Sharks may be more mobile as climate changes

Scientists believe changes in the Earth’s climate could be allowing sharks to swim further than ever before.

James Cook University’s Dr. Nicolas Lubitz was part of a team that tracked a bull shark as it moved from the Indian Ocean to the Atlantic in 2022.

Dr Lubitz said the tracking of the shark’s immense journey between two oceans was unprecedented.

“The movement from Bazaruto in Mozambique to Mossel Bay in South Africa and to Lagos in Nigeria, a minimum distance of 7290 km, is the furthest movement on record for the species,” said Dr Lubitz

He said an upwelling of cold water off South Africa’s coast, caused by wind pushing surface water away from the shore and allowing cold water to rise from the depths, usually kept sharks from transiting through the area.

“Bull sharks don’t like water under about 19C and we have two different upwelling regimes exist on either side of South Africa’s Western Cape. Genetic data shows that coastal species such as bull sharks have not travelled between the Indian and Atlantic before, because the cold water barrier has prevented them,” said Dr Lubitz.

He said the shark’s journey represents the first recorded instance of a bull shark transiting from the Indian Ocean to the Atlantic Ocean around the upwelling system.

“We believe the upwelling system has formed a barrier for the species for at least 55,000 years. But during the week of 25 March 2022 when the shark was on the move, there was an unusual corridor of sea surface temperature warmer than 19C between the Indian and Atlantic Oceans,” said Dr Lubitz.

He said global breakdown of cold-water barriers to species movement is being driven by climate change and the unprecedented transoceanic movement of the shark highlights a need for future research.

“There is a need to focus on the frequency of barrier breakdowns and the associated impacts on the extent of animal movements and their drivers.

“In the context of climate change, this will help us better understand and predict the consequences of climate change-driven breakdowns in barriers to gene flow and future changes in species distributions,” said Dr Lubitz.

Link to paper here.