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International Trade in Farmed Fish and Shellfish: the Impact of Disease Spread



B J Hill
CEFAS Laboratory, The Nothe, Weymouth, Dorset DT4 8UB

During the 1990s, the world's total production of fish and shellfish (molluscs and crustacea) expanded rapidly from 99 million tonnes in 1990 to about 122 million tonnes by 1997. Whilst capture fisheries production increased only slightly, output from aquaculture (farmed fish, shellfish and algae) grew strongly from just over 13 million tonnes in 1990 to 28.3 million tonnes in 1997. Movement of live fish and shellfish between countries has been a necessity for much of this expansion in aquaculture, but has contributed significantly to the occurrence and spread of economically-serious diseases in the industry.

Fish, shellfish and fishery products are widely traded and the international trade has continued to grow at an accelerating rate in recent years. In 1996, some 195 countries exported part of their production and export volumes reached 22 million tonnes, nearly three times the volume traded in 1976. This international trade accounted for about 40% of total production from capture fisheries and aquaculture and has been estimated to have a value of US$52.5 billion, with developing countries achieving a net trade surplus of US$16.6 billion (FAO). Aquaculture (the farming of fish, shellfish and algae) contributed over 20% of the global fisheries production (and 29% of food fish). Whilst output from capture fisheries continues to flatten out, aquaculture production continues to grow at approximately 9% p.a. It is estimated by FAO that global demand for food fish by the year 2010 will be in the range of 110-120 million tonnes from the level of 90 million tonnes in 1996. There is considerable potential for further expansion of aquaculture and under favourable conditions it is estimated that total aquaculture production could rise from the level of 26 million tonnes in 1996 to 40 million tonnes by 2010.

In many countries, the rapid increase in aquaculture output has been based on species diversification which has led to an increase in the demand for introduction and transfers of live non-indigenous aquaculture animals. Although local pathogens, inadequate farm-management, environmental factors and poor water quality continue to be the most common causes of disease outbreaks in farmed fish and shellfish, pathogen transfer due to international trade in live aquaculture animals and their products is a major underlying reason for major epizootics. Disease outbreaks cause significant losses in aquaculture production and trade and are affecting economic development of some countries. An indication of the magnitude of economic loss is seen in the fact that the value of losses in shrimp farm output in China in 1993 due to one introduced disease has been calculated to be about US$400million, and that in recent estimates, based on farm surveys in 16 Asian countries, annual losses due to disease in the region total more than US$3.0 billion.

Probably the most striking example of spread of disease and consequential major economic loss in aquaculture is white spot disease in farmed shrimp. The disease first emerged in 1991 or early 1992 in a shrimp farm in Taiwan and was observed later in 1992 in mainland China. There is some evidence that the virus which causes the disease was introduced to the mainland with trade in live post-larvae of shrimp for on-growing. From Taiwan, thereafter, the disease spread rapidly along the coast of mainland China and in the same year appeared in Japan, Korea and India. In 1994, the disease appeared in Thailand and subsequently spread to all shrimp farming regions of the country and has since been reported in most other shrimp farming countries of Asia, including Indonesia, Malaysia, Sri Lanka, Bangladesh and Vietnam. Annual conomic losses have been estimated to be in the range of more than US$ 400 million in China (1993), US$ 17.6 million in India (1994), and over US$ 500 million in Thailand (1996). The Philippines remain free of WSD and Australia continues to be free of the disease almost certainly due to strict controls on importation of live shrimp and uncooked dead shrimp for use as fish bait. In the mid-1990s the disease was detected in the USA and during 1999 and 2000 the disease flared up in all shrimp farming countries on the Pacific coast from Mexico to Peru. The socio-economic effects of the disease in the region have been dramatic - for example, in Ecuador there were losses of US$ 280 million and 150,000 jobs lost in the sector in 1999 alone. The source of the WSD introduction to the Americas from Asia has not been identified with certainty, but trade in live shrimp for hatcheries and dead shrimp for processing or for bait are thought to be the most likely routes. The current global estimate of economic loss due to this disease is US$ 3000 million/year.

Serious diseases of molluscs and fish have also been spread between countries by international trade. Examples are the diseases Bonamiosis and Haplosporidiosis, which are believed to have been introduced into France and the east coast of the USA respectively via importation of live oysters for farming. These diseases have caused major reductions in the production of the native species of oysters in the affected areas. In fish, one of the most ecologically serious disease introductions has been the transfer of the parasite Gyrodactylus salaris to Norway via importations of live juvenile salmon from hatcheries in Sweden for stock enhancement of Norwegian rivers. The result was a rapid and severe reduction in the highly sensitive local wild salmon populations in affected rivers and draconian steps have been taken by the Norwegian authorities to eradicate the parasite from almost 30 rivers by destruction of all resident fish stocks.

Such introductions of damaging diseases has inevitably led some countries to introduce internal controls on transfers of live and dead aquatic species and also stricter control on imports. Whilst quarantine and health certification programmes are a valid part of a first line of defence against introduction or transfer of exotic fish and shellfish diseases, they must be developed within the context of larger national and international standards addressing this problem, and must not be used as an unjustified barrier to trade. The OIE International Aquatic Animal Health Code provides the only international standards recognised under the SPS Agreement of the World Trade Organisation for health certification requirements for international trade in fish and shellfish. These standards, along with national measures to reduce the risk of importation of disease by means which are scientifically as well as politically justified, will be briefly discussed.

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