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The oceans constitute around 70% of the Earth’s surface and contain around 97% of its water. A large proportion of all life on Earth exists in the oceans although the actual proportion of global biodiversity present in the oceans is unknown as many species are still to be discovered given large areas of the oceans are unexplored. Ocean movements and marine life also influence the fundamental requirements for life. Marine organisms are significant contributors to the oxygen cycle and ocean currents play a major role in determining the Earth’s climate and the water cycle.
Human activities are affecting the health of oceans, most notably and pervasively through the contribution of climate change to rising ocean temperatures and acidification, which is affecting sea levels, precipitation patterns, the incidence of extreme weather events and, possibly, ocean circulatory patterns. Increasing urbanisation in coastal areas is also having significant impacts in many coastal ecosystems. Dredging, land-filling and the construction of physical barriers such as jetties cause disruptions to currents as well as sediment flow and discharge, with potentially significant impacts on these sensitive ecosystems.
The marine life supported by oceans represents a vast resource providing food, medicine, and raw materials to support human life and economic activities. In 2007 fish accounted for 16% of the global population’s intake of animal protein and 6% of all protein consumed. In low-income food-deficit (LIFD) countries, which typically have a relatively low consumption of animal protein, the contribution of fish to total animal protein intake, at 20%, is notably higher. Of the 66 LIFD nations in 2012, 53 are in the Tropics. As around 57% of fisheries production is from marine capture and around half of this is in small-scale fisheries, sustainable ocean fish stocks are critical to the everyday lives of millions of people in developing nations.
Demand for marine commodities is increasing, driven by rising incomes and changing consumer patterns, increased globalisation and trade, population growth and high levels of poverty in many tropical coastal countries. In some areas – notably where poverty overshadows environmental concerns and where unregulated and illegal fishing is prevalent – persistent over-fishing is having long term impacts on the capacity of marine ecosystems to recover and again become productive.
To some extent aquaculture is reducing pressure on wild fish stocks, but its benefits are offset because of the extensive use of fish meal in aquaculture. Globally, aquaculture’s proportion of total fisheries production is increasing rapidly, though the output is increasingly high-value fish destined for export markets rather than for local consumption. As such, the sustainability of wild marine stocks remains a critical issue for the wellbeing of many small-scale fishing communities. For these communities the collapse of their fisheries would have significant food and human security implications.
While decreasing in the rest of the world, the wild marine catch in the Tropics is increasing, and currently accounts for almost 45% of the global catch, up from 12% in 1950. Nonetheless, growth has slowed considerably in recent years as more fishing resources become fully exploited.