Crash in sardine population may explain sick sea lion pups

Pew Charitable Trusts graphic

Colder water in the Pacific beside California may be why we're seeing more giant squid and kinds of whales — the annual gray whale migration toward Baja California is booming this year, by the way — but it may also be part of the cascading causes of an alarming crash in the numbers of sardines. The lack of oily sardines may be behind the 1,600 or so malnourished young sea lions found along the the coast last year — the mothers may have been forced to eat less-fatty prey and thus could not produce as much or as nutritious milk. Brown pelicans on the Channel Islands are also showing signs of hunger that some scientists think is related to the sardines. The schools of small fish turn out to be pretty important in the Pacific ecosystem off the West Coast, as well as to fishermen, but sardines are becoming scarce. "It's a terribly difficult scientific problem," said Russ Vetter, director of the Fisheries Resources Division at NOAA's Southwest Fisheries Science Center, in an LA Times story.

The decline has prompted steep cuts in the amount fishermen are allowed to catch, and scientists say the effects are probably radiating throughout the ecosystem, starving brown pelicans, sea lions and other predators that rely on the oily, energy-rich fish for food.

If sardines don't recover soon, experts warn, the West Coast's marine mammals, seabirds and fishermen could suffer for years.

The alarm was sounded in December by a report from the Pew Charitable Trusts, which has a project monitoring Pacific fisheries.

The Pacific coast of North America supports one of the most vibrant and diverse marine ecosystems on Earth, largely because of the presence of thick schools of small prey fish such as Pacific sardines. Unfortunately, this crucial forage fish appears to be in the midst of a severe population decline. Its absence will be felt by dozens of species of West Coast seabirds, whales, sharks, dolphins, and commercially important fish such as salmon and tuna that depend on sardines as a major food source. In addition, because sardines have been a staple of commercial purse-seine fishing on the West Coast, their decline raises the potential for fishing pressure to shift to similar, but more abundant, schooling species of forage fish....

Populations of forage fish along the West Coast fluctuate widely, so a species can be abundant one year and dwindle unexpectedly the next. That’s because forage fish are highly dependent on the upwelling of cold nutrient- rich waters to stimulate the growth of phytoplankton, their primary food source.

The Pacific sardine fishery, immortalized in John Steinbeck’s novel Cannery Row, collapsed notoriously the 1950s. The November 2013 population estimate of 378,000 tons is the lowest in more than a decade, far below the peak of 1.5 million tons estimated in 2000 and a major decline by historical standards. Geological records of fish scales deposited off Southern California indicate that the unfished sardine population fluctuated naturally between a low of 400,000 tons to as much as 16 million tons.

Forage fish account for more than one-third of the global catch of marine fish and are mostly used for industrial purposes such as feed for livestock, poultry, and farmed fish rather than being directly eaten by people. Most forage fish landed on the West Coast are exported for purposes such as bait in tuna longlining in Asia or as feed for farmed fish. In 2012, the Lenfest Forage Fish Task Force, a group of eminent scientists from around the world, calculated that forage fish worldwide are worth twice as much when left in the water—about $11.3 billion—as they are when caught because of their value as food for commercially important predators

Check out Pew's report, Pacific Sardines: Critical Food Source in Steep Decline

More by Kevin Roderick:
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Recent Pacific stories on LA Observed:
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