The state of high-seas resources has been conveniently summarized by Garcia and Majkowski (1990) and FAO (1993 c, k). The main high-seas resources are: whales; tunas and related species; salmon; oceanic squids; sharks; oceanic horse mackerel; mesopelagic fishes; marine turtles; Alaska pollack; pomfrets; Pacific saury; and a few other potentially important species.
Of the 400 or so commercial or potentially commercial species considered to be oceanic, few are subject to directed fishing. The biological information available on most oceanic resource species is usually poor, and is only relatively good for large tunas and some whales. Tunas, salmon, sharks, billfish and squid are now the main resources being exploited on the high seas, except for the demersal and small pelagic resources of continental shelves lying outside 200-mile limits, which from a special case. Tunas, being apical predators in oceanic systems, feed on a number of smaller species such as frigate mackerel, squid etc., which, at least in theory, could yield perhaps ten times the landings from tuna stocks. However, tunas effectively integrate the whole oceanic food chain and, as apical predators, make it available to man in high-value, accessible schools. With the exception of some squid stocks, tuna prey species lower in the trophic chain are not often exploited, partly because of the costs of fishing far from port, of low market prices, or because densities of occurrence and availability to fishing are low.
Some tuna stocks are heavily exploited, most marine turtle and some seabird populations populations are under direct or indirect pressure from human activities, and few shark resources have sustained prolonged local exploitation without collapse. Many of the large whale species have been overfished in the past, and may still be depleted or even on the verge of extinction, but whale population estimates are imprecise and now largely based on sightings. Concern has recently focussed on dolphin populations, and these may be endangered in some enclosed seas and coastal areas. There is some evidence, however, that populations offshore in areas such as the eastern Pacific, are being maintained, even though by-catches in some fishing gears need to be monitored, and population estimates improved.
New fisheries are now possible for relatively few important unexploited resources, but oceanic squid, mesopelagic fish, and krill in the Antarctic, could still have significant unused potential, although scientific opinion here is less optimistic than formerly. For mesopelagic fish, potential yields could be large,but given low unit values, high cost of fuel and the high level of harvesting technology required, net economic yield may not be great. Such a development merits encouragement, since a proportion of these large resources, if used for producing fish meal, may substitute for small pelagic fish, and increase the availability of the latter for human food instead of for the production of meal, as is presently substantially the case (FAO, 1993b).
The GESAMP report on the State of the Marine Environment (GESAMP, 1990) noted that, although the open ocean was still relatively clean, some contamination was occurring, with atmospheric routes for contaminant transmission being of primary importance. Also of considerable concern is the widespread occurrence throughout the world oceans of floating plastic debris which may impede (by entanglement etc.) movement, and interfere with the feeding of birds, mammals and fish species living in or off the suface layers of the oceans.
2.4.3.1 The management units for ocean systems
We know that the exploitation of certain species affects the abundance of the others through predator/prey linkages or by inter-specific competition. Current perceptions of this linkage of individual species in an oceanic food web raise the problem, analogous to that of stock boudaries for single species, of deciding what are the practical geographical limits of oceanic systems within which an integrated approach to management should operate. This recognizes the Darwinian concept (e.g. Sinclair, 1988), that self-reproducing populations should be managed throughout their range, irrespective of jurisdictional boundaries that lie across the range of the unit stock in question (FAO, 1993b, k, 1995e).
One currently popular paradigm is the Large-Scale Marine Ecosystem (LME) concept which would see certain large areas of ocean, such as the Benguela Current system or the Bering Sea, under co-ordinated management by concerned States having a legitimate interest in the marine resources of the area. LMEs would necessarily cut across maritime boundaries, would require an intensificaion of research by all parties to understand functional linkages, and would need to be integrated with existing management structures, or require new ones. Decisions would have to be made as to the priorities to be given to different exploitation scenarios. It seems certain, however, that management on a species-by-species basis, the approach that has most commonly been used to date, is less than satisfactory. Interrelationships between species (competitors, prey and predators) and environment and fishery need to be well understood for LME management to be applied, which is not currently the case.
