The largest fish on Earth is a shark. Capable of reaching lengths of up to 60 feet — about the height of a four-story building — whale sharks, named for their size, are so large that they make great whites look like minnows.
But even giants can disappear. In recent decades, more than half of all whale sharks have disappeared from the ocean. Some populations have declined by more than 60 percent.
This decline is something of a scientific mystery. It cannot be explained by known threats such as overfishing. And because whale sharks sink when they die, there are no bodies that wash ashore for researchers to study.
Now a new clue has emerged, and it’s a big one. A study in the news Proceedings of the National Academy of Sciences reveals that cargo ships are probably one of the leading causes of death for whale sharks. Where you’ll find high densities of these endangered fish, you’ll often find marine traffic, the authors found, and ships are already known to attack and kill these animals.
Our life as consumers connects us to this seemingly distant problem. More than 80 percent of all internationally traded products are carried by cargo ships, such as TVs and cooking utensils and whatever device you are reading right now. And the world’s naval fleet is multiplying rapidly, growing from 1,771 large ships in 1995 to more than 94,000 in 2020. The ocean is now full of highways full of ships.
Whale sharks are not the only road fatalities. Large cargo ships damage many species of sea giants, such as the endangered North Atlantic right whales, and some smaller creatures, such as sea turtles. Ships also emit loud noises that disrupt marine life and spew carbon dioxide that warms the planet into the atmosphere.
“Shipping is a serious problem for the giants of the sea,” said Robert Harcourt, a marine ecologist at Macquarie University in Australia who was not involved in the study. “We have an economy derived from moving things around the world in a way that doesn’t consider environmental costs.”
Ships hit at least 75 different species of sea creatures
Last fall, a large tanker painted red, white and blue drove into a port in southern Japan. Was draped slenderly over his bow a dead, 39-foot whale†
Tragic photos documenting whale attacks are rare, but the attacks themselves are not. They affect at least 75 different species of marine life, according to: a recent review, and probably thousands of deaths every year. Creatures that tend to hang out near the ocean surface are especially vulnerable, such as whale sharks and sea turtles.
A good step toward reducing collisions is figuring out where animals are most at risk, and that’s where this new whale shark study comes in handy. Large ships have to report their locations, and the authors compared those points to the movement of hundreds of whale sharks, which they had previously tagged with satellite trackers. (This is no easy feat: “You have to have some nice long fins, a good pair of lungs, and sprint after them underwater,” said David Sims, a marine ecologist at the University of Southampton and a co-author of the study. . )
The results showed how vulnerable these fish are: More than 90 percent of the ocean surface used by whale sharks overlaps the routes of tankers, passenger ships and fishing vessels. Whale sharks tend to congregate near shore, where shipping is particularly busy, according to Freya Womersley, a doctoral student at the University of Southhampton and the study’s lead author.
She also found that much of the sharks’ tracking equipment stopped working when the animals entered busy shipping lanes, perhaps because they were being killed by ships. (Some trackers even showed sharks swimming in dense shipping lanes and then sinking slowly to the seabed – “the smoking gun for a deadly ship attack”, as Womersley and Sims wrote in The Conversation.)
According to Womersley, sharks cruising in the Gulf of Mexico, Arabian Gulf and Red Sea were most at risk of collision. “Not only do they spend a lot of time on the surface where they can be vulnerable to being hit, but they also occupy the same places that some of these ships pass through,” she told cafemadrid.
While scientists don’t know exactly how many shark boats killed, they do have this information for other marine giants, including the North Atlantic right whales. ships died at least a third of the right whales that have died in recent years, and they have more injured. Today, only about 360 to stay. (“Right whales are notoriously bad at not getting run over by ships,” Harcourt said.)
Other species of whales, mako sharks, otters, manatees and a host of other creatures are also vulnerable, according to the review. But physical strikes are only part of the problem.
Noisy ships mess with animal senses
While most people perceive the world through sight and dogs see the world through smell, many whales and dolphins rely on sound. For them, sound is everything: they map their surroundings, find prey and talk to each other, often through hundreds or thousands of kilometers of ocean.
Shipping throws a big, jingling wrench into this strategy. In the past 50 years there has been a 32-fold increase in low frequencies of sound along the world’s major shipping lanes, caused in large part by giant propellers. Some whales use the same frequencies to communicate. (Fish — including whale sharks — don’t use sonar to communicate, so this probably isn’t a big deal for them.)
As a result, some whales seem to get louder in noisier areas, for the same reason you might scream when talking to friends at a loud bar, said Daniel Costa, a marine ecologist at the University of California Santa Cruz who was not involved. in the whale shark study. “Whales have already started talking louder to compensate for the increased noise,” he said.
Scientists discovered too that noise can disrupt communication and disrupt behaviors such as hunting prey, sleeping and mating. More than 150 studies have shown that noise has significant effects on marine life, according to a recent review† (I recommend listening to part of these six minutes audio file that comes with the paper. You can hear what the ocean sounds like with and without transmission.)
Large cargo ships also pollute the air with carbon emissions. They use some of the dirtiest fuels in the world and produce a comparable amount of carbon emissions to the aviation industry (about 3 percent of global greenhouse gas emissions), as cafemadrid’s Umair Irfan reports.
Those emissions accelerate climate change, which is harming all types of marine life. Ironically, warming may actually make some animals more susceptible to ship attacks. For example, North Atlantic whales are: travel north in the spring and summer to Canadian waters as the ocean warms, where until recently they were not protected from ship attacks. “Climate change continues to rearrange the deck,” making it difficult for regulations to keep up, Costa said.
Towards a safer sea
Making oceans safer for sea giants is conceptually simple, and one option is to divert ships away from animal hot spots. A 2015 study, for example, found that shifting a shipping lane near Sri Lanka just 15 nautical miles south could reduce the risk of ships hitting blue whales by 95 percent. (Lawyers are now push for this change†
Even slowing ships can make a huge difference. A freighter’s chance of killing a whale drops to less than 50 percent when it moves at about half speed (10 knots, or 18 miles per hour), compared to nearly 100 percent when it moves faster, according to one 2006 study†
This so-called “slow steaming” is also less noisy and requires less fuel. Just a 10 percent reduction in speed can lead to a 19 percent reduction in greenhouse gas emissions, as Irfan reports. And the fuel bill is cheaper too.
But there is a major drawback to ships that slow down or take a different route: it takes longer to deliver goods. That’s one of the reasons why studies like this don’t always translate into shipping restrictions. That drawback also makes alternative approaches, such as designing quieter ships or adding wildlife deterrents or propeller guardsattractive (although the advantages of these technologies) are not well established†
But besides shopping locally to reduce shipping, it’s something we can do now, Womersley said, and the payoff would be huge. Many sea giants are at the top of the food chain, where they stabilize the ocean’s ecosystems. They also help fertilize the ocean and sequester massive amounts of carbon that could otherwise fuel climate change like old trees do. These animals are great too. They contain not only the largest fish on earth, but also the largest animal that ever lived (the blue whale). All this makes it a pretty reasonable trade-off to get our goods a little late.