The Bizarre Fish of Pink Lake
Pink Lake in Gatineau is home to fish who absolutely should not exist there. Today we find out why!
EPISODE NOTES
TRANSCRIPT
Three-spined sticklebacks are a funky fish. Some live in the ocean and only return to fresh water to spawn. Others live entirely in fresh water. But you can find them just about everywhere in the Northern Hemisphere.
Sticklebacks are really useful for scientists. They’re widespread and seem to adapt to local conditions at lightning speed. Even within a body of water, they can divide into a ‘limnetic’ form that feeds in the water column and a ‘benthic’ form that feeds at the bottom, to the point there’s almost two subspecies in a single pond.
Last episode, we travelled to Pink Lake in Gatineau Park. It’s a rare meromictic lake where the water never mixes, leaving it with a hypoxic layer at the bottom. But it’s got another claim to fame: a very strange population of sticklebacks.
You can find sticklebacks in other lakes nearby: Kidder Lake, Holly Lake, Ramsay Lake. But those in Pink Lake have much more in common with saltwater sticklebacks. A unique population in this one, tiny lake - and no others.
So how did this lake end up with saltwater sticklebacks? And how is it they’ve survived in this freshwater environment? Does it have anything to do with the fact that Pink Lake is meromictic? To answer these questions, we’ll need to travel back 10,000 years.
It’s the end of the last ice age, a time of such monumental climatic shifts that the country still bears its scars from end to end.
The Laurentide ice sheet is sitting on Canada, up to 3km thick. Think about the sheer weight of that ice. We tend to imagine the land beneath our feet, on a big enough scale, is solid. But enough pressure can change that, like a 13,000,000 square kilometer block of ice. It’s called isostatic depression, that ice forces the land lower into the asthenosphere. Ontario, for example, is pressed down 280 meters.
That put it below sea level. The salt water that comes rushing up the St Lawrence and inundates Ontario is called the Champlain Sea. And that is our first big clue.
Let’s look at the bodies of water around Pink Lake again, home to freshwater stickleback. If we overlay the estimated extent of the Champlain Sea… Pink Lake was a part of it. The other lakes weren’t. So that tells us how saltwater sticklebacks would end up in one but not the others.
That still leaves the question: how did they manage to survive in what is today a freshwater lake?
Well, what happens when the Laurentide ice sheet melts, and all that weight is no longer pressing down on Canada? Exactly what you’d expect, on a massive scale: the land bounces back. That’s called isostatic rebound and it’s still happening today. At its most extreme on the shores of Hudson Bay, the land is still rising 1.4 meters every hundred years.
Locally, Pink Lake rises and the Champlain Sea retreats. It leaves those saltwater sticklebacks stranded.
That should have been a death sentence. In most cases where saltwater lakes are cut off, the water cycle flushes out the salt in a few decades, killing off species dependent on salinity.
But Pink Lake, as we saw last time, is special. It’s isolated with high walls and no inflow or outflow. The same things that make it a meromictic lake slowed down the desalination to around 3000 years. And that was enough time for the already adaptable sticklebacks to adapt.
So Pink Lake is not just one of only twelve meromictic lakes we’ve found in Canada. It is also home to a miraculous population of totally unique fish.