Dolphins hit by Deepwater Horizon spill at risk from new drilling and river plan

Nearly 80% of dolphins exposed to oil in the Deepwater Horizon disaster remain badly affected nearly 12 years later, according to new research, even as the Biden administration continues to approve leases for oil and gas drilling in the Gulf of Mexico.

Scientists looked at the long-term impact of the oil spill on bottlenose dolphins living in Barataria Bay, near New Orleans.

The lagoon off the Louisiana coast was heavily polluted by oil, which killed scores of dolphins directly or within months, and their population is now slightly over half of what it was.

The surviving dolphins did not escape ill effects, however, according to the peer-reviewed study in Conservation Biology. Lung disease has been the most common issue, according to Lori Schwacke, an epidemiologist of the National Marine Mammal Foundation who was the study’s lead author.

Other deterioration in the dolphins’ health has led Schwacke to believe the dolphins may be suffering from an illness similar to chronic obstructive pulmonary disease (COPD), a progressive lung condition. Age-related effects could also play a role.

Recent surveys suggest Barataria Bay’s bottlenose dolphin population has diminished by up to 45% since the disaster, to approximately 2,000. The reproductive success of the remaining females was significantly reduced.

Those dolphins born after the spill do not show signs of health impairment, however. ‘The hope is that, over time, the young animals will take over the population,’ said Schwacke. Recovery to baseline numbers will probably take about 35 years, she estimated, providing there are no severe threats in the near future.

Last November, however, the US government leased huge parts of the Gulf of Mexico’s seabed for oil and gas drilling. Although the deals were recently annulled in court, there could be an appeal against the decision, making the possibility of another oil spill a strong possibility.

Moreover, a plan to divert large amounts of water and sediment from the Mississippi River into Barataria Bay poses an even greater risk. The aim of the Louisiana Coastal Protection and Restoration Authority, which is behind the work, is to restore coastal ecosystems such as intertidal marshes and to enhance flood protection, with the project set to start next year.

But the influx of freshwater will lower the lagoon’s salinity to concentrations of less than 5 parts in a thousand. This is expected to kill dolphins, said Schwacke. Low salinity triggers severe physiological reactions, causing their skin to develop lesions and become inflamed before killing them.

The federal National Oceanic and Atmospheric Administration has predicted that about a third of the population will be lost each year as a result of the project.

Schwacke said the dolphins were unlikely to move to avoid the impact of the Mississippi project. ‘These animals have high site fidelity,’ she said, adding that if the sediment diversion scheme proceeds, the dolphin population would almost certainly be wiped out.