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This study offers economic analyses of exploited marine ecosystems aimed at providing clear insights for policy and management of fisheries and other activities that affect these ecosystems. There is a large body of biological research and a smaller body of social science research aimed at understanding and managing marine ecosystems. So far, however, these have developed quite independently. The present study tries to provide various links between approaches and insights arising from the two bodies of research. In particular, it tries to move beyond traditional economic fishery analyses, in two respects. First, several theoretical and numerical models are offered that combine economic and ecological descriptions of fisheries.

In the last decades numerous integrated models have been developed that combine elements of the natural sciences with elements of the socio-economic sciences with the aim to formulate policies to effectively and efficiently combat environmental problems. Most integrated modeling studies aim at scenario analysis or policy optimization for environmental problems, such as climate change and acid rain. But many bioeconomic models developed for fishery, forestry, or other renewable resource management purposes also integrate biology or physics with economic behavior. To allow comparison among different areas of application, this chapter will concentrate on models developed not only for fisheries and marine ecosystems but also for the problem of climatic change.

Avast amount of literature is devoted to integrated analysis of management strategies to control fishing industries and to sustain the stock of exploited fish populations. The rise in interest in managing the fisheries is due to a globally perceived decrease in ocean and sea productivity as a result of overfishing and mismanagement of the fishing resources. An increase in fishing power due to improved technologies, a rise in world population, and a lack of knowledge about the characteristics of the exploited fish species, have all contributed to fish populations world-wide having become or running the risk of becoming eroded.

Fisheries management in the past was primarily focused on maximizing sustainable yield from the fishery by regulating fishing effort. As the effects of overfishing became more apparent, fisheries management objectives shifted from maximizing sustainable yield to maintaining a minimum spawning biomass (Weeks and Berkeley, 2001). In order to determine the optimal effort levels that would satisfy fisheries management, a high degree of trust was put into fish population growth models. Fish populations, however, have not proven easy to manage with the result that many fish populations are currently overfished. In large, this was due to the fact that fisheries management tended to rely on oversimplified models that underestimated the complexity of fish population dynamics (Caddy and Cochrane, 2001).

After a period of substantial investment of resources in the fishing industry, a significant portion of fish populations worldwide is either overfished or is on the verge of being overfished. Catch levels tend to be unsustainable because economic factors driving the fishing industry are not in balance with ecological factors influencing fish population dynamics.

The subject of harvesting in predator–prey systems has been of interest to economists and ecologists for some time now. Most research has focused attention on optimal exploitation, guided entirely by profits from harvesting. The present study emphasizes that the ecosystem offers more than the exploitation of a species. This is expressed through a non-use value, which is indirectly influenced by harvesting.

In accordance with the recognition that fish populations generally are subject to complex dynamic population processes, there has been an increase over the last years in bioeconomic analysis that steps away from simple stock growth modeling techniques. Greater realism has been provided by modeling interdependency of fish species and by recognizing that fish species display different population dynamic characteristics at the adult life and recruitment life stages (Eggert, 1998). In line with these developments, the last decade has seen an increase in the literature focused on modeling sedentary fish population dynamics as metapopulations.

The last decade has seen an increase in models focusing on marine reserves as a fisheries management tool. An important reason is that in many fisheries worldwide traditional measures of fisheries management have failed (Bohnsack, 1993; Caddy and Cochrane, 2001). The idea of using marine reserves as a fisheries management tool is not new. Beverton and Holt (1957) were the first to consider areas closed to the fishery. They concluded that when a fishery was overfished establishing large marine reserves would result in a higher yield per recruit level. Nevertheless, they also concluded that large marine reserveswould lead to higher fishing pressure on remaining fishing grounds,which could increase the cost of finding fish. This led them to favor management approaches that restricted fishing effort in other, currently more traditional, ways. Measures used to regulate fishing effort include minimum catch allowances, capacity reduction programs, seasonal closure of fisheries and fishing quota allocations.

The study of management of renewable resources has a long-standing tradition. Fisheries for example have been studied extensively since the 1950s. Most of the early studies focus on single-species and single-user systems with just one management goal, usually profit maximization. For these types of systems, analytical solutions can sometimes be found (Clark, 1976). Obviously, the importance of species interactions such as predator–prey relations or competition (see e.g. May et al., 1979) are important for the dynamic behavior of the system and make it difficult to find the optimal control. Therefore, numerical modeling and simulation have become necessary to study management strategies in complex ecosystems.

Shellfishing has been an important economic activity in Dutch coastal areas for centuries. The shellfishery has been active predominantly in the Dutch province of Zeeland and in the Wadden Sea (Dijkema, 1997). The Wadden Sea is a shallow inshore body of water, which is characterized by large expanses of intertidal mud flats. It extends from the Netherlands to Denmark and is bordered by a row of islands. The total area of the Wadden Sea that is part of the Netherlands is 2500 km (Dijkema, 1997). Fishing activities in the Wadden Sea have largely focused on shellfish and shrimps. The shell- fish fishery has predominantly been targeted at oyster (), cockle (), and mussel () populations. While the oyster population disappeared from theWadden Sea between 1940 and 1950 due to overfishing (Dijkema, 1997), shellfishing for mussels, and cockles continues at present. Over the second half of the last century, fishing pressure has dramatically increased in the cockle sector. The increase in landings in the cockle fishing sector has resulted from the advent of mechanized fishing techniques, whereby suction dredges were implemented to harvest cockles.