A new study of the distribution of the endangered great white shark in Canadian waters says an underwater detection network suggests the population remains stable but is not growing.
That runs counter to worries the oceanB次元官网网址檚 greatest predators are increasingly prowling the region B次元官网网址� perceptions fuelled by a suspected attack last August on a woman in the waters off Nova ScotiaB次元官网网址檚 Cape Breton Island and cellphone videos the same month depicting a shark chewing a seal carcass.
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 leading great white shark experts studying the animalB次元官网网址檚 behaviour says sightings in Canada arenB次元官网网址檛 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 tagged sharks and the bigger array of detection systems are taken into account, the number of great whites in Canadian waters appears to be holding steady.
It says while there have been theories of increased numbers of great whites on the basis of sightings, B次元官网网址渨e found limited corroborating evidence.B次元官网网址�
B次元官网网址淭here was no systematic increase in the proportion of the tagged population visiting Canadian waters, which has remained relatively constant during the years where an appreciable number of animals had been tagged (2016 onward),B次元官网网址� says the study.
The document is co-authored by Heather Bowlby, the lead researcher at the federal governmentB次元官网网址檚 Canadian Atlantic Shark Research Laboratory, Megan Winton of the Atlantic White Shark Conservancy in North Chatham, Mass., and Gregory Skomal of the Massachusetts Division of Marine Fisheries.
The vast majority of the sharks were tagged off Cape Cod between 2009 and 2021, with about three per cent of the sharks tagged in Canadian waters in 2018 and 2019.
Of the total 227 tagged sharks, only about a quarter make the annual trip to Atlantic Canadian waters, according to the study of the past decadeB次元官网网址檚 migrations.
Bowlby said in a recent telephone interview that when the scientists accounted for increases in monitoring, they found a B次元官网网址渃onsistent proportion of the total number (of sharks) taggedB次元官网网址� were showing up on the acoustic networks 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 great whites, while four years later, with three times as many receivers, nine great whites were detected B次元官网网址� even though more sharks had been tagged. Over the last five years, the study found, between 11 and 19 per cent of acoustically tagged sharks were detected in Canadian waters.
Bowlby said the paperB次元官网网址檚 main purpose is B次元官网网址渂uild the foundationB次元官网网址� to describe the critical habitat for the great white sharks in the region.
She said observations on the sharkB次元官网网址檚 behaviour B次元官网网址� collected from satellite tags that can track the sharkB次元官网网址檚 depths B次元官网网址� has raised important questions about prevailing views that temperature and other environmental aspects of the ocean are the only factors in the animalsB次元官网网址� location.
She noted the tags show the sharks were diving to depths of about 50 metres in coastal locations during the summer months, and seemed to undertake this behaviour regardless of temperature ranges of the water.
The data also indicated that most of the sharks coming into Canadian waters from Cape Cod are younger, swimming long distances to hunt prey that includes seals.
Bowlby has a nuanced message on how swimmers and other recreational users of Nova ScotiaB次元官网网址檚 waters should react to the presence of the sharks.
She said that since the research shows no B次元官网网址渁ppreciableB次元官网网址� increase in the sharksB次元官网网址� abundance in Canada, recreational users of the Atlantic regionB次元官网网址檚 beaches are not at greater risk. However, Bowlby says B次元官网网址渢he great white is a powerful marine predator, and a bit of prudence is warranted sometimes.B次元官网网址�
Paul DB次元官网网址橢on, the 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 anecdotes of catching great white sharks. HeB次元官网网址檚 come to believe little has changed over the decades.
B次元官网网址淚 think the risk is extremely low,B次元官网网址� he said. B次元官网网址淚tB次元官网网址檚 more reasonable to be injured in a drive to the beach than in being attacked there by a shark.B次元官网网址�
Nonetheless, the lifeguard service has a policy on shark sightings where water is cleared for a minimum of two hours following a sighting at a patrolled beach.
B次元官网网址擬ichael Tutton, The Canadian Press
