It would have been presumptuous to expect the Conference to succeed in identifying and solving all the problems related to the study of the biology and culture of shrimps and prawns. This was well recognized at the outset by all those involved in organizing the Conference. It was generally felt that the technical discussions and the exchange of ideas and views would clarify the problems confronting scientists and technicians. This would result in some new knowledge becoming available immediately and provide the basis for future lines of research and possible cooperation of a regional or international character, and also be of use for shrimp industry development. Based on these criteria, it is generally believed that the Conference has been successful. As very appropriately pointed out by the Chairman in his concluding remarks (Appendix 5), one of the chief benefits resulting from this Conference was the great improvement in personal understanding and communication between people engaged in this particular field.
In reviewing the present status of research in various parts of the world directed towards assessment of the complex life history of exploited species, the Conference recognized that many aspects are still not well understood and further studies are required. As present trends indicate greater demand for shrimp and prawn products in national and international trade, these studies should be intensified and accelerated. Although new shrimping grounds are being located every year, some important stocks have approached their peak of production. Evidently no improvement in the natural resources and protective measures for overfished stocks can be suggested unless some important ecological factors are fully understood.
Although the concept of shrimp and prawn farming on a large scale has been prevalent over a long period, the numerous impasses encountered, particularly in the initial rearing stages, discouraged continuation and new undertakings. The successful results achieved in Japan in this particular field were most stimulating and encouraging and could be considered as a breakthrough. Nonetheless many difficult problems have to be overcome before shrimps and prawns can be farmed at an economic level. Meanwhile the principal source of production will be the harvesting of wild stocks at sea.
3.1 Resource appraisal
The need to develop standards to appraise resource potential became evident from documentation presented and ensuing discussions. Although information on resource potential is required by the industry and FAO's Indicative World Plan for Agricultural Development (IWP), such knowledge is fragmentary at present. The consensus indicated no spectacular increases in production from many presently exploited grounds through improved fishing methods. The initial promising results of the electric trawl, which raised high expectations, have not yet been substantiated. Further research was found to be required in the development of echo-sounding equipment capable of detecting distinctly benthic and bathypelagic populations. The possibility was put forward of developing hypersensitive electronic techniques to discriminate between bioacoustic emissions of shrimp and other species, despite the limited advances in this field. The value was stressed of projecting abundance by assessing types of ecological habitats populated by various known groups of shrimp.
Though considerable attention had been paid to the study and exploitation of shrimp and prawn resources, the potentialities of unconventional species like the galatheid crabs or krill had been overlooked in the past. The utilization of untapped resources in various parts of the world provided an interesting discussion.
3.2 Life history
Despite numerous studies on the biology of species exploited over many years, and on which substantial fisheries are based, many aspects are yet to be explained adequately. Knowledge of life histories was considered scanty for relatively “unknown” species on which fisheries have recently been established. The Conference noted that lack of knowledge existed on development, transport and survival of larvae - thus seriously affecting understanding of fluctuations in recruitment. Similar gaps existed on the understanding of ecological factors influencing schooling, horizontal and vertical displacement, food preferences and predation, and also on growth and mortality rates - two important parameters in understanding population dynamics. It was also noted that knowledge on the parasitology and diseases of shrimps and prawns was extremely limited, although such diseases affected quality and culture methods.
Numerous problems confronting research workers were discussed. Two ad hoc working parties were established to consider the need for further taxonomic research on commercial shrimp and the necessity of taxonomic identification of larvae and early postlarvae of shrimps and prawns.
The need was stressed for further information on larval abundance to assist in predicting future stocks. Estuarine pollution through disposal of mineral and chemical agents, and oil prospecting were considered as possible deleterious factors in larval and postlarval development.
Although not directly related to the subject under discussion, the utilization of incidental catches of fish and other animals made by shrimp vessels was raised. The return of “trash” fish to the sea was considered as assisting the biological cycle of nutrition. A partial solution to the problem from the economic view point was given by the development and installation of small fish-meal plants aboard Mexican vessels. Such plants could produce 8 tons of fish meal on a 15-day fishing trip.
3.3 Physiology and behaviour
Through study of the physiology of shrimps and prawns and other crustacean forms it has been possible partially to explain certain phases of exhibited behaviour.
