- With protection, many of California’s marine mammals — including whales, sea lions and seals — have made remarkable recoveries over the last half-century since bipartisan passage of the U.S. Marine Mammal Protection Act.
- However, climate-linked changes have now pushed the gray whale population into a state of collapse.
- Despite comebacks, marine mammals face a plethora of threats from pathogens, pollutants — including oil and plastic — disappearing food and more.
- In California, people and institutions are fighting for marine mammals and ocean biodiversity, but federal protections could be substantially weakened if proposed amendments to the Act move ahead.
SAN DIEGO, U.S. — The bluff at La Jolla Cove in San Diego is covered with pelicans and cormorants; below, some two dozen sea lions lounge on a rocky ledge or bark and frolic in the shallows, some leaping clear out of the water.
On the shore, a volunteer from the local Sierra Club’s Seal Society, an organization that educates and advocates for pinniped protection, is monitoring an emaciated 13.5-kilogram (30-pound) pup, just a few months old, that has spent the last several days hauling up on the beach, with no sign of an adult nearby. Now, Hubbs Sea World has a response team on the way to rescue it. Hubbs is part of a marine mammal stranding network that covers California’s entire 1,770-kilometer (1,100-mile) coastline.
Snorkeling in the cove amid healthy green surf grass, with bright orange Garibaldi damselfish (Hypsypops rubicundus) swimming by (think goldfish on steroids), my cameraman friend Charlie Landon and I are suddenly surrounded by swooping, barrel-rolling sea lions. They move like flexible torpedoes, twisting through the water column, some streaming bubbles from their snouts.
Watching a rockfish near the bottom of the cove, I sense movement and turn to see a large sea lion, maybe 110 kg (250 lbs), eyeing me from less than arm’s length away before gliding on. A curious juvenile bites down on Charlie’s GoPro camera before approaching me, close enough that I put my hands on my chest lest it “mouth feel” my fingers. Then it heads back into the swirling pack of pinnipeds that I can’t help but anthropomorphize: They seem to be having ecstatic fun.
La Jolla has one rookery of harbor seals (Phoca vitulina) and two of sea lions (Zalophus californianus), with a few hundred animals each. Up north in Monterey, about 1,000 sea lions have taken over San Carlos Beach near Cannery Row, in a spot where scuba certification classes usually take place. It’s temporarily closed to the public while the sea lions, recently arrived from their breeding colonies in the Channel Islands, have stopped to gorge on squid and sardines. They also regularly chase fish into San Francisco Bay and take over a former boat dock at Pier 39 — which attracts thousands of tourists.
In my book, The Golden Shore — California’s Love Affair with the Sea, I point out that California, which boasts the world’s fourth-largest economy, is proof you can grow a blue economy while protecting the environment. If you count whale-watching tours, festivals, sea otter tourism, visits to Monterey Bay Aquarium (where you can see wild otters from the deck) and other attractions, marine mammals generate several billion dollars a year in ecotourism revenue.
Dramatic recovery — and new threats
California is an ideal place to be a marine mammal, thanks to an abundance of prey provided by the California Current and nutrient-rich deep-water upwellings. Its coastline is presently home to 250,000 California sea lions, as well as about 200,000 northern elephant seals (Mirounga angustirostris) that visit each year to breed and molt, 40,000 harbor seals, tens of thousands of whales, dolphins and porpoises, and some 3,000 southern sea otters (Enhydra lutris nereis) — more than 40 species in all.
Sixty years ago, many of these animals were heavily depleted by historic whaling and hunting, but reforms including the Marine Mammal Protection Act, passed in 1972, and the Endangered Species Act, enacted the next year, provided legal protections for all marine mammals, not just endangered ones, and mandated conservation of their habitats. At the time, California’s coastal waters still had good breeding sites and food sources. The result: rapid rebound.
But today, marine mammals are facing new dangers, living in a rapidly changing ocean, altered by climate change, pollution and pathogens. Meanwhile, proposed changes would substantially weaken both laws.
California’s gray whales (Eschrichtius robustus) face the most immediate threat, though they have long been seen as an environmental success story and become a tourist attraction during their annual Pacific migration between the Arctic and their breeding lagoons in Mexico. In 1972, there were about 10,000. Their numbers slowly grew to 27,000 by 2016.
But over the last nine years, their population has crashed, plummeting to 12,950, according to a recent report by the National Oceanic and Atmospheric Administration (NOAA) — the lowest since the 1970s.
