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Intensive culture of shrimp Penaeus vannamei in floating cages: zootechnical, economic and environmental aspects
Aquaculture 164 Ž1998. 151–166
Intensive culture of shrimp Penaeus Õannamei in floating cages: zootechnical, economic and environmental aspects P. Paquotte
a,)
, L. Chim a , J.-L.M. Martin b, E. Lemos c , M. Stern d , G. Tosta d
a
Institut Franc¸ais de Recherche pour l’Exploitation de la Mer (IFREMER), 155 rue˙ Jean-Jacques Rousseau, 92138, Issy les Moulineaux, France b Centre de Recherche Ecologie Marine et Aquaculture, IFREMER r CNRS, BP 5, 17137, L’Houmeau, France c Littoral Sul Maricultura, Almeda das Espatodias, 915, Edificio Odebrecht, Pituba, SalÕador, Bahia, Brazil d Bahia Pesca, SalÕador, AÕenida Adhemar de Barros 967, Ondina, SalÕador, Bahia, Brazil
Abstract In the framework of the France–Brazil cooperation in Oceanology, experiments have been carried out in the State of Bahia ŽBrazil. from 1992 on, in order to design a new technology for culture shrimps in floating cages in an estuarine zone. The zootechnical research has focused on the species Penaeus Õannamei which has been tested in different rearing conditions Ždensity in the cages. and seasons Žwet and dry.. The results may be compared with the most intensive and costly technologies which are practised in Asian countries. The average growth rate is about 0.8 g wky1 and the average final biomass is 800 g my2 . The achieved results are all the more important as they are obtained with a simple technology which does not require energy for pumping and mechanical water aeration. Investigations on the impact of this kind of technology, carried out on a pilot site with estuarine conditions after three years of farming activity, showed no measurable effect on the sediment Žin terms of organic matter. and in the water Žin terms of oxygen.. Economic analysis was recorded from the very beginning of the project, making it possible to design a computerised simulation tool in order to assess the feasibility of such an operation and to help in decision making for future research and development. Initial results indicate that ex-farm production costs for shrimps weighing 15 g would be around US$ 4.7 per kg. The major competitive advantages of such a technique are the high yield, the quality of the product, the
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Corresponding author. Tel.: q33-01-46-48-22-65; fax: q33-01-46-48-22-76; e-mail: [email protected].
0044-8486r98r$19.00 q 1998 Elsevier Science B.V. All rights reserved. PII S 0 0 4 4 - 8 4 8 6 Ž 9 8 . 0 0 1 8 3 - 5
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environmental friendliness and the positive social impact for a fishing community. q 1998 Elsevier Science B.V. All rights reserved. Keywords: Shrimp farming; Floating cages; Economic analysis; Environment
1. Introduction Because of the high demand for shrimps in Japan, the United States and Europe, shrimp aquaculture production has been soaring during the last 10 yr in tropical areas, especially in Southeast Asia and Latin America. Serious environmental problems have resulted from this huge development. In many cases, the construction of ponds has destroyed large areas of mangrove forests which are not economically valued, although they are the source of many local activities such as lumber, thatching material and a variety of foodstuffs ŽPrimavera, 1994.. Besides, they play a major role in the environment as a shelter for fish spawning, and as a water purifier ŽPhillips et al., 1993.. The environment has not only been often damaged by the development of such an activity, but shrimp farming is now seriously hampered by problems of self-pollution. Indeed, the intensification of aquaculture means more water requirements, more fertilisers, more industrial feed and more veterinary products which are eventually discharged into the environment. In some sites characterised by little water renewal and weak currents, the waste dispersion capacity is not efficient enough to protect the farms from their own wastes. In farms operating for several years, the shrimps suffer from their being in contact with a polluted substrate in the ponds and from viral diseases. Moreover, in many farms in China, Indonesia or Ecuador where the production has collapsed, the polluted ponds turn out to be of no use for any other activity. That is the reason why, from 1992 on, experiments have been carried out in Brazil in order to design a new farming technology using floating cages. This research program is aimed at developing environmentally friendly techniques suitable for specific geographical and socio-economic conditions. From a social standpoint, the objective is to give a community of fishfolk the opportunity of having a supplemental livelihood and consequently additional income in order to reduce the rural emigration. Very few tests have been carried out on shrimp culture in cages. Most of them were devoted to net pen rearing ŽNatarajan et al., 1987; Perera and Samaranayake, 1987; Samaranayake, 1990; Tookwinas, 1990.. Particularly in floating cages, the number of tests was too limited ŽLi and Chen, 1987; Martinez-Cordova, 1988; Srikrishnadhas and Sundararaj, 1993. to extrapolate the results into an economic feasibility study. In our experiments, the biological and technical results proved to be interesting in comparison with traditional pond culture. Nevertheless, a cost-benefit analysis is necessary to assess the economic feasibility of such an innovative technique. Moreover, the sustainability of this technique has to be estimated before starting a development phase. So, the purposes of this research are Ži. to assess the zootechnical feasibility of raising tropical shrimps in floating cages, Žii. to evaluate the economic feasibility of this type of technique, and Žiii. to consider the potential impact on the environment after three years of experiments in an estuarine area in Brazil.
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2. Material and methods 2.1. Location of experiment This study was carried out in Baixo de Baiano, 150 km south of the city of Salvador, in the State of Bahia. It is an estuarine area of 2000 km2 where 30,000 persons practice small scale fishing with unmotorized dugout canoes. 2.2. Aquaculture techniques and experimental procedures 2.2.1. Floating cages The growing cage frame consists of four PVC Žpolyvinyl chloride. pipes closed at each end. Two of the pipes are 5 m long with a 110 mm diameter, and the other two are 3 m long with a 50 mm diameter. The pipes are fixed to each other by their ends, by means of ropes. Four 1-m long steel bars are wound around each of the two longer pipes. The steel bars fixed vertically allow the net to maintain its shape in the water. The net Žpolyester yarn PVC coated, 5-mm mesh size. is 5.5 m long, 2.8 m wide and 1 m high. Half of the net remains immersed while the other half is above the water. The emergent part of the net prevents the shrimp from jumping out of the cage. Nursery cages are built with the same design Ž0.5 mm mesh spacing.. The cages are tied to each other by means of ropes, so as to constitute a set of 10 cages. The sets of cages are positioned to minimize resistance to the tide. Each set of cages is anchored to the substrate at its four corners. 2.2.2. Rearing conditions Penaeus Õannamei postlarvae which came from local commercial hatcheries were acclimatised before stocking in the nursery cages at the rate of 5000 postlarvae per 10 m2 . The animals were then nursed for 2 months until their average weight reached 0.5 g. During the nursery phase, the animals were fed with pelletized feed. After the nursery stage, the animals were transferred into the growing cages. During the transfer the animals were counted so as to adjust the number of stocked animals. The ongrowing phase started with 0.5 g average weight animals and ended once commercial sizes were attained Ž15 to 18 g.. Growing was done exclusively in cages, the nets of which were entirely covered with biological fouling organisms. New cages were set in the water at least three weeks before stocking so as to enable bio-fouling to develop. A small surface of the net Ž50 cm = 50 cm. on both ends of the cages was cleaned every fortnight to improve the water flow through the cage. Feed consisted of commercial pellets which were sprinkled into the cage. Biofouling at the bottom of the cages prevented the pellets from falling into the water. Once the desired commercial sizes were attained, all the animals were harvested. The nets were raised into a boat and the animals caught manually and placed in cases containing ice. The animals were weighed as a group and the average weight computed for each cage. 2.2.3. Zootechnical tests This study aims at defining optimal conditions for rearing in cages, including the relations between density Žnumber of shrimps per cage or per m2 ., growth rate and
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Table 1 Experimental conditions in cage rearing of Penaeus Õannamei Trial
Period Žnumber of days.
Number of cages
Initial density Žshrimps per cage.
A Žhot season.
23r11r93 to 23r03r94 Ž120 days.
B Žhot season.
19r01r94 to 06r04r94 Ž76 days.
