On April 20, 2010, the Deepwater Horizon drilling platform exploded—leading to the catastrophic release of approximately 134 million gallons of oil into the Gulf of America (formerly Gulf of Mexico)—the largest marine oil spill in history. NOAA has been a lead agency in many aspects of the response to the spill. Specifically, the Southeast Fisheries Science Center has played an integral role in assessing the injuries. We have been working on research and restoration efforts since 2010—including 45 ongoing projects. Here’s a glimpse of what we’ve been up to.
The first step following this disaster was to respond to the spill and assess the damage. The injury assessment was led by NOAA’s Damage Assessment, Remediation, and Restoration Program. Working closely with other state and federal agencies and partners, NOAA’s Southeast Fisheries Science Center scientists identified and quantified the impacts of the spill on marine life and ecosystems.
Beyond the immediate impacts, we recognized there was damage far beyond what could be seen on the surface and near the spill. Scientists worked to determine which resources were impacted, including:
- Sea turtles
- Marine mammals
- Fish and water column invertebrates
- Mesophotic and deep benthic communities
Assessing Impacts on Sea Turtles
As part of the injury assessment, our staff conducted aerial surveys that lasted for weeks after the spill to scan the impacted areas for oiled or sick animals. We diverted resources from other projects to focus our efforts on response and assessment—including vessels, satellite tags, other equipment, and an enormous amount of staff time.
We also documented numerous marine life deaths and conducted necropsies when possible. Our staff and others spent weeks coordinating both marine mammal and sea turtle stranding responses along the Gulf states. “Teams from across NOAA Fisheries came to assist with documenting sea turtle strandings,” said Lisa Belskis, a center biologist flying aerial surveys and providing strandings response. “It was a very busy time for all involved, but we worked together as a really big team incorporating regular guidance and updates from Unified Command.”
Approximately 1,800 sea turtles were directly observed within the oil footprint. We assessed nearly 600 of these for the degree of oil exposure. More than 300 were rehabilitated and eventually released. Unfortunately, for most species, baseline species information before the oil spill was lacking to assess the magnitude of the impacts. could compare these numbers. “We needed prior monitoring in the region to get a handle on what was going on,” said Dr. Chris Sasso, a biologist within the center’s Sea Turtle Branch who directly responded to the event.
Our data showed green turtles and Kemp’s ridleys were impacted more severely than loggerhead turtles. However, due to species- or life-stage specific data deficiencies and intrinsic species’ life history traits, scientists feared there would be cascading ecological impacts not initially apparent.
Between 4,900 and 7,600 large juvenile and adult sea turtles, and between 55,000 and 160,000 small juvenile sea turtles, were killed as a result of the spill.
Assessing Impacts on Marine Mammals
There were similar challenges in assessing marine mammals. “A lack of baseline data prior to the spill was a real challenge when it came time to assess the injuries,” added Dr. Lance Garrison, a senior scientist in the Marine Mammal Branch. Before the spill, there were aerial and vessel surveys in the northern Gulf, but these were infrequent and sparse at the time. Immediately following the spill, we quickly mobilized aerial surveys in nearshore areas impacted by oil. We followed those with larger-scale surveys that continued for a year to monitor for shifts in sea turtle and dolphin abundance. We also:
- Conducted large vessel surveys to document habitat use and distribution of oceanic marine mammals in the area affected by oil
- Deployed tags to document sperm whale movements
- Sampled for marine mammal prey
Closer to shore, we worked with many partners to conduct photo-identification surveys and live capture health assessment surveys. These allowed us to evaluate the impacts on bottlenose dolphins, particularly in Barataria Bay and Mississippi Sound. All of these studies supported the assessment of injuries from the spill for 16 species of marine mammals.
Our response to marine mammal strandings also played an important role in the injury assessment. Just months before the spill occurred, NOAA Fisheries—in collaboration with marine mammal stranding network organizations in the northern Gulf—began monitoring an increase in bottlenose dolphin strandings around the Lake Pontchartrain area of Louisiana and western Mississippi. We also consulted with the Working Group for Marine Mammal Unusual Mortality Events. The mortalities occurred during a period of unusually low salinity and cold weather. Some of the dolphins had characteristic skin lesions often associated with freshwater exposure. Following the Deepwater Horizon explosion, dolphin mortalities continued throughout a broader geographic area, from Louisiana to the Florida panhandle. An analysis published in 2014 found that the largest and most prolonged cluster of mortalities occurred in Barataria Bay, Louisiana, in late 2010 and 2011. An unusual mortality event was declared across the northern Gulf, occurring from March 2010 through July 2014. This event included 1,141 cetacean strandings, primarily bottlenose dolphin mortalities. Ultimately, the investigation found that the dead dolphins had lung and adrenal lesions consistent with petroleum exposure. The high level of near-term or stillborn dolphin deaths was likely caused by weakened and ill mothers following exposure to oil from the Deepwater Horizon oil spill.
Data from live-dolphin health assessments and photo-identification studies in Barataria Bay, Louisiana, also showed evidence of lung disease, adrenal dysfunction, and poor reproductive success in the live dolphins. “The marine mammal injury assessment was an unprecedented effort that involved more than 40 researchers and numerous partner agencies.” Dr. Jenny Litz, the center’s Marine Mammal Branch Chief, explained. “The resources allowed for a massive effort to combine the morality event data, live capture health assessments, and photo-identification data all from the same time and place to better understand the impacts on dolphins caused by the oil exposure.”
