APPENDIX I
SURVEY MISSION SCHEDULE

12 February - 10 April 1986

APPENDIX II
List of Persons Met

APPENDIX III
PROBLEMS OF POND CONSTRUCTION AND MAINTENANCE ON CAT CLAY SOILS

Ricardo G. Hechanova
Manila, Philippines

from: FAO (1984) Inland Aquaculture Engineering - Lectures presented at the ADCP Interregional Training Course in Inland Aquaculture Engineering, Budapest, 6 June-3 September 1983. Rome, p. 267–74. ADCP/REP/84/21.

1. INTRODUCTION

With the increased demands for freshwater and brackishwater aquaculture, areas with potential acid sulphate conditions are increasingly being placed under cultivation. Aquaculture is probably the most suitable use for areas with actual acidity.

The distribution of acid sulphate soils is world-wide with large areas found in the tropical deltaic and coastal zones. Tang (1979) estimated that at least 60 percent of the fishponds in the Philippines are affected by acid sulphate conditions. The low production of milkfish ponds in the Philippines for instance, could be attributable at least in part to the occurrence of acid sulphate soils.

Of the estimated 500 million ha of fine-textured soils in coastal areas, 11.4 million ha are highly pyritic, which will acidify upon aeration. The extent of actual and potential acid sulphate soils in West Africa may be about 3.7 million ha (FAO/Unesco, 1974) and smaller areas are also found in the coastal zones of the Netherlands, Sweden and Finland (Bloomfield and Coulter, 1973).

About 6 million ha are found in Southeast and East Asia, with Indonesia having 2 million (Driessen and Suproptohardjo, 1974) and Vietnam having 1 million (Tram and Lieu, 1975), the largest share.

Improved technology in reclamation of these soils has been developed at the Brackish-water Aquaculture Centre (BAC) of the University of the Philippines in Leganes, Iloilo in the Philippines. Improved methods of construction and maintenance have been developed in Southeast Asia and elsewhere where acid sulphate soils have been reported.

The use of the prefix ‘cat’ in the cat-clay soil name comes from the Dutch vernacular ‘kattekleigronden’. ‘Cat-clay soils’, the English derived from this, was connotative of harmful, mysterious influences or qualities. Traditionally, the expression ‘acid sulphate soils’ is used to denote soils with cat clay phenomena, those which have a very low pH and yellow jarositic mottles after drainage and aeration of the originally waterlogged parent material.

A potential acid sulphate soil or material is a soil or a reduced parent material which is expected by the person identifying it to become acid sulphate soil upon drainage and oxidation.

2. FORMATION OF ACID SULPHATE SOILS

The genesis of acid sulphate soils is mainly in the formation of pyrite. Pyrite formation involves the bacterial reduction of sulphate to sulphide, partial oxidation of the sulphide to elemental sulphur, and the interaction between ferrous and feric iron with the sulphide and elemental sulphur. The basic factors therefore required for the formation of acid sulphate soils are a sufficient supply of sulphate, iron, high organic matter, presence of the sulphate reducing bacteria Desulfovibric desulfuricans and Desulfomacultom and an aerobic environment alternated with limited aeration.

Fine-grained iron oxide is found in sufficient quantities in the clayey sediments of tidal swamps, though iron could be limited in sandy and peaty soils. Dense mangrove vegetation supplies abundant organic matter. Fine-grained iron oxide and metabolizable organic matter are the essential ingredients required for pyrite formation (Singh, 1980).

In the zone between mean high water and mean low water, pyrite formation is most favourable due to aeration during periods of tide changes. Less pyrite is accumulated in the zone below low tide level. In the better drained zone above the high water level which is aerobic most of the time, there is less occurrence of pyrite.

Potential acidity develops gradually due to the removal from the system by tidal action of a part of the alkalinity in the form of bicarbonates (HCO₃) formed during sulphate reduction.

The reaction of sulphur reducing bacteria involved in pyrite formation can be described as follows:

The final pH of the soil after drainage and drying depends on the amount of pyrite oxidized and the acid neutralizing component in the soil, as silicates, carbonates and exchangeable bases. In the humid tropics carbonates are practically absent in coastal sediments. Volcanic areas provide sediments rich in weatherable silicate minerals and the presence of such minerals provides a high amount of acid neutralizing agent. This prevents development of potential acidity in the coastal tidal flats.

3. FIELD IDENTIFICATION

There is no single commonly accepted method for the identification and for the prediction of acid sulphate soils. Actual acid sulphate soils are not common; far more abundant are potential acid sulphate soils for which recognition in undrained or waterlogged areas is generally difficult.

Evaluation of a technique for determining potential acidity was conducted in BAC fishponds in 1972 (IFP Technical Report 10). It was found that incubation of the moist soil samples in thin plastic bags for a period of 30 days appears to be an effective technique for the identification of potential acid sulphate soils.

The rate of oxidation is regulated by the iron oxidizing bacteria. If a soil is dried rapidly, the bacteria is inactivated, oxidation is slow, and it may take many months for the soil to reach its maximum acidity. If the soil is kept in a moist aerobic condition, the iron oxide bacteria thrive and the development of soil acidity is attained within a few weeks. The plastic bags allow pyrite oxidation to proceed while maintaining the soil moisture. The pH of the samples with potential acidity dropped to 4.0 or less in this time period. Yellow, jarositic mottles appeared on the sample. This technique of soil survey has been accepted due to ease of use.

