They have been crawling ashore by the hundreds—California sea lion pups so emaciated that their skins drape like cloaks over knobs of bone. At sea, the usual patterns of winds and currents that the marine food web depends upon have failed. The sea is warmer than usual and conspicuously lacking in prey items, including plankton and sardines. With little available for large predators to eat, the most visible consequence has been the baby sea lions, which have shown up stranded on beaches from Mexico to San Francisco for the past three years.
Fortunately for these moony-eyed, clumsy-footed juveniles, a network of coastal rescue centers has been ready to help. Run largely by volunteers, these facilities have received more than 2,200 young sea lions since January 1, 2015. Many of the youngsters have bounced back to health under human care, and the goal is to return them to the wild.
But some in the marine science community are asking whether putting such animals back into the ecosystem is the right thing to do.
“Where are those sea lions going to go? Right now, there just isn’t enough food out there,” says Josiah Clark, a consulting ecologist in San Francisco who has studied birds and marine life for more than 20 years. Clark says starving predators like the sea lions are a clear symptom of serious problems lower down on the food chain. In this case, climate change may be disrupting essential weather patterns—and bottle-feeding baby sea lions, he says, is not helping.
Efforts to rehabilitate the pups might even be making life harder for the rest of the sea lion population, by placing greater pressure on already limited fish stocks, according to Jim Harvey, director of the Moss Landing Marine Laboratories near Monterey. Harvey believes the pups’ odds of survival after release may be slim.
“They’re releasing them into the wild, and the wild hasn’t changed in the time they’ve been in captivity,” he says. “They’re going right back into the same environment where they were just starving.”
California sea lions are probably more numerous now than they’ve been at any time in the past 13,000 years, according to Bob DeLong, a pinniped biologist with the National Oceanic and Atmospheric Administration. Humans have been hunting sea lions since the Bering land bridge allowed the first North Americans to access the continent during the last ice age. European Americans accelerated the species’ mortality with firearms, collecting sea lion pelts and turning their meat into pet food. By the early 20th century, there may have been just several thousand of the animals left.
But thanks to strict protections for marine mammals, the population of California sea lions has since exploded to 300,000 or more. There are now so many of the grizzly-sized carnivores along the West Coast that they’re pushing up the Sacramento River into the farmlands of the Central Valley. In places, they may be threatening the success of ailing salmon and steelhead runs, prompting officials to selectively shoot the animals. As of 2008, the International Union for Conservation of Nature listed the California sea lion as a species of least concern, noting that the "population is abundant and probably reaching carrying capacity in most of its wide geographic distribution."
And now, with a steep decline in sardine abundance, that plethora of sea lions can’t find enough to eat. Lactating mothers are especially dependent on high-fat species like sardines, and when their multi-day sojourns at sea last longer than normal, their famished pups may leave the rookeries—mostly at the Channel Islands—to try and feed themselves.
These are the animals showing up en masse on mainland beaches, where they may skirmish with off-leash dogs, crawl under beach home decks or curl up in flower pots. The pups are basically doomed to die unless assisted, a fact that many biologists accept as nature at work. Sean Van Sommeran, founder of the Pelagic Shark Research Foundation in Santa Cruz, says a better use of time would be to simply pick up trash—especially plastic—off the beach, and let nature have its way with sea lion pups.
“It’s a tough planet,” he says. “Nine out of ten Bambis don’t make it.”
In general, scientists who have placed identification markers on young pups for inclusion in long-term population studies will remove stranded animals from their data sets. Though they may later reintegrate into the wild through luck or human intervention, from a research perspective, they are considered to be dead. “Because we’re trying to study the biology of the system, we have to remove those animals from our sample, because, all of a sudden, nature has not carried out its intent,” DeLong explains.
At The Marine Mammal Center, three miles north of the Golden Gate Bridge, hundreds of volunteers have helped with nearly 700 pups so far this year. The sea lions are being fed ten pounds of herring daily, fish that are imported from Alaska to avoid utilizing California’s scarce fish stocks, according to Claire Simeone, a conservation medicine veterinarian with the facility. After about six weeks of care, the pups may be ready to go back to the wild. The center has been treating sea lions recovered from all parts of the state but releasing them only in the state’s more northern waters, where small fish currently seem to be more abundant. How many of the treated animals will survive after release is not known, Simeone says.
For science, the rescue efforts could provide a net benefit, says Harvey, of the Moss Landing Marine Laboratories: “The treatment of so many individuals is creating a huge database of information on sea lions,” Harvey says. Seals and sea lions collected and studied by The Marine Mammal Center through the decades have provided opportunities to study disease, toxicity and shark predation, says Peter Pyle, a biologist with the Point Reyes Bird Observatory. For instance, he and several colleagues produced a paper in 1996 analyzing white shark bites on pinnipeds that were delivered to the center for analysis. And Simeone of the Marine Mammal Center adds that they are working with research institutions around the world to use data from their rehabilitation efforts to see how animal diseases might relate to humans. For instance, studying cancer in stranded sea lions has led to a better understanding of cervical cancer in people, she says.
"It's not a question of either doing rescue work or mitigating the effects of climate change. It is precisely the Center's work in researching how a top predator is starting to fail that puts a magnifying glass to the larger issues of climate change, pollution and overfishing that are destroying our oceans,” Simeone says in an emailed statement. "This work aids in understanding the effects of unprecedented changes in the environment and hopefully in mitigating and reversing them through increased scientific knowledge and shifts in environmental policy.”
Highly publicized rescue work also draws in donations that may aid species in greater need. “That allows them to do important work when it’s needed,” says Ainley, who works with the ecological consulting firm H.T. Harvey & Associates. The Marine Mammal Center, for example, is facilitating conservation efforts aimed at saving the tiny and extremely rare porpoise called the vaquita as well as the Hawaiian monk seal.
Shawn Johnson, the Marine Mammal Center’s director of veterinary science, says the fact that top predators are failing demands attention. Studying the sick sea lion pups—and, while they’re at it, rehabbing them—can help scientists understand what is happening in the troubled waters off California. Yet there remains a lingering feeling among conservationists that one of the most abundant pinnipeds on the planet has become a distraction from the underlying cause of the crisis.
“People want to help,” says Clark. “People feel the pain in the world and they want to make a difference, but they’re doing it wrong. It’s like if you polished the brass doorknob on a house that’s fallen down. They’re dealing with the problem in reverse.”
Update 4/8/2015: This story now includes additional comment on the scientific benefits of rehabilitating sea lions from the Marine Mammal Center.