4. REPORTS OF TECHNICAL SESSIONS AND AD HOC WORKING PARTIES

4.1 Resource appraisal

Two main topics were dealt with in this session: Resource Appraisal and Appraisal Methods.

Under the first, the Conference reviewed reports of new knowledge on the status, size, distribution and potential of world shrimp stocks; under the latter, reports and discussions on new techniques employed in exploratory fishing and in projecting yields. A summary of the information available from the submitted documents follows. Papers were not submitted on some areas, therefore many regions are not mentioned in the following summary:

North Atlantic The Greenland fishery based on Pandalus borealis is not yet fully exploited. Fluctuations in production are attributable to marked environmental thermal changes. Fishing pressure on undersized shrimps could be alleviated by encouraging fishing operations in deeper water where larger specimens predominate. According to one opinion future annual production was not expected to exceed 6,000 tons.

Central Atlantic Results of exploratory surveys made off the southeast coast of Cuba demonstrated that catches of Penaeus duorarum and P. schmitti were lower from unexploited areas than those intensively harvested. Although possibilities for appreciable expansion appeared to be negligible, construction of new specially designed vessels is being carried out.

The rapid development of the inshore bait fishery in Florida, based on small-sized P. duorarum, was discussed and it was conjectured that heavy demands on undersized shrimp could result in less shrimp reaching the traditional offshore fishing grounds.

South Atlantic The decline of the Penaeus schmitti and P. duorarum fishery in Venezuela during 1966 was believed to be related more to natural fluctuations in abundance than to overfishing. There is great concern regarding the probable effect on the resource of the proposed restrictions at the mouth of Lake Maracaibo to prevent further intrusion of seawater, and to correct sedimentation problems. Fears were expressed that such restrictions could inhibit movement of young shrimp into nursery areas.

The waters of northeastern Brazil may not be rich in shrimp resources, although good concentrations of Penaeus aztecus were detected off northern Brazil (Lat 1° to 3° N, Long 48° to 49° W), at depths between 36 and 73 m. The density of the mantis shrimp, Squilla lijdingi, was a useful indicator of the presence of commercial shrimps.

An appraisal of shrimp resources, mainly penaeids, in the eastern Atlantic from Spain to Senegal showed that yields have increased significantly during the past 25 years. Catches in the region have generally stabilized although overfishing is suspected on the Spanish and Balearic continental platform. Increased landings can be expected if more attention is paid to species occurring in deep water (200 to 1,000 m).

North Pacific Prospects for greater yields from Pandalus and Pandalopsis resources in British Columbia are considered good. Production is expected to increase from 750 to 1,200 tons over the next 10 years.

Central Pacific The potential of the red crab resource (Pleuroncodes planipes) in the eastern central Pacific was rated as very good and a possible production of 30,000 to 300,000 tons per year was postulated; but the usefulness of these figures and the manner of their projection was questioned. From this discussion arose the opinion that standards for appraising resource potential from available data should be developed, taking into consideration the acceptable level of production per unit effort, differential size of vessels generating abundance data, etc.

South Pacific A small fishery based on two Penaeus species in Shark Bay, Western Australia, was not expected to produce more than 92,000 tons by 1975.

Indo-Pacific Shrimp and prawn resources in this important region were dealt with in two papers, one describing resources in India and the other summarizing existing knowledge on resources distribution, and capture and culture methods practised in the Indo-Pacific Fisheries Council region. No estimation of future production was attempted, but according to one paper Indian resources are not overfished and rational increases in their exploitation are possible. It was suggested that the unutilized extensive estuarine and brackish areas in India be converted and adapted to prawn and fish culture.

4.1.1 Appraisal methods

Various opinions were expressed on the type of data required for the establishment of resource potential through exploratory surveys. The required information and phases to be followed, as presented in one paper, were considered by some as too sophisticated and unrealistic for many areas. The importance of the contrast of efficiency between survey and commercial fishing vessels was not overlooked. It was generally accepted that the latter outfish the former because skippers tend to concentrate their efforts in areas where the species being evaluated appears to be most abundant. The value was stressed of charts depicting types of bottom, location of nursery areas, etc. as aids to both fishermen and biologists in locating and appraising shrimp resources inhabiting specific regions.

Progress on the development of electric shrimp trawls and unresolved problems, particularly related to the differential conductivity of substrates, created useful discussion. Although promising results have been achieved, the gear was not considered sufficiently advanced for general use. Calcareous sediments appeared to retard the penetration of the electrical field and thus reduce its efficiency. At present electric trawls are not available commercially, though the cost of parts required for the system is approximately US$ 500.

The desirability of employing improved fishing techniques was unquestionable. Nevertheless, fears were expressed that the employment of more efficient gears without restraint might accelerate the demise of important shrimp fisheries. The Conference hoped that proper guidelines for managing shrimp resources and the fullest use of shrimp gear efficiency would develop in such a manner that conflicts, which otherwise could occur if gear efficiency outpaced the necessary fishery regulations, would be obviated.

In a review on shrimp detection and fishing techniques employed in principal producing areas, the author emphasized the importance of intensified research on shrimp behaviour in relation to their catchability. It was recognized that advances in shrimp detection by echo sounding had not achieved the same progress as that of fish; nevertheless, Japanese shrimp fisheries rely heavily on this method, particularly as applied to the mid-water trawling for Penaeus orientalis in the Yellow Sea and East China Sea. Shrimp detection by echo sounding required two types of apparatus - a high-frequency equipment to depict the fine detail of benthic and bathypelagic populations, and a medium-frequency instrument to unravel large organisms of interest - or a dual-frequency sounder of high power. Some scepticism was expressed whether echograms could actually depict commercial shrimp concentrations.

The possibility was examined of developing electronic techniques capable of differentiating between bioacoustic emissions of shrimp resources on the bottom. It was conceded that such hyper-sensitive equipment had not yet been developed.

4.1.2 Recommendation

The Conference recommended that FAO establish a working party to consider the development of methodology and standards for appraising crustacean resources, with particular reference to:

1. Determining an acceptable level of future production per unit of effort in the country

2. Intercalibrating different forms of fishing effort

3. Making an inventory of the world's shrimp resources by assessing the types of ecological habitat in which various groups of shrimps are most likely to occur, and then projecting abundance with a suitable factor

4.2 Life history

Taxonomy and distribution Information on the taxonomy and distribution of the most important exploited species of shrimps and prawns belonging to the Genera Crangon, Pandalus, Penaeus, Metapenaeus and Macrobrachium was provided by species synopses or experience papers, some documents dealing only with morphological and identification aspects of larval, postlarval and mature stages. The world-wide distribution of commercial shrimps and prawns was presented in INF/2.

Serious gaps were revealed in the state of knowledge regarding pandalid distribution, and differences of opinion were expressed on the taxonomic status of Penaeus duorarum found in West Africa, and of Metapenaeus affinis reported from India. The need for further research on (a) the taxonomy of shrimps and prawns of commercial value and (b) taxonomy and identification of larvae and early postlarvae, led to the establishment of two ad hoc working parties to deal with the specific problems raised.