They’re starving to death as their main food sources are disappearing, including tiny shrimp-like amphipods in the whales’ summer feeding grounds in the Arctic. It’s caused by a domino effect: With retreating sea ice, there is less under-ice algae that feeds the amphipods, that in turn, feed the whales. Malnourished whales also produce fewer offspring.
With more whale strandings and malnourished animals and whales washing up dead, NOAA declared an Unusual Mortality Event in California in 2019. Between 2019 and 2025, at least 1,235 gray whales stranded dead along the West Coast of North America. That’s eight times greater than any previous 10-year average.
While there appeared to be some recovery in 2024, 2025 has again seen high casualties, including 21 gray whale deaths so far this year in San Francisco Bay, along with a minke (Balaenoptera acutorostrata) and two unidentified species of baleen whales. The hungry whales now come into the crowded estuary to feed, making them vulnerable to ship traffic; ship strikes have killed nine so far this year. The rest died from apparent starvation.
Michael Stocker, executive director of the acoustics group Ocean Conservation Research, has been leading whale-viewing trips to San Ignacio Lagoon in Baja, Mexico since 2006. He described the drastically different situation there now.
“When we started going, there would be 400 adult whales in the lagoon, including 100 moms and their babies.” Back then, he said, “the killer whales — pelagic orcas [Orcinus orca] that feed on young grays — wouldn’t come into the lagoon because the adults would just mob them. This year we saw about 100 adult whales, only five of which were in momma-baby pairs. The orcas came into the lagoon and ate a couple of the babies because there were not enough adult whales to fend them off.”
Southern California’s Gray Whale Census and Behavior Project reported record-low calf counts earlier this year.
HABs bite
Climate change is exacerbating threats, including marine heat waves. Harmful algal blooms (HABs) that produce deadly toxins are more frequent, fed by nutrient pollution runoff from farms and cities and supercharged by warming seas. Among the most common are red tides and blue-green algae outbreaks caused by cyanobacteria.
A type of algae called Pseudo-nitzschia australis produces a potent neurotoxin, domoic acid. It caused mass strandings and killed hundreds of sea lions, dolphins and whales that washed up on California beaches in 2022 and 2023, and again this year, with several reports of poisoned and disoriented sea lions wandering onto highways or turning aggressive and biting surfers. Southern California is now experiencing the worst harmful algal bloom on record.
“Twenty years ago, we’d just see [outbreaks] in the summer. Now it’s year-round,” says Giancarlo Rulli, a spokesperson for the Marine Mammal Center, which is located in Northern California’s Marin Headlands and is the largest rescue and rehabilitation center of its kind in the world.
On the day I visited in September, the center’s 30 patients — all adult and sub-adult sea lions — were victims of a mass outbreak of leptospirosis. This bacterial infection is easily contracted from infected urine when mobs of sea lions share rocky pools and beaches. It usually leads to kidney failure.
Some of the sea lions looked listless; others, inert. All were being treated with fluids, fish and antibiotics. When it’s busy, the center can go through 450 kg (1,000 lbs) of herring in a day.
But there was good news. Four recovered animals had just been released at the Point Reyes seashore that morning, and I saw another adult male that lay in a fenced enclosure, anesthetized, being given a pre-release exam.
Cancers and contagions
Other sea lions are getting cancer. From the late 1940s to the early 1970s, the Montrose Chemical Plant discharged an estimated 1,800 tons of the pesticide DDT (dichlorodiphenyltrichloroethane) into Los Angeles county sewers that empty into the Pacific Ocean, according to the California Department of Fish And Wildlife.
Sea lions coming into the Pacific Marine Mammal Center in Laguna Beach carry high levels of DDT. “These animals are accumulating it through nursing as well as the food they eat,” says Kirsten Donald, a marine biologist and lead educator with the center. “And what we’ve discovered is that they will develop cancer because the DDT interacts with a herpes virus — which they pretty much all have — and that is a catalyst for cancer. And so about 25% of the adult patients that come through here are diagnosed with terminal cancer, unfortunately,” she says.
Despite growing concern among experts about marine mammal health, NOAA’s California Current Ecosystem Program, which, among other things, tracks the size and health of the sea lion populations, is shutting down much of its work due to budget cuts.
“We’re heartbroken because their data is critical to the work we’re doing, and really for anyone researching California sea lions,” says Katie Prager, a disease ecologist at the University of California, Los Angeles.
Northern elephant seals, like gray whales, are considered a great wildlife success story. In the late 1800s, between 20 and 100 were left. Today, there are 200,000. At Piedras Blancas State Marine Reserve, south of Big Sur, some 26,000 northern elephant seals visit year-round.
