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Ecosystem Services Generated by Fish Populations

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Ecosystem Services Generated by Fish Populations Ecological Economics 29 (1999) 253–268 ANALYSIS Ecosystem services generated by fish populations Cecilia M. Holmlund *, Monica Hammer Natural Resources Management, Department of Systems Ecology, Stockholm Uni6ersity, S-106 91, Stockholm, Sweden Abstract In this paper, we review the role of fish populations in generating ecosystem services based on documented ecological functions and human demands of fish. The ongoing overexploitation of global fish resources concerns our societies, not only in terms of decreasing fish populations important for consumption and recreational activities. Rather, a number of ecosystem services generated by fish populations are also at risk, with consequences for biodiversity, ecosystem functioning, and ultimately human welfare. Examples are provided from marine and freshwater ecosystems, in various parts of the world, and include all life-stages of fish. Ecosystem services are here defined as fundamental services for maintaining ecosystem functioning and resilience, or demand-derived services based on human values. To secure the generation of ecosystem services from fish populations, management approaches need to address the fact that fish are embedded in ecosystems and that substitutions for declining populations and habitat losses, such as fish stocking and nature reserves, rarely replace losses of all services. © 1999 Elsevier Science B.V. All rights reserved. Keywords: Ecosystem services; Fish populations; Fisheries management; Biodiversity 1. Introduction 15 000 are marine and nearly 10 000 are freshwa- ter (Nelson, 1994). Global capture fisheries har- Fish constitute one of the major protein sources vested 101 million tonnes of fish including 27 for humans around the world. There are to date million tonnes of bycatch in 1995, and 11 million some 25 000 different known fish species of which tonnes were produced in aquaculture the same year (FAO, 1997). Despite the abundance and * Corresponding author. Tel.: +46-8-164252; fax: +46-8- variation of fish, most western fisheries focus on a 158417. few target species. Approximately 75% of the E-mail address: [email protected] (C.M. Holm- world’s marine fish landings consist of 200 ( lund) 0921-8009/99/$ - see front matter © 1999 Elsevier Science B.V. All rights reserved. PII: S0921-8009(99)00015-4 254 C.M. Holmlund, M. Hammer / Ecological Economics 29 (1999) 253–268 1%) known existing marine fish species (FAO, al., 1995). We also discuss some of the conse- 1997). Further, recreational fishing in lakes and quences of human impacts on fish populations, along coasts is a major tourism activity (FAO, such as overfishing in relation to ecosystem re- 1996; Postel and Carpenter, 1997). Estimates of silience. We define resilience here as the amount the value of fish populations for human societies of change or disruption that is required to trans- have predominantly focused on these goods. The form a system from being maintained by one set fact that such values are derived from ecosystems of mutually reinforcing processes to a different set with complex interactions, and that both econom- of processes (Holling, 1973). Identifying ecosys- ically and non-economically valuable fish popula- tem services that various fish populations are part tions play active roles in the maintenance of these of, or generate for human societies, is one step ecosystems and in the provision of a range of toward holistic, ecosystem-based, resource man- ecosystem services, is seldom taken into account. agement with increased understanding of effects Ecosystem services have been defined as ‘‘condi- on the dynamic, often unpredictable ecosystems tions and processes through which natural ecosys- by fisheries. tems, and the species that make them up, sustain and fulfill human life’’ (Daily, 1997, p. 3). This includes the life-support functions (Odum, 1989) 2. Ecosystem services of ecosystems and nature’s capacity to provide aesthetic and cultural quality to human life In this paper, we distinguish between two major (Daily, 1997). categories of ecosystem services: fundamental and In 1995, almost 70% of the world’s major demand-derived ecosystem services (Table 1). By marine fish resources were fully- to overharvested, ‘fundamental ecosystem services’ we mean those or depleted (World Resources Institute, 1996). that are essential for ecosystem function and re- Capture fisheries not only reduce the abundance silience, such as nutrient cycling. These are ulti- of targeted stocks with cascading responses in the mately a prerequisite for human existence, food web and with consequences in other ecologi- irrespective of whether humans are aware of it or cal and fishery dependent systems, but also impact not. Such services are