C Žcool season.
07r04r94 to 07r09r96 Ž153 days.
3 2 2 2 1 5 2 1 2 3 4 4 2
1,500 2,000 2,500 2,000 2,500 2,800 3,000 3,500 625 1,250 1,500 2,000 2,500
season Žcool and hot.. Survival rate and food conversion ratio ŽFCR. have been determined for each cage. Animals came from the same batch Žsame hatchery and identical nursing period. in each trial. Animals were distributed randomly in the cages. Cage stockings were done on the same day for a single experiment. In the same way, the animals in cages of a single experiment were harvested the same day. Three tests were completed according to conditions given in Table 1. For test C, sampling was performed every week to check growth rates. 2.3. Simulation tool for economic analysis The use of a computerised simulation tool with a spreadsheet software in order to link technical, biological and financial data proved to be very useful in project economic analysis. This technique has been widely used in aquaculture for different species such as shrimps, fishes and bivalves ŽMcBryde, 1994.. To help decision making, a project has to be analysed from different viewpoints using several financial criteria which include profitability on the long run, breakdown of production costs and internal rate of return on a 10-yr horizon ŽMeade, 1989.. The present technico-economic analysis has been done using PROJAQ, a software based on Microsoft Excel previously used to assess a scallop farming project ŽPaquotte and Fleury, 1994.. A sensitivity analysis has also been conducted to point out the major factors of variation in profitability and to assess the specific risks of the activity. A market study has been carried out in Salvador de Bahia to give a price estimation of the products delivered by the project. All the financial data are expressed in US dollars on the basis of the official exchange rate between the US dollar and the Brazilian real as of January 1995. 2.4. Presentation of the pilot scale project Shrimp farming in cages is not developed enough in Brazil to make a relevant economic analysis. Therefore, a pilot scale project has been designed to assess the
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economic feasibility of this new technique. The phase of project identification is a key point because it leads to planning the organisational aspects of the activity and to make biological, technical and economic assumptions ŽInsull and Nash, 1990.. The ex-farm production capacity of such a project has been fixed at 60 tons of live shrimps per year. As the construction of a hatchery has not been planned yet, an annual amount of 9 million postlarvae have to be purchased from commercial hatcheries. The project would involve 28 fishermen, each one running 40 cages for ongrowing and 7 cages for nursery. Fishermen would be in charge of feeding the shrimps and would participate in the activities of cages building and cleaning, postlarvae seeding, transferring juveniles into ongrowing cages and harvesting. A central organisation would be responsible for collective tasks such as buying inputs Žfeed, seed, energy., monitoring water quality and shrimp growth, and conducting husbandry operations from seeding till harvesting. Moreover, the project would integrate a processing activity and a commercial unit in order to supply caterers and retailers of the Salvador de Bahia area with frozen heads-off shrimps. The project would employ a total of 17 persons full-time and the equivalent of three persons part-time, in addition to the 28 fishermen. At this stage of the project, only the area of Salvador of Bahia is considered for marketing the shrimps. 2.5. Assessment of the enÕironmental impact The environmental studies consisted in a one-off operation which was carried out in order to determine the state of the environment on the pilot site, nearby the cage train, after three years of rearing activities on the site. One of the characteristics of shrimp rearing, like any kind of rearing, is the production of organic sewage Žfaeces, unconsumed feeds.. In earthen ponds, the major consequence of sewage production is an accumulation of organic matter on the pond bottom. Furthermore, mineralisation of the
Fig. 1. Sampling stations for sediment ŽA. and for oxygen measurement ŽB..
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organic matter Žessentially nitrification. and microbial process lead to oxygen consumption in the sediment and in water. In this study, the impact of the rearing has been evaluated through the accumulation of organic matter in the sediment, and the concentration of oxygen in the water. Samples of sediment were taken from 9 stations located beneath and nearby the cages ŽFig. 1A.. Station 1 located 100 m upstream of the cages train is considered a reference station not affected by the rearing cages. Only the upper layer of the sediment Žlayer 0–2 cm. was sampled. Concentration of organic matter in the sediment was determined using the method of ignition loss Ž4508C during 4 h.. The concentration of oxygen was determined with a polarographic probe, type YSI 58, during a 24-h cycle ŽFig. 1B.. Two of five stations Žstations 2 and 4. were located close to Ž- 20 cm. the cages. At station 3, measurements were carried out in the rearing cage. Station 1 located 100 m upstream of the cages was considered as a reference station. Oxygen concentration was determined at 20 cm depth for surface measurements, and at 10 cm above the bottom for deep measurements. Due to the tide, the water depth varied from 1.5 m to 2.5 m during the 24-h cycle period.
3. Results 3.1. Growth and surÕiÕal Average survival rate and FCR for the three tests are given in Table 2. Test C has made possible to obtain a growth curve ŽFig. 2.. Each curve stands for the average between the various cages stocked with the same number of animals. Fig. 3 shows that yield is positively correlated with the final density in tests A Ž r 2 s 0.58; P - 0.05., B Ž r 2 s 0.7; P - 0.01. and C Ž r 2 s 0.89; P - 0.01.. Similarly, growth rate significantly decreases as the rearing density increases ŽFig. 4. with a negative correlation in the three tests: A Ž r 2 s 0.49., B Ž r 2 s 0.56; P - 0.01. and C Ž r 2 s 0.58; P - 0.01.. The regression line for test C is parallel and significantly lower than for tests A and B. The growth rate during the hot season is approximately 23% higher than that obtained during the cool season at similar rearing density. Results show average growth rate of 0.76 g wky1 at a rearing density of 72 animals my2 , monthly mortality rate of 6% and FCR of 2.5 for the 5 months ongrowing phase. The average final weight is 15 g at harvest.
Table 2 Average survival rates and FCR of Penaeus Õannamei in cages Trial
Average survival rate
Average FCR
A B C
76%"13,5 ŽP - 0.05. 63%"10,3 ŽP - 0.05. 57%"8,2 ŽP - 0.05.
2,58"0,22 ŽP - 0.05. 3"0,88 ŽP - 0.05. 3,15"0,24 ŽP - 0.05.
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Fig. 2. Growth curve of P. Õannamei at different stocking densities.
Fig. 3. Correlation curve between yield and final density for trials ŽA., ŽB. and ŽC..
Fig. 4. Correlation curve between daily growth rate and final density for trials ŽA., ŽB. and ŽC..
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Table 3 Investment costs Item
Purchase price ŽUS$.
Useful life Žyears.
Depreciation ŽUS$.
Land with services Buildings Cages Nets Žjuveniles. Nets Žongrowing. Canoes Small motorized boats Fishing boat Ice maker Freezers Laboratory and office equipment Miscellaneous
12,000 79,425 126,504 41,952 93,408 11,200 6,100 15,000 10,000 31,800 9,840 36,762
10 8 3 4 10 10 15 10 5 4 5
7,943 15,813 13,984 23,352 1,120 610 1,000 1,000 6,360 2,460 7,352
Total
473,991
80,994
3.2. InÕestment and operating costs Total capital investment amounting to US$ 474,000 was completed in the first year. Total annual depreciation cost is US$ 81,000 ŽTable 3.. The buildings include a shelter for boats, feed and equipment, an office–laboratory, a processing plant and a storage place for frozen shrimps. The main equipment are 28 unmotorized dugout canoes, one 13-m long wooden fishing boat with a 35 HP engine, two small aluminium boats with a 15 HP off-board engine, 37 household freezers Ž100 l. and a light truck for delivery. Total annual operating costs was computed at US$ 252,000. Total cost including depreciation is US$ 333,200, excluding financial cost ŽTable 4.. Fishermen are assumed to receive a monthly compensation equivalent to the minimum legal salary for their participation in the project. In 1995, the minimum salary in Brazil was US$ 82 per Table 4 Costs of production per year Item
A. Operating costs Post-larvae Feed Fishermen payment Salaries and welfare contributions Gas, oil, electricity Miscellaneous B. Other costs Depreciation Total
Farming ŽUS$.
Processing and Marketing ŽUS$.
