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Sea Lion Strandings Up Along So. Calif. Coast This Year

April 5, 2013

By WeatherBug Meteorologist, Andrew Rosenthal

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Marine scientists along the California coast have had their hands full this year, with an unusually high number of sea lion pups becoming stranded along the Pacific shore. What`s not clear is whether the weather is to blame for this.

The California sea lion is typically a sea-faring animal which travels the near-shore eastern Pacific in search of fish such as salmon, anchovy and herring. The most famous pack of California sea lions reside at San Francisco`s Pier 39, where they`ve slept, bellowed and piqued the curiosity of residents and tourists since 1989.

In a typical year, the sea lions beach on the California coast during the late spring months in order to give birth to pups, quickly returning to the sea for feeding trips. During the winter, the young pups will either join their mothers on a hunt or set out on their own.

However, since the start of the year more than 1,100 sea lion pups have washed ashore from San Diego to the San Francisco Bay area. This quantity is more than three times the average for the first three months of the year and higher than typical strandings for the entire year. Worse still, marine scientists are certain that these numbers are only a small fraction of the total number of distressed animals.

The situation became dire enough for the National Oceanic and Atmospheric Administration (NOAA) to declare an Unusual Mortality Event along the Golden State`s coastline last week. An Unusual Mortality Event is a broad term, defined by the Federal Marine Mammal Protection Act, as an event that "involves a significant die-off of any marine mammal population," and can be caused by anything from infection to toxins to human interaction. As the seals wash ashore at record levels, sea lion experts in southern California have acted quickly to limit the die-off by rescuing the strongest of these distressed animals. However, the increase has pushed the centers to their limits.

Scientists aren`t completely sure as to why the young animals are heading to beaches. Weather and ocean patterns have shifted since a major El Nino in 1997-98, with the water off California unusually cool. This may have caused the sea lions` fishy treats to relocate to warmer water further offshore or disappear completely.

A private oceanography company in the region has noted an overall decrease in the near-shore fish population. Studies of the seawater along the southern California coast show that populations have dropped to just 22 percent of what they were in the 1970s.

Yet another theory proposed by NOAA is that weather patterns over the past few years caused plankton numbers to shift southward, causing the fish population that feeds upon the plankton to also shift southward and decrease along the California coast. Thus, the sea lions lack a sufficient food supply as they hunt. As a result, the younger sea lions end up hungry at the end of their hunts and return to shore exhausted and unable to swim.

None of the theories offer much hope in the near-term, as it would likely take a year or more for fish populations to recover. As a result, experts anticipate that the strandings will continue at the same rate well into the summer. Further down the line, if it is a matter of a bad spawning year for the fish, next year could see the sea lions` food supply return to normal.

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Story image: Rescued sea lions rest at the Pacific Marine Mammal Center in Laguna Beach, Calif. (AP Photo/Pacific Marine Mammal Center)

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