Alberta naturalist Brian Keating got up close and personal this week with some of the largest and most mysterious underwater creatures in the Baja Peninsula.

The wildlife columnist for CBC's The Homestretch and Radio Active spent the past week swimming alongside whale sharks in the Sea of Cortez at La Paz, Mexico.

Weighing in at roughly 20 tonnes, whale sharks are the largest non-cetacean living creatures on the planet.

"When you're swimming with them, it's like swimming with a Winnebago. They're such huge animals," said Keating, who saw his first whale shark less than 15 minutes out of the bay.

By the day's end, Keating had met at least a dozen whale sharks. He even managed to snap a few underwater photos from their tail end as proof.

Brian and Dee Keating

Brian and Dee Keating took this underwater selfie while swimming alongside whale sharks in the Sea of Cortez. (Brian Keating)

Filter feeders 

Whale sharks are a one of just three species of shark filter feeders, Keating said. 

The animals, which have mouths that can be up to a metre and a half wide, eat by swimming with their mouths wide open and forcing food in, or by gulping in water at the surface. 

"We floated hardly a meter from the whale shark's head, giving us an incredible opportunity to see how she sucked in sea water, sometimes creating a vortex of downward spiralling bubbles," Keating said. 

"We could actually see some remora fish inside the mouth, which are suction cup fish, hanging on for the ride. It was an extremely remarkable experience."

Remora fish whale

Note the remora hanging on for dear life inside this whale shark's mouth. (Brian Keating)

Mysterious animals

"The thing about the whale shark that is so remarkable is that nobody really knows where they breed, or how they breed, or where they give birth," Keating said.

The 1995 capture and study of a female whale shark that was pregnant with 304 embryos has led scientists to believe that whale sharks actually store sperm from one mating and produce their young over a period of time. 

This allows them to give birth to live young, known as pups, at different locations and times.

"There's lots of mysteries about these animals," said Keating, who noted that small whale sharks are hardly ever seen. 

"The good news about whale sharks is that there's now pretty well entirely an international ban on killing these," he said.

"The flesh apparently is not very good to eat anyway. It tastes apparently like tofu."

You can follow Keating's adventures online on Twitter and Facebook.