Blue whales, grays and humpbacks are traveling south along the California coast this month to their annual breeding grounds in warm Mexican waters. They feed in the same spots where cargo ships travel to some of the world’s busiest ports — and one strike could be deadly.

Scientists have tried for four years to reduce the number of whales killed by ships, but so far it hasn’t worked. Every year, several dozen whales are killed by ship strikes along the West Coast.

In the past 14 months, two dead blue whales have washed up on Northern California beaches. A 65-foot long blue whale washed up in Daly City October 2016 and a 79-foot long blue whale came ashore May 2017 in Bolinas.

On the Bolinas beach, onlookers gathered three weeks after the animal washed ashore, where the stench was putrid. Flies buzzed around the carcass, and the decaying blubber reeked like roadkill.

“It’s like that but extreme, more pungent — and it actually — you almost taste it at the same time,” says Barbie Halaska, a biologist with The Marine Mammal Center, an animal rescue group in Sausalito. And she’s right, it was akin to sweaty gym shorts.

She says the ship strike is obvious from the whale’s 10 broken ribs.

“Whale ribs are tough, but to be able to break in two to three places for each rib, it—she had to be hit very hard,” Halaska says.

Most years, between one and three whales wash up on California beaches after being struck by a ship. But those are only the ones we see. A recent paper in the scientific journal PLOS One, estimates that ships kill roughly 80 whales each year along the U.S. west coast.

That study looked at blue and fin whales, which are both endangered. It also included humpback whales, which have distinct populations off the west coast, some of which are threatened.

All three species dive to great depths off the California coast—sometimes hundreds of feet—searching for food. The bristly baleen in their mouths acts like an enormous fine-toothed comb, filtering organisms from the cold, nutrient-rich California water. Protein-packed organisms like zooplankton and krill are mainstays of this aquatic buffet.

The problem, according to Sean Hastings with the National Oceanic and Atmospheric Administration, or NOAA, is that this buffet sits in the middle of a freeway—a cargo ship super-highway.

“The whales are busy eating,” he says, “the ships are busy moving to the ports, and unfortunately they collide in the same place.”

Oakland is the fifth busiest container port in the U.S. Roughly 1,500 ships motor into the port each year. John Berge, Vice President of the industry trade group, the Pacific Merchant Shipping Association, says ships have limited ability to maneuver in the narrow shipping lanes.

“It’s terrible,” says Berge. “Some of the larger ships probably don’t know that they’ve actually struck a whale until, eventually, there is evidence that the whale is draped across the bow.”

He says captains in the control room might be ten stories up off the water, and set back hundreds of feet from the bow.

In 2013, NOAA and the Coast Guard narrowed the shipping lanes outside San Francisco and the Santa Barbara Channel, to reduce the overlap between whale feeding grounds and ships.

NOAA also developed a free app called ‘Whale Alert,’ with real-time notifications of whale sightings, to encourage captains to slow down when the animals are nearby. According to a 2016 report from UC Santa Barbara, reducing speed from roughly 23  to 14 miles an hour would cut in half the chance that a whale would die when struck by a ship.

But Hastings says it’s difficult to know if these management measures are working. Ships do seem to be staying within the new shipping lanes but they aren’t necessarily slowing down.

“We’ve been trying non-incentivized approaches just asking ships to slow down,” says Hastings. “That hasn’t been working.”

The number of whales killed by ships now is about the same as before these efforts. On the East Coast, captains must slow down during whale season. That and other measures have cut the number of documented deaths from ship strikes for the extremely endangered North Atlantic right whale—from 2 to 1.

Population numbers for the animal are so low that they hover around 450. They could go extinct within the next 20 to 30 years, given the rate at which they’re dying, which is what scientists are trying to prevent.

“I think they’re doing amazing things already in this space but it’s also not enough,” says Doug McCauley, a UC Santa Barbara ecologist.

He directs the Benioff Ocean Initiative, a $10 million fund started by Salesforce CEO Marc Benioff and his wife Lynne. The initiative’s first big project seeks to reduce fatal whale ship strikes.

The initiative granted $100,000 to Mark Baumgartner from the Woods Hole Oceanographic Institution in Massachusetts, for his underwater microphones that record whale sounds, which can be used to tell ship captains that whales are nearby.

The recorded whale sounds show up on a computer graph as curved lines and dashes. Like sheet music, the symbols represent the “notes” the whale is singing.

“On the y-axis is frequency or pitch,” says Baumgartner, “so I like to say Barry White is down here and Mariah Carey is up here.”

Baumgartner programmed the devices to identify each species of whale by its song, but he didn’t know if it would work.

“I was actually shocked,” he says. “When we did the numbers and came up with nearly 100 percent accuracy, I was kind of dumbfounded.”

If a fleet of these underwater devices were installed off the California coast, they could provide real-time feedback around the clock. That would be more reliable than and less expensive than relying on volunteers in boats or planes looking for whales, or other citizen scientists who infrequently post to the ‘Whale Alert’ app.

Right now the underwater microphones are attached to buoys off Martha’s Vineyard and the New York Bight, a coastal indentation between New Jersey and New York.

Baumgartner also developed custom sensors for two types of underwater robots—the Slocum glider and Wave Glider that actively search for whales off the East Coast.

Wave gliders sit at the ocean’s surface and use fins for propulsion to search for whales, while Slocum gliders dive underwater moving between the surface and seafloor listening for whale calls.

Both gliders record whale songs and transmit data via satellite to scientists on land who can send that information to cargo ships or the U.S. Coast Guard.

Eventually, McCauley of the Benioff Initiative hopes data from the robots could be incorporated to ships’ automated information system or ‘AIS,’ which is like “air traffic control” for vessels and would appear on ships’ computers. Captains could then use the the real-time whale alert information to slow down.

“A couple less news stories about blue whales that are washing up on shore is, for me, a grand success,” says McCauley.

By next year McCauley wants to bring these devices to the California coast. The first pilot project involves attaching one of Baumgartner’s instruments to an oil rig off Santa Barbara.

But whether these instruments work or not, might depend on questions like whether ships can slow down without blowing budgets and deadlines.