Scientists identify global hotspots for whale-ship collisions—and hardly any have protections in place

This story was originally published by Inside Climate News and appears here as part of the Climate Desk collaboration

An estimated 90 percent of all traded goods travel by sea, where vessels tap into a vast network of shipping routes that connect even the most far-flung places. 

But humans aren’t the only ones traversing vast distances across these marine highways. A new study found that shipping occurs in more than 90 percent of whale ranges, where the animals can often get hit—becoming what scientists grimly refer to as “ocean roadkill.” By combining shipping and whale distribution data, the researchers pinpointed the areas with the highest risk of whale-vessel collision for several species. They discovered just a small fraction of these hotspots have any collision protection measures in place. 

“There’s just extremely high overlap of shipping traffic with whales,” said study co-author Briana Abrahms, a wildlife biologist at the University of Washington. “These whales are just having to contend with an incredibly, incredibly busy ocean, and shipping traffic is a leading cause of mortality for several whale species.” 

Shipping, cruise and fishing vessels fatally strike an estimated 20,000 whales around the world each year. Scientists say this is likely an underestimate because vessels could unwittingly hit a whale whose body sinks to the seafloor before it is recorded. Climate change could be increasing vessel strike risk as ocean warming and marine heatwaves push whales closer to human activity.

There is a bright spot. Research shows that low-speed zones and shipping reroutes can help keep whales out of danger, while reducing emissions and improving air quality for people. And a little protection could go a long way: Expanding these management measures across an additional 2.6 percent of the ocean could mitigate the highest-risk collision hotspots, according to the study. 

Pinpointing Vessel-Strike Hotspots 

Whales are some of the most well-traveled cosmopolitans of the sea. For example, humpbacks can swim around 5,000 miles each year during their seasonal migration. Yet the exact hang-out spots or routes that different cetacean species use on their journeys are still largely a mystery. 

To help change that, the researchers collated more than 435,000 whale sightings from a variety of sources, including government surveys, scientific tagging studies, whale-watching citizen scientists and even historic whaling records. They focused on four globally ranging species: fin whales, sperm whales, humpbacks and blue whales—the largest mammals on Earth. 

The scientists then inputted this deluge of data into a predictive model, and created some of the first comprehensive worldwide maps for where these ocean giants spend their time.

Now, scientists can “take a really global look at where these animals are in the ocean where we haven’t really always had eyes on in the past,” Abrahms said. 

But the team also wanted to better understand where whales face the greatest threats from shipping traffic. To do this, the study’s authors—including researchers across five continents—compiled billions of positioning data points from 176,000 shipping vessels during journeys made from 2017 to 2022. This information is tracked through each ship’s automatic identification system, and was processed using an algorithm developed by Global Fishing Watch, a nonprofit that monitors vessel activity to increase transparency at sea. 

By combining the ship and whale databases, the researchers made an unsettling discovery: Every ocean region contains “substantial” ship-strike risk for all four species. Within the blue, humpback and sperm whales’ ranges, large vessels traveled the equivalent of more than 4,600 times the distance to the moon and back each year, according to the study. 

“I think one of the key takeaways from this paper is that ship collisions between large vessels and wildlife are a global issue,” said Freya Womersley, a researcher at the Marine Biological Association who studies whale-vessel collisions. She was not involved in the new study. “That means that we really need to come together if we’re going to have any hope in solving this issue.”

The highest level of risk was identified in the Indian Ocean, western North Pacific Ocean and the Mediterranean Sea. Hotspots—areas with the top 1 percent of ship-strike risk—were mostly concentrated around coastlines, where the ships congregate to drop off or pick up goods. Some of the hotspots fell within marine protected areas, but these preserves often lack the targeted approaches necessary to reduce collision risk. 

Many of the hotspots are already known to have high cases of vessel strikes. That includes the West Coast of the United States, which has some of the heaviest ship traffic in the country due to its abundance of ports. From 2007 to 2020, there were 70 incidents of ship strikes on large whales—many of them fatal—in California alone, according to the nonprofit Greater Farallones Association. However, the new study revealed that more than 15 percent of the area in the world’s oceans has risk levels equivalent to the California Current Ecosystem. 

“That’s a great incentive for us to start studying in these other areas of the ocean and also to try and mitigate beyond some of the more well-known regions for strike risk,” Womersley said. “The methods of this paper show another great example of big data analyses for addressing modern conservation issues.”

