The depletion of global fisheries, the degradation of marine ecosystems and despoliation events like the Exxon Valdez, the Gulf of Mexico oil disaster and closer to home, our own Rena stranding, are all mileposts of the ever-increasing strain we're exerting on the oceans.
It's reminiscent of limits that the unbridled exploitation of land hit only a few hundred years ago. We've all heard of the tragedy of the commons - the idea that given half a chance villagers will overgraze a patch of common land with their cattle, leaving it fit for no one. Nowadays the commons have largely been erased on land, most commonly replaced with individual property rights such as our own fee-simple title.
But two huge commons remain in our world - the ocean and the atmosphere. Each is at risk, with issues such as climate change and unsustainable fishing at the forefront of the stresses they're under thanks to a lack of effective governance of the resource.
In the ocean the tragedy of the commons sees fisheries being stuffed, both economically and biologically. As we explore in Hook, Line and Blinkers, the individual race for personal gain leads to a collective madness, with too many fishers, and too much gear, chasing too few fish.
Yet it turns out that a bit of fishing actually increases the productivity of a fishery, in terms of what can be harvested each year. By removing the older fish, the younger fish have more food to eat and can grow faster. So in theory there is a "sweet spot" - a level of fishing that produces the greatest quantum of fish harvest a year (known in the business as Maximum Sustainable Yield, or MSY). Surprisingly, most fish populations are quite resilient, and can be fished all the way down to 20 to 35 per cent of their original size and still generate the largest possible sustainable catch.
From the perspective of economic benefit at least, there is no need to protect the original biomass.
But there are limits. Unfortunately in the commons, fishers are more concerned with short-term profit than biology and what's sustainable. Finding a new fish stock is akin to a gold rush and, as we saw with the Chathams crayfish boom of the 1960s, this encourages more fishers to pile into the industry. Standard commercial profit maximisation sees to it that fishing effort keeps increasing until the costs outweigh the benefits - when it is no longer profitable to haul another fish on board. At that point new boats stop joining the plunder.
With new technology making fishing cheaper and cheaper, nowadays the fishing effort usually doesn't stop intensifying until well after the fish population is beyond that sweet spot of maximum sustainable yield. By this stage the fish population is stuffed, unable to replenish itself in the numbers that give us the highest annual catch.
As a fish population dwindles towards extinction, we are left with too many fishers. This leads to a rather strange outcome, where fishers could collectively catch more in the long term, if only there were fewer people fishing. Do less, get more - sounds like a bargain. But who wants to be the person hanging up their net for the benefit of others?
Typically what has happened once the local fishing industry has over-extended itself is that the fishers approach their government for a hand-out.
These sorts of subsidies are popular, in fact huge, in Europe for instance, but only serve to make the problem worse. By lowering the costs of fishing further, more fishing happens until there are even fewer fish left in the water! The World Bank puts the total cost of subsidies and overfishing around the world at US$50 billion ($66 billion) a year - or one eighth of the total income of the global fishing industry.
Many developed nations have "solved" this conundrum by sending their fleets to plunder the waters of other, less developed countries.
The Pacific, for example, has been the recipient of Europe's surplus fishing fleet activity. With this crazy state of affairs it was only a matter of time before the world hit Peak Fish.
Depending on which data you use, catches of wild fish peaked somewhere in the 1980s or 1990s. Despite continued greater fishing effort (more boats, more effective technologies) the global catch has stagnated for the past 25 years.
The likelihood is that we're continuing to fish down the global fish stock further and further below the level which would yield a sustainable annual catch. In other words, this peaking of the catch looks to be the plateau before it starts to plunge, rather than any pause that refreshes the global sustainable catch.
Of course all this fishing also has considerable impact on the environment. Even fishing a population down to the so-called "sustainable" level can change an ecosystem.
We have seen this in New Zealand where the fishing of large snapper and crayfish led to a population explosion of kina, which in turn munched all the available kelp. But overfishing can be even more devastating; the plundering of the Grand Banks cod fishery seems to have permanently changed the ecosystem; without the cod around the prawns have taken over.
Perhaps the greatest illustration of the devastation from overfishing is when the wholesale removal of large fish - so often the top predators in an ecosystem - increases the chance of an ocean area developing into a toxic dead zone - where no sea life exists any more. Such dead zones cost the world US$16 billion each year in health problems.
Scientists disagree over the size of the overfishing problem. Getting reliable catch data is hard enough, data on fish populations is a lot more difficult - we can't see them, and they move around. You may recognise some of the more alarmist claims - that most large fish populations are 10 per cent of their original size and that the oceans could collapse by 2046.
More reliable stock assessments show that around a third of all fisheries are now overfished - in a state where the annual catch is a lot less than what could have been achieved, and worse - still falling.
But even this data has its problems - it is only available for a handful of fisheries, and we often don't know what the original state of the fish population was so estimating the true sustainable yield is impossible.
But what everyone can agree on is that the tragedy of the commons still exists in the global fishery, and that the only way around this problem is to manage our fisheries.
It is safe to say that most populations of large fish have been reduced by at least 70 per cent since World War II. As technology improves, fisheries management is the only thing that could stop the same happening again in the next 60 years to the next tranche of largest fish. With only 7 per cent of global fisheries under any form of management regime, this looks inevitable.
In 1986, New Zealand took bold action and embarked on the world's greatest experiment in fisheries management by creating the Quota Management System.
The scheme is lauded as the best in the world by successive governments here, in spite of mixed reviews around the world. Has it actually worked? Despite the self-congratulatory claims, this question has never been officially answered by our government. We will do that in next week's column.
