Sustainable food production from aquatic ecosystems E 3.4 165 tions of 100–10,000 individuals, the genetic diversity andthe survival of some species of baleen whales are immediately endangered. E 188.8.131.52 Scientific foundations for safeguarding utilizable populations The starting point for combating overfishing and for the regeneration of fish populations is the determination of sustainable fish yields.Whereas the technological options for fishing have continuously improved in the last few decades, biological and ecological data on the subjects being caught are still largely inadequate. The marine food chain Although the oceans cover 71 per cent ofthe Earth’s surface, only around half ofthe organic matter formed on the Earth is produced in them, around 45–60Gt carbon per year (Longhurst et al, 1995).This means that on average the oceans produce only around half as much per unit area as the land. The food chain comprises the microalgae (phytoplankton) floating in the water as primary producers, phytoplankton-eating zooplankton, fish, predatory fish, squid and whales. However, with every transfer stage within the food chain, 80–90 per cent ofthe energy absorbed with the food is lost. Since plankton algae in nutrient-rich, and thus production-rich, buoyant areas are usually larger than those in low-production areas far from the coast, the food chain here is shorter andtherefore the total transfer-efficiency rate from the microalgae to the fish is up to 4 per cent higher than in waters far from the coasts, where is it is usually well below 1 per cent (Lalli and Parsons, 1997). Determining sustainable fish yields Because ofthe large difference in the structure of marine food chains, only rough statements – based on assessments ofthe ocean’s primary productivity – can be made about potential mean fish yields, and only for limited marine areas, usually based on correlation analyses. However, in individual cases these do not provide a sufficient foundation for the management of fish populations. Sustainable fish yields can only be achieved if the natural rate of increment at least balances out the total mortality ofthe fished population. Total mortality is made up of natural mortality (of which only a rough assessment is possible) and fisheries-related mortality. In the case of fish species with large number of young (high-recruiting), high fisheries mortalities can be tolerated, without endangering the continued existence of a population. The recruitment and, thus, the annual size of populations available for fishing are subject to strong interannual fluctuations (Box E 3.4-1).These annual sizes therefore have to be identified and considered for sustainable fishing quotas to be set. This requires considerable technical, logistical and administrative effort. Unfortunately, data availability on the population development and recruitment of important commercial fish species has deteriorated in recent years, due to cuts in research funding. Box E 3.4-1 Why do the annual sizes of fish populations fluctuate? The reasons for the major fluctuations in the annual sizes of commercial fish stocks have not yet been identified, in spite of intensive research efforts.This knowledge deficit is one ofthe main reasons why the long-term forecasts of population sizes and, thus, the determination of long-term sustainable fishing quotas has not been possible to date. Most bony fish produce very large numbers of eggs or young larva. But usually only a very small proportion (at most just a few per cent) ofthe hatched young reach sexual maturity. Relatively small fluctuations in the mortality ofthe larvae therefore have a great impact on the population size ofthe young fish concerned (so-called recruiting). The following attempts at explaining the variability of recruiting have been made so far (Lalli and Parsons, 1997): • Hunger hypothesis: First of all, fish larvae eat the yolks oftheir eggs before they start to feed. If no food is available then, the young larvae die off. • Predator hypothesis: Below a certain minimum size young fish larvae are easily eaten, there is then a high mortality rate in the populations. With unfavourable feeding conditions the fish grow more slowly than when the feeding conditions are favourable. For this reason, the time in which they can be eliminated by being eaten is longer. • Advection hypothesis:As a result of sea currents fish larvae can be drifted into areas abundant in food – or poor in food – and recruiting reflects this. • Growth hypothesis: In higher water temperatures the fish reach sexual maturity sooner with a smaller body size. Moreover, their growth depends on the nutrient value ofthe food (above all the protein content) andtheir metabolic intensity (eg the energy required for acquiring food). A change in the food spectrum therefore generates different growth rates that have an impact on the fish yields that can be achieved. Experimental findings support all the hypotheses that do not necessarily rule each other out.A great deal of research is needed to clarify these questions that are essential to fisheries and to draw up forecasts for the longer term.