The detection of actual acid sulphate soils presents no difficulty as these soils are characterized by pale yellow, jarositic mottles.

Black stained and odorous mud due to ferrous and hydrogen sulphides that turn brown upon exposure is also an indication of soil that may contain pyrite.

The occurrence of mounds of the mud lobster, Thalassina anomala in brackishwater tidal swamps indicate the occurrence of acid sulphate soils.

Acid sulphate in pond soil can be recognized by the very low pH values (below 4) measured in the pond water when it is flooded for the first time after a drying period, by the reddish iron oxides that form on the pond bottom shortly after flooding, and by the poor growth or absence of algae (Brinkman and Singh, 1982).

Association of Rhizophora, Nypa fruticans and Meleuca stands found in tidal brackish-water swamps is usually a strong indication of potential acid sulphate soils, whereas those of Avicenia are less acidic.

Surface efflorescence of water soluble aluminium sulphate, formed under strongly evaporative conditions when pyrite oxidizes at shallow depth, are commonly found in ponds which are newly constructed on potential acid sulphate soils.

Fish kills and the bitter taste of river water that drains sulphidic materials are indicative of a potential acid sulphate area.

Acid sulphate in the dikes can be recognized by the poor and spotty growth of vegetation on them several years after construction.

The sharp sour-bitter taste (like alum) of pale yellow coloured salts generally found near the base of the dikes is also a clear indication of acid sulphate salts.

A potential acid sulphate soil may have a pH near normal, but when oxidized by drying or with 30 percent hydrogen peroxide, the pH drops by about two or three units, generally below 4 (Singh, 1980).

The red lead pole test can be conducted during a field survey. Stakes coated with red lead paint are driven into the soil. Hydrogen sulphide generated in sulphate reduction turns the red lead marking to black within one week.

These field characteristics are often not well-defined indications. A number of complementary tests are required to determine the physical and chemical properties so as to be able to assess the degree of acidity quantitatively and to design improvement schemes and measures.

Acid sulphate conditions are not permanent although they may cause tremendous problems while they exist. The problems faced by farmers in fishponds built on acid sulphate soil include low fish yields (Rabanal and Tang, 1974), slow growth of fish, slow rate of natural fish food production, fish kills due to acidity, erosion of the pond dikes, and soft shell prawns (IFP, 1974; Potter, 1976; Camacho, 1977; Singh, 1980, 1982, and Cook, 1978).

In acidic ponds, the growth of algae is discouraged by the low pH of the water, by the dark brown of the water, and the high aluminium and low phosphate concentrations.

Poor response to phosphorous fertilizer is another indication in fishponds with acid sulphate soils.

Active iron and aluminium in acid sulphate soils are capable of precipitating phosphate as compounds at low pH and oxidizing conditions. Phosphate already bound with aluminium generally does not become available (Singh, 1982).

4. PROBLEMS OF POND CONSTRUCTION AND PLANNING

When fishponds are constructed, blocks of silty clay are dug and built into earth dikes. On exposure, the surface of these clay blocks becomes grey-coloured due to the oxidation of the ferric sulphide, FeS₂. Pond systems which have been excavated from this typical clay present an uneconomical development in the utilization of the land for aquaculture.

Where dikes are constructed from acid soil excavated from the pond bottom area, it is best to place the ‘bad’ soil at the dike bottom and make the outer dike shell of pond top soil. The poor subsoil can be used for the dike core and the outer surface can be covered with the top soil, as generally soil with low potential acidity overlies soil with high potential acidity. It was found during research studies at the BAC that the top soil (0–30 cm in depth) was less acidic than the subsoil (30–100 cm in depth) upon oxidation.

Another method of fishpond construction is to build the dikes of soil taken from alternate borrow trenches paralleling the dike. The remaining alternate trenches are levelled to the desired pond bottom elevation. This method is a sort of compromise with the dike built of half the bad and half the good soil.

A ratio of dike soil mass to pond soil mass to 0.15 m depth has been determined from recent experimental studies and research at the Brackishwater Aquaculture Centre (BAC) in the Philippines. Reduction of the amount of rainwater runoff from the dikes to the ponds is better accomplished when the size of the pond is increased with a relative decrease in dike size. A minimum ratio, for soil improvement in the least period of time, is when the mass of soil in the pond, to a depth of 0.15 m, is equal to the mass of dike soil.

If the pond bottom is low and the earth excavated is put into large dikes the effective pond area is reduced, with consequent increase in the acid runoff into the ponds. A better approach would be to build the ponds with higher bottoms and have the tidal water supplemented by pumping water into the ponds. Pumping increases operating costs, but this may be offset by reduced construction cost and by increases in production.

