ANNEX 6
REVIEW OF POTENTIAL SITES FOR FRESHWATER/BRACKISHWATER AQUACULTURE IN JAMAICA

During their field trip, the study group visited several sites believed by the Jamaican Government to have potential for freshwater/brackishwater aquaculture. Other potential sites have been identified by previous missions and by the Inland Fisheries Unit (IFU) of the Ministry of Agriculture. The principal characteristics of these sites are given below.

1. THE HAGUE DRAINAGE SCHEME

1.1 Introduction and Background

The Hague Polders, called North and South Polders, are located on both banks of the Martha Brae River on the coastal plain east of Falmouth. Before reclamation, both Polders were prone to frequent flooding by the Martha Brae River. The only agricultural activities taking place in the North Polder was the growing of swamp rice. In the South Polder a drainage system was established and a primitive irrigation system constructed. The area was utilized by the Agricultural Development Corporation and in extensive pasture (Jamaica, 1982).

In 1978, work started on a reclamation plan for the North and South Polders. Both Polders were to be put into rice production. The design therefore included flood protection, drainage and the construction of irrigation and road systems. No detailed soil survey was carried out prior to these engineering activities. The first soil survey was carried out by the Agricultural Chemistry Division in 1978 for the North Polder and the second for the South Polder in 1979. They revealed that major parts of both Polders could not be considered as suitable for rice cultivation since soil units included sand and peat. Therefore a review mission recommended that all reclamation work be stopped immediately. The Rural Physical Planning Unit was requested to carry out a soil and water survey and make recommendations.

The Hague Polders comprise approximately 561 acres (or 224 ha) (gross) of lowlying, flat lands. Elevations are within a range from 1–1.20 m above mean sea level.

The following soils occur:

A large part (about 80 percent) of the North Polder (about 175 acres or 70 ha) has a surface layer (of at least 1.5 m) of peat and 20 percent (northern parts) consist of poor sands. Throughout, saline and alcaline conditions prevail and the peat is young and not yet decomposed.

The South Polder (about 300 acres or 120 ha) presents a similar picture, except for a minor area of peaty clay to clay. Spot checks revealed that the peat layer locally is over 4 m deep. Acid-sulphate conditions are found in occasional areas.

The coarse loamy-sandy soils and the peat soils are very saline as indicated by their electrical conductivity levels of groundwater in auger holes of up to 25 mmho/cm. The poorly drained clay soils have lower salinity levels, whereas the well drained clay soils which are associated with limestone outcrops have low salinity levels.

Salinity levels of the groundwater range from 3.4 mmho/cm to 25 mmho/cm. This is due to the Karstic limestone substrata. In several places, salt water springs exist. A salinity measurement carried out during 24 hours by the Agronomy Division, clearly shows the tidal influence of the sea (Jamaica, 1982).

Average annual rainfall in the area is 39.2 (996.8 mm)¹. The tidal range near the bridge crossing the Martha Brae River is about three feet (0.91 cm).

1.2 Reclamation Works

For both Polders, a flood protection dike along the Martha Brae was constructed. A road is laid out on top of this embankment. In addition to this, a catchment drain was excavated along the southern side of the South Polder to intercept surface runoff from the hills. A complete road system has been built in both Polders consisting of marled field roads, giving easy access to the area.

In the North Polder all main drains are completed and two pumps (capacity 16 000 litres/min each, driven by two Armstrong Siddeley 16.4 hp diesel engines) have been installed in the pumping station and the land can now be drained.

In the South Polder, main and field drains exist but are in a very dilapidated state. The pumping station has not yet been constructed.

1.3 Comments

Since the start of the reclamation works, an estimated J$ 2.0 million have been spent on infrastructure in the Polder. It is felt that an effort should be made to make use of this investment.

Because of the poor drainage conditions of most soils of the Hague Polders, the reclamation area is unsuited for annual and tree crops which require well drained conditions (the well drained clay soils are excluded from this but they occupy only a minor portion of the total area) (Jamaica, 1982).

Irrigated rice can be grown on the poorly drained and well drained clay soils. It is possible to bring irrigation water from the Martha Brae River to these clay soils for this purpose. Rice farming preferably should be done with small machinery and hand labour, and this is very strongly recommended given the limited bearing capacity of the clay soils. The course loamy and sandy soils are unsuited for rice, vegetables and pasture.

¹ Source: 30-year Annual Rainfall Totals in Jamaica (period 1931–60)

Vegetable farming is feasible on all soils except the poorly drained, coarse, loamy and sandy soils. The major problem to be overcome will be the salinity, especially in the dry season when salinity levels due to evapo-transpiration are high. A solution to this is leaching. Leaching in peat soils is very rapid (as experienced during the rice trials). Leached rice plots had a salinity level of 2.0 mmho/cm, whereas original salinity levels were as high as 10 mmho/cm. This suggests that vegetable growing on these peat soils is possible if reclamation is undertaken. For this purpose, fresh water should be drained from the Martha Brae. Transporting the water by gravity is possible because of the higher elevation of the dam in the Martha Brae River. Construction of an irrigation canal would be costly however, since the canal would have to be lined with concrete to prevent loss of water through the porus limestone (Jamaica, 1982).

It has been suggested to replant parts of the Polders with mangroves for subsequent extraction of wood and charcoal production. Some experts feel that, if properly drained, the area can be used for a housing scheme.

The Martha Brae River flows out at sea through the drainage area. There has been a proposal made that fresh water from the river should be taken and led along the western embankment (drainage canal) and the water then let into the lands with the purpose of flushing them and thereby reducing the salinity.

Several species of fishes and crustaceans occur in the reclaimed area: snappers (Lutjanus sp.), snook (Centropomus sp.), tarpon (Megalops atlantica), mullet (Mugil sp.), Tilapia mossambica and Macrobrachium sp. (R. Morlese, person. comm., 1983). A fisherman encountered by the study group displayed 25 fishes of which 21 were Tilapia mossambica taken in the brownish waters in the diked area.

1.4 Conclusions and Recommendations

The Hague Polders are a potential site for aquaculture but with certain reservations, in particular, (a) the level of the soil and water salinity in the diked areas. and (b) the acid-sulphate conditions prevailing in some areas. These problems can be overcome by leaching.

To decide if aquaculture is feasible in the Hague Polders, the following programme should be implemented:

1. Monitoring of salinity and acidity of soil and water in the diked parts of the polders;

2. A detailed survey to identify a suitable area of about 5 ha to be used for rearing of fish and shrimp on a pilot scale. The decision to start a pilot project should await the results of the analysis of the soil and water samples (levels of salinity and acidity);

3. Recommended species for these pilot trials in ponds are Tilapia nilotica, T. mossambica, common carp (tolerates salinities of up to 100 percent), mullets (if fry available in the wild) and Macrobrachium rosenbergii.

2. PEAR TREE BOTTOM RIVER

2.1 Description of the Site

Most of this section is based on information published by Wiles (1982).

The Pear Tree Bottom River, which rises in a limestone plateau near Orange Valley, runs through the “Belle Air Estate”, a Government-owned property, and drains to the sea at about 5 km east of Discovery Bay, St. Ann.

At the site, at least 50 ha of the bottom land is swamp surrounded by perhaps 150 ha of flat land which can readily be flooded by controlling river water flows through a network of channels. Inland of the swamp and bottom land there rises a limestone escarpment from which fresh water issues at 18 springs or “Blue holes” to collectively form what is known as Pear Tree Bottom River. This river consists of a normally dry gulley through the lower part of the escarpment inland (which collects surface runoff after rainfall) and a series of ill-defined channels through the bottom land that converge to form a coastal swamp. The freshwaters drain to the sea through three main outflows which are located between Discovery Bay and Runaway Bay, St. Ann. About 70 percent of the water in this system comes out of one large spring called the Main Blue Hole with a diameter of about 15 m and two main outlet channels of variable position. The land

purchased by the Government of Jamaica in 1978, was once a cattle ranch with coastal mangrove swamps on its shoreline. The mangroves were cleared out, the land partly drained and channelled, and coconuts planted on raised banks between the channels. This venture failed. Later, the coconuts became infected with a mycoplasma that causes lethal yellowing disease, and the plantation was virtually abandoned. Today the land is derelict (Wiles, 1982).