With respect to high-seas fisheries management, the principal conclusions of the FAO Technical Consultation on High-Seas Fishing (Rome, 7–15 September 1992; FAO, 1992a)
high-seas fishing will continue to increase, as will the need for management; problems of shortage of date are unlikely to be resolved; hence, the “precautionary approach” (see section 4.4.2) should be applied to development in this field;
the UN Convention on the Law of the Sea (Annex IV), supplemented by the relevant decisions of the UN Conference on Environment and Development (see sections 7.1 and 7.3) and the Declaration of Cancù(see Annex V), provide the principal legal framework for the sustainable development of high-seas resources;
there is a need for a code of conduct for responsible fishing of high-seas and other marine resources; see also section 4.4);
the reflagging of fishing vessels to flags of convenience, so as to avoid conservation and management measures and fair-trade practices, should be strongly discouraged;
flag States should maintain a national register of fishing vessels capable of operating on the high seas and so authorized;
high-seas fishery management should be, wherever possible, undertaken by regional or sub-regional organizations, which will require the strengthening of regional fishery bodies, and should also, cover whole stocks and take into account all removals therefrom;
high-seas fishery management should take environmental considerations fully into account and be based on the best possible scientific data and information, including accurate and complete fishery statistics, with due consideration being given to legitimate confidentiality of such data, information and statistics;
effective monitoring, control and surveillance (MCS) is essential for high-seas fishery management, and requires application of new technology;
there is a need for more research on high-seas resources and environment and for its application to fishery management;
Maximum Sustainable Yield is no longer a valid target reference point for high-seas fishery management, and other reference points should be examined;
developing countries must be assisted to obtain the necessary capacity to participate in and manage high-seas fisheries;
greater public awareness of high-seas fisheries should be pursued.
The FAO Council, at its 102nd session (November 1992), endorsed the conclusions of the Technical Consultation as well as accepting the Declaration of Cancùn on responsible fishing as a basis for future action in developing a code of practice for responsible fishing.
2.4.3.2 The problems of stocks straddling EEZs and the high seas
The UN Convention on the Law of the Sea extended the provisions for conservation of highly migratory species to areas and resources beyond national EEZs by asserting that “Coastal States and other States” should “co-operate directly or through appropriate international organizations with a view to ensuring conservation and promoting the objective of optimal utilization of such species throughout the region”. However, the need for more explicit conservation mechanisms, and a code of practice governing fishing operations on the high seas, has become progressively more evident in recent years.
Although the Convention's term “High Seas Resources” refers to oceanic resources lying beyond 200-mile limits, there are, in practice, few living marine resources whose ranges do not overlap to some extent one or more coastal State jurisdictions. This has profound implications for resource exploitation and management, since many nominally “High Seas Resources” should more properly be regarded as stradding stocks with adjacent EEZs.
Distant-water fishing vessels operate outside the jurisdiction of their countries and although reporting by their own fleets is often required by distant-water fishing nations as a condition of fishing, it is very difficult for the flag State to enforce, given the prohibitive cost of at-sea surveillance. This problem includes the difficulty of obtaining unbiased fishery data, especially on by-catch (Alverson et al., 1994). The incentive for falsification of declarations is a real one, with several real sources of bias being possible; for example:
a proportion of catches of a species taken under licence in one EEZ may be declared as coming from an unregulated (high seas) area or from the EEZ of the flag State;
given the mobility of distant-water fleets and the significant time spend at sea in one trip, catches may be taken from sea areas under different jurisdictions, possibly including more than one ocean;
illegal catches of a regulated species may be declared as coming from an unregulated area, or, after transformation at sea, as consisting of an unregulated species;
illegal catches may be sold or trans-shipped at sea or in an unregulated port to another vessel.
