Whale shark study finds collisions with large vessels may be factor in population decline

A new study from the UK points to collisions with large marine vessels as a possible reason for the year-long decline in whale shark populations.

Marine biologists from the Marine Biological Association and the University of Southampton led the study, started in 2019 and were published earlier this month in the journal Proceedings of the National Academy of Scienceswhich tracked the movements of ships and whale sharks around the world.

The researchers said that fatal collisions are greatly underestimated and that their work shows that more than 90 percent of the whale shark’s movements overlap with global fleets of cargo, tankers, passenger and fishing vessels.

The team satellite-tracked the movements of 348 individual whale sharks, tagged between 2005 and 2019 in the Atlantic, Indian and Pacific Oceans, and mapped their various “hotspots”.

The researchers submitted the data to Global Shark Movement Projectled by the Marine Biological Association.

“The shipping industry, which allows us to buy a variety of everyday products from around the world, can cause the decline of whale sharks, which are an extremely important species in our oceans,” said Freya Womersley, a doctoral student at the University of Southampton. led the study as part of the Global Shark Movement Project, said in a press release.

International Union for Conservation of Nature’s Red list of endangered species lists the whale shark as endangered.

Described as “slow sea giants”, the researchers said that whale sharks can grow up to 20 meters long and help regulate plankton levels in the ocean by feeding on microscopic zooplankton.

The researchers said that the number of whale sharks has dropped in recent years in many places. However, the reasons for why are not entirely clear.

Because whale sharks spend a lot of time in surface waters and congregate in coastal areas, experts believed that collisions with ships could cause “significant” deaths.

The study indicates that shipments of whale shark tags stopped more often in busy waterways than expected, even after ruling out technical errors.

Of the 61 tracked tags that stopped transmitting on busy routes, more than 85 percent were not related to random technical errors, the study said.

The researchers suggest that this is probably due to whale sharks hitting and killing and sinking to the seabed.

“Incredibly, some of the spikes that recorded depth and location showed whale sharks moving into fairways and then slowly sinking to the seabed hundreds of meters below, which is the ‘smoking gun’ for a deadly ship attack,” says Professor David. Sims, founder of the Global Shark Movement Project and senior researcher at the Marine Biological Association and the University of Southampton.

“It’s sad to think that many deaths of these incredible animals have occurred globally due to ships without us even knowing about taking preventative measures.”

The research team said that there are currently no international rules to protect whale sharks from ship collisions, and that this “hidden mortality” can occur with other marine megafauna.

“Together, we must invest time and energy in developing strategies to protect this endangered species from commercial shipping now, before it is too late,” Womersley said, “so that the largest fish on earth can withstand threats that are predicted to intensify in the future. , such as changing sea climates. “

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