Last year the world's wild fish catch weighed in at 90 million tonnes - a scale so vast that it is almost impossible to understand.
The world's fishing fleet has about four million commercial vessels. Just one percent of these are factory ships - yet they account for 60 per cent of the world's fish catch. Several hundred feet in length, with nets comparable to the size of football pitches, they fish 24 hours a day on fishing trips that last over a year. Capturing, grading, processing and freezing in a never-ending cycle they can store up to 7,000 tonnes of frozen catch. That's the weight of 40 blue whales.
But where the fishing fleets hunt so too do the oceans' other predators: the cetaceans - dolphins, porpoises and whales - and fish like merlins, sharks and rays. Seals, turtles, sea birds and a myriad of other animals also rely on the oceans for their food. Inevitably some of these get caught too.
This unintended catch - the bycatch, or what some call 'trawler trash' - accounts for 20 - 40 million tonnes of animals a year and also includes fish that are too small or over-quota or not profitable enough or prohibited and endangered species like the wild Atlantic salmon, the Atlantic halibut, the bluefin tuna, the Chilean sea bass, the hoki, the orange roughy, several species of sharks - and many, many more. According to Greenpeace every year 300,000 cetaceans and 100 million sharks and rays are thrown overboard. Nearly all 'discards' are dead or injured, or at the very least severely traumatised. Such is the story of 'mid-water' trawling.
As if this wasn't carnage enough bottom trawls are more destructive still. Dragged over the ocean floor - of shallow coastal waters and down to depths of 6,000 feet - trawling can persist for hours. As the huge nets drag along the sea bed they rip up everything in their way leaving clouds of silt in the water, destroying habitats and leaving a barren wasteland behind. Trapped inside are targeted species like sole, plaice, and turbot; rockfish, squid and octopus; shrimps, lobsters, scallops. But the nets also scoop up all manner of other sea creatures: starfish, crabs, sea urchins, brittle stars, molluscs, sponges, worms and a lot more besides, including rocks and other debris.
But not all nets are trawled. Drift nets - as their name implies - are left to float freely. Hanging like vast curtains on the high seas some are 40 kilometres long. Fish are caught when they get snagged, or entangled, in them. Although drift nets are set to catch herring, tuna, squid, shark and salmon they also trap marine mammals and birds. Broken jaws and beaks are evidence of their struggle to escape.
Sometimes nets break free from their floats. Called 'ghost nets', they continue fishing until the weight of their catch makes them sink to the sea bed. There, bottom dwellers feed on the animals caught in them: a profusion of fish, birds and sea mammals. And then, freed of their load, the nets rise again to repeat the cycle. Ghost nets can drift like this for up to 5 years. Also littering the oceans - in ever increasing abundance - is other jettisoned fishing tackle that reaps its own environmental and lethal havoc: tangles of nylon nets, long-lines with hundreds of hooks attached, floats, ropes, traps - on a ghastly scale.
If you wanted an example of the 'tragedy of the commons' you couldn't do better than this. Fishing revenue contributes about £4.3 billion to the UK economy; and worldwide about 500 million people rely for employment - in whole or part - on the commercial fishing trade: people such as fishermen, chandlers, fuel providers, distributors, retailers. Meanwhile we haul out of the oceans as many species as we can possibly use; dumping those we can't; demolishing habitats; depleting fish stocks beyond their ability to recover.
According to a report for the United Nations Environment Program ("In Dead Water), if fishing carries on at its present rate all the species currently caught will have disappeared by 2048. According to Greenpeace up to 90% of the world's large predatory fish have already been wiped out. And according to Dr. Melanie Stiassny of the American Museum of National History "One of the shocking realities of the global fishing industry is that about a third of all of the economic revenue from fisheries is actually provided by government subsidy."
To save the oceans from environmental catastrophe fishing needs to be cut back to a level which allows fisheries to recover. Destructive fishing practices - like bottom trawling - need to stop. Marine reserves - where fishing is prohibited - need to be set up. But that requires world governments to forego their self-interests. The tragedy is that that is not going to happen. Is it?