Development, transport and survival of larvae The dissimilarity in the number of free larval stages in the life cycle of various species of shrimps and prawns is considerable, varying from none, as in Sclerocrangon boreas, to 15, as in some species of Penaeus. The number of stages for a given species can vary when reared under different experimental temperature conditions. Pandalus montagui showed eleven zoeal stages at 10°C and only five at 18°C. Because of the effect this may have on the duration of planktonic life and hence on the distribution of the species, the need for further studies was stressed.

In view of the importance of larval distribution in the assessment of spawning stocks, the Conference considered that more attention should be paid to larval surveys, and indicated the benefits which could result from closer international cooperation in these studies, particularly in the fields of gear and methodology.

Quantitative data are non-existent on larval survival for most shrimp species, and factors influencing survival rates, such as predation, food supply, sudden changes in hydrographic conditions and molting, have hardly been determined. Research is urgently required on food requirements at different larval stages, availability of the respective food items, and resistance of larval stages to environmental changes. The usefulness of such studies has been demonstrated in south Florida where it has been calculated that the annual production of first protozoea of Penaeus duorarum was approximately 87 × 10¹¹, with a daily survival rate of 84 percent, thus yielding about 85 × 10⁸ postlarvae available to enter the inshore nursery areas.

Larval mortality under laboratory conditions is variable and depends on the initial stocking rate and the amount of food available. In most experiments the estimated survival rate from nauplius I to first postlarvae has been approximately 50 percent. The desirability of standardization on larval collection techniques with regard to regions or groups of species is evident.

Ecology of juveniles The ecology of juveniles of shallow-water shrimps is better understood than that of the deep-sea shrimps. Postlarval stages of Crangon crangon are benthic, their distribution during the summer being similar to that of adults, while penaeid postlarvae are pelagic. One paper suggested that differences in salinity appear to have no effect on the abundance of penaeid postlarval forms, while temperatures exert a significant effect.

Information on the ecology of juveniles is urgently needed to understand the population dynamics of shrimps and prawns. There has been considerable progress in research in this field but gaps of knowledge in many areas need to be closed.

Life span As reported in various papers, Penaeus species appear to have the shortest life span (1 to 2 years) and Pandalus species the longest (3 to 7 years). The life span of C. crangon is 3 to 4 years.

Schooling While information is available on schooling behaviour of some shallow-water demersal shrimps and prawns, there is an acute lack of knowledge with respect to bathypelagic forms. In view of the potential commercial importance of these species, attention was drawn to the need of research on their schooling behaviour.

Schools may consist of individuals of all sizes and ages, as in Pandalus jordani, or of individuals of approximately the same length or age, as in Penaeus spp. Often only one school is encountered on the fishing ground, as observed in catches of P. jordani, and in such cases the catch of other animals is minimal. The distribution pattern of the school is forever changing in size and shape, possibly due to environmental influences. It has been shown that light itensity affects the schooling behaviour of C. crangon.

Migration of adults A considerable variety of migratory movements is exhibited by shrimps and prawns in response to maturity, spawning, feeding and environmental stimuli, particularly temperature, salinity and light intensity.

Pandalus montagui migrates onshore in spring and offshore in autumn, while C. crangon exhibits feeding and spawning migrations. At the beginning of March, C. crangon migrate onshore to feeding grounds encountered in brackish waters, and from May to July large concentrations of ovigerous females migrate offshore but return close to the coast after hatching. By October a displacement occurs to the deeper and more saline waters.

Young Penaeus setiferus move out of the estuaries where they have entered as postlarvae and have grown in the less saline waters. Movement out of the estuaries appears to be associated with stage of maturity and with temperature. In the sea, movements vary with size, locality and season. In some areas shrimp displacement is parallel to the coast and does not extend into deeper waters. In other areas the only definite pattern is offshore and onshore movements. The longest migration recorded for this species was 360 miles (667 km), the period of liberty being 95 days.

P. schmitti exhibits a similar pattern of inshore and offshore movement during its life cycle. Local movements are attributed to search for food, protection and to external stimuli, such as temperature, light intensity and water movements.

Most penaeid shrimps on the southwest coast of India move out into the deepest zone from February to March onwards, and return to the shallower fishing grounds by September. The movement into deeper waters has been related to upwelling which occurs during the monsoon. Metapenaeus dobsoni seems to exhibit movement in the opposite direction. The two types of movements exhibited by Solenocera indica are related to spawning and salinity influence. The daily vertical migrations of Pandalus borealis and of other pandalids are associated with light intensity. The off-the-bottom movement occurs only in darkness and duration is related to the length period of darkness.

In summary, despite the small number of marking experiments on shrimp, the results obtained are noteworthy. For fuller understanding of migrations and their population identification, an intensification of marking experiments is highly recommended. The use of magnetic tags for activity studies was suggested.

Parasites No parasites have been detected on C. crangon, but P. montagui is parasitized by the bopyrid isopod Hemiarthrus abdominalis, and an unidentified bopyrid isopod has been recorded from Metapenaeus dobsoni. Of the eight parasites recorded from P. setiferus only those belonging to Cnidosporidia can affect quality, while the others appear to be harmless to human beings. A microsporidian appears to be responsible for the “black spot” disease in P. schmitti.

Although indications exist of increased mortality rates through parasitical infection, particularly in culture practices, its importance has been underrated and it was suggested that further research be undertaken in this particular field.

Predators All shrimp and prawn species seem to be heavily preyed upon by a large number of aquatic animals, including their own species. For a better understanding of population dynamics, knowledge of predation rates appears to be indispensable. The annual loss to the C. crangon stocks along the German North Sea coast during a ten-year period due to predation has been calculated to be 145 billion shrimps, predation being 1.7 to 4.3 times higher than the fishery.

In view of the great significance in assessing the quantitative loss of shrimp stock through predation, considered as the most important factor of natural mortality, research in this field is strongly recommended.

Sex change No sex change has been reported in penaeid shrimps, but it is exhibited by many pandalids. The percent of protandric hermaphrodites in pandalids may vary within and among species. In P. montagui the percentage of primary females can be as high as 50, while in P. montagui tridens and P. platyceros no primary females have been observed. Evidence was offered that pandalid populations in Alaska comprise primary females.

Sex change is not related to age and varies from species to species. In P. montagui males become secondary females at an age between 1 and 1½ years, in P. jordani between 2 and 3 years, in P. platyceros at 2½ years, while in P. borealis the period varies from region to region: 2½ years in southern Norwegian waters, 4 to 5 in Greenland and Gulf of Alaska, and 5 in the far northern waters of Norway.

The recent suggestion of C. crangon exhibiting sex change is questionable since no transitional stages have been observed in secondary male sexual characters (first and second pair of pleopods) and German laboratory breeding experiments have not confirmed the change.

4.2.1 Recommendations

The Conference recommended that:

4.2.1.1 A few major institutions with adequate manpower and equipment be selected to act as depositories for specimens and reference collections to facilitate the examination of material on a world-wide basis. The cooperation of institutions and organizations interested in shrimp and prawn research should be sought:

4.2.1.2 A working party be established by FAO to prepare a selected bibliography on the identification of commercial shrimps; and to revise and, if necessary, expand INF/2, “List of species of shrimps and prawns of economic value”, paying special attention to the checking of distribution areas, scientific nomenclature and synonyms, vernacular names and the vertical distribution range of species listed. Dr. L. B. Holthuis was proposed as the Convenor.

