Collisions between whales and ships can prove fatal for the marine mammals, but researchers say expanding mitigation measures to just 2.6% of the ocean’s surface would reduce the chance of such strikes 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 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 revealed almost all of these lack measures to mitigate such strikes.
Dr Jennifer Jackson, of the British Antarctic Survey and a co-author of the research, said: “This is the first study to look at this problem at a global scale, enabling global patterns of collision risk to be identified using an extremely large contemporary dataset of four recovering whale species.”
Writing in the journal Science, the team report how they compiled a dataset of 435,000 whale locations, recorded between 1960 to 2020, for blue, fin, humpback and sperm whales.
“These are four highly migratory species with a global distribution, that have shown evidence they are impacted by ship strikes, and have lots of sightings reports,” Jackson said. “They provide an opportunity to investigate this problem at a global scale.”
The team then combined this dataset with more than 35bn positions from 175,960 ships to estimate the risk of whale-ship collisions across the world’s oceans.
The results reveal that marine shipping occurs across 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 these were mostly concentrated around continental coastlines, and the highest percentage was 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 almost 5% of the hotspots affected three of the four whale species, with almost 20% affecting two of the species.
“Over 95% of the risk hotspots for all species were found in exclusive economic zone (EEZ) waters, pointing to the importance of national regulation to reduce this risk globally,” said Jackson.
When the team looked at ship-strike management measures, such as speed reduction zones or changes in vessel routes, they found levels of protection varied across hotspots.
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 compulsory measures.
Yet such interventions could have a big impact. “Full coverage of hotspots could be achieved by expanding management over only 2.6% of the ocean’s surface,” the team write, with Jackson noting that vessel slowdowns were 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 make the situation worse, noting declining sea ice in the Arctic could open new trade routes and result in whale populations moving northwards.
Sally Hamilton, the chief executive of the charity Orca, and who was not involved in the research, said large whales were facing the equivalent of marine motorways.
“The shipping industry have 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. “In doing so they can help undo the damage caused by industrial whaling and mitigate the future impacts of vessel strikes.”
Dr Freya Womersley, of the Marine Biology Association, said the research emphasised that wildlife-ship collisions were a global issue and therefore required a global response.
“It’s encouraging to see that targeted shipping management – over a relatively small ocean area – could achieve full strike-risk hotspot coverage, making positive conservation outcomes very achievable for these species,” she said.
