NOAA report links Exxon oil spill, fish defects

ANCHORAGE, Alaska – Federal scientists have determined that extremely low levels of crude oil spilled by the Exxon Valdez caused heart problems in embryonic fish, a conclusion that could shape how damage is assessed in other spills.

In a study published Tuesday in the online journal Scientific Reports, researchers from the National Oceanic and Atmospheric Administration found that embryonic herring and salmon exposed to low levels of crude oil developed misshapen hearts.

“Metabolically, they’re different,” said John Incardona, a research toxicologist at the Northwest Fisheries Science Center in Seattle. “They can’t grow as well. They can’t swim as fast.”

The defects and subsequent vulnerability may explain why the herring population crashed several years after the spill in Alaska’s Prince William Sound and has not recovered, scientists said.

The 986-foot Exxon Valdez struck a charted Bligh Reef on March 24, 1989, spilling 11 million gallons of crude oil. Oil fouled shoreline spawning habitat of herring and pink salmon, the two most important commercial fish species in Prince William Sound.

Pink salmon declined but recovered. The herring population collapsed three to four years after the Exxon Valdez ran aground.

The fish is a key species because it is eaten by salmon, seabirds and marine mammals. Four years after the spill, the estimated herring population based on modeling shrank from 120 metric tons to less than 30 metric tons.

For the study, the scientists temporarily exposed herring and salmon embryos to low levels of Alaska North Slope crude oil before placing them back into clean water. The threshold for harm in herring was remarkably low, Incardona said.

“Herring in particular, they are really, really very sensitive,” in part because their eggs and yolk sacs are so much smaller.

After exposure, scientists transferred fish embryos to clean water, let them grow for seven to eight months, and tested their swimming speed as a measure of cardiorespiratory fitness. Fish exposed to the highest levels of oil swam slowest, likely making them easier targets for predators.

In water samples collected in Prince William Sound during the 1989 herring spawning season, 98 percent had oil concentrations above the level that caused heart development problems among herring in the study. The findings should contribute to more accurate assessments of other spills.

“And not just other spills,” Incardona said. “For us down here in Puget Sound, one of our big concerns is just urbanization. … Large spills and everyday chronic pollution from fossil fuel use are potentially producing the same kinds of effects.”