More than two-thirds of the world's surface is covered by water and the total yearly production of organic material in the aquatic environment has been estimated at about 40 000 million t (Moeller Christensen, 1968). Tiny microscopic plants, the phytoplankton, are the primary producers of organic material using the energy supplied by the sun (see Figure 2.1).


Figure 2.1 The annual aquatic production of organic material is estimated at 40 000 million t (Moeller Christensen, 1968)

This enormous primary production is the first link in the food chain and forms the basis for all life in the sea. How much harvestable fish results from this primary production has been the subject of much speculation. However, there are great difficulties in estimating the ecological efficiency, i.e., the ratio of total production at each successive trophic level. Gulland (1971) reports a range from 10 to 25 % but suggests 25 % as the absolute upper limit of ecological efficiency; for example, not all of the production at one trophic level is consumed by the next. Ecological efficiency also varies between levels, being higher at the lower levels of the food chain with smaller organisms using proportionally more of their food intake for growth rather than for maintenance. Diseases, mortality, pollution, etc. may also influence ecological efficiency. As an example, the conditions in the North Sea, an area with very rich fishing waters, are shown in Figure 2.2.


Figure 2.2 Annual production (in million t) in the North Sea, one of the richest fishing grounds in the world (Moeller Christensen and Nystroem, 1977)

Since production is greater in the early stages of the food chain, the potential catch is also greater if harvesting is carried out at these stages.

Up to 1970, the world catch of marine fish continued to rise at an overall rate of 6 percent per year, according to FAO statistics. Great optimism was expressed by various authors who estimated the potential world catch to be somewhere between 200 million t/year to 2 thousand t/year (Gulland, 1971); most of this wide variation being due to uncertainties concerning the trophic level at which the harvest would be taken. The world fish catch since 1970 is shown in Figure 2.3.


Figure 2.3 Total world fish catch from 1970 to 1992 (FAO, 1994 a)

It is clear from Figure 2.3 that the yearly increase in catches has slowed down since 1970, and the total catch reached a peak of 100 million t in 1989. Since then it has started to drop as a number of fish stocks have begun to collapse, in many cases due to overfishing. However, a slight upward trend is noticed for 1992 and for 1993 world catch is estimated to reach 101 million t. While total catch has started to decline since the peak in 1989, the catch from developing countries as a group is still increasing and since 1985 has exceeded that from developed countries. Thus in 1992 little more than 60 % of the total world catch was taken by developing countries, and it is estimated that this figure will increase to 66% in 1993. This also means that an increasing part of the world fish catch is taken from warm tropical waters.

Are we then reaching the limits of production from "wild" aquatic resources now or do the optimistic predictions from the 1970s still hold? The answer to this question is not only in the affirmative, but for many resources the limit was reached decades earlier than the peak in global landings (FAO, 1993 a). A combination of factors has helped to mark the depletion of many conventional resources. One of these is that continued investments in fishing fleets throughout the world has meant that although catch rates and abundance of high value fish species have often declined, the overall level of fishing effort has increased so that roughly similar levels of landings are being taken at much greater cost to many fishing nations.

The real problems with decreasing fish stocks are familiar. First there is "the tragedy of the commons" - whatever lacks a known owner, whether buffalo or fish - which everyone will race to exploit and ultimately destroy.

The next problem which can be identified is the exceptionally poor management of the aquatic resources. What has been done has been too late and too little. The 1982 Law of the Sea, which extended the territorial seas from 12 to 200 miles, gave the coastal States an opportunity to take a protective interest in their fishing grounds. Instead, many of them rushed to plunder the resources by offering generous subsidies and tax relief for new vessels. Also, the much used quota-system is subject to severe criticism. Often, the net result is increased fishing and increased waste, as perfectly good fish are thrown overboard if quotas are already reached. Many fish stocks (such as pollack, haddock and halibut off New England) are now considered "commercially extinct"; that is, there are now too few fish to warrant catching.

The typical history of the use of a single fish stock has been illustrated as shown in Figure 2.4.


Figure 2.4 Schematic changes in stock abundance, catch and fishing effort in situations of development, overexploitation and management of fisheries. (SOURCE: Danish International Development Agency, DANIDA, 1989)

From an initial stage of under-utilization the fishing passes through a phase of rapid expansion until the limit of the resource is reached. This is then followed by a period o overfishing with high fishing effort, but reduced catches until finally - and hopefully - a phase of proper management is reached. Details on resource management are beyond the scope of this book, but should include the concept of sustainability, environmental aspects and responsible fishing. However, in an FAO publication (FAO, 1994) it is stated that change from a focus on short-term development of fishing fleets to proper management is a necessary, but insufficient condition for sustainable development. In the same report it is further stated that "Sustainable Development" as promoted at the United Nations Conference on Environment and Development (UNCED) in 1992 cannot be achieved under open-access regimes, whether these are within or outside national territorial waters.

In contrast, the world aquaculture production inclusive of aquatic plants has steadily increased over the last decade totalling 19.3 million t in 1992, almost half of this (49% is produced in marine aquaculture, 44% in inland aquaculture, and the rest in brackish environment. About 49% of world aquaculture production are fish. Production of aquati plants is increasing rapidly and reached 5.4 million t in 1992, while smaller increases if production of molluscs and crustaceans are seen (Figure 2.5). The total value of the aquaculture production is estimated to more than $US 32.5 billion in 1992.

To summarize, it can be said that further increases in supply of fish can be expected from better utilization/ reduction of losses and further expansion of aquaculture.

Table 2.1 shows the breakdown of world fish production.

Table 2.1 Breakdown of world fish production (percentage of world total in live weight) (FAO, 1993 a)


For human consumption

Other purposes Animal Feed




















Table 2.1 shows relatively modest differences in the breakdown of the fish production during the decade 1982-92. However, there was a significant increase in fresh fish consumption. Total fish for human consumption increased by 1.2% while fish used for curing and canning continued to decrease.


Figure 2.5  World Aquaculture Production by species category, 1984-91 (FAO, 1993 c)

In value terms, fishery exports reached an estimated $US 40.1 billion in 1993 (FISHDAB, 1994). Exports of fish and fishery products from developing countries continued to increase reaching a total value of $US 19.4 billion in 1993. In the same year exports from developed countries dropped by 5% to an estimated total value of $US 20.7 billion. Developing countries recorded an increasingly positive trade balance in fish trade, which reached $US 12.7 billion in 1993 (FISHDAB, 1994).

It should be noted that Table 2.1 does not give a true picture of the amount of fish available for human food. An enormous amount of fish is wasted due to discards on board or post-harvest losses during processing and distribution. It has been estimated that the global amount of discards is in the range of 17-39 million t/year with an average of 27 million t/year (Alverson et al., 1994). It has been further estimated that the total post-harvest losses in fish products are about 10 % (James, D., personal communication 1994). These high losses are mainly due to problems of fisheries management, and lack of proper technology and of economic incentives.