Fisheries for sharks and rays are common throughout the world and differ in both the species taken and in the type of gears and vessels used. This diversity contributes to the difficulty in studying the fisheries and to the problems of collecting accurate data on yields and fishing effort. This is evident from the scarcity of information about most of the cases reviewed here. Few countries have sufficient information on their shark and ray fisheries for assessment purposes. Statistics for elasmobranchs around the world need to be improved: major species and species groups in the catch should be recorded and the elasmobranch bycatch from bottom trawl and high seas large-scale fisheries should be reported. This is best done through observer programmes on high seas fishing vessels and the inclusion of sharks in research programmes and statistical requirements (logbooks) of major international tuna programmes, e.g. ICCAT, IPTP, IATTC and SPC. Much data compilation and reviewing must be done on a country and regional basis to enable appraisal of exploitation levels and to make assessments of the status of elasmobranch stocks. This will require coordinated efforts of fisheries managers, shark specialists and volunteers in each country and region.
Another important characteristic is the predominantly incidental nature of the elasmobranch catch. The number of fisheries which primarily target sharks or rays is few. The majority of fisheries taking sharks and rays, are targeted at other species which makes assessment, and especially management, difficult to achieve. Few managers will constrain economically or socially important fisheries to manage elasmobranchs stocks.
The increasing global trend in reported shark and ray catches suggests that yields will be continue to rise as there is no evidence of decline in production. This is misleading if interpreted uncritically as there is a change in the types of fisheries and species exploited; while some fisheries for elasmobranchs fall, others increase. This indicates that exploitation levels are not sustainable in many cases. Almost 30% of the major fishing countries analyzed in section 2.1.2 show a falling trend on catches. Reasons for an apparent increase in catches could be increases in reporting and more landings of by catches from other fisheries.
Although the analyses of trends in yield in each FAO fishing area (section 2.1) suggest that an expansion of the catches could be achieved from some stocks, in the Northern Indian Ocean, the North Sea and North East Atlantic stocks are probably overexploited. These analyses are approximate and a better index of relative production could be developed to provide a better assessment of the possibilities for increased elasmobranch exploitation. A simple improvement would be to incorporate in the index of relative production the area of continental shelf included in each Major Fishing Area to weigh the production of sharks and rays in a similar way in that which as the surface of sea of each area is used here.
The likelihood that fisheries for elasmobranchs will be sustainably exploited in the near future is not promising as general lack of management and research directed towards these resources is evident in most cases. Only three of 26 major elasmobranch-fishing countries (Australia, USA and New Zealand) are known to have management and research programmes for their shark or ray fisheries. Not one them play a leading role in worldwide elasmobranch production. Moreover, those few countries with fisheries information have apparent problems of over exploitation for some elasmobranch stocks (e.g. shark fisheries in souther Brazil, on both coasts of the USA and in southern Australia). Many of the countries with major elasmobranch fisheries have very limited or non-existent research programmes and probably no management for these resources. If this situation continues stocks will eventually be driven to such low population levels that fishing will probably cease for a very long time. A particular case is Indonesia, where catches have grown quickly in the last 20 years and will probably collapse dramatically if no catch limits are set.
World catches of elasmobranchs are substantially higher than indicated by the different official statistics. Statistics reported to FAO amounted to just below 700 000t in 1991. Results presented here suggest that the total catch (as opposed to landings) is closer to 1 000 000t. This includes the estimated catch of the People's Republic of China and the by catch from large-scale high seas fisheries, but does not include discards from the bottom trawl fisheries around the world. Recreational fisheries are also not included since little information is available. However, they are important fisheries in many places, e.g. the USA, South Africa and Australia. Hoff and Musick (1990) estimate that the mortality of sharks in recreational fisheries of the eastern USA alone, is more than 10 000t/yr. The real total level of sharks, rays and chimaeras caught around the world is probably closer to 1 350 000t, twice official statistics!
One of the chief problems in dealing with elasmobranch fisheries is that their biological and ecological characteristics make them particularly vulnerable to overexploitation. Most shark and many ray species can be classified as strong K strategists, i.e., they are long-lived with slow growth rates and late sexual maturation. Most species have low fecundity and these factors results in low reproductive potential. Further, they are usually the top predators in their communities (at least in the case of sharks) and thus have comparatively low abundances.
Some important areas of elasmobranch population dynamics are largely unknown. First, stock-recruitment relationships have never been demonstrated for any elasmobranch group though strong relationship is expected because of the reproductive strategies of the group. Second, there is a general lack of evidence about density-dependent mechanisms regulating elasmobranch population size. Third, the spatial structure and dynamics of most stocks are almost totally unknown. This is of particular importance to fisheries management at both the local and international level. Inadequate knowledge of migration routes, stock structure and movementrates may undermine otherwise good assessments and management regimes. Much research, both practical and theoretical is still needed in these areas.
Another constraint to assessment and management of sharks and rays is inadequate population theory. For example, classical stock production models assume that there is an immediate response in the rate of population growth to changes in stock density, that the rate of natural increase at a given density is independent of the age composition of the stock and that exploited populations are in equilibrium. Neither of the first two assumptions seem to hold for elasmobranchs (Holden 1977, Wood et al. 1979); while the third probably does not hold for any fishery and surplus production models have been used for assessing of shark and ray fisheries without examination of the suitability of the model to the specific fishery. However, the difficulties in finding adequate models for elasmobranchs are exacerbated by the gaps in the understanding of their biology.
