Study suggests surly Montana turtles may live to 100 (Spiny Softshell Turtles) via Herp Digest

Karl Puckett, Great Falls Tribune Sept. 1, 2018

A secretive turtle that lives in Montana's Missouri and Yellowstone rivers may live much longer than once thought, possibly as long as 100 years, a new study suggests.

Last summer, NorthWestern Energy, which operates dams on the Missouri River, teamed with Montana Fish, Wildlife and Parks on a population study of spiny softshell turtles on the Missouri River.

"We thought it would be good to set up long-term population monitoring to make sure they are hanging in there and doing alright because they are a fairly sensitive species," said Steve Leathe, hydro license compliance professional with NorthWestern Energy.

The population study began at a 10-mile section of the Missouri River below the Judith River in the Judith Landing area.

In that section, 430 turtles were documented, 250 females and 180 males.

In a 10-mile section of the Missouri River 250 females spiny softshell turtles and 180 males were captured. (Photo: Steve Leathe)

"Probably the most surprising thing was during that work we recaptured 16 different turtles that were tagged in the same area 9 to 10 years ago," Leathe said. "We looked at the growth rate of those turtles. And it suggests these turtles live a lot longer than we ever thought.

"It's quite possible they live to be 50 to 100 years old. We won't know until we continue to track their growth and longevity," Leathe said.

Previously, most people thought the turtles lived 20 to 30 years, Leathe said.

The belief that the turtles may live longer is based on the observed growth rates of the recaptured turtles.

"We're seeing just really slow growth rates and when you project that out it suggests the biggest turtles out there we've handled could be well over 50 years old," Leathe said.

Spiny softshell turtles were captured as part of study in a 10-mile section of the Missouri River in the Judith Landing area. (Photo: Steve Leathe)

The age of fish can be determined by looking at scales which have growth rings but that's not possible with turtles, said Leathe, noting that the only way to verify turtle ages will be to continue the study over decades.

"They are pretty secretive so you don't see them that often," said Leathe, adding the turtles "are really cool.”

"But they are there.”

The latest population study of the elusive spiny softshell dovetails the first ever river-wide survey of the turtle in 2006 and 2008 from Morony Dam 15 miles northeast of Great Falls to Fort Peck Reservoir by PPL, which owned the dams at the time, Montana Fish, Wildlife and Parks, the U.S. Bureau of Reclamation and the U.S. Fish and Wildlife Service.

That work found that the highest density of turtles was in an 80-mile core area in the middle of that 200-mile stretch, Leathe said.

Then, from 2010 to 2012, Brian Tornabene, a graduate research assistant at Montana State University at the time, attached transmitters on the turtles and tracked them. The groundbreaking work led to new discoveries about the little-studied turtles including where they nest, lay eggs and hybernate.

The turtle is uniquely adapted to the river and spends almost all of its time in the water.

Its long snout functions as a snorkel so it can lie unnoticed under the surface while breathing through the tip that pokes through the water. Its long neck darts to snatch fish and crayfish. 

In the winter, turtles hibernate underneath the ice, and they're feisty, biting and clawing at researchers who handle them

Leathe invented a  "turtle table," a wooden frame where the turtles can be placed to help keep them under control when they are being measured and tagged.

Steve Leathe invented a "turtle table" that helps to control spiny softshell turtles when they are being tagged and measured. "They are hard to handle," said Leathe, NorthWestern Energy's hydro license compliance professional. (Photo: Courtesy photo)

"They are hard to handle," he said.

As opposed to their hard-shelled cousins, spiny softshell turtles have soft, flat and flexible shells that allow them to swim like rockets through the water.

And the females are much larger than the males, Leathe said. That's called sexual dimorphism, a condition when there are marked dissimilarities in the appearance of the sexes. Males are sometimes 1 to 2 pounds. The largest female that researchers have documented in the Missouri River work weighed 16 pounds.

Steve Leathe of NorthWestern Energy holds two spiny softshell turtles. Males are much smaller than females. (Photo: Courtesy photo)