Climate Change Drives Grey Whales into San Francisco Bay Amid Rising Deaths
Ferries, cargo ships, and tankers navigate the turbulent waters of San Francisco Bay on Tuesday as a whale surfaces nearby, its blow barely discernible against the whitecaps. Historically, whales could easily go unnoticed by mariners, but a newly launched AI-powered detection network aims to monitor them continuously.
The system, named WhaleSpotter, operates around the clock, scanning the bay for whale blows and heat signatures up to two nautical miles away. It alerts mariners to reduce speed or alter course when whales are detected nearby.
“They’ll be able to make adjustments way before they get anywhere close,” said Thomas Hall, director of operations for the Bay ferry. “It will also allow us to track data over time and see where the whales are camping out so we can adjust our routes during whale season to avoid those areas completely.”
Alarming Increase in Grey Whale Deaths Linked to Ship Strikes
This initiative arises amid a concerning surge in gray whale fatalities in the bay. In the previous year, 21 dead gray whales were discovered in the broader Bay Area—the highest number in 25 years, according to the Marine Mammal Center—with at least 40% of these deaths attributed to ship strikes. So far this year, at least 10 additional deaths have been recorded in the Bay Area.
Scientists caution that these numbers likely underestimate the actual impact, as many whale carcasses sink or are carried back out to sea before discovery or reporting.
Shifts in Migration Patterns Linked to Climate Change
Gray whales have traditionally migrated along the California coast on their approximately 12,000-mile (19,300-km) journey between breeding lagoons in Mexico and Arctic feeding grounds.
However, an increasing number of whales are now diverting into San Francisco Bay, remaining for days or even weeks within the congested estuary. Scientists increasingly associate this behavioral change with climate change. Warming temperatures and alterations in Arctic sea ice are disrupting the food web that gray whales depend on during summer feeding months, according to a 2023 study published in Science, resulting in many whales being malnourished during migration.
Many whales concentrate in a high-traffic corridor between Angel Island, Alcatraz, and Treasure Island, overlapping directly with ferry routes and shipping lanes.
“It’s the worst place possible in terms of all the ship traffic,” said Rachel Rhodes, a project scientist at the Benioff Ocean Science Laboratory who led the initiative. There have been so many collisions that “the teams responding to strandings said they ran out of places to even land dead whales.”
Population Decline Despite Past Conservation Success
The eastern North Pacific gray whale population was once celebrated as a conservation success story after recovering from commercial whaling and being removed from the Endangered Species Act in 1994. However, numbers have since declined by half over the last decade, according to the National Oceanic and Atmospheric Administration (NOAA), with only about 13,000 individuals remaining.
“They may not be getting the quality or quantity of food they’re used to in the Arctic,” Rhodes said. “That means they’re starting this incredibly long migration at a disadvantage.”
WhaleSpotter System Enhances Detection and Alerts
The WhaleSpotter system uses artificial intelligence to automatically flag potential whale sightings, which are then verified by trained marine mammal observers. Verified alerts are communicated via radio to ferry operators, vessel traffic controllers, and are posted publicly on the Whale Safe website.
While WhaleSpotter systems are already deployed on vessels and fixed installations such as lighthouses and coastal towers in the United States, Canada, and Australia, researchers note that the San Francisco Bay network is the first to integrate land-based and vessel-mounted detections with official mariner alerts. This integration enables near-real-time communication of whale sightings to ships navigating the bay.
The initial hours of testing generated a significant number of detections.
“Suddenly to have a full sense of how much whale activity is in this space honestly put me a little bit on edge,” said Douglas McCauley, director of the Benioff lab. “But we’re going to use that data and we’re going to be smart about how we use that space and share it with the whales.”
Continuous Monitoring Through Thermal Cameras
Researchers emphasize that the system’s primary advantage is its constant monitoring capability. Unlike human observers, thermal cameras can operate during nighttime and in many foggy conditions common in the bay.
One camera has been installed on Angel Island, and a second will soon be mounted aboard a ferry traveling between downtown San Francisco and Vallejo, creating what Rhodes describes as a “moving data collection platform.” Scientists hope to expand coverage across the bay with additional cameras on the Golden Gate Bridge and Alcatraz.
Marine Heat Wave Impacts Prey and Whale Behavior
A severe marine heat wave off the California coast is reducing the band of cold, nutrient-rich water where krill, anchovies, and sardines thrive. As offshore waters warm, humpback whales are increasingly following their prey closer to shore, overlapping with California’s Dungeness crab fishery operations.
The crab fishery employs tens of thousands of vertical lines connecting traps on the seafloor to surface buoys, creating entanglement hazards for whales migrating and feeding along the coast.
This spring, regulators again closed parts of the fishery off central California to conventional gear, a measure increasingly common in recent years as warming waters increase whale overlap with crab fishing seasons.
While gray whales are also at risk, humpbacks are particularly vulnerable.
“Humpbacks are curious and they’ll scratch their backs on the gear,” said Kathi George, director of cetacean conservation biology at the Marine Mammal Center. “If they get a line caught on their body, they’ll breach and they’ll roll and end up entangling themselves.”
Whales can drag heavy gear for months, impairing their ability to dive or feed properly, which can lead to starvation, infection, and drowning.
In 2024, 36 whales were confirmed entangled off the California coast—the highest number since 2018, according to NOAA—though scientists note that many cases go undocumented.
Innovative Ropeless Crab Fishing Gear Approved
California approved commercial use of ropeless pop-up crab fishing gear for the first time this spring, allowing fishermen to continue harvesting through the end of the season.
Instead of floating surface buoys tethered to traps, this system stores ropes and buoys on the seafloor until fishermen return and trigger an acoustic release that brings the gear to the surface.
Supporters argue that this technology enables continued crab harvesting while significantly reducing risks to whales.
Ongoing Adaptation Needed as Climate Change Alters Ocean Conditions
As climate change continues to reshape ocean conditions and whale migration patterns, scientists anticipate persistent overlap between whales, ships, and fishing gear.
“We will have to continue to be adaptive and science driven in terms of our management to reduce wildlife risk and keep fishermen on the water,” said Caitlynn Birch, Oceana’s Pacific campaign manager and a marine scientist. “California has been a national leader in developing whale-safe fishing technologies and we hope that model can help guide other fisheries on the West Coast and nationally.”
