Ship strikes blamed for dive in whale shark population
WHALE sharks are bumping into large ships, scientists fear, as they warned that fatal collisions could be behind the alarming decline in populations.
Globally, whale shark numbers have fallen more than 50 per cent over the past 75 years, with marine biologists puzzled as to what was causing the downturn.
An international team of experts has found that many of the preferred habitats of the sharks overlap with shipping lanes, with tagged sharks more likely to stop transmitting in such areas.
An analysis of 61 shark tags that fell silent in major shipping lanes found that 85.5 per cent had no technical problem, leading researchers to infer that a lethal collision had occurred.
“Incredibly, some of the tags recording depth as well as location showed whale sharks moving into shipping lanes and then sinking slowly to the sea floor hundreds of metres below, which is the smoking gun of a lethal ship strike,” said Prof David Sims, of the Marine Biological Association at Southampton University.
Whale sharks are the world’s biggest fish and can grow up to 65ft in length, they move slowly through the water, hoovering up microscopic zooplankton with their enormous mouths. And that leaves them vulnerable to collisions with high-speed vessels.
The team mapped hotspots of shark activity and found that 90 per cent fell within areas used by fleets of freighters, tankers and fishing boats.
Currently there are no international regulations to protect whale sharks against ship collisions and researchers are calling for a reporting scheme to monitor strikes as well as a reduction of vessel speeds in high-risk areas such as the southern Red Sea and Arabian Gulf.
Freya Womersley, of Southampton University, who led the study as part of the Global Shark Movement Project, said: “The maritime shipping industry may be causing the decline of whale sharks, which are a hugely important species in our oceans. We need to put time and energy into developing strategies to protect this endangered species, before it is too late.”
The research was published in the journal PNAS.