Understanding how bottlenose dolphins were impacted by the oil allowed us to extrapolate to offshore marine mammal species exposed in inaccessible habitats. This led to an impact or injury assessment for each species and stock affected. We developed population models to estimate injury extent and the time to recovery for the stocks affected by the spill. These models take into account long-term impacts resulting from mortality, reproductive failure, reduced survival rates, and the proportion of the stock exposed to oil. These models still inform our annual marine mammal stock assessments today.
Influencing How We Work Today
While our scientists describe the event as “unprecedented,” “challenging,” and “stressful,” they identified positive outcomes from the experience. “We used every tool we had available to us to conduct these assessments and developed some new ones,” according to Dr. Garrison. “We established long-term, productive working relationships with external researchers. It led us to develop standards for everything from laboratory testing to paperwork. We established systems for data and sample management and metadata, and now that’s standard practice. At the end of the day, we provided good science, provided meaningful and useful products, and learned a lot of lessons along the way.” Many of the sampling techniques, scientific knowledge, and collaborations developed during this event are still being used to study the impact of the spill on marine mammal populations and health in the Gulf and elsewhere.
Learn more about how sea turtles, dolphins, and whales were affected by Deepwater Horizon >
What Happened to the Fish?
The most immediate, tangible effects on fisheries were geographic closures that changed daily depending on the location and projection of surface oil. This was done as a precautionary measure to prevent the harvest of potentially contaminated fish and to ensure public safety.
Fish biologists from the Southeast Fisheries Science Center were redirected from their regularly scheduled research to focus efforts on the impacted area. Eric Orbesen had been studying yellowfin tuna in the Gulf just before the spill. Tagging data showed that, unlike bluefin tuna that migrate to the North Atlantic in the spring, Gulf yellowfin tend to stay within the Gulf for prolonged periods. If these fish were exposed to oil and didn’t move away—would they be a human health concern if the fishery continued?
“One of the biggest questions at the time was: if we detect oil in muscle tissue, how extensive should fisheries closures be?” Eric stated. Eric was part of a team that set out on the R/V Delaware II—one of several research vessels brought to the Gulf from another region to focus on the spill—to assess seafood safety of pelagic species.
It was challenging to quantify the total impacts on fish species as a result of the spill. Analyses of long-term fisheries-independent datasets did not detect significant changes to fisheries populations due to their broad spatial coverage. However, due to the inherent variability in fisheries datasets, scientists couldn’t rule out the possibility of population-level effects.
Small Fish Help To See the Big Picture
Fortunately, NOAA Fisheries and Southeast Area Monitoring and Assessment Program partners have conducted plankton surveys in the Gulf since 1982 that allow us to understand long-term trends in abundance. During these surveys, we collect larval fish and invertebrate zooplankton samples, along with environmental data, twice a year, down to 200 meters. In response to the spill, we designed and organized additional sampling efforts within the oil footprint to quantify effects on Gulf fish species at different depths throughout the water column. Numerous partners were involved in this concerted effort from the time of the spill through 2011. This resulted in more than 125,000 plankton samples, each of which can contain thousands of individual planktonic organisms and take up to 30 hours to process. In fact, we had to recruit help from other laboratories to process the samples. Dr. Trika Gerard, deputy director for science and operations, noted, “This was a herculean effort and relied on several of our labs, as well as partners. The analyses conducted by our scientists were crucial for determining impacts of the spill on early life stage fishes.” Based on our analyses of plankton abundance and distribution, and accounting for exposure to oil in the surface slick and underwater, an estimated 2 to 5 trillion larval fish and 37 to 68 trillion invertebrates were killed as a result of the spill.
The outcomes don’t just end there. The team also incorporated resources and methodologies that are still being used today. The unprecedented sampling effort led to the establishment of the Deepwater Horizon Plankton Assessment Archive at the Stennis Space Center in Mississippi that contains more than 120,000 individual samples of fish larvae, fish eggs, and decapod larvae. “This dataset was inherently important for understanding impacts from the spill,” said Glenn Zapfe, research fishery biologist in the Trawl and Plankton Branch. “But, now we also have these unique samples in our archive to answer important questions about the deep Gulf like carbon transfer, stomach contents, stable isotope ecology, and more.” These samples are still available for any researchers to study today.
“This event also led to us incorporating innovative technology to assist with sample processing,” added Dr. Gerard. “We acquired several ZooSCAN devices to help expedite and automate plankton sample analysis.” These devices are essentially scanners that can accept a water sample instead of paper. Scientists can then analyze the images to identify and count the critters inside. Since sample processing is quite time-intensive, we've traditionally focused our efforts on identifying and quantifying ichthyoplankton—mostly fish larvae—for species of economic and management interest. Using this technology helps expedite the process so we can examine zooplankton composition more comprehensively. “With these capabilities, we can start to quantify the really important creatures at the bottom of the food chain that feed everything from fish to whales,” explained Zapfe. “Between the archive and new technology, we’re able to better study the entire ecosystem within this body of water that’s right here in our own backyard.” These data are being used to inform ecosystem-wide assessments to holistically understand how the Gulf of America changes through time.
Follow Along to Explore Our Role in Restoration
Southeast Fisheries Science Center scientists are among the leaders in dealing with disaster response and have applied the knowledge, approach, and technologies to respond and mitigate other oil spills and disasters in the marine environment.
The next story in this series will explain the role of the Southeast Fisheries Science Center in supporting restoration efforts over the past 15 years.
The projects described in this story are funded by the Deepwater Horizon Natural Resource Damage Assessment Trustees and the NOAA RESTORE Science Program.