Studies on osmoregulation have assisted in the understanding of tolerance to broad fluctuations in salinity. Salinity per se was not considered as the principal factor influencing displacement or production but instead the combined effect of salinity and temperature are thought to be important. Temperature has been considered as an important independent factor affecting production, through its influence on early and postlarval survival and by accelerating or decelerating the metabolic processes related to food intake and growth. Although analyses of observations made in temperate and sub-Arctic areas indicated an apparent relationship between increased catches and warmer ambient temperatures, in tropical and sub-tropical areas temperature appeared to be of less importance than salinity.
Where estuarine conditions are influenced by the outflow of large rivers (e. g. Mississippi), significant correlations between catches of Penaeus setiferus and rainfall have been found. Such correlations were not evident for other shrimp species nor in the lagoonal systems of southern Brasil, and further assessment of other possible factors being involved was required. The possibility was suggested of increased production after heavy precipitation being attributable to an increased food supply, resulting from run-off of land-based nutrient salts.
An understanding of the behaviour of inshore postlarval displacement during flood tide and offshore displacement of juveniles at ebb tide resulted from experimental work on Penaeus duorarum. A positive rheotaxis was exhibited at constant salinity but direction was reversed when salinity decreased.
In view of the small reserves stored in the bodies of shrimps and prawns, the importance of food supply to their reproduction, growth and migration was stressed. Lack of food could adversely influence oviposition, and availability of food could induce the emergence of one shrimp species (P. duorarum). Starved shrimps consume less oxygen than fed shrimps, a useful application in shrimp storage during transport.
In spite of studies which have provided an insight into the intricate and complex behaviour mechanism, many physiological aspects remain unsolved. Any knowledge elucidating the influence of environmental factors on physiological processes would improve capture techniques and culture practices. More information is required on cannibalism, feeding efficiency and food preference.
3.4 Statistics of catch and effort
The appreciation that statistics are essential for resource assessment, government planning and business decisions stimulated an interesting discussion on the problems encountered in the collection of accurate statistical data and on the nature of data required to meet these multi-purpose uses. Although useful information could be obtained from the existing presentation of statistics, as provided by governmental and inter-governmental agencies and by FAO, further improvements were desirable and necessary. The need for better coverage, inclusion of more detailed data, and standardization of methods was stressed. An important point, also raised in another technical session, was the lack of definition in official landings of whether data refer to headless or heads-on shrimps and prawns.
Considering the importance and serviceability of statistical data to biologists, economists and industrialists engaged in this sphere of activity, it was suggested that an ad hoc working party be formed to consider the pertinent problems discussed. There was general agreement that FAO should assume a leading role in promoting the accurate compilation of statistical data.
3.5 Stock assessment
As the world shrimp and prawn fisheries expand, so does the requisite for further knowledge on stock assessment. An expanding fishing industry requires in particular that scientists predict size and composition of stocks subjected to exploitation, and determine the maximum sustainable yield.
Although some progress had been made in the studies related to shrimp and prawn population dynamics, further research was required in the development of new methods and models designed to provide an estimation of stock size and density. Because the life span of the majority of exploitable shrimp and prawn species is short, methods applied to the dynamics of teleost fish populations may require adaptation. When the life span is relatively short, the effect of fluctuating environmental conditions on recruitment, growth and natural mortality - important parameters in the discipline of population dynamics - is more pronounced, thus making predictions on relative abundance on fishing grounds difficult. When life span is longer, as in Pandalids, prediction estimates are made easier through appraisal of the possible effect on recruitment by the prevailing environmental conditions during and following hatching.
The documents presented at the Conference revealed the variability of approaches to stock assessment. These included appraisal of environmental and ecological factors influencing recruitment, growth, displacement and natural mortality; calculations of mortality rates by use of predators; studies on growth rates from shift in modal sizes; quantitative surveys of larvae, postlarvae and juveniles in order to estimate pre-recruitment survival or to forecast relative abundance on the fishing grounds. Though each approach was considered functional, the desirability of employing more than one approach was stressed. All approaches required further understanding of the environmental and ecological factors involved and accurate data of catch composition and catch/fishing effort.
3.6 Culture of shrimps and prawns
The recent increased interest in aquiculture by academic, industrial and private sectors led to considerable discussion following the review of the status of pond and artificial culture of shrimps and prawns.
3.6.1 Pond culture
Although pond culture has been pursued over a long period of time, particularly in Southeast Asia, studies based on scientific discipline and aimed at assessing possible factors influencing production are relatively recent. These studies were also considered to be mainly biologically oriented and it was recognized that more emphasis is required on the physical-chemical conditions in ponds. Any knowledge obtained would assist in improving existing empirical methods. The necessity was stressed of further work on tropho-dynamics and on mortality, particularly caused by cannibalism. Although interest in capital investment in pond culture was considerable, the necessity was pointed out of detailed information on the yields and economics, as compared with actual fishing operations in the same region. It was felt that an adequate understanding of the prerequisites in pond culture techniques would undoubtedly assist in the introduction and development of such practices in other suitable areas of the world, for example in Central America and Central West Africa.
