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(Click to enlarge)
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There is a strong link between areas with high densities of
industrial activity and zones of seasonally oxygen depleted waters.
In recent years, there has been an increasing focus on treating
and reducing municipal and industrial wastes, and on reducing nitrogen
levels in agricultural runoff. However, less attention has been
paid to the continually increasing nitrogen emissions into the atmosphere.
It is believed that between 10% and 70% of the fixed nitrogen input
in many coastal regions is currently delivered by rain and the fallout
of nitrogen compounds from the atmosphere.
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GESAMP recommends that atmospheric nitrogen must be
included among the nutrient sources assessed as part of the management
of coastal water quality. Political factors are also of major significance,
as the primary causes of atmospheric anthropogenic nitrogen result
from energy generation and transportation, and thus from society's
economic and social activities (GESAMP, 2001b). |
| Urgent Actions for Controlling
Land-Based Activities |
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At the technical, management and policy levels, the
most urgent actions for controlling land-based activities, in order
to improve the quality of the marine environment, are:
- Preventing habitat destruction and the loss of biodiversity
through education, combined with the development and enforcement
of legal, institutional and economic measures appropriate to local
circumstances;
- Establishing protected areas for habitats and sites of exceptional
scenic beauty or cultural value;
- Devoting primary management attention to the control of pollution
from sewage, nutrients (especially nitrogen) and sediment mobilisation;
- Designing national policies that take account of the economic
value of environmental goods and services, and provide for the
internalisation of environmental costs; and
- Integrating the management of coastal areas and associated watersheds.
Source: GESAMP, 2001b.
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It has been estimated that about 80% of all marine pollution
originates from land-based activites. It reaches the ocean directly,
via rivers, or through atmospheric depositions.
- Inputs of nitrates to the North Sea, for example, have risen
four-fold, and phosphate inputs eight-fold, since the 1970s, causing
eutrophication and tides of toxic algae that have killed stocks
in offshore fish farms (Harrison and Pearce, 2001).
- Severe eutrophication has been discovered in several enclosed
or semi-enclosed seas (UNEP, 2002).
- Eutrophication has been linked to the formation of 'dead zones'
on the ocean floor. One of the largest known 'dead zones' is found
along the United States shoreline of the Gulf of Mexico, which
receives large volumes of fertilizer from the Mississippi River
system (Harrison and Pearce, 2001).
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- The collapse of the Baltic Sea cod fishery in the early 1990s
is blamed on oxygen loss in deep waters due to eutrophication,
which interfered with the development of cod eggs.
- Eutrophication can also cause Harmful Algal Blooms (HABs), which
can harm fish and shellfish, as well as the people who consume
them. Some algae can cause negative effects when they appear in
dense blooms, while others have potent neurotoxins and need not
be present in large numbers.
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Losses Caused to Fisheries and Aquaculture by Harmful Algal Blooms
| Date |
Location |
Species |
Loss(Millions of US$) |
| 1972 |
Japan |
Yellowtails |
47 |
| 1977 |
Japan |
Yellowtails |
20 |
| 1978 |
Japan |
Yellowtails |
22 |
| 1978 |
Korea |
Oysters |
4.6 |
| 1979 |
Maine, USA |
Many species |
2.8 |
| 1980 |
New England, USA |
Many species |
7 |
| 1981 |
Korea |
Oysters |
>60 |
| 1985 |
Long Island, NY USA |
Scallops |
2 |
| 1986 |
Chile |
Red salmon |
21 |
| 1987 |
Japan |
Yellowtails |
15 |
| 1988 |
Norway and Sweden |
Salmon |
5 |
| 1989 |
Norway |
Salmon, rainbow trout |
4.5 |
| 1989-1990 |
Puget Sound, WA USA |
Salmon |
4-5 |
| 1991 |
Washington State, USA |
Oysters |
15-20 |
| 1991-1992 |
Korea |
Farm fish |
133 |
| 1996 |
Texas, USA |
Oysters |
24 |
| 1998 |
Hong Kong |
Farm fish |
32 |
| Source: Vital Signs 1999 in GESAMP, 2001a. |
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According to the Joint Group of Experts on the Scientific Aspects
of Marine Environmental Protection (GESAMP), the crisis in capture
fisheries stems from three main causes:
- Free and open access to fishing areas, particularly the high
seas, which encourages over-fishing without concern for stock
sustainability;
- Subsidies for fishing fleets, estimated at up to US $20 billion
a year, which encourage unprofitable fishing;
- Non-compliance of seasonal closures of fisheries or fishing
limits, which, although designed to conserve stocks, are countered
by fishermen working harder during the periods when fishing is
allowed.
Unless governments and the fishing industry take effective action,
over-fishing and long-term declines in catches will invariably continue.
At the moment, the major fisheries bodies and agreements are not
particularly effective, with their members exhibiting little commitment
to cooperating on the conservation of stocks and failing to fulfil
previously made commitments (GESAMP, 2001a).
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Aquaculture is having several detrimental long-term environmental
impacts, among them:
- Increased releases of nutrients, pathogens and potentially
hazardous chemicals into coastal waters;
- Salinisation of groundwater and nutrient pollution of waterways,
resulting from the creation of shrimp farms;
- The clearing of mangroves for shrimp farms. It is estimated
that 60% of all Asia's mangroves have been converted to aquaculture
farms (UNEP, 2002).
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