Any management scheme that is intended to control fishing in high-seas areas must find a solution to these potential loopholes and, to the problem of at-sea surveillance.
The above-mentioned unresolved issues, and the need for a common data base for high-seas fisheries, have become progressively more evident in recent years, but the poor state of our knowledge of high seas resources, and the lack of an established framework for limiting the impact of human activities on these resources, were highlighted most recently by Resolution 44/225 adopted on 22 December 1989 by the United Nations General Assembly on the issue of large-scale pelagic driftnet fishing.
Following the principle that “evaluation and management of a stock must take account of removals throughout its range of distribution”, an exchange of information and co-ordination of harvesting are prescribed under the UN Convention on the Law of the Sea for marine resources, including those taken outside EEZs.
Several major problems are evident in practice:
Few individual nations whose EEZs overlap the distribution of a high-seas resource are likely to reduce their exploitation rate to accommodate catches taken by the fleets of other nations in adjacent EEZs, and even fewer are likely to accommodate, within an overall total allowable catch, the needs of distant-water fleets fishing the same stocks in international waters, unless they are signatories to an international agreement or are members of a fishery commission to which they have delegated powers to manage catches of the species in question throughout its range. They are more likely to complain, justifiably, that catch rates within their EEZ could be affected by uncontrolled fishing on the same stock in areas outside their jurisdiction. In these circumstances of a lack of reciprocal recognition of a right by others to use the same resource, over-exploitation inevitably reduces the value of the resource to all parties (Caddy, 1982).
Vessels from flag States that are not signatories to a fishery commission or to a joint fishing agreement at present, have no legal obligation under international law to control their catches on the high seas; nor is there currently any international control and surveillance capability for areas outside EEZs.
Catches taken on the high seas by individual vessels of a distant-water fishing nation or an adjacent coastal State (whether or not the flag State is signatory to an accord), are not always recorded accurately as to place of origin. As a result, the data on catch, effort and by-catch needed to carry out a stock assessment are usually incomplete or biased, making evaluation of the impact of fishing imprecise.
Distant-water fleets are at sea for long periods, making the presence of an official observer on board difficult. These fleets may move rapidly from one jurisdiction to another in the course of a fishing trip, may process the catches at sea into a less easily recognizable form, and may trans-ship them to another vessel in port or at sea, thus making it difficult, on landing, to establish the place and date of origin and the quantities caught.
These kinds of problems require radical new solutions in which the uncertainty of current information as resources will require a precautionary approach (e.g. Garcia, 1994a, b) but also where the application of high technology will certainly play an important part, and in which a new legal and management framework will be needed to oversee exploitation of high-seas resources. These issues and others are currently being addressed at the United Nations Conference on Straddling Fish Stocks and Highly Migratory Fish Stocks underway in New York, and will hopefully lead to a more controlled exploitation regime.
2.4.3.3 Oceanic data bases for decision-making, and potential control measures
International fishery management evidently depends on the exploitation of a wide variety of types of information, and there is a growing realization that it would greatly benefit from the development of Geographical Information Systems (GIS) (e.g. Maguire et al., 1991). This tool, first developed for rationalizing multiple land use, has been extended to coastal zones and should be further developed for oceanic resources. However, information on the ocean environment is not easily accessible to fishery decision-makers, and this applies in reverse to other users of the marine environment who have not always taken the needs of marine resource management into account.
All of the foregoing considerations suggest the need for some coordinating mechanism to monitor and regulate high-seas fisheries. Such a body or bodies should maintain close contacts with all States having a legitimate interest in high-seas fisheries, and should receive guidance from existing regional fishery commissions nominally responsible for such resources but which, in practice, lack the mandate to control resource harvests that fall under more than one jurisdiction. A global mandate would be required to maintain a common data base of high-seas catches by statistical areas, or lists of vessels fishing high-seas resources, with standard international marking of vessels and gear. Mandatory reporting procedures for registered vessels would need to be set up and controlled. Progress towards such a goal has been notable in recent years but such a uniform global system does not yet exist.
