The bottom of a lake or ocean can sometimes resemble a desert - a flat, open, and hostile landscape.
Now add a huge structure of stable rocks, with plenty of crevices, nutrients, and oxygen. Well now, you’ve got a city. That’s essentially what a reef is – and it can form naturally or be artificially created.
Historically, Thunder Bay was home to a couple of natural reefs that served as important spawning habitats for lake trout. But as a result of human activities, these reefs have essentially been “filled in.”
In 2010, researchers built 29 different types of artificial reefs in Thunder Bay. The project was in an effort to restore the reef - and unlock the secrets of what lake trout look for when searching for a place to lay their eggs.
“We're asking the fish, what would you prefer: big, small, high, low, different orientations, right angles to each other?" said Ellen Marsden, with the University of Vermont.
Marsden is the project’s lead researcher. She said there are a lot of misconceptions about artificial reefs.
“There's a tendency if you look it up on Google, people go, ‘oh, fish, like piles of things. Oh, I've got stuff. Let's sink a bunch of tires together," Marsden said. "And they work, but that’s a temporary attractive structure, not an artificial reef. People can use artificial reefs as an excuse to dump stuff.”
Marsden said her team hopes to make building artificial reefs more of a science – and potentially develop some best practices.
The constructed reefs in Thunder Bay were a success, and lake trout egg counts showed. But Marsden said lake trout have some preferences...
“...Height: they seem to be totally indifferent to. Orientation: they couldn't care less. Size: they care about," Marsden said. "Bigger reefs tend to be more attractive and ignore the little, tiny ones. Adjacency to the natural reef, which is where they were, before we built these was important.”
Marsden said an artificial reef will vary depending on the waterbody and the species it’s serving, but overall -
“The basic principles: size and height and slope and cobbles, rock sizes seem to hold true everywhere we look,” Marsden said.
In Thunder Bay, lake trout will be pleased to know that the artificial reefs built by researchers are staying in the water.
Researchers said there are still lots of opportunities to evaluate the reefs, like examining different variables or looking at different fish species.