The importance of safeguarding estuaries and inland waters from pollution, a major threat to the survival of existing shellfish fisheries in industrial countries, was not overlooked by the Conference. It was recommended that this important problem be brought to the attention of the forthcoming FAO Conference on Marine Pollution and its Effects on Fishery Resources and Fishing.
3.6.2 Artificial culture
At present shrimp and prawn farming on a commercial scale has been achieved only in Japan, Malaysia and Korea. Although considerable progress has been made in the United Kingdom in rearing Palaemon serratus, problems related to pond preference, cannibalism and disease have not been solved. Similar impasses with rearing experiments on commercially important species have been reported from North American and European research institutions and private enterprises. Possible factors contributing to failures of artificial culture were considered and suggestions were made for overcoming difficulties encountered, based on individual observations and experiments.
It was reported that spawning could be activated by increasing pH. Abundant food required by larvae kept in large open tanks could be provided more easily by filtering coastal water than by culturing plant food separately. Postlarval cannibalism can be reduced if an ample supply of Artemia nauplii is added to the mysis stage. Japanese experiments indicated higher juvenile survival if food consisted of mixed components rather than solely of fish, because shrimps are reportedly unable to digest vertebrate food unless the temperature is high. Other experiments in Japan showed shrimp preference for animal food (clams) free from haemoglobin.
Since past and present attempts have been mainly oriented towards rearing species with numerous and prolonged stages of larval development, the difficulties in providing optimum food and environmental conditions at each stage have been increased. Consideration was therefore given to the rearing of species with direct or abbreviated development. Reference was made to species exhibiting such biological aspects.
The possibility was suggested of experimenting with encapsulated foods specifically flavoured to diminish cannibalism, or of inducing sex change at the appropriate stage through the incorporation of chemicals or hormones. In view of the limited knowledge on food preference and food efficiency - apparently of paramount importance to larval survival and growth - it was recommended that more research be undertaken on this topic.
3.7 Standardization of research methods
Since this theme had not been considered by the Consultative Group at the outset as one of the main objectives of the Conference, so that it did not appear as a principal agenda item, the number of technical documents directly related to methodology on shrimp and prawn research methods was relatively small. Nevertheless, many authors referred to methods pursued, occasionally with suggestions for their improvement, in accounts of the collection of biological and oceanographical data during exploratory surveys, of larval and postlarval sampling, size and weight measurements, maturity and fecundity determination, data analysis by computers and rearing techniques.
Although in some geographical areas inter-governmental agencies or regional bodies have given consideration to the importance of method standardization on shrimp and prawn research and have accordingly adopted some resolutions proposed (e. g. ICES' adoption of carapace length as a standard measurement in decapod crustaceans), no further progress has been achieved for the promotion and adoption of other methodological procedures on a wider scale or at an international level. The usefulness of method standardization for comparing and evaluating results obtained from different parts of the world was unquestionable. It was recognized, however, that some particular problems, i.e. sampling frequency, number of individuals per sample, size and weight measurements and data grouping, required further study before proposals for their regional or universal adoption were made.
3.8 Recommendations
The Conference considered the suggestions and proposals made by the technical sessions for filling the gaps of knowledge now existing in all aspects of the subject matter. These recommendations are listed under the reports of the respective technical sessions (Part 4). The Conference also approved the following recommendation:
Regional cooperation for the study of shrimp resources
Whereas international cooperation is required in order to make more effective the rational exploitation and conservation of marine resources in a given area; and
Considering that this cooperation in studies of marine species populations exploited by various countries makes necessary the exchange of knowledge obtained through fishing and biological research activities, in order to have required basic information; and
Being aware that international cooperation permits a better utilization of human resources, ships and other facilities indispensable for implementing programs of common interest;
The Conference recommends:
That closer attention be paid to cooperative studies of shrimp resources, and to use for this purpose, whenever possible, existing regional committees; and if there are no such committees, to utilize temporary or ad hoc arrangements with this same objective.
Considering that there are in the Caribbean area several national institutions and programs under the United Nations Development Program that have important projects devoted to the study of shrimp resources, it is recommended to FAO to explore the possibility of adoption of pertinent measures to facilitate such regional cooperation.
