HALIFAX -- Looking for a missing, 70-tonne whale? There's an app for that.

Researchers in Canada and the U.S. are asking for the public's help as they continue their search for the elusive and endangered population of North Atlantic right whales.

In the last few years, the massive mammals have changed their migration patterns, prompting researchers to rejig a mobile app called Whale Alert to enable citizen observers to report sightings in real time.

Sean Brillant, senior conservation officer with the Canadian Wildlife Federation, said sightings are crucial because the summertime whereabouts of the 500 remaining North Atlantic right whales has become a mystery.

"The more eyes that are on the ocean, whether they are trained scientists or people in pleasure craft, a sighting of a right whale could be a really valuable find," Brillant said Tuesday in an interview from Halifax.

For more than 30 years, the whales have migrated to areas in the Bay of Fundy and off the southwestern tip of Nova Scotia -- the Grand Manan Basin and Roseway Basin. However, that route has changed.

"It could be part of a regular cycle," Brillant said, adding that scientists have collected only 30 years of data about animals that can live up to 70 years.

"It shows us how little we know about what these whales are doing ... We don't even know where they're going. It's been a real shock to the system for a lot of people."

The mobile application -- available for Apple and Android devices -- was initially used to alert large commercial ships to the presence of right whales near Boston harbour. When underwater listening devices detect the whales' calls, an alert is sent to the app.

The application has since been modified to incorporate the details of whale sightings in Canada.

There's speculation the whales are now moving on to the Gulf of St. Lawrence to find zooplankton, the microscopic shrimp-like animals that are a staple of the right whale diet.

Cathy Merriman, a species at risk biologist with the Federal Fisheries Department, said zooplankton data collected for years by federal scientists in Quebec will be used to test that theory.

The search for the whales has encouraged Canadian and American researchers and scientists from different disciplines to join forces and share their findings, she said.

"Two years ago, we realized there's all of this stuff going on, so let's get everybody together at a meeting or on the phone," she said.

The result has been an unprecedented level of co-operation, said Brillant.

"It's like what happens when somebody loses a dog, and everyone who is outside agrees to help find the dog. Except, these are 70-tonne dogs."

There will be surveys from the air and water. And a group of autonomous, underwater drones that look like chubby torpedoes will be dispatched to prowl the ocean, listening for whale song and transmitting a variety of data via satellite.

Finding and tracking beasts that can be as big as a city bus is difficult, said Brillant.

"It is a reflection of just how big the ocean is," he said, adding the North Atlantic right whale typically spends 15 to 20 per cent of its time at the surface.

The whales bump into each other so often and with such force that tracking devices attached with suction cups rarely last more than a few weeks. And embedding beacons in their flesh can lead to nasty wounds.

The North Atlantic right whale was hunted to near extinction in the late 18th century and has struggled ever since. They are particularly vulnerable to ship strikes because they are oblivious to their surroundings while eating.