Protected Species in Gulf of Mexico Could Take Decades to Recover From Deepwater Horizon Oil Spill

Research released last month suggested that the 2010 Deepwater Horizon disaster and oil spill caused $17.2 billion in damages to the Gulf of Mexico’s natural resources — and a slew of other recent studies provide even more detail on just how severe those impacts were for many of the protected marine mammal and sea turtle species found in the Gulf.

What started as a blowout at an ultra-deepwater well operated by British oil major BP on April 20, 2010 led to an explosion on the Deepwater Horizon offshore drilling rig and ultimately the largest offshore oil spill in United States history. The well would not be successfully capped for another 87 days, by which time approximately 3.19 million barrels (or 134 million gallons) of oil had spewed into the Gulf of Mexico. That oil contaminated more than 112,000 square kilometers (over 43,200 square miles) of surface waters and fouled 2,100 kilometers (a little over 1,300 miles) of shoreline in five states.

The Deepwater Horizon oil spill also killed thousands of marine mammals and sea turtles in the Gulf, according to findings detailed in a special issue of the journal Endangered Species Research published in January, comprised of 20 studies that collectively represent more than five years’-worth of data collection and analysis by scientists with the US National Oceanic and Atmospheric Administration (NOAA) and their partners.

“This extensive oiling contaminated vital foraging, migratory, and breeding habitats of protected marine species (e.g. sea turtles and marine mammals) at the surface, in the water column, and on the ocean bottom throughout the northern [Gulf of Mexico],” the editors of the special issue write in an overview paper.

In a statement, NOAA offered this succinct summation of the results of the studies: “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 research methods for the studies, including surveys conducted from the air and by boat, recoveries and examinations of stranded animals, satellite tracking of live animals (while the spill was ongoing and afterward), and veterinary assessments. The research was performed as part of a Natural Resource Damage Assessment (NRDA), a process required under the Oil Pollution Act of 1990 in which NOAA investigates the types of injuries to wildlife caused by an oil spill, determines the number of animals that were harmed, and develops a restoration plan designed to address the primary threats to impacted species.

The researchers found that thousands of the Gulf’s protected species were exposed to oil from the Deepwater Horizon spill throughout their habitats. “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,” according to NOAA.

Some 22 species of marine mammals call the northern Gulf of Mexico home, and all are protected under the Marine Mammal Protection Act. The scientists determined that Deepwater Horizon oil contaminated every type of habitat that the Gulf of Mexico’s marine mammals rely on, from the coastal seagrasses favored by manatees to the estuarine, nearshore, and offshore habitats frequented by whales and dolphins. Exposure to this oil caused “a wide range of adverse health effects,” NOAA reports, including organ damage and reproductive failure, leading to “the largest and longest marine mammal unusual mortality event ever recorded in the Gulf of Mexico.”

Increased incidence of dolphin strandings in the northern Gulf of Mexico for several years after the Deepwater Horizon spill supported the evidence of reduced survival and reproductive rates for the surviving dolphin populations, the researchers found. Health impacts associated with oil exposure suffered by bottlenose dolphins (Tursiops truncatus) in Barataria Bay, Louisiana reportedly led to a 50 percent decline in their numbers, while Mississippi Sound bottlenose dolphin abundance declined by 62 percent.

Five species of sea turtles, all of which are protected under the Endangered Species Act, can also be found in the Gulf, which provides important habitat for the turtles’ feeding, migration, and reproduction. The scientists determined that four species — green turtles (Chelonia mydas), hawksbill sea turtles (Eretmochelys imbricata), Kemp’s ridley sea turtles (Lepidochelys kempii), and loggerheads (Caretta caretta) — were exposed to Deepwater Horizon oil in their habitats in the open ocean, across the continental shelf, and in nearshore and coastal areas, including beaches where the turtles nest.

Researchers concluded that as much as 20 percent of the juvenile Kemp’s ridley sea turtles that were in the Gulf of Mexico during the Deepwater Horizon oil spill died of oil exposure. Some members of the fifth sea turtle species in the Gulf, leatherbacks (Dermochelys coriacea), were also likely killed as a result of exposure to Deepwater Horizon oil, the researchers added.

These findings helped inform the $8.8 billion for natural resource damage included in the $20 billion settlement with BP approved by a US federal judge last year, the largest environmental settlement in the nation’s history. The funds will be used for a variety of projects aimed at decreasing and mitigating the numerous threats faced by marine mammals and sea turtles in the Gulf of Mexico in order to allow for the restoration of their population numbers.

“Sea turtles and marine mammals fulfill unique ecological roles as long-lived, large-bodied animals that move through several habitats during their lives, and they are often focal species in assessments of marine ecosystem health and function,” the editors of the special issue of Endangered Species Researcj write in the overview paper.

“Considering their long lifespans and generation time — including slow maturation times and low reproductive rates — and wide distributions over which resource availability and impacts of threats can vary greatly, the [NOAA scientists and partners] concluded that full recovery of [Gulf of Mexico] sea turtle and marine mammal populations… from these losses will take decades and will require extensive restoration efforts.”


  • Bishop, R.C., Boyle, K.J., Carson, R.T., Chapman, D., Hanemann, W.M., Kanninen, B., Kopp, R.J., Krosnick, J., List, J., Meade, N., Paterson, R., Presser, S., Smith, V.K., Tourangeau, R., Welsh, M., Wooldridge, J.M., De Bell, M., Donovan, C., Konopka, M., & Scherer, N. (2017). Putting a value on injuries to natural assets: The BP oil spill. Science 356(6335). doi:10.1126/science.aam8124
  • Wallace, B. P., Brosnan, T., McLamb, D., Rowles, T., Ruder, E., Schroeder, B., … & Wehner, D. (2017). Effects of the Deepwater Horizon oil spill on protected marine species. Endangered Species Research, 33, 1-7. doi:10.3354/esr00789