The FAO periodically reviews the state of world fishery resources by FAO Statistical Area, separately for the marine resources, and for inland fisheries and aquaculture (FAO, 1992b,f). The most recent revisions were in 1994-95 (FAO, 1994b; 1995b, f). A parallel classification and much more general description is ginven in the following, that divides resources by major ecological zone.
The world population is expected to double in less than a century to some 10 billion people. UN figures (United Nations, 1985;1994) suggest that 75% of these, with the highest rate of growth, will occupy a narrow strip some 60 km in width along the shores of the continents. In southeast Asia, about 65% of all major cities are already located along the coasts (United Nations op. cit.). These figures illustrate the major and gowing impact that human activities will be having on one of the most productive of global ecosystems: the shallow marine and brackish-water areas.
The exploitation of coastal resources and habitats is a function of human population size and its level of socio-economic development. The countiuning population growth, and its accelerated concentration in coastal zones and coastal urban centres (the so-called ‘littoralization’ of populations), implies intensive resource use and higher values for coastal land. At the same time, uncontrolled industrialization of coastal areas and the dishcharge of industrial by-products close to the coast is in conflict with recreational and living-resource uses, including fisheries and aquaculture (e.g.Pullin, 1991). All of these human impacts affect the marine ecosystem in unexpected ways; see e.g. Fig.4). Poorly planned industrial developments, together with the consequences of high densities of transient and permanent human populations, as well as industrial-scale agriculture, have collectively lead to greatly increased adverse impacts on natural coastal systems throughout the world (UNEP, 1990a, b, 1994;Williamson, 1992).
Controlling coastal development and protecting habitates will require improved planning procedures, and will often involve painful social and political choices. The framework within which these choices must be made is commonly reffered to as integrated Coastal Area Management (ICAM: Clark, 1992). As noted, an alternative context for considering land-influenced events within coastal seas has been referred to as the Marine Catchment Basin (MCB) concept (Caddy, 1993a), which recongnizes that human development of watersheds inland can also have a significant impact on coastal seas.
Such management must consider all uses of the coastal zone and take into account human activities, particularly in river basins (watersheds) discharging into coastal seas. The unrestrained use of rivers and estuaties for the discharge of nuterients and toxic compounds leads to signgificantly adverse impacts on critical marine habitats, but water extraction and, more generally, the regulation of rivers for navigation and flood prevention often have adverse effets on riverine fish (Welcomme, 1979) and diadromous species such as salmon, eels, and shad, if not allowed for. The effect of inappropriate land management within the watershed on siltation of coastal and estuarine areas, with its adverse effects on coastal habitats, is another environmental factor due to human activities in the coastal zone, and falls at the interface between ecology and economics (Tisdel, 1982).
Figure 4. Schematic relationship between changes in human activities, and their current impact on the Environment and Fisheries of the Seto lnland Sea (from Tatara, 1991)
Soil erosion due to the removal of plant cover (e.g., deforestation) in watersheds, increases sediment loading of rivers and changes the seasonal cycle and amount of fresh-water run-off to coastal seas, as well as the levels of siltation (see e.g. Milliman, 1981; Milliman et al., 1987; GESAMP, 1994). High riverine sediment loads adversely affect anadromous species such as salmon and sturgeon, and estuarine organisms such as oysters. It also has a serious negative impact on coastal coral reefs (Grigg and Dollar, 1988) and on aquatic vegetation which is often of key importance as fish habitat.
Exchanges across the land-water and air-water interfaces are obviously of particular importance for living marine resources (Martin et al., 1982; Prospero,1981; Liss and Slinn, 1983; Martin and Gordeev, 1986; GESAMP, 1987), and require the reconcilation of sustainable development objectives in aquatic and terrestrial environments relevant to the nearshore and estuarine ecosystems.
Coastal wetlands and shallow nearshore waters play an important role as nursery areas for shrimp and fish (Boesch and Turner, 1984), and act, on the one hand, to moderate the impact of terrestrial activities on enclosed aquatic systems (e.g. GESAMP, 1994); activities commonly manifested as pulses of nutrients, suspended sediments and toxic materials entering coastal and inland seas. At the same time, wetlands and nearshore waters reduce the impact of the marine environment on terrestrial systems; this impact is manifested through such processes as storm surges, tsunamis and consequent coastal erosion (Murty, 1977,1984; Pugh, 1987). (See Welcomme 1979). Such wetland areas are being lost at an alarming rate, world wide (e.g. Stroud, 1992).
New tools and approaches, remote sensing and Geographic Information Systems (GIS) in particular, make the investigation of cross-boundary processes more feasible than ever before (FAO, 1986a), and deserve wide promotion since they help to provide a sound, geographically based, foundation for decision-making in the management of a complex environment. Estuaries play a major role in the life cycle of many economically important fish species by providing breeding, nursery and feeding grounds from which about 95% of the world's marine production is currently obtained (Deegan and Day 1987; Turner 1987). The accelerated degradation of these critical habitats by indiscriminate trawling, by land reclamation, drainage, coastal construction and mining and accompanying sediment deposition, threatens marine fisheries and wildlife and, in many areas, has already had destructive effects (ICES, 1992a; Campbell, 1993).
The role of contaminants in affecting marine ecosystems and their products has already aroused major concern. Thus, in GESAMP (1990) it is noted that:
“the major causes of immediate concern … are coastal development and the attendant contamination of seafood, fouling of the seas by plastic litter, continued build-up of chlorinated hydrocarbons, especially in the trpoics and subtropics, and accumulation of tar on beaches”.
The top priority for this key sector of the marine environment is to preserve current options and, in many cases, to rehabilitate degraded coastal systems essential to the early life cycles of many living marine resources that are exploited farther offshore, as adults. Estuarine fish production is often related to the characteristics of the estuary, including the water runoff pattern (e.g. Houde and Ruthrford, 1993). The negative impacts of agricultural pesticide run- off on coastal westlands and fisheries is now being more widely recongnized, because of its particular impact on coastal low-salinity nursery areas (for shrimp larvae, for example), which can be decimated by “flash run-off” of flood water conatminated by pesticides following tropical storms.
So-called eco-tourismand eco-recreation place progressive emphasis on the persistence of unchanged and unexploited ecosystems, although even these activities are not sustainable in the face of unlimited access, as has been of concern to, for example, for the Australian Great Barrier Reef Marine Park Authority (GBRMPA, 1992/93). Conservation of marine habitat is progressively being associated with conservation of ecosystem complexity and biodiversity, and some habitats play a natural role in pollution abatement and the mitigation of natural environmental impacts on coastal systems. The intangible benefits of conservation are receiving an increasingly higher profile as the public becomes more aware of impacts on marine wildlife (e.g., IUCN, UNEP and WWF, 1980). An upward evaluation of non-exploitive uses is to be expected.
The coastal fringes of the world's oceans are the location of a high proportion of the production of living material directly or indirectly used by man (Marten and Polovina, 1982). Artisanal fishermen fishing nearshore coastal waters and shallow shelf seas represent over 90 percent of the employment possibilities in fisheries, and are an essential and conservative component of coastal communities. Estuarine and lagoon fisheries in particular, have a major socio economic importance (e.g. FAO, 1993e,j; Kapetsky, 1984; Lenanton and Potter, 1987; Willmann and Insull, 1993). Given a specific allocation of rights to a limited number of fishermen, artisanal fisheries are highly efficient in terms of quantity of fish produced per unit of energy input and per unit of capital invested: quality protein is produced for direct human consumption at affordable prices. Preservation of their rights to a reasonable proportion of fishery production, through the firm application of the juridical “polluter pays” principle, should be ensured within the framework of an appropriate management plan for the coastal environment and its living resources. Development and implementation of such a plan is one precondition for a good quality marine environment for the future. However, traditional systems of management are important, involving recognition of user rights for many indigenous people. These have, in some cases, broken down under the impact of foreign and industrial fishing, population influx to the coastal zone, and the competition from other users of the coastal zone, and there could be good reasons for their restoration (e.g., Doulman, 1993; Flood, 1994). A few systems such as mangrove forests play muliple roles in coastal environments (Fig.5). The interface between freshwater and the marine environment is not only a dynamic one ecologically, but poses legal and institutional complexities (e.g. Hayton, 1990).
Estuarine fisheries, especially those for anadromous species, are particularly liable to uncontrolled water use, including the use of dams and barrages (e.g. Neu, 1975). These may also dramatically affect nutrient runoff into coastal seas, and have even had a dramatic effect on the salinity of some semi-enclosed seas (see Volovik et al., 1993).
