techniques, said Edward Baker, research station manager at the Michigan Department of Natural Resources’ Marquette Fisheries Research Station. Scientists typically age lake sturgeon by counting growth rings in their fin spines. But as the fish grow older, the rings become closer together and harder to distinguish.
“That’s just going to cause you to underestimate the age of that fish,” Baker said.
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The oldest documented lake sturgeon before this study was 152 years old, based on growth rings in a fin spine. Scientists had generally believed sturgeon could typically live 70, 80 or perhaps 100 years.
But decades of monitoring provided another way to examine their age.
Researchers have been catching, tagging and measuring lake sturgeon for decades as part of conservation and population-monitoring programs. When a tagged fish is caught again years later, scientists can identify the same individual and compare its size over time.
The researchers could then determine exactly how much an individual fish had grown between captures. By combining those measurements across decades of monitoring, they developed growth curves for different populations and sexes.
The results showed just how slowly some lake sturgeon grow after reaching maturity.
Baker pointed to one male in the Sturgeon River that was first captured at 46.1 inches long. When researchers recaptured it 34 years later, it had grown just 2.7 inches.
“That’s a growth rate of less than a tenth of an inch per year,” Baker said.
Growth rates differed substantially between populations, which also produced large differences in estimated longevity.
Sturgeon in the St. Clair River, for example, grow faster than those in the Black River.
One possible explanation is the productivity of the systems themselves, said Scott Colborne, an assistant professor in Michigan State University’s Department of Fisheries and Wildlife and a co-author of the study. The Black River is smaller, colder and has fewer resources, while the St. Clair River is warmer and has more food available.
“It basically comes down to it being a bit of a slower lifestyle,” Colborne said of the Black River population.
The differences are important because they suggest lake sturgeon may grow and live differently depending on their environment.
Researchers caution that the longevity estimates are not exact ages.
The farther the models extend beyond the sizes of fish that researchers directly measured, the wider the uncertainty becomes. The oldest estimate came from a male in Michigan’s Black River, which researchers estimated at 435 years old. That estimate has a wide range of uncertainty, however, and the fish could be anywhere from 318 to 737 years old.
Colborne said the finding was surprising even to researchers who already expected lake sturgeon to live for at least a century.
The findings could also have consequences for how managers approach sturgeon conservation.
Lake sturgeon populations were heavily depleted by overharvest and habitat changes in the late 19th and early 20th centuries. Today, Michigan managers tightly restrict harvest in the populations where fishing is allowed.
Baker said the new findings do not necessarily change current management practices, but they reinforce the need for conservative harvest policies.
In Michigan’s Black Lake system, for example, the annual harvest quota is six fish from an estimated adult population of about 1,200. In the St. Clair system, harvest is allowed within a restrictive size range.
The study suggests that even when populations recover enough to eventually support additional harvest opportunities, managers will need to account for how long individual fish can take to mature and reproduce.
“If sturgeon are living 200 or 300 years, in order to be a sustainable population, the adults have to survive that long,” Colborne said.
The researchers also say the method could be applied to other long-lived fish like lake trout, which live up to 60 years old.
The approach was adapted from research on Greenland sharks, whose extraordinary longevity was later independently supported using radiocarbon dating of eye lenses.
That kind of independent validation is still needed for lake sturgeon.
Baker said researchers would need another method capable of confirming whether the oldest estimates produced by the models reflect the actual ages of individual fish.
For now, the study offers another reminder of how much scientists can learn from simply continuing to monitor a species over time.
Neither Baker nor Colborne expected the decades of tagging and recapture work to eventually reveal evidence of fish that could have been alive for centuries. The data were collected primarily for sturgeon conservation and rehabilitation, not to answer questions about extreme longevity.
But without those decades of work, the question may never have been answerable.
“Sturgeon live such a long time,” Colborne said. “In order to really understand these animals, we have to invest in them for decades.”
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