Oil spill is prime suspect in hundreds of dolphin deaths
Published: Wednesday, April 18, 2012 at 5:51 p.m.
Last Modified: Thursday, April 19, 2012 at 1:19 p.m.
Dying dolphins and whales in the northern Gulf of Mexico provide a grim reminder that the ecosystem there still has not recovered two years after the BP Deepwater Horizon oil disaster.
More than 600 dolphins have been found fatally ill or dead since oil reached the Louisiana shoreline following the explosion of the Deepwater Horizon rig on April 20, 2010. This year alone, nearly 100 have washed up dead or deathly ill, mostly in Louisiana's Barataria Bay, where oil lingers in the marshes and sediment.
Signs increasingly implicate BP oil in the die-off, although federal scientists caution that they cannot yet draw a definitive link. The dolphins' illnesses are consistent with what marine biologists would expect from oil exposure: weight loss, anemia, low blood sugar, lung and liver disease, and dangerous hormone imbalances.
Dolphins remain healthy in areas of the Gulf not touched by oil, including Sarasota Bay, where scientists have tested for similar problems for comparison.
"We are concerned that many of the dolphins we evaluated in Barataria Bay are in such poor health that they are not likely to survive," Lori Schwacke, lead investigator for the dolphin studies and chief of the National Ocean Service's Oceans and Human Health branch, said during a recent news conference.
Dolphins are among the most visible casualties of the disaster, which killed 11 people and sent more than 200 million gallons of crude into the Gulf. They also serve as sentinels for the entire ecosystem, which sustained damage beyond what is visible from shore or even the surface of the sea.
The oil killed deep-sea corals, poisoned plankton that forms the basis of the food chain and caused lesions on popular sport fish, among other reported observations. But scientists expect damage from the spill to reveal itself over time measured in years — perhaps even decades.
Besides the dolphins, whales, sea turtles and other creatures that scientists found dead in the months after the spill, many more likely died at sea, out of sight, said Matthew Huelsenbeck, a marine scientist with the environmental advocacy group Oceana. Citing past research, he estimated that the 600 dolphins stranded since the disaster represent 2 percent of the overall number killed.
Craig Savage, a BP spokesman, emphasized the unknown and said federal scientists still need to evaluate more data before making conclusions about the dolphin deaths.
Fate of the oil
The Deepwater Horizon explosion severed a riser pipe that tapped into an oil reservoir a mile deep and about 60 miles offshore of the Mississippi Delta. Oil erupted from the pipe for three months, spoiling the Gulf with more than 200 million gallons of crude, one of the planet's largest oil spills.
Nearly 2 million gallons of toxic dispersants were applied at the pipe and at the surface to dissolve the oil. Despite the heavy use of dispersants, oil coated about a thousand miles of coastline in the northern Gulf from Texas to the Florida Panhandle.
Only a fraction — about 15 percent of the oil and gas released — made it to the surface, federal scientists estimated in a report this year. Most of it lingered in underwater plumes that left large parts of the gulf bottom littered with a thick rain of oily debris. The fate of about a quarter of the oil is still unknown.
BP will pay tens of billions of dollars in civil settlements and government fines and penalties for the environmental, economic and human health damage caused by the spill. On Wednesday, BP agreed to pay $7.8 billion to resolve claims from 100,000 individuals and businesses for economic, property and medical losses, according to the Associated Press.
Federal, state and local governments around the Gulf are still collecting evidence of spill damage to make sure BP pays to restore lost natural resources — a cost likely in the tens of billions of dollars. BP will also be liable for fines under the Clean Water Act up to about $20 billion.
While most of the visible oil has vanished, some of it still lies in marshes and sediments; stormy weather continues to deposit tarballs on beaches.
Research by Jeff Chanton, a professor of oceanography at Florida State University, shows that oil settled in sediments generally southwest of the spill site.
Evidence of oil was also found in the bottom of the food chain, particularly in Louisiana estuaries, where plankton, oysters and catfish contained traces of oil carbon.
"Somehow the oil carbon is getting into the food web of the Gulf," said Chanton, whose work did not focus on toxins.
In August, researchers evaluated the health of 32 dolphins in Barataria Bay, which received heavy and prolonged exposure to the oil.
"The dolphins that we sampled from Barataria Bay were overall not in good health," Schwacke said. One of the evaluated dolphins was found dead on Grand Isle in January, severely emaciated.
They had anemia, low blood sugar, liver disease, lung disease and, most importantly, low stress hormones — a symptom of oil exposure documented in experimental studies on mink.
Stress hormones are critical for essential body functions, and imbalances can lead to organ failure and death.
Similar health evaluations are under way in Alabama and Mississippi, where dolphin deaths also remain higher than normal. Scientists did not have data available from that work.
It is not surprising that dolphins are still sick and dying, said Huelsenbeck, the Oceana marine scientist.
Because oil remains in the sediments, the dolphins are still getting exposed to it and eating other animals that are still getting exposed to it, he said.
"They are basically going out and sampling different species," Huelsenbeck said. "They're constantly having to live in the environment. Imagine having to live in a living room with trash and eating that trash, too."
Sarasota Bay's dolphins are playing an important role in the oil spill research, primarily because they were not exposed.
Federal researchers consider Sarasota Bay dolphins a reference population.
"The idea is, you're trying to look for significant deviations from an unperturbed population," said Randall Wells, director of the Sarasota Dolphin Research Program at Mote Marine Laboratory.
The health differences between the dolphins in Sarasota Bay and the dolphins in the northern Gulf are very clear, Wells said.
The biggest question is how much of the illness in dolphins to the north can be attributed to the Deepwater Horizon oil and how much is due to chronic exposure over time. That question will be difficult to answer because the dolphins in the northern Gulf were not well studied before the spill.
An unusual spike in dolphin strandings began about three months before the Deepwater Horizon accident, further complicating the issue. The carcasses of those animals were more decomposed, making it difficult to determine whether they suffered from the same illnesses, scientists said last year when several dolphin tested positive for brucellosis.
"It's very tricky to try to sort out what is going on up there," Wells said. "The importance of having longer-term studies in place is something that doesn't receive the appreciation that it should."
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