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May 24, 2024

New insights into great white shark behaviour off California coast

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A new study has estimated there are 5,500 great white sharks living along the east coast. (Wikipedia)

Marine scientists using tracking devices have been able to shine a spotlight on the behaviour of great white sharks (Carcharodon carcharias) with the publication of two new studies this week.

Australian-led research in the journal Ecosphere revealed that great whites along the US California coast adapt their routines to suit the specific habitat they are hunting in. The finding highlights the importance of a shark’s location when considering how or why it may be behaving in a certain way.

Between 2017 and 2021, researchers fitted 21 great white sharks with motion-sensitive biologging tags that measured swimming depths and body movements for up to six days at a time. The sharks ranged from small juveniles to large adults and were tagged in four contrasting environments: two offshore islands, a coastal headland, and an inshore cove.

‘We found the greatest differences in movements were from sharks from different areas, while the size of the shark and time of day were also important,’ says marine scientist and spatial ecologist Oliver Jewell of the University of Western Australia, who led the research as a PhD student at Murdoch University.

They found that sharks at all sites were generally more active during the day, swimming up and down the water column and in ‘tortuous’ paths – moving back and forth in a non-linear path. This suggests they were searching for prey.

A great white shark. Photo Ken Bondy/flickr.com

However, sharks showed more active behaviour at both dawn and dusk in places where they were thought to feed on fish rather than marine mammals.  

‘This means the sharks are adapting their movements and routines to suit their local environment, rather than behaving the same way everywhere they’re found,’ says Jewell.

A separate study in Frontiers in Marine Science has found that juvenile great whites gather in nurseries in warm, shallow waters up to 1 kilometre from the shore in California.

In 2020 and 2021, researchers tagged 22 pups aged from 1 to 6 years old with sensor-transmitters that measured their position and local water pressure and temperature.

The baby great whites, which don’t receive any maternal care after birth, were found to congregate without adults in nearshore waters up to 10 meters deep.

First author Emily Spurgeon, a researcher in the Shark Lab at California State University, says: ‘We showed that juveniles directly altered their vertical position in the water column to stay between 16 and 22 °C, and if possible between 20 and 22 °C.

‘This may be their optimum to maximise growth efficiency within the nursery.’

The findings will inform great white shark conservation efforts and help avoid unwanted encounters with swimmers.

Great White Shark, Great Australian Bight. Photo Brad Leue.

South Australian great white expert Professor Charlie Huveneers, who wasn’t involved in the research, says the tagging and data collection represents excellent science.

‘Advances in technology now enables scientists to delve into the fine-scale movement patterns, behaviours, and habitat selection of sharks in more details than ever before,’ Huveneers told Cosmos.

‘These two papers are outstanding examples of studies using tags that incorporates 3D-accelerometers and/or temperature/depth sensors to go beyond where and when white sharks are, towards better understanding of why and how white sharks use these areas.

‘Similar tags are being used in New South Wales and South Australia and have provided us with new insights in white shark activity and predatory behaviour at key Australian aggregation sites.’

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