Total ŽUS$.
Ratio
49,000 74,200 27,400 28,000 18,600 5,000
0 0 0 31,500 8,000 10,500
49,000 74,200 27,400 59,500 26,600 15,500
14.71% 22.27% 8.22% 17.86% 7.98% 4.65%
62,000
19,000
81,000
24.31%
264,200
69,000
333,200
100.00%
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Table 5 Expected costs and revenues over a 10 years horizon year Investment Ž1000 $. Final salvage value Ž1000 $. Operating costs Ž1000 $. Revenues Ž1000 $.
1
2
3
474 262 200
251 460
251 460
4
5
6
7
42
103
69
42
251 460
251 460
251 460
251 460
8
251 460
9
10
230
42 190 251 460
251 460
month. Salaries and welfare contributions of employees amounted to US$ 59,500 per year. Postlarvae cost US$ 4.6 a thousand. Brazilian feed is bought at US$ 0.5 per kg. The production cost of ex-farm shrimps at an average weight of 15 g is estimated at US$ 4.7 per kg. The annual production of processed shrimps is 36 tons on the assumption that 100 kg of shrimp yield 65 kg of tails. The production cost of frozen head-off shrimp at an average weight of 9.9 g Žcount 41–50. is US$ 9.2 per kg, including delivery cost. 3.3. Analysis of profitability The market study points out that shrimp price in the Salvador area depends on the period of the year. When fish landings are low and touristic demand is high, wholesale price for frozen head-off shrimps Žcount 41–50. is high ŽUS$ 14 per kg. from December to March. However prices are below US$ 10 from May to June. On the assumption of an annual average price of US$ 12.6 per kg, annual turn-over is US$ 460,000. With a result of US$ 126,800, a profitability ratio Žresultrturn-over. of 27% may be expected prior deduction of financial expenses and taxes. In order to assess the profitability of the investment, the expected costs and revenues have been calculated over a 10-yr horizon ŽTable 5.. Reinvestment takes place at the end of the expected life value of the equipment, especially year 5 with the renewal of nets and year 9 with the renewal of both nets and cages. The salvage value is calculated for year 10 by deducting ten times the annual depreciation from the total of investment realised during the 10 yr. In these conditions, the Internal Rate of Return is 30%. However, this result has to be put in regard with the high inflation rate in Brazil. Since the implementation of the ‘Real Plan’ in 1994, this rate has been considerably reduced but is still around 24% per year. If the discount rate in Brazil is assumed at 28%, the time for return on investment is seven years. Table 6 Sensitivity analysis Žfor the whole project including farming, processing and marketing. parameter
value of reference
new assumption
new new production profitability cost Žper kg. ratio
Growth rate Food conversion ratio Availability of post-larvae from May to July Yield of tails from a 100 kg of shrimp Minimum monthly legal salary Brazilian market price for shrimp
0.80 g weeky1 2.5 yes 65 kg 82 US$ 12.6 US$ kgy1
0.67 g weeky1 2.0 no 60 kg 100 US$ 10.0 US$ kgy1
9.3 US$ 8.8 US$ 10.9 US$ 10.2 US$ 9.9 US$ 9.2 US$
-0 31% 4% 19% 21% 8%
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3.4. SensitiÕity analysis As a project is designed on the basis of assumptions, it is interesting to assess the impact of the variations of relevant parameters Žbiological, technical or economic. by means of a computerised simulation tool ŽTable 6.. If growth is slower than expected, production cost increases and selling price decreases because shrimps are smaller. In this case, the profitability of the project would be jeopardised. With a FCR of 2, the expected profitability ratio is 15% higher than in reference situation. The dependence of fry from private hatcheries may affect the stocking in the months of May and June. This would lead to lack of shrimps in December when the market price is at the highest. The resulting profitability ratio of 4% would put the project in a very difficult financial position. The process of separating head from tail is critical. Careless or improper separation increases the waste and decreases the profit ŽAiken, 1990.. At this stage, a waste of weight of only 8% will reduce the profitability by 30% for the whole project. The present minimum salary is very low in Brazil. The new socio-economic policy which is in the process of being implemented could lead to better redistribution of the national income. Nevertheless, a moderate increase of 10% in the minimum legal salary would reduce the profitability ratio by 22%. At the moment, the Brazilian shrimp market is not yet pressured by the international competition but it is impossible to exclude an evolution of the price according to the world-wide trend. With a liberalized global market, international prices will pressure Brazilian shrimp growers to lower their prices. Should the price in Salvador fall to US$ 10 per kg, the profitability ratio of the project will decrease to 8%. 3.5. Impact on the enÕironment The concentrations of organic matter in the sediment Žessentially of yellow siliceous sand. samples range from 0.39% to 0.52% ŽTable 7.. At the reference station Žstation 1. the concentration of organic matter is 0.50%. Values observed at stations located beneath the cages are lower or similar to the value of station 1. No gradient of concentration, which would give evidence of organic matter accumulation in the sediment due to rearing activities could be observed. Fig. 5 shows the variations of oxygen concentration during the 24-h cycle for sub-surface ŽFig. 5A. and for bottom ŽFig. 5B. measurements. For surface measurements, values were never lower than 5 mg ly1 . At station 3, the concentrations varied
Table 7 Concentration of organic matter ŽO.M.. in surface layer Ž2 cm. sediment sampled aroud and beneath the rearing cages. STATION O.M. Ž%.
1 0.50
2 0.39
3 0.58
4 0.42
5 0.41
6 0.35
7 0.54
8 0.38
9 0.52
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Fig. 5. Circadian fluctuations of oxygen concentration in and outside the cages. ŽA. concentration at 20 cm deep; ŽB. concentration at 10 cm from bottom sediment; B station 1 I station 2 % station 3 v station 4 ' station 5.
from 5.2 mgy1 Žat 0500 h. in the rearing cage. Oxygen saturation in the cage ranged from 76% to 94%. At 0500 h, the lowest concentrations were observed in the cage Žstation 3., while the highest concentration was in the reference station Žstation 1.. Nevertheless, the difference between the cage and the reference station did not exceed 0.5 mg ly1 and 10% in terms of oxygen concentration and saturation, respectively. A decrease in concentrations was observed in surface measurements at every station, at 1200 h. Generally speaking, the range of variation in oxygen concentrations was less important for bottom than for surface measurements.