166 E Diversity of landscapes and ecosystems E 184.108.40.206 Sustainable fisheries management at international level The guidelines for sustainable fisheries management are the principles on marine environmental protection andthe long-term use and conservation of living marine resources laid down in Chapter 17 of AGENDA 21, in the Convention on the Law ofthe Sea and in the Biodiversity Convention. The FAO voluntary code of conduct on responsible fisheries andthe binding United Nations Convention on Conservationand Management of Straddling and Highly Migratory Fish Stocks, which has not yet come into force, are important foundations for the sustainable management of fish populations, and expressly include consideration ofthe precautionary principle. A lack of or (as yet) inadequate scientific studies should not therefore be a reason for postponing or omitting the introduction of measures to conserve fished and unfished species andtheir habitats. However, the precautionary principle is still not used enough throughout the world.This lends all the more importance to the judgement of August 27, 1999 by the International Tribunal for the Law ofthe Sea on provisional measures to conserve the bluefin tuna, which took the precautionary principle as a basis. Moreover, another important step on the way towards international sustainable fisheries management is the rapid ratification and implementation ofthe UN Convention on theConservationand Management of Straddling and Highly Migratory Fish Stocks, especially by the EU states that have not yet done so.This would bring the number of ratifications to the 30 needed for the Convention to come into force. Safeguarding stocks of commercial fish An internationally recognized and organized system of research and administrative institutions is needed for the annual specification of sustainable fishing quotas. Under the scientific coordination ofthe International Council for the Exploration ofthe Sea (ICES), the Advisory Committee for Fisheries Management (ACFM) submits annual management analyses for over 100 fished stocks in the North Atlantic. The Federal Government should push for the specification ofthe total annual catch in the EU to be based more on the scientific recommendations ofthe ICES than on politically motivated demands. Where there are no scientific findings, the precautionary principle should take effect and research should be intensified at the same time. Furthermore, the Council feels it is necessary to extend the management analyses to cover further stocks. Internationally recognized fisheries protection zones and moratoria have proved to be effective instruments for the protection of endangered stocks; their use continues to be advocated and should be expanded. For example, the American National Research Council recommends that permanent fisheries protection zones should be established in the coastal area ofthe USA, which should comprise 20 per cent ofthe potential fisheries zone (NRC, 1999). Adapting fisheries capacities to needs In order to achieve the sustainable use ofthe available resources, the FAO code of conduct calls for the reduction of excessive catching capacities, amongst other things. The Council feels that this is a key instrument for sustainable fisheries management because the continuing overcapacity ofthe fishing fleet is the main reason for the overfishing of stocks. Furthermore, the reduction of capacities can assist with better adherence to quotas, which so far have been undermined in various ways which are difficult to police, eg by neglecting to land catches, but trading them immediately on the high seas (passing the catch on to refrigeration ships). The targets for reducing the fleet segments laid down within the context ofthe EU’s Common Fisheries Policy (CFP) have been too low in the past to counteract overfishing effectively. Moreover, not all ofthe member states have fulfilled the requirements. The Council is also critical ofthe possibility of limiting the catching activities of fishing vessels instead of permanently setting them aside. The Federal Government should press for the necessary dismantling of overcapacities to be pursued more rigorously and to be accompanied by structural measures. In a continuation of this approach, the reduction of capacities should also be attempted worldwide, within the context of appropriate conventions and conferences. The problem of flags of convenience (‘outflagging’), with which the actual world fleet is just shifted around but not reduced, can also only be solved at international level. The abolition of subsidies for fishing fleets is a key requirement for the reduction of overcapacities. The funds that are freed up in this way can be used to establish proven environmentally sound fishing and to finance technical measures and institutions to control compliance. Preventing degradation of aquatic ecosystems In view ofthe fact that the vast majority of marine pollution comes from land-based sources, concepts and measures that also take account of terrestrial sources of pollution are urgently required to protect the ecosystems concerned.Whereas some substantial improvements have been made in the highly devel-