Information sent today from Promed-Mail indicates that domoic acid is indeed implicated in the sea-lion die-off in California. Domoic acid is a neurotoxin produced by certain algal blooms that can bioaccumulate as it moves up trophic chains. Fisheries and Oceans Canada has a terrific resource page with extensive references on domoic acid. The report on the die-off comes from Southern California via the Ventura County Star, but it seems likely that it is related to the Central California die-off I wrote about last week. Also implicated -- as I suggested last week -- is a shortage in fish resulting from the El Niño warmed Pacific waters.
I just read this story about the alarming number of dead sea lions showing up around Monterey Bay in Central California. We were just down at Moss Landing State Beach and saw for ourselves evidence of this die-off. The sea lion had a couple of bites taken out of it but its unclear whether they were pre- or post-mortem.
A likely candidate for the cause of this excess mortality is food shortages due to unusually warm waters from the recent El Niño conditions, though no one has yet (to my knowledge) ruled out infectious disease, domoic acid, red tide, or any of the other possible causes of such die-offs.