There are, of course, potential and actual conflicts of interest of coastal fishermen with agriculture and forestry (e.g., mangrove clearance and wetland drainage has occurred on a massive scale, especially in South America and Asia, for coastal rice growing, and shrimp and fish pond culture), but since fishermen generally do not hold property rights, they are rarely compensated for such land-based impacts on their livelihood (MacNae, 1974). Proper planning for such activities within a scheme of coastal zonation requires GIS systems for land and water use planning (Kapetsky et al., 1987). Cash crops of rice, fish and other products almost inevitably replace the less intensive benefits which may arise in the future from maintaining the genetic diversity of complex habitats such as mangrove forests (Fig. 5), despite, for example, the latter's potential for production of new pharmaceuticals), and the less tangible and less enforceable common property benefits of preserving coastal vegetation for flood control, as ecological reserves and as nursery areas for coastal and shelf stocks of fish and shrimp (e.g. Turner, 1987; Mepham and Petr, 1987; Kapetsky, 1985). A systematic approach to conserving these fragile coastal ecosystems is needed (e.g. Hamilton and Snadeker, 1984) if the rich resource harvests they provide are to be conserved (McHugh, 1976).
Figure 5. Some functional relationship of mangrove with artisanal fisheries, fishery resources and aquaculture (after Kapetsky, 1985)
The uncontrolled use of large trees for building dug-out canoes was one direct and inefficient consequence of uncontrolled artisanal fishery development, but is only a very minor cause of the rapid clearance of coastal forests, particularly in the developing world. The demand for timber for building houses and boats, the clearing of coastal forests for coastal development and, in some places, for fuel and foreign exchange requirements, are among those factors that have contributed to deforestation of the coastal belt. This has had disastrous effects due to increased run-off of silt or sewage (Pastorok and Bilyard 1985) onto nearshore coral reefs and fish and shellfish nursery areas (Unesco, 1986; UNEP/IUCN, 1988) and can also lead to outbreaks of harmful organisms (e.g. Birkland, 1982).
These types of interaction are often outside the control of coastal communities, even though such communities may be best aware of the solution to these problems. This seems to call for specific devolution of decision-making capability to the local-government level. Evidently, such activities should take place within overall government guidelines provided by a multi-sectorial policy developed at the national level for coastal-zone development (e.g. Knox and Miyabara, 1984). Inshore fishing by large vessels, especially trawlers, competes with artisanal fishing, but if uncontrolled, will have an adverse effect on the nearshore marine environment, and may force artisanal fishermen into ever-shrinking areas of shallow water and to fish juvenile fish in coastal nursery areas (e.g. Caddy, 1993c). Under such circumstances some coastal fishermen may react by resorting to the use of damaging fishing methods such as bleach, poisons and dynamite, or the destructive harvesting of coral rock for construction. All of these activities impacting important fish habitat need to be rigidly controlled (Hoss and Thayer, 1994).
Increases in market demand without controls of fleet size; technical advances in gear, vessels and navigational and fish-finding equipment, as well as rapid population growth, have all contributed to increased fishing pressure and the breakdown of many traditional fishery management systems for which modern management mechanisms have not always been substituted. A key to rational resource use, hence to sustainable development, is the appropriate allocation of space and resources (FAO, 1986b), with direct community participation; and the adequate protection of resources from explotation by outside interests. This may include the effects of inshore fishing by large trawlers outside the control of the local community, or the similarly uncontrolled effects of industrial or domestic pollution. Local authorities themselves may play an important role in the management and development of coastal fisheries and aquaculture (Barg and Wijkstrom, 1994).
Monitoring of environmental changes in coastal waters (e.g. Mclntyre and Pearce, 1980), especially in estuaries and associated nearshore areas, deserves priority attention from coastal States, since not only are they biologically important loci along the land-water interface where many harmful materials in river water are discharged, but are also nursery areas for many valuable species, and areas where marine systems are fertilized from the land. Several broad generalizations can be made:
The risks of environmental degradation and the consequent loss of economic potential, generally outweigh the future benefits offered by further uncontrolled exploitation of the living marine resources of nearshore and estuarine areas.
Such areas are under the direct influence of a wide variety of terrestrial inputs, and their wellbeing and integrity is essential to most marine resources harvested farther
Their importance is, by and large, even greater in tropical areas.
In heavily populated coastal zones, many areas are already degraded and for sustainable development to offer a wide range of options, many coastal ecosystems will need to be rehabilitated.
The legal aspects of the management and conservation of the freshwater-seawater interface have been little studied (Hayton, 1990) and estuaries are regularly subject to degradation as a result of this lack, in spite of the fact that many marine organisms feed, reproduce and have their nursery areas in estuaries.
At present, a relatively small proportion of the world aquatic production comes from marine aquaculture; most of this is centred on coastal waters, estuaries, lagoons, and semi-enclosed seas (FAO, 1992b). Essential to the sustained development of marine aquaculture, and to habitat enhancement measures such as the construction of artificial reefs, is the allocation of exclusive rights to users over the area of operation, and the protection of standing crops against the harmful effects of other users of the environment. Not all potential uses of the marine environment can be allowed to co-exist locally with marine aquaculture, and an appropriate legal regime must be developed (Van Houtte, 1994).
One of the serious current constraints on marine aquaculture, other than seaweed and bivalve culture (and a currently limited number of commercial fish species such as milkfish and mullet), is that most cultivated fish species are carnivorous and depend on animal-protein feeds (Tacon, 1994). This leads to economically important marine products commanding high market prices but does not necessarily contribute to food security. Aquaculture in 1988 was estimated to use some 10% of global supplies of fish meal as feed (Tacon, 1993).
In areas of high density of cultivation and reduced water exchange, aquaculture itself can provoke problems such as benthic enrichment and hypoxic water conditions. Excessive nutrient loadings from aquaculture may lead to local eutrophication in areas with low water exchange. In extreme cases red-tide outbreaks (GESAMP, 1991; Baden et al., 1990) may result from discharge of nutrients (Ackefors and Enell, 1990). These have serious repercussions on aquaculture itself and on other sectors. In some tropical areas the extensive conversion of coastal wetlands and mangrove forest to fish and shrimp pond culture has significantly reduced the replenishment of natural shrimp populations which use these areas as nursery grounds (Chua, 1993; Phillips et al., 1993). It has also eliminated areas of high biodiversity and had impacts on other functions of coastal wetlands (Chua, 1992; Chua, et al., 1984; Saclauso, 1989; Barg, 1992). For example, it has compromised the role these coastal wetlands play in providing breeding and nursery grounds of fish and other species, and in protecting the coastal zone from storms, and as buffer zones reducing nutrient and silt run-off into the marine environment. To avoid adverse impacts, coastal aquaculture, among other coastal activities, should be planned within a framework of ICAM of Integrated Coastal Area Management (Clark, 1992; Barg, 1992; Chua, 1993).
Of particular concern and relevance to the integration of studies on the river basin and related coastal and inland seas, is the question of nutrient transfer from terrestrial to freshwater and marine systems (Howarth, 1993) and, most particularly, the largely one-way flux of phosphorus from terrestrial ecosystems to the aquatic environment (Fig. 6). The leves of nutrient flux across the level-water boundary in many countries are historically a function of drainage and land use (Lehtonen and Hilden, 1980). In its various forms, phosphorus is a key element, potentially economically limiting for intensive agriculture, an important ocean component of domestic and industrial wastes, and for which, unlike nitrogenous compounds, environmental transport is largely aquatic. Excess quantities of both elements in runoff can have negative influences on the fisheries of semi-enclosed water bodies (Lehtonen and Hilden, 1980).
Human activities are estimated to have caused an approximately five-fold increase in river inputs of nitrogen to the oceans, and, for phosphorus, about four-fold, as judged by the well-documented history of one European river, the Rhine (Lelek, 1989). The annual total for input of phosphorus to the oceans has been estimated to be about 0.59 Tmol (1 teramole of phosphorus is equivalent to 31 million tons of phosphorus). This is made up of a long-term background level of some 0.15 Tmol in river outflow, 0.32 Tmol due to soil leaching and land erosion, and 0.12 Tmol due to waste discharges from human populations, industry and fertilizers (van Bennekom and Salomons, 1981). Not all phosphorus in suspension is available to marine food chains; as for silt, metals and many toxic compounds, much is precipitated out in estuarine and marine sediments. The figures given above for run-off of phosphorus into the oceans may be contrasted with those given by the same authors for the world production of 0.37 Tmol of phosphate fertilizer in 1975, and of 0.026 Tmol for detergent phosphate. Although all of these figures are very approximate, it seems that mining of phosphorus is only replacing some 70% of that lost in freshwater run-off to the oceans annually (FAO, 1991c).
Much scientific debate has focussed on whether primary production in aquatic systems is limited by phosphorus or by other nutrients or trace elements (e.g. Ursin and Andersen, 1991). Other elements may be limiting in particular circumstances (for example, iron has been shown to be limiting in some tropical offshore waters (Martin et al., 1989; Fuhrman and Capone, 1991) and silicon levels in river outflows may be reduced by pollution; (Doering et al., 1989).
Nitrogen is usually limiting in coastal waters in north-temperate latitudes, and phosphorus may be limiting in lakes and in tropical seas (see Mann and Lazier 1991). However, the precedent for considering phosphorus as a measure of biological production (e.g. Andersen and Ursin, 1977), and with carbon, as a ‘marker’ for flows of energy throughout the marine food web appears well established, since unlike nitrogen, it remains within the water and sediments. Other elements than phosphorus and nitrogen, such as silicon and iron, also deserve special attention from terrestrial and aquatic ecologists and from fishery and agricultural research institutes. The practical measures to control the effects of run-off relate largely to actions on land: to improve land use strategies; to encourage riparian control of run-off into waterways; and to improve effluent treatment and discharge practices. The overall productivity of coastal and inland seas is normally increased by nutrient run-off, but above a limited level of runoff, it is very doubtful that the net benefit to fisheries is positive.