often not linked to any an array of other species, including mammals, as specific economic market value. The ‘demand- bycatch (Dayton et al., 1995; Steneck, 1998). In derived ecosystem services’, such as recreational addition, many nearshore ecosystems are substan- values, are formed by human values and de- tially altered through the destruction of benthic mands, and not necessarily fundamental for the habitats by detrimental fishing methods survival of human societies. Nevertheless, all de- (Malakoff, 1997). Indirect effects of fishing can mand-derived ecosystem services ultimately de- have more important impacts on aquatic ecosys- pend on natural systems and the fundamental tem structure and function than the removal of ecosystem services provided by fish, and are not the fish (Hammer et al., 1993; Hughes, 1994; replaceable by technological innovations. Botsford et al., 1997; Estes et al., 1998). In this paper, we review some of the current knowledge about how fish populations provide 3. Fundamental ecosystem services generated by ecosystem services for human societies, and the fish populations relations between these services and functioning ecosystems in different regions of the world. 3.1. Regulating ser6ices Available literature relating to large-scale marine systems is limited owing to the obvious difficulty Consumption of organisms by fish is a salient of performing ecosystem experiments here. Small- feature which can regulate trophic structure and scale freshwater ecosystems, on the other hand, thus influence the stability, resilience, and food are better understood in terms of influences of fish web dynamics of aquatic ecosystems; moreover, on ecosystem structure and function (Carpenter et these regulatory influences change as fish pass C.M. Holmlund, M. Hammer / Ecological Economics 29 (1999) 253–268 255 from one life stage to another (Carpenter et al., ing in an increase of zooplankton, which in turn 1992; Post et al., 1997). A fish larva, feeding on increases the predation on phytoplankton (Car- zooplankton, is as distinct ecologically from its penter et al., 1985). Although most trophic cas- adult form as it is from its planktonic prey. cade studies have been done in calm freshwater Piscivores (fish that eat fish), preying on environments such as lakes, some studies have zooplanktivores (fish that eat zooplankton), can been done in freshwater streams, the brackish exert a strong top-down control resulting in a Baltic Sea, and coral reefs (Hughes, 1994; Rud- cascade of effects down the food chain (Fig. 1). stam et al., 1994; Deegan et al., 1997). The degree The general mechanism is explained as a decrease of regulatory influence on foodchain relationships in the predation pressure on zooplankton result- by fish varies with physical and climatological preconditions, including stream flow, temperature, upwelling fronts, storms, seasonal variability, and Table 1 also with nutrient content and water depth (Rud- Major fundamental and demand-derived ecosystem services generated by marine and freshwater fish populations stam et al., 1994; MacKenzie et al., 1996; Deegan et al., 1997; Jeppesen et al., 1998a). Also, Carpen- Fundamental ecosystem services ter and Kitchell (1993) suggest that regulatory effects on species composition can be strong with- Regulating services Linking services out affecting the overall function of the ecosys- Regulation of food web Linkage within aquatic tem. We illustrate these general concepts with dynamics ecosystems several examples that follow. Recycling of nutrients Linkage between aquatic and terrestrial ecosystems 3.1.1. Regulating food web dynamics and nutrient Regulation of ecosystem Transport of nutrients, balances resilience carbon and minerals Redistribution of bottom Transport of energy Removal of fish with key characteristics and substrates functions from the ecosystem may result in loss of Regulation of carbon fluxes Acting as ecological memory resilience and in the ecosystem changing from one from water to atmosphere equilibrium state to another (Holling, 1986; Maintenance of sediment Chapin et al., 1997; Grime, 1997; Tilman et al., processes Maintenance of genetic, 1997) (cf. multiple stable states, e.g. Sutherland, species, ecosystem 1974; Sheffer, 1990; Levin, 1992; Walker, 1993). biodiversity Coral reef ecosystems in shallow coastal waters are exposed to hurricanes, typhoons, or cyclones Demand-derived ecosystem services which are irregularly occurring events. Thus, the regeneration of a healthy reef system is dependent Cultural services Information services on rapid colonization of larval recruits. Hughes Production of food Assessment of ecosystem (1994) showed how this recovery mechanism has stress been hindered in Jamaican coral reefs by human Aquaculture production Assessment of ecosystem activities. Since the 1950/1960s the Jamaican coral resilience
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