4. Discussion 4.1. Production P. Õannamei is almost exclusively produced on the American continent, from Southern United States to Northern Peru and Brazil. Its growth rate in ponds ranges between 0.6 and 1.2 g wky1 . The rates obtained during our tests, i.e., 0.84 g wky1 during the warm season and 0.63 g wky1 during the cool season are within the usual range. An average yield of 800 g my2 cycley1 is obtained in the cages, which gives an annual yield of 2 kg my2 . The high production capacity of cage rearing can result from the conjunction of three phenomena. First, the natural and continuous renewal of the water in the cages allows to maintain its quality for the animals. Contrary to pond rearing, the variations of physico-chemical parameters are moderate and slow, buffered by the huge volume of water all around the cages. The rearing water quality is quite similar to that of the environmental medium and thus depends on the area in which the cages are located. Second, the substrate on which the shrimps rest in the cages, which is constituted by the net covered by the bio-fouling, is continuously oxygenated by the water circulating
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through and on each side of the net. Thus, we were not faced with the problems on accumulation of organic matter or sediment reduction currently observed in earthen ponds ŽHopkins et al., 1994.. Lastly, natural food which consists of the bio-fouling settling on the net, and to a lesser extent of the phytoplankton and the zooplankton. Based on the studies of Anderson et al. Ž1987. and Reymond and Lagardere ` Ž1990., bio-fouling could represent a significant part of the food of the shrimps reared in cage. The contribution of natural food with regard to essential nutrients may make up for the probable nutritional deficiency of commercial pellets available in Brazil. 4.2. Economic aspects In spite of innovative aquaculture technique, relevant social goal and willingness to protect the environment, long term profitability will be adversely affected because of the pressure from international competition. Although the world shrimp aquaculture production has been steady after a long period of soaring expansion, the international market has been rather bleak in 1995. In these conditions, the buyers will give priority for the cheapest products in the market. In the particular context of the project, an expected profitability ratio of 27% seems high enough to take into account the risks connected with a new aquaculture technique. This good profitability is mainly due to the low cost of the processing and marketing activities involved in the project. But the breakdown of the production costs shows that the cage farming technique is not less costly than usual pond farming techniques. Although very little accurate information is available on this topic, production costs for P. Õannamei in Latin America are assessed between US$ 3.50 and US$ 4.50 per kg for an average weight of 16 g ŽVillalon and Preis, 1993.. The main economic constraints in cage shrimp farming are the high cost of capital use Žover US$ 1000 annual depreciation per ton. and the low labour productivity Ž1.3 tons per employee and per year.. Because of the high price and the short useful life of the nets, the cost of capital use is twice as expensive as in pond farms, either in Ecuador or in Thailand ŽChong, 1990.. Despite the very low salary level for unskilled workers in Brazil, the share of labour in the farming production costs is as high as 21% while it is usually under 13% in Latin American pond shrimp farming ŽWeidner, 1993.. This high cost is due to the scattering of shrimp stocks throughout a large area in small units managed by the fishermen with little possibility of automation. Although the initial investment is lower than for an onshore farm using ponds, it is still too high for the local community of fishermen. Private capital or public subsidies should be required, but in both cases the profitability of the investment has not to be the only expectation. Indeed, an Internal Rate of Return of 30% is not very high in the Brazilian context. Moreover, the estimated cash-flow after 10 yr of operation is not high enough to consider wider developments of the project without loans or new contributions from the shareholders. So, such a project should be considered as part of a coastal management programme or as additional activity of a sea-products processing company looking for a better control of the supply. The fact that the fishermen are responsible of their own cages may be considered as a guarantee of efficiency and quality in contrast to
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industrial farms who just hire manpower for basic tasks ŽKongkeo, 1995.. Fair sharing of the benefits between the fishermen and the central organisation should be a corporate policy. 4.3. Impact on the enÕironment After three years of rearing activities, no significant accumulation of organic matter in the sediment could be observed. The concentrations of organic matter beneath or downstream the cages train are not higher than those observed upstream. For rearing activities in earthen ponds, solid organic wastes Žfaeces, unconsumed feeds. pass through a transitory stage, i.e., a settling on the sediment, before being drained off the pond consequently causing accumulation of organic wastes on the pond bottom ŽBoyd, 1992; Fast and Boyd, 1992; Hopkins et al., 1994.. Furthermore, the process of microbial degradation of organic matter occurs essentially on the sediment ŽBlackburn et al., 1988.. The respiration of shrimps, bacterial activity, and plant respiration Žphytoplankton and phytobenthos. in earthen ponds affect consumption of oxygen which is higher than the accumulation of organic matter ŽHansen et al., 1991.. That is the reason why, in earthen ponds, drastic decrease in oxygen concentrations can be observed during the night ŽMadenjian, 1990., which requires the use of mechanical aerators to keep the level of oxygen concentration acceptable for shrimp survival and growth. In the case of rearing cages located in running water, solid wastes are not accumulated near the cages. Unlike ponds, the estuary is not a closed confined system. The low concentrations of organic matter in the sediment observed near the cages and the relatively high concentrations of oxygen during the night demonstrated that the wastes are carried away from the cages. The processes of oxygenation of the sediment due to tide and currents may also be sufficient to allow a quick degradation of organic matter and to compensate the shrimps and of plants Žmacrophytes, phytoplankon. respiration, so that no significant accumulation of organic matter or drastic decrease of oxygen is noted. A decrease in oxygen concentration was observed at 1200 h during the 24-h cycle. This may be due to an inhibition of photosynthesis under the influence of solar irradiation ŽPlatt et al., 1980., which is maximum at that time of the day. This hypothesis is confirmed by the fact that the decrease of concentration and rate of saturation is lower beneath the table, and near the bottom than the surface of the water. In cages, the shrimps are not ‘sheltered’ from solar irradiation. Preliminary results showed that near and in the cages, the concentrations of total suspended matter were lower than 12 mg ly1 and 5 mg ly1 at low tide and high tide respectively ŽJ.L.M. Martin, unpublished data.. The quick turn-over of water in the estuary and in the cages prevents the development of phytoplanktonic blooms. In earthen ponds the shrimps are sheltered by the phytoplanktonic bloom. In ponds, the sestonic condition corresponds to controlled eutrophic conditions ŽPruder, 1986. where concentrations of total suspended matter are often higher than 100 mg ly1 ŽHopkins et al., 1993; Briggs and Funge-Smith, 1994.. Furthermore, shrimps can not bury themselves in mesh cages. P. Õannamei is not a burying species but like most other penaeide shrimps ŽWassenberg and Hill, 1994., it is nocturnal and emerges from the bottom in the evening, when light is dim. It slows down activities in the morning and goes to the bottom, usually before dawn. Therefore,
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experiments are needed to determine whether the shading of the cages can affect shrimp growth.
5. Conclusion After three years of field experiments, the technology and husbandry practices of shrimp culture in floating cages have been proven to be very efficient from a zootechnical standpoint. Such parameters as growth rate, survival rate and FCR are at the same level than the best results obtained in intensive pond farming. The economic analysis shows that a pilot scale project aiming at producing 60 tons of shrimps per year would be profitable in the context of the market of Salvador de Bahia and would make possible to provide an additional income to the local community of fishermen on their own living spot. As far as the studied area is concerned, the zootechnical, economic and environmental data are good basis to plan a future development for this project. Such a development could be done without damaging the coastal ecosystem since there is no irreversible construction and no high concentration of shrimps in a closed space. According to the environmental or economic conditions, it would be easy to add or suppress cages, or to move them to another place. This rearing technique seems appropriate for a good resource management. However, the profitability of the technique is still sensitive to variations of biological parameters and market conditions. So, the results may be different in other geographical and socio-economic environments. No impact on the environment has been noticed under the experimental cages during the time of experiments, and the shrimps are in very good rearing conditions since they are not in contact with organic wastes. Therefore, the premium quality of the product should be a feature to valorise. Thanks to the original ongrowing conditions, the yield is very homogeneous in size, the gills are mud-free and there are very few wounds or spots on the shells. That is the reason why this project has to look for competitive advantages more in terms of quality and image than in terms of low price. The production costs in cages are hampered by the short useful life of the nets and by the weak labour productivity of the system. On the contrary, the environmental friendliness and the positive social impact of the technique are assets to take into account. Like other shrimp farming projects which cannot take advantage of low production costs, it should aim at developing niche markets, thanks to quality monitoring, control of the marketing and brand promotion ŽRhodes, 1990.. As such a policy would induce higher costs in processing and marketing, productivity gains during the cage farming phase are still a major goal for the future experiments.
Acknowledgements This research project has been developed in the framework of the France–Brazil cooperation in Oceanology with the support of the State of Bahia, the Odebrecht company ŽBrazil., the French Embassy in Brazil and IFREMER ŽInstitut Franc¸ais de Recherche pour l’Exploitation de la Mer..
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Reymond, H., Lagardere, ` J.-P., 1990. Feeding rhythms and food of Penaeus japonicus Bate ŽCrustacea, Penaeidae. in salt marsh ponds: role of halophilic entomofauna. Aquaculture 84, 125–143. Rhodes, R.J., 1990. Will US shrimp farms survive?: the South Carolina experience. In: Sandifer, P.A., ŽEd.., Shrimp Culture in North America and the Caribbean Advances in World Aquaculture, 4, 202–215. Samaranayake, R.A.D.B., 1990. Pen culture trials with the tiger prawn, Penaeus monodon in Chilaw Lagoon, Sri Lanka. In: Hirano, R., Hanyu, I. ŽEds.., Proceedings of the Second Asian Fisheries Forum. Tokyo, Japan, 17–22 April 1989. The Asian Fisheries Society, Manila, Philippines, pp. 107–108. Srikrishnadhas, B., Sundararaj, V., 1993. Studies on the growth of marine shrimps in floating cages and pen. In: Natarajan, P., Jayaprakas, V. ŽEds.., Proceedings of the National Seminar on Aquaculture Development in India—Problems and Prospects. Kerala University, Kerala, India, 27–29 November 1990, pp. 53–58. Tookwinas, S., 1990. Pen culture techniques of marine shrimp in Thailand. Infofish International, 2r90, 38–40. Villalon, J.R., Preis, F., 1993. A brief overview of the shrimp industry in Ecuador. J. Aquatic. Food Product Technol. 2 Ž1., 5–22. Wassenberg, T.J., Hill, B.J., 1994. Laboratory study of the effect of light on the emergence behavior of eight species of commercially important adult penaeid prawns. Aust. J. Mar. Freshwat. Res. 1, 43–50. Weidner, D., 1993. Shrimp farming in Colombia. Infofish International, 2r93, 56–61.
Intensive culture of shrimp Penaeus Õannamei in floating cages: zootechnical, economic and environmental aspects P. Paquotte
a,)
, L. Chim a , J.-L.M. Martin b, E. Lemos c , M. Stern d , G. Tosta d
a
Institut Franc¸ais de Recherche pour l’Exploitation de la Mer (IFREMER), 155 rue˙ Jean-Jacques Rousseau, 92138, Issy les Moulineaux, France b Centre de Recherche Ecologie Marine et Aquaculture, IFREMER r CNRS, BP 5, 17137, L’Houmeau, France c Littoral Sul Maricultura, Almeda das Espatodias, 915, Edificio Odebrecht, Pituba, SalÕador, Bahia, Brazil d Bahia Pesca, SalÕador, AÕenida Adhemar de Barros 967, Ondina, SalÕador, Bahia, Brazil
Abstract In the framework of the France–Brazil cooperation in Oceanology, experiments have been carried out in the State of Bahia ŽBrazil. from 1992 on, in order to design a new technology for culture shrimps in floating cages in an estuarine zone. The zootechnical research has focused on the species Penaeus Õannamei which has been tested in different rearing conditions Ždensity in the cages. and seasons Žwet and dry.. The results may be compared with the most intensive and costly technologies which are practised in Asian countries. The average growth rate is about 0.8 g wky1 and the average final biomass is 800 g my2 . The achieved results are all the more important as they are obtained with a simple technology which does not require energy for pumping and mechanical water aeration. Investigations on the impact of this kind of technology, carried out on a pilot site with estuarine conditions after three years of farming activity, showed no measurable effect on the sediment Žin terms of organic matter. and in the water Žin terms of oxygen.. Economic analysis was recorded from the very beginning of the project, making it possible to design a computerised simulation tool in order to assess the feasibility of such an operation and to help in decision making for future research and development. Initial results indicate that ex-farm production costs for shrimps weighing 15 g would be around US$ 4.7 per kg. The major competitive advantages of such a technique are the high yield, the quality of the product, the
)
Corresponding author. Tel.: q33-01-46-48-22-65; fax: q33-01-46-48-22-76; e-mail: [email protected].
0044-8486r98r$19.00 q 1998 Elsevier Science B.V. All rights reserved. PII S 0 0 4 4 - 8 4 8 6 Ž 9 8 . 0 0 1 8 3 - 5
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environmental friendliness and the positive social impact for a fishing community. q 1998 Elsevier Science B.V. All rights reserved. Keywords: Shrimp farming; Floating cages; Economic analysis; Environment
1. Introduction Because of the high demand for shrimps in Japan, the United States and Europe, shrimp aquaculture production has been soaring during the last 10 yr in tropical areas, especially in Southeast Asia and Latin America. Serious environmental problems have resulted from this huge development. In many cases, the construction of ponds has destroyed large areas of mangrove forests which are not economically valued, although they are the source of many local activities such as lumber, thatching material and a variety of foodstuffs ŽPrimavera, 1994.. Besides, they play a major role in the environment as a shelter for fish spawning, and as a water purifier ŽPhillips et al., 1993.. The environment has not only been often damaged by the development of such an activity, but shrimp farming is now seriously hampered by problems of self-pollution. Indeed, the intensification of aquaculture means more water requirements, more fertilisers, more industrial feed and more veterinary products which are eventually discharged into the environment. In some sites characterised by little water renewal and weak currents, the waste dispersion capacity is not efficient enough to protect the farms from their own wastes. In farms operating for several years, the shrimps suffer from their being in contact with a polluted substrate in the ponds and from viral diseases. Moreover, in many farms in China, Indonesia or Ecuador where the production has collapsed, the polluted ponds turn out to be of no use for any other activity. That is the reason why, from 1992 on, experiments have been carried out in Brazil in order to design a new farming technology using floating cages. This research program is aimed at developing environmentally friendly techniques suitable for specific geographical and socio-economic conditions. From a social standpoint, the objective is to give a community of fishfolk the opportunity of having a supplemental livelihood and consequently additional income in order to reduce the rural emigration. Very few tests have been carried out on shrimp culture in cages. Most of them were devoted to net pen rearing ŽNatarajan et al., 1987; Perera and Samaranayake, 1987; Samaranayake, 1990; Tookwinas, 1990.. Particularly in floating cages, the number of tests was too limited ŽLi and Chen, 1987; Martinez-Cordova, 1988; Srikrishnadhas and Sundararaj, 1993. to extrapolate the results into an economic feasibility study. In our experiments, the biological and technical results proved to be interesting in comparison with traditional pond culture. Nevertheless, a cost-benefit analysis is necessary to assess the economic feasibility of such an innovative technique. Moreover, the sustainability of this technique has to be estimated before starting a development phase. So, the purposes of this research are Ži. to assess the zootechnical feasibility of raising tropical shrimps in floating cages, Žii. to evaluate the economic feasibility of this type of technique, and Žiii. to consider the potential impact on the environment after three years of experiments in an estuarine area in Brazil.
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2. Material and methods 2.1. Location of experiment This study was carried out in Baixo de Baiano, 150 km south of the city of Salvador, in the State of Bahia. It is an estuarine area of 2000 km2 where 30,000 persons practice small scale fishing with unmotorized dugout canoes. 2.2. Aquaculture techniques and experimental procedures 2.2.1. Floating cages The growing cage frame consists of four PVC Žpolyvinyl chloride. pipes closed at each end. Two of the pipes are 5 m long with a 110 mm diameter, and the other two are 3 m long with a 50 mm diameter. The pipes are fixed to each other by their ends, by means of ropes. Four 1-m long steel bars are wound around each of the two longer pipes. The steel bars fixed vertically allow the net to maintain its shape in the water. The net Žpolyester yarn PVC coated, 5-mm mesh size. is 5.5 m long, 2.8 m wide and 1 m high. Half of the net remains immersed while the other half is above the water. The emergent part of the net prevents the shrimp from jumping out of the cage. Nursery cages are built with the same design Ž0.5 mm mesh spacing.. The cages are tied to each other by means of ropes, so as to constitute a set of 10 cages. The sets of cages are positioned to minimize resistance to the tide. Each set of cages is anchored to the substrate at its four corners. 2.2.2. Rearing conditions Penaeus Õannamei postlarvae which came from local commercial hatcheries were acclimatised before stocking in the nursery cages at the rate of 5000 postlarvae per 10 m2 . The animals were then nursed for 2 months until their average weight reached 0.5 g. During the nursery phase, the animals were fed with pelletized feed. After the nursery stage, the animals were transferred into the growing cages. During the transfer the animals were counted so as to adjust the number of stocked animals. The ongrowing phase started with 0.5 g average weight animals and ended once commercial sizes were attained Ž15 to 18 g.. Growing was done exclusively in cages, the nets of which were entirely covered with biological fouling organisms. New cages were set in the water at least three weeks before stocking so as to enable bio-fouling to develop. A small surface of the net Ž50 cm = 50 cm. on both ends of the cages was cleaned every fortnight to improve the water flow through the cage. Feed consisted of commercial pellets which were sprinkled into the cage. Biofouling at the bottom of the cages prevented the pellets from falling into the water. Once the desired commercial sizes were attained, all the animals were harvested. The nets were raised into a boat and the animals caught manually and placed in cases containing ice. The animals were weighed as a group and the average weight computed for each cage. 2.2.3. Zootechnical tests This study aims at defining optimal conditions for rearing in cages, including the relations between density Žnumber of shrimps per cage or per m2 ., growth rate and
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Table 1 Experimental conditions in cage rearing of Penaeus Õannamei Trial
Period Žnumber of days.
Number of cages
Initial density Žshrimps per cage.
A Žhot season.
23r11r93 to 23r03r94 Ž120 days.
B Žhot season.
19r01r94 to 06r04r94 Ž76 days.
C Žcool season.
07r04r94 to 07r09r96 Ž153 days.
3 2 2 2 1 5 2 1 2 3 4 4 2
1,500 2,000 2,500 2,000 2,500 2,800 3,000 3,500 625 1,250 1,500 2,000 2,500
season Žcool and hot.. Survival rate and food conversion ratio ŽFCR. have been determined for each cage. Animals came from the same batch Žsame hatchery and identical nursing period. in each trial. Animals were distributed randomly in the cages. Cage stockings were done on the same day for a single experiment. In the same way, the animals in cages of a single experiment were harvested the same day. Three tests were completed according to conditions given in Table 1. For test C, sampling was performed every week to check growth rates. 2.3. Simulation tool for economic analysis The use of a computerised simulation tool with a spreadsheet software in order to link technical, biological and financial data proved to be very useful in project economic analysis. This technique has been widely used in aquaculture for different species such as shrimps, fishes and bivalves ŽMcBryde, 1994.. To help decision making, a project has to be analysed from different viewpoints using several financial criteria which include profitability on the long run, breakdown of production costs and internal rate of return on a 10-yr horizon ŽMeade, 1989.. The present technico-economic analysis has been done using PROJAQ, a software based on Microsoft Excel previously used to assess a scallop farming project ŽPaquotte and Fleury, 1994.. A sensitivity analysis has also been conducted to point out the major factors of variation in profitability and to assess the specific risks of the activity. A market study has been carried out in Salvador de Bahia to give a price estimation of the products delivered by the project. All the financial data are expressed in US dollars on the basis of the official exchange rate between the US dollar and the Brazilian real as of January 1995. 2.4. Presentation of the pilot scale project Shrimp farming in cages is not developed enough in Brazil to make a relevant economic analysis. Therefore, a pilot scale project has been designed to assess the
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economic feasibility of this new technique. The phase of project identification is a key point because it leads to planning the organisational aspects of the activity and to make biological, technical and economic assumptions ŽInsull and Nash, 1990.. The ex-farm production capacity of such a project has been fixed at 60 tons of live shrimps per year. As the construction of a hatchery has not been planned yet, an annual amount of 9 million postlarvae have to be purchased from commercial hatcheries. The project would involve 28 fishermen, each one running 40 cages for ongrowing and 7 cages for nursery. Fishermen would be in charge of feeding the shrimps and would participate in the activities of cages building and cleaning, postlarvae seeding, transferring juveniles into ongrowing cages and harvesting. A central organisation would be responsible for collective tasks such as buying inputs Žfeed, seed, energy., monitoring water quality and shrimp growth, and conducting husbandry operations from seeding till harvesting. Moreover, the project would integrate a processing activity and a commercial unit in order to supply caterers and retailers of the Salvador de Bahia area with frozen heads-off shrimps. The project would employ a total of 17 persons full-time and the equivalent of three persons part-time, in addition to the 28 fishermen. At this stage of the project, only the area of Salvador of Bahia is considered for marketing the shrimps. 2.5. Assessment of the enÕironmental impact The environmental studies consisted in a one-off operation which was carried out in order to determine the state of the environment on the pilot site, nearby the cage train, after three years of rearing activities on the site. One of the characteristics of shrimp rearing, like any kind of rearing, is the production of organic sewage Žfaeces, unconsumed feeds.. In earthen ponds, the major consequence of sewage production is an accumulation of organic matter on the pond bottom. Furthermore, mineralisation of the
Fig. 1. Sampling stations for sediment ŽA. and for oxygen measurement ŽB..
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organic matter Žessentially nitrification. and microbial process lead to oxygen consumption in the sediment and in water. In this study, the impact of the rearing has been evaluated through the accumulation of organic matter in the sediment, and the concentration of oxygen in the water. Samples of sediment were taken from 9 stations located beneath and nearby the cages ŽFig. 1A.. Station 1 located 100 m upstream of the cages train is considered a reference station not affected by the rearing cages. Only the upper layer of the sediment Žlayer 0–2 cm. was sampled. Concentration of organic matter in the sediment was determined using the method of ignition loss Ž4508C during 4 h.. The concentration of oxygen was determined with a polarographic probe, type YSI 58, during a 24-h cycle ŽFig. 1B.. Two of five stations Žstations 2 and 4. were located close to Ž- 20 cm. the cages. At station 3, measurements were carried out in the rearing cage. Station 1 located 100 m upstream of the cages was considered as a reference station. Oxygen concentration was determined at 20 cm depth for surface measurements, and at 10 cm above the bottom for deep measurements. Due to the tide, the water depth varied from 1.5 m to 2.5 m during the 24-h cycle period.
3. Results 3.1. Growth and surÕiÕal Average survival rate and FCR for the three tests are given in Table 2. Test C has made possible to obtain a growth curve ŽFig. 2.. Each curve stands for the average between the various cages stocked with the same number of animals. Fig. 3 shows that yield is positively correlated with the final density in tests A Ž r 2 s 0.58; P - 0.05., B Ž r 2 s 0.7; P - 0.01. and C Ž r 2 s 0.89; P - 0.01.. Similarly, growth rate significantly decreases as the rearing density increases ŽFig. 4. with a negative correlation in the three tests: A Ž r 2 s 0.49., B Ž r 2 s 0.56; P - 0.01. and C Ž r 2 s 0.58; P - 0.01.. The regression line for test C is parallel and significantly lower than for tests A and B. The growth rate during the hot season is approximately 23% higher than that obtained during the cool season at similar rearing density. Results show average growth rate of 0.76 g wky1 at a rearing density of 72 animals my2 , monthly mortality rate of 6% and FCR of 2.5 for the 5 months ongrowing phase. The average final weight is 15 g at harvest.
Table 2 Average survival rates and FCR of Penaeus Õannamei in cages Trial
Average survival rate
Average FCR
A B C
76%"13,5 ŽP - 0.05. 63%"10,3 ŽP - 0.05. 57%"8,2 ŽP - 0.05.
2,58"0,22 ŽP - 0.05. 3"0,88 ŽP - 0.05. 3,15"0,24 ŽP - 0.05.
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Fig. 2. Growth curve of P. Õannamei at different stocking densities.
Fig. 3. Correlation curve between yield and final density for trials ŽA., ŽB. and ŽC..
Fig. 4. Correlation curve between daily growth rate and final density for trials ŽA., ŽB. and ŽC..
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Table 3 Investment costs Item
Purchase price ŽUS$.
Useful life Žyears.
Depreciation ŽUS$.
