Marine Biodiversity was the theme for International Day for Biological Diversity (IDB) in 2012. Designation of IDB 2012 on the theme of marine ecosystems provides Parties to the Convention on Biological Diversity (CBD) and everyone interested in marine life, the opportunity to raise awareness of the issue and increase practical action.

How Much Life Is in the Sea?

From 2000 to 2010, an unprecedented worldwide collaboration by scientists around the world set out to try and determine how much life is in the sea.

Dubbed the ‘Census of Marine Life’, the effort involved 2,700 scientists from over 80 nations, who participated in 540 expeditions around the world. They studied surface seawater and probed the deepest, darkest depths of the ocean, sailed tropical seas and explored ice-strewn oceans in the Arctic and Antarctic.

By the time the Census ended, it had added 1,200 species to the known roster of life in the sea; scientists are still working their way through another 5,000 specimens to determine whether they are also newly-discovered species. The estimate of the number of known marine species - the species that have been identified and the ones that have been documented but await classification - has increased as a direct result of the Census efforts, and is now around 250,000. (This total does not include some microbial life forms such as marine viruses.) In its final report, the Census team suggested it could be at least a million. Some think the figure could be twice as high.

Marine and Coastal Biodiversity

Along the Coast

The Continental Shelf

The Open Ocean

The Deep

Great Migrations

The Human Impact

Causes of Decline

A Warmer Ocean

A More Acidic Ocean

The Problem of Over-Fishing

Why We Should Care

Blue Carbon

The Value of Marine Reserves

CBD and the Jakarta Mandate

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The Problem of Over-Fishing

The earliest known example of humans turning to the sea for food dates back approximately 164,000 years, when people began using shellfish to supplement their diet at Pinnacle Point in southern Africa. Recent studies suggest that people may actually have been hunting tuna off the coast of Australia as early as 42,000 years ago. Prehistoric Native American fisheries were taking place along the central California coast at least 7,000 years ago.

Today, more than four million fishing vessels of all kinds in the world, from industrial trawlers to small boats powered by sails and oars, provide, in combination with the world’s fish farms, over 140 million tonnes of fish every year. That averages out to approximately 17 kg for everyone in the world, with fish providing more than 1.5 billion people with almost 20 percent of their average per capita intake of animal protein.

But, although numerous small fishing operations in coastal communities provide subsistence-level catches without causing severe environmental consequences, the commercial fishery worldwide comprises too many ships, with too much capacity, chasing an insufficient number of fish, with predictable consequences.

A 2011 study estimated that 28-33 percent of all fish stocks are being over-exploited, and 7 to 13 percent have collapsed completely. For example, in 1992, the cod fishery off Newfoundland collapsed, after dire warnings of impending disaster from scientists, with the loss of 40,000 jobs. Meanwhile, the southern bluefin tuna has been depleted by an estimated 92 percent, and catch quotas for Atlantic bluefin tuna continue to be set at levels higher than those recommended by scientists, leading to concerns for the future of that species.

Commercial fishing has had a particularly devastating effect on large, predatory fish species such as tuna, billfish and sharks. A 2003 study found that, on average, industrial fisheries required no more than 15 years to reduce communities of such fish, and estimated that, overall, 90 percent of predatory fish worldwide have been removed from the ocean. In many cases, these declines have been accompanied by significant decreases in those species’ ranges: that is to say, as a result of over-fishing, there are areas of the ocean where some species of tuna, billfish and sharks no longer exist.

In their search for more fish, commercial fisheries are even extending into the dark, deep ocean. Bottom trawl nets scrape along the floor, devastating sea bed communities, damaging sea mounts and crippling the long-lived cold water corals that live on them, and targeting deep-sea fishes such as orange roughy.

The very slow reproduction and growth rates of many deep sea fishes makes them especially vulnerable to the impacts of fishing – so much so, in fact, that it seems likely that for many species, once a stock has been depleted, it will take decades, and potentially centuries, before it will recover.

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