The pair were diving in Bravo Crater, a 75m (246ft) deep and 1.5km (0.9 miles) wide crater in the north of the island chain. The water column is relatively low in radiation, with amounts comparable to background levels in most parts of the world. But the sediment on the bottom tells another story – to this day, there are high concentrations of radioactive plutonium, americium and bismuth, higher than anywhere else in the Marshall Islands. This is where, on the morning of March 1, 1954, the US conducted its largest ever thermonuclear test.
More than six decades later, Palummbi and his colleague were amazed at what they saw. The center of the crater is still quite bare, with only a thick layer of silt. But on the edges, they found a hidden haven, where rainbows of small fish circled boulder corals the size of small cars, and the distinctive torpedo-like forms of black and gray reef sharks were ubiquitous.
“It’s mental,” says Palummbi. Despite combating the effects of radiation, which is thought to have created a population of it mutant sharks missing their second dorsal fin, the reef was very much alive. And the fish were giants – at least, compared to those you would find in places where their fish are regularly hunted.
This is the most obvious consequence of the abandonment of fishing – there would be more fish, and they would be much larger than in modern generations.
Back in March 2006, George W Bush – then president of the United States – was watching television in the White House. According to popular rumors, a PBS documentary was on the program that day about the Northwest Hawaiian Islands, a remote archipelago in the Pacific Ocean. It seems he was so enchanted, that he immediately began to look inward ways to protect them. With the help of an obscure, century-old law, he created the Papahānaumokuākea Marine National Monument – now the largest marine conservation area in the world.
Unlike vast expanses of other marine protected areas, which still allow fishing – no-take zones make up only a fifth of this category – the new reserve has completely banned fishing.
The impact was almost immediate. “We started to see effects after about a year and a half,” says John Lynham, a professor of economics at the University of Hawaii who specializes in ocean recovery. There was more marine life overall, and the most rapid recoveries of previously harvested species, he says. Amazingly, yellowfin tuna and bigeye were among the answer first – although they are top predators and adults average 6ft (1.8m) in length, they are fast growing.
Like Bikini Atoll, the other notable remains were complete accidents. Take the advent of the Second World War in September 1939. For the next six years, the North Sea was almost entirely without fishing. With large, sturdy designs and clear, open decks, fishing trawlers were relatively easy to convert into minesweepers – warships that scoured the oceans for mines and dropped them. Together with the dangers of mines, warships and bombing to civilian navies, this meant that very few fishing vessels were active throughout the war.