A Deadly Toll

The Devastating Wildlife Effects of Deepwater Horizon — and the Next Catastrophic Oil Spill

The BP Deepwater Horizon catastrophe in 2010 spilled 205.8 million gallons of oil and 225,000 tons of methane into the Gulf of Mexico. Only about 25 percent of the oil was recovered, leaving more than 154 million gallons of oil at sea. In addition to the oil, nearly 2 million gallons of toxic dispersants were sprayed into the Gulf's waters. This did not actually reduce the amount of oil left in the ocean, but merely broke it into smaller particles that may actually make the oil more toxic for some ocean life and ease its entry into the food chain.

Catastrophic oil spills like Deepwater Horizon are deadly, they’re costly, and they can forever change sensitive ocean ecosystems. Unfortunately the Trump administration has refused to learn the lessons of this disaster. Instead Trump and his appointees have rolled back most offshore drilling safety rules adopted in its wake — meanwhile proposing to drastically expand offshore drilling. This all makes the next tragic spill far more likely.

So it’s more important than ever to remember Deepwater Horizon and understand its deadly toll on wildlife and habitat.



The Center for Biological Diversity combed government figures, news reports and scientific articles to assess this oil spill’s likely effects. To provide a more accurate death-toll estimate, we used multiplication factors from leading scientists to estimate how many more animals are killed than are actually observed or collected.

We found that the spill likely harmed or killed about 82,000 birds of 102 species; about 6,165 sea turtles; as many as 25,900 marine mammals; and a vast (but unknown) number of fish — from the great bluefin tuna to our nation's smallest seahorse — plus oysters, crabs, corals and other creatures.

As for habitat: Besides destroying underwater areas, including substantial habitat for the rare dwarf seahorse, the spill oiled more than a thousand miles of shoreline, including beaches and marshes. This took a terrible toll on species like seagrass, beach mice and shorebirds.

Read on for devastating details.


More than 82,000 birds may have been harmed by the spill.

At least 102 species of birds are known to have been harmed by the BP oil spill, including black skimmers, brown pelicans, clapper rails, common loons, laughing gulls, northern gannets and several species of tern. Oiled birds have been collected from west of Galveston, Texas, to south of Fort Myers, Fla.

The number of birds reported by the government as being injured by the spill represents only a portion of the total affected. The official number refers only to birds that wildlife officials collected, not including oiled birds seen but not collected — not to mention the many birds that vanished undetected. On-the-scene biologists say the official count greatly underestimates the number of birds actually harmed. In fact, scientific research shows we can assume actual mortality to be four to 11 times higher than the number of birds retrieved. A common rule of thumb estimates actual mortality at likely 10 times higher than reported.

Thus the 8,200-plus birds collected indicates that more than 82,000 may have been harmed by the spill. Of particular concern are brown pelicans and federally threatened piping plovers. Brown pelicans were removed from the endangered species list just five months before the Gulf disaster. Since the spill, 932 brown pelicans have been collected, so we can assumed that more than 9,300 have likely been harmed. Scientists reported oiled pelicans still being found a year after the spill.

Unfortunately even cleaning oiled pelicans doesn't guarantee they’ll live — and those that do survive may never reproduce. Only one dead piping plover has been collected, but oil pollution has soiled the imperiled plover's critical habitat on the Chandeleur Islands.


Approximately 6,000 sea turtles have likely been harmed by the spill.

The five sea turtles species found in the Gulf (green, Kemp's ridley, hawksbill, leatherback and loggerhead) are all federally listed as endangered or threatened, and the spill harmed them all. Oiled turtles have been collected from Port Arthur, Texas, to Apalachicola Bay, Fla., and seaside residents reported dead turtles continuing to wash up daily long after the event.

The official number of turtle deaths attributed to the spill is 1,146, but this dramatically underestimates total mortality because it doesn’t include turtles that perished undetected, and it counts only turtles collected the winter after the spill. (The feds weren’t adding turtles washing ashore the following spring — at least 87, according to media reports — due to an ongoing criminal investigation of the spill's effects.)

Scientists estimate that at least five times as many turtles die as wash up on shore, indicating that between 5,730 and 6,165 sea turtles have likely been harmed by the oil spill.


As many as 25,900 marine mammals may have been harmed by the spill.

