Humankind's heavy hand
After thousands of years, humankind's often heavy-handed presence on the sea has begun to take its toll.
Overfishing is not the only problem, but rather just one of many.
Indeed, despite some advances in recent years, pollution -- urban sewage, agricultural runoff, and industrial effluent -- is still a major problem in the Mediterranean.
The coastal population of the region is estimated at around 150 million, and nearly half (48 percent) of the urban centres in which they live lack sewage treatment facilities, according to the United Nations Environmental Programme (UNEP).
A staggering 80 percent of all Mediterranean wastewater -- three billion cubic meters -- enters the sea untreated each year.
Industry, too, takes a toll.
UNEP calculates that 66 million m3 of untreated waters containing phenols, mercury, lead, chromium, zinc and mineral oils enter directly into the sea annually. Chemical runoff from agriculture is a significant concern, too.
The situation is particularly troubling since the Mediterranean is a nearly closed basin whose only natural outlet, through the Straights of Gibraltar, is so narrow that it takes 80 to 100 years for the sea's water to be recycled.
The Mediterranean is also under pressure from intense maritime shipping activities, UNEP reports: 30 percent of international sea-borne trade volume originates in or is directed through it, while 28 percent of the world's sea-borne oil traffic transits the sea.
Beyond pollution, another impact that maritime traffic has is the introduction of alien aquatic plant and animal species, which occurs when ships dump ballast water taken on overseas.
Some observers also warn that the new practice of capture-based aquaculture could potentially introduce alien aquatic diseases, as large amounts of fish are imported from other waters in order to feed the penned tuna.
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