Species Status

Abundance and Trends

Barataria Bay is a shallow estuary in southern Louisiana, approximately 110 km long and 50 km wide. The southern portion of the bay is connected to the Gulf of Mexico by channels, or ‘passes’. The Barataria Bay population (stock) of bottlenose dolphins is genetically distinct from other dolphin populations occurring in Gulf of Mexico coastal waters, including other bay, sound, and estuary (BSE) dolphin populations. Among the 31 BSE bottlenose dolphin populations in the northern Gulf of Mexico, 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 of Mexico 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. However, the greatest threat to the Barataria Bay dolphin population comes from building and operating the Mid-Barataria Sediment Diversion (MBSD) project in Plaquemines Parish, Louisiana. The MBSD project will divert water and sediment from the Mississippi River into the northern portion of Barataria Bay. The goal of the project is 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 will also significantly alter 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 predict 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 are 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 will be almost entirely gone, with only a small number remaining near the bay’s barrier islands.

The Marine Mammal Protection Act (MMPA) generally prohibits taking marine mammals, absent authorization. It was doubtful that the project would meet the requirements to secure an authorization under the MMPA’s existing provisions, so, Congress passed legislation directing the Secretary of Commerce to waive the MMPA’s taking prohibition in spite of the predicted consequences of the MBSD project for the Barataria Bay dolphin population. Additional information about the MMPA waiver can be found on the “More” tab.

A Dolphin Intervention Plan was included in the Final Environmental Impact Statement as part of the MBSD project’s monitoring and adaptive management plan. However, the activities outlined in the plan are not focused on mitigation measures to avoid the project’s adverse impacts on the Barataria Bay dolphin population. Instead, they are focused on documenting and responding to dolphins that are injured, become ill, or are killed by the environmental changes in Barataria Bay that result from the MBSD project.

Given the large number of dolphins that will be exposed to extremely low salinity for prolonged periods of time, intervention (i.e., rescue and rehabilitation or relocation) will not be practical for more than a few animals. There is limited capacity to care for sick and distressed dolphins at marine mammal rehabilitation facilities in the northern Gulf of Mexico. Even if some dolphins are rescued and rehabilitated, the changes to their habitat would preclude successful reintroduction, forcing them to either remain in captivity or be relocated to another area, assuming another area with suitable habitat could be found. Rescue and rehabilitation efforts could save a small number of individual dolphins, but will not prevent the population from declining towards extinction.

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 has since recommended several alternatives and additional measures that could be taken to reduce impacts on dolphins while arguably allowing the project to meet its objectives.

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.

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 of Mexico 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

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Marine Mammal Take Authorization

The Marine Mammal Protect Act (MMPA) generally prohibits taking of marine mammals, that is “to harass, hunt, capture or kill, or attempt to harass, hunt, capture, or kill” them, absent authorization. The Act includes a variety of ways for securing such authorization to “take” marine mammals. One common way of securing authorization is through issuance of an incidental take authorization (under section 101(a)(5)) that authorizes the taking of small numbers of marine mammals incidental to an otherwise lawful activity. However, this type of authorization requires a finding that the taking will have no more than a negligible impact on the affected species and stocks, a finding that could not be made for the Barataria Bay dolphin population as the project was proposed.

Another type of generally available authorization is a waiver of the MMPA’s moratorium on taking marine mammals. A key finding for obtaining a waiver is that the taking will not disadvantage any species or stock (i.e., population) of marine mammals. Such a finding could not be made for the Barataria Bay dolphins, given the projected impacts of the freshwater diversion on the population. Hence, a waiver would not normally be available for the project. However, Congress passed legislation in 2018 {Section 20201 of Public Law 115-123, the Bipartisan Budget Act of 2018) directing the Secretary of Commerce to issue a waiver under the MMPA notwithstanding the otherwise applicable requirements. The waiver applies to three Louisiana wetland restoration projects-the Mid-Barataria Sediment Diversion, the Mid-Breton Sound Sediment Diversion, and the Calcasieu Ship Channel Salinity Control Measures project. The waiver required only that the State of Louisiana, in consultation with the Secretary, “upon issuance of [the] waiver,” take steps to:

1. to the extent practicable and consistent with the purposes of the projects, minimize impacts on marine mammal species and population stocks; and
2. monitor and evaluate the impacts of the projects on such species and population stocks.