Land with services Buildings Cages Nets Žjuveniles. Nets Žongrowing. Canoes Small motorized boats Fishing boat Ice maker Freezers Laboratory and office equipment Miscellaneous
12,000 79,425 126,504 41,952 93,408 11,200 6,100 15,000 10,000 31,800 9,840 36,762
10 8 3 4 10 10 15 10 5 4 5
7,943 15,813 13,984 23,352 1,120 610 1,000 1,000 6,360 2,460 7,352
Total
473,991
80,994
3.2. InÕestment and operating costs Total capital investment amounting to US$ 474,000 was completed in the first year. Total annual depreciation cost is US$ 81,000 ŽTable 3.. The buildings include a shelter for boats, feed and equipment, an office–laboratory, a processing plant and a storage place for frozen shrimps. The main equipment are 28 unmotorized dugout canoes, one 13-m long wooden fishing boat with a 35 HP engine, two small aluminium boats with a 15 HP off-board engine, 37 household freezers Ž100 l. and a light truck for delivery. Total annual operating costs was computed at US$ 252,000. Total cost including depreciation is US$ 333,200, excluding financial cost ŽTable 4.. Fishermen are assumed to receive a monthly compensation equivalent to the minimum legal salary for their participation in the project. In 1995, the minimum salary in Brazil was US$ 82 per Table 4 Costs of production per year Item
A. Operating costs Post-larvae Feed Fishermen payment Salaries and welfare contributions Gas, oil, electricity Miscellaneous B. Other costs Depreciation Total
Farming ŽUS$.
Processing and Marketing ŽUS$.
Total ŽUS$.
Ratio
49,000 74,200 27,400 28,000 18,600 5,000
0 0 0 31,500 8,000 10,500
49,000 74,200 27,400 59,500 26,600 15,500
14.71% 22.27% 8.22% 17.86% 7.98% 4.65%
62,000
19,000
81,000
24.31%
264,200
69,000
333,200
100.00%
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159
Table 5 Expected costs and revenues over a 10 years horizon year Investment Ž1000 $. Final salvage value Ž1000 $. Operating costs Ž1000 $. Revenues Ž1000 $.
1
2
3
474 262 200
251 460
251 460
4
5
6
7
42
103
69
42
251 460
251 460
251 460
251 460
8
251 460
9
10
230
42 190 251 460
251 460
month. Salaries and welfare contributions of employees amounted to US$ 59,500 per year. Postlarvae cost US$ 4.6 a thousand. Brazilian feed is bought at US$ 0.5 per kg. The production cost of ex-farm shrimps at an average weight of 15 g is estimated at US$ 4.7 per kg. The annual production of processed shrimps is 36 tons on the assumption that 100 kg of shrimp yield 65 kg of tails. The production cost of frozen head-off shrimp at an average weight of 9.9 g Žcount 41–50. is US$ 9.2 per kg, including delivery cost. 3.3. Analysis of profitability The market study points out that shrimp price in the Salvador area depends on the period of the year. When fish landings are low and touristic demand is high, wholesale price for frozen head-off shrimps Žcount 41–50. is high ŽUS$ 14 per kg. from December to March. However prices are below US$ 10 from May to June. On the assumption of an annual average price of US$ 12.6 per kg, annual turn-over is US$ 460,000. With a result of US$ 126,800, a profitability ratio Žresultrturn-over. of 27% may be expected prior deduction of financial expenses and taxes. In order to assess the profitability of the investment, the expected costs and revenues have been calculated over a 10-yr horizon ŽTable 5.. Reinvestment takes place at the end of the expected life value of the equipment, especially year 5 with the renewal of nets and year 9 with the renewal of both nets and cages. The salvage value is calculated for year 10 by deducting ten times the annual depreciation from the total of investment realised during the 10 yr. In these conditions, the Internal Rate of Return is 30%. However, this result has to be put in regard with the high inflation rate in Brazil. Since the implementation of the ‘Real Plan’ in 1994, this rate has been considerably reduced but is still around 24% per year. If the discount rate in Brazil is assumed at 28%, the time for return on investment is seven years. Table 6 Sensitivity analysis Žfor the whole project including farming, processing and marketing. parameter
value of reference
new assumption
new new production profitability cost Žper kg. ratio
Growth rate Food conversion ratio Availability of post-larvae from May to July Yield of tails from a 100 kg of shrimp Minimum monthly legal salary Brazilian market price for shrimp
0.80 g weeky1 2.5 yes 65 kg 82 US$ 12.6 US$ kgy1
0.67 g weeky1 2.0 no 60 kg 100 US$ 10.0 US$ kgy1
9.3 US$ 8.8 US$ 10.9 US$ 10.2 US$ 9.9 US$ 9.2 US$
-0 31% 4% 19% 21% 8%
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3.4. SensitiÕity analysis As a project is designed on the basis of assumptions, it is interesting to assess the impact of the variations of relevant parameters Žbiological, technical or economic. by means of a computerised simulation tool ŽTable 6.. If growth is slower than expected, production cost increases and selling price decreases because shrimps are smaller. In this case, the profitability of the project would be jeopardised. With a FCR of 2, the expected profitability ratio is 15% higher than in reference situation. The dependence of fry from private hatcheries may affect the stocking in the months of May and June. This would lead to lack of shrimps in December when the market price is at the highest. The resulting profitability ratio of 4% would put the project in a very difficult financial position. The process of separating head from tail is critical. Careless or improper separation increases the waste and decreases the profit ŽAiken, 1990.. At this stage, a waste of weight of only 8% will reduce the profitability by 30% for the whole project. The present minimum salary is very low in Brazil. The new socio-economic policy which is in the process of being implemented could lead to better redistribution of the national income. Nevertheless, a moderate increase of 10% in the minimum legal salary would reduce the profitability ratio by 22%. At the moment, the Brazilian shrimp market is not yet pressured by the international competition but it is impossible to exclude an evolution of the price according to the world-wide trend. With a liberalized global market, international prices will pressure Brazilian shrimp growers to lower their prices. Should the price in Salvador fall to US$ 10 per kg, the profitability ratio of the project will decrease to 8%. 3.5. Impact on the enÕironment The concentrations of organic matter in the sediment Žessentially of yellow siliceous sand. samples range from 0.39% to 0.52% ŽTable 7.. At the reference station Žstation 1. the concentration of organic matter is 0.50%. Values observed at stations located beneath the cages are lower or similar to the value of station 1. No gradient of concentration, which would give evidence of organic matter accumulation in the sediment due to rearing activities could be observed. Fig. 5 shows the variations of oxygen concentration during the 24-h cycle for sub-surface ŽFig. 5A. and for bottom ŽFig. 5B. measurements. For surface measurements, values were never lower than 5 mg ly1 . At station 3, the concentrations varied
Table 7 Concentration of organic matter ŽO.M.. in surface layer Ž2 cm. sediment sampled aroud and beneath the rearing cages. STATION O.M. Ž%.
1 0.50
2 0.39
3 0.58
4 0.42
5 0.41
6 0.35
7 0.54
8 0.38
9 0.52
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Fig. 5. Circadian fluctuations of oxygen concentration in and outside the cages. ŽA. concentration at 20 cm deep; ŽB. concentration at 10 cm from bottom sediment; B station 1 I station 2 % station 3 v station 4 ' station 5.
from 5.2 mgy1 Žat 0500 h. in the rearing cage. Oxygen saturation in the cage ranged from 76% to 94%. At 0500 h, the lowest concentrations were observed in the cage Žstation 3., while the highest concentration was in the reference station Žstation 1.. Nevertheless, the difference between the cage and the reference station did not exceed 0.5 mg ly1 and 10% in terms of oxygen concentration and saturation, respectively. A decrease in concentrations was observed in surface measurements at every station, at 1200 h. Generally speaking, the range of variation in oxygen concentrations was less important for bottom than for surface measurements.
