Sexy capelin: It's how they roll

While you're dipping your net to catch some coveted capelin this time of year,have you stopped to think about what's actually happeningon the beach, beneath your feet?

Craig Purchase,aMemorial University biologist who studies fish reproduction,has made some important discoveries about the little silver fish so loved by cod and whales.

As Purchase explains, capelin engage in a kind of kinky copulation on the shore.

First of all, the male capelin change shape when they're about to spawn.

"Males develop enlarged anal fins, the fin at the bottom of the body, and our best guess is the reason they do that is so they can dig a trench into the gravel," Purchase told The Broadcast.

The scales of the male fish also change during the spawning process.

"It's very unique, like nothing else, this alternation of the scales along the lateral line on the side of the body. The scales stick out and it creates this ridge that runs down each side of the male. We don't know why this happens, but one of the guesses is that they use it to hold onto the female," explained Purchase.

Group sex

Capelin can spawn as pairs, one female and one male. But more commonly, thelittle devils prefer group spawning.

"Two males will have one female in between them and I think their unusual shape of the male's body is related to being able to pin that female between them in the chaos of the surf," said Purchase.

Capelin reproduce by external fertilization, meaning the eggs and the sperm are released outside their bodies.

I think their unusual shape of the male's body is related to being able to pin that female between them in the chaos of the surf.- Craig Purchase

But when there are two males on one female, Purchase is trying to figure out how much choice the female has in what fella fertilizes her eggs.

"In many cases, of other fish such as salmonids, the ovarian fluid she releases will preferentially select sperm of different males to swim faster to fertilize her eggs, known as post copulatory selection."

Sadly, rolling on the beach is the last hurrah for male capelin. "As far as we know, male capelin die after spawning," said Purchase.

A team of five people is studying capelin reproduction this summer along with Craig Purchase.They hope to confirm some of the theories they've developed.

As for you, you'll probably never watch them roll the same way again.

For more details on how capelin spawn, you can listen to Jane Adey's interview with Craig Purchase.

The Broadcast17:58Cod are scarce in many parts

We'll take you to Petty Harbour for a report on the food fishery. We'll hear all about what those little capelin get up to on the beaches when they roll.

You can hear The Broadcast weekdays at 6:05 pm and the following day at 1:05 pm.