Asia dominates world aquaculture, producing four-fifths of all farmed fish, shrimp, and shellfish (FAO, 1997). Farming of fish, shrimp, shellfish, and seaweeds has become a vital source of food supply in Asia in recent decades. Fishery products are staples for the Asian population and are embedded in its culture. Fish, an important source of food protein, is critical to food security in many countries of Asia, particularly among poor communities in coastal areas. The annual fish catch and aquaculture production in Asia reached a peak at about 20.7 and 19.1 Mt, respectively, in the year 1998. Japan has the largest distant-waters fishery production. Inland fishery production is dominated by China and India, which have shown increases in recent years as a result of stock enhancement practices.
Fish farming requires land and watertwo resources that already are in short supply in many countries in Asia. Nearly half of the land now used for shrimp ponds in Thailand was formerly used for rice paddies; water diversion for shrimp ponds has lowered groundwater levels noticeably in coastal areas of Thailand. In China, concern over the loss of arable land has led to restrictions on any further conversion of farmland to aquaculture ponds. Intensive production systems and large-scale facilities used to raise high-value shrimp, salmon, and other premium species has taken a heavy toll on coastal habitats, with mangrove swamps in southeast Asia being cleared at an alarming rate. Thailand lost more than 15% of its mangrove forests to shrimp ponds from 1987 to 1993 (World Bank, 1996). Destruction of mangroves has left these coastal areas exposed to erosion and flooding, altered natural drainage patterns, and increased salt intrusion.
The fishery resources of Japan, China, and many other countries of Asia are being depleted by overfishing, excessive use of pesticides, industrial pollution, red tide, and even construction of dikes and other coastal structures (Zou and Wu, 1993; Sato and Mimura, 1997). Loss of inshore fish nursery habitats to coastal development, as well as pollution from land-based activities, causes significant change to ecosystems supporting fisheries (see also Chapter 6). Marine productivity is greatly affected by temperature changes that control plankton shift, such as seasonal shifting of sardine in the Sea of Japan and induced during the cyclical occurrence of the ENSO in low latitudes (Chen and Shen, 1999; Piyakarnchana, 1999; Terazaki, 1999). The impact of global warming on fisheries will depend on the complicated food chain, which could be disturbed by sea-level rise, changes in ocean currents, and alteration of mixing layer thickness.
Anomalies in the water temperatures of major oceanic currents (e.g., declines in sardine catch in the Sea of Japan associated with changing patterns of the Kuroshio current in ENSO years) have resulted in low commercial fish catch in recent years (Yoshino, 1998b). The steady wintertime decrease in mean wind speed observed over the Sea of Japan between 1960 and 1990 has accelerated surface temperature increase and stagnated bottom water formation in recent years (Varlamov et al., 1997). The rise in SST will shift the southern limit of salmon species further to the north (Seino et al., 1998). It is also suggested that the Sea of Japan bottom water will become anoxic within a few hundred years; a decreased oxygen supply will lead to major losses in biological productivity in deep waters (Gamo, 1999). Fish production of certain species may decrease because of the decline of river volume (Zhou, 1991). Increases in marine culture products and declines in marine fishery output are current trends in most south Asian countries that are engaged in commercial fishery activity. It is likely that increased surface runoff and higher nutrient load might lead to potentially beneficial increases in plankton within the coastal zone of boreal Asia. However, increased frequency of El Niño events, which are likely in a warmer atmosphere, could lead to measurable declines in plankton biomass and fish larvae abundance in coastal waters of south and southeast Asia (see also Chapter 6). Such declines in lower levels of the food chain will have negative impacts on fisheries in Asia.
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