4.2.1.3 Studies be made on the characteristics and performance of gear used at present for the quantitative collection of larvae and postlarvae, as well as the standardization of methods to permit comparison of results. This problem should be brought to the attention of the Scientific Committee for Oceanic Research (SCOR) for consideration by its working parties dealing with the standardization of plankton methods

4.2.1.4 The attention of research workers be drawn to the need for studying the following aspects of life history:

1. Ecology of juveniles

2. Schooling behaviour of shrimps, especially bentho-pelagic

3. Marking experiments

4. Parasitic infection and diseases

5. Quantitative assessment of loss of shrimp and prawn stocks through predation

4.2.1.5 Research be coordinated in promoting the collection and compilation of data, the standardization and intercalibration of methods and equipment, to facilitate the exchange of information and experts between laboratories

The Conference requested the Director-General of FAO to take steps to implement these recommendations and suggested that his Advisory Committee on Marine Resources Research (ACMRR) be asked to study ways and means of doing so.

4.2.2 Ad hoc Working Party on the Taxonomy and Identification of Larvae and Early Postlarvae of Shrimps and Prawns

Convenor: S. Dobkin ²

² See Appendix 1 for members of the Working Party

Recommendations

4.2.2.1 That the Working Party should undertake an updating of Guerney's Bibliography of the Larvae of Decapod Crustacea, as it concerns shrimps and prawns, such revision to include all members of Natantia and thus provide literature for comparison of commercially important species with others in the same area.

4.2.2.2 That the Working Party undertake the compilation of a list of specialists on taxonomy and identification of larvae and early postlarvae of shrimps and prawns who might be willing to examine material sent to them

4.2.2.3 That selected specialists be requested to prepare regional illustrated keys and atlases to the larvae and early postlarvae of shrimps and prawns; and that FAO be requested to investigate means of financing this work

4.2.2.4 That the Working Party continue in existence, under the guidance of the Marine Biology and Environment Branch of the FAO Fishery Resources and Exploitation Division, until accomplishment of its presently assigned task. In addition to its present membership, D. I. Williamson (United Kingdom) and D. F. Makarov (U.S.S.R.) should be asked to serve on the Working Party

4.2.2.5 That participants in the Conference to be asked to contact workers on Natantia larvae and early postlarvae in their own countries and ask them to send to the Convenor of the Working Party reprints and literature citations of their scientific contributions from 1962 onwards

4.2.3 Ad hoc Working Party on the List of Species of Shrimps and Prawns of Economic value

Convenor: L. B. Holthuis ³

³ See Appendix 1 for members of the Working Party

Recommendations

4.2.3.1 The following recommendations for the improvement of INF/2, “List of species of shrimps and prawns of economic value” by L. B. Holthuis and H. Rosa, were made:

1. The title should be changed to “List of species of shrimps and prawns of commercial value” so its scope is more precisely indicated

2. The paper should be provided with an introduction describing its scope and purpose, explaining the diversity in the usage of the terms “shrimps” and “prawns” without, however, attempting to standardize these terms

3. The tabular approach should be replaced by short paragraphs for each species; the method of indicating land and water areas by code replaced by a short description of the range of natural distribution; and the areas where the species are cultured indicated separately. The code could however be retained additionally for computer purposes.

4. Only those species which constitute substantive landings should be included in the list, but if it is considered advisable to include other species these should be printed in a distinctive type

5. Nomenclature should follow strictly the existing International Code of Zoological Nomenclature. Disputes on purely nomenclatural grounds should be submitted to the International Commission on Zoological Nomenclature, but for differences of opinion on taxonomic grounds the Working Party should accept the solution it thinks best, indicating the existence of other viewpoints

6. The following information should be given for each species:

   1. the more important synonyms

   2. vernacular names, with indication of the language and area where applied

   3. land and water areas inhabited (see iii)

   4. maximum size, both total length (including rostrum and telson) and carapace length (from post-orbital margin to mid-dorsal point of the posterior margin of the carapace)

   5. nature of sea bottom preferred

   6. depth range, both total known range and that of exploited area

   7. whether marine, brackish or freshwater

7. The bibliography should be considerably extended but at the same time restricted to taxonomic treatises, particularly those containing keys to genera and species

8. There should be two indexes:

   1. listing by taxonomic groups and geographical regions

   2. generic and specific names, including synonyms

The Working Party also recommended that:

4.2.3.2 Dr. L.B. Holthuis (Netherlands) should undertake the revision of INF/2, in collaboration with the other members of the Working Party and with FAO

4.2.3.3 The questionnaire, reproduced on page 19, be circulated by FAO to its regional fishery officers for further distribution in their region; if possible, questionnaires should be returned with a sample for identity verification

4.2.3.4 A list of shrimp and prawn taxonomy specialists who would be willing to undertake identifications should be prepared for the purpose of assisting field workers; it should indicate taxonomic groups and geographic areas from which the specialists are prepared to accept material

4.2.3.5 The preparation of two additional types of publications:

1. Lists along the lines of those proposed above, but complete with keys and illustrations to all species noted

2. Simple, illustrated loose-leaf pocket books for the use of market officers and other concerned in the collection of statistics. Only those species likely to be encountered by the officer concerned would be included in the book issued to him but major laboratories in his country would have a complete set of all issued pages

The possibility of their publication under the auspices of FAO should be examined.

QUESTIONNAIRE RELATING TO PRAWNS AND SHRIMPS OF COMMERCIAL IMPORTANCE

(one form to be used for each species)

1.	Scientific name of species:
2.	Source of identification: (handbook, key, etc.)
3.	Vernacular name(s): (indicate with each name its language or dialect; if the name is used in a restricted area, this area should be indicated)
4.	Whether cultured or natural populations:
5.	Geographic area(s) where the species is caught: (list separately for cultured and natural occurring populations)
6.	Depth range where caught:
7.	Maximum size: (indicate which length used: (i) carapace length [posterior margin of orbit to mid-posterior point of carapace] or (ii) total length [including rostrum and telson] or, preferably, both)
8.	Nature of bottom where species is found:
9.	Salinity of the water: (the indications fresh, brackish or marine are sufficient, more accurate indications are welcome)
10.	Commercial importance: (check one of the following):	major	medium	minor
11.	Usage: (indicate whether (a) for food, (b) for bait, or (c) otherwise (specify). For (a) indicate whether (i) as such, or (ii) for preparation of meal, cakes, paste, sauces, etc. (specify which); (iii) whether whole or peeled; (iv) whether fresh, cooked, dried, fried, etc.)
12.	Accurate locality, date of capture, collector and other details of sample sent with this list:

4.3 Physiology and behaviour

In brackish waters marine animals are compelled to counteract the dilution of their body fluids by active processes. The degree of osmoregulation which animals can maintain is an index of their salinity tolerance. Estuarine and coastal shrimp and prawns display differences in their osmotic behaviour, particularly in relation to their points of isotonicity, but in general they tend to be hypotonic in sea water and hypertonic under estuarine conditions. The metabolic processes and the activities of shrimp and prawn depend to a great extent on the temperature of their environment; low temperatures depress these functions while higher temperatures accelerate them. Although postlarval and juvenile penaeids are fairly tolerant to a wide range of salinity and temperature, adult penaeids are generally intolerant to low salinities and temperatures.