Unlike nitrogen, phosphorus compounds are not broken down to the gaseous inactive element, and a large proportion of phosphorus in run-off is stored in oxygenated sediments. Although partially inactivated, it may be more easily recycled from deoxygenated bottom sediments back into the pelagic food web (including fish: Kraft, 1992), and contribute once again to eutrophication. From the standpoint of agriculture this loss from terrestrial systems is surely not beneficial, and one cause of unnecessarily high fertilizer budgets for plant husbandry on land is that “downstream” aquatic impacts are not entered in the cost/benefit calculation.
A recent study of marine food webs leading to fish production (Pauly and Christensen, 1995) found surprisingly high rates of utilizations of 24-35% of primary production in freshwater and shelf (marine) ecosystems, and not surprisingly, much lower rates for open ocean systems. The first of these sets of figures suggests that nutrients should be limiting to fish production, and illustrates how close mankind is to fully exploiting all of the biological resources of coastal and shelf areas.
Figure 6. Diagrammatic representation of the interchange of phosphorous between terrestrial and aquatic systems. Width of arrows roughly indicate relative rates of flow (although the 3 lowest rates of flow are exaggerated for ease of illustration).
Concern has also been expressed over the possible reduction of marine biomass due to the effects of toxic waste discharge into the oceans, as well as to the growing ozone hole in the atmosphere; this biomass, and the oceans themselves, act as “sinks” for carbon, and hence reduces the free carbon dioxide and methane in the atmosphere thus limiting the so-called “greenhouse” effect (Sarmiento et al., 1988). An alternative effect might follow from nutrient enrichment if a large proportion of organic material produced as a result of eutrophication enters carbon “sinks” such as bottom sediments underlying anoxic water masses; besides the effect this storage of material containing carbon in bottom sediments might have on the benthic and demersal resources of an area.
Many marine algae, as well as some sea grasses and salt-marsh grasses, produce dimethylsulphonium compounds. Dimethylsulphonium propionate (DMSP), which is one of the principal metabolites in many benthic and planktonic marine algae, is broken down enzymatically to produce dimethylsulphide (DMS) and acrylic acid (Andreae, 1989). Although production is variable according to region and season of sampling, eutrophication, by favouring algal growth, may favour production of DMS, which may be lost to the atmosphere where the DMS is oxidized to such products as methane sulphonate, sulphur dioxide and sulphate; such compounds play an important role in the formation of acid rain, while DMS itself is an important source of cloud-condensation nuclei (Holligan and Kirst, 1989).
Methane may be produced in a number of ways in the marine environment: from reducing bottom sediments, as the result of hydrocarbon extraction by Man from the sea bed; and in situ in the water column, either by methane-forming bacteria in reducing micro-environments or by algal metabolism; eutrophication can be expected to play a role in this flux of methane between the sea and the atmosphere. Some of this methane, which is relatively stable in the marine environment, is released into the marine atmosphere (Liss, 1989).
The effects of the ozone hole on marine resources has already begun to be of concern, particularly with respect to the effects of increased intensity of ultraviolet light on eggs and larvae of fish and other organisms in the surface areas of the ocean (e.g. Hunter et al., 1979), and experiments in Antarctic Seas have begun to investigate this effect (Gieskes and Kraay, 1990).
The following actions (in boldface), in some cases supported by complementary text (in lightface), were proposed in FAO(1991c) with respect to sustainable development of nearshore and estuarine areas:
Classification and mapping of nearshore and estuarine areas in a Geographical Information System (GIS), showing their current multiple usage.
Establishment of an inventory of particularly sensitive areas or critical habitats, which should be given special recognition in national legislation.
The conservation of coastal wetlands and other areas of marine vegetation, as critical habitats for many commercial and non-commercial species, and as a means of maintaining biodiversity.
Classification of proposed new developments and their consideration for approval only in the context of an Integrated Coastal Area Management (ICAM) Plan, according to an assigned priority of use, or mix of uses, with local inputs which can be shown to co-exist without damaging mutual impacts.
The formal control of access to coastal resources and environments, with mechanisms ranging from seasonal and permanent closure of areas to exploitation, to assignment of specific and carefully delimited user-rights to individuals or coastal communities whose livelihoods depend on the health of these resources.
Definition and establishment of user-rights and responsibilities with respect to living marine resources, whether for harvesting or recreational purposes, including the right to legal redress in the event of adverse impacts on these resources and environments by third parties, and, if appropriate, a mechanism for transfer of user rights between bona fide users.
The setting up of a management and consultative framework for users of the coastal resource and environment, within a legal context, subject to government guidelines. For larger countries, it may be appropriate within these national guidelines that rights and responsibilities be explicitly devolved to regional and local levels, and include mechanisms for the resolution of conflicts of interest.
Severely restricted and controlled use of inshore waters and incoming rivers as points of dumping or discharge of unwanted materials. Routes whereby airborne effluents enter the coastal marine environment also need to be documented. Where these effects can be reduced, appropriate treatment and disposal mechanisms should be introduced. Legislation needs to take into account the fact that some materials placed in coastal waters (e.g., artificial reefs and other structures) may enhance fish production or discourage inshore trawling in prohibited areas.
Governmental recognition and addressing of the impact on the marine resources and environment of human activities outside the immediate marine context is called for, and there is the need for specifically addressing these impacts, increasing co-operation and exchange of information between those national entities, governmental and private, responsible for fisheries, agriculture, water resources, forestry, tourism, and with such sectors as coastal urban planning, industry, transportation and other land and sea users.
Explicit recognition is needed, with respect to estuarine, anadromous and catadromous resources, of the impact of land-and water-use practices throughout each marine catchment basin (MCB). Engineering modifications for controlling water flow should require a prior assessment of their downstream effects.
The separation and, to the extent possible, individual treatment of discharges of biodegradable organic material and nutrients, and of non-biodegradable and toxic wastes, into the aquatic and marine environments, should be allowed for. The discharge of toxic wastes into the aquatic environment directly, or via the atmosphere, should be forbidden. The discharge of biodegradable materials should be closely tied to the assimilative capacity of the receiving environment and to the relevant Integrated Coastal Area Management scheme.
Reduction in the loss of nutrients and topsoil to aquatic systems requires the adoption of riparian measures along watercourses, by evaluating the role of flood plains, by preventing deforestation of the upper reaches of MCBs, and by conservation of wetlands in deltas. These nutrient losses represent a high cost to terrestrial ecosystems, agriculture and forestry, and need to be specifically addressed when considering human water use and modifications to watercourses.
Recognition that the normal estuarine or lagunar fauna and flora, flourishing runs of diadromous fishes, and coastal wetlands and wildlife, are the best indicators of the health of the aquatic system as a whole. The contrary situation implies human health problems, contamination of water, high costs of environmental rehabilitation, and the loss of living resources for food and recreation.
Roughly 86% of the total world aquatic production of finfish and invertebrates, estimated by FAO at 98.3 million tons in 1990, came from the sea, and about 95% of this marine catch came from Exclusive Economic Zones (FAO, 1994c, 1995c,e). In the tropics, most of the marine catch is taken over the continental shelf close to the coast (ICLARM, 1992). The maximum production obtainable by capture fisheries on traditional species is considered to be around 100 million tons (FAO, 1993b; 1994b) but it is clear from recent studies that sustaining this level of production will only be possible, if at all, with proper management to avoid serious impacts on conventional resources and their biotic environment and coastal ecosystems (Pauly and Christensen, 1995). Clearly, the maintenance of marine food supply at recent levels requires strategies for sustainable development of fisheries (e.g. FAO, 1991d)
As a broad generalization, coastal marine resources may be considered fully exploited or overfished practically everywhere, especially those with high commercial value (shrimps, lobsters, crabs, large fish species etc.), and the main potential mechanism to attain sustainable development is through improved management of these resources, with the principal management objective being to attain sustainable use while preventing stock declines. The classical ‘Reference Point’ for sustainable use was the ‘Maximum Sustainable Yield’(MSY). More recently, pursuing MSY as a Management Target has been shown to be a ‘high risk’ strategy (e.g. Larkin, 1977; Sissenwine, 1978) as well as being in excess of safe biological (Caddy and Mahon, 1995) and economic optima (Clark, 1976).