5. REMEDIES FOR PONDS BUILT ON ACID SULPHATE SOILS

Experiments in unreclaimed ponds of the BAC were conducted by Poernomo in 1982 using a rapid reclamation scheme. Earlier experiments were also conducted by Camacho in 1977 at BAC and at different locations in Panay Island by Singh in 1980. The basic concept in all these studies was to remove the source of acidity by oxidizing the pyrite from the pond bottom and flushing it out. At the same time the acid materials and other toxic elements from the big dikes were also leached and removed. The details of the workplan adopted by Poernomo (1982) from Brinkman and Singh (1982) are quoted below:

'The procedure involves a precisely planned sequence of filling, draining and drying the ponds, cultivation by tooth harrow and finally broadcasting a small amount of lime in the pond soil. In the same period, the top of the surrounding dikes should be made into a series of long narrow paddies by small levees along their edges, and seawater pumped or carried into them.

A pH meter or a roll or strips of pH indicator paper should be available. A tooth harrow and draft animal are needed for the cultivation of the pond bottom. A small diesel-powered pump mounted in a small boat or on a raft of bamboo or oil drums makes it possible to rapidly inundate the tops of the dikes. About 1 ton of powdered agricultural lime per ha is also required.

The workplan can be completed in about 3 months. All the work should be done in the dry season. Treatment of the pond bottom and of the dikes should proceed at the same time. During the first heavy rains after the pond is again in operation, some further work should be done, as described below.

Treatment of the pond bottom

In the early part of the dry season, the pond has to be prepared for removal of the acid. This is done by drying the pond thoroughly. Small drains should be dug to let all remaining patches of standing water run dry. The pond bottom should be tilled after one week by tooth harrow in two directions. It should be harrowed after thorough drying (cracks to appear in the soil to about 10 cm depth) so that the surface layer is broken into small pieces. If there is no rain, the total drying period will probably take 2 to 3 weeks.

The acid in the dry layer is ready to be removed. Brackishwater or salt water is brought in to fill the pond. Measure the pH of the water immediately after filling and every few hours thereafter. The pH is expected to drop rapidly from that of seawater (7 to 9) to a value lower than 4, often 3.

At the first opportunity after the pH has become constant, drain the pond and make sure that this water goes to the sea and not to any other pond. This treatment removes part of the acid.

Refill the pond and again check the pH. Again drain the water as soon as possible after it has a constant pH. Repeat the refilling and the draining process as long as constant pH is about 4 or below. This may take less than a week (4–6 refills) to about 2 weeks. When the water remains at a higher pH, drain it and thoroughly dry the pond bottom again as described above.

After thorough drying, cultivate the pond bottom and again refill as described above. This time, the pH probably will not drop as low as in the first series of filling and drying. When the pH remains above 5 after 1 to 3 drying cycles, drain and broadcast 500 kg agricultural lime per ha (not calcium oxide or calcium hydroxide) well-distributed over the pond bottom. Do not incorporate the lime into the soil. The pond is then ready to start normal operations if the dikes have also been treated.

Treatment of the dikes

At the same time as the acids are removed out of the pond bottom, the acids in and on the dikes should also be removed. Because the dikes are normally dry, the acid can be washed out without first drying as is needed for the pond bottom. Small levees, similar to the levees between wetland rice fields, should be constructed on the top of the dikes along both sides and the surface between them should be levelled. At the same time, any holes in the top surface should be filled.

To avoid excessive amounts of earth removal, this bunding and levelling can be done separately for each section of dike depending on its elevation. The work should be completed by the time the pond bottom has dried out and is ready for the first filling with water.

At that time, seawater or brackishwater should be pumped or brought into the levelled paddies on top of the dikes, enough to keep them flooded to more than 10 cm depth. At first it will be necessary to check the whole top surface and the length of the small levees for leaks. Acid water will soon seep out toward the pond or the canal. Pumping of seawater from the intake canal should be continued as necessary to keep all the tops of the dikes flooded. When the pond bottom is ready to be dried thoroughly again, stop pumping and allow the top of the dikes to dry out. If there is still some water standing after two days, drain this, to the canal if possible, otherwise through the pond. When the pond bottom has thoroughly dried and has been cultivated, the top of the dike should be flooded again during the next series of filling and draining the pond. When the pH of the water in the pond remains 5, stop flooding the top of the dike and remove the standing water.

On dikes between two ponds, remove both levees and bring this soil toward the centre. Make the top of the dikes smooth and slightly sloping from the centre to both sides. Do not leave loose soil lying about. On dikes along a canal remove only the levee along the side of the canal and bring the soil toward the other levee. Make the top of these dikes smooth and slightly sloping toward the canal.

Then broadcast 1 kg of agricultural lime per 10 m² on the slope of the dike along each pond and 1 kg per 20 m² on the top of the dikes between the ponds.

The same problem of acidic rainwater runoff from the dikes to the ponds was encountered at the Brackishwater Aquaculture Centre in Gelang Patah, Johore Bahru in peninsular Malaysia, causing fish kills and retarded growth of the fish. The acidic runoff was found to be potentially due to acid sulphate condition of the soil material of the dikes which are massive and with flat side slopes.