Osmoregulation At temperatures of 8.7° to 8.8°C the osmoregulatory activities of Penaeus aztecus and P. duorarum are impaired, and their blood becomes isotonic. The blood osmotic pressure of Palaemon serratus increases with a reduction in temperature under constant salinity. C. crangon moves to higher salinities at low temperatures. Many temperate marine species tend to be represented by brackish and freshwater counterparts in the tropics. Culture of prawns is easiest above 15°C.

The foregoing appears to indicate that at low temperatures metabolic processes become too slow for efficient osmoregulation, but at higher temperatures it is operative enough to allow animals enter less saline waters.

Temperature Temperature appears to influence growth. At temperatures between 15° and 25°C, P. setiferus showed a constant growth rate increase; between 25° and 32.5°C the rate remained constant, but between 32.5°C and 35°C a decrease occurred. P. aztecus exhibited a rapid increase in growth rate from 15° to 20°C, slower increases from 20° to 25°C, and no increase from 25° to 32.5°C. At 35°C the rate declined and no animals survived these temperatures for more than 11 days. The period of acclimatization is very important for survival.

It has been postulated that application of knowledge of optimum conditions for a particular shrimp, as determined in the laboratory, could assist in locating new resources. An apparent relationship between increased catches and warmer ambient temperatures has been detected from studies on P. setiferus, P. duorarum and P. aztecus catches made from North Carolina to Texas.

C. crangon catches per unit of effort along the German North Sea coast are higher during warm summers, but this is partly dependent upon stock size. Alternatively, it has been observed in the Gulf of Tehuantepec, Mexico, that no correlation between temperature and catches is evident except for an aberrant year in which catches were higher with cool temperatures. In addition, a good correlation has been observed between increased catches and temperature decrease produced by upwelling.

In tropical and subtropical areas catches are affected less by temperature than by salinity, except when high temperature is associated with low oxygen water content.

A comparison of Pandalus borealis populations occurring in Newfoundland waters between 4° to 6°C showed that the first contained larger sized individuals, a higher percentage of females, all spawning annually, while the latter comprised smaller individuals, few females and annual spawning was less than 65 percent. Evidently in cold waters males reach their growth limit before they become females. On the basis of this study, recommendations for future fishing activities in the area were made.

In Skagerrak waters, temperature decreases of 2°C have resulted in a 50 percent catch reduction. In Alaska colder than normal winters may send P. borealis populations into deeper waters. When temperatures are not near limiting extremes, shrimps and prawns appear to be free to move within their salinity limitations.

Salinity Under experimental conditions juvenile Penaeus duorarum exhibit a strong positive rheotaxis at constant salinity, but direction is reversed with a salinity decrease of 2‰/20 min. Postlarvae do not swim against strong currents, but a salinity reduction results in decreased activity and settling of the organisms on the bottom. A salinity increase reverses this motion. Such behaviour may explain the inshore displacement of postlarvae during flood tide and the offshore displacement of juveniles at ebb tide. Isolated changes, such as a salinity decrease from 60 to less than 10 ‰ in an Ecuadorian lagoon, have not resulted in emigration of juveniles from the affected area. It is suggested that responses among juvenile shrimp are usually the result of rate of change than absolute variations in salinity. The effect of other environmental influences on rheotactic responses requires further research.

Although significant correlations between catches of Penaeus setiferus and rainfall during the two previous years have been found in Texas, no such relationship has been observed for P. aztecus. It was felt that relationship between shrimp catch, temperature and river runoff should be assessed. Increases in catch, both in lagoonal systems and in certain shallow sea-water areas following storms, may be the result of increased food supply.

Results of studies near Galveston Bay indicated that sharp water temperature decreases appear to stimulate emigration of P. setiferus, and it is believed that temperature is the deciding influencing factor here.

Food supply Growth, reproduction and migrations are all dependent on food supply. The presence of abundant food stimulates continued growth of the reproductive gland of female C. crangon, permitting oviposition after each moult. With suboptimal food supply oviposition did not occur after each moult.

Shrimps do not store large amounts of reserves in their bodies. During an 11-day starvation period the fat content of the hepatopancreas of P. duorarum decreased from 52 to 8 percent. The glycogen content of the hepatopancreas also decreased, but at a much slower rate. The protein content, as expressed by total nitrogen, remained constant, but gland size declined from 38mg/g of body weight to 22mg/g after 7-day starvation. Of the reserve materials available to starved shrimps, the fat, protein and glycogen content is 85.8, 14.07 and 0.12 percent respectively. The rapid decline of fat content indicates that these stores will disappear in a relatively short time.

It was suggested that dense populations of shrimp are unlikely to be maintained by masses of large food particles, and that the epifauna and epiflora of mud substrata contribute to a large extent to the nutrition of these populations. Some species show food preferences, and feeding habits change with size. Shrimp held in ponds under conditions of constant salinity, temperature and food supply show greatly accelerated growth upon release. Some fluctuations in population size might be due also to changes in environmental factors affecting food supply.

Food supply affects the emergence of P. duorarum from the bottom. The emergence cycle in this species obeys a 24-hour feeding rhythm as well as a dark-light cycle. P. duorarum burrows into the substratum during periods of light and emerges at the onset of darkness, but food prompted its emergence during light periods.

Oxygen Penaeus indicus and P. semisulcatus consume less oxygen during starvation than when fed. Oxygen consumption was reduced by 32 and 57 percent respectively after one-day and two-day starvation periods. Starved shrimp also survived longer than fed shrimp in water containing the same amount of oxygen, a useful application in shrimp storage. P. schmitti survives longer out of sea water at low temperatures, and oxygen consumption in this species shows a direct relationship to body weight.

Moulting The moulting cycle alters the metabolic processes of shrimps and prawns and may obscure changes originated by other factors. The microscopic examination of endopodite setae of pleopods shows discernible changes in the internal structure which permits identification of early post-moult and inter-moult in P. duorarum.

General Although some aspects of physiology and behaviour of shrimps and prawns have been observed, there are large lacunae requiring investigation. Knowledge of shrimp responses to certain stimuli, and of their physiological processes, would be useful in elucidating their migrations, growth, mortality and reproduction, and for devising better methods of capture. A thorough understanding of the environmental factors affecting the physiological process would also permit cultural practices. This knowledge would also improve catch prediction.

Certain environmental factors such as rainfall and air temperature are at present beyond human control; nevertheless, man is often able to alter the environment to his purposes. Unfortunately in most cases these changes have been detrimental to the shrimp and prawn fisheries; estuaries have been polluted, access channels closed, substrata altered by dredging, and freshwater supplies blocked by drainage operations. These trends could be reversed, however, and efforts made to modify the environmental conditions in estuaries and coastal lagoons, thus improving shrimp and prawn survival and growth during some stages of their life cycle.

4.3.1 Recommendation

The Conference recommended that:

To rectify the present gaps in knowledge of physiology and behaviour, the attention of research workers should be drawn to the following subjects requiring particular study:

1. Tolerance limits for physical environmental factors at different ages among shrimps

2. Assessment of the combined effect of environmental factors on shrimp populations

3. Clarification of the meaning of the terms “postlarvae”, “juvenile”, “sub-adult”, etc.

4. Reasons for cannibalism among captive or cultured populations

5. Feeding efficiency and food preferences

4.4 Statistics of catch and effort

The purpose of this session was to discuss and define standardization, compilation and quality of shrimp and prawn data.

