Worldwide, 90 per cent of large predatory fish stocks are now gone due to overfishing.
The UN Food and Agriculture Organization (FAO) estimates that 85 per cent of fish stocks are "overexploited, depleted, or recovering from depletion".
Speaking on the occasion of International World Biodiversity Day on May 22, UN chief Ban Ki-Moon warned that over-consumption and rampant pollution was threatening the world's oceans and marine biodiversity.
"Commercial over-exploitation of the world's fish stocks is severe," he said. "Many species have been hunted to fractions of their original populations. More than half of global fisheries are exhausted, and a further third are depleted."
This critical convergence of rapidly declining fish stocks and a growing number of the planet's inhabitants depending on seafood will be discussed at the Rio+20 United Nations Conference on Sustainability coming up next month in Brazil.
Are the talks it too late, or is this still a solvable problem?
Dr Maria Salta, a biological oceanographer at the University of Southampton in the United Kingdom, gave Al Jazeera a bleak prognosis about the state of the oceans.
"It is clear that if we continue like this, in a few years time there is not going to be much left," she said of the rampant over-fishing going on across the globe, along with the overall treatment of oceans at the hands of humans. "We are losing species every day without ever knowing about them. Sometimes humans can be like a plague to the environment."
Dr Salta's statement might be shocking to some, but there is ample scientific evidence to back it. Overfishing is simply a matter of taking wildlife from the sea at rates that are too high for the fished species to replace themselves. Atlantic cod and herring, along with California's sardines, were overfished to the brink of extinction by the 1950s, and by the late 20th century, isolated depletions had become both global and catastrophic.
Fisheries for the most sought-after species have since collapsed. Boris Worm and Ransom Myers, both scientists with Dalhousie University in Halifax, Canada, published a shocking paper in the journal Nature in 2003 explaining that the populations of all large predator fish in the oceans have declined by 90 per cent in the 50 years since modern industrial fishing became widespread.
Three years later the same scientists, along with colleagues from across the world, published an even more startling paper that predicted a total collapse of all fish that are currently caught commercially by 2048.
Daniel Pauly of the University of British Columbia, along with others, has calculated that the world's total fish catch peaked in the mid-1980's and has been in decline every since.
Dr Simon Boxall, also with the University of Southampton, has been an oceanographer for over 30 years. He sees the three largest threats to the oceans as climate change, plastic, and overfishing.
"But the big problem is that we are overfishing," Boxall told Al Jazeera. "The [fisheries] management isn't working, and is in fact causing just as much destruction than if there was no management in the first place."
Sharks are an example of this problem. The International Union for Conservation of Nature has listed about a third of all open-ocean shark species as currently threatened with extinction because of overfishing. "The oceanic white-tip shark populations declined by 99 per cent from 1950 to 1999, making it now an endangered species," Salta said, giving an example. "Also, when sharks are removed from the environment you change the balance of the ecosystem and how it functions."
An issue that works in tandem with overfishing is bycatch, which is sea life that is caught along with the fish being sought commercially. Dr Salta thinks bycatch could be one of the most worrying problems facing the oceans, and goes as far as saying that bycatch is "a mode of mass marine extinction".
"From 1994 onwards, 27 million tonnes of bycatch are discarded every year," she said. "Thirty per cent of marine catch is thrown overboard dead. For shrimpers, 80 per cent of everything caught is bycatch and thrown back for dead."
Disturbingly, according to the Pew Environmental report Protecting Life in the Sea, nearly one-third of the world supply of commercially caught fish has already collapsed.
Dr Salta explained how many of the problems besetting the oceans converge to create a cascading effect on sea life.
"If organisms drop out of the food chain, the entire ecosystem is impacted," she said. "And temperature affects biodiversity and fish stock. Changes in this variable can impact the entire ecosystem and impact fish stocks."
She cites copepods (tiny crustaceans) in the North Sea as an example. "There was a specific species that hatched in the spring, that was for cod, but during the 1990's because of temperature change, these were replaced with a warmer weather copepod and these hatched too late," she said. "So the cod have vanished there, coupled with exploitation by man."
Dr Boxall also cites the North Sea cod fishery as an example of how climate change is affecting fisheries. "Those cod were overfished, but we also see climate change kicking in and warming the waters, and cod, which like a cooler climate, are being pushed further north," he explained. "Our cod are migrating to Iceland."
|Many scientists believe that 'artisan fishing', using more fishermen in smaller boats as opposed to factory fishing ships, is one solution to the over-fishing crisis [Reuters]
Salta said that 25 per cent of the planet's biodiversity is in danger of extinction within the next 30 years due to commercial fishing.
"When fish become overfished, the human response is to fish down the species to smaller species, so this shifts the target group down, and this affects biodiversity and the ocean ecology," she explained.
Another aspect of overfishing is trawling - a fishing method that involves pulling fishing net through the water behind a boat. Bottom trawling, when the net literally drags across the seafloor, has obviously negative impacts.
"It's the equivalent of forest clear-cutting, but in the ocean, because when they [fishermen] trawl the entire bottom, whatever is there is removed from the environment and changes the entire ecosystem," Salta said. "Biomass of the deep sea is in sharp decline because of trawling."
Salta said that by doing all of this, the commercial fishing industry is affecting evolution of sea life by causing many fish species to mature earlier, hence causing them to grow to smaller sizes, which causes females to produce smaller eggs of lower quality.
Dr Debora Iglesias-Rodriguez is a biological oceanographer at the UK's National Oceanography Centre. She specialises in the study of how human impact on the atmosphere is changing the chemistry of the oceans and how this causes acidification. Her concern is that climate change plays a role in lowering fish stocks.
"Calcifying organisms are essentially chalk-producing organisms, and when seawater becomes more alkaline, this is impacted negatively by dissolving them," Iglesias-Rodriguez told Al Jazeera. "Calcification affects fisheries because many fish's diet is based on these organisms. So this has food security impacts as well."
Boxall, like many scientists, is distressed about the current state of the oceans. "The sea is over 73 per cent of our world. The scale of it means that anyone actually trying to go out and clean them is not physically possible. We have to find ways to change our impacts, because we can't change what has been done already."
But he believes there are solutions to many of these problems.
"A sustainable fishery looks like an artisan fishery," he said. "Small vessels with small nets, catching what might be considered commercially unviable is what we need. 100 small boats would be better than one large factory ship that is scraping the seabed and taking everything out of an area. On small boats, after the sorting, much of it is alive when it goes back into the water."
Boxall suggests we start thinking more about an environmentally driven market, as opposed to a commercially driven market.
"Fishing as it's running at the moment isn't sustainable," he explained. "The industry will collapse because there won't be fish to catch. But if we manage it properly now, and come to agreements driven by science and not commerce and politics, we'll have fisheries in the future. But it's almost becoming not viable to fish anymore because there are fewer and fewer fish to catch every day."
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