2010 is shaping up to be a tough year for Calfornia Sea Lions. Many prematurely born pups have already been found dead. Live strandings are far above normal in Monterey and Santa Cruz Counties, as reported by the Marine Mammal Center.
A researcher at the University of California at Santa Cruz has documented about 300 aborted premature fetuses on Ano Nuevo Island. Usually they about 10-20. Numbers of dead stranded yearlings are also high, for 2009 and 2010. Those have apparently died of malnutrition.
California Sea Lions usually give birth in large rookeries on off-shore islands. Some full-term births have taken place along the populated coastline this year: on the Coast Guard jetty in Monterey, under the Santa Cruz boardwalk, on San Francisco's Pier 39. Mothers often abandon these pups, but some have been observed nursing, so that's cause for hope.
Researchers aren't certain as to what the cause is. The warm El Nino water temperatures may be the cause. The warmer coastal waters drive the sea lions' prey fish, sardines and anchovies, further out to the colder waters offshore. The pregnant mothers use up too much energy swimming further to catch prey. They aren't able to nourish the fetus adequately and can't make it back to the rookery to give birth. Yearlings aren't able to catch enough food to survive.
Domoic acid poisoning, a neurotoxin produced by diatoms, may also be a factor. The algae are eaten by small fish, and the toxin accumulates as predators and prey move up the food chain. The neural effects include disorientation, lethargy and seizures. Domoic acid poisoning may be transferred from mother to pup, and has been associated with premature births. Combined with the difficulties of finding prey due to the El Nino, it could be contributing to the deaths.
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