Dolphins in the area of BP's 2010 oil spill suffered from extreme health problems, with many not expected to survive, a study conducted a year after the spill shows.

Nearly half of the 32 dolphins examined from Louisiana's Barataria Bay in 2011 were found to be in "guarded or worse" condition, according to the study led by the National Oceanic and Atmospheric Administration and published Wednesday in the journal Environmental Science and Technology. Seventeen percent were listed as "grave" and "not expected to survive."

The Deepwater Horizon spill dumped up to four million barrels of oil (according to government estimates) in the Gulf of Mexico's Barataria Bay. The study was conducted in August 2011 as part of the Natural Resource Damage Assessment (NRDA) by a team of government, academic and non-governmental researchers.

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The condition of the Louisiana dolphins was assessed by veterinarians and compared with the health of dolphins from Sarasota Bay, Fla. who were tested as a control group. Fourteen of the 29 Louisiana dolphins examined in 2011 were in guarded, poor or grave condition. That compared to one out of 15 examined from Sarasota Bay.

Among the afflictions found in the Louisiana dolphins were severe lung disease and deficient levels of adrenal stress-response hormones. A quarter of the Louisiana dolphins were also underweight. The researchers said that many disease conditions seen in the Barataria Bay dolphins are rare but consistent with oil exposure and toxicity.

The research is among the strongest evidence yet to link the oil spill to sick dolphins.

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"I've never seen such a high prevalence of very sick animals — and with unusual conditions such as the adrenal hormone abnormalities," lead author Dr. Lori Schwacke, a chief with NOAA Centers for Coastal and Ocean Sciences, said in a NOAA press release.

BP financed the study but is disputing its finding. A BP spokesman told the Wall Street Journal that NOAA "still hasn't provided BP with any data demonstrating that the alleged poor health of any dolphins was caused by oil exposure."

NOAA researchers acknowledge in the study that dolphin deaths had been occurring in the region since February 2010 -- with at least 1,050 marine animal strandings documented before the spill. Schwacke and the others wrote they "cannot dismiss the possibility that other pre-existing environmental stressors made this population particularly vulnerable to effects from the oil spill."

The researchers looked at alternative explanations for the Louisiana dolphins' conditions, including exposure to other man-made chemicals that have been measured in high concentrations in marine mammals.

But blubber samples from the Barataria Bay dolphins showed relatively low concentrations for these common culprits as compared with other coastal dolphin populations. In fact, levels of these chemicals were lower than in the sampled Sarasota Bay dolphins.

Photo: Dolphins swimming in the Gulf of Mexico after the 2010 BP oil spill. Credit: NOAA