6. MANAGEMENT MEASURES

The usual amount of chicken manure of 2 t/ha is distributed over the pond bottom. To increase the rate of phosphate fixation, rice hulls, ash of rice hulls or filterpress mud from the sugar mills can be spread over the pond bottom before spreading the chicken manure. A few days later, initial amounts of nitrogen fertilizer are broadcast in the pond water. In contrast to the usual practice in non-acid fishponds of broadcasting the recommended phosphate amounts once every 2 or 3 weeks, the phosphate should be divided into portions and broadcast every 2 days, or weekly portions should be placed in jute bags on floating platforms at two platforms per hectare, to dissolve slowly. By these methods the phosphate concentration in the pond water can be kept high enough for good growth of algae, without excessive amounts of fixation on the material of the pond bottom.

Experimental and research work was conducted at BAC by D.J. Hechanova from January to August, 1981, on the effects of various organic materials on the changes in the chemical properties of soil and water systems of submerged acid sulphate soils. Seven treatments were used including the application of burnt rice hulls, partly decomposed rice hulls, chicken manure at 2 t/ha, and Fertilex, an organic commercial fertilizer, all in combination with mono ammonium phosphate (16-20-0), and mono ammonium phosphate alone. Marfon, a fertilizer/soil conditioner produced from fermented rice hulls was also used at 5 t/ha.

The findings showed that the Marfon and chicken manure applications showed the lowest concentration of sulphates resulting in the soil and the supernatant. The decrease was due to the reduction of sulphate or sulphates under anaerobic conditions and also due to the high organic matter content of these materials.

7. SUMMARY AND CONCLUSIONS

Low rates of liming give more favourable results than large-scale liming. Regular application at 500 kg/ha of powdered lime on the pond bottom before the first flooding of the pond speeds up the reduction and lowers peak concentrations of toxins. Toxins may be released into the pond water following the application of organic material. The lime is not incorporated into the soil.

Phosphate should be made available by a slow release or in frequent and small doses. Slow release is attained by the construction of a fertilizer platform inside the pond at such elevation so that the water surface is above the platform to wet half of the fertilizer mass, usually contained in a sack. The fertilizer on the platform is released in small doses as it is partly wetted.

Prior to pond development, a detailed soil survey should be conducted and when the area is identified to be potential acid sulphate soil, appropriate designs and construction methods should be adopted.

If no growth of algae is observed within a week, the water should be inoculated with algae collected from normal fishponds.

The pond water pH should be monitored regularly and if it becomes acidic and below the tolerable limit, a small quantity of agricultural lime should be broadcast in the water, but when the pond water becomes turbid it should be replaced by new brackishwater before fertilization. The new pond water is left to stay for a week after fertilizer and lime application.

Fish culture is started in the first year after reclamation, with stocking of older and heavier fingerlings than is usual for non-acidic ponds.

8. REFERENCES

Bloomfield, C. and J.K. Coulter, 1973 Genesis and management of acid sulfate soils. Adv.Agron., 25:265–326

Brinkman, R. and L.J. Pons, 1973 Recognition and prediction of acid sulfate soil conditions. In Proceedings of an International Symposium. Publ.Inst.Land Reclam.Improv., Wageningen, (18) Vol. 2

Brinkman, R. and V.P. Singh, 1982 Rapid reclamation of brackishwater fishponds in acid sulfate soils. Publ.Inst.Land Reclam.Improv., Wageningen, (31): 318-30

Camacho, A.S., 1977 Implications of acid sulfate soils in tropical fish culture. Manila, South China Sea Fisheries Development and Coordinating Programme, SCS/GEN/77/5:97–102

Cook, H.L., 1978 Problems in shrimp culture in the South China Sea Region, SCS/76/WP/40, SCP, Manila, Philippines

Driessen, P.M. and Suproptohardjo, 1974 Soils for agricultural expansion in Indonesia. Bull.Soil Res.Inst., Bogor, (1): 63 p.

FAO/Unesco, Soil map of the world, 1:5 000 000. Paris, Unesco, 59 p.

Hechanova, D.J., 1983 Chemical changes in sumberged acid sulfate soils-water system treated with some organic materials. Masters thesis. University of the Philippines, Iloilo City, (Unpubl.)

Inland Fisheries Project, 1974 Causes of bangus kills in ponds at the Brackishwater Aquaculture Centre following a heavy rain. Tech.Rep.Inland Fish.Proj.Philipp., (5): 21–43

Institute for Land Reclamation and Improvement, 1973 Proceedings of the International Symposium on acid sulphate soils. Publ.Inst.Land Reclam.Improv., Wageningen, (18) 2 vols.

Poernomo, A.T. and V.P. Singh, 1982 Problems, field identification and practical solutions of acid sulfate soils for brackishwater fishponds. In Report of Consultation/Seminar on coastal fishpond engineering. 4–12 August 1982, Surabaya. Manila, South China Sea Fisheries Development and Coordinating Programme, SCS/GEN/82/42:49–62

Pons, L.J., 1973 Outline of genesis, characteristics, classification and improvement of acid sulfate soils. Publ.Inst.Land Reclam.Improv., Wageningen, (18) Vol. 2:3–27

Potter, T., 1976 The problems to fish culture associated with acid sulfate soils and methods for their improvement. In Report on the ASEAN Seminar/Workshop on Shrimp Culture, 15–23 Nov. 1976, Iloilo, Philippines. Manila, ASEAN National Coordinating Agency of the Philippines

