Collisions between whales and ships can be deadly for the marine mammals, but researchers say extending mitigation measures to just 2.6% of the ocean’s surface will reduce the chance of such attacks in all risk hotspots.
While experts say many whale-ship collisions go unobserved and unreported, making it difficult to put a figure on the scale of the problem, some estimates suggest that tens of thousands of the animals are killed each year.
Now researchers say they have not only identified hotspots where the risk of collisions is greatest, but have revealed that almost all of these lack measures to mitigate such strikes.
Dr Jennifer Jackson, from the British Antarctic Survey and a co-author of the research, said: “This is the first study to look at this problem on a global scale, making it possible to identify global patterns of collision risk using an extremely large contemporary dataset of four recovering cetacean species.”
Write in the journal Sciencethe team reports how they compiled a dataset of 435,000 whale locations, recorded between 1960 and 2020, for blue, fin, humpback and sperm whales.
“These are four highly migratory species with a global distribution, which have been shown to be affected by ship strikes, and have many sighting reports,” Jackson said. “They provide an opportunity to investigate this problem on a global scale.”
The team then combined this data set with more than 35 billion positions of 175,960 ships to estimate the risk of whale-ship collisions across the world’s oceans.
The results show that seafaring occurs over 91.5% of the combined range of these whales, putting them at risk of collisions.
The researchers were also able to identify hotspots – defined as areas with the top 1% of ship strike risk.
While it was mostly concentrated around continental coastlines, with the highest percentage in the Indian Ocean, the researchers said hotspots were also found in areas of open sea such as the Azores, at least for blue and sperm whales.
The researchers added that nearly 5% of the outbreaks affected three of the four whale species, with nearly 20% affecting two of the species.
“More than 95% of the risk hotspots for all species were found in exclusive economic zone (EEZ) waters, highlighting the importance of national regulation to reduce this risk globally,” Jackson said.
When the team looked at ship strike management measures, such as speed reduction zones or changes in vessel routes, they found that levels of protection varied between hotspots.
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Overall, however, less than 7% of the risk hotspots for any of the four species were covered by voluntary measures, and less than 1% were covered by mandatory measures.
Yet such interventions can have a major impact. “Complete coverage of hotspots can be achieved by extending management over only 2.6% of the ocean’s surface,” the team writes, with Jackson noting that slowing down vessels is the most effective way to reduce collision risk.
While the threat of collisions has grown with increasing marine shipping, the team said the climate crisis could exacerbate the situation, noting declining sea ice in the Arctic could open up new trade routes and result in whale populations moving north.
Sally Hamilton, chief executive of the charity Orca, who was not involved in the research, said large whales were facing the equivalent of marine highways.
“The shipping industry has an opportunity to put vessel strike at the heart of their environmental strategy by working with conservationists and governments to establish safe marine spaces,” she said. “By doing so, they can help undo the damage caused by industrial whaling and mitigate the future impact of vessel strikes.”
Dr Freya Womersley, from the Marine Biology Association, said the research highlighted that wildlife-ship collisions were a global issue and therefore required a global response.
“It is encouraging to see that targeted ship management – across a relatively small sea area – can achieve full strike risk hotspot coverage, making positive conservation outcomes for these species very achievable,” she said.