In essence, Congress determined that completing these projects took precedence over the anticipated detrimental effects on dolphins. Louisiana is required to take steps to minimize these impacts, but only if doing so would be practicable to implement and would not undermine achieving the purposes of the project. The state of Louisiana and the Secretary of Commerce are responsible for determining whether mitigation measures are practicable, and whether such measures would undermine achieving the purposes of the project.

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. 

Species Status

Abundance and Trends

The first documented aerial survey of Pacific walruses was conducted jointly by the United States and the former Soviet Union in 1975, after the enactment of the Marine Mammal Protection Act (MMPA) in 1972. This survey provided an estimate of about 246,000 animals and subsequent surveys suggested a population decrease to about 201,000 by 1990. The most recent aerial survey, conducted in 2006 by the U.S. Fish and Wildlife Service (FWS), estimated the walrus population to be about 129,000 but with a large confidence interval of 55,000-550,000 animals. The 2006 survey did not cover the entire walrus range and therefore is likely to be an underestimate of the total population size.

Although the estimates between 1975 and 2006 suggest that the population has declined, the differences in methods and geographic coverage between the surveys make it impossible to determine population trends over time. Surveying walruses is difficult because during the spring, when the surveys are conducted, walruses are distributed widely across the Bering Sea pack ice and spend a significant portion of their time in the water. Adverse weather conditions in this region further hinder survey efforts.

Faced with these difficulties, FWS began testing new population estimation methods in 2012 using a mark-recapture approach, which provided a preliminary estimate of 283,000 animals in 2014 with another large confidence interval. The final study, published in 2022, analyzed data from 2013 to 2017 and estimated Pacific walrus abundance to be approximately 257,000 animals. Pacific walrus abundance is expected to decline as sea ice loss continues, although the magnitude of the predicted decline is unknown. Overall, walrus population growth rates tend to be slow, with mature females producing a calf on average every 3 years. However, natural mortality also tends to be low and walruses can be long-lived. Their only natural predators include polar bears and killer whales. They are also harvested for subsistence purposes by Alaska Natives, as authorized under the MMPA.

Distribution

Pacific walruses range across the continental shelf waters of the northern Bering Sea and Chukchi Sea. Because they rely on broken ice habitat and coastal haulouts to access feeding areas on the ocean floor, their distribution varies in response to seasonal and annual changes in sea ice cover. In the winter, breeding aggregations form in the Bering Sea pack ice where there is access to open water. As the sea ice retreats in the spring, most walruses migrate north to feeding areas in the Chukchi Sea. In years with low sea ice, walruses may migrate into the Beaufort and East Siberian Seas. Those walruses are often associated with loose pack ice, but will use coastal haulouts once the sea ice retreats north of the continental shelf waters. Most adult male walruses, as well as some adult females and juveniles, remain in the Bering Sea and use coastal haulouts throughout the summer feeding season. As sea ice begins to form again in the fall, walruses that migrated north for the summer typically return south.

Pacific Walruses and Climate Change

Walruses rest on sea ice when it is available, but will use coastal haulouts when sea ice is not present. Since 2007, summer sea ice in the Chukchi Sea has retreated offshore to areas too deep for walruses to reach the ocean floor to feed. As a result, many walruses have to travel farther to reach their foraging grounds and are now using coastal haulouts to rest between foraging trips. Thousands of walruses have been observed on land in the U.S. and Russia during late summer. Some of the coastal haulouts are located near communities where human activity and the presence of predators, like polar bears, may disturb walruses. When large groups of walruses are disturbed, subsequent stampedes can cause the trampling and death of many walruses. Stampedes not only result in trampled young animals, but can separate mothers and calves and cause injury and death of weak animals recovering from prolonged foraging trips. Additionally, traveling farther to reach foraging grounds will increase walrus energetic demands. It is unknown whether this may affect body condition, reproduction rates, and survival.

To gain a better understanding of walrus distribution, abundance, and the formation of large coastal haulouts in response to climate change, USGS has developed methods to monitor walruses using satellite imagery. Satellite imagery allows scientists to easily monitor extremely remote locations, and recent methods using synthetic aperture radar, which relies on radar signals bouncing off Earth’s surface, can capture images of haulouts regardless of weather or time of day. Satellite imagery is being used to detect coastal haulouts and methods to estimate walrus abundance with improved precision and to detect carcasses are under development.

