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How we found what kills so many whale sharks

How we found what kills so many whale sharks


They’re the world’s greatest fish, however it isn’t fishing that’s the predominant explanation for their declining numbers, as FREYA WOMERSLEY and DAVID SIMS of the College of Southampton clarify

Over 80% of worldwide commerce is carried by sea. A lot of what we use and devour every single day both has been or will likely be transported on large vessels that plough the worldwide ocean.

The programs these container vessels take are mounted transport routes generally known as marine highways, which aren’t in contrast to motorways on land. These highways, which vessels journey backwards and forwards, join distant ports, typically on reverse sides of huge oceans.

Marine highways may reduce throughout the actions and migratory routes of marine animals. Big plankton-feeding whales and sharks are notably susceptible to being struck and killed by massive vessels, as a result of they spend lengthy intervals close to the floor. Our new research discovered that this risk could also be a better explanation for loss of life for the world’s largest fish, the whale shark, than anybody beforehand realised.

Whale sharks can attain lengths of as much as 20m. Regardless of their sturdy look, their numbers have declined by greater than 50% previously 75 years. In 2016, they had been added to the rising record of endangered shark species.

In contrast to most different species of shark that roam the open ocean, intentional or unintentional catches by industrial fishing fleets should not regarded as a number one explanation for whale shark decline. It is because main whale shark fisheries have been closed down, and the species has been protected by worldwide commerce bans since 2003. As a substitute, a number of components level to transport being a number one, but hidden explanation for loss of life.



If a big one collides with a whale shark, the shark most likely stands little likelihood of survival. There’s typically no hint of those occasions as a result of, if a deadly collision happens, the physique sinks. Whale sharks advanced from smaller, bottom-dwelling sharks and have retained their unfavourable buoyancy.

This makes detecting and recording collisions tough. Prior to now, the one proof out there was a sparse set of eyewitness accounts, information studies and encounters with sharks harbouring accidents from collisions with smaller vessels.

How we found what kills so many whale sharks
Scars attest to how widespread ship strikes are prone to be (Simon Pierce, creator supplied)

We got down to uncover the hidden deaths of whale sharks by bringing collectively a world crew of greater than 60 scientists from 18 nations. Our World Shark Motion Mission satellite tv for pc tracked virtually 350 whale sharks by becoming them with digital tags, mapping their positions throughout all main oceans in unprecedented element. This revealed essentially the most densely occupied areas, which had been typically in coastal areas the place the species is thought to congregate.

A whale shark dorsal fin with electronic tag attached.
Digital tags enable scientists to trace sharks utilizing satellites (Mark Erdmann, creator supplied)

Placing overlap

We in contrast these actions with a compulsory ship monitoring system, which was initially developed to forestall ships colliding with one another. This helped us observe world fleets of cargo, tanker, passenger, and fishing vessels – the sorts of massive ships (heavier than 300 gross tons) able to hanging and killing a whale shark.

We discovered {that a} staggering 92% of the horizontal area occupied by whale sharks and almost 50% of their depth layers overlapped with the actions of those fleets.

We then developed state-of-the-art fashions to establish the collision threat inside these overlapping areas and located that the Gulf of Mexico, Arabian Gulf and Crimson Sea posed the best threat to whale sharks.


These areas are residence to a few of the world’s busiest ports and sea passages, and since our estimated ranges of threat correlated with identified deadly collisions right here, they seem like a few of the most harmful locations on the planet for whale sharks to inhabit.

A diver swimming alongside a whale shark.
Coastal seas are among the many most harmful areas for whale sharks (Sofia Inexperienced, creator supplied)

Inside high-risk areas, whale sharks recurrently crossed vessel paths and handed near ships that had been travelling about 10 instances sooner than they had been swimming. This gave the sharks little or no time to answer an oncoming ship, and these close-range encounters may be occurring extra typically than we’ve got the capability to watch, probably ending in deadly strikes.

Alarmingly, whale shark tag transmissions ended extra typically in busy transport lanes than we anticipated. Even after accounting for the random technical failures of transmitters, we discovered 24% of tags stopped transmitting in busy transport lanes, most definitely as a consequence of whale sharks being lethally struck and sinking to the ocean flooring.

We could even have recorded whale sharks dying as a consequence of collisions. A few of the tags report depth in addition to location and confirmed sharks shifting into transport lanes however then sinking slowly to the seafloor a whole bunch of metres under – the smoking gun for a deadly ship strike.

A large container vessel on the horizon.
World transport routes are an under-appreciated risk to marine life (Simon Pierce, creator supplied)

En path to hazard

The substantial risk to whale sharks uncovered by our research makes a robust case for pressing safety measures. At current, there are not any worldwide rules to guard whale sharks from ship collisions. In mild of our research, this species faces an unsure future if motion is just not taken quickly.

As a primary step to deal with this disaster, the Worldwide Maritime Group (IMO) may develop a worldwide reporting scheme that consolidates information of ship-wildlife collisions for whale sharks and different threatened species. Such a community would assist regional authorities implement safety measures by offering proof of the place collisions are occurring.


Initiatives to decrease the danger of ship strikes may emulate measures to guard whales from collisions, comparable to IMO rules that require ships to decelerate or navigate extra fastidiously. Our research might help by figuring out high-risk areas the place these measures may very well be trialled.

Fast motion could be the solely option to forestall whale shark numbers from sinking additional in the direction of extinction.

Freya Womersley
Freya Womersley
David Sims
David Sims

Additionally on Divernet: Need To See Whale Sharks? No Downside, The place The Whale Sharks Are, Sharks Dive Deeper Than We Thought, Large Fish Draw Large Spenders

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