Thick, tarry fuel oil disgorged into San Francisco Bay from a damaged cargo ship in 2007 was surprisingly toxic to fish embryos, devastating the herring population that feeds seabirds, whales and the bay's last commercial fishery, scientists reported Monday.
Although the bay's herring spawning grounds are now free of toxic oil, studies have found that the moderate-size spill of 54,000 gallons had an unexpectedly large and lethal effect.
The culprit, a common type of ship fuel called "bunker fuel," appears to be especially toxic to fish embryos, particularly when exposed to sunlight, according to a study published Monday in the Proceedings of the National Academy of Sciences.
"That's the big lesson," said John Incardona, a toxicologist with the National Marine Fisheries Service. "This bunker oil is literally the dregs of the barrel, and it's much more toxic than crude oil."
The container ship Cosco Busan spilled low-grade bunker fuel after it sideswiped the San Francisco-Oakland Bay Bridge on a foggy November morning four years ago. This type of sludge-like fuel is cheap and thus popular among operators of commercial shipping fleets that transport raw materials and goods around the globe.
Scientists have traditionally focused on larger crude oil spills, such as last year's Deepwater Horizon drilling rig blowout in the Gulf of Mexico or 1989's Exxon Valdez tanker disaster, in which 11 million gallons of oil were discharged into Alaska's Prince William Sound. The Exxon spill is suspected of wiping out the sound's herring fishery, which has never bounced back.
From studies in Alaska, scientists knew that oil could cause heart deformities to developing herring in their embryonic sacs.
But after examining herring embryos placed in cages in shallow waters near the Cosco Busan spill site, researchers were surprised to find that nearly all had died, and their ...