Major problems remain with such a hypothetical global scheme, mainly of a legal, organizational and financial nature, but also of a technical nature, particularly with respect to verification. Technological solutions are feasible in theory: a “black box” could be installed on registered fishing vessels which would continuously monitor, via satellite, vessel position and various telemetric devices, engine and winch operation etc., which would indicate that fishing operations are underway. Such systems will not, however, assist in documenting illegal fishing practices, and the simplest but not infallible solution has been the recourse to prohibition of fishing by certain gears within specified areas.
A particular problem of high international profile in recent years arises from the poor species selectivity of the monofilament nets used in the so-called large-scale pelagic drift-net fishery; these nets differ considerably from inshore gill-nets in their size (up to 100 km) and in their fishing action, which tangles all species coming into contact with the gear, including fish, squid, birds (e.g. ICES, 1994b) and mammals (Northridge, 1991) (FAO, 1990; Northridge, 1984, 1991). Discards of non-target species caught in these large-scale nets can be high, and may include not only marine mammals and birds but also small tunas and other fish not considered of commercial importance. Difficult, legal issues are raised here for high seas fisheries (Hey et al., 1991), and the UN General Assembly resolution 44/225 of 22 December 1989 addressed this problem and recognized the need to ensure that fishing gear is designed in such a way that the target species is caught preferentially, with only minor catches of other species. This poses a major challenge to fishery technologists. One other disincentive to irresponsible fishing practices discussed recently involves trade measures against products resulting from harmful fishing practices.
There are other difficulties with respect to illegal by-catch of non-target species: incidental catches of regulated species outside prescribed areas, seasons and catch limits. Prohibited salmon catches in squid gill-net fisheries can in theory be monitored in port, since these species are less likely to be discarded. Kills of species that are taken incidentally and discarded at sea, such as marine mammals, cannot be quantified using this approach which requires rigorous, but problematic, evaluation at sea of the impact of fishing gears according to season, area and mode of fishing, and the development of more selective gear and procedures that satisfy ecological criteria (ICES, 1994a). More imaginative solutions to monitoring high-seas fisheries may permit a more flexible response than wholesale banning of a whole category of fishing methods which are capable of being improved and, after modification, of contributing to the achievement of sustainable development.
The following actions (boldface, with complementary text in italics) seem appropriate with respect to the sustainable development of high-seas resources:
Mechanisms are required for managing the resources of high-seas areas. The results of the ongoing UN Conference on Straddling Fish Stocks and Highly Migratory Fish Stocks may provide a basis for this, which would depend on, inter alia: maintaining and exchanging up-to-date registries of licensed vessels; employing real-time fishery reporting procedures and a system of surveillance using the latest modern technology; developing and maintaining a data base on stock sizes and removals and on changes in the ocean environment relevant to living resources; providing to the regional fishery commissions timely national information on fishing activities and on the state of resources overlapping relevant jurisdictions; and co-ordinating resource evaluations with the countries and regional fishery commissions concerned. It would also provide, particularly for the major oceans, a mechanism for co-ordinating the various regional commissions, and could incorporate the requirement for preservation of the oceanic environment, as well as the resources, within their terms of reference.
The Antarctic Ocean is one of the few areas where an ecosystem modelling approach is specifically incorporated in the framework underlying resource management (CCAMLR, 1993a, b). If we examine the state of the resources that are currently exploitable in the Antarctic, (see Fischer and Hureau 1985), there is little reason for congratulation with respect to most whale stocks and finfish, even if for most non-exploitable Antarctic and sub-Antarctic living resources (with the exception of some species such as Albatrosses taken incidentally in some types of fishing operations further north), the situation is relatively good.
