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Bulté's monitoring of the lake dates back to 2003 and has offered long-term insights into the turtle. The Carleton University biology professor just recently confirmed what he believes is the oldest turtle of its kind documented in the wild, at 57 years old. 

What he found that day in April 2022 was unlike anything he, or maybe even that old turtle, had seen before. 

It wasn't just one dead turtle. Broken shells and dismembered bodies riddled the bottom of the lake. In all, Bulté and his team found about 142 dead turtles. 

Almost 10 per cent of the lake's turtles had been wiped out. 

"After looking into it in more details, this really seems to be ... what we call a mass mortality event," he said. 

Like any good scientist, or detective, he had questions: "Why did it happen that year? Is it something that we should be worried that might happen in the future?" 

Years later, the first question remains a mystery to Bulté. On the second question, he now suggests there may be cause for concern. 

A warming climate may prove to be an abettor to the perpetrators of the turtle die-off at Opinicon Lake. 

To understand why, Bulté first pinned down the suspect. In this area northeast of Kingston, Ont., there are only two predators who could inflict this type of damage during a turtle's winter hibernation: the American mink and the river otter. 

The evidence piled up against the otter. It's heavier than the mink, with a history of wreaking turtle havoc, and a bite more likely to break shell.

"It really seemed to point toward the river otter," Bulté said. 

Climate change, driven by the burning of fossil fuels, is reshaping Canada's winters. The season's average temperature is up by 3.7 degrees since the mid-20th century. Studies have consistently shown a warmer world is producing thinner lake ice for shorter stretches of the year. 

It's thought that northern map turtles depend on the ice to protect themselves from predators in the winter, Bulté said. 

"If we have less reliable ice covers, then we might expect more mortality like this," he said.

"So, at this point it is a concern, but it's not something that we know is happening."

Climate change poses some other questions for the turtle. It may influence the population's male-female ratio, according to a 2019 federal species management plan. 

The sex of the turtles is temperature dependent and takes place while the eggs are incubating in their nests. Some research suggests temperatures around 25 degrees will produce more males, while those of 30 degrees or warmer will produce the much larger females, who grow to be about the size of a dinner plate or twice as large as males.

Climate change is by no means the only, or even the most significant, threat to the turtle, which is listed as a special concern under wildlife protection laws. The 2019 assessment suggests their main threat comes from habitat loss and degradation from shoreline development, along with boat crashes and fishing bycatch. 

Bulté says another possible accomplice to future winter turtle mortality is the growing use of devices to keep docks and boats ice-free during the winters. There's no evidence the devices, called bubblers, played any part in the 2022 die-off but Bulté said he's concerned by their growing use. 

"Eventually we might see more of these kinds of events," he said. 

Despite some warm winters in recent years, there have been no more turtle die-offs recorded at Opinicon Lake, Bulté said. His team is currently crunching the numbers on how long it may take for the local population to recover. 

This report by ¹ú²úÓÕ»ó¸£Àû was first published Feb. 4, 2026.