New research shows that the oceans’ gentle giants are being wiped out by human activity.
The spotted fish (sharks, not whales) are cutely volatile and surprisingly docile, despite their intimidating size. Whale sharks are the largest fish in the ocean, reaching 40 feet or more, but they are no match for even bigger boats. So thanks to the global shipping industry, they are turning into the ocean’s road deaths.
For decades, researchers weren’t sure why whale shark populations worldwide were declining. Their numbers have reduced by 50% in the past 75 years. A new report in the Proceedings of the National Academy of Sciences finds that the international shipping industry is harming already endangered species.
To unravel this mystery, scientists from 50 research institutions worldwide and universities teamed up to track ships and sharks in the oceans to understand the possibility of collisions between the two. They looked at tagged shark data from 2005 to 2019 and analyzed the movements of 300 whale sharks along shipping lanes in the Indian, Pacific, and Atlantic Oceans. They found that tag transmissions ended earlier in areas with more shipping traffic. Unfortunately, the sharks they studied were constantly in the path of shipping ships — in fact, about 90% of their movement occurred near shipping activities.
“Some tags that recorded both depth and location showed whale sharks moving into shipping lanes and then slowly sinking to the seafloor hundreds of feet below, which is the ‘smoking gun’ of a deadly ship attack,” David Sims, senior research associate at the Marine Biomedical Association and the University of Southampton, in a press release. “It’s sad to think that there have been so many deaths worldwide from these incredible animals from ships without us even knowing we had to take preventative measures.”
In the report, the researchers note that many shark deaths go unreported because the sharks sink to the bottom of the ocean when they die. These huge sharks like to hang out near surface waters, increasing their chances of being hit by the bottom or side of large ships. They are also quite slow swimmers, reacting slowly and frequently migrating, increasing their risk of encountering boats.
Losing whale sharks has more ripple effects than just losing these majestic creatures. These huge fish feed mainly on microscopic sea creatures called zooplankton. They regulate the plankton levels in their environment, which helps to stop harmful algal blooms.
There are rules to protect whale sharks from commercial fishing, but the team says there are no international rules for ships dealing with shark migration. They argue governments should try to save whale sharks from ship movements by diverting some shipping traffic. They stress that they must intervene “before it’s too late” so these sharks can stand a chance against other looming threats, including changing ocean conditions due to climate change.
Editor’s Note: The release dates in this article are based in the US but will be updated with local Australian dates as we learn more.