What the Commission Is Doing

The Marine Mammal Commission maintains close contact with Alaska Native communities that rely on walruses as a source of subsistence. In February 2016, the Commission led a series of listening sessions in Alaska to learn more about the challenges that Alaska Natives are facing as a result of climate change. Participants in those sessions noted that walruses are becoming more difficult to access due to adverse ice and weather conditions.

Commission Reports and Publications

For more information on the Pacific walrus, see the Commission’s 2010-2011 Annual report (pages 178-182) and 2012 Annual Report (pages 55-59).

Commission Letters

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Threats

The greatest threat to the Pacific walrus is climate change. As the pack ice that they rely on during the summer foraging season in the Chukchi Sea diminishes, walruses are increasingly forced to seek refuge at land-based haul out sites. Over the last decade, large aggregations of animals have been observed at haulout sites near Point Lay, Alaska. Such aggregations may be dangerous for calves and juveniles if disturbance by humans or other factors cause adults to stampede. Local communities have taken important measures, in collaboration with FWS, to limit the potential for such disturbance.

Reduction of sea ice and ocean warming are also expected to increase the frequency, intensity, and geographic range of harmful algal blooms (HABs) in the Arctic. Two of the most common HAB toxins on the west coast of North America are domoic acid and saxitoxin. Those toxins, associated with amnesic and paralytic shellfish poisoning in humans, can also cause illness and death in marine mammals. A 2016 study reported that out of 13 Alaskan marine mammal species, Pacific walruses contained the highest concentrations of both domoic acid and saxitoxin. No abnormal behaviors of the sampled walruses were reported, so it is unlikely that toxicological effects have occurred; however, toxin concentrations were in the range known to cause illness and/or death in California sea lions, humpback whales, and humans, and two walruses sampled in 2019 had saxitoxin concentrations near the seafood safety regulatory limit. There is concern that increased exposure to biotoxins as sea ice continues to melt may increase the risk to both marine mammals and the people that rely on them for subsistence.

Disturbance from a variety of human activities in the Arctic, such as shipping and oil and gas development, can also have negative impacts on walruses. Marine traffic and noise associated with seismic surveys could interfere with the walrus migration or cause changes in behavior in the foraging grounds.

Although hunting of walruses for subsistence use could be considered a threat to the walrus population, current harvest levels are thought to be sustainable. Alaska Native hunters have expressed concern that walruses are sometimes difficult to hunt due to the lack of sea ice habitat. In 2015, a reduced harvest of walrus by subsistence hunters because of sea ice and weather conditions led to a food security crisis in the Bering Strait region of Alaska.

Current Conservation Efforts

In 2008, FWS was petitioned to list the walrus as threatened or endangered under the Endangered Species Act (ESA) and to designate critical habitat for the species. After a review of the best available science in 2011, FWS found that listing the walrus as threatened or endangered was warranted. However, the walrus remained a candidate species as FWS first considered other higher-priority species for listing. FWS made a final decision on the listing of Pacific walrus in October 2017 with the determination that the species does not warrant listing as threatened or endangered under the ESA. The Center for Biological Diversity (CBD) subsequently sued FWS in 2018 for not listing the walrus under the ESA, which was then rejected by a federal judge. After an appeal from CBD, the appeals court ruled in June 2021 that FWS had not provided sufficient justification for reversing its 2011 listing decision and must still do so. Walruses currently are afforded protection in the United States (with the exception of subsistence harvest by Alaska Natives) under the MMPA and they are listed in Appendix III of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES).

In 2020, the U.S. Coast Guard requested input on routing measures to minimize the impact of increased shipping on marine mammals, Alaska Native communities, and the marine ecosystem. The Commission analyzed the distribution and seasonal movements of numerous marine mammal species, including Pacific walrus, and submitted a letter to the U.S. Coast Guard recommending preferred and alternative shipping routes to protect marine mammals. Recommended areas to be avoided to minimize disturbance to walruses included areas where they aggregate in large groups to feed and rest, such as Hanna Shoal and Point Lay. The public comment period for this Port Access Route Study closed in September 2021.