However, Christine Heinrichs is worried. She’s written about elephant seals and has worked as a docent for Friends of the Elephant Seals for decades, closely observing these iconic animals. She’s concerned, she says, because “bird flu is the emerging threat.”
Avian influenza, or bird flu, is a highly contagious, deadly virus. A particularly virulent strain, H5N1, emerged in 2020 and jumped between more than 500 species, both birds and mammals. A catastrophic outbreak in 2024 in Argentina killed some 17,000 southern elephant seals (Mirounga leonina), including 97% of pups.
The fear is that infected migrating birds will transmit the virus to northern elephant seals. “Presently we report dead birds, but there’s not much else we can do,” Heinrichs says.
Researchers at the Marine Mammal Center are currently testing a bird flu vaccine on elephant seals. If successful, the first marine mammal recipients would be the highly endangered Hawaiian monk seals (Monachus schauinslandi). Just 1,600 animals remain in the wild in Hawai‘i.
Sea otters float back from the brink
Southern sea otters, also known as California sea otters, were once thought to be extinct, wiped out by the slaughter of the 18th– and 19th-century fur trade. But a small raft survived, living below the tall, fog-bound cliffs of Big Sur. In the 1960s, they began migrating into Monterey Bay, where, as keystone predators, they restored its long-lost kelp forests. They now number about 3,000. Sixty percent live in the Monterey Bay area.
But unlike their 120,000 northern cousins (Enhydra lutris kenyoni) and despite legal protections, their population has not expanded in decades. One limiting factor is the resurgence of California’s great white sharks (Carcharodon carcharias) that bite them to see if they have any blubber. (They don’t.) The numbers of sharks to the north and south make it hard for the otters to recolonize beyond their current home range.
The U.S. Fish and Wildlife Service has explored the possibility of reintroducing them to their historical range in northern California and Oregon, which has generated opposition from the commercial fishing industry and support from Native American coastal tribes. But for now, there has been no formal proposal.
Threatened policies
A range of other human activities challenge marine mammal survival, including ship strikes on whales, noise pollution, and entanglement in fishing gear — as well as ingesting plastic, oil and other toxins.
But the biggest threat is the potential loss of legal safeguards, specifically proposed amendments to the Marine Mammal Protection Act. One of the most concerning changes would limit the federal government’s ability to act against “incidental take.” That would, for example, include killing of whales, dolphins and seals by sonic blasts from oil exploration, ship strikes or entanglement in fishing gear.
A bill that would weaken the Endangered Species Act, H.R.1897, was introduced into the U.S. House of Representatives in March 2025. It would redefine “harm” in a way that would permit destroying the habitat of an endangered species. It has not yet come up for a vote.
Even in California, a model of marine mammal protection, state and local efforts are faltering in the face of increasing local challenges as well as larger global impacts, which is leading to more starved, sick and injured animals.
Rocky, a young sea lion, offers a poignant example of the threats they face. He was found stranded in Malibu in late August, malnourished with a fishhook in his stomach and bullet lodged in his head. On Sept. 29, the Marine Mammal Care Center of Los Angeles announced that he’d undergone successful surgery and was recovering.
Experts stress that protections are critical, and that our collective actions or inactions will determine the future of our marine mammal relatives.
“Things are becoming unpredictable as the ocean is changing in real time, with mammals having to adapt to it in real time,” says Rulli, from the Marine Mammal Center, where he first volunteered when he was 14. “The ocean environment is more stressed. Even with federal protections, things are really on the edge.”
Banner image: A harbor seal pup is carefully restrained by an animal care volunteer during a tube feeding at The Marine Mammal Center’s hospital and visitor center in Sausalito, California. Image © Bill Hunnewell, The Marine Mammal Center.
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Citations:
Sandoval-Belmar, M., Smith, J., Moreno, A. R., Anderson, C., Kudela, R. M., Sutula, M., … Bianchi, D. (2023). A cross-regional examination of patterns and environmental drivers of Pseudo-nitzschia harmful algal blooms along the California coast. Harmful Algae, 126, 102435. doi:10.1016/j.hal.2023.102435
Uhart, M. M., Vanstreels, R. E., Nelson, M. I., Olivera, V., Campagna, J., Zavattieri, V., … Rimondi, A. (2024). Epidemiological data of an influenza A/H5N1 outbreak in elephant seals in Argentina indicates mammal-to-mammal transmission. Nature Communications, 15(1). doi:10.1038/s41467-024-53766-5