Gulf Oil Spill-Settlement

In this June 15, 2010 file photo, a member of Louisiana Gov. Bobby Jindal's staff wearing a glove reaches into thick oil on the surface of the northern regions of Barataria Bay in Plaquemines Parish, La. Over BPAAAAC/AAAAAAAAs objections, a federal appeals court on Friday Jan. 10, 2014, upheld a judge's approval of the companyAAAAC/AAAAAAAAs multibillion-dollar settlement with lawyers for businesses and residents who claim the massive 2010 oil spill in the Gulf of Mexico cost them money. (AP Photo/Gerald Herbert, File)

Crude oil from the 2010 Deepwater Horizon disaster causes severe defects in the developing hearts of bluefin and yellowfin tunas, according to a new study by a team of National Oceanic and Atmospheric Administration and academic scientists.

The findings, published in the Proceedings of the National Academy of Sciences on the 25th anniversary of the Exxon Valdez oil spill, show how the largest marine oil spill in United States history may have affected tunas and other species that spawned in oiled offshore habitats in the northern Gulf of Mexico.



BP spokesman Jason Ryan issued a statement Friday afternoon challenging the study, saying it "provides no evidence to suggest a population-level impact on tuna, amberjack or other pelagic fish species in the Gulf of Mexico."

Atlantic bluefin tuna, yellowfin tuna, and other large predatory fish spawn in the northern Gulf during the spring and summer months, a time that coincided with the Deepwater Horizon spill in 2010. These fish produce buoyant embryos that float near the ocean surface, potentially in harm's way as crude oil from the damaged wellhead rose from the seafloor to form large surface slicks.

The new study shows that crude oil exposures adversely affect heart development in the two species of tuna and an amberjack species by slowing the heartbeat or causing an uncoordinated rhythm, which can ultimately lead to heart failure.

James Wink of Mobile caught this 182-pound yellow fin tuna on the closing day of the 2012 Alabama Deep Sea Fishing Rodeo. It not only set a rodeo record, it set a lot of mouths to watering with the prospect of fresh tuna steaks. (File photo)

"The timing and location of the spill raised immediate concerns for bluefin tuna," said Barbara Block, Ph.D., a study coauthor and professor of biology at Stanford University. "This spill occurred in prime bluefin spawning habitats, and the new evidence indicates a compromising effect of oil on the physiology and morphology of bluefin embryos and larvae."

Recent studies are increasingly painting a more detailed picture of how oil-derived polycyclic aromatic hydrocarbons act (PAHs) on the heart. Earlier this year, the Stanford-NOAA team showed in a related paper published in Science that Deepwater Horizon crude oil samples block excitation-contraction coupling -- vital processes for normal beat-to-beat contraction and pacing of the heart -- in individual heart muscle cells isolated from juvenile bluefin and yellowfin tuna.

"We now have a better understanding why crude oil is toxic, and it doesn't bode well for bluefin or yellowfin embryos floating in oiled habitats," Block said.

Crude oil is a complex mixture of chemicals, some of which are known to be toxic to marine animals. Past research has focused in particular on PAHs, which can also be found in coal tar, creosote, air pollution and stormwater runoff from land. In the aftermath of an oil spill, PAHs can persist for many years in marine habitats and cause a variety of adverse environmental effects.

Developmental abnormalities were evident in bluefin and yellowfin tunas at very low concentrations, in the range of approximately one to 15 parts per billion total PAHs. These levels are below the measured PAH concentrations in many samples collected from the upper water column of the northern Gulf during the active Deepwater Horizon spill phase.

Severely affected fish with heart failure and deformed jaws are likely to have died soon after hatching. However, the NOAA team has shown in previous work that fish surviving transient crude oil exposures with only mild effects on the still-forming heart have permanent changes in heart shape that reduce swimming performance later in life.

"This creates a potential for delayed mortality," Incardona said. "Swimming is everything for these species."

The research was funded by NOAA as part of the on-going Natural Resource Damage Assessment for the Gulf ecosystem following the April 20, 2010 Deepwater Horizon oil spill. Contributing to the findings in addition to NOAA and Stanford University were researchers from the University of Miami's Rosenstiel School of Marine and Atmospheric Sciences and the University of the Sunshine Coast in Queensland, Australia.

This post was updated at 3:47 p.m. to include a statement from a BP spokesman.