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A new study of the distribution of endangered great white sharks in Canada’s waters suggests that underwater detection networks have stable but not growing populations.
This is contrary to concerns that the largest predators in the ocean are increasingly wandering around the area. It was caused by a suspected attack on a woman off Cape Breton Island in Nova Scotia last August, and a mobile phone video of a shark biting a dead seal the same month.
Shark tracking apps have also become popular as the Ocearch group has tagged animals for several seasons in the region, allowing the general public to track creatures online as they travel to the Northwest Atlantic from July to November. I am.
However, according to a study by a consortium of leading great white shark experts studying animal behavior, sightings in Canada translate into increased detection by underwater acoustic networks that pick up signals from tagged animals. Not.
According to a collaborative study published last month in the Canadian Journal of Fisheries and Aquatic Sciences, the number of great white sharks in the Canadian waters is stable, taking into account the increasing number of tagged sharks and detection systems. Looks like you are.
There is a theory that the number of great white sharks is increasing based on sightings, but it says, “There is limited evidence to support it.”
“There was no systematic increase in the proportion of tagged populations visiting Canadian waters, which is relatively constant during the years when a significant number of animals were tagged (since 2016). That’s it, “says the study.
This document was co-authored by Heather Bowlby, Senior Research Fellow of the Federal Atlantic Shark Institute of Canada, Megan Winton of the Atlantic White Shark Reserve in North Chatham, Massachusetts, and Gregory Scomal of the Massachusetts Department of Marine and Fisheries. ..
The majority of sharks were tagged off Cape Cod between 2009 and 2021, and about 3 percent of sharks were tagged in Canadian waters in 2018 and 2019.
Of the 227 tagged sharks, only about a quarter of the 227 tagged sharks travel annually to Atlantic Canada, according to a survey of migrations over the last decade.
Bowlby said in a recent telephone interview that when scientists explained the increase in surveillance, they found that “a consistent percentage of the total number of tagged (sharks)” appeared in the acoustic network that received the signal. Said.
For example, data show that in the Bay of Fundy in 2016, 70 acoustic receivers deployed in the area detected three great white sharks, but four years later, three times as many receivers and nine. Great white shark was detected. It was tagged. Over the last five years, the study found that 11 to 19 percent of acoustically tagged sharks were detected in Canadian waters.
According to Bowlby, the main purpose of this treatise is to “build the foundation” to explain the important habitat of great white sharks in the region.
She said that observations of shark behavior collected from satellite tags that can track shark depth are important for the general view that sea temperature and other environmental aspects are the only factors in animal position. He said he raised a question.
She states that the tag indicates that sharks have dived to a depth of about 50 meters in coastal areas during the summer months and appear to be doing this regardless of the temperature range of the water. I did.
Data also show that most of the sharks that come from Cape Cod to Canada’s waters are young and swim long distances to hunt for prey, including seals.
Bowlby has a subtle message about how swimmers and other recreational users in Nova Scotia’s waters should react to the presence of sharks.
She said the survey did not show a “perceptible” increase in shark numbers in Canada, so beach recreational users in the Atlantic region were not at great risk. However, Bowlby states that “great white sharks are powerful marine predators and sometimes require a little caution.”
Paul Deon, director of Nova Scotia Lifeguard Services, said in an interview Monday that he heard anecdotes about fishermen catching great white sharks, even in the late 1970s, even when he began his 48-year career in service. I did. He came to believe that it hadn’t changed much over the decades.
“I think the risk is very low,” he said. “It makes more sense to get hurt on a drive to the beach than to be attacked by a shark.”
Nonetheless, Lifeguard Services has a policy on witnessing sharks that clean the water for at least two hours after witnessing on a patrol beach.
Michael Tutton
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