The property is ideally located for freshwater fish and shrimp culture, for there is easy access to both fresh water and salt water, the latter being required for the earlier larval phases in the life cycle and the former being the medium for growth of shrimp juveniles and adults. The bottom land could be modified inexpensively to contain ponds in which the shrimps and fish could be cultured and protected from predators.

The swamp itself extends over about 50 ha and surrounding it on three sides are about 150 ha of flat land that could serve as the pond construction area. The permanent freshwater flow comes from springs at the base of the limestone escarpment and from general seepage, so that there is very little variation in flow rates through the year. By the coastline the water is brackish so that a salinity gradient exists between the sea and the river proper. This constitutes an excellent environment for the completion of the life cycle and for the growth to adult sizes of freshwater Macrobrachium prawns.

The fresh water on the property is unpolluted, clear and abundant. As its source is underground it is little affected by rainfall. The hydrological data show that its flow is practically constant throughout the year. The qualities of this water are ideal especially for shrimps, the total dissolved solids levels being in the optimal range of 150–220 mg/1, with highest amounts in the blue holes and lowest ones in the river channels themselves. The hardness range of the spring waters is 140–160 mg/1 which is an ideal level. The freshwaters are affected by seawater influxes close to the coast where levels of sodium, chloride and sulphate are much higher than further inland. Consequently, total dissolved solids near the river outlets approach 1 000 mg/1, and total hardness levels exceed 300 mg/1. For the culture of freshwater shrimp a seawater encroachment like that at Pear Tree Bottom provides an optimal environment for the growth and moulting of the first six or seven larval phases (Wiles, 1982).

River water temperatures vary little over the year, the range being 22°C–25°C which is optimal for fish and shrimp growth.

Ground water levels fluctuate, yet they do so in response to withdrawals or additions of water, not to rainfall (although the rainy season in April-May causes a general pronounced rise). Heavy rains cause turbid water to appear at seepages and in the main surface drainage gulley, but at the same time spring water from the blue holes remains clear. Overall, the spring waters in this area are remarkably clear. Thus the freshwater supply is ample and dependable for drinking, domestic and laboratory use and for aquaculture. However, clearing out the vegetation in the swamp channels would be necessary to use this resource effectively. To maintain acceptable water levels in the swamp thereafter, a regular programme of vegetation removal would have to be carried out (Wiles, 1982).

The Main Blue Hole is the obvious spring to use as a source of freshwater for the building (including laboratories and living quarters) and the aquaculture facilities. Its discharge varies little through the year, the range being 13–17 m/sec and the mean 15 m/sec, while the change in the height of a gauge installed in it for about three and one-half months was less than 3 mm in one day. This spring provides about 0.7 of the water in Pear Tree River Bottom system. The rest comes from at least 17 other blue holes, nine of which have had their water flows measured (their flows are constant too) and from limestone seepage. The second largest blue hole has a constant discharge rate of 4.5 m/sec. Some water flow data for the three main discharge channels flowing into the sea (and subject to tidal backwater) have been collected. Mean values reported are 28.5 m/sec in March, 30.3 m/sec in June and 23.4 m/sec in October. Impedence of freshwater flow into the sea by tidal seawater is overcome by an increased flow rate from the blue holes at high tide, the freshwater flow and tidal flow maxima coinciding quite precisely. Whereas there is reason to think that the tidal rise reduces underground outflow of freshwater into the sea, it apparently interferes little with the above surface flow so that saline water intrudes only a very short distance into the Pear Tree River Bottom system (Wiles, 1982).

2.2 Conclusions and Recommendations

Since the site at Pear Tree Bottom is extensive and well suited for both shrimp and fish farming, it can be made into an excellent training and demonstration centre for brackish and freshwater aquaculture. Existing buildings, once rehabilitated, can be used for this purpose.

It is recommended to carry out a complete topographic survey of this site to evaluate the feasibility of constructing ponds for rearing of Macrobrachium rosenbergii (about 5 ha) and building of a raceway unit for T. nilotica culture.

3. THE NEGRO RIVER BASIN AND PORT MORANT DISTRICT, ST. THOMAS

The study group visited two private farmers at Potosi and Belvedere.