As shrimp and prawn fisheries expand, so does the requirement for statistics by governments, industrialists, economists and fishery biologists. The data required include total catch and value by species, sizes of shrimp caught, fishing effort, units of effort, landing ports and fishing areas. Its acquisition in some instances necessitates the utilization of log books on vessels and interviews with vessel captains.

The methods applied to data collection and the problems encountered were outlined in the papers discussed by the Conference. The principal problems considered were:

1. Accuracy and authenticity of data

2. Fishermen's reluctance to reveal catch data (for fear of taxation) and area of catch, especially when new grounds have been located

3. Difficulty in obtaining complete coverage, particularly when a coastline is extensive

4. Difficulty in accurate compilation by species, due to the usage of different common names for identical species in different areas

5. Conversion factors

6. Establishment of ex-vessel catch value

Methods for handling, processing, storing and rapid availability for analysis of voluminous data through electronic computers were described, and the following suggestions for improving present-day statistics were made:

1. Standardization of collection and presentation, to facilitate data comparison and to increase their use by research workers

2. Grouping of species into categories

3. Determination of shrimp and prawn catches by foreign-based vessels when fishing in offshore areas of other countries

4. Establishment of a list of common and scientific names to be applied in the presentation of statistics, first on a regional and later on a universal basis, to eliminate confusion in statistical classification

5. Differentiation in official statistics between headless or heads-on shrimps and prawns

6. Improvement of data collection on quantities discarded at sea

7. Inclusion of the value of catches, because of its importance in economic studies and for making business decisions

The discussion revealed that the majority of commercial and economic data are collected by census methods and that very little research has been carried out on collection by stratified sampling. The Conference agreed that more research is required to develop methods of collecting business and economic shrimp statistics by utilizing stratified sampling techniques to reduce the cost of collection and to improve the currency of the data.

4.4.1 It was considered that an ad hoc Working Party on Fishery Statistics (Crustacea), with Mr. G. G. Snow as Convenor ⁴, should be established to deal with the problems raised. The following recommendations were endorsed by the Conference:

4.4.1.1 That all countries be encouraged to make full use of FAO regional facilities and those of other international agencies to develop sound statistical programs related to Crustacea; and that the free exchange of information between countries concerning methods and results obtained in statistical programs related to Crustacea be encouraged.

4.4.1.2 That greater accuracy in landing data be achieved through the use of standardized conversion factors for the calculation of live-weight poundage, and that FAO be requested to compile and publish a list of such factors for use by all countries, and to develop a set of conversion factors for processed products in foreign trade

4.4.1.3 That biologists be included in all standing committees and working parties concerning fishery statistics, thus ensuring that programs are designed to furnish data for multi-purpose needs

4.4.1.4 That FAO establish guidelines for eliminating duplication in the reporting of landing data.

4.4.1.5 That the “List of species of shrimps and prawns of economic value” be used for establishing standardized species nomenclatures for FAO statistical publications

4.4.1.6 That FAO publish in regional bulletins landings by major gear types, and include catch per unit of effort when it can be established

4.4.1.7 That FAO encourage each country to issue statistics on the amounts of shrimp and prawns produced by culture, and that these data be reported separately in the FAO Yearbook of Fishery Statistics

⁴ See Appendix 1 for members of the Working Party

4.5 Stock assessment

The documents presented, having as their principal objective the assessment of stocks rather than a descriptive biology of species, permitted a review of the knowledge of stock assessment of shrimps and prawns, progress made to date, and existing gaps. Papers were also included when they attempted to determine growth or natural mortality parameters, since these are employed for stock assessment.

The assessment of stocks may be used to compare the present level of exploitation with the maximum sustainable yield. Alternately, assessment may be attempted with a view to predict production from fishable stocks.

Some of the general characteristics of shrimp and prawn populations pertinent to the studies of their population dynamics include a short life span, very high fecundity and high larval and juvenile mortality. Recruitment is high, the newly recruited group forming a large proportion (in some species the total) of annual fishable stock. But what may be the most important difference between the dynamics of most teleost fish populations is that in shrimp and prawn populations recruitment is more variable, apparently owing to variations in components of fecundity, growth and especially natural mortality.

Ecological aspects can be important in stock assessment, and the suggestion that the Conference should stress the need for more studies in this field was strongly supported.

Progress indicated

(a) Species Synopses The 11 papers available constitute only a small fraction of the total number of species referred to, but they indicate progress towards assessment of shrimp and prawn stocks.

Under population structure, they indicate that a good deal is known of sex ratio and size composition but rather less about age. In the longer living species, such as pandalids and Crangon crangon, age structure has been recorded for some populations.

Growth rates have been recorded with considerable precision for some of these longer living species. Growth data recorded for penaeids under cultivation are very necessary, but it was agreed in other sessions that, when studying the dynamics of wild populations, such data may not be applicable or should be used with caution. Growth rates derived from the shift in modal size groups, using samples from wild populations, require a clear understanding of migration and dispersal to ensure that the same group is being followed.

Measurements of fecundity have been made on some species, but there is little indication of the influence of environment upon fecundity.

The only information on recruitment which has been noted in the Species Synopses papers was for Pandalus jordani and C. crangon.

Data on mortality rates are very sparse. There are some estimates for P. jordani showing variations between year classes as well as annual variations. Estimates of total mortality coefficient have been recorded only for Metapenaeus dobsoni and Penaeus setiferus.

There are a few records of relative abundance in terms of catch per unit effort, but only in the case of P. jordani have estimates of absolute density been attempted on the basis of catches and area swept by trawling gear.

No information whatsoever on population dynamics is provided by these 11 papers, suggesting that although a certain amount of descriptive data has been gathered, it is still not possible to understand for any shrimp and prawn population how these variables interact under the various environmental and fishing conditions. It is recognized that stock assessment may be achieved without conclusive results on every variable discussed above.

Although these Species Synopses do not cover the state of our knowledge on stock assessment of shrimps and prawns very effectively, approaches have been made in previous publications towards estimating population size, fishing mortality, immigration, and a combined figure for emigration and natural mortality for Penaeus duorarum in south Florida.

Recruitment appears to be the key to shrimp and prawn stock assessments, since recruits form a large proportion, if not the whole, of stock present at the beginning of a fishing season, so that the success of fishing varies as recruitment fluctuates. Three approaches towards estimating recruitment have been applied in shrimp and prawn research. The first employs quantitative or semiquantitative sampling of postlarvae or juveniles to predict level of recruitment. The second uses the marking and recapture technique, and the third is based on commercial catch and effort statistics. Each requires some knowledge of ecological aspects such as natural mortality, growth, and migration, in order to be applied effectively. Occasionally methods have been combined, as for example marking and catch per unit effort in a population of P. duorarum.

(b) Experience Papers Since Pandalus borealis is one of the longer lived species, peaks in size composition within samples of the population, together with a knowledge of growth rate, enable relative strengths of year classes to be compared for several year classes. These fluctuations in abundance of year classes have been linked with the severity of the first winter immediately following hatching. Although these are relative rather than absolute values, they are interesting because annual fluctuations in recruitment are being linked with fluctuations in environmental conditions during the critical early phase. This is a useful step towards the understanding of dynamics of the Pribil of population of P. borealis.