Rabanal, H.R. and Y. Tang, 1974 Comprehensive fishfarm development training course (4th session). Field Extension Unit II. Report No. 1

Singh, V.P., 1980 The management of fishponds with acid sulfate soils. Asian Aquacult., 3(4):4–6

Singh, V.P., 1982 Kinetics of acidification during drying and inundation of acid sulfate soil material: implications for the management of brackishwater fishponds. Publ.Inst.Land Reclam.Improv., Wageningen, (31):331–53

Singh, V.P., 1982 Management of acid sulfate soils for brackishwater fishponds: experience in the Philippines. Publ.Inst.Land Reclam.Improv., Wageningen, (31):354–66

Tang, Y.A., 1979 Physical problems in fishfarm construction. In Advances in aquaculture, edited by T.V.R. Pillay and W.A. Dill. Farnham, Surrey, Fishing News Books Ltd., for FAO, pp. 99–104

Tram, H.V. and L. Pham Ng, 1975 Problem soils in the Mekong delta of Vietnam: a general description and implication of rice cultivation. Paper presented at the International Rice Research Conference, Los Baños, Philippines, 9 p. (mimeo)

APPENDIX IV
THE SALT INDUSTRY IN KENYA AND ITS POTENTIAL ROLE IN COASTAL AQUACULTURE DEVELOPMENT

1. History

The salt industry in Kenya dates back as early as 1910 when it was introduced by the Germans at the Fundisa area, about 40 km north of Malindi. The original site was later abandoned and the Fundisa saltworks is now actually in Gogoni. Up to 1977, the industry remained small, with only two companies involved.

In 1977, the Government of Kenya together with Saltech of Italy invested in a salt refinery in Mombasa using raw salt imported from Eritrea and Australia. With that as a start, the company now known as Kensalt expanded backward into solar salt-making, occupying the area left by Fundisa and expanding the area to eventually occupy 2 264 ha of which 50 percent was mangrove area.

The industry has since grown, with a total of six companies already operating and two more in the developmental stage. Together the eight companies occupy a total of 7 922 ha of tidal swamps and tidal flats within the Ngomeni to Kurawa area as shown in Figure A-1. Attempts by small, individual investors were made at Mida Creek, Bodo (near Shimoni) and Kilifi Creek. It appears that only the one in Kilifi is still operating.

Total volume of raw salt produce in Kenya is estimated at 70 000 tons per year which at KSh. 700/ton translates to KSh. 49 million.

2. Saltworks Design and Operation

The saltworks in Kenya are generally built mostly within the tidal flats behind the mangrove zone. Within this area, development would not be costly since these are clear areas with very little patches of vegetation if any. As much as possible, the companies have tried to restrict themselves to these clear areas, but many have since expanded toward the mangrove.

The typical saltworks consist of a series of ponds where the brine is transferred as it gets progressively more saline. As many as six transfers are involved from the first reservoir through a series of three evaporation ponds, then to a serving pond, an finally to the crystallizers, as shown in the Figure A-2.

While the basic pattern would be the same from one saltworks to another, the saltworks do not seem to follow any standard design, in terms of percentage area allocation for the various ponds or in terms of the number of times that a pump has to be used to move the brine.

Some companies would have their first reservoir set at the lowest elevation (normally the mangrove area) to allow seawater to enter during high tide through large concrete gates. In the first reservoir, the impounded water is then pumped to a second reservoir from where the water is simply moved by gravity from one evaporation pond to another. In some other companies water is pumped into the first reservoir from a small pre-storage pond which actually acts as an oversized sump. In still other companies pumps may be needed in as many as three different points to transfer the brine from one pond to another.

3. Possible Role in Aquaculture Development

3.1 Foundation for coastal aquaculture

Although there is no coastal aquaculture as yet in Kenya, such an industry will not exactly be starting from scratch. The physical facilities, civil works and equipment required for aquaculture is common with that for the salt industry. This means that work norms and pond construction approaches under local conditions are already established. This can already be used as a basis for estimting development costs at a fairly high confidence level. Furthermore, this would also mean that there is an existing pool of manpower with actual experience in all aspects of pond construction.

But perhaps the most significant role that the salt industry can play in the development of coastal aquaculture in Kenya is something more direct and immediate. With very little or perhaps even no modification, the first reservoirs of the saltworks are ready-made extensive ponds awaiting only the introduction of seed material.

3.2 Reservoir as extensive shrimp pond

The seawater in the reservoir is always freshly drawn and would therefore have a salinity which would not yet vary too much from that of the Indian Ocean's 35–37 ppm. The rate of exchange is very high since the pumps are constantly in operation. The depth of water in this pond could range between 0.5 m to as deep as 2.0 m. There would normally always be some residual water left due to the irregularity of the bottom.

The reservoir would occupy from 7 to 15 percent of the saltworks' total area. The existing companies now in operation would have an aggregate reservoir area of 600 ha. Once the two new saltworks become operational the total area would reach 800 ha.