3.1 The Potosi Farms Ltd.

The Potosi farm produces eggs, broilers, pigs and has 47 heads of cattle. The owner of the farm wants to enter fish farming and would like to start with a 4 acre (1.60 ha) pilot project on land presently controlled by the Ministry of Agriculture. If his pilot project works out correctly, he would like to expand into 25 acres (10 ha), all of which he would rent from the Government. The land which is identified is so located that it could be fed by gravity from a water source which reportedly never runs dry. The land consists of undeveloped pasture land, but with clay soils and would be worth about J$ 1 000/acre, compared to developed land for banana or coconuts worth up to J$ 3 000/acre.

A US consultant has prepared a feasibility study for a Macrobrachium rosenbergii farm on this site. This study indicates a per acre cost of about J$ 12 000 for a farm of 20 acres (8 ha), including investment in ponds, ancillary equipment and infrastructures.

The owner of the Potosi Farm cannot find the “cheap money” he needs to finance the enterprise. He would have to pay something like 18 percent interest on a loan from a commercial bank.

3.2 The Belvedere Estate Ltd.

The second farm, Belvedere Ltd., is located some kilometers north of the coastal road, just west of Morant Bay. There are presently four ponds at Belvedere. The oldest pond has a depth of over 3 m at its deepest part. This pond was stocked with about 4 000 T. nilotica male fingerlings of 8–10 cm. The pond was fertilized with chicken manure (obtained free of charge from the Potosi farm but costing J$ 30 for transport), and the fish were fed compounded feed (“Jet Pets Food” at J$ 10 for one bag of 25 1b = J$ 0.91/kg). After a rearing period of eight weeks (56 days) the harvest was 2 660 lb (1 197 kg). The fish at harvest were reported to be just under half a pound in size (0.200–0.220 kg). The harvest was done through drainage by personnel from the Ministry of Fisheries. A wholesaler bought the fish for J$ 1.50/1b (J$ 3.33/kg).

According to this information and assuming fingerlings of 30 g at stocking, the growth rate works out to about (210 g - 30 g) 180 g over a growth period of 56 days, that is, about (180 g : 56 g) 3 g/day, a high growth rate for T. nilotica in ponds.

The three other 0.5 acre ponds have been constructed by bulldozers between February and November 1982 and are not yet completely finished. They have been constructed by the Ministry of Fisheries, but the cost of the ponds and other indirect charges are not known at this time. These three ponds have been constructed by excavation and their bunds are wide and apparently, at least in part, not properly compacted. As the outlets were not in place as soon as desired, the owners had filled in the part of the bunds where the pipes were planned to be. This may be an additional reason for the leaks.

The new pond which holds water has been stocked with a few grass carps. Someone has referred to the fish as “trash fish” and the owners seemed unaware of the type of fish they had in their pond. Weeds were almost not available in the pond and no additional grasses are fed to the grass carps.

The fish farm suffers from predation by the grey heron. Also, at times there are long delays in obtaining the fingerlings needed for stocking the ponds. The owners intend to expand to include an additional six half-acre ponds if the present three ponds can be put into good use, since only one of the three ponds is now under production.

Jamaica Aqua-Farms Ltd. has approached the Belvedere Estate with an offer to sell M. rosenbergii post-larvae at a cost of J$ 0.29 per thousand. The farmers are uncertain about what to do. In the area of Port Morant there are another 8–10 farmers who would consider going into fish farming on the same scale as at Belvedere.

The Potosi Farms Ltd. and the Belvedere farm have both been approached by Dragon Fly Farms in Florida and by Natural Systems Inc., also in Florida, regarding the red Tilapia, a hybrid available in Florida for which almost no information is available concerning pilot scale trials and commercial farming.

3.3 Conclusions and Recommendations

The Negro River basin and the Port Morant District have a great potential for aquaculture development and several farmers have expressed their intention of going into fish farming.

Once the fish ponds have been completed, polyculture of T. nilotica males and grass carp with feeding and fertilization would seem suitable.

More attention should be given to this area by the fish farming extension team and sites for aquaculture should be surveyed to investigate their potential for farming of fish and freshwater shrimp.

