Scientists and ocean experts have found compelling data correlating the 2010 Deepwater Horizon oil spill – a disaster that produced a 149,000-square-kilometre ocean oil slick in the Gulf of Mexico – with steep declines in whale and dolphin populations in the region.
While firm conclusions still can’t be drawn that the oil spill itself is the root cause of the dramatic drop-off, this is the first time data has been used in this way to show a ‘strong correlation’ between the event and the severe declines suffered by populations of cetaceans species in the region.
In its most severe cases, the data, which captured and measured the echolocation clicks and communication signals of a diverse set of marine mammals, documents a decline by as much as 30% for sperm whales and a staggering 80% for beaked whales since the spill.
To bring this compelling correlation to light, researchers from UC San Diego’s Scripps Institution of Oceanography analysed acoustic recordings collected over a ten year period during, and immediately after, the 2010 oil spill. To study the deep-diving species that live in the waters affected by the spill, they maintained autonomous listening stations at depths of more than 915 metres (3,000 feet) in the northern Gulf of Mexico.
Their findings have since revealed ‘significant declines’ in the presence of several species of beaked whales (by as much as 80%), sperm whales (declines of up to 30%), and dolphins.
The study’s lead author, Kaitlin Frasier, a research oceanographer at Scripps Oceanography, emphasised that while the research shows a strong correlation between the spill and marine mammal declines, it does not prove that the spill caused the drop-off.
“While predicting where and when a disaster will occur is challenging, advancements in technology and long-term monitoring can help us better understand and address their impacts,” said Frasier.
“By focusing on innovative solutions and sustained efforts, we can improve our ability to assess and mitigate the effects of events like oil spills, even in the most challenging offshore environments.”
The spill itself was estimated to have released 210 million gallons of oil, making it the largest marine oil spill in the history of the petroleum industry. This study, like others in the wake of the disaster, was initially funded by a trust fund created as part of the legal settlements following the spill.
It was Scripps oceanographer John Hildebrand, however, who secured an emergency funding to launch the project during the period of the spill, piecing together support from various organisations to sustain the effort over a decade.
“The Deepwater Horizon oil spill was an unprecedented disaster that demanded a nationwide response,” said Hildebrand. “We quickly relocated instruments from southern California to the Gulf of Mexico to gather critical data needed to understand the spill’s impact on marine mammals.”
Studies unrelated to this one have previously found rates of infant dolphin deaths in coastal waters were six times higher than normal. A 2015 study led by the NOAA linked the spill to increased deaths of bottlenose dolphins in the gulf. Today, settlement funds remain to assist coastal remediation efforts, but offshore impacts have been difficult to assess.
“Experts predicted minimal effects and recovery within a decade, and there is no evidence that they were correct,” said Frasier. “Those opinions were used as the basis for the post-spill damage assessment and legal settlement. To me, this says that we still have a lot to learn about the deep ocean and how interconnected everything in it is.”
While some locations outside of the 2010 surface oil slick showed an increase in whale and dolphin activity, it remains unclear whether these patterns indicate animals relocating to less impacted regions. Frasier and her colleagues continue to investigate this question using the same High-Frequency Acoustic Recording Packages (HARPs) used in the initial study, now expanded across the entire Gulf of Mexico, including in Mexican waters.
‘So far, we haven’t found evidence suggesting an unexpectedly large number of animals in the western Gulf,” said Frasier. “It’s unlikely that the populations simply moved out of the affected area.”
The research has gone lengths to highlight the importance of long-term acoustic monitoring for understanding the impacts of environmental disasters on marine life.