Using the Philippine experience as a basis, where extensive shrimp ponds can be stocked at a maximum of only 5 000 P. monodon per ha if they are to subsist and grow on the naturally occurring food in the ponds, these reservoir ponds could be made to produce at least 120 tons a year. (This figure is based on 50 percent survival, 30 individuals per kg at harvest, two cycles a year). This projection could be considered very conservative since the deeper water of the reservoir plus the constant renewal would in most likelihood allow for much higher stocking rates and carrying capacity.

3.3 Evaporation pond as Artemia ponds

Another entry point for aquaculture are the evaporation ponds where the brine attains a concentration of 60–90 ppm. This would be ideal for the brine shrimp, Artemia salina. The use of saltfarms for brine shrimp culture is already being practiced in Thailand where both cysts and biomass are being harvested. Here in Kenya experiments are now in progress under the joint auspices of the Kenya Marine and Fisheries Research Institute, and the Artemia Reference Center, University of Ghent, Belgium. Two saltworks have been seeded: Kensalt and Kurawa.

The brine shrimp offers two valuable products: cysts both for the shrimp hatcheries to be established in Kenya and for export where it can command as high as $ 50 per kg, and live biomass as feed for P. monodon. The production of live biomass as direct feed even at a supplemental basis could help alleviate one possible constraint to shrimp production in Kenya.

3.4 Inteqrating aquaculture with saltworks

Perhaps the most exciting concept that should be explored is integrating brine shrimp and P. monodon production with the saltworks. Once the baseline data on biomass production per unit area per unit time is established, then it would not be difficult to determine the maximum amount of P. monodon biomass that a given saltworks area could sustain. From there the right ration of shrimp farm to evaporating pond could be calculated. Once a good rate of return can be demonstrated, the saltworks companies will not need any more convincing to go into shrimp production simultaneous with salt-making.

Figure A 1. Extent of area claimed or occupied by saltwork companies along the Kurawa to Ngomeni coastline, Kenya.

Figure A -2. Generalized layout of a saltwork in Kenya.

APPENDIX V
COST COMPARISON ON MANUAL VERSUS MECHANICAL POND CONSTRUCTION

1. Cost Estimates for the Construction of 5.0 ha Coastal Pond by Manual Labour in Kenya

¹ Materials to be taken along areas parallel to the dike

² Materials to be taken from higher ground to fill and level areas where diking materials were taken.

2. Cost Estimates for the Construction of 5.0 ha Pond by Mechanized Method in Kenya ¹

Earthworks

(a) Diking/levelling ² - 8 400 mm³ at KSh. 16/m³ 134 400

Pond Structures

¹ Estimates obtained from construction data of saltworks

² Materials to be taken from inside of the ponds and pushing distance of not more than 50 m.

APPENDIX VI
SINGLE-FAMILY VERSUS ESTATE CONCEPTS OF AQUACULTURE DEVELOPMENT

1. Pre-Investment Phase

1.1 Similarities

There are many points in common to the two concepts during the pre-investment stage. In both cases an appropriate government agency or parastatal body conducts a baseline socio-economic study to identify and determine target beneficiaries, and a feasibility study to determine the magnitude, technical and financial viability, as well as economic and other social benefits. Once the magnitude of investment is ascertained the necessary funding is obtained either through budgetary allocations, domestic or foreign loans or through combinations of any of these three funding sources. The similarity ends here.

In the case of bank loans, a financial and technical appraisal follows the feasibility study.

1.2 Differences

In single-family schemes, the funds are deposited with an appropriate financing institution such as a development bank, for on-lending to qualified borrowers on agreed terms and conditions. In the estate concept the funds coming from budgetary allocations will be given to a specially formed parastatal body as government equity and will be used used as counterpart funds to obtain further financing through domestic or foreign borrowing, as well as to finance the design and detailed engineering phase.

2. Development Phase

2.1 Single-Family Scheme

In the single-family schemes, the financing and loan implementation is handled by the designated bank, and technical aspects are handled either by specially trained in-house technical staff or through fisheries extension officers. A training programme for qualified and interested beneficiaries will be launched and made as precondition for borrowing, and indeed the training of lending bank's staff is sometimes necessary and would be part of the financing package. Each participant will find a suitable area with the assistance of the bank's technical staff or the fisheries extension officers. Each participant will then be asked to prepare either a full feasibility study or a pro forma study to determine the exact financial requirements and the financial and technical viability of the proposal. Each participant would have considerable liberty, within prescribed guidelines, in determining total areas to be developed (up to some predetermined ceiling), stocking density and culture method. The money will be released in stages based upon progress of work. The participating borrower will be responsible for getting his ponds developed.

2.2 Estate Concept

Under the estate concept, a project implementation unit is established and adequately staffed. A large site is selected based upon a previous feasibility study. The estate management then sets out to develop the area according to a predetermined work programme. The family-size ponds, hatchery, feedmill, processing plant, and other support infrastructures are constructed. Simultaneously the participant beneficiaries shall be selected, based on certain criteria. Training programmes are also launched as a precondition to selection. Ideally the participants should already have received proper training by the time the family ponds are ready for allocation and the support facilities already operational.

