Deepwater Horizon Oil Spill

Longterm Effects on Marine Mammals, Sea Turtles

A recent Endangered Species Research special issue summarizes some of the devastating longterm effects of the Deepwater Horizon oil spill on protected marine mammals and sea turtles. The issue compiles 20 scientific studies authored by NOAA scientists and partners covering more than five years' worth of data collection, analysis, and interpretation. The research indicates that populations of several marine mammal and sea turtle species will take decades to rebound. Significant habitat restoration in the region will also be needed.

NOAA scientists used a variety of cutting-edge research methods in these studies and many others as part of a Natural Resource Damage Assessment. This is the legal process where we investigate the type of injuries caused by the oil spill, quantify how many animals were harmed, develop a restoration plan to compensate for the natural resource injuries, and hold responsible parties liable to pay for the restoration.  

1. The largest offshore oil spill in U.S. history

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.

Heavy band of oil seen during an overflight

Heavy band of oil seen during an overflight on May 12, 2010. Download

Dr. Brian Stacy, NOAA veterinarian, prepares to clean an oiled Kemp's ridley turtle. Veterinarians and scientists from NOAA, the Florida Fish and Wildlife Commission, and other partners working under the Unified Command captured heavily-oiled young turtles 20 to 40 miles offshore as part of ongoing animal rescue and rehabilitation efforts. Credit: NOAA and Georgia Department of Natural Resources.

Dr. Brian Stacy, NOAA veterinarian, prepares to clean an oiled Kemp's ridley turtle. Veterinarians and scientists from NOAA, the Florida Fish and Wildlife Commission, and other partners working under the Unified Command captured heavily-oiled young turtles 20 to 40 miles offshore as part of ongoing animal rescue and rehabilitation efforts. Credit: NOAA and Georgia Department of Natural Resources. Download

2. Thousands of protected species were exposed to oil throughout 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.

Close-up of an oiled Kemp's ridley turtle captured during a June 1 survey. The turtle was cleaned, provided veterinary care, and taken to the Audubon Aquarium. Efforts continue to assess the condition of these endangered sea turtles and capture turtles caught in heavy oil. Credit: NOAA.

Oiled Turtle. Close-up of an oiled Kemp's ridley turtle captured during a June 1, 2010 survey. The turtle was cleaned, provided veterinary care, and taken to the Audubon Aquarium. Efforts continued throughout the duration of the spill to assess the condition of these endangered sea turtles and to capture turtles caught in heavy oil. Download

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.

Bottlenose dolphin with oil adhered to the head, July 2010. Credit: NOAA.

Bottlenose dolphin with oil adhered to the head, July 2010. The oil spill contaminated prime marine mammal habitat in the estuarine, nearshore, and offshore waters of the northern Gulf of Mexico. Photo taken under research permit. Download

Deepwater Horizon oil contaminated every type of habitat that northern Gulf of Mexico marine mammals occupy.

3. We investigated the types of injuries

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.

A veterinarian performs an ultrasound to assess a Barataria Bay dolphin's health in Aug 2011.

A veterinarian performs an ultrasound to assess a Barataria Bay dolphin's health in Aug. 2011. As soon as the examination was complete, the dolphin was returned to the water. Photo taken under research permit. Download

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.

Juvenile Kemp's ridley sea turtle oiled in the Deepwater Horizon spill. Photo Credit: Blair Witherington, Florida Fish and Wildlife Conservation Commission

Juvenile Kemp's ridley sea turtle oiled in the Deepwater Horizon spill in 2010. Photo Credit: Blair Witherington, Florida Fish and Wildlife Conservation Commission Download

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.

4. We quantified how many animals were harmed

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.

A dead stranded bottlenose dolphin calf in Louisiana. (photo:Fauquier et al.)

Dead bottlenose dolphin calf stranded on Grande Isle, Louisiana, in 2013. There was an increase in dolphin strandings in the northern Gulf of Mexico for several years following the Deepwater Horizon spill. Findings from the dead animals supported evidence of decreased survival and reproductive rates found in live animal studies. Credit: Louisiana Department of Wildlife and Fisheries Download

Kemps Ridely Turtle after cleaning and treatment. Distressed and oiled turtles recuperated at the Audubon Nature Institute during the spill in 2010.

Kemp's ridely turtle after cleaning and treatment. Distressed and oiled turtles recuperated at the Audubon Nature Institute during the spill in 2010. Download

5. We planned the restoration

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.

Group of common bottlenose dolphins swimming in Barataria Bay, Louisiana

A group of dolphins photographed in May 2015 during monitoring surveys in Barataria Bay, Louisiana. The faint markings on 2nd fin indicate the dolphin is "Y79", a subadult female dolphin that had been temporarily captured for health assessment the prior year. Photo taken under research permit. Download

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.

Turtle excluder devices on nets allow sea turtles to escape unharmed. Restoration activities could include promoting the use of such devices.

Turtle excluder devices on nets allow sea turtles to escape unharmed. Restoration activities could include promoting the use of such devices. Download