Since P. jordani are not vulnerable to nets until their second year of life, a predator, the Pacific hake, is regarded as a better sampler than fishing nets. From length frequencies of shrimp samples taken by hake, and information on growth rates and age of sex transition, age composition was determined. The relative abundance of each year class was then expressed in terms of catch per unit effort by a fishing net. However, the drawback in this method is that it must be assumed the predator-prey relationship remains the same from one year to the other. Mortality rates were calculated from successive estimates of catch of each year class per predator-effort. Carefully planned sea surveys carried out while the independent samples were being collected from fish stomachs enabled some of the results to be cross-checked. Population estimates from the sea surveys were obtained by scaling up the mean catch per trawl by the ratio of survey area to area swept by one unit of effort.

By sampling the population of Artemesia longinaris in Argentina at frequent intervals and from the shift in modal sizes (aided by moulting studies in aquaria), it was possible to obtain von Bertalanffy growth curves for the population present during one year. If these studies could be continued some measure could be made of the variability in growth rate from year to year, and correlations sought with environment factors.

One paper dealt with size at maturity, spawning frequency, and fecundity of several penaeid species of southwest India. If this work is to be taken as the first step towards assessments of stocks, two lines might be followed. If first-stage larvae of a species were readily accessible, a census of these might be applied to the fecundity which has just been measured, to obtain an estimate of the size of breeding stock. Alternatively, quantitative surveys of larvae or postlarvae might be implemented in order to measure pre-recruit survival.

The latter approach, quantitative sampling of larvae and postlarvae to determine density, and hence total crop passing through various stages of development, was demonstrated in another paper. By this method estimates of P. duorarum through to the Everglades nursery area were obtained. This approach represents an important step forward in understanding the dynamics of shrimp populations.

A good positive correlation between relative abundance of juvenile P. duorarum leaving the nursery areas and the landings of the smallest size groups of the commercial catch a short time later was demonstrated in another contribution. This approach, applying quantitative methods, has already reached the stage where a system can be formulated for forecasting relative abundance of pink shrimp on the fishing grounds. Perhaps in the future it will be possible to measure survival rates and thus predict actual yields for each crop of juveniles.

An attempt was made to link the relative abundance of postlarvae entering a nursery area with the juveniles departing from the area, and linking both peaks in abundance with the commercial catch off shore. The results obtained give a fair understanding of the annual fluctuations in adult stock over the past seven years.

Models for stock assessment of shrimp and prawns are very limited. However, an impressive model for the Shark Bay prawn fishery, designed to obtain specific information on the dynamics of the two populations involved, was presented. The pre-requisite of precise and complete data on catch, effort, and catch composition is underlined by this model.

Discussions in this session made it evident that for many of the measurements required in the dynamic equation some limited information is available for most of the shrimp and prawn species referred to. Relatively complete data on the subject of population dynamics are available only for a few species.

4.5.1 Recommendations

The Conference recommended that:

4.5.1.1 For effective stock assessment of shrimps and prawns, considerable descriptive work on their biology is required. It is urged that these studies be designed with the specific objective of assessing stock size and its variability

4.5.1.2 Rather than make standing crop estimates, stock assessment should cover several years so that:

1. variations in recruitment into the fishable stock can be related to fluctuations in environmental conditions

2. The level of fishing can be related to the maximum sustainable yield from the fishery

4.5.1.3 Because of the many pitfalls involved in estimating population dynamics in this group, including the wide variability, investigations should employ more than a single approach so that results may be cross-checked

4.5.1.4 Investigators should continue to develop new methods and techniques to estimate stock density and size. Possible lines include the use of sonar and visual scanning aids

4.5.1.5 Estimates of stock size should be translated into terminology which is directly understandable by and applicable to the fishing industry. Frequently stock size alone is insufficient to help the fishing industry and the economics of the fishery must be considered. In the final event, the biologist, economist and industrialist must work together to capitalize the results from the biological data which has been obtained

4.6 Culture of shrimps and prawns

Since the papers submitted covered two kinds of culture techniques, it was considered appropriate that this topic be dealt with in two separate sessions: pond culture and artificial culture.

4.6.1 Pond culture

Pond culture has been practised for a long period in the Indo-Pacific area, and the papers presented reviewed methods in India, Malaysia and the Philippines. Basically, pond culture in this region depends on the habit of penaeid shrimps to arrive in shallow coastal areas at postlarval and juvenile stages, when they enter artificial ponds through open sluices during flood tide. During their stay in these ponds they grow by feeding on natural food found there as well as that carried in by the tide. Subsequently these shrimps are harvested by means of filter nets placed on the sluices during the receding tide, or when the ponds are completely drained.

In India rice fields of 1 to 10 ha are used during the six-month period when rice cultivation is not pursued, while in Malaysia the carefully chosen ponds in the mangrove swamp areas are of 12 to 16 ha. Culture methods in the latter are similar to those employed in India.

One paper reported results from experiments designed to study the effects of rearing shrimps in the Indian paddy fields for different periods. It was concluded that harvesting at monthly intervals gave greater yield than harvesting at the end of a long culture period. Experiments on size composition of shrimps entering and leaving the ponds showed that these remained for approximately 5 to 6 weeks before being caught in the outgoing water.

Discussions revealed that three major kinds of pond culture are pursued in India: (a) rotation with rice, (b) together with rice, and (c) in compartments along the river banks on low areas of poor agricultural value. Pond culture in Pakistan, Singapore, Viet-Nam and Cambodia is basically similar to India but none exists in Burma and Hong Kong. In Thailand, both converted rice fields and converted salt fields are utilized, while in Indonesia shrimp harvesting is incidental to the farming of brackish-water fish. In Taiwan, culture by both methods, as practised in India and the Philippines, yields a harvest approximately three times that in the Philippines. It is not clear whether generally it is more economic to culture shrimps alone or with fish, but in Taiwan the latter method is very successful.

In the Philippines methods are more advanced and culture is based on a single species, Penaeus monodon, known as sugpo. In the past, sugpo culture was carried out in association with the fish Chanos chanos, but as a result of higher prices paid for sugpo it is being replaced by pure sugpo culture. Selected areas, portioned into nursery and rearing ponds, are carefully prepared to induce growth of bottom flora and fauna (lab-lab), serving as food for the young fry. Sugpo fry, caught by various means in the shallow areas, are placed in nursery ponds and transferred after a period of 1 to 1½ months to the rearing ponds at about 20,000/ha, where supplementary food is given. Harvesting is carried out by nets and traps. It was mentioned that the pond area of 130,000 to 150,000 ha is expected to increase.

Discussions on comparative economics showed that pond culture is expensive but returns can be high, especially where live shrimps are in demand. On the other hand, harvesting by fishing vessels can also be expensive and the economics of the two systems should be examined. If the causes of mortality in pond culture could be overcome, the running costs would be reduced. Great interest is shown in investment in this field; however, the opinion was expressed that the risk of destruction by typhoons discourages extensive investment.

