Large groups of basking sharks detected in Nova Scotia waters are a good sign for the species, a marine biology professor at Dalhousie University says.

Groups of the second-largest fish in the ocean have been gathering in numbers of 30 to 1,400 along the coast of Nova Scotia to Long Island, N.Y., according to scientists at the National Oceanic and Atmospheric Administration.

The data looked at numbers between June 1980 and November 2013.

"They do aggregate at times, at least in the Pacific, but I have not observed that here or heard of it. So it would be exciting to hear of a large group travelling together," said Boris Worm of Dalhousie University.

Worm said the fish, which can grow more than 7.6 metres in length, are commonly found in waters around Nova Scotia. But seeing them in such large numbers is unusual.

"The population estimates, that I'm aware of, are kind of in the hundreds for this whole area. So 1,400 would be not just a large group, but a large chunk of the population. But, of course, we don't really know how many there are, so we might be surprised," Worm said.

Basking sharks are very large and use their gaping mouths to feed on tiny plankton at the surface of the water, as seen in this undated photo with human divers. (Chris Gotschalk)

"To see large aggregations of them would be a good sign and would be very hopeful, but we do have to keep an eye out for these because they do get caught in fishing gear, they do get run over by ships, so we really need to take care that the species stays around."

A news release from the National Oceanic and Atmospheric Administration (NOAA) suggests the reasons the basking sharks congregate could have to do with feeding, socializing or mating.

But Leah Crowe, the lead researcher on the recent paper looking at the aggregations of basking sharks in the North Atlantic, said they still don't know exactly why these animals come together.

"It's been speculated in other species that it may be for protection, or it may be for mating purposes or for feeding purposes, so we really don't know with basking sharks because there hasn't been [the research]," she said.

The sharks typically appear as singletons or in small groups, she said.

Groupings are getting larger

Crowe said in their research, 89 per cent of basking sharks were recorded in a group size of one and 99 per cent in group sizes of seven or fewer.

But she stressed that the sightings used in the data were pulled from research following North Atlantic right whales, and not basking sharks specifically. Crowe said she hopes to see more dedicated research done in order to better understand these creatures.

"We did know that basking sharks aggregated in large groups, that's been in the literature for a while. But what we stumbled upon was the largest aggregation that had been in the literature yet," Crowe said.

The largest aggregation of basking sharks ever recorded was on Nov. 5, 2013, when at least 1,398 of these fish were spotted in southern New England waters.

'One of the weirdest'

Worm said one way to know if a fin sticking out of the water belongs to a basking shark is if you can see both the dorsal and tail fin sticking out at the same time.

While they aren't aggressive, Worm said these are still enormous creatures and anyone seeing them in the water should be cautious.

"I just think they're one of the most fascinating, one of the weirdest and one of the least-known, most mysterious creatures in our waters," he said.

"Most people never ever get to see one although they are around. So I think it's something we should really celebrate."