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close this bookSmall-Scale Processing of Fish (ILO - WEP, 1982, 140 p.)
View the document(introduction...)
View the documentI. FISH RESOURCES
View the documentII. WASTE DISPOSAL
View the documentIII. AIR POLLUTION


Fish resources are renewable and under normal conditions it is possible to harvest a proportion of that resource one year without reducing its size during the following year. The largest amount of fish that may be harvested each year without permanent damage to the resource is known as the maximum sustainable yield (MSY). When the fish catch is less than the MSY, there is no serious environmental impact, at least as far as the fish resource is concerned. However, if the demand is such that the resource is reduced below the level at which it can reproduce itself, the effect on the environment can be devastating in that greater and greater effort is expanded in an attempt to catch fewer and fewer fish. This situation will have serious consequences on the aquatic fauna and the socio-economic conditions of the fishing community.

Fortunately, traditional small-scale or artisanal fisheries in the tropics rarely indulge in over-fishing. There are, however, a few cases on record where this has happened. In areas, such as the Malacca Straits and the Northern coast of Java, the artisanal fisheries, conducted on a most intense scale has resulted in a considerable reduction of the catches by individual boat crews and fishermen. These are multi-species fisheries, and, unfortunately, statistical records did not adequately indicate the decline in productivity which was taking place. In some other cases, the statistical records are somewhat better. In a number of African freshwater lakes, for example, gill netting has been the dominant fishing method for over a century and it is possible to note how the average size of the fish (mainly Tilapia spp.) has declined over the years. Although size is not in itself necessarily of great importance1, it does mean that the situation must be watched very carefully if damage to the environment is to be avoided.

1 In terms of food production, it is the tonnage of fish caught annually which is the determinant factor rather than the average fish size.

In general, small scale fish processing in the tropics has little effect on fish resources but the introduction of modern fishing methods to supply highly industrialised fish processing factories has sometimes had disastrous effects on the fish stocks. Two examples are well documented. The anchoveta fishing industry of Peru provides an excellent illustration of the way in which a fishing industry may affect an ecological system (Loftas, 1972). Until the early 1950s, the anchoveta were only lightly fished. It was then discovered that a rich resource existed and a purse seining industry developed in which the entire catch was converted to fish meal. Whereas in 1955 there were only 16 relatively small fish meal plants in Peru, the industry grew until in 1970 Peru accounted for 44% of world production of fish meal. In that year, the Peruvian fleet caught 12 million tonnes of fish which was processed into a little over 2 million tonnes of fish meal. However, in 1972, the anchoveta fishery failed almost completely with devastating effect on the population which had become dependent upon it. Many companies and individuals became bankrupt and although the anchoveta stocks have now recovered to a certain extent, they have still not reached their former size. An interesting sideline is provided by the variation in the seabird population over a similar period. In earlier years, the guano produced by the sea birds was one of the more important Peruvian exports but, during the late 1960s and early 1970s, when fishing for anchoveta was in its peak, the bird population fell to less than 4% of its former total.

The development of trawl fishery in Thailand offers a further example of the problems which can result from over-fishing (Tiews, 1973). Until the early 1960s, despite a number of attempts, trawl fishing had not been established in Thailand. At almost the same time, pair trawling was introduced from Taiwan and single boat otter trawling was introduced by a German bilateral aid project. The single boat trawl proved to be the most profitable to operate and soon predominated. As a result of trawling activity, the landing of marine fish in Thailand increased by a factor of 10 from approximately 150 thousand tonnes in 1958 to almost 1.5 million tonnes in 1970. The catch consisted of upwards of 200 species of bottom-dwelling fish, many of which are used for reduction to fish meal in Thailand although they are potentially perfectly good for human food. The fishery was permitted to develop without control, a large number of wooden trawlers were built and eventually trawling operations became uneconomic again causing bankruptcies and severe hardship for many fishermen and their families.