A UC Santa Cruz scientist who specializes in research at the intersection of big data and marine-life conservation has contributed to a new study that shows the vast majority of “hotspots” where ships collide with whales in the world’s oceans lack protections for the majestic giants.
The paper, co-authored by UC Santa Cruz research fellow Heather Welch, was published online November 21 in the journal Science and reports that global shipping traffic overlaps with about 92% of the habitat ranges for blue, fin, humpback, and sperm whales. The study, led by the University of Washington, combined big data and statistical modeling to produce the first estimates of risk for whale-ship collisions worldwide for these four geographically widespread ocean species.
Thousands of whales are injured or killed each year after being struck by ships, particularly the large container vessels that ferry 80% of the world’s traded goods across the oceans. Collisions are the leading cause of death worldwide for large whale species. Yet global data on ship strikes of whales are hard to come by—impeding efforts to protect vulnerable whale species.
"It’s hard to directly observe where and when whale strikes happen. Vessels may not recognize they’ve struck a whale, and dead or injured whales may drift or travel far from collision sites,” said Welch, also a research scientist with the National Oceanic and Atmospheric Administration. “This lack of immediate evidence makes statistical modeling—which predicts over unobserved locations and times—a critical tool for understanding when and where whale strikes occur.”
Warning: More collisions ahead
The problem is only projected to increase as global trade grows in the coming decades, explained senior author Briana Abrahms, assistant professor of biology and researcher at the University of Washington’s Center for Ecosystem Sentinels. To make the high-risk vessel traffic tangible, Abrahms said: “This translates to ships traveling thousands of times the distance to the moon and back within these species’ ranges each and every year.”
Whale-ship collisions have typically only been studied at a local or regional level—like off the U.S. East and West coasts—leaving patterns of risk unknown for large areas, according to the study’s lead author, Anna Nisi, a postdoctoral researcher at the center. “Our study is an attempt to fill those knowledge gaps and understand the risk of ship strikes on a global level,” Nisi said. “It’s important to understand where these collisions are likely to occur because there are some really simple interventions that can substantially reduce collision risk.”
Lanka. (Credit: Sopaka Karunasundara)
The team found that only about 7% of areas at highest risk for whale-ship collisions have any measures in place to protect whales from this threat. These measures include speed reductions, both mandatory and voluntary, for ships crossing waters that overlap with whale-migration or feeding areas.
Fortunately, the researchers also determined that implementing management measures across only an additional 2.6% of the ocean’s surface would protect all of the highest-risk collision hotspots they identified. Those hotspots for the four species included in the study lie largely along coastal areas in the Mediterranean, portions of the Americas, southern Africa, and parts of Asia.
“Trade-offs between industrial and conservation outcomes are not usually this optimal,” Welch said. “Oftentimes, industrial activities must be greatly limited to achieve conservation goals, or vice versa. In this case, there is a potentially large conservation benefit to whales for not much cost to the shipping industry.”
Global datasets reveal hotspots
The international team behind the study, which includes researchers across five continents, looked at the waters where these four whale species live, feed, and migrate by pooling data from disparate sources—including government surveys, sightings by members of the public, tagging studies, and even whaling records.
The team collected some 435,000 unique whale sightings. They then combined this novel database with information on the courses of 176,000 cargo vessels from 2017 to 2022—tracked by each ship’s automatic identification system and processed using an algorithm from Global Fishing Watch—to identify where whales and ships are most likely to meet.
The study uncovered regions already known to be high-risk areas for ship strikes: North America’s Pacific coast, Panama, the Arabian Sea, Sri Lanka, the Canary Islands, and the Mediterranean Sea. But it also identified understudied regions at high risk for whale- ship collisions, including southern Africa; South America along the coasts of Brazil, Chile, Peru and Ecuador; the Azores; and East Asia off the coasts of China, Japan, and South Korea.
The team found that mandatory measures to reduce whale-ship collisions were very rare, overlapping just 0.54% of blue whale hotspots and 0.27% of humpback hotspots, and not overlapping any fin or sperm whale hotspots. Though many collision hotspots fell within marine protected areas, these preserves often lack speed limits for vessels, as they were largely established to curb fishing and industrial pollution.
Speed limits, detours, and jurisdictional enforcement
For all four species, the vast majority of hotpots for whale-ship strikes—more than 95%—hugged coastlines, falling within a nation’s exclusive economic zone. That means that each country could implement its own protection measures in coordination with the U.N.’s International Maritime Organization.
“From the standpoint of conservation, the fact that most high-risk areas lie within exclusive economic zones is actually encouraging,” Nisi said. “It means individual countries have the ability to protect the riskiest areas.”
Of the limited measures now in place, most are along the Pacific coast of North America and in the Mediterranean Sea. In addition to speed reduction, other options to reduce whale-ship strikes include changing vessel routings away from where whales are located, or creating alert systems to notify authorities and mariners when whales are nearby.
“Lowering vessel speed in hotspots also carries additional benefits, such as reducing underwater noise pollution, reducing greenhouse gas emissions, and cutting air pollution, which helps people living in coastal areas,” said Nisi.
The authors hope their global study could spur local or regional research to map out the hotspot zones in finer detail, inform advocacy efforts, and consider the impact of climate change, which will change both whale and ship distributions as sea ice melts and ecosystems shift. They point to the benefits of slowing ships down at local scales, as seen through programs like Blue Whales Blue Skies in California.
But scaling up such programs will require a concerted effort by conservation organizations, governments and shipping companies, said co- author Jono Wilson, director of ocean science at the California Chapter of The Nature Conservancy, which helped identify the need for this study and secured its funding. “Whales play a critical role in marine ecosystems,” Wilson said. “Through this study, we have measurable insights into ship-collision hotspots and risk and where we need to focus to make the most impact.”
The full list of authors and funders are named in the paper, “Ship collision risk threatens whales across the world’s oceans.”
