Call it Shark Weeks.

Fisheries and Oceans Canada scientists are preparing to study sharks caught in the annual shark fishing derbies held around the province over the next two weeks.

Meanwhile, two sharks were captured on video in waters off Nova Scotia in recent days — a great white filmed near St. Andrews, N.B., and a shark attacking a pod of porpoises in St. Margaret's Bay, N.S.

The video of the porpoises was taken by Sean Potter and Abbey LeFrank.

Since much about sharks is still unknown, shark derbies — where fishermen attempt to land sharks that are turned over to the federal government — are an important resource for scientists.

A scientific team measures a shark during a 2003 shark derby. Shark derbies — where fishermen attempt to land sharks that are turned over to Fisheries and Oceans Canada — are an important resource for scientists. (Canadian Shark Research Lab)

"They're the only source of information that we have for blue shark, which is one of our more common species," said Warren Joyce, a fisheries biologist with Fisheries and Oceans Canada.

Scientists at the derbies gather information about the sharks' length, weight, sex, and stomach contents. This information helps to shape shark management plans, and tells DFO whether the populations continue to be healthy and sustainable.

Millions of sharks

"From what we can tell in our waters they are [healthy]," Joyce said. "The unfortunate thing is that most of these species are highly migratory, and they're going outside of Canadian waters, where we have no control."

Warren Joyce will be one of the scientists at the annual shark derbies. (CBC)

Nova Scotian waters are visited by 19 different species, with the most common being blue sharks at an estimated population of one million. Porbeagle sharks are also relatively common at an estimated 250,000.

There are even a few great whites.

"It seems like each year we might be getting a few more sightings here and there, with more people out on the water and more people aware that these animals are out there," said Joyce.

"There is an idea that the numbers of white sharks in the North Atlantic is increasing, but we don't know for sure yet, because we don't know what numbers are out there."

A recent video captured in St. Margaret's Bay could be one of those sightings. It shows a pod of porpoises being attacked.

'They were very lucky to see that'

"I think it is definitely a shark. I can't tell by the video what species it is — we do have an idea that it might be either a large mako or possibly a great white. Both of these species do feed on harbour porpoises," said Joyce.

Lockeport Sea Derby is one of four annual shark derbies in Nova Scotia. (Lockeport Sea Derby/Facebook)

"It seems to be fairly typical feeding behaviour. The shark will approach the animal from underneath and attack it where it's most vulnerable, in the belly area. So it seems like a pretty standard attack. It's pretty rare to actually catch that on video, so I think they were very lucky to see that event."

Joyce said in the past 100 years there have only been about 50 reported encounters with great white sharks off Nova Scotia.

He said if people do encounter the animals on the water they should observe from a safe distance, report the encounter to DFO, and remember the endangered great white shark is protected under the Species at Risk Act.