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Ship collisions linked to deaths of endangered whale sharks

The ocean's largest fish can't move quickly enough to get away from ships — a problem since they also live and feed in some of the world's most heavily trafficked shipping lanes.

(CN) — Scientists want to see maritime legislation to protect whale sharks after a study found that large ships are responsible for a staggering number of lethal injuries to the creatures.

Monday's study published in the journal PNAS is a sub-project of a global undertaking by The Global Shark Movement Project (GSMP). Founded in 2016, the group is an international scientific research team with more the 40 research teams across 26 countries and 100 different institutes.

Researchers tagged almost 350 whale sharks and tracked their movements. These tags showed whale shark hotspots and allowed researchers to compare the animals' travel alongside cargo, passenger, fishing, and other large vessels capable of killing whale sharks.

An endangered species, whale sharks are the largest fish in the ocean, averaging from 18 feet to 33 feet in length, yet they eat the smallest creatures. As filter feeders, they spend a significant amount of time at the surface of coastal waters, eating plankton and other small species. Unfortunately, these waters also contain the most shipping traffic.

“We had that shipping satellite track data; we had our whale shark satellite track data. And what we did is map the two together to determine where we’re seeing some overlap between these individuals. And when we did that, we found that 92% of the spaces used by whale sharks overlap with shipping,” said study author Freya Womersley, a doctoral researcher at the University of Southampton.

Some areas with the highest risk include the Red Sea, the Gulf of Mexico, and the Arabian Gulf due to the well-trafficked canals and passes — spaces that are also whale shark hotspots. Researchers also found a significant number of tag signals ended in areas of high ship traffic. After ruling out tags that stopped sharing data due to battery loss and other causes, scientists concluded that the signal loss was due to lethal boat injury.

“We found that of 219 tags, there were 52 that ended in the busiest shipping lanes. So, these are shipping lanes that have vessel activity have three times higher than other sorts of areas,” said study co-author David Sims, also with the University of Southampton and a senior research fellow at the U.K.'s Marine Biological Association.

While all tags transmitted satellite movements, some also recorded depth.

“We also managed to track what we think is whale sharks to their death," Sims said. "What we found for seven sharks, for which we had these depth recording tags, was when they went into those busy shipping lanes they then started dropping, sinking very slowly through the water column."

Comparing the depths and speed of diving behaviors to the sinking data, it was evident the whale sharks had died and were sinking to the bottom of the ocean.

“Because the scale of the problem looks very large, then this is something we want to draw attention to, and we don’t think should be ignored by the industry,” Sims said.

The post-study research will largely revolve around mitigation — whale shark behaviors around boats and different ways to prevent collisions. Whale sharks move slowly and can’t avoid incoming ships quickly, so the maritime industry must take responsibility. Current mitigation ideas range from international and local legislation to marine national parks and sensor technologies.

“The extra thing is that these animals are moving all the time, and the places they are are pretty dynamic, so it’s also a good idea to have a system that can react to where the whales or whale sharks are and change what’s going on at the time,” said Stanford marine biologist Stephen Palumbi.

Womersley added: “I think it should be enough of an incentive for an endangered shark species that many coastal regions rely upon for income, for tourism, and has an important role to play within our oceans — it should be enough of an incentive to really try and get some discussions going."

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