The open Gulf's deep-water animals — a vast community most people will never see — have fallen by roughly two-thirds since 2011 and show no clear sign of rebounding. A study published Oct. 19 in the journal Proceedings of the National Academy of Sciences found that deep-pelagic fish declined 63.5%, bristlemouths and krill about 73%, and squid and other cephalopods about 60%, according to a summary from NOAA Fisheries.

The research team, led by biological oceanographer Tracey Sutton of Nova Southeastern University in Florida, concluded that the 2010 Deepwater Horizon spill is the most likely cause. They reached that view after finding that water temperature, oxygen levels, and food supply did not change in ways that could explain the drop.

The animals in question are small, often just a few inches long, but they are the food base for tuna, swordfish, dolphins, and deep-diving whales. If that base stays depleted, the effects can ripple up to the species that Gulf Coast fishing fleets, charter captains, and coastal tourism depend on.

A Food Web Most People Never See

The study focused on the deep-pelagic zone, the open water from about 650 feet to more than 3,000 feet below the surface, far from any seafloor. Many of its residents, including lanternfish, migrate toward the surface each night to feed and return to darkness by day. That daily trip makes them a critical link between surface food webs and the deep sea.

Sutton described the results to NOAA as "the largest faunal decline recorded for Earth's largest ecosystem type."Lanternfish fell 62.9%, all larger crustaceans 62%, and nighttime acoustic readings of animals near the surface about 40%. Researchers also found a significant loss of genetic diversity in three dominant lanternfish species, a sign of population bottlenecks that can leave a species less able to recover.

Separate research has documented declines of up to 80% in deep-diving marine mammals in the region, including sperm whales, beaked whales and the endangered Rice's whale. The new study does not prove those losses are linked, but those whales feed heavily on the squid and fish that dropped.

Three Lines of Evidence Over 12 Years

The findings rest on more than a decade of work by the Deep-Pelagic Nekton Dynamics of the Gulf consortium, known as DEEPEND. A 2011 survey, run for about nine months after the spill, serves as the baseline, and NOAA says those counts resembled data from the 1980s and 1990s. Teams returned for six sampling efforts from 2015 to 2018 and three from 2021 to 2023.

The researchers used the same large net, which samples discrete depths down to about 4,900 feet (1,500 meters), along with echosounder readings and genetic analysis. Populations stayed low through the most recent sampling, with a slight uptick in 2022 and 2023 that was not statistically significant, the Associated Press reported.

Boris Worm, a marine ecologist at Dalhousie University who was not involved in the research, told the AP it was shocking that "a single failure in a drilling rig can have this vast and sustained impact."

Spill Damage That Took Years to Surface

One reason the decline was not obvious right away is that many of these animals live only a year or two. Researchers told the AP that pollutants may have passed into eggs, weakening later generations rather than killing adults outright. The spill also involved about 770,000 gallons of chemical dispersant injected at the wellhead, which broke oil into smaller droplets that spread through deep water.

The study has real limits, and the authors acknowledge them. NOAA notes the declines cannot be tied directly to the spill, and the AP reported the team could not prove an exact causal link. There were no surveys from 2012 to 2014 or in 2019 and 2020, and there is little detailed pre-spill data for the deep open Gulf. The work does not show what is happening in other ocean basins.

Study coauthor John Quinlan, a fisheries biologist with NOAA's Southeast Fisheries Science Center, said the spill exposed how little scientists had measured in the deep Gulf beforehand. The research was funded by the NOAA RESTORE Science Program, the Gulf of Mexico Research Initiative and NOAA's Office of Response and Restoration.

Fisheries, Restoration Dollars and Next Steps

The most direct effects fall on predators that rely on these prey, including yellowfin tuna, swordfish and marine mammals, and on the commercial and recreational fisheries that follow them from Texas to Florida. The study does not measure fish catches or prices, so any effect on seafood supply or charter fishing remains unconfirmed.

The findings could shape how restoration money is spent. Much of the Deepwater Horizon settlement money has gone to coastal and nearshore projects, and NOAA has said the results may point to a system-wide regime shift in the deep Gulf.

BP told ITV News the 2010 accident changed the company and that it has made "many changes intended to help prevent an event like this" from happening again, as reported by ITV.

For Gulf residents and anglers, there is no new seafood advisory tied to this study, and current federal and state fishing rules remain in place. Readers can follow updates from NOAA Fisheries and state wildlife agencies on stock assessments. The DEEPEND team plans to continue monitoring to see whether a recovery begins.

The bottom line: a decade of deep-sea sampling shows the Gulf's midwater food web is far smaller than it was in 2011. The spill is the leading explanation, not a proven cause, and the key open question is whether these populations can rebuild on their own.

What Readers Want to Know

What did the new Gulf study find? Deep-water fish fell 63.5%, bristlemouths and krill about 73%, and cephalopods about 60% between 2011 and 2023 sampling.

Did the oil spill cause the decline? The researchers call the 2010 spill the most likely cause after ruling out temperature, oxygen, and food, but they could not prove a direct causal link.

Why does this matter if people never see these animals? They are a main food source for tuna, swordfish, dolphins, and deep-diving whales that support Gulf fisheries and tourism.

Why did the damage appear years after the spill? Researchers suspect pollutants weakened later generations through eggs, and short-lived species declined as reproduction faltered.

Is Gulf seafood affected? The study did not test seafood safety or catches, and no new advisory has been issued. Follow NOAA and state agency guidance.

Will these populations recover? It is unclear. Numbers stayed low through 2023, and researchers plan further monitoring.