Some of the most surprising ship-strike hotspots, Abrahms said, were identified in the middle of the ocean. For example, the Azores—Portugal islands famed for whale-watching—contains high levels of risk because it bisects major transit pathways for ships crossing the Atlantic Ocean, the study found. 

“Ship strike mitigation efforts in the past have really focused on coastal areas, and that makes total sense, right? Because we know that there’s going to be a lot of shipping traffic coming into those coastlines,” Abrahms said. But this paper shows that there can be collision risk hotspots “way out in the middle of the ocean” that don’t get as much attention for protecting whales, she added.

Shipping Speed Limits

Since the early 1990s, shipping traffic has quadrupled at sea. As demand for goods skyrockets, maritime trade is projected to grow even more by 2050. That could spell trouble for whales, which face a revolving door of threats from climate change, entanglements with fishing rope and habitat loss. 

When it comes to vessel strikes, research shows that several management techniques can drastically reduce risk. The most effective strategy is to reroute shipping traffic to avoid whale habitat and migration corridors altogether—a step that the Mediterranean Shipping Company Group took in 2022 off the west coast of Greece to circumvent sperm whales in the area. 

But in an ever-globalizing world, this approach isn’t always simple or possible, the shipping industry argues. In those cases, ocean managers and conservationists point to another efficient technique for minimizing vessel strikes: whale “school zones.” When ships go slower, it gives whales time to move out of the way. 

Along the U.S. East and West Coast, the National Oceanic and Atmospheric Administration (NOAA) has implemented speed limits—both mandatory and voluntary—in several areas during certain times of the year when whales have been known to pass through. Other countries, including Spain and Panama, have created these zones as well. 

The new study found that implementing vessel speed restriction zones over an additional 2.6 percent of the ocean’s surface would reduce risk in every ship-strike hotspot the researchers identified. Slowing down can also help ships shrink their carbon footprint and improve air quality. For example, in California, NOAA created the Protecting Blue Whales and Blue Skies program that partners with shipping companies to encourage them to follow voluntary vessel speed reductions throughout the California coast. Last year, participating ships reduced their air pollutant emissions by approximately 1,250 tons of nitrogen oxides and 45,000 metric tons of greenhouse gases, according to the program’s website. 

Although the premise sounds simple, creating and enforcing speed limits in these zones can be complex. In 2022, NOAA proposed a modified set of vessel speed restriction rules in the Northeast to protect endangered North Atlantic right whales, which would expand the areas that ships are required to slow down, among other regulations. However, the proposal sparked outrage among representatives in the fishing and shipping industries and pushback in Congress. It has yet to be finalized, and a bill proposed this summer could delay modifications until at least 2030 if passed.

Similar to cars on the road, ships also don’t always follow speed limits when they do exist—and enforcement can be scarce. In 2020, scientists at the University of California, Santa Barbara’s Benioff Ocean Initiative developed Whale Safe, an app that tracks both whale populations off Santa Barbara and San Francisco and speed limit compliance. While some ships steadily slowed down, the app identified several fleets that followed the speed limit less than 15 percent of the time during the 2024 whale migration season. 

Research shows that climate change can also increase the risk of vessel strikes and complicate efforts to reduce them. As waters warm, whales are following their food into new areas with little to no protections in place. To account for this, some scientists and politicians have pitched creating “dynamic slowdown zones” to put in place when a high number of whales are present in an area. 

The new study also notes that melting sea ice in the Arctic is projected to open up new trade routes that could increase ship traffic, potentially resulting in higher rates of collision for some whale species. 

“Climate change is a really important element to consider in studies like this, because we know that it has the capacity to alter the distributions of species that we’re including in some of these strike risk assessments,” Womersley said.

To address this, Abrahm’s team is working on applying the new whale distribution models under future climate change scenarios. She added that the maps can also be used to uncover whales’ exposure to other human activities, such as fishing, to get a better sense of the many threats these species face—and how best to protect them. 

“We’re really excited not only for the maps that we were able to generate looking at ship collision risk, but also just the ability to make these whale maps at all is a big feat,” she said. It’s time, she said, to start thinking about “what are management opportunities that can both protect whales now, but then also protect whales as they move around in the future.”