Researchers see little evidence that more white sharks are prowling 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 remaining stable but not increasing.

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 remaining stable but not increasing.

It runs counter to concerns that the ocean’s top predators are increasingly prowling the region – perceptions fueled by an alleged attack last August on a woman in waters off Cape Island. -Breton in Nova Scotia and cellphone videos the same month showing a shark chewing on a seal carcass.

Shark tracking apps have also become popular, as the Ocearch group has been operating in the region for several seasons to tag animals and allow the public to follow the creatures online as they migrate across the northwest Atlantic from July to november.

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

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

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

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

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

The vast majority of sharks were tagged off Cape Cod between 2009 and 2021, with approximately 3% of sharks tagged in Canadian waters in 2018 and 2019.

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

Bowlby said in a recent phone interview that when scientists factored in the increase in surveillance, they found that a “constant proportion of the total number (of sharks) tagged” appeared on the acoustic arrays that receive their signals. .

For example, data shows that in the Bay of Fundy in 2016, the 70 acoustic receivers deployed in the area detected three great whites, while four years later, with three times as many receivers, nine great whites were detected — even though more sharks had been tagged. Over the past five years, the study found that between 11 and 19 percent of acoustically tagged sharks have been detected in Canadian waters.

Bowlby said the main purpose of the paper was to “build the foundation” for outlining critical habitat for great white sharks in the region.

She said observations of the shark’s behavior – collected from satellite beacons capable of tracking the shark’s depths – raised important questions about prevailing views that temperature and other environmental aspects of the ocean are the only factors of the location of the animals.

She noted that the tags show the sharks diving to depths of around 50 meters in coastal areas during the summer months and appeared to engage in this behavior regardless of water temperature ranges.

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

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

She said that since research shows no “appreciable” increase in shark abundance in Canada, recreational users of beaches in the Atlantic region are not at greater risk. However, Bowlby says “the great white 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, as he began his 48-year career with the service, he heard anecdotes from fishermen on the capture of great white sharks. He came 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 the way to the beach than to be attacked by a shark there.”

Nevertheless, the rescue service has a policy on shark sightings where the water is clear for at least two hours after a sighting at a supervised beach.

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

Michael Tutton, The Canadian Press


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