4. ST. JAGO AREA, CLARENDON

The St. Jago Properties Ltd. owns an approximate 200 ha-sized area of flat, water-tight clay soil, excellent for fishpond construction and also an adjacent area of some 200 ha more which has a slightly lighter soil texture.

The site has an existing irrigation facility. Water of very good quality could be supplied by electric pumps from two wells (about 0.5 m³/sec). Another 0.2–0.6 m³/sec can be taken from a creek bordering the area (Agrober-Agroinvest, 1982). The St. Jago area was not visited by the study group.

5. THE BLACK RIVER AREA, ST. ELIZABETH

5.1 Background

The Upper Morass has an area of about 24 000 acres (9 600 ha) of which 11 500 acres (4 600 ha) are under the BRUMDEC (Black River Upper Morass Development Company) project. Of the 11 500 acres, BRUMDEC is now managing 7 500 acres (3 000 ha), the drainage and land preparation of which were completed in July 1982. About half of these 7 500 acres is peat soil.

In 1980, the Government was engaged in three irrigation and drainage projects, all managed by BRUMDEC. At Elim, it was intended to have 3 000 acres under rice; at Meylersfield, Westmorland, 1 350 acres, and at Hague, Trelawny (close to Falmouth) 500 acres. If the projects are implemented according to schedule, some 4 850 acres (1 950 ha) should be under cultivation by 1985 (ADCP, 1981).

Both at Elim and Meylersfield, the Government intended to transfer to farmers the land being developed. At Elim, plots were to vary between 5 and 25 acres, at Meylersfield small-holders with from 2 to 5 acres would be encouraged to acquire the Government land (ADCP, 1981).

In 1980, BRUMDEC was giving priority to rice cultivation (amongst many possible crops) partly as a means of reducing Jamaica's foreign exchange bill.

The Government's policy regarding the use of these irrigation and drainage projects has changed since 1980, and BRUMDEC's responsibilities are now (i) to maintain all physical facilities installed under the drainage and irrigation scheme of which a large part of the initial investment was financed by IDB; (ii) to act as a catalyst for development schemes, either in the form of joint ventures or wholly owned by BRUMDEC. The culture of irrigated rice is no longer a priority for BRUMDEC in the Black River Upper and Great Morasses.

Tilapia mossambica is present in almost all the waterways in the BRUMDEC area, but the local Macrobrachium species have disappeared. Some 50 men are supposed to earn a livelihood by fishing. Unemployment is high in the area. A reasonable family income is thought to be in the order of J$ 5 000 per year.

At present BRUMDEC is exploiting about 500 acres; the rest of the land is waiting. Experiments are carried out with a variety of vegetables and rice. The vegetables have grown excellently on the peat soil, while, on the other hand, rice has not. Even the rice brought in especially for the peat soil has not given a good yield - 2 000 lb against an expected 4 000 lb/acre.

BRUMDEC has not yet identified the best rice varieties for the clay soils, and they are presently trying out primarily the ICA 8 which has a growing period of 135 days during the January to July season, and a growing period of 120 days if grown in the second half of the calendar year. The water level in the rice fields is kept at 4 in (about 10 cm), the rice itself being about 45 cm high. With a water depth of only 10 cm rice-cum-fish culture is almost impossible.

There have been several proposals to use some parts of the BRUMDEC area for aquaculture. One project involves Jamaica Broilers and JNIC. They have been assigned two areas: one of about 100 acres (40 ha) for their initial pilot project and a second plot of 955 acres (382 ha) in the north western part, just west of the Black River, for later expansion.

Another project has been proposed by Tissona (Israel), BRUMDEC and JNIC and concerns 1 500 acres (600 ha) of land having about the best clay soils in the BRUMDEC area, located in the north eastern part of the irrigation scheme. Initially it was intended to use this land for rice culture.

ADC (Agricultural Development Corporation) owns about 4 000 acres (1 600 ha) in the southern part. However, the land is undulating and with peat soils. Consultants from Tissona who visited this site felt it was unsuitable. The pH of the water in the peat soil area was reported to be 6.2 by the BRUMDEC agricultural manager. The peat is varying in depth from a few inches to 9 ft (2.74 m). Vegetables have been grown in the peat using a bed system, but in order to be continuously useful, the peat should be under water six month of the year.

5.2 Recommendations

The proposed projects for aquaculture development in the BRUMDEC area should be carefully evaluated by the Government, not only for what concerns the financial part of the projects, but particularly on the technical aspects (species proposed, growth rates, prices of fingerlings and post-larvae, market prices, etc.). Only when they have been technically cleared should they be evaluated for the financial aspects.

6. THE NEGRIL GREAT MORASS

6.1 Background

The existence of substantial deposits of peat in Jamaica presents an opportunity for decreasing Jamaica's dependence on foreign exchange.

The major peat deposits are located in two large wetlands, the Negril Morass and the Black River Morass. Studies have shown that enough peat exists in these two wetlands to fuel electric power productions at a level of 80 megawatts for a period of about 30 years. This level of electric power production would satisfy approximately 30 percent of Jamaica's current demand. This would decrease dependency on foreign oil by approximately 850 000 barrels/year, thus providing significant foreign exchange savings (Jamaica, 1981). A peat environmental feasibility study was carried out during the phase II of the project and led to the following findings (Jamaica, 1981):

1. The direct environmental effects of the peat mining on the beaches, coral reefs and rivers near the peat areas appear to be be moderate.

2. The inshore fishery and shrimpery at Black River will be drastically reduced by the mining of peat.

3. The existing wetland system at Negril will be reduced by 80 percent. At Black River, the wetlands will be reduced by 40 percent. In both cases, the removal of wetlands will be irreversible. This means that these wetlands will not return within dozens, if not hundreds, of human life times.

4. The wetland system of Negril and Black River represents over 75 percent of all of Jamaica's wetlands. They are one of the few, if not the only, large integrated natural wetlands in the Caribbean. As such, they represent a wild life habitat and biological genetic pool unique in the Caribbean. Proposed peat mining will mean that Jamaica's store of wetlands will be reduced by 50 percent.

5. The social-cultural effects of peat removal will be substantial. The project is forecast to have an adverse effect on the people who live in the area of the two wetlands. Their life styles, income and security are directly determined by the biological productivity of the wetlands in their present forms.

6. The economic viability of the peat as an energy source has been analysed and shown to be positive. However, this conclusion does not account for the many intangible values of the wetlands, such as education, recreation, natural genetic pool, etc. Furthermore, the various alternative uses of the wetlands for such activities as fish and shrimp farming, forestry biomass crops, expanded shrimp farming, rice, etc. have not yet been examined to compare with the economic value of peat mining.

Concerning the mining alternatives, the study focused on the worst case approach to the mining of peat. This approach assumes that no engineering works would be carried out to mitigate adverse environmental impacts so that a single lake, some 9 m deep, would result from the worst case approach. This approach was ecologically unacceptable.

The Negril Great Morass occupies an area of approximately 2 290 ha within the Negril Basin. The natural surface drainage pattern in the wetlands has been altered extensively by a network of canals in order to facilitate land reclamation. The principal conveyors of surface water within the Morass are: Orange River/North Canal at the northern extremity and South Negril to the south. Both discharge into the sea at Salt Creek and Negril respectively. The inflow contribution from the surrounding hills is by way of numerous springs on the eastern edge of the Morass (Jamaica, 1981).

For the Negril wetlands, the study indicated that after mining 68 percent (1 553 ha) the evaporation losses will increase by 33 percent while the surface outflow will decrease by 7 percent. No changes are expected in the surface or groundwater inflows. However, it was discovered that the Negril area is extremely sensitive during prolonged dry periods, resulting in significant net inflow of sea water into the channels (Jamaica, 1981).

The ground water quality will not be adversely affected if the hydraulic head is now lowered due to pumping or drainage. There are no indications that peat mining will create flood hazards in this area. However, limited potential circulation in the resultant water bodies requires management to prevent stagnation.

Concerning water quality, the definition of the present water chemistry of the Black River and Negril areas, and the identification and quantification of sensitive parameters were performed in 1981 to elucidate the potential impact of peat mining on water quality. Predictions with respect to future water quality at the outflows from both wetlands were based on the amount of peat which may be spilled into the waterways. Available nutrients in the peat substrate were computed based on laboratory leachate tests and the assumption of ideal mixing of available nutrients from peat with those present in the river. Assumptions on settling were made