Take a deep breath, compose yourself and get ready for another shock. This one concerns the oceans, the largest ecology on the planet and the one that probably has the greatest single influence on the smooth functioning of the Earth's biosphere ‹ the place, incidently, where we just happen to live.

This shock is not about the acidification of the world's oceans caused by the formation of carbon dioxide into carbonic acid, a process that is threatening the entire marine food chain. Nor is it about the rising temperature of the oceans, a process that is compromising the viability of many species, killing coral reefs and altering worldwide weather patterns. Nor is it about nation-sized masses of floating plastics that are congregating in mid-ocean gyres, a process that is producing poisonous islands of contaminants that toxify the flesh of every associated marine organism. Nor is it about the run-off of fertilizers from industrial agriculture, a process that is causing algae blooms that subsequently rot and create "dead zones" where the absence of oxygen kills every living thing ‹ the 58 such zones identified in 2000 have increased to 408 in 2008.

Each of these events should be shocking enough to give us the incentive to radically change the way we conduct ourselves on this planet. But the latest shock is related to the findings of the United Nations' Food and Agriculture Organization that 80 percent of all marine fish stocks are currently fully exploited, over exploited, depleted or trying to recover from depletion. Consequently, ocean predators around the world ‹ whales, dolphins, seals, sea lions, birds and large fish species such as tuna, striped bass, halibut and salmon ‹ are showing signs of emaciation from a shortage of food. In some cases, they just die of starvation. In other cases, their reproductive capability is compromised, they are more vulnerable to disease and parasites, and their ability to hunt for diminishing food is impaired.

This catastrophe was inevitable. As the large species become more scarce from industrial overfishing, we have started to satisfy our own demands by targeting smaller fish ‹ the same fish that are the primary food of the large marine predators.

The Independence (Apr. 19/09) reports that "seven of the world's largest 10 fisheries now go after [these smaller fish]" and that "four times as much of these 'prey fish' are now brought to shore as half a century ago." The term marine biologists use to describe this process of catching ever-smaller species is "fishing down the food chain". And it includes everything from herring and anchovies to squid and even krill.

Krill is a pinkish, tiny crustacea that is a foundation species in the marine food chain, providing nutritious feed for everything from prey fish to birds and whales. It is also used by the salmon farming industry in food pellets and as a flesh colorant. Just one company, Aker BioMarine, catches 200,000 tonnes annually. As a measure of the impact of such a commercial krill harvest on the food chain, just 11 kilograms gathered in four hours of feeding can provide a whale with its nutritional requirement for an entire day. As Oceana marine scientist Margot Stiles puts the problem, "We have caught all the big fish and now we are going after their food."

Ironically, about 30 percent of global fish catch of 145 million tonnes is processed into fish oil and fish meal to be consumed by industrial agriculture. Of the prey fish caught, more than 80 percent are not fed directly to people but go to producing livestock and farmed salmon. Although salmon ‹ being cold blooded ‹ have the lowest feed conversion ratio (FCR) in this industry, non-industry sources estimate that 3 kilograms of feed fish are required to grow 1 kilogram of farmed fish.

The salmon farming industry argues in defence of itself that it is feeding a quality food to a hungry world with its approximately 1.5 million tonnes of annual global production. Beyond causing direct damage to wild salmon stocks because of sea lice, disease transfer and environmental degradation, inefficiency alone makes this argument disingenuous. Not only are farmed salmon unaffordable for most of the planet's people but their production pulls valuable feed fish from the oceans that could be better used to nourish people directly. Alternately, these feed fish could be left in the oceans to sustain its faltering ecologies. Regardless, salmon farming becomes another industrial player in the pillaging of the world's oceans, an abuse contributing to the collapse of the entire marine ecosystem.

Tragically, the same feed fish that are used to grow the industrial crops of salmon, pigs, chickens and cattle are also critical to sustaining the countless creatures that constitute healthy, living oceans. If this human demand for fish is likely to increase 70 percent by 2030 ‹ a contention the salmon farming industry uses to justify its ambition to expand ‹ then an already serious problem will simply get worse.

We have now reached a critical juncture in our dysfunctional relationship with the planet's largest and most impressive ecology. If we don't begin to allocate its resources more wisely ‹ if we don't begin to take more frugally and to leave more generously ‹ then we will have left nothing for the most noble of sea creatures and we will eventually have nothing left for ourselves.

The prospect is shocking. But, it can be avoided if we just had the political will to implement moratoriums, to enact catch limits and to establish marine protected area where absolutely no fishing is allowed. Does anyone want the alternative?