At least four species of marine mammals have been killed by the oil spill, including bottlenose dolphins, spinner dolphins, melon-headed whales and sperm whales. Oiled marine mammals have been collected from west of Cameron, Texas, to Port St. Joe, Fla. Researchers reported carcasses washing up daily — half being stillborn or dead infant dolphins. This oil spill could impair marine mammal reproduction in the Gulf for decades, as some orca whales that were exposed to the Exxon Valdez oil spill haven’t been able to reproduce since that spill in 1989.

As with birds and sea turtles, the number of marine mammals reported as harmed by the spill grossly underestimates the true number affected. Scientists estimate that this number may be up to 50 times higher than the number collected. The government has collected 128 dead or affected dolphins and whales whose harm was attributed to the BP spill, showing that at least 6,400 marine mammals may have actually been harmed. Though oil on some of the dolphins that have washed ashore has been traced to the BP disaster, the government isn’t adding those dolphins to the official tally because of the ongoing criminal investigation. And the media has reported 390 marine-mammal strandings this spring. If these animals are included in the tally, we can estimate that up to 25,900 marine mammals may have been harmed by the oil spill.


It’s difficult to conceive of how many fish have been killed by the Gulf disaster. The widespread pollution from the BP oil spill caused fishing closures across 88,500 square miles. The Gulf of Mexico is home to more than 500 fish species, with new species continuing to be discovered. Oil and dispersed oil are toxic to all life stages of fish, and oil spills affect fish reproduction for at least decades. The BP disaster particularly threatens species that are already at risk of extinction such as Atlantic bluefin tuna, Gulf sturgeon, smalltooth sawfish and the dwarf seahorse. The oil spill occurred during the peak spawning months for the bluefin tuna, pushing this severely overfished species closer to the brink of extinction. The spill could still extirpate our nation's smallest seahorse, the one-inch long dwarf seahorse, from much of its range, as both oil and dispersants are toxic to seahorses and the seagrass they need to survive.


Oil and dispersed oil are toxic to marine invertebrates like corals, lobsters, crabs, oysters, clams, zooplankton, starfish and sand-dwelling organisms. As with fish, it’s impossible to tally how many invertebrates have been harmed by the BP oil spill. The federal government stated that resources invertebrates rely on have been injured, ecological services have been disrupted, and the potential for invertebrate recovery is limited. Researchers observed dead and dying corals in deep waters southwest of the BP well, reporting that the corals were covered with a brown substance. Fishermen reported vanishing oysters and pulling up tar balls in their shrimp nets. Oiled crabs were found on beaches.

For as long as oil pollution persists in the Gulf — for decades or longer — invertebrate life will feel the impacts. (Forty years after an oil spill off the coast of Massachusetts, fiddler crabs are still being harmed by persistent pollution.) Scientists tracing the fate of the dispersed oil in the water column have found that oil particles are being transferred within the food web, posing ongoing risks to all Gulf marine life, including tiny invertebrates.


Oil, dispersed oil and dispersants are all toxic to marine and onshore plants like seagrasses, mangroves and wetland vegetation, which provide habitat and food for many species. Oil pollution can have long-term negative effects on plants, and oil trapped in plant roots can become re-suspended in the water column during storms.

Pollution from the BP spill oiled more than 1,000 linear miles of shoreline and contaminated marshes and mangrove habitats that support nesting birds. Seagrass beds that support sea turtles and seahorses were also harmed by the spill.


Tarballs and subsurface oil on beaches threaten terrestrial mammals such as federally protected beach mice, including the Alabama, Choctawhatchee, St. Andrews and Perdido Key beach mice. Mice can ingest tar balls and subsurface oil when building their burrows, putting them at risk of tumors and lowered immune response.


The price paid by Gulf wildlife for the BP oil spill is unacceptable. And despite its massive size, this spill was just the latest in a string of ongoing and inevitable spills in the region. Several hundred known spills involving offshore drilling have occurred there since 1964. Spills massively degrade ecosystems and devastate all the wildlife dependent on those ecosystems in the Gulf. Clean-up efforts only remove a fraction of the persistent oil and gas spilled. The remainder of the oil, including millions of gallons remaining in the Gulf, will continue to poison wildlife for generations. Besides the direct harm to wildlife, the spill impoverishes the people of the Gulf and the nation, who depend on this rich body of water for food, culture, environmental enrichment and recreation.

We need to learn these lessons from the Deepwater Horizon disaster — otherwise we’re doomed to repeat it.


Banner photo by kris krüg/Flickr