3. Operation Phase

3.1 Single-Family Scheme

Once the ponds have been developed, each participant borrower shall then have to acquire the inputs required using a pre-set working capital. He then prepares the ponds and stock under close supervision of the extension technicians especially during the initial phase. Each farm is managed and operated as an independent unit. At harvest, he is responsible for marketing the products, and is then expected to repay his loan according to a pre-set schedule.

3.2 Estate Concept

The estate's central hatchery produces the fry, sells them to beneficiaries, who stock them in the individual family ponds according to a set schedule. Once stocked, each participant shall be responsible for their care and maintenance. He shall see to it that the water is changed and adequate food is available. All pond inputs shall be provided by a central estate storehouse. The estate management monitors the progress through extension technicians and determines whether the stock is ready for harvest. Harvesting is then done by the estate's harvest crew. The harvest is sent to a processing centre, weighed and receipted. Marketing is done by the estate management. The amounts needed for amortizing the loan and payment for the inputs are deducted from the proceeds and the remaining balance is released to each participant as his earnings.

4. Financial Management Aspects

4.1 Flow of Funds

In the estate concept the flow of funds is greatly simplified: Financing institutions lend money to the Government which on-lends to parastatals on agreed terms or subscribe to quity. The Parastatal, which in this case is estate management, on-lend to participants, either in kind for various inputs or in cash for reimbursement of expenses connected with pond preparation, stocking, etc. The repayment from the borrower to the estate management also is in the form of a percentage of the harvest. Money flows from the estate management to the beneficiaries only in the form of duly earned income. During the initial operation phase, arrangements may be made for working capital to be released to the beneficiaries as anadvance chargeable against future harvest.

In the single-family supervised credit scheme, money changes hands for each activity from bank to beneficiaries during the development phase, then from beneficiaries to the bank during operations.

4.2 Risks

In the estate concept, the programme shall be run by a professional management staff with each participant expected to concentrate only on the culture aspects under close supervision. In the single-family scheme each beneficiary has to act as his own operations and financial manager. Since the programme will be designed to benefit the poorest of the poor, it can be assumed that they will lack the necessary skill and experience necessary to effectively manage the fund released to them as a loan. While the estate concept, like all other ventures, is not without its risks, these are greatly minimized. Thus, from the point of view of a financing institution, the estate concept under a professional management will be more bankable, provided the estate approach is undertaken as a sound commercial operation.

APPENDIX VII
BEYOND SHRIMP FARMING

1. Rationale

There are several reasons why it would be advisable to explore other species and culture schemes, rather than pond shrimp farming, in a long-range plan to develop coastal aquaculture in Kenya:

1. The physical limitations in the form of area available for shrimp farm development as determined in this present survey

2. The need to balance off luxury cash-crop production with low-cost protein production

3. The need to benefit more people in any such development programme which would be severely limited in shrimp farming due to the high investment required per viable production unit

4. The possibility of extending some form of aquaculture development even in those areas found unsuitable for shrimp farm development.

2. Species Selection

In selecting a species it would be important to consider the following factors: availability of seed material or availability of technology for mass propagation, feeding habits, environmental requirements, hardiness, rate of growth and marketability. The bottom line, of course, is ultimately economic viability.

It is unfortunate that in the face of the bewildering diversity of marine life, the option available in terms of species is severely limited. It should be remembered that project KEN/80/018 originally considered rabbitfish and mullet, but dropped them early on due to the apparent paucity of natural fry supply and initial preference to concentrate on a single crop (P. indicus). Thus, in Kenya it appears that coastal aquaculture may have to “borrow” a species from inland fisheries: Tilapia. Another species that could be looked into is the brine shrimp Artemia. Finally, the profuse growth of oysters within the mangroves of Lamu, suggests itself as a potential species to be looked into, although careful handling and quality control requirements will mean that strong logistic support will be needed.

3. Exploratory Approach

At present, Tilapia mossambica already occurs as a pest species at the pilot shrimp ponds of Ngomeni. Ordinarily a total of some 5–10 kg of Tilapia is reportedly harvested together with the shrimps. These fish are however undersized with weights of no more than 50 g each. Consequently, these have a very low market value of no more than K.Sh. 5/kg.

With very minimal costs, it should be possible for the Ngomeni farm to set aside some ponds, perhaps those which are considered problem ponds for shrimp, and to attempt trial rearing of tilapia.

Arrangements should be made for the nearby Baobab farm in Mombasa (which keeps broodstocks of all if not most Tilapia species) to supply fingerlings T. spilurus, which are reported to show some degree of tolerance to saline water. The tilapia would most likely match very well with the lablab which appears to grow very easily in the Ngomeni ponds.

Simultaneously, all litterature available on Tilapia culture in salt water should be acquired and compiled. At present work along this line is being conducted on Taiwan under the joint auspices of the International Center for Living Aquatic Resources Management (ICLARM) and the Council for Agricultural Planning and Development (CAPD), Taiwan. Internally within FAO some reports should be available on the result of the Red Sea experiments on Tilapia spilurus cage culture in marine water.

Another possibility is to duplicate the Red Sea experiment on cage culture in Kenya. This could probably be done at Port Reitz or Port Tudor at Mombasa, or in Lamu. Of particular interest would be to find out whether the natural productivity of the water could sustain a captured stock and allow them to grow to marketable size economically.

