Buzz
These traffic accidents have halved the global population of whale sharks in the last 75 years.
As whales are actually mammals, not fish, the current title of the largest fish on Earth belongs to the whale shark (Rhincodon typus). These creatures can reach lengths of up to 16 meters and weigh over 20 tons. They are as wide as a double-decker bus.
Yet, during their participation in traffic, specifically while swimming underwater, whale sharks still frequently encounter accidents. Ironically, in these accidents, they are the victims, getting hit, injured, and sometimes killed.
The culprits can be none other than the giant cargo ships of our fellow humans.
A recent study published in the Proceedings of the National Academy of Sciences (PNAS) on May 9 reveals that up to 90% of the current migration routes of whale sharks will intersect with the high-speed oceanic transportation routes of humans.
Due to their close proximity to the water surface, whale sharks are vulnerable to collisions with massive container ships. Just one collision with a vessel weighing over 300 tons can be fatal for a whale shark.
Scientists reveal that these marine accidents have led to a 50% decline in the global whale shark population over the past 75 years. This has pushed the largest fish on Earth into the list of the most critically endangered shark species worldwide.
Human vessels are carving paths across the oceans, disrupting natural habitats and migration routes.
According to the Organization for Economic Co-operation and Development (OECD), global trade heavily relies on these maritime highways. Up to 90% of international cargo is currently transported via the sea on vessels carrying thousands of colossal containers.
The advantage of maritime transport lies in manufacturers being able to ship large volumes at low costs, while receivers can consolidate shipments to reduce expenses. These containers can then continue their journey by road, once ocean-going vessels have completed their voyage across continents.
Unfortunately, what benefits humans often harms nature and wild animal species.
A wounded whale shark struggles after being struck by a passing ship.
Human maritime routes often connect distant seaports on opposite sides of vast oceans. They're referred to as sea highways, cutting across the migration paths of many fish species.
Whale sharks and sperm whales are often victims of human transport vessels colliding with them, as they spend extended periods feeding near the water's surface. If a whale shark is struck by a large vessel, its chances of survival are slim.
Accidents often go unreported, as whale sharks are a species with negative buoyancy. Meaning, when critically injured and unable to swim, they'll sink to the ocean floor and quietly perish.
In their recent study, marine ecologists at the University of Southampton sought to tag 350 whale sharks to track their movements and map their locations via satellite.
These maps were cross-referenced with GPS tracking systems of ocean vessels, including cargo ships, oil tankers, cruise liners, and fishing vessels weighing over 300 tons—capable of fatally injuring a whale shark upon collision.
'Our recent research has uncovered this threat could be the leading cause of death for the world's largest fish, the whale shark, more than any previously recorded cause,' Professor of marine ecology David Sims stated.
'Unlike most other shark species roaming the open ocean, deliberate or accidental fishing activities by industrial fishing fleets are not considered the top culprit in the decline of whale shark populations. Instead, for this marine species, there are indications that human transport activities are the underlying killer,' said Sims.
92% of the whale shark's habitat is intersected by human shipping routes
This is the result of the first satellite data analysis showing the extent to which human shipping routes overlap with the habitat of whale sharks. Scientists point out areas like the Gulf of Mexico, the Arabian Gulf, and the Red Sea - where there are high concentrations of seaports and bustling maritime traffic - are also where whale sharks frequently encounter accidents with ships the most.
Human shipping routes map onto the habitat of whale sharks.
GPS data reveals whale sharks frequently cross paths with shipping lanes and collide with vessels many times their speed and size. This leaves the sharks with very little time to react to an oncoming ship.
Scientists observed that 24% of GPS signals from tagged whale sharks vanished as they crossed a shipping lane. Even after accounting for random technical glitches in the transmitters, they believe this represents the number of sharks struck and sunk by ships.
Some devices attached to whale shark fins recorded their final locations near those of cargo ships. Meanwhile, their depth steadily decreased to hundreds of meters below the sea surface.
This is direct evidence of a collision from a ship that killed the whale shark.
The locations where whale shark GPS signals end coincide with human shipping lanes.
Professor David Sims noted there is currently no international convention to protect whale sharks from ship collisions like these. In fact, many ships are too large to even notice they've struck a whale shark.
Therefore, he suggests that to safeguard the planet's largest fish, the International Maritime Organization (IMO) should establish a reporting channel for ship-shark collisions. This way, they can document accidents and map out areas most prone to shark collisions.
Subsequently, IMO could further enforce regulations requiring ships to reduce speed or navigate more cautiously when entering areas with whale sharks. Professor Sims stated he is willing to provide maps of these areas to test such regulations.
'Acting now is the only way to prevent further decline in whale shark numbers and avoid the risk of extinction,' he said. 'I am deeply saddened to witness the deaths of these magnificent animals, occurring right on human shipping routes, for which we currently have no measures to prevent such accidents'.
References: Theconversation, PNAS
