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The Marine Environment is under increasing pressure from fisheries, pollution, mineral extraction and climate change.

The greatest and most serious impact on marine ecosystems is caused by the annual removal of more than 100 million tonnes of fish and shellfish.
This harvest affects the species composition of pelagic communities as well as nutrient concentrations in surface waters. Bottom trawling disrupts and changes the habitats on the sea bed.

In 1995 the United Nations Food and Agriculture Organisation concluded that 70% of the oceans fishing stocks are either fully exploited, overfished or recovering from being overfished. By 2004 this had risen to 77%. Of these 28% are more or less seriously overfished (based on 1999 data).

20% of the world catches are taken from stocks for which there is not sufficient information to assess their state of exploitation.

Man has now depleted fish poplutaion and altered oceanic ecosystems over vast regions. Large oxygen depleted dead zones are appearing in the open ocean, toxic algal blooms are resulting in dead zones in productive inshore waters and contaminating shellfish, Toxic 'stinking' fish are being caught in the arctic.

International regulations are difficult to enforce and ecomonic issues , not scientific management , continue to drive the industry. This must change if sustainable management of the worlds oceans is to become a reality.

Sources:

http://www.fao.org/fishery/topic/2681

Lalli, Carol M. and Parsons, T.R. Biological Oceanography 2nd edition (1997) Elsevier.