Oceans in peril

There is a growing scientific consensus around the world that the oceans are in deep trouble - and that humanity is responsible.

The symptoms include collapses in fish populations, deaths of coral reefs, the contamination of sea life with toxic chemicals, the pollution of shallow seas with sediment and nutrients causing algal blooms, changes in the currents which distribute energy around the planet and signs that the oceans themselves are becoming more acidic.

Such issues are remote from the daily interests and concerns of ordinary people. It is true that in Europe one can pay $80-90 a kilo for fish fillets, and that thanks to globalisation similar prices will prevail worldwide within a few years, placing fish out of the reach of most consumers. But the real menace seems to lie beyond our collective imagination.

In The Silent Deep (UNSW Press, 2007), due out shortly, Australian marine scientist Dr Tony Koslow - formerly of CSIRO, now at the Scripps Institute in California - traces the discovery, exploration and plunder of the deep oceans in the last few decades. In it he states: “We may think of the deep sea as pristine, but in fact no portion of (it) is today unaffected by human activities.”

Koslow likens the unsustainable deep-sea harvest to the destruction by Stone Age hunters of the megafauna of Europe, Asia, the Americas and Australia. Orange Roughy stocks collapsed, he explains, because they were fished down too fast, before we understood their size and turnover rates and could manage the fishing pressure.

Similar tragedies are occurring worldwide, wherever fish and corals gather on the peaks of deep seamounts: “Fishers in 25-metre boats can level a pristine coral reef at 1,000m depth as readily as loggers with chain saws and bulldozers can clear an old-growth forest.”

Writing in The Australian, John Schubert (Don’t let our corals lose their colour, January 2, 2007) warned of the impact of climate change on the Great Barrier Reef, giving as an example the death of half the corals off Great Keppel Island due to bleaching. Scientists at the ARC Centre of Excellence for Coral Reef Studies are finding evidence that intact fish populations are essential for corals to recover from such blows.

Australia has been shrewd enough to introduce “green zones” (no-take areas) on a third of the Great Barrier Reef (GBR), but this doesn’t apply to most of the world’s coral reefs, whose 200 million human dependents will be destitute if the corals die.

One interesting development is the Australian Marine Conservation Society’s increasingly popular Sustainable Seafood Guide, which advises consumers which fish to choose or avoid on the basis of their sustainability.

While the experts may argue about what is and isn’t a sustainable fish stock, the idea of transferring the onus for protecting marine species to consumers, rather than fishers, is a good one. Fishers can hardly be blamed for trying to make a living - but consumers can always purchase and consume more wisely, sending fishers the correct market signals.

The destruction of shallow seas - and their aquaculture industries - by the discharge of sediment, nutrients and pesticides from the land is a global problem which as yet has few answers, though efforts are being made to solve this in the catchments of the GBR and elsewhere.

An as-yet undefined danger from the deep ocean is the “clathrate gun” - a theory that warming could cause the violent release of trillions of tonnes of frozen methane from the seabed, precipitating a runaway greenhouse effect that would leave the planet more like Venus than Earth.