Barataria Bay Bottlenose Dolphins

Species Status

Abundance and Trends

Barataria Bay is a shallow (mean depth = 2 m) estuarine system in southern Louisiana separated from the Gulf of America (formerly the Gulf of Mexico) by a chain of barrier islands. The Barataria Bay population (stock) of bottlenose dolphins is genetically distinct from other dolphin populations occurring in Gulf coastal waters, including other bay, sound, and estuary (BSE) dolphin populations. Among the 31 BSE bottlenose dolphin populations in the northern Gulf, the Barataria Bay population is one of the largest with around 2,000 dolphins.

The Barataria Bay dolphin population was heavily impacted by the 2010 Deepwater Horizon (DWH) oil spill, which released an estimated 168 million gallons of oil into the Gulf over 87 days. The oil contaminated surface waters and nearshore habitats hundreds of miles away from the wellhead, including Barataria Bay.

At the time of the DWH spill, the abundance of Barataria Bay dolphins was unknown. However, analysis of data from photographic surveys done shortly after the spill indicated that there were over 3,000 dolphins in Barataria Bay at that time. Following the spill, many dolphins in Barataria Bay died, and many of those that survived could not successfully reproduce. Many of the dolphins that survived also had lung disease, impaired stress response, and other chronic diseases.  A population dynamics model predicted that, due to disease and failed reproduction, the Barataria Bay population would continue to decline for 10 years after the spill, dipping to a low point less than half of its pre-spill abundance before beginning a slow recovery. Analysis of subsequent photographic survey data suggests that the abundance of the Barataria Bay dolphin population was around 2,000 dolphins in 2019.

Threats to the Population

Ongoing threats to Barataria Bay dolphins include chronic disease and reproductive failure in dolphins that were exposed to oil from the DWH spill, and interactions with commercial and recreational fisheries. Recent studies have also documented that Barataria Bay dolphins have a high prevalence of scars from propellor strikes, and suggest that dolphins previously exposed to the DWH oil are more likely to be struck by vessels (Pirotta et al. 2026).

The Mid-Barataria Sediment Diversion (MBSD) project, previously proposed by the State of Louisiana to divert water and sediment from the Mississippi River into the northern portion of Barataria Bay, also threatened the Barataria Bay dolphins, but the project was terminated in 2025. The goal of the project was to rebuild marshland that has been eroding for decades due to oil and gas extraction, canal excavations, extreme weather events, subsidence, and sea level rise. However, operation of the MBSD would have also significantly altered the dolphins’ estuarine habitat by adding large amounts of freshwater into the bay and thereby lowering its salinity.

Scientists modeled the habitat changes expected to happen with the MBSD project to determine the likely impacts to the Barataria Bay dolphin population.  They predicted a catastrophic decline in the Barataria Bay dolphin population, with over 500 dolphins (one quarter of the population) dying within the first year of the MBSD operation. Dolphins that reside in the central and western portions of the bay were expected to be “functionally extinct” after just 10 years of the MBSD’s operation. After 50 years of operation, bottlenose dolphins across the entire bay would have been almost entirely gone, with only a small number remaining near the bay’s barrier islands. The decision to terminate the project was based on a determination that the project was no longer viable for multiple factors, including ongoing litigation, and ultimately the suspension of a federal permit by the U.S. Army Corps of Engineers.

What the Commission Is Doing

When the Louisiana Mid-Barataria Sediment Diversion (MBSD) project was first proposed as a Deepwater Horizon oil spill restoration activity in 2015, the Marine Mammal Commission identified threats to the Barataria Bay dolphin population posed by the project. The Commission provided detailed comments on its concerns and suggested alternative approaches to entities responsible for planning, reviewing, and approving the MBSD project, including the Louisiana Coastal Protection and Restoration Authority, the Louisiana  Deepwater Horizon Trustee Implementation Group, NOAA’s National Marine Fisheries Service, the U.S. Army Corps of Engineers, and the RESTORE Act Gulf Coast Ecosystem Restoration Council. Despite the Commission’s recommendations, the project was approved without the inclusion of additional measures to reduce adverse impacts on dolphins. Construction of the project began in August 2023, but the project was ultimately terminated in 2025. The decision to terminate the project was made after Louisiana’s Coastal Protection and Restoration Authority (CPRA) determined that the project was no longer viable for a number of reasons, including ongoing litigation and the suspension of the U.S. Army Corps of Engineers permit for the project.

The plans for the MBSD project highlighted potential impacts to dolphins from freshwater influx in coastal habitats, whether from natural processes such as extreme storm events, or human activities such as water or sediment diversion. The Commission convened a webinar in March 2021 to provide information on the potential impacts of low-salinity exposure on dolphins and their prey, review the findings of the 2019 northern Gulf bottlenose dolphin Unusual Mortality Event, identify data needs, and discuss options for mitigating and monitoring impacts to dolphins and their prey from future low-salinity exposure. For more information and to view the webinar, see ‘Effects of Low-Salinity Exposure on Bottlenose Dolphins.’

Commission Reports and Publications

For more information on the effects of low salinity water on bottlenose dolphin health and survival, please refer to the Commission’s March 2021 webinar on “Effects of Low-Salinity Exposure on Bottlenose Dolphins.”

Commission Letters

Learn More

Research and Monitoring

Following the Deepwater Horizon oil spill, a number of studies were conducted to understand and quantify the effects on the bottlenose dolphins in Barataria Bay, as well as other dolphin and cetacean populations throughout the northern Gulf of Mexico. These studies, part of the Natural Resource Damage Assessment (NRDA) led by the National Oceanic and Atmospheric Administration with other co-trustees, included necropsies of dead stranded dolphins, capture-release health assessments of live dolphins, and photographic surveys to determine dolphin abundance, reproductive success, and survival rate. Collectively, the findings from the studies demonstrated that the Deepwater Horizon oil spill substantially impacted the health of Barataria Bay dolphins, leading to reproductive failure and increased mortality. Findings from the NRDA studies were summarized in the Deepwater Horizon Trustees’ Final Programmatic Damage Assessment and Restoration Plan. In addition, many of the studies were compiled and published in a Special Issue of the scientific journal Endangered Species Research: Effects of the Deepwater Horizon oil spill on protected marine species (Volume 33, 2018).

The Gulf of Mexico Research Initiative (GoMRI) provided funding for continued studies of Barataria Bay dolphins that were exposed to the Deepwater Horizon oil spill. The GoMRI studies documented the persistence of chronic disease such as lung disease and impaired stress response. A model developed by the GoMRI researchers estimated that in the ten years following the Deepwater Horizon oil spill, the Barataria Bay dolphin population had declined by 45 percent.