220.127.116.11 Shelf upwelling systems
Wide variations in the abundance of fish stocks are particularly noteworthy in upwelling areas which contain very abundant pelagic resources and contribute between one third and one half of the world's catch (e.g. Flores, 1989). The over-exploitation of such stocks with a high natural variability has contributed to population collapses, although, as illustrated by the Peruvian anchovy (Flores, op. cit.) and the small pelagic fish stocks of the Chilean, NW African, Namibian and Californian areas, (Kawasaki, 1983) these resources show wide, and often close to synchronous changes in abundance (Lluch Belder et al., 1992) (Fig. 7), in which long term climatic changes associated with the ENSO (El Niño - Southern Oscillation) phenomenon (Bakun, in press), rather than overfishing, appear to play the key role (Bakun, 1993). A high level of natural variation must be allowed for, therefore, in management plans for the fishery resources of these areas. Upwelling is tied to local wind regimes which, in turn, tend to be tied to large-scale changes in the coupled atmosphericoceanic systems. The dominant global phenomena here are ENSO events (Bakun, 1992), the major mode of short-term climatic changes throughout the world (e.g. Kiladis and Diaz, 1989), with important interannual and interdecadal time scales (Bakun and Parrish, 1980).
Figure 7. Landing trends for three widely separated Pacific ocean fisheries for the sardine Sardinops spp. showing apparent scheduling through basin-wide environmental process illustrated here together with the North Pacific temperature anomaly (from Sharp and Mclain, 1993 with date from Kawasaki).
The geographical distribution of major sources of nutrients for coastal fisheries are shown in Fig. 6 and the accompanying table from Caddy and Bakun (1994).
18.104.22.168 Shelf areas fertilized by land run-off and/or tidal mixing
Shelf areas make up a significant proportion of productive fishery systems: the North Sea, the Bay of Bengal and the Yellow Sea are good examples (Caddy and Bakun, 1994). Such systems have predominant characteristics which determine the main source of nutrients and hence their productivity. Caddy and Bakun (1994) distinguished two typical sources of nutrients for shelf food webs in addition to upwelling: these are tidal mixing (characteristic inter alia of the N.W.Pacific, Patagonian and North Sea Shelves, Mann and Lazier, 1991); and land-based runoff (e.g. South China Sea, Gulf of Mexico and Gulf of Guinea) (Figure 8).
Figure 8. Composite map showing areas of predominant nutrient sources for coastal fishery production (Caddy and Bakun, 1994).
As for semi-enclosed seas, shelf areas merit special attention in developing fishery management plans and in designing environmental monitoring systems. Specific problems and potential benefits of such management and monitoring are discussed in some detail in sections 2.1.4, above, and 2.2.2, below.
Features known as “shelf-sea-fronts” often appear on continental shelves where substantial mixing of the water column by tides carries nutrients up from deeper water where they become available to support photosynthesis. Such areas (e.g. the North Sea, North Pacific, Patagonian Shelf) are typically rich fishing areas (Caddy and Bakun, 1994).
22.214.171.124 Coral reefs
Coral reefs are characterized by many specialized species each with a particular food preference and/or mode of feeding. These species and habits have evolved over long periods of geological time within a very stable environment and, although the overall biological production of coral reefs is surprisingly high for a nutrient-poor environment (Jones and Endean, 1973; ICLARM, 1992), a significant proportion of the nutrients is bound up in the biotic components and only slowly replenished once the biota have been harvested (Jones and Endean, op.cit.). This is in contrast to the less complex and “younger” ecosystems typical of upwelling areas and the shelf seas of northern latitudes, which are charcterized by significant quantities of free nutrients during certain seasons, wide flucturations in abundance, and communities dominated by species with broad, flexible feeding patterns, which are relatively resistant to intensive fishing (Ursin, 1982).
Coral-reef communities have not developed the ability to react in a flexible manner to unusual stress such as heavy human exploitation and more than light nutrient or sediment inputs (Hughes, 1994; UNEP/IUCN, 1988; Johannes, 1975). There is evidence that many such communities have been irreversibly degraded by human activities, their fish communities modified, and the living substrate replaced by much less complex systems based on algae growing on the former dead coral heads, and disturbed coral ecosystems have been attacked by predeators such as crown-of-thorns starfish (UNEP/IUCN, op. cit.). The problems of preserving and restoring production coral reefs will have to be tackled at the community level; by removing damaging influences; in part by restoring traditional harvesting rights (e.g. Doulman, 1993; Flood, 1994) or other means of restricting access to reefs and their resources. Coral-reef systems are extremely sensitive to environmental change, and perhaps more so than for most other marine ecosystems (Grassle et al., 1990), their biodiversity is adversely affected by turbidity and nutrients.
In addition to the very real problems faced by reef resources such as the negative effects of overfishing, inappropriate and damaging fishing methods, reef mining, siltation and nutrient run-off, of more recent concern is the “bleaching” of shallow reefs (UNEP/IUCN , op. cit.). This may be an indication of deteriorating conditions such as destruction of the ozone layer with a subsequent increased exposure to ultraviolet radiation. Such effects risk being worsened in the event of climate change.
Areas of pristine coral reef have a major recreational potential under conditions of controlled access to commercial fishermen (Tilmant, 1987; GBRMPA, 1992/93; Jones, 1994)), and this potential grows in value as more reefs are degraded around the world as a result of inappropriate usage. It may be necessary to decide between exploitive and non-exploitive use for certain areas; for the latter, resource exploitation may need to be reduced to low levels, given that this detracts from visual appreciation of the unique biodiversity of these habitats (UNEP/IUCN, 1988): a new source of economic wealth through “ecotourism”.
It is no longer possible to make the assumption that the only way that Man can influence the state of shelf resources is by the application of classical fishery regulatory mechanisms, as by imposing size limits or quotas, by seasonal closure of fishing areas (Garcia and Demetropoulos, 1986), or by controlling fishing effort (Caddy 1993c, 1993c). Human activities are influencing the renewable resources of shelf areas directly and indirectly, in other ways, and this has been a subject of debate at a number of FAO conferences in recent years (e.g. FAO, 1991a).
In general, the surface waters of the open oceans are characterized by a serious shortage of nutrients, and the theory of nutrients in the marine environment is concerned with deciding which chemical element is limiting on phytoplankton growth (see Gerlach, 1988). In many areas of the world's oceans, water masses along the “open” coast may retain their identity for considerable periods of time, so their resources may be presumed to be particularly susceptible to “land effects”, especially those due to run-off of materials (Caddy and Bakun, 1994). Figure 1 shows one classification of such habitats on the basis of major sources of nutrients to coastal waters. Some examples in temperate seas are the eastern North sea, the Bering Sea, the Gulf of St. Lawrence and Scotian Shelf, the Sea of Japan and the Patagonian Shelf (Caddy and Bakun,op.cit.). In the tropics, areas receiving and retaining run-off from large rivers are those most likely to be affected, such as the Bay of Bengal, the South China Sea, and the Gulf of Guinea. These marine areas are heavily influenced by the nutrients and large sediment loads discharged into coastal seas. This is particularly the case for Asian rivers with their long histories of watershed development, but is also a steadily augmenting process in many estuaries throughout the World (Meade, 1981). coastal water masses receiving river discharged in open sea areas would appear to merit the same priotity attention for environmental monitoring as semi-enclosed seas (e.g. Drinkwater, 1986).
There have been a growing number of human uses of shelf areas that will have to be reconciled with sustainable development of marine resources. Potential conflicts between these two general objectives have so far been recorded in the following areas:
dumping of chemical wastes, sewage sludge and fly ash in shelf areas, and anoxic conditions caused by eutrophication, have both been implicated in the increased incidence of diseases and skin cancers of some bottom fish in the North Sea (Dethlesfsen, 1980);
extraction of sand and gravel from the sea bed affects many benthic species and damages spawning grounds of some fish (ices, 1992a; Campbell, 1993), and can have particularly negative impacts on beaches; effects are, however, limited in time and space and can be reduced by careful planning and attention to operational procedures and appropriate zonation under ICAM;
at-sea oil and gas extraction rigs and pipelines may cause loss of fishing gear to trawlers, but may also act as refuges for heavily fished bottom fish (e.g. Dugas et al., 1979; Reggio, 1987).
In general, these effects, with the possible exception of local impacts of heavy oil spills, tend to be of less concern, and have less impact on marine systems than do other effects resulting from human activities on land. As mentioned earlier, the most serious impacts show up in nearshore waters and semi-enclosed seas. Any disposal of effluents at sea should take into account conditions at the point of discharge, current patterns, and the zoning by use of the affected areas. The negative effects of coastal development on the marine environment now extends to many developing countries in the tropics (Linden, 1990).
As a priority, fishery and coastal zone resources and aquatic habitats that are not yet degraded need to be brought within effective management regimes. Rehabitlitation of resources is a more costly way of achienvieng sustainable development than timely action. Coastal marine parks or protected areas (e.g. Dixon and sherman, 1990) may contribute to revenues from non-exploited use of resources, as well as preserving important stock components (e.g. for spawning). In general, low cost improvements in position-fixing (both of locations and fishing vessels), including satellite navigation systems, promise to make zonations and season-area closure, much more effective management systems than formerly was the case, even in offshore waters.
The application of high technology to increasing marine productivity of shelf and open-ocean systems is still in the planning stage and will require significant investment that currently is being overexpended in maintaining excess fleet capacity. As for inshore aquaculture, the exploitation of resource enhancement measures also depends on more specific allocation of user-rights, and this is probably also the context for the futuristic vision of “offshore communities” or “floating cities”, which are already in the design phase (Simard, 1986). It is perhaps not a coincidence that major developments in this direction have arisen in Japan, where a well-developed system of user rights has long been established (Simard, 1986; Ruddle, 1987).