The very slow-growing and late-maturing demersal fish resources (e.g. Notothenia sp and Champsocephalus sp, and others in Fischer and Hureau (1985) and Gon and Heemstra (1990)), have been heavily affected by fishing. This was carried out from the 1970's, largely by former socialist countries operating under non-economic criteria (Koch, 1992). In some cases, earlier quotas set by CCAMLR have not been filled, for reasons of current low population sizes. No catches of icefish were reported in 1992/3; in part due to continued declines in stock size. The problem of control of Antarctic fisheries seems not one of the adequacy of the underlying philosophy, but that monitoring of fishery regulations in such a large, inhospitable area (as well as obtaining the necessary data for stock assessment) is close to impossible.
The same comments on fish may also apply to the harvest of the krill, Euphausia superba; a species which underlies most food webs, (e.g. Miller and Hampton, n.d.), and is present at very large biomasses. Although previously the catch had been some 300,000 t, in the 1992/3 fishing season it fell to about 87,000 t, and the likelihood that a fishery operating under market conditions can make a profit with current technology on these resources remains uncertain. Some parties have expressed concerns however that even harvesting a small proportion of the standing stock locally to bird or seal colonies could lead to food depletion for less mobile breeding concentrations of land or ice-based resources.
The incidental capture of widely migrating albatross in tuna surface fisheries in the South Pacific has been considered one responsible factor why some bird populations, such as the Southern Albatross, are at low levels. The formerly heavy exploitation of baleen whales, which preferentially feed on krill in the Antarctic, may have allowed increases in other species dependent on the krill-based ecosystem, such as the crabeater, leopard, Weddell and fur seals (Institute of Biology (UK), 1985), although other authors have found relatively minor overlaps in the diets of these latter species (Siniff 1988). The recovery of the large whale populations is proving to be slow and they may need protection during their migrations outside the Antarctic Whale sanctuary recently declared by the Whaling Commission south of Latitude 40 degrees S.
Other resources of the Antarctic and sub-Antarctic have attracted attention, including some crustaceans, and the cephalopods (Rodhouse 1989), but commercial exploitation is yet to get underway for obvious reasons of high costs of operation. The risk remains, however, that in absence of the usual level of coastal State control that applies in other areas, it will be difficult to effect proper surveillance of responsible harvesting levels.
The natural environmental stresses in the Antarctic ecosystem make it particularly susceptible to changes due to external factors. Beside fishing, atmospheric contamination, albeit at low levels, due to human activities in the Northern Hemisphere, is growing, and has already affected the ozone layer which provides important protection against ultra-violet radiation (Bidigare, 1989; Karentz, 1991).
The Convention on the Conservation of Antarctic Marine Living Resources (CCAMLR) covers all marine resources, including mammals and birds, south of latitude 60°S, and provides a prototype for any management scheme of the LME type. The objective of the Convention (CCAMLR, 1993a) is “Conservation” which it equates with “Rational Use”. It aims at preventing the reduction of any population, whether by direct exploitation, exploitation of its essential prey species, or deleterious transformation of the environment, to a level that may endanger its stable recruitment. Thus, despite the large biomass of, for example, krill and cephalopods in the Antarctic, their rate of replenishment, distribution pattern, and importance as food for terrestrial and aquatic species is intended to determine the allowable extent, area and season of removals. Protection is particularly required near bird and mammal colonies, and for birds and mammals, close to expanding areas of human activity in the Antarctic. In this connection, the role of the Antarctic for monitoring global environmental changes is well recognized (SCAR 1993).
The following actions, inter alia, seem appropriate with respect to the sustainable development of Antarctic resources:
Increased research on Antarctic living marine resources, with the requirement that this research be co-ordinated so as to reduce unnecessary duplication of effort, and should take into account the growing impact that Antarctic scientific settlements themselves are having on an undeveloped area. Research in the Antarctic plays an essential role with respect to the monitoring of global climate variations and of global environmental conditions in general.
A careful approach to exploitation is needed that would not impede utilization of Antarctic resources but would ensure that access to these resources be subject to a harvesting regime limited in time ans space.
