As the largest offshore oil spill in U.S. history, the Deepwater Horizon oil spill released 134 million gallons of oil into the Gulf of Mexico over a period of 87 days, fouling 1,300 miles of shoreline along five states. The scientists concluded that the Deepwater Horizon oil spill killed thousands of marine mammals and sea turtles, and contaminated their habitats.
The northern Gulf of Mexico is home to 22 species of marine mammals, including manatees in coastal seagrasses and dolphins and whales in estuarine, nearshore, and offshore habitats.
Five species of sea turtles live in the Gulf of Mexico: loggerhead, Kemp's ridley, green turtle, hawksbill, and leatherback. All of these species are protected under the Endangered Species Act. The Gulf of Mexico provides critically important habitats for sea turtle reproduction, feeding, migration, and refuge, including extensive Sargassum habitat in the open ocean that small juvenile turtles depend on for survival.
The scientists determined that four species of sea turtles (Kemp's ridley, loggerhead, green turtle, and hawksbill) and their habitats were exposed to Deepwater Horizon oil in the open ocean, across the continental shelf, and into nearshore and coastal areas, including beaches. A fifth species, the leatherback, was likely exposed to Deepwater Horizon oil, and some exposed leatherbacks likely died.
Deepwater Horizon oil contaminated every type of habitat that northern Gulf of Mexico marine mammals occupy.
To determine the types of injuries to whales and dolphins due to the spill, the scientists collected a variety of information, including field studies, stranded carcasses, historical data on marine mammal populations, and toxicity testing studies.
Marine mammals and sea turtles may have been exposed to the oil by inhalation, aspiration, ingesting contaminated sediment, water, or prey, or by absorbing contaminants through their skin.
Marine mammal researchers concluded that exposure to the oil caused a wide range of adverse health effects such as reproductive failure and organ damage, and that animals killed by these adverse effects contributed to the largest and longest marine mammal unusual mortality event ever recorded in the Gulf of Mexico.
Miring in oil and exposure to oiled surface habitat caused significant harm to sea turtles, including decreased mobility, exhaustion, dehydration, overheating, likely decreased ability to feed and evade predators, and death.
Examples of impacts to species included: up to 20 percent of all oceanic juvenile Kemp's Ridley sea turtles present during the Deepwater Horizon oil spill perished from oil exposure; and oil-associated health effects to Barataria Bay, Louisiana, bottlenosed dolphins reduced their survival and reproductive success in years following the spill, leading to a 50 percent decline in the population, according to NOAA scientists and partners.
Findings from these research studies, in addition to other studies on other parts of the ecosystem, formed the basis of the natural resources damage assessment settlement with BP for up to $8.8 billion for restoration projects.
Because marine mammals face a wide range of threats, a portfolio of restoration approaches include: decreasing and mitigating interactions with commercial and recreational fishing gear, characterizing and reducing impacts from noise, reducing illegal feeding and harassment, and increasing understanding of causes of marine mammal illness and death.
Specific activities for sea turtles could include reducing fisheries bycatch, enhancing sea turtle stranding response and mortality investigation, and improving nesting habitat by protecting nests and reducing artificial sources of light that can disorient hatchlings at night.
The data collected in the marine mammal and sea turtle assessments are available to the public in NOAA's Data Integration Visualization Exploration and Reporting Explorer tool known as DIVER. The complete injury assessment is contained in the Deepwater Horizon Programmatic Damage Assessment and Restoration Plan (PDARP) and Programmatic Environmental Impact Statement (PEIS).