4. Discussion 4.1. Production P. Õannamei is almost exclusively produced on the American continent, from Southern United States to Northern Peru and Brazil. Its growth rate in ponds ranges between 0.6 and 1.2 g wky1 . The rates obtained during our tests, i.e., 0.84 g wky1 during the warm season and 0.63 g wky1 during the cool season are within the usual range. An average yield of 800 g my2 cycley1 is obtained in the cages, which gives an annual yield of 2 kg my2 . The high production capacity of cage rearing can result from the conjunction of three phenomena. First, the natural and continuous renewal of the water in the cages allows to maintain its quality for the animals. Contrary to pond rearing, the variations of physico-chemical parameters are moderate and slow, buffered by the huge volume of water all around the cages. The rearing water quality is quite similar to that of the environmental medium and thus depends on the area in which the cages are located. Second, the substrate on which the shrimps rest in the cages, which is constituted by the net covered by the bio-fouling, is continuously oxygenated by the water circulating
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through and on each side of the net. Thus, we were not faced with the problems on accumulation of organic matter or sediment reduction currently observed in earthen ponds ŽHopkins et al., 1994.. Lastly, natural food which consists of the bio-fouling settling on the net, and to a lesser extent of the phytoplankton and the zooplankton. Based on the studies of Anderson et al. Ž1987. and Reymond and Lagardere ` Ž1990., bio-fouling could represent a significant part of the food of the shrimps reared in cage. The contribution of natural food with regard to essential nutrients may make up for the probable nutritional deficiency of commercial pellets available in Brazil. 4.2. Economic aspects In spite of innovative aquaculture technique, relevant social goal and willingness to protect the environment, long term profitability will be adversely affected because of the pressure from international competition. Although the world shrimp aquaculture production has been steady after a long period of soaring expansion, the international market has been rather bleak in 1995. In these conditions, the buyers will give priority for the cheapest products in the market. In the particular context of the project, an expected profitability ratio of 27% seems high enough to take into account the risks connected with a new aquaculture technique. This good profitability is mainly due to the low cost of the processing and marketing activities involved in the project. But the breakdown of the production costs shows that the cage farming technique is not less costly than usual pond farming techniques. Although very little accurate information is available on this topic, production costs for P. Õannamei in Latin America are assessed between US$ 3.50 and US$ 4.50 per kg for an average weight of 16 g ŽVillalon and Preis, 1993.. The main economic constraints in cage shrimp farming are the high cost of capital use Žover US$ 1000 annual depreciation per ton. and the low labour productivity Ž1.3 tons per employee and per year.. Because of the high price and the short useful life of the nets, the cost of capital use is twice as expensive as in pond farms, either in Ecuador or in Thailand ŽChong, 1990.. Despite the very low salary level for unskilled workers in Brazil, the share of labour in the farming production costs is as high as 21% while it is usually under 13% in Latin American pond shrimp farming ŽWeidner, 1993.. This high cost is due to the scattering of shrimp stocks throughout a large area in small units managed by the fishermen with little possibility of automation. Although the initial investment is lower than for an onshore farm using ponds, it is still too high for the local community of fishermen. Private capital or public subsidies should be required, but in both cases the profitability of the investment has not to be the only expectation. Indeed, an Internal Rate of Return of 30% is not very high in the Brazilian context. Moreover, the estimated cash-flow after 10 yr of operation is not high enough to consider wider developments of the project without loans or new contributions from the shareholders. So, such a project should be considered as part of a coastal management programme or as additional activity of a sea-products processing company looking for a better control of the supply. The fact that the fishermen are responsible of their own cages may be considered as a guarantee of efficiency and quality in contrast to
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industrial farms who just hire manpower for basic tasks ŽKongkeo, 1995.. Fair sharing of the benefits between the fishermen and the central organisation should be a corporate policy. 4.3. Impact on the enÕironment After three years of rearing activities, no significant accumulation of organic matter in the sediment could be observed. The concentrations of organic matter beneath or downstream the cages train are not higher than those observed upstream. For rearing activities in earthen ponds, solid organic wastes Žfaeces, unconsumed feeds. pass through a transitory stage, i.e., a settling on the sediment, before being drained off the pond consequently causing accumulation of organic wastes on the pond bottom ŽBoyd, 1992; Fast and Boyd, 1992; Hopkins et al., 1994.. Furthermore, the process of microbial degradation of organic matter occurs essentially on the sediment ŽBlackburn et al., 1988.. The respiration of shrimps, bacterial activity, and plant respiration Žphytoplankton and phytobenthos. in earthen ponds affect consumption of oxygen which is higher than the accumulation of organic matter ŽHansen et al., 1991.. That is the reason why, in earthen ponds, drastic decrease in oxygen concentrations can be observed during the night ŽMadenjian, 1990., which requires the use of mechanical aerators to keep the level of oxygen concentration acceptable for shrimp survival and growth. In the case of rearing cages located in running water, solid wastes are not accumulated near the cages. Unlike ponds, the estuary is not a closed confined system. The low concentrations of organic matter in the sediment observed near the cages and the relatively high concentrations of oxygen during the night demonstrated that the wastes are carried away from the cages. The processes of oxygenation of the sediment due to tide and currents may also be sufficient to allow a quick degradation of organic matter and to compensate the shrimps and of plants Žmacrophytes, phytoplankon. respiration, so that no significant accumulation of organic matter or drastic decrease of oxygen is noted. A decrease in oxygen concentration was observed at 1200 h during the 24-h cycle. This may be due to an inhibition of photosynthesis under the influence of solar irradiation ŽPlatt et al., 1980., which is maximum at that time of the day. This hypothesis is confirmed by the fact that the decrease of concentration and rate of saturation is lower beneath the table, and near the bottom than the surface of the water. In cages, the shrimps are not ‘sheltered’ from solar irradiation. Preliminary results showed that near and in the cages, the concentrations of total suspended matter were lower than 12 mg ly1 and 5 mg ly1 at low tide and high tide respectively ŽJ.L.M. Martin, unpublished data.. The quick turn-over of water in the estuary and in the cages prevents the development of phytoplanktonic blooms. In earthen ponds the shrimps are sheltered by the phytoplanktonic bloom. In ponds, the sestonic condition corresponds to controlled eutrophic conditions ŽPruder, 1986. where concentrations of total suspended matter are often higher than 100 mg ly1 ŽHopkins et al., 1993; Briggs and Funge-Smith, 1994.. Furthermore, shrimps can not bury themselves in mesh cages. P. Õannamei is not a burying species but like most other penaeide shrimps ŽWassenberg and Hill, 1994., it is nocturnal and emerges from the bottom in the evening, when light is dim. It slows down activities in the morning and goes to the bottom, usually before dawn. Therefore,
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experiments are needed to determine whether the shading of the cages can affect shrimp growth.
5. Conclusion After three years of field experiments, the technology and husbandry practices of shrimp culture in floating cages have been proven to be very efficient from a zootechnical standpoint. Such parameters as growth rate, survival rate and FCR are at the same level than the best results obtained in intensive pond farming. The economic analysis shows that a pilot scale project aiming at producing 60 tons of shrimps per year would be profitable in the context of the market of Salvador de Bahia and would make possible to provide an additional income to the local community of fishermen on their own living spot. As far as the studied area is concerned, the zootechnical, economic and environmental data are good basis to plan a future development for this project. Such a development could be done without damaging the coastal ecosystem since there is no irreversible construction and no high concentration of shrimps in a closed space. According to the environmental or economic conditions, it would be easy to add or suppress cages, or to move them to another place. This rearing technique seems appropriate for a good resource management. However, the profitability of the technique is still sensitive to variations of biological parameters and market conditions. So, the results may be different in other geographical and socio-economic environments. No impact on the environment has been noticed under the experimental cages during the time of experiments, and the shrimps are in very good rearing conditions since they are not in contact with organic wastes. Therefore, the premium quality of the product should be a feature to valorise. Thanks to the original ongrowing conditions, the yield is very homogeneous in size, the gills are mud-free and there are very few wounds or spots on the shells. That is the reason why this project has to look for competitive advantages more in terms of quality and image than in terms of low price. The production costs in cages are hampered by the short useful life of the nets and by the weak labour productivity of the system. On the contrary, the environmental friendliness and the positive social impact of the technique are assets to take into account. Like other shrimp farming projects which cannot take advantage of low production costs, it should aim at developing niche markets, thanks to quality monitoring, control of the marketing and brand promotion ŽRhodes, 1990.. As such a policy would induce higher costs in processing and marketing, productivity gains during the cage farming phase are still a major goal for the future experiments.
Acknowledgements This research project has been developed in the framework of the France–Brazil cooperation in Oceanology with the support of the State of Bahia, the Odebrecht company ŽBrazil., the French Embassy in Brazil and IFREMER ŽInstitut Franc¸ais de Recherche pour l’Exploitation de la Mer..
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