The last two centuries have witnessed the depletion of a number of populations of marine birds, reptiles and mammals which interact directly, or indirectly, with man's harvest of marine products (see Northridge, 1984). In certain cases, e.g., the sea otter and several seal populations, (Ridgeway and Harrison 1985) such as the Pacific fur seal (Mitchell, 1973; FAO 1978b), recovery occurred once appropriate legislation was introduced, aided evidently by regeneration from small surviving fringe populations or unprofitable low-density populations. Several cases of extinction have occurred (e.g. the Steller sea cow; FAO, 1978b; Ridgeway and Harrison, op. cit.), and there are others where the species is currently considered to be threatened or endangered (Jefferson et al., 1993). Fishing or hunting has been the cause of many of these near-extinction. In other cases, such as those of the dugong and sea turtles (Ogden, 1989), human competition for suitable environment, often degraded by man, may have been the predominant cause. Natural fluctuations and sudden crashes and recoveries in the abundance of sea bird colonies close to exploited small pelagic stocks (Anon, 1995) may be rendered more extreme by the direct action of man, such that the heavy exploitation of their principal prey species may be an important factor. Viral or bacterial infections, perhaps due to pollution, have been implicated in die-offs of marine mammals in the Baltic and Mediterranean Seas (Heide-Joergensen et al., 1992; Calzada et al., 1994).
Apical predators, which include marine mammals such as some seal, dolphin and whale species, and large predatory fish such as sharks, tunas and halibut, played a role in controlling the densities of their prey species, but have also been among the first to be reduced in numbers by harvesting. However, given the complexity of many marine food webs, the commercial elimination of the main apical species often results in other organisms taking over part or all of the role of apical predator until, perhaps, they themselves are overfished (Kerr, 1977, Ursin, 1982) or change the composition of their prey (Glasser, 1978).
Marine food webs are complex (Caddy and Sharp, 1986) and pose difficulties in quantification of the impacts of human actions (May et al., 1979). Not always has the elimination of an apical predator led to a major increase in the yield of its prey species (Pauly, 1979a). On the other hand, considering stock sizes of predator species prior to depletion, there would presumably have been a degree of competition between man and the apical predators for their common prey, if the latter were still present in their original numbers. Thus, a number of calculations (e.g. discussed in Katona and Whitehead, 1988) have shown that marine mammal populations, even though many are now reduced in size in many areas of the world, may still consume at least as much of some prey species as is harvested by man. It has been postulated that sperm whales alone, consume a greater quantity of squid than is harvested by the world's fisheries (Voss, 1973). Similar calculations are common in the literature. For the Bering Sea ecosystem, for example, in FAO (1978b) it was estimated that a (then) biomass of 450 000 metric tons of 25 species of marine mammals, could have been as high as 9–10 million metric tons annually: roughly four times the (then) commercial catch weight (but of course dominated by nekton and benthos species not exploited by man). More recently, concern has been expressed as to the impact of heavy fishing of Alaskan pollock on populations of their natural predators, such as the northern fur seal. Baleen whales, prior to the onset of whaling, were estimated to have required some 190 million tons of krill per year, or twice the weight of current world fish landings (FAO, 1992f).
Some seal populations are vectors for parasites, which also infect some commercial fish species such as cod (McClelland et al., 1983; FAO, 1978b) and incidentally may cause damage to the gear of fishermen. This partly explains the antagonistic behaviour of fishermen in some parts of the world towards some marine mammals. Calculations have been made of the “loss” to the fishery, but it is not certain that such calculations represent real effects on the fishery. Nor can they be simplistically applied to the estimation of the “surplus” yield to man released by fishing down natural predators on fish. Such calculations do not take account of ecological linkages, ecosystem stability, or the growing appreciation of the ecological role of marine mammals and their cultural significance to man, due to their intelligence, means of communication and social behaviour. Most arctic and subarctic seal populations are now recovering to former levels and concern has been expressed that the impacts of large populations of harp seals, sealions and others (outside the Antarctic) on those resources harvested by man, may justify population control measures.
