March 12, 2011 in Nation/World

Die-off of fish still a mystery

Researchers believe low oxygen levels to blame
Tony Barboza Los Angeles Times
 

LOS ANGELES – Sardines that suffocated and died en masse this week in Redondo Beach’s King Harbor have tested positive for a powerful neurotoxin that scientists believe may have distressed a million or more fish off the Los Angeles coastline and caused them to swim chaotically into the marina.

Researchers still believe critically low oxygen levels, not the toxin or an algae bloom, caused the fish to suddenly die Monday night in the Redondo Beach marina.

But the discovery of domoic acid in dead fish – reported Friday by University of Southern California biologists – could help explain why millions of sardines swam into the harbor in the first place.

Domoic acid is often found in the stomachs of fish that have been feeding on plankton on the ocean’s surface during toxic algae blooms. The toxin has been linked to neurological disorders, illnesses and deaths of seabirds, sea lions, sea otters and whales. When it accumulates in edible fish and shellfish, it can sicken humans.

More than 35 tons of dead sardines have been scooped, pulled or vacuumed from the marina, but officials believe an equal number may have settled on the ocean floor. Workers are racing to cleanse the harbor, fearing that if the dead fish are left to decompose, they could trigger an algae bloom themselves.

Scientists are also looking into another theory: that a pulse of oxygen-starved ocean water swept into the harbor just before the die-off and worsened conditions for the fish.

“We know that low oxygen killed them, so the question is: Why was there low oxygen?” USC professor David Caron said. “Were the waters charged with low oxygen to begin with?”

The California Department of Fish and Game has blamed the die-off on oxygen deprivation and is also testing fish for toxins at its animal forensics laboratory near Sacramento, where results are not expected until next week.

“It’s going to be a full-on CSI thing with these fish,” said spokesman Andrew Hughan. “We’re trying to find out what drove them and why they swam in there. There’s the predator theory, there’s the rough-water theory; it could be anything, and there may never be a definitive answer.”

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