Experiments on the use of Tilapia hybrids, known to perform well in salt water, should also be conducted. Eventually should the initial experiments prove to be encouraging and have all indications of generating an economically viable technology, a Tilapia hatchery should be built within the coastal area.

A market survey on oysters should be conducted within the hotel and restaurant industries of Kenya to determine the potential demand level. It is ironic that while coastal Kenya prides itself in its variety and quality of seafood, oysters are very hard to find. It would be interesting to find out whether a market could be established if supply can be assured. The oyster grows in Lamu, in an unmanaged environment at such a high density that growth is stunted. It therefore requires considerable time and effort to gather enough large and well-shaped shells acceptable to the restaurant industry.

Should the potential demand prove to be substantial, then a pilot farm should be established in Lamu. Oyster cultivation is relatively simple and would be very easy to disseminate. The investment required per production unit will be very low or perhaps on the level of KSh 10 000 to KSh 20 000. This will be perfect for dissemination to the coastal poor.

The idea of creating artificial hypersaline lagoons out of the tidal sand flats to be seeded with Artemia is perhaps too far-fetched, but nevertheless it should perhaps be looked into. Test ponds could be dug at some accessible areas. In fact such ponds are already existing at Mida Creek. Creating a lagoon it should be noted is more within the realm of public work project than fisheries development.

The present attempt at Ngomeni at producing Artemia is a positive step toward exploring the possibilities of integration. This could be upgraded by actually constructing a mini-salt farm for experiments, or arrangements could be made with an existing salt farm for a cooperative venture.

APPENDIX VIII
SUGGESTED COURSE OF ACTION FOR THE VARIOUS AGENCIES INVOLVED IN COASTAL AQUACULTURE DEVELOPMENT IN KENYA

1. Government of Kenya (Fisheries Department

1.1 Activate the proposed Fisheries Development Authority as embodied in the 1984–88 Kenya Development Plan.

1.2 Conduct a survey among saltworks to ascertain their interest in having their reservoirs stocked with shrimps, emphasizing that such a production activity could be done without interfering with salt production.

1.3 On the basis of this survey, prepare a feasibility study for the development of a commercial shrimp hatchery.

1.4 Conduct a survey on the potential market demand for oysters within the hotel and restaurant industry.

1.5 Proceed with the implementation of projects found viable.

2. Project KEN/80/018

2.1 Proceed with pilot-scale shrimp hatchery.

2.2 Develop linkages with commercial saltworks for testing an integrated approach including Artemia.

2.3 Improve the Ngomeni aquafarm by setting up pumps, additional gates, etc.

2.4 Test the culture of Tilapia spilurus using lablab.

2.5 Provide technical backstopping to the Fisheries Department or to the Fisheries Development Authority in conducting surveys, feasibility studies as well as in project implementation.

2.6 Compile relevant litterature for all proposed activities.

2.7 Arrange for training/study tours for fisheries officers/technicians.

2.8 Provide short-term and long-term experts as required.

APPENDIX IX
TERMS OF REFERENCE

1. Consultant Aquaculturist (Shrimp Farming)

Under the general direction of the Project Manager and in close collaboration with the Aquaculturist (Fishfarm Development and Management) and national experts, the Consultant Aquculturist is required to review the background documentation available in FIR and AGRT, FAO Rome, and in Nairobi, in Malindi, Kenya, in order to assist the Government to prepare a master plan for aquaculture development (shrimp farming) in the entire coastal area.

Specifically he should:

• identify coastal areas where the existing technology employed on project KEN/80/018 at Ngomeni (P. indicus, labour-intensive pond construction, simple tidal water exchange), could be expanded for production development;

• identify coastal areas where relatively large-scale commercial shrimp farming (P. monodon/ P. indicus, mechanized pond construction, seawater pumping, hatchery or post larvae) might be possible or suitable.

The Consultant will prepare a first draft mission report for discussions with the representatives of the Government, FAO and UNDP in Kenya, to be presented to the Director, FIOD, Rome.

Duty station:   Malindi, Kenya, with visits to Rome, Nairobi, Mombasa, Ngomeni and other coastal sites as appropriate.

Duration:   Six weeks in August-September, with possibility of extension.

2. Consultant Aquaculture Engineer (Shrimp Farming)

Under the general direction of the Project Manager, and in close collaboration with the resident Aquaculturist (Fishfarm Development and Management), and with other national experts, the Consultant Aquaculture Engineer is required to assist the Consultant Aquaculturist (Shrimp Farming) in identifying and presenting a report on those coastal areas which are suitable for either the present extensive technology or alternatively for semi-intensive technology.

Duty station:   Malindi, Kenya, with visits to Rome, Nairobi, Mombasa, Ngomeni and other coastal areas as appropriate.

Duration:   Six weeks in August-September, with possibility of extension.

Note:These terms of reference were originally established in August 1985, but the mission was only able to be mounted in February-April 1986. During the latter part of the mission, the Government of Kenya requested through the FAO Representative that the mission report should also include:

• recommendations on mangrove swamp utilization and methodologies
• comments on single family versus estate concept, with positive recommendations for 1986 implementation
• comments on implications for Ngomeni site
• comments on other fishfarming possibilities