Oil Spill Impacts on Mammals

The Gulf oil disaster poses several threats to sperm whales, bottlenose dolphins, blue whales, West Indian manatees and other marine mammals in the Gulf.

Dolphin Covered in Oil 

How Many Dolphins and Whales Were Affected?

During the six months following the Deepwater Horizon explosion, about 100 marine mammals were collected in the spill area. Since the spill there have been a record-shattering 26 consecutive months of above-average dolphin strandings.

The following map shows when and where dead dolphins and whales were picked up after the oil spill began:


Where Did These Numbers Come From?

This map is based on the consolidated numbers from the National Oceanic and Atmospheric Administration (NOAA). These records were used to map the animals collected each day. There are minor variations from official government records in the total number of animals shown, for several reasons. The date marked on each map is the date the data were posted online by the government. Since then, a few additional animals have been collected. Furthermore, due to the time needed to process and verify data, animals collected just a week to 10 days prior to the date of data release may have not yet been recorded.

Was the Oil Spill the Cause of All These Deaths and Injuries?

These numbers include all mammals collected in the oil spill area. The actual cause of death has yet to be determined for most of the animals.

Dolphin pod

Will the Total Number Ever Be Known?

No. Although the marine mammals tallied in these maps may include some that were injured or died of causes unrelated to the spill, given the vastness of the Gulf others surely disappeared without being observed or collected by authorities.

Scientists are also concerned about other impacts on mammals that can be even more difficult to discern, ranging from the sublethal effects of oil exposure on reproduction and other physiological functions, to the loss of important habitat.

How Does Oil Impact Marine Mammals?

  • Oil can cause chemical burns and irritation from direct contact.

  • Oil can cause ulcers and internal bleeding if ingested.

  • Oil floating at the surface can emit toxic fumes that surfacing whales and dolphins will breathe.

  • Oil can coat baleen—comblike growths in the mouths of toothless whales used for filtering prey out of ingested water—and make it ineffective for capturing prey.

  • The spilled oil and toxic chemical dispersants used by BP to break up the oil is potentially harming prey species deep under water. Even if not killed outright, prey animals are likely to absorb the toxins and pass them on to marine mammals. This factor could impair reproduction in both mammals and their prey.

"The spill is from the Gulf floor, so contaminating the entire water column, from top to bottom, is a very grave concern for all marine life in the area," says NWF senior wildlife biologist Doug Inkley.

In other spills, marine mammals have suffered major losses to their populations. Two orca pods affected by the Exxon Valdez lost 40 percent of their numbers and still have not fully recovered; the pods' reproductive success appears to have suffered long-term damage.

How Does Oil Impact Terrestrial Mammals?

Other terrestrial mammals, including river otters, mink and swamp rabbits are also at risk from the spill, as they are potentially going to lose habitat and food sources as oil washes into coastal wetlands.

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Five Years and Counting, a report by the National Wildlife Federation