Beginning early this year, people visiting beaches along California’s central and southern coasts, particularly from Santa Barbara to San Diego, found severely undernourished Sea Lion pups washed up on the sand. Some clinging to life. Many already dead.
Sadly, 2016 marks the fourth year in a row that malnourished juvenile Sea Lions have overwhelmed rescue facilities. Strandings in January and February grew particularly high, exceeding the average number set from 2003 to 2012 by nearly 400%. By June, the number of strandings fell but still remained 200% higher than historical levels.
Gregarious crowd pleasers, Sea Lions frequent the entire Pacific coast—from Canada to Mexico—delighting those visiting beaches, marinas, and piers with their antics. At beaches and open waterways, people watch them diving for food, porpoising through the water, and floating just beneath the surface with one flipper exposed. At some marinas, they’ve laid claim to floating and permanent piers, hundreds of sea lions lying right next to and on top of one another in “haul outs” that include sea lions of all ages—from adult males (700+ pound and nearly 8-feet long) to females (roughly 200 pounds and about 6-feet long) and smaller pups and juveniles. Some sleeping. Others, usually the majority, barking loudly.
But during the last few years, far fewer sea lions have frequented popular haul outs, and 2016 marked the fourth consecutive year that the National Oceanic and Atmospheric Administration (NOAA) declared an Unusual Mortality Event because of the high number of mortalities in California.
Researchers investigated numerous possible explanations for these mortality events, but as a 2015 National Geographic article—Mysterious Sea Lion Die-Off Strikes again on California Coast—explains,
Scientists still don’t know what triggered such a precipitous and ongoing struggle; they’ve ruled out known diseases and environmental toxins, which might be expected to affect more than just pups. Some researchers question whether the sea lion population has grown so large that the offshore environment simply can’t sustain their numbers.
But scientists have determined that a decline of forage fish—specifically the fatty and nutrient-rich sardines that represent a highly important food source for nursing females—is the principal culprit.
The sardine decline is “causing nursing sea lion mothers to swim farther in search of fish. Those extended forays keep sea lion moms away from their pups. For so long, perhaps, that the tiny animals wait on their beaches and starve until they eventually strike out on their own, long before they’re ready to tackle the Pacific Ocean.”
But what has precipitated the decline?
Rising ocean temperatures—likely a result of climate change and exacerbated this year by the now-abating El Niño event—may be forcing sardines (and other fish) to relocate to areas with cooler water further out to sea. NOAA scientists are also investigating a “massive, persistent patch of warm ocean water that has settled offshore and may be knocking the ecosystems of western North America off-kilter.”
Other NOAA researchers believe that overfishing may be responsible for the decline. In fact, in 2010, as reported by Ben Enticknap in Oceana, “two NOAA scientists (Zwolinski and Demer 2012) published a paper predicting the collapse of the Pacific sardine population.” Three years before the first Unusual Mortality Event.
By comparing the current sardine decline with historic scientific literature, they determined that a drop in water temperature in the northern Pacific ocean has, on numerous occasions in the past, drawn sardines from the California coast to the northern Pacific. When this phenomenon began recurring several years ago, the fishing industry reacted to the decline—as it had in the past—by “progressively higher exploitation rates targeting the oldest, largest, and most fecund fish.” In other words, the commercial fish industry not only further depleted the sardine population; they also significantly reduced the very breeding population that could help it to rebound from the decline. “Thus, a near-term recovery of this important stock is unlikely,” Zwolinski and Demer concluded.
The California Sea Lion population has been growing, so the strandings and deaths that have occurred over the past four years (even adding to them the number of pups that likely died at sea or at off-shore rookeries) is unlikely to threaten the survival of the species. But what if the rise in ocean temperature just off the California coast becomes more permanent? Or increases? Although “U.S. fishery managers have reduced sardine catches in recent years,” as recently as 2014, “the federal fishery management council voted to change its harvest management regime to allow for [an] overall increased sardine harvest, while ignoring calls to address the international distribution of the sardine population and the drastically low cutoff for when fishing ultimately stops,” according to Entiknap.
Still more disturbing, the Sea Lion is far from the only species affected by the decline in sardines. “Biologists also suspect the drop is hurting brown pelicans that breed on California’s northern Channel Islands. The seabirds, which scoop up sardines close to the ocean surface, have shown signs of starvation and have largely failed to breed or rear chicks there since 2010,” according to West Coast Sardine Crash Could Radiate throughout Ecosytem. What’s more, “if sardines don’t recover soon, experts warn, the West Coast’s marine mammals, seabirds and fishermen could suffer for years.”
We need to find a way to balance the economic benefit of commercially valuable fish with the systemic value of the marine ecosystem that makes that resource available to us. How long can we continue to exploit the seeming abundance of life in the oceans before the populations of far more species collapse? Are we prepared for far more strandings? Of Sea Lions? Elephant Seal? Pelicans? Dolphins? Orca?
To learn more about the California Sea Lion and the issues surrounding the strandings of Sea Lion pups, you may find the following articles of interest:
• California Sea Lion [Marine Mammal Center]
• California Sea Lion [Wikipedia]
• Young California Sea Lions Still Struggling to Survive
• Mysterious Sea Lion Die-Off Strikes Again on California Coast
• Why are California Sea Lion Pups Starving?
• West Coast Sardine Crash Could Radiate throughout Ecosystem
• 2016 Elevated Californa Sea Lions Strandings in California: FAQs
• “Unusual mortality event” Is Declared for the California Sea Lion
• 2013-2016 California Sea Lion Unusual Mortality Event in California
• California Sea Lion Crisis Lingers; Falling Births Reported
• A Cold Oceanographic Regime with High Exploitation Rates in the Northeast Pacific Forecasts a Collapse of the Sardine Stock