Three main areas of application of technology technology with potential for realization early in the next century, seem worth mentioning however:
Induced upwelling of cold, nutrient-rich bottom water into warm nutrient-poor surface water has been proposed as a potential non-polluting energy source (OTEC) and would incidentally increase productivity around for example, deep-water islands; induced upwelling could also be associated with food production of wild or cultivated species.
Artificial reefs, if installed on a large enough scale (of the order of tens to hundreds of hectares), would increase productivity of valuable benthic and demersal species and provide a focus for coastal community development in the context of exclusive user rights (e.g. Christie, 1982; D'ltri, 1985; IPFC, 1991;). Experience with this type of application is to be found in Japan (Simard, op. cit.).
The application of high technology to support the transfer of aquaculture technology to offshore areas where natural or artificially enhanced productivity can be maintained is a possibility that deserves further research.
In many parts of the world, traditional systems of management operate (e.g. IPFC, 1994). Here, fishermen's guilds or close-knit fishing communities have restricted access by outsiders to local marine resources (e.g. Berkes, 1985; Berkes et al., 1993; Flood, 1994). In these systems fishing opportunities are shared by participants and a degree of resource conservation has often been achieved.
The development of long-range fleets in the 1960s and 1970s, and major technical innovations in gear, vessels and handling and storage of the catch, was closely followed by the application of similar efficient harvesting methods in coastal fisheries in many areas. Both trends have tended to disrupt traditional patterns of resource use and placed greater pressure on resources, without modern management systems being introduced as a framework for limited access to living marine resources. The emphasis on industrial fisheries development over the last 40 years has perhaps understated the importance, cost-effectiveness and socio-economic importance of managing small scale fleets in light of their role in food production (Pollnac and Morrissey, 1982; Panaystou, 1982).
In fact, most shelf fisheries throughout the world still operate under open-access conditions, which implies that they are being harvested under conditions of high exploitation and low return on investment (World Bank, 1992; FAO 1992e). The effectiveness of current strategies to achieve sustainable development of coastal and shelf resources under open access is debatable and new, and if necessary experimental approaches, need to be tested and evaluated. At the same time, high pressures in the tropical coastal zone and the consequent high levels of exploitation (e.g. Pauly, 1979b) lead to use of fisheries as the “employment of last resort” for economically disadvantaged persons displaced from agricultural, industrial or urban communities. This makes the necessary control of access a politically delicate matter.
Even in the developed world the management of fisheries has run into difficulties which can also be traced to a lack of action in restriciting access to natural resources that have a limited potential for self reproduction. Systems for controlling fishing effort indirectly through the use of catch quotas or Total Allowable Catches (TACs) have been running into increasing difficulties for a combination of reasons (Beddington and May 1977; Sissenwine 1978, FAO 1993b, 1994b, 1995e), the most important of which come down to the difficulty of reducing access to reasonable number of participants wherever historical access rights have been established. Some of these difficulties are aggravated by over-optimistic interpretation of catch and research data as to the state of stocks, by misreporting of catches, and by the inability to forecast true levels of abundance. In the case of unobserved stock declines, fixed TACs lead to overfishing by a quota that, under constant numbers of new recruits added annually, would correspond to moderate levels of fishing. The use of the concept of Maximum Sustainable Yield (see section 4.1) under conditions of high uncertainty about stock abundance and interactions between fleets and stocks, can also contribute to accidental overfishing and the instability of resources (Garcia et al., 1986; FAO, 1992e).
Inasmuch as there is no simple solution to these difficulties, strict control of the number of fishing licences and the fishing power of individual vessels (e.g. Robson, 1966) appear essential preconditions if a workable management is to be found. The removal of open-access conditions for all fisheries, national and international, the payment of user fees, the establishment of maximum allowable effort levels, allocation schemes, and systems of transmitting user rights between individuals, can also be expected to contribute to the sustainability of fisheries (Gordon, 1954; Hardin, 1968; Berkes, 1985). Otherwise, costly redeployment schemes for fishermen must be sought in other sectors of the coastal economy, including aquaculture.
Apart from the pressures for employment in shelf-sea fisheries, long considered a marginal and uncontrolled sector of the national economy, the fact that real landings have reached a plateau and due to poor management have even declined in many cases, means that a constant level of supply with a steadily increasing demand has the effect of increasing real prices for fish (FAO, 1992e). This then generates pressure for increased rates of fishing on these resources and, in turn, leads inevitably to a decline in landings.
The UN Convention on the Law of the Sea (Annex IV), by stipulating the rights and obligations of coastal States in extending their jurisdiction over fisheries, removed the condition of free and open access that the distant-water fleets formerly operated under on most continental shelves within 200 miles of the coast. Subsequently, many coastal States internalized the problem of effort control, allowing an increase in fishing effort under the free and open-access conditions prevailing within national maritime jurisdicitions (e.g., FAO, 1993b). This occurred because no specific rights were assigned to national harvesters and, in many cases, through excessive use of inappropriate subsidy schemes, this led to excessive fishing effort and further deterioration of the national resource base. Special cases are the highly migratory resources and those straddling stocks lying across 200-mile EEZ boundaries with international waters. Here access is effectively uncontrolled beyond 200 miles, and the prospects for joint management of the stock are even more problematical, given that a unit stock must be managed in a co-ordinated fashion based on information on catches throughout its range. These latter problems are among the matters currently being discussed by the United Nations Conference on Straddling Fish Species Stocks and Highly Migratory Stocks (FAO, 1994) and in development of the FAO Code of Conduct for Responsible Fisheries.
Among other possible mechanisms for controlling fishing effort are the implementation of fishing fees, and the assignment of territorial rights to fishermen. Fishing fees could be used to offset the effect of rising real prices and would discourage fishing at low levels of stock abundance. The extraction of some rent from the fishery would incidentally provide the necessary budgetary framework for financing fishery conservation, research and management measures that are essential if rates of use are to be limited to sustainable levels. The other alternative mentioned is that of specific geographical rights to areas within the EEZ, referred to as TURFs (Territorial User Rights of Fishermen) (Christy, 1982; Smith and Panayotou, 1984).
Developing coastal States have perceived the benefits from the exploitation of their marine resources quickly for food or foreign currency by acquiring foreign fishing technology and the skills to use it through a variety of indirect mechanisms, each with its advantages and risks. Among these mechanisms is the licensing of foreign vessels for specified resources, areas, and levels of removal and, if the establishment of a national fishery is the final objective, through joint ventures, with full participation of nationals at all levels in the fishery. These mechanisms, while not excluding the possibility of developing a national fishery at a later date, allow some resources and resource rent to be extracted nationally, at the same time that data on the resource are being collected. All developmental strategies have major risks in the absence of adequate data; priority should be given to analysis of population dynamics, and should assist in avoiding ill-advised foreign over-investment in fleet and facilities, as well as providing the possibility of revenue through the use of shore facilities.
It is essential to ensure that exploitation levels in shelf fisheries do not exceed those that would result in radical changes to marine ecosystems and hence lead to a reduction of the possible options available to future generations of users of the marine resource (i.e. destroy intergenerational equity). Consequently, the control of overall fishing effort is emerging as a major priority for fisheries management (e.g. FAO, 1984b). The intensity of direct and incidental exploitation of resources and ecosystems, and the indirect effects of other human activities on the well-being of marine resources, should not exceed levels that compromise the attainment of a sustainable yield. Evaluation of the effect of exploitation requires continuous monitoring of the resource and its environment. Through an appropriate legislative framework, the level of exploitation should be responsive to changes in resource abundance and environmental change, and this is the context which has given rise to a Code of Conduct for Responsible Fisheries currently being developed by FAO (1994d, 1995a).
Developing appropriate models of the fishery and its ecosystem is an important step towards defining a desirable ‘state’ of the fishery, whether this is defined in terms of fishing mortality rate, biomass or allowable catch. The quality of the data needed for defining the appropriate state of the fishery and the long-term objectives for management is the first stage for management by a technical reference point based on a population model of the fish stock (FAO, 1993h, Caddy and Mahon, 1995) (Fig. 9). The second stage is determining the position of the fishery in relation to the reference point chosen. Experience shows that our accuracy of ‘location’ of the fishery in relation to a given management model is rarely better than plus or minus 20–30%, so that, to avoid overfishing, a precautionary approach is necessary (Garcia 1994a, b).
In most coastal and shelf seas, especially in the tropics and sub-tropics, the fishery resources are multi-specific and the fishery is multi-gear (e.g. FAO, 1978; Pauly and Murphy 1982; Smith et al., 1983; Christen and Pauly, 1993). At the same time, the abundance of the few species of principal interest may vary considerably, seasonally and interannually, making fishing a risky business economically. This risk can be reduced, and fishing pressure eased on key species in the multi-species system, by first controlling the number of participants and their pressure on the stocks, but also by changing fishing gear according to season. Such a strategy, in a multi-species, multi-gear context, may be called “successional fishing” (Nagasaki and Chikuni, 1989). Multispecies gears such as trawls and some fish traps capture a range of species and pose a particular management problem, in that at high fishing pressure, the slow-growing, top predators can be reduced to a low abundance. It will be necessary to take trophic and other life history linkages into account in managing separate fisheries on trophically-linked species (see Brander and Bennett, 1989 for a simple example of this problem). One safeguard against over-exploitation and other adverse effects is the conduct of regular resource surveys.
