At over four metres (almost 14 feet) long and weighing around 770 kilograms (1700 pounds), Mahone, the great white shark, might seem out of place in the waters off Nova Scotia. But shark sightings are becoming a more common occurrence along the Eastern coast of Canada
You can track Mahone now at www.ocearch.org/tracker/detail/mahone
Climate change may be responsible for the increased sightings however research is in its early stages. Recent studies involving tiger sharks in the North Atlantic have shown that ocean warming is affecting them, causing them to migrate as far north as Cape Cod. In 2018 a tiger shark was caught as far north as Halifax but that may have been result of the creature being carried off course in a warm eddy off the Gulf Stream.
Compared to other ocean species, some sharks are not as affected by changes in the temperature of the water. In fact, they can tolerate quite a range of temperatures. White sharks, for example, may prefer temperatures above 12 degrees Celsius, but they have been detected in waters as cold as two degrees Celsius and warm as 27 degrees!
It could be that the sharks have always been there but we just were not fully aware of their presence. Over the past ten to 15 years, tagging and tracking technology has greatly improved.
“The tracking technology is fairly new and equipment like Pop-up Satellite Archival Tags (PSAT’s) and Acoustic Telemetry Tags and Acoustic receivers have greatly helped us to understand shark distribution better than in the past,” says Warren Joyce, an aquatic fisheries technician with the Department of Fisheries and Oceans. “Researchers in the past were limited by the technology of the time and didn’t really track shifts in distribution of shark populations until more recently.”
Pop-up Satellite Archival Tags -when attached to the animal these tags record Information such as depth, water temperature and light levels, which scientists can use to determine location. They then release from the animal, float to the surface and send data to a satellite and then back down to scientists.
Acoustic Telemetry Tags -these tags emit unique sounds that are picked up by tracking stations (acoustic receivers) anchored on the floor of the ocean. Trackers can hear fish from 300-1000 metres away and can record water temperature and depth.
It also may be that there are just more sharks now which is great news. White sharks are listed as an endangered species in both Canada and the US meaning they cannot be harvested. This has likely led to the white shark numbers returning to a more natural population level.
Many shark scientists and conservation groups actively engage the public with their studies and research through apps, programs and events. An excellent example of this is the Atlantic White Shark Conservancy out of Cape Cod https://www.atlanticwhiteshark.org/ .
Atlantic Canada boasts more than 22 species of sharks ranging from small spiny dogfish to the second largest fish/shark in the ocean, the basking shark. Some of the more regular species include blue sharks, porbeagle sharks, mako, white sharks, Greenland sharks and deep-sea sharks like the black dogfish.