Current theories of the role of predators in ecosystems in terrestrial ecology have emphasized their importance in culling sick or unfit individuals, and keeping population sizes of prey species in balance with available resources, but hard evidence as to the extent to which this argument applies in the sea where human predation pressure is also high, is not easy to come by. It has not been confirmed in the marine environment whether with the reduction in populations of top predators, prey fish populations are more unstable, and/or whether a ‘surplus’ harvestable production can be estimated in excess of the needs of natural predator species competing for the same food. For example, the 150 million tons of Antarctic krill not being eaten by depleted rorqual whale populations are now being consumed by other species, some of which may have increased in population size (FAO, 1978b). It may be supposed that the return of many marine mammal populations to the numbers that existed prior to man's assumption of the dominant role as apical predator in marine food chains, would only be possible by, and would certainly result in, a significant cuts in overall global fish catch. Since food availability is one of the factors that limits predator populations, given the existence of industrial fisheries, this limitation is likely to come into play at lower stock sizes of marine mammals than formerly. This would not necessarily affect the sustainability of the marine mammal populations concerned, and, at least in theory, could be taken explicitly into account when catch levels are decided upon.
Clearly specious arguments are common in the conservation versus development debate, and not always is there an examination of the conflicting evidence on either side. It has been speculated that reducing the abundance of those cephalopods which feed on juvenile fish could increase fishery yields of conventional fish species. This argument does not take into account the growth in squid fisheries going on around the world, and that this could be due to cephalopods occupying part of the niche left by depleted groundfish species; nor the fact that squid may now command higher unit values than most fish. It is difficult to avoid the conclusion that one of the objectives of sustainable development of endangered stocks of unharvestable spical predators is their recovery to stock sizes that can reproduce themselves without danger of population collapse. However, uncontrolled population sizes of apical predators are not necessarily without adverse repercussions on the availability of fish for human food. Clearly, the return of stock sizes of some apical predators to former unharvested levels would only be possible at a considerable cost to man in terms of the loss of animal protein from the oceans. This must be taken into account in the context of sustainable development of marine resources as a whole.
In the case of the reduction in population size of apical fish predators, such as grouper, cod and halibut, some increase in yields from species lower in the food web may result, but since these yields are dominated by small forage fish which tend to be lower in unit value than the apical fish predators, the net value to the fishery is likely to decrease as a result.
Another important aspect of the management of apical predators is the possible accumulation, through food webs, of contaminants such as mercury organochlorines (e.g. Olsson, 1994), or even natural substances, such as ciguatoxins (Pulos, 1986), which may be a threat to apical predator species and a health hazard to the human consumer.
The principles of sustainable development require that marine resources be exploited in a way that ensures the continuity of populations and species, but they do not assist in making a choice between different levels of direct or indirect exploitation that otherwise satisfy these principles but result in different relative abundances of ecosystem components. Just what the level of exploitation should be has become a matter of controversy between those concerned with food security and those concerned to see populations of some species maintained in as close to an unexploited state as possible (Beddington and May, 1977; Beddington, 1978). Achievement of the latter objective will impose significant costs in terms of its impact on the nature and the extent of harvesting activities, and at present, this cost will have to be borne almost exclusively by the fishing industry which still plays the major role in terms of extracting rent from living marine resources.
The following actions are suggested as central with respect to the sustainable development of apical predators and endangered species:
More - and more intensive - investigation is needed of the role of marine mammals and other apical predators in marine ecosystems, their role in controlling prey populations, and their indirect interactions with man through the food chain.
The incidental catches of marine mammals, turtles and birds must be reduced, especially in the case of endangered species, and an effort made to maintain these incidental catches at levels allowing resource recovery.
The harvesting of marine mammals for food, through deaths incidental to harvesting, or for other reasons such as predator control within EEZs, should recognize that these populations have a slow rate of replenishment, are susceptible to other types of interference by man, and have non-consumptive uses.
