Scientists have identified "rainforests" under the oceans where biological diversity is at its greatest. And these wildlife hotspots should be preserved to give the marine environment a chance of recovering from decades of over-exploitation, the researchers said.
Boris Worm of the University of Kiel, Germany, and Ransom Myers of Dalhousie University in Halifax, Canada, want the major nations of the world to demarcate thousands of square miles of the open water for unprecedented environmental protection.
In effect, they want the oceans to have their own national parks where any form of industrial or large-scale fishing is banned, regions they describe as the "Serengetis of the sea" after the famous wildlife park in East Africa.
"We have discovered for the first time in the open ocean there are hotspots of species diversity which we have meta-phorically called ocean Serengetis," Dr Worm said. "We were looking for the equivalent of the Serengeti on land, which is an area that is important for many large animals but also where they are vulnerable to exploitation," he said.
The oceans are home to a vast array of animals and plants, from the smallest plankton to the largest whales. Life in this world is, however, mostly invisible, little understood and, in many respects, as mysterious as outer space.
Not too long ago, scientists believed the oceans were so vast they were essentially immune to the destructive activities of humankind. No matter what we did to the land, we imagined that the sea would remain a pristine and bountiful resource.
A series of studies published over the past two years has shattered that naive belief. Teams of marine biologists analysed the powerful evidence showing the oceans are in fact dying. Using data gathered by the highly destructive long-line fishing industry, Dr Worm and Dr Myers located the areas of the North Atlantic, and the North and South Pacific where the long-line fishermen caught the most abundant and most diverse range of animals - ranging from the actual targets of their trade, such as tuna and marlin, to the "bycatch" animals such as turtles, dolphins and albatross.
"We concentrated on large species such as shark and tuna to find those special places, to find out whether they existed and, if so, where they were," Dr Worm said.
"It was surprising to find out that these major species - which roam the entire ocean basins - tend to aggregate relatively close to the major landmasses," he said. "It's not somewhere way out in the open ocean, it tends to be a few hundred miles from land."
They found the biodiversity hotspots tended to be in subtropical waters between 20 degrees and 30 degrees north and south of the equator.
That contrasts with the terrestrial hotspots, such as rainforests, which invariably occur in the tropics. One possible reason why subtropical waters are rich in species diversity is because they are regions where cold and warm-water animals can live side by side.
But the scientists also discovered these Serengetis of the high seas needed some other geological or geophysical features, such as intersecting currents bringing warm and cold water together, to create the necessary habitat for a hotspot to survive.
"You have cold and warm water masses meeting each other forming eddies with layers at different temperatures. You have a rich structure and these features together seem to be what attracts many species," Dr Worm said.
"We know, for instance, that eddies in the open ocean concentrate food supply and enhance primary production so that may be a draw, but I don't think food is the only thing. You need a rich habitat structure," he explained.
The study, published in the Proceedings of the National Academy of Sciences, found the richest hotspots tended to be off prominent topographical features, such islands, coral reefs and the point at which the relatively shallow waters of a continental shelf break down into the much deeper regions.
That explained why the scientists found their marine Serengetis off the islands of Hawaii, the Great Barrier Reef off Australia and the shelf breaks off the north-west Atlantic and north-east Australia, and the seamounts off the coast of south-east Australia.
But it was one thing knowing that hotspots exist, it is another to gauge what would happen if they were closed off to the fishing industry. Dr Worm and Dr Myers used computer models to test the idea.
"We simulated what would happen if you closed this particular area or any other area. We did this in the north-west Atlantic where we had the best data and it came out always that the hotspot area was always, consistently the best option for conservation," Dr Worm said. "This is not surprising because on land it has been shown over and over again that protection of hot-spots is the most efficient way to do conservation because you protect many species at once. This seems to apply equally well for the open ocean. To some extent it surprised us in how well this came out," he said.
Most of the data came from long-line fishing in American and Australian waters because those two countries pay for scientific observers to record the bycatch hauled up by the fishermen. Unknown hotspots are, therefore, likely in other parts of the world where observers do not exist.
"There may be some unrecognised hotspots in the Indian Ocean or say off Antarctica which we don't know about," Dr Worm said.
Never the less, America and Australia are well placed to take unilateral action in order to protect the richest part of the oceans so that fishing can hopefully become a more sustainable activity.
"The first step is that national jurisdictions need to do everything in their power to protect those key areas within their national waters. They can't wait for an international consensus on this. They don't have to." As for what needs to be done.
He suggests three things. "First, you have to reduce fishing effort, to a limit where the most sensitive species have a chance to survive.
"Second, you have to protect some key areas that are shared by many species and that appear to be something like a Serengeti that deserves protection.
"And third, you need to eliminate fishing techniques and subsidies that encourage techniques that are simply too destructive, such as trawling and drift nets."Reuse content