One in five whale sharks has been injured by a commercial vessel due to increasingly busy shipping routes, new study finds
- A new study in Australia tracked 913 whale sharks between 2008 and 2013
- The team found around 20 percent showed significant scarring or amputation
- These injuries are believed to primarily come from collisions with ship
- Whale sharks swim near the surface, making them a frequent obstacle for ships
A new study of whale sharks around the Ningaloo Reef off the western coast of Australia has found that one in five has been injured in a collision with a commercial boat of some kind.
Researchers from the Australian Institute of Marine Science tracked a population of 913 whale sharks between 2008 and 2013 and found that around 20 percent showed new scarring or signs of fin amputation.
While the team believed some of the scarring came from predator bites, the majority was blamed on collisions with large marine vehicles.
Researchers in Australia tracked 913 whale sharks between 2008 and 2013 and found some 20 percent should signs of injury consistent with having collided with a commercial ship, including injuries such as amputation or deep laceration
‘These big animals rest on the surface of the ocean for an hour or so at a time,’ researcher Mark Meekan told Australia’s ABC News, ‘and of course at that time, while they’re lolling about and gently swimming along at the surface, they’re very susceptible to boat strikes.’
According to the researchers, it’s difficult to identify where and when the sharks are injured since they travel across a wide region, as far as Indonesia, the Timor Sea and beyond.
‘We see some animals at the start of the season that are unmarked and by the end of the season have scars on them,’ Meekan said.
‘So there is some scarring happening in Ningaloo… But it may well be that the majority of this threat is actually happening in other places.’
To complete their study, the team relied on a database of photos and video taken by 15 different whale shark touring companies that operate around the Ningaloo reef.
Those companies are required by Australian law to document the animals during their daily expeditions as part of the country’s preservation efforts.
The team found the rate of injury had grown faster over time, nearly doubling between 2011 and 2013
The team used a database of video and photographs collected by whale shark tour operators in western Australia, which are required by law to help document the animals
The photos and video revealed a wide variety of injuries, including surface wounds, fin amputations, and deep lacerations.
Worryingly, they found the rate of injury seemed to be accelerating, and had almost doubled between 2011 and 2013.
Researchers worry that they might still be underestimating the frequency of injuries for a number of reason.
‘A collision between a large ocean-going vessel and a whale shark wouldn’t be felt by the ship, as a result,’ researcher Emily Lester said, ‘it’s likely that we’re underestimating the number of mortalities from ship strike, since our study could only document sharks that survived their injuries,’
The team believe the main cause of injury come from shipping vessels, which are often so large they likely wouldn’t even feel a collision with a whale shark
Also, because whale sharks have negative buoyancy, they sink to the ocean floor when they die, something that makes it hard to classify a particular whale shark’s absence was due to death or simple migrational shift.
Commercial shipping vehicles have long been a threat to whale populations around the world.
One study of North Atlantic right whales found more than half of the recorded fatalities was caused by commercial ships.
‘It’s clearly in places like the big shipping lanes that we might actually have to think about what’s going on,’ Meekan said.
Whale advocates have pushed to change commercial shipping routes to avoid whale hot spots, but with international waters involved along with companies from many different countries it can be difficult to reach an agreement.
The team hope that by using their data to show injury hot spots it might be easier to negotiate on alternate routes.
WHAT ARE WHALE SHARKS?
Whale sharks are the largest breed of fish in the world.
A mature male shark can grow upwards of 32 feet, with the longest animal measuring 61 feet.
Despite their name, whale sharks are not whales – they are slow-moving, filter-feeding carpet sharks.
The sharks prefer warmer water and migrate every spring to the west coast of Australia.
According to CSIRO research scientist Richard Pillan, whale sharks gather at Ningaloo Reef between March and October before they migrate to other parts of the world
The sharks feed on smaller fish – with their favourite meal being plankton – and rise to the surface during feeding.
They are most at danger of being run over and killed by passing fishing vessels and commercial boats when they come to the surface to feed.
Their numbers have dramatically decreased over the last 15, years in large part to illegal fishing which is still pratcised in parts of the world such as Asia.
Very little is known about their mating behaviour. The only litter size that has ever been documented had more than 300 pups
Source: National Geographic and CSIRO research scientist Richard Pillan