Sea Lion Pups Starving Along California Coast
March 29, 2015
By Courtney Mattison
Sea lion pups are starving and washing up on California beaches for the third consecutive year. Every winter since January 2013, throngs of sickly young sea lions have stranded themselves on beaches and in seaside backyards and parking lots in California coastal communities, often weighing less than half of their ideal body weight. “They’re extremely emaciated, basically starving to death,” says veterinarian Shawn Johnson of the Marine Mammal Center in Sausalito.
Over 2,000 emaciated, dehydrated and diseased sea lion pups have washed up on California’s shores from San Diego to San Francisco since the beginning of 2015. For the two-month period of January and February this year, California sea lion strandings were almost 20 times the average stranding rate.[i] Last year, it took until April for the Sausalito Marine Mammal Center to receive 100 distressed sea lions, but this year the center saw that many individuals in the first half of February alone.[ii] Rehabilitation centers including the Sausalito Marine Mammal Center and the Pacific Marine Mammal Center in Laguna Beach, CA are overwhelmed. “These animals are coming in really desperate. They’re at the end of life. They’re in a crisis … and not all animals are going to make it,” said Keith A. Matassa, executive director at the Pacific Marine Mammal Center, which has taken in nearly 300 pups so far this year compared to 28 during the same time period last year.[iii]
Because these strandings are beginning so early – before sea lion pups are usually weaned from their mothers’ fattening milk – marine mammal centers have already spent considerable resources before peak stranding season even begins in April, when pups are typically weaned. The rehabilitation process can take months, with sick pups feeding on either whole fish or, if they’re too young or weak, being tube-fed pureed herring, Pedialyte, vitamins and milk three or four times a day after starting out with a simple broth of hydrating fluids and dextrose. As the pups get stronger and put on weight they must learn how to catch fish for themselves and graduate from “fish school” before being released back to the wild.[iv] Sadly, many pups are beyond help by the time they are reported to authorities and must be euthanized if their body weight is less than one third of what’s normal for their age.
As an “indicator species,” the California sea lion (Zalophus californianus) is known to be especially sensitive to changes in offshore ocean health. Earlier this month, the National Oceanic and Atmospheric Administration (NOAA) declared the situation an “Unusual Mortality Event” and launched an investigation. Scientists are just beginning to understand this year’s combination of environmental factors playing into the event, but it appears that unusually warm sea temperatures are causing populations of sardines, anchovies and other forage fish to shift to cooler northern waters, leading nursing mother sea lions to stray farther from their pups in search of food. Most sea lion rookeries are on the Channel Islands off the southern California coast, meaning that mothers are leaving their pups for up to eight days at a time to reach cooler waters.[v] The pups, left without sustenance on the beach far before they are capable to eat (much less catch) fish, have been prematurely striking out on their own.
“It’s been a really unusually warm year, and disruptive to the normal marine food web, from Baja all the way up to Alaska,” says Nate Mantua of NOAA’s Southwest Fisheries Science Center. This year, NOAA reports that coastal waters off the western United States are 2-6°F above the long-term average.[vi] This change is likely due to large-scale El Niño climate patterns affecting the Pacific Ocean, making waters off the West Coast warmer and less productive, meaning decreased food availability for the entire food web.[vii] NOAA’s 2015 State of the California Current Report delivered to the Pacific Fishery Management Council suggests that high sea lion pup mortality – in addition to high seabird mortality in the Pacific Northwest – may be an early indicator of the shift, which is expected to affect numerous other marine species including the Pacific salmon.[viii]
During the 1998 El Niño event, approximately 2,500 sea lion pups washed up on California beaches. This year’s El Niño event is not expected to be as severe, but total sea lion mortality numbers may surpass the 1998 record according to Justin Viezbicke, coordinator for NOAA’s California Stranding Network.[ix] “The tricky part is we’re putting them back into the same environment that they just came from. And that’s going to be a challenge for them,” Viezbicke said.[x]
El Niño may not be the entire problem, however. When this latest trend in sea lion strandings began in 2013, waters off the West Coast were experiencing a period of high productivity rather than the austerity of El Niño. “The forage fishery in California is a big industry,” says Mission Blue Board Director Shari Sant Plummer. “Could it be that the valuable market for these fish, too low on the food chain for our dinner, but a popular source of food for livestock, fish farms, fertilizer, and even those omega 3’s the doctor told you to take, could be overfished?”[xi] The pattern doesn’t appear to be linked to an environmental toxin or infectious disease, leading some researchers to believe that overfishing is contributing to the fish shortage. The California forage fishery is recognized as being very sustainably managed,[xii] but fish caught in the high seas 200 nautical miles off the U.S. coast are significantly less protected.
California residents interested in helping to rehabilitate sea lions can volunteer at or donate to marine mammal rescue centers. Most centers are working at full capacity and could use extra help. Learn where and how to volunteer HERE.
Featured image (top): In 2013, the Marine Mammal Center in Sausalito, CA, took in 45 malnourished sea lion pups (including those pictured above), seven harbor seals, 12 elephant seals and two fur seals from centers in southern California that were overcrowded and needed more room to accommodate incoming patients. Photo © Ingrid Overgard / Marine Mammal Center.