Production figures given for the Philippines appeared to be too low. It was mentioned that females are known to grow faster than males and those harvested from ponds are 2 to 3 times as large as males. Food conversion by female C. crangon is also more efficient than male and it was suggested that, on the basis of work on Crangon done in the Federal Republic of Germany, similar research be undertaken on penaeids with the possibility of (a) early separation and rejection of males from culture, and (b) influencing sex by producing ecological conditions favourable to females.

Comments made on the paper related to pond culture in Singapore indicated that the industry is dying due to shortage of land and for political reasons. Although the pond culture comprises a balanced ecosystem including 13 penaeids and 7 carideans, only 6 penaeids are commercially important; the remaining trash prawns, although edible, are disliked locally. Year-round availability is based on one breeding season of Penaeus, alternating between two of Metapenaeus per year. Fertilization has been found of doubtful value and is said to increase silting.

Reference was made to the extensive occurrence and future developments of shrimp culture along the Pacific coast of Mexico, in ponds distant from the sea but connected by long channels, and where yields are still low. It was suggested that suitable areas for pond shrimp culture exist in Nicaragua. In Peru efforts are being made to restock coastal rivers and ponds with fry of the freshwater shrimp, Cryphiops caementarius. In 1965 one breeder was supplied with 10 million fry. Fry up to 60,000 per 15 minutes can be harvested from the lower parts of rivers.

The conclusion that adequate additional food is necessary to reduce cannibalism was supported, with emphasis on the right kind of food. Suggestions were made that overdensity of population aggravates cannibalism. The provision of hiding places for molting shrimps may, however, reduce it.

It was considered that more research is required on (a) diseases of shrimps in ponds, (b) chemical and physical conditions and trophic levels in ponds, and (c) yields and economics of pond culture compared with normal harvesting. Closer liaison is needed between scientists and industrialists, with greater conference participation and more experimental work undertaken by the industry.

Pollution problems require urgent attention. In the United States, legislation to reduce pollution and control physical alterations to estuaries has already been discussed by Congress during 1966 and 1967.

4.6.2 Artificial culture

The subject matter of this session was divided into (a) procedures of rearing and (b) the choice of suitable species for rearing.

4.6.2.1 Procedures for rearing The successful rearing of shrimps and prawns on a commercial scale has as yet been achieved only with Penaeus japonicus in Japan and Macrobrachium rosenbergii in Malaysia, though considerable progress is reported for Palaemon serratus in the United Kingdom.

Comparison of the features of spawning and larval stages

The culture of M. rosenbergii has now reached a stage where it permits juveniles to be grown by private producers on a large scale, all the major problems having been overcome. Rearing of P. serratus is still on a laboratory scale but substantial numbers have been reared through all stages, and knowledge of optimum conditions of temperature, salinity, light, food and density have been established for the larvae. However, more studies are required on diseases and an alternative food to Artemia and the selection of fast-growing and disease-resistant strains should be investigated.

4.6.2.2 Choice of suitable species for culture The consideration of appropriate species for rearing has led to the view that rearing would be simplified if caridean prawns with abbreviated or no larval stage were used, such species being found particularly among fresh and brackish waters or in cold or deep seas. Experiments using related species with long or short larval stages supported this perspective. During discussion it became clear that larvae can live for long periods undergoing numerous moults but without growth or metamorphosis, and that incorrect feeding is likely to be the cause.

Attempts to assess the potential value of freshwater prawns in Malaysia as food organisms led to research on suitable species for culture. The freshwater species Cryphiops lanchesteri has been recommended for culture in view of its being able to proliferate in stagnant water of low mineral content, to tolerate reduced oxygen and temperature up to 35°C, and because it is believed to be herbivorous and therefore less likely to exhibit cannibalism.

Other desirable characteristics required from shrimps and prawns for culture are:

1. High-protein conversion factor and fast growth

2. Herbivorous habits so food cost can be reduced

3. Tolerance to change in environmental conditions

4. Non-aggressive habits, thus reducing cannibalism

In searching for suitable species, it was suggested that:

1. The less common species be studied

2. Several favourable species are needed to meet the required conditions in different parts of the world

3. Coastal and freshwater species are most likely to be more tolerant to artificial conditions

The highlight of this session was the presentation of papers related to advances made in Japan and Malaysia on artificial culture techniques and the evoked discussion. In view of the importance and commanding interest of this subject, the important points disclosed by the author on methods practised in Japan are given below:

The system whereby Penaeus japonicus are reared artificially to juvenile stage has been adopted also for P. semisulcatus and Metapenaeus monoceros. Since 1964 the system has changed from indoor to outdoor concrete tanks of a capacity 100 times greater. Instead of rearing pure cultures of plant food separately, diatoms are retained by filtering coastal water through vinylon cloth and intense proliferation encouraged by full sunlight, strong aeration, and the addition of nutrient salts. The culture obtained affords protection to larvae from the sun and provides abundant healthful food. Eggs are obtained from a batch of female shrimps ready to spawn. Twenty females are placed in small tanks; about half of them spawn overnight and the eggs hatch in a few hours but hatching is not total. Development to juveniles weighing 0.02 g takes 25 days. Once this stage is reached, they are placed in polythene bags containing water and sufficient air for 20 hours and distributed to commercial shrimp culturists.

Survival from nauplii to zoea is 90 percent, from zoea to mysis 70 percent and from mysis to postlarval 90 percent, the zoeal stage requiring 4 to 5 days and mysis 3 to 4 days. Artemia nauplii are added to the mysis stage and need to be abundant to reduce cannibalism among postlarvae. Four days after the postlarval stage has been reached, feeding with clams and partial changing of the water commences and postlarvae settle to the bottom. At the zoeal stage the water is fertilized every 24 hours with 50 kg of potassium nitrate and 5 kg of potassium phosphate per 100 t of water.

No attempt is being made to control temperature or salinity, and survival is not affected up to 30°C and down to 20‰. Production has increased from 1 million juveniles per tank in 1964 to 1.6 million in 1966, and at present exceeds the requirements of culturists. The surplus has been utilized to improve shrimp stocks in selected bays and some improvement to yields has been observed. During 1966, 13 million juveniles were liberated between Hokkaido and south Japan. Although no survival rates are available, it appears these are higher in shallow waters with gentle slopes and algal abundance than in deep bays. Production costs have decreased considerably. Since 1965 the cost of 20 to 30 juveniles is 1 U.S. cent, all costs included, and production of 50 million can be achieved by 5 men. Tanks can be utilized throughout the 6 summer months by collecting breeding females from different parts of Japan. Production is not practicable during the cold winter months. Growth to the desired market sizes of 20 g takes about 5 months, and two culturists with 11 stations supplied 200 tons to restaurants.

During the ensuing discussion it emerged that Mytilus is also used to feed juveniles and that spawning can be activated by increasing pH. Females grow faster than males, but the difference is not apparent until the animals weigh 15 to 20 g, shortly before market size. There is no reported flavour change related to different food, although one author found the flavour of C. crangon fed on crustacea to be superior to those fed on worms. There were no disease problems, except for a darkening of gills. Some experiments suggest that shrimps prefer animal food free from haemoglobin.

Artificial culture of Penaeus orientalis on a commercial scale, based on Japanese methods, has been achieved also in Korea.

