The Gulf of Mexico's midwater after Deepwater Horizon

In 2010 the Deepwater Horizon well released 4.0 to 4.9 million barrels of oil into the Gulf of Mexico over 87 days, 1,500 metres down, and 770,000 gallons of dispersant were injected at the wellhead.^1,2 A thirteen-year study of the open water below the surface found its fishes, krill, shrimps and small squid fell 60 to 85% within three and a half years and have stayed down.¹ The Gulf's deep-diving whales have fallen too, by more than the models of the spill's damage predicted.¹

Who needs an answer

• Fisheries managers, because tunas, swordfish and other caught species feed on these animals.
• The agencies responsible for endangered whales, Rice's whale among them, which are now seen failing to feed.¹
• Whoever spends restoration money, deciding whether anything can be done offshore at all.
• Anyone weighing the next deep-water well, or deep-sea mining, in open water elsewhere.

The domains it chains

Oil and dispersant moving with deep currents and resettling from the sea floor; exposure of eggs and adults at depth; a food web that lost its middle; whales, fish and seabirds above it; the carbon these animals carry down each night; fisheries and the towns that depend on them.

What a twin should let people try

• Recovery: under what conditions does a population knocked this low climb back, given that sparse animals find mates less often?
• Attribution: how much of the whale decline does the loss of prey explain?
• The next spill: how would a different response, less dispersant at depth for instance, change what reaches the midwater?

Where to start

The study's counts, net sensor logs, echosounder files and genetic data are public in GRIIDC.¹ A food-web model such as Ecopath with Ecosim can take them; the use case on oil spills lists the rest.