Additional problems for assessment and management are posed by the multispecific and multigear nature of most of the fisheries for sharks and rays. For example, elasmobranch catches in major tropical elasmobranch fishing countries account for 42% of reported world catches and are a mixture of several species of sharks, captured with a variety of gears from several types of vessels. Multispecies fisheries present difficult methodological problems because of the complexity of the biological and the technological interactions in the fisheries. Consequently, theoretical development of multispecies assessment and management still lags behind the rest of fisheries science (Hilborn and Walters 1992). In addition, the usage of multiple gears and fleets introduces difficulties in assessment and management, e.g. standardization of effort and allocation of quotas for the various types of gear and vessels.
Many problems associated with elasmobranch exploitation are related to the economics of the fisheries. The economic processes involved in elasmobranch fisheries cause what could be called the “tragedy of sharks”. This comes from two contradictory factors. First, research and management of sharks and rays are hampered by their low economic value: research funds are usually given to resources economically more important than elasmobranchs. Second, the high price attained by shark fins in the international market. This stimulates fisheries to target sharks and explains why incidental catches are usually “finned”. The dynamics of the two processes means little hope for viable management consistent with both economic and conservation interests.
“Finning”, i.e. cutting off the fins from the shark and dumping the carcass, is extremely wasteful but is common among fishermen throughout the world. Apart from being inhumane, finning is responsible for high death rates of sharks at sea. Finning is suspected to be particularly widespread in tuna fisheries but the extent and impacts of this habit are difficult to assess due to poor or non-existent information. This is another area where observer programmes of high seas fisheries could provide reliable information.
The low economic value of elasmobranchs results in fishery statistics which are not accurately maintained together with problems of species identification, specially for tropical species. Most records aggregate skates in a single group and sharks in two categories, large and small. Or even worse, the elasmobranchs are reported in a single category “various elasmobranchs”. Without accurate statistics by species or species groups it is difficult to get insights into the dynamics of the stocks. Part of the answer to this problem lies in the economic field. When a specific market is developed for an elasmobranch species, catch statistics soon become available. Active development of markets for specific elasmobranch species may encourage better fishery statistics.
The top predator niche occupied by many sharks raises the question of their importance as regulators of other species' densities. Although it could be desirable to control shark populations in specific situations e.g., because they can affect the economy of important beach resort areas such a Natal or Hawaii, it is also possible that in other cases their removal would cause undesirable ecological and economical consequences (van der Elst 1979). It is difficult to assess these effects or to know which stocks of elasmobranchs are actually endangered when there is insufficient information about their ecology, size and state of their stocks, basic biology and the magnitude of their exploitation through fishing.
The size of the by catch of elasmobranchs in high seas fisheries is a major concern for conservation. Blue sharks might be facing extreme pressure in many parts of the globe but more specific studies are needed to determine the real situation. The threat that high seas fisheries pose to elasmobranchs is only one part of a complex interaction, e.g., There is substantial gear and catch damage caused by sharks in most of these fisheries (Taniuchi 1990, Sivasubramaniam 1963,1964, Pillai and Honma 1978, Berkeley and Campos 1988) and this causes financial loss for the fishing industries involved.
A solution to these problems could be to install shark deterrent devices in passive fishing gears (these account for most of the elasmobranch kill). The Natal Shark Board in South Africa is currently testing a electroacoustic device to protect bathers from shark attacks without having to kill the sharks. Another possibility is the design of selective fishing gear to reduce shark hooking rates. However, the only present viable alternative is the implementation of suitable by catch quotas for elasmobranchs in the high seas fisheries through international agreement and their enforcement through observer programmes.
The concern over elasmobranch exploitation arises from both theoretical considerations about their biological and ecological traits and for historical reasons. The record of fisheries for sharks and rays includes collapses and rapidly falling catch rates (Holden 1977). Examples include the California fishery for tope sharks, the piked dogfish fishery of British Columbia (1940's), the school shark fishery of Southern Australia (1950's), the porbeagle shark fishery in the Northwest Atlantic and the piked dogfish fishery in the North Sea (1960's) (Anderson 1990). Although the reasons for some of these collapses are partly understood and though decreasing CPUEs are a natural characteristic of fisheries development, these failures warn against high levels of exploitation in view of the special biological attributes of sharks and rays discussed above.
Protection of sharks and rays from the impacts of large-scale fisheries is not impossible. The efforts of international collaboration that regulated the catches of salmonids, marine birds and marine mammals in the North Pacific Ocean and the recent banning of all driftnet fisheries in the high seas of the world demonstrate it is possible. The strong pressure that some countries are imposing on fleets that take dolphins in purse seine tuna operations are another example that, where the will is there, protection becomes a reality.
Effective management and protection of elasmobranchs should begin with education and awareness. Only through intensive and widespread educational programmes is it possible to motivate fishermen, scientists, the public and governments to achieve effective protection and management of sharks and rays. Some of these efforts have already been successful. The South African Government has recently protected the great white shark; the Government of Australia forbids the killing of grey-nurse sharks and is considering protection of white sharks; California passed legislation banning the catch of great white sharks. During 1991, an international meeting, “Sharks Down Under”, was held in Australia, focusing attention on the need for the conservation of elasmobranchs. The American Elasmobranch Society held a Symposium on Conservation of Elasmobranchs during its 1991 meeting and is presently establishing a Conservation Committee at the international level and the Species Survival Commission of the IUCN has recently formed a Shark Specialist Group. This is evidence of international concern about the future of elasmobranchs.