One paper dealt with the culture of M. rosenbergii in Malaysia. The most important remaining problems are of food and feeding and controlling mortality due to diseases and cannibalism. Governmental hatcheries supply juveniles free of charge to encourage industrial developments, and at present costs are not available. When juvenile prawns are reared in ponds, usually with non-carnivorous fish, natural food is supplemented by trash fish. Prawn production of 100 to 200 kg/ha per annum by culturists is in addition to the primary product of fish.

During the general discussion it was suggested that in addition to attempting to initiate natural conditions and natural food, more efforts should be concentrated on methodology and novel practices and less on economics at this stage. Investigations should be oriented towards foods more readily banked, like synthetic, freeze-dried, and even encapsulated foods of chemically defined character, in which might be incorporated flavours to reduce cannibalism, chemicals to produce sex change, etc. It was pointed out that micro-encapsulation has already been used for feeding molluscs, and perhaps dried and solubilized waste animal protein may have a role. Food like Artemia has the advantage of calibrating feeding rates and efficiency, though Artemia has not always been found to be of high food value.

4.6.3 Recommendations

The Conference recommended that:

4.6.3.1 Statistics of yield from pond and artificial culture be recorded separately from those of normal harvesting

4.6.3.2 A survey be undertaken of the economics and yields of pond culture as compared with normal harvesting

4.6.3.3 Closer liaison be established between scientists and industry in the planning and application of research on pond and artificial culture

4.6.3.4 At the FAO Conference on Marine Pollution and its Effects on Fishery Resources and Fishing, to be held in 1969, special attention be given to:

1. Pollution in shallow waters and its effects on crustacean and molluscan resources

2. The future development of artificial cultures

4.6.3.5 A FAO World Conference be organized on the subjects of artificial rearing of marine organisms of commercial importance and habitat improvement

4.6.3.6 More research be undertaken on:

1. Preferences between different shrimp and prawn species for different types of food and their relationship to survival and growth

2. The role of synthetic and other food materials in artificial culture

3. The possible use of hormones and other chemical regulatory substance and their effects on behaviour and growth

4.7 Standardization of research methods

Although descriptions of methods employed have been referred to in various documents, only eight were directed to methodology. Methods pertaining to shrimp and prawn culture and to statistics have not been considered here.

In view of the variety of methods employed and the usefulness of comparing and evaluating results, the objectives of this session were to explore problems related to shrimp and prawn research methods, and to consider possibilities of their standardization. The various methods applied by authors on a particular research subject, and comments made during discussion on their improvement, are summarized below. The necessity of preparing a manual on methodological procedure was recognized.

Exploratory fishing One paper described methods of collecting biological data during operations off north-northeast Brazil, and another around Cuba, the latter referring in addition to meteorological and oceanographical observations made. Sampling of catches to determine species, sex ratio, size composition of shrimps and prawns, and species composition of associated fauna was considered essential. Sample size could be determined statistically prior to surveying. Exploratory fishing can be assisted by the application of life history and ecological knowledge of shrimp and prawn species occurring in the region. Although location of fishing grounds and fishing methods had not been considered, it was suggested that sonic methods and echogram interpretation be included in a manual.

Measurements In measuring size, most commonly expressed as length, three dimensions are used: total, carapace, and body or tail length. As a matter of interest, in the papers reviewed, 23 refer to total length, 7 to carapace, and 16 to both dimensions; in addition, one refers to body length and one to body depth. If carapace length is applied, the relationship of this measurement to total length should be expressed as a conversion factor. A single factor may be inadequate for some species. It was agreed that standardization of length dimensions is not practical among species, but is within a species. Whatever dimensions are applied, they should be well defined.

Only one paper described a method of weighing. In view of the importance of length-weight relationships some standardization on weighing was considered desirable.

Marking Although marking methods have been referred to in the species synopses on Crangon crangon and Penaeus setiferus, no review paper on this topic had been presented. A summary of marking techniques with biological stains was provided by a participant in the Conference. Shrimps as small as 40 mm in total length may be marked, with the stain being visible up to 11 months. Between 300 and 400 may be marked per hour, and cooking does not reduce color intensity substantially.

Larval and postlarval sampling Two papers dealt directly with this subject. For larval stages, high-speed plankton nets appear to be adequate, except for shallow waters, where a standard 1 m net is more successful. For postlarvae sampling, the latter also appears to be preferable. Errors in depth and flow determinations may be avoided by employing accurate indicators which have recently become available.

Maturity and fecundity Methods to determine maturity in Penaeus californiensis, Solenocera indica and five other penaeid species of the southwest coast of India are dealt with in three papers. In two, the definition of five maturity stages appear to be acceptable to research workers on penaeid shrimps. Fecundity has been determined either by subsampling the mature ovary, or by direct count.

Other methods Description of methods related to examination of penaeid stomachs, determination of stages of the moulting cycle in Penaeus duorarum, determination of P. vannamei postlarval entry into estuarine waters, rearing of penaeid larvae, and of a computer program, were dealt with in five experience papers. A description of a method for clearing appendices of postlarval shrimp was also handed to the Convenor at this session.

4.7.1 Recommendations

The Conference recommended that:

4.7.1.1 FAO should undertake the preparation of a manual of accepted methods on shrimp and prawn research. Before the manual is drafted, preliminary circulars should be issued to specialists according to the following priorities:

1. Measurements

2. Sampling during exploratory fishing

3. Sampling of larval and postlarval shrimps and prawns

4. Determination of maturity and fecundity

so their comments and suggestions can be sought

4.7.1.2 A training centre on research methods be organized by FAO, bearing in mind regional needs

4.7.1.3 The use of circulars by national and international agencies be promoted and the texts revised continually in the light of experience gained by their use

4.7.1.4 The FAO series of manuals on fishery methods be brought up to date and given wide distribution

4.8 Ad Hoc Working Party on FAO Indicative World Plan (IWP) Survey of Crustacean Resources

The origin and scope of FAO's Indicative World Plan for Agricultural Development, (a section of which implied a world-wide survey of crustacean resources) was outlined on the basis of a draft document. Discussions followed on the actual form of the document as distinct from its contents. It was generally agreed that the final document would be improved if it contained (a) an introduction to the ecological nature of crustacean resources, (b) an agreed taxonomic list of economically important species such as is being studied (see 4.2.3), and (c) a bibliography considerably more extensive than that provided in the draft, which might best be subdivided by geographical regions and which should treat well-explored and little-explored regions of the world differently, ensuring that coverage of the latter included more basic references than recent reviews.

Views were expressed that distinctions must be made in the included data between economic and biological potential and it was emphasized that the data are required on three levels: (a) present knowledge of exploited stocks, (b) predictions of potential resources based on actual surveys and (c) hypotheses concerning probable resources, based on educated guesses rather than actual exploration.

It was suggested that a coding for species stocks, areas and the state of the stocks would be useful, and it was pointed out that this would be covered by tabulation of data from the text of the final document.

The Convenor led a discussion of the draft document, region by region, and specialists from each region were appointed to report on resources from their areas according to the requirements of the original request for information. These people agreed to contact other sources of information in their regions to obtain the data required to amend the draft document, and to send such information to the Convenor, who agreed to collate it and submit it to FAO, who will produce the amended draft. It was hoped that FAO would be able to feed back to regional rapporteurs the original data on which the document was based.

⁵ See Appendix 1 for members of the Working Party

The regional rapporteurs were: