Researchers see little evidence that more white sharks are roaming the North Atlantic

HALIFAX – A new study on the distribution of the endangered great white shark in Canadian waters says an underwater detection network suggests the population is stable but not growing.

That runs counter to concerns that the ocean’s biggest predators are increasingly prowling the region — perceptions fueled by an alleged attack on a woman last August in the waters off Nova Scotia’s Cape Breton Island and cellphone video. from the same month showing a shark chewing on the carcass of a seal.

Shark-tracking apps have also become popular, as the Ocearch group has operated in the region for several seasons, tagging animals and allowing the public to follow the creatures online as they migrate into the Northwest Atlantic from July to November.

However, work by a consortium of great white shark experts studying the animal’s behavior says the sightings in Canada are not translating into increased detection by underwater acoustic networks that pick up signals from tagged animals.

The collaborative study published last month in the Canadian Journal of Fisheries and Aquatic Sciences says that when the increased number of sharks tagged and the greater variety of detection systems are taken into account, the number of white sharks in Canadian waters appears to be holding steady.

He says that while there have been theories of increased white shark numbers based on sightings, “we found limited corroborating evidence.”

“There was no systematic increase in the proportion of the tagged population visiting Canadian waters, which has remained relatively constant during years when appreciable numbers of animals were tagged (2016 onwards),” the study says.

The paper is co-authored by Heather Bowlby, a principal investigator at the federal government’s Atlantic Canadian Shark Research Laboratory, Megan Winton of the Atlantic White Shark Conservancy in North Chatham, Massachusetts, and Gregory Skomal of the Massachusetts Division of Marine Fisheries.

The vast majority of sharks were tagged off Cape Cod between 2009 and 2021, with about three percent of sharks tagged in Canadian waters in 2018 and 2019.

Of the total 227 sharks tagged, only about a quarter make the annual trip to Atlantic Canadian waters, according to the study of migrations over the past decade.

Bowlby said in a recent phone interview that when scientists accounted for increases in monitoring, they found that a “constant proportion of the total number (of sharks) tagged” showed up in acoustic nets that receive their signals.

For example, the data shows that in the Bay of Fundy in 2016, the 70 acoustic receivers deployed in the area detected three white sharks, while four years later, with three times as many receivers, nine white sharks were detected, although there were more sharks. had been tagged. In the last five years, according to the study, between 11 and 19 percent of acoustically tagged sharks were detected in Canadian waters.

Bowlby said the main purpose of the document is to “build the foundation” for describing critical habitat for great white sharks in the region.

She said observations of shark behavior, gathered from satellite tags that can track shark depths, have raised important questions about prevailing views that ocean temperature and other environmental aspects are the only factors in the location of sharks. animals.

He noted that the tags show that the sharks dived to depths of about 50 meters in coastal locations during the summer months and appeared to engage in this behavior regardless of water temperature ranges.

The data also indicated that most of the sharks entering Canadian waters from Cape Cod are younger and swim long distances to hunt prey that includes seals.

Bowlby has a nuanced message about how swimmers and other recreational users of Nova Scotia waters should react to the presence of sharks.

He said that since the research shows no “appreciable” increase in shark abundance in Canada, recreational beach users in the Atlantic region are not at increased risk. However, Bowlby says that “the great white shark is a powerful marine predator, and a little caution is sometimes warranted.”

Paul D’Eon, director of the Nova Scotia Lifeguard Service, said in an interview Monday that even in the late 1970s, when he was beginning his 48-year career with the service, he heard fishermen tell stories of the catch. of great white sharks. He has come to believe that little has changed over the decades.

“I think the risk is extremely low,” he said. “It is more reasonable to be injured on a trip to the beach than to be attacked by a shark.”

However, the lifeguard service has a policy on shark sightings where the water is cleaned for a minimum of two hours after the sighting at a patrolled beach.

This report from The Canadian Press was first published on July 4, 2022.


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