A number of lakes in Asia are being reduced in size due to abstraction of water for agriculture and other uses. Other lakes undergo eutrophication, increased sedimentation and intensified aquatic plant growth, as well as encroachment of agriculture into their margins, with consequent changes in their ecosystem. While much attention has been devoted to the problems faced in tropical and subtropical water bodies, concerns have been raised for more attention to be paid to the preservation of cold water habitats in developing countries.
Impacts of the external environment on aquaculture may be positive or negative. Nutrient enrichment of water bodies may provide nutrients beneficial to aquaculture production in some extensive culture systems (e.g. seaweeds, molluscs). However, excessive loadings with urban and industrial wastes can have severe consequences for aquaculture operations, particularly shellfish culture, when exposed to contamination with toxic pollutants, pathogens and phycotoxins. With increasing aquatic pollution and physical degradation of aquatic habitats by other developments, aquaculturists can face risks of mass mortalities of farmed stock, disease outbreaks, product contamination and reduced availability of wild seed or broodstock.
Coastal zones can best be protected under integrated coastal area management schemes which aim at optimizing the sustainable utilization of that highly productive environment. Fisheries and aquaculture, although often considered secondary in economic value compared to other stakeholders, need to receive proper attention. At regional and sub-regional level, river and lake basin management schemes are needed, giving proper attention to all stakeholders, including fisheries, in the allocation of water resources and ensuring adequate water quality for the different legitimate uses of the systems. It is vital that governments empower fisheries and aquaculture authorities to promote actively the interests of fisheries and aquaculture as well as adequately participate in resource management decision-making.
The concept of Integrated Coastal Area Management has been largely adopted (included in UNCED Agenda 21) and aims at increasing the compatibility and overall sustainability of competing resources use in coastal areas. FAO has elaborated a set of guidelines for the management of agriculture, forestry and fisheries within coastal area management and also developed specific guidelines for Integrated Coastal Fisheries Management (ICFM) to assist the fishery sector in dealing with this growing concern. Overall, however, the key corrective actions are needed from the coastal and inland industries that are responsible for the coastal pollution and degradation. In that respect, UNEP is implementing a Global Plan of Action for the Protection of the Marine Environment from Land-based Activities. Further actions taken to protect marine environments inlcude the 1972 London Convention with a purpose to control the disposal of land-based waste in the sea, particularly those detrimental to marine resources. IMO Resolution A.672(16) Adopted on 19 October 1989, prescribes that any installations or structures that are abandoned or disused shall be removed to ensure safety of navigation and to prevent any potential effect on the marine environment. In the European Union, member countries must establish river basin management plans.
In 2001 the Joint Group of Experts on the Scientific Aspects of Marine Environmental Protection (GESAMP) concluded that, at global level, the most serious sources of environmental problems associated with land-based activities are sewage, physical alteration and destruction of habitat, nutrients, and sediment mobilization. Litter, heavy metals, hydrocarbons and radionuclides, although often meriting a high priority at local levels, are not considered as priorities at the global level. Persistent organic pollutants (POPs) such as pesticides, although currently receiving high attention at international level, may well divert attention from the before mentioned anthropogenic causes of more serious and widespread damage to the marine environment.
Demand by, and competition among various sectors for water - in terms of quantity and quality - will increase significantly in the future. Degradation of aquatic habitats in many areas is on increase, resulting from expansion of industries, mining, agriculture and from deforestation. Ever increasing pollution in many regions represents major threat to inland aquatic ecosystems and habitats. Further disturbances result from impoundment and channelling of water bodies, excessive abstraction or diversion of water, soil erosion and manipulation of hydrological characteristics of rivers, lakes and floodplains. While the water quality in many European river systems is steadily improving, environmental degradation affecting freshwater areas is increasing in Africa, Asia-Pacific, Latin America and the Caribbean. Recent global assessments of freshwater resource availability confirmed that some regions are or will be facing serious water shortages. Environmental stresses are particularly severe in those watersheds that are already substantially modified or degraded. As a result, most inland fish producers there will suffer from the lack or inadequacy of rights and institutional support and from the non-integration of inland fisheries management with water and land management.
Unlike capture fisheries, aquaculture at least offers opportunities to adapt farming systems and management practices to optimize aquatic food production under sometimes sub-optimal environmental conditions.