11.2.4.4. Fisheries and Aquaculture
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 water—two 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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