A new study led by the Marine Biological Association of the U.K. and the University of Southampton, along with experts in Australia and New Zealand, found that industrialized shipping could be killing large numbers of whale sharks.
Marine biologists have said that whale shark numbers have been falling in recent years, but it has not been clear why.
But a new international study suggests that collisions with shipping traffic could be a major factor.
Researchers examined satellite data to track about 350 whale sharks. They found that the world’s largest fish spend most of their time in waters used by freighters and other larger vessels.
The study showed that transmissions from the tags that monitor their movements often ended in busy shipping lanes. The international team, including experts from Britain, Australia and New Zealand, believe many sharks are probably being hit and killed by boats before sinking to the ocean floor.
Mark Erdmann is from the University of Auckland in New Zealand and a scientist at Conservation International, a non-profit environmental organization.
He co-authored the study, and believes shipping is a major threat to whale shark populations, which are a protected species.
“If we are protecting them from fisheries, why are their populations still declining? And one thought is the fact that these are big oceanic plankti vores that move relatively slowly, feeding on the surface, spend 50% of their time in, kind of, top 10-20 meters of the water. So, it is possible that they are actually running into a lot of the global shipping. Now, what the study found is that, indeed, there is a tremendous amount of overlap between where whale sharks are moving and global shipping traffic. So, those are real collision-risk areas,” he said.
Most lethal strikes are likely to go undetected or unreported. At present, there are no regulations to protect endangered whale sharks against these types of collisions.
Whale sharks play an important role in the marine food web and healthy ocean ecosystems.
They can grow up to 20 meters long.
The study is published in the PNAS — Proceedings of the National Academy of Sciences — journal.