Rideau Canal - Snapping Turtles Are Impossible
The ludicrous numbers behind snapping turtle reproduction.
EPISODE NOTES
TRANSCRIPT
Snapping turtles look like they still belong in a prehistoric swamp. And that’s kinda true - they’ve been around for 90 million years. But it wasn’t until recently that we found out just how timeless they really are.
Our last campsite on the Rideau was here at Poonamalie lockstation. As soon as we stepped out of the canoes, we came across… this.
The size and spherical shape of the eggshells tells us that this was a snapping turtle nesting site. But evidence also suggests it ended up as someone’s lunch.
The way the nest has been dug out completely points to a predator - and snapping turtle nests have no shortage of those. Rats, raccoons, foxes, skunks, opossums, otters, minks, crows… some of them can sniff out the eggs even when they’re buried.
And if the idea of a snapping turtle nest being ransacked and devoured strikes you as a little sad… well, buckle up.
Exploring the area, I found a number of other nests, also dug up. And that is no surprise. Because the hard numbers around snapping turtle reproduction… are ridiculous.
A lot of this info was taken from a study in Algonquin Park that started in the early 1970s.
Their focus was population biology - what are the birth and death rates of snapping turtles. And the conclusion of the study, not in their words, was basically: ‘no snapping turtle is ever born or ever dies’.
OK, that can’t literally be true, but let’s use some numbers so we can see how close to true that actually is.
Say we start with a hypothetical 100 snapping turtle eggs. Right away, 80 will be found and eaten by predators.
Of the 20 that are left, 5 will hatch into baby turtles. Something as simple as a cooler summer can prevent them hatching at all.
Now, of those 5 baby turtles, how many will grow up to be 18-year-old adults? Statistically? Zero.
Ok so what if we start with 200 eggs? How many of those get to adulthood? Zero. 500? Zero. A thousand? Zero.
So how many eggs does a snapping turtle need to lay just to replace herself? About 1,400.
Just to really hammer this home: researchers safely incubated 6,000 snapping turtle eggs, then released and tracked the hatchlings. Of those 6,000… ONE survived.
And as crazy as the numbers are on that end, they’re just as extreme at the other.
Say we start with 100 adult snapping turtles. How many will die in a given year? Zero.
Two years? Zero. Five years? Zero. You get it. There is a far less than 1% chance of a given turtle dying in a given year. That means if they do, almost impossibly, make it to adulthood? They can pretty confidently expect to live more than a hundred years. How much more? Well, we usually take their age from growth marks on their shell plates, kind of like rings in a tree. But they stop growing after 45 years or so. So we don’t even know how old they get.
So snapping turtles truly live up to their look, as creatures frozen in time. On average: never being born, and never dying.
But don’t let that lull you into a false sense of security. The longevity of snapping turtles needs stability. As you can imagine, any new factor in the ecosystem that ups their death rate throws off this strange and delicate balance. If anything we need to be even more careful with a species for whom each adult member is this much of a miracle.