Governments need to be fully aware of the economic and social penalties imposed by mismanagement, or lack of management, of fisheries. In the light of current Third World debt levels and economic restructuring, the governmental role in fishery management, especially in developing countries is still essential. Applying management measures successfully requires a degree of development of responsibility to local or regional levels in order to be successful.
126.96.36.199 Special problems of shared and straddling resources
Under the 1982 UN Convention on the Law of the Sea, jurisdiction over shelf resources lies with the coastal States, except for limited areas of shelf beyond 200 miles (see section 7.1). However, many resources, particularly for regions where many small EEZs have been delineated, as in the Caribbean Sea, are exploited by two or more States (so-called “shared stocks”). These lie across, or migrate across, boundaries between EEZs and the high seas (so-called “stradding stocks and highly migratory stocks”). Under the 1982 Convention, States are charged with co-operating to ensure sustainable management of shared marine resources, to use an existing fishery commission, or to set up such a body for this purpose. A significant number of such bodies now exist (see section 7.5). Such commissions should, inter alia, co-ordinate national management, set overall limits on removals, apply allocations decided by agreement between States, and co-ordinate surveillance to ensure that such regulations are respected. To date, there are a number of shared resources for which such a formal mechanism has not yet been applied. The resulting conflict of objectives, or lack of co-ordination between management authorities responsible for the exploitation of a shared fishery resource, has been one of the main reasons for declines in transboundary stocks in shelf areas (FAO, 1994c). The legal framework for managing transboundary resources under the 1982 Convention are discussed in Hayashi, 1993, and some of the practical problems of managing transboundary resources are discussed by Gulland (1980) and Caddy (1982).
Figure 9. Some relative ranges for the fishing mortality rates corresponding to different objectives for marine resource use in the context of a surplus yield model (after Caddy and Mahon, 1995).
In the case of adjacent countries fishing a common stock, agreements on reciprocal access, as well as on surveillance, statistics, surveys and assessment, may reduce the costs of a managed fishery to both parties. States should co-operate to harmonize their management regimes and, as far as possible, their respective fishery research and national legislation in this field.
Serious problems are faced by fishery management authorities in managing the operations of modern fishing fleets, which can harvest a significant proportion of a stock in a short time and which are extreamely mobile and independent in their operation. “Real-time” management, not only for a stock within a single EEZ but particularly for a shared stock (as defined above), requires integration of many diverse elements, such as inspection of catches and vessels in port and at sea, and the radio transmission of daily fishing data (e.g., catches, fishing effort, fishing area) by participating vessels. A computerized data system is needed so that the fishery can be closed when an agreed fishery management objective (e.g., the total allowable catch (TAC) or minimum catch rate) has been achieved.
Such a projected high-seas management system would be made up of a number of elements: a vessel licensing system and data base of vessel operations; realistic fishing fees by resource and category of vessel which reflect current market prices; regular updating of the results of regular research-vessel surveys to establish abundance of the resource; the existence of a team of resource experts to estimate and advise on allocating the resource of fishing opportunity; and mechanisms for consultation between all parties concerned. Aerial surveillance, involving standardized marking of vessels and fishing gear, and standard call signs for vessels authorized to participate in the fishery, are modern options. A number of these aspects are touched upon in the FAO Compliance Agreement (FAO, 1994e) which encourages compliance of fishing vessels on the high seas with conservation measures in force, through a number of technical considerations. Vessel licence fees, penalties and other revenues should ideally be used to cover the cost of the above-mentioned operations before any surplus is returned to the national treasury.
The following actions (in boldface, with complementary text in italics) appear desireable options with respect to the sustainable development of coastal and shelf-sea resources:
Extraction of a realistic rent from users of the marine environment and resources, with appropriate penalties for misuse, and the elimination, where possible, of subsidies which encourage overcapitalization. (In practice, the only way that environments can be preserved and rent extracted is by reducing the access of users of the environment and resource to levels that can be supported without affecting the long-term productivity of the system, and can generate resource rent to pay for research and surveillance. Such measures include the issuing of limited licences to fish and the avoidance of financial incentives. Exclusive user rights to areas of shelf and the institution of closed fishery zones and/or seasons, (including marine parks or reserves) may be other applicable management mechanisms.
The collection of licence fees for use of the resources, and realistic penalties for infringements, such as illegal fishing or pollution, that affect the sustainability of the resource. Such fees should be commensurate with the value of the resource and collected by a designated resource management authority with powers of enforcement. Ideally, a proportion of the rent should be used for sustainable management of the resource before the surplus reverts to the national treasuries concerned. The use of some of the national income from the fisheries to pay for monitoring and control measures and, if possible, to support regional fishery management bodies and relevant research and conservation measures, should also be considered.
The establishment of a code of conduct for responsible fishing to guide the formulation of a management plan, with regular consultation between the industry and government, is a precondition for a successfully managed fishery. Modification of harvesting practices (seasons, areas, methods, gears), so as to avoid wastage (discarded fish) and to reduce the capture of non-target, regulated, protected or endangered species, and generally to reduce the impact of fishing on particular species and on the environment, inter alia fall under the provisions of a code of responsible fishing.
The provision of realistic financial support to fishery commissions and other bodies concerned with management of transboundary and straddling and migratory stocks is necessary if management is to be accomplished. The success of management of high-seas and transboundary stocks will also require verification of the location of fishing activities by independent monitoring or telemetry.
The setting of explicit targets for management in relation to agreed reference points derived from accepted population models, the location of the current state of the fishery in relation to them, while taking a precautionary approach, are essential bearing in mind our uncertain knowledge of the state of the fishery.
Promotion of studies aimed at improving fishing gear, gear selectivity, and understanding the reaction of fish, marine mammals and marine reptiles to fishing gear and other man-made obstacles, and prohibition of the discarding of entangling debris such as fish netting and plastics at sea are needed to reduce the incidence of “ghost” fishing.
Development of contingency plans to deal with potential natural and man-made environmental disasters, and elaboration of mechanisms to resolve conflicts of interest among users of the marine resources and environment, are essential.
The promotion of investment in infrastructure to improve environmentally sustainable food-production capacity, such as zoned aquaculture facilities at appropriate levels of density, and artificial reefs is recommended. This promotion will require specific recognition of user rights over shelf resources, and the integration of coastal tourism and recreation. These actions can bring financially important inputs to coastal communities and the fishery sector, since successful sports fishing and underwater tourism enterprises require a higher abundance of fish and large specimens.
Measures should be instituted to protect biodiversity, in addition to specific measures to control fisheries. For example, the uncontrolled collection of shells and curios, and indiscriminate spearfishing will also have to be effectively discouraged to maintain biological diversity and ecosystem integrity of ecologically susceptible areas. Consideration should be given to incorporation into marine parks of significant proportions of critical habitats important to fisheries, such as inshore nursery areas, critical habitats or otherwise especially sensitive areas.
Strict monitoring and control of the disposal of organic waste and nutrients into the shallow shelf-sea environment, should take into account the zonation of areas under ICZM or other such schemes, and not exceed the assimilative capacity of the receiving environment.
Enclosed and semi-enclosed seas and, in some circumstances, archipelagic seas, are recognized as areas of particular value to mankind, because of the favourable environments they provide for human life along their littoral zones, and for the renewable resources and unique fauna and habitats they contain. They are also, actually and potentially, the most susceptible of marine water bodies to human influences, and have some of the features of large estuaries, with limited flushing characteristics and enhanced susceptibility to the effects of terrestrial activities.
Various criteria have been suggested for deciding whether a geographically distinct body of marine water constitutes a semi-enclosed sea; Alexander (1973) suggests an area of at least 50,000 km2 with at least 50% of the circumference consisting of coastline and the connection to the outside sea consisting of no more than 20% thereof. The definition under Article 122 of the UN Convention on the Law of the Sea is less specific geographically: “a gulf, basin or sea surrounded by two or more States and connected to another sea or the ocean by a narrow outlet or consisting entirely or primarily of the territorial seas and Exclusive Economic Zones of two or more coastal States”.
This definition incorporates several key ideas:
the potential effect of land on the marine system;
the direct involvement of two or more States;
a connection with another sea or ocean through a strait;
the division of the sea area into territorial seas and/or Exclusive Economic Zones, in theory at least.
There are at least two other categories of semi-enclosed sea: those comprising areas beyond territorial seas where either EEZ claims have not been made (e.g., the Mediterranean) or where they conflict and the conflict has not been resolved (e.g., the Yellow Sea, the South China Sea).
The Convention definition excludes seas that are wholly national, such as the Beaufort Sea, the Sea of Marmara, or the Seto Inland Sea, even though, as for archipelagic seas and straits in general, the unhindered passage of marine resources from one jurisdiction to another through such wholly national waters is internationally recognized and accepted. This imposes a special obligation on the concerned States for conservation of international migratory resources while they are traversing straits and national seas.
Other climatic and social factors may be useful in the consideration of the categorization of semi-enclosed seas. Thus, Smith and Vallega (1990) refer to “core” seas, such as the North Sea, the Mediterranean, the Yellow Sea etc., mostly in temperate areas, along whose littorals large human populations enhance the risk of environmental and resource impacts, but where, until recently, a degree of resilience to the impacts of human activities has been evident.
Another category of semi-enclosed seas exists, comprising frigid seas (e.g., Hudson Bay, the Sea of Okhotsk, and the entire Arctic Ocean) and tropical seas (e.g., the Great Barrier Reef lagoon), in which the biological systems are intrinsically less robust to the influence of human activities, the effects of which are now beginning to be felt.
Fisheries of enclosed and semi-enclosed seas provide the first basis for evaluating human impacts on marine ecosystems as a whole. Some of the key features of semi-enclosed seas have been described by Ketchum (1983). The susceptibility of such seas to human activities can be summarized under four headings (adapted from Caddy, 1993a):
the scale of riverine, atmospheric and coastal (direct terrestrial run-off) inputs relative to the rate of flushing to the ocean, and the catchment area and its rainfall relative to the extent of the semi-enclosed sea;
the extent to which sills or basins modify the exchange of water with the ocean and within the semi-enclosed sea itself;
the latitude, depth and, consequently to a significant extent, the temperature and stratification of the water mass;
the size of the human populations residing along the littoral and within the catchment basin, the level of human activities and the land-use practices.
Hydrological complications may arise, depending on whether flushing is irregular, as in the Baltic (Rosemarin, 1990; Anon, 1990), or periodic, as may be suggested by long-term cycles in productivity, e.g. in the Adriatic Sea (Regner and Gacic, 1974) and the Bay of Fundy (Caddy, 1979).
Semi-enclosed seas with narrow connecting straits may show a gradient of features: in tropical and sub-tropical seas, the transition may be gradual, from fully marine, close to the entrance, to more saline water within the semi-enclosed sea which acts as an evaporation basin (e.g., Mediterranean Sea, Persian Gulf); in cold-temperature seas, the transition may be from fully marine characteristics, at the entrance, to near-fresh water within (e.g., the Sea of Marmara - Black Sea - Sea of Azov system and the Kattegat - Baltic Sea - Gulf of Bothnia system). Even largely open coastal seas such as the North Sea may show evidence of similar ecological transitions (e.g. Daan, 1989; DANA, 1989).
In the case of fully enclosed systems, such as the Caspian Sea and Aral Sea (Williams and Aladin, 1991) changes in water level have resulted from diversion or excessive use of inflowing rivers. This is a growing problem globally, with increased water withdrawals for human activities on land often being accompanied by increased loadings of nutrients and other materials in the remaining discharge. This has changed the nature of marine aquatic systems in general and estuarine systems in particular. The effects of runoff of domestic wastes on species diversity may be positive or negative depending on the amount of effluent discharged per day (Reish, 1980) and the assimilative capacity of the receiving basin, but is rarely positive on anadromous species.
The exchange rate with the ocean is very low in the Black Sea, the Baltic, the Mediterranean, the Red Sea, and the Persian Gulf. It is much higher in the Gulf of Thailand, the Yellow Sea, the North Sea, the Caribbean, the Sea of Japan and the South China Sea, but evidence is now accumulating that retention of polluted water masses close to the coast may lead to significant impacts of uncontrolled development even in more “open” systems such as the North Sea, (Boddeke and Hagel, 1991); the Adriatic (Degobbis, 1989), and the Mediterranean as a whole (UNEP/Unesco/FAO, 1988).
A significant proportion of the loadings of “core” seas, such as the Baltic and Black Seas comes from agriculture, especially excessive application of fertilizers, and intensive livestock rearing (Barg and Wijkstrom, 1994; Fan Zhijie and Cote, 1991). Phosphorus in runoff water is in part, eventually stored in sediments, but may be released into the water column especially under anoxic conditions (e.g. Abe and Pekpiroon, 1991). The discharge of nutrient-rich wastes is affected by human impacts, and in turn, affects riverine fish production (Ward and Stanford, 1989; Welcomme, in press). River runoff may boost primary production in otherwise nutrient-poor waters (e.g. Edwards and Pullin, 1990; Caddy, 1990). Such nutrient discharges, if in moderation and if contamination by toxic wastes could be excluded, may enhance biological production in some fishery resources (Boddeke and Hagel, 1991; Caddy, 1993a). However, nutrient enrichment inshore and imbalance of nutritive elements also lead to unusual and dense phytoplanktonic blooms which, on decomposition affect benthis and demersal species and produce unaesthetic conditions close to the points of discharge, thus adversely affecting coastal activities such as tourism; the Adriatic Sea (a semi-enclosed “sub-system” of the Mediterranean) is a good example (see Vollenweider et al., 1992).
The concentration of phytoplankton production in some marine areas is readily detectable from space, through the chlorophyll pigments involved (e.g. NSF/NASA, 1989) and has been used to build a global atlas, which illustrates the overriding importance of inshore areas for marine food production.
High production of microscopic algae in coastal waters of the North Sea has even been implicated in the generation of acid rain, through oxidation of dimethylsulphide (DMS) to sulphur oxides; DMS is a gas given off by marine plants under nutrified conditions (Holligan and Kirst, 1989).
Nutrient enrichment has long been recognized as important in freshwater ecosystems. Its role in marine environment is more recently becoming recognized (e.g. Brockmann et al., 1988); and the need for environmental management of enclosed coastal seas is becoming more evident and urgent (see Goda et al., 1991). Several levels of eutrophication may be distinguished, to which the following descriptors may be applied (adapted from Caddy, 1993a):
Oligotrophic - characterized by low biomass, low availability of nutrients, trace metals and/or growth factors. The south and eastern Mediterranean, as well as many semi-enclosed seas in their pristine state, and the Sargasso Sea, are (or were) examples of oligotrophic water bodies.
Mesotrophic - moderately-enriched systems with a well developed pelagic ecosystem dominated by a resident biomass of small pelagic fishes and an oxygenated benthic ecosystem contributing significantly to fishery production. River-driven marine catchment basins, such as the North and Yellow Seas, are typical examples.
Eutrophic - very high primary production as a result of high nutrient levels, with substantial detrital “rain” promoting heterotrophic bacteria and flagellates leading to seasonal or permanent anoxic zones in bottom water and sediments, with corresponding adverse impact on the benthos and on demersal food webs and high standing crop of small pelagic fishes and zooplanktivores supported by high densities of planktonic herbivores. Certain coastal Zones become eutrophic due to high levels of nutrient discharge arising from human activities, and, to a lesser degree, this occurs naturally in upwelling areas. Examples here are the Black and Azov Seas in the 1940s to 60s, and the upper Adriatic.
Dystrophic - important chemical changes due to excessive input of nutrients, with close to permanently low oxygen levels or anoxia leading to the elimination of most benthic and exploitable demersal fish stocks. The northwestern Black Sea is currently the best example.
Experience in the Mediterranean, the Seto Inland Sea and the Black Sea suggests that, although moderate levels of enrichment of originally nutrient-limited marine systems may favour production and even suspension culture of some bivalve species and higher production of small pelagic fish of low economic value, they do so at the expense of often more valuable bottom-dwelling fish and crustacea. Increased nutrients in fresh-water run-off to semi-enclosed seas may also accelerate phytoplankton growth to the point that it adversely affects aquatic vegetation by reducing light penetration, especially if accompanied by a high load of suspended sediments. Contrarywise, the reduction of nutrient runoff (as in the case of the River Nile following construction of the Aswan Dam) can lead to a decline in marine fish catches (Wahby and Bishara, 1981)
As noted, waste discharges, if uncontrolled, lead to eutrophication, subsequent oxygen depletion and seasonal (as for the upper Adriatic) or semi-permanent anoxic conditions in deeper water (e.g., in the Baltic Sea (Hannson, 1985; Hannson and Rudstam, 1990; Wulff et al., 1990). Anoxic conditions have also moved upwards onto shelf areas in the Black Sea (Mee, 1992; Sorokin, 1983, 1993; Zaitser, 1993), thus extending the naturally anoxic conditions that prevail in the bottom waters of this water body, with disastrous effects on the benthos and demersal fish. Long-lived reptant and burrowing macro-invertebrates may disappear, and short-lived species adapted to very low environmental oxygen levels may become abundant. There is an ecosystem adaptation up to the biological limits posed by the environment, but the new components of this ecosystem added by accidental introduction or immigration of exotic species, (now better adapted than the native species to the changed environment) are rarely those of interest for human exploitation.
Blooms of toxic phytoplankton species arising from the disposal of nutrients and other compounds into the sea can lead to impacts on mariculture and fisheries (ICES, 1992b; Richardson, 1989), necessitating the temporary prohibition of the sale of affected fish products. Untreated sewage can lead to the risk of viral contamination of shellfish and consequent human illness. Environmental degradation can promote the outbreak of infectious diseases (Snieszko, 1974), and can also affect the health of fish in contaminated areas (e.g. Dethlefsen, 1980, 1989; Mellergaard and Nielsen, 1990) and cause fish disease. Note that, even with primary treatment, the nutrient impact of sewage outflows remains largely unchanged; consequent over-fertilization can cause fouling and clogging of nets and cages used in aquaculture (Barg, 1992).
Intensive aquaculture is itself a source of over-fertilization of those semi-enclosed seas that have a limited exchange of water with the ocean, even though their sheltered conditions and ease of access make them initially attractive for aquaculture. Setting criteria for biological loadings of fjords, bays and lagoons as a result of cage culture of fish is already feasible, but defining a “favourable” level of aquatic enrichment, from the standpoint of the wild fishery resource, is still very difficult.
A comparative approach to describing the changes in these ecosystems is needed. The main features of semi-enclosed seas (and even more so, enclosed seas such as the Caspian and Aral Seas) show close parallels with stressed freshwater systems, notably such well studied systems as the North American Great Lakes (Regier, 1973; Regier and Henderson, 1973; Regier, 1979; Rapport et al., 1985). Flushing times may be long: for example, a time of some 80 years has been estimated for the Mediterranean as a whole. In such environments, nutrients and toxic materials can accumulate rapidly. The effects of nutrient enrichment and overfishing in the North American Great Lakes as well as being synergistic are, in many ways, similar to those in semi-enclosed seas; (Regier et al, 1988). There is a decline in ecosystem diversity, progressive dominance of the production system by short-lived, especially pelagic, species, and by exotic or introduced species (Regier, 1973, 1979).
The separation of these two types of human impacts on inland and semi-enclosed seas has been rendered especially difficult by the concurrent growth of industrial fishing and of impacts of population growth, industrialization and agro-industry, especially since the Second World War.
Recruitment, mortality and growth of a fish stock are affected by the impacts of other users of the aquatic habitat and its catchment area; such impacts arise potentially from all up-stream economic activities, such as industry and agriculture, as well as from fishing. One of the major constraints to effective action relates to the dispersion of responsibility among many national and international institutions having competence in various aspects of resource and environment use.
Intergovernmental bodies have already been set up for several semi-enclosed seas. The Helsinki Commission and Baltic Sea Fishery Commission are concerned, respectively, with the environment and fisheries of the Baltic; likewise, the UN Environment Programme's Mediterranean Action Plan and FAO's General Fisheries Council for the Mediterranean, for this semi-enclosed sea. Improved collaboration between these bodies is essential.
The development of the fisheries of semi-enclosed seas has witnessed a number of dramatic changes in the ecology of these water bodies that are attributable not only to the effects of fishing, but also, and perhaps independently, to the effects of the discharge of wastes from human activities, toxic or nutrifying or otherwise into the marine environment.
Two largely simultaneous and synergistic processes may be noted:
The reduction in the numbers of apical predators (notably seals and small cetaceans, as in the Baltic, Mediterranean and Black Seas), and in the numbers of large predatory fish (such as bluefin tuna in the Mediterranean, and turbot, bonito and bluefish, in the Black Sea: Ivanov and Beverton, 1985; Caddy and Griffiths, 1990). Some, but not all of these effects can be attributed to overfishing. Reductions in predator-population size may, in some cases, have contributed to increases in prey species. In some heavily fished areas, such as the North Sea, fishing has been progressively aimed at species lower in the marine food chain, with larger catches of less valuable small, short-lived species (e.g. Pope and Knights 1982; Daan 1989).
Increased discharges of organic materials and nutrients have had impacts on the biological systems supporting fisheries, and in particular have also led to increases in planktonic production, thus increasing food available to larger components of the food web.
Two types of effect corresponding to these processes may be distinguished:
“Top-down” effects: The removal of predator control can lead to increases in abundance of prey species of fish and other organisms. This is rarely of significant advantage to fisheries, since other predators may emerge and the larger predatory species lost generally have a higher value. As in large lakes (e.g. Northcote, 1980), a high abundance of plankton-feeding fish may lead to reductions in the zooplankton and to increases in phytoplankton, with loss of water clarity and adverse impacts on the bottom vegetation which is essential to many demersal species.
“Bottom-up” effects: These lead to increased phytoplankton blooma as a result of enrichment; these phytoplankton blooms are often of species different from those found in unenriched waters. These blooms can affect marine vegetation by reducing light penetration, and in decomposition, lead to seasonal and eventually permanent anoxia of bottom and shelf waters. After an initial increase in production at low levels of impact, this can cause a decline in the benthos, the crustacean and molluscan shellfish, and in the demersal fish. In the pelagic food web, zooplankton species, often atypical of the unenriched environment, increase in abundance. Initially, they support growth of populations of small pelagic fish, but also of other pelagic predators of no commercial value, such as medusae (jellyfish) and ctenophores (Black Sea). Conditions for the production of jellyfish may be related to intrusions of salt water into shallow fertile estuaries, such as those leading into the Sea of Azov (Volovik et al., 1993): these intrusions, in turn, are related to excessive withdrawals of fresh water for agriculture and industry. Invertebrate predators, such as jellyfish and, more recently, ctenophores, feed on fish larvae and, in combination with intensive industrial fishing on fish populations, may have been responsible for collapses in anchovy stocks in the Sea of Azov (Avedikova et al., 1982; Zaitsev, 1993) and in the Black Sea (Caddy and Griffiths, 1990), and more recently, also in the Sea of Marmara (GFCM, 1993; Shiganova et al., 1993).
We may note incidentally that a ‘mixed mode’ mechanism has been described, namely, ‘wasp-waisted’ food webs (Rice, in press). These appear typical of some low diversity, high productivity, food webs in upwelling areas, where fluctuations in the large biomass of small pelagic fish such as anchovy or sardinella plays a key role in impacting both their predators (bottom up) and their prey (top down). Such fluctuations involving changes in species dominance, occurred in these systems even prior to human exploitation (Holmgren-Urba and Baumgartner, 1993).
The introduction of exotic species into a particular marine environment by man, intentionally or by accident, has increased considerably, and changes in the environment have both facilitated this process and resulted from it (Carlton, 1989; Carlton and Yeller, 1993). The establishment of exotic species introduced as pests or parasites through careless aquaculture, through pumping of ballast tanks of shipping, or through man made canals, has changed the fauna of many enclosed and semi-enclosed seas. The introduction of pathogenic organisms has often adversely affected native and introduced species alike, particularly cultured shellfish. The context for such issues is addressed in Article 196 of the 1982 UN Convention on the Law of the Sea.
In relation to the introduction of foreign organisms, FAO has collaborated with ICES in the preparation of a “Code of Practice for Consideration of Transfers and productions of Marine and Freshwater Organisms” (ICES, 1995). The International Maritime Organization (IMO), in cooperation with ICES is also preparing guidelines for minimizing the possibility of transmission of harmful organisms in ship ballast water.
Smith and Vallega (1990), suggest a sequence of actions for assesing the use of semi-enclosed seas. Their ideas provide some inputs to the following proposals for sustainable development of these marine areas:
Coastal States should cooperate through meetings of a regional management body attended by involving decision-makes representing those States, charged with developing, co-ordinating and implementing national actions, and with maintaining the resources and the marine environment in a condition such that living marine resource management is a feasible option for the indefinite future. (Ideally, the same body should concern itself with management of both the environment and living marine resources; otherwise, the bodies having such separate competencies should coordinate their work. The membership of such bodies should ideally include all entities lying within the corresponding Marine Catchment Basin (MCB), whose inland and offshore boundaries for action should be defined).
Marine Basin (MCB) principles should be introduced into the management of the enclosed or semi-enclosed sea and its watershed, with target levels set for discharge of toxic wastes, nutrients, silt and soil run-offs and airborne pollution entering the sea, and strict control of such discharges. (Development planning for the sea should be based on integrated environmental management of the entire catchment basin, including the inflowing rivers, their effluent discharges, as well as the marine environment they affect).
Alternative regional scenarios should be developed for the use of the living resources and the environment, taking into account the interest and interactions between concerned parties.
Common data bases on the environment, resources and socio-economic activities within and around the sea of concern, are needed as a basis for action.
Solutions to the problems of transit through straits and estuaries of migratory fish species should be sought, especially where such transit affects traditional access to a resource within other jurisdictions.
A co-ordinated programme of research with free exchange of information between the countries concerned should be pursued, having as priorities: resource management and ecosystem studies, the monitoring and estimation of discharges of water-borne pollutants and suspended solids, as well as their transmission via the atmosphere from land to the sea; and the economic consequences of consequent ecosystem changes.
Measures to avoid activities harmful to enclosed and semi-enclosed seas need reinforcing, notably the discharge of industrial and domestic wastes and oil, and of practices that encourage the introduction of exotic species into these ecologically unique environments.
Local initiatives should be subordinated to regional agreements, since actions within each sub-zone of an enclosed or semi-enclosed sea are ineffective without proper reference to human interactions in the whole marine ecosystem and its surrounding catchment basins.