Deadly whale shark collisions with large ships are vastly underestimated and could be the reason why populations are declining.
This is the conclusion of a study published in the journal ‘PNAS’ by marine biologists from the Marine Biological Association (MBA) and the University of Southampton.
Whale shark numbers have declined in recent years in many places, but it’s not entirely clear why that is. Since these endangered animals spend much of their time in surface waters and gather in coastal regions, experts have theorized that collisions with ships could be causing major whale shark deaths, but until now there was no way to control this threat.
Scientists tracked the movements of whale sharks
Scientists from 50 international research institutions and universities followed the movements of whale sharks and ships around the world to identify risk zones and potential collisions. Data from the satellite-tracked movements of nearly 350 whale sharks were presented at the Global Shark Movement Project, led by MBA researchers.
The team mapped shark “hot spots” that overlapped with the world’s fleets of cargo, oil, passenger and fishing vessels – the kinds of large vessels capable of hitting and killing a whale shark – to reveal that more than 90% of whale shark movements fell under the footprint of shipping activity.
The study also showed that whale shark tag transmissions ended more frequently than expected on the busiest shipping lanes, even when technical glitches were ruled out. The team concluded that the loss of transmissions was likely due to whale sharks being hit, killed and sinking to the bottom of the ocean.
They can reach up to 20 meters
University of Southampton PhD researcher Freya Womersley, who led the study as part of the Global Movement of Sharks Project, points out that “the shipping industry, which allows us to source a wide variety of everyday goods from around the world, may be causing the decline of whale sharks, which are a hugely important species in our oceans.”
Whale sharks are slow-moving ocean giants that can grow up to 20 meters in length and feed on microscopic animals called zooplankton. Whale sharks help regulate ocean plankton levels and play an important role in the marine food web and in the health of ocean ecosystems.
Professor David Sims, Principal Investigator at the MBA and the University of Southampton and founder of the Global Shark Movement Project, said: “Incredibly, some of the tags that record depth, as well as location, showed whale sharks moving towards shipping lanes and then slowly sinking to the seafloor hundreds of meters deep, which is the sign of a lethal hit by a ship.”
“It is sad to think that there have been so many deaths of these amazing animals around the world from ships without us realizing it to take preventative action,” adds Sims.
There is no international regulation
There are currently no international regulations to protect whale sharks from collisions with ships. The research team states that this species faces an uncertain future if action is not taken soon. They hope their findings can inform management decisions and protect whale sharks from further population declines in the future.
“Collectively, we need to spend time and energy developing strategies to protect this endangered species from commercial shipping now, before it’s too late, so that the largest fish on Earth can withstand the threats it’s predicted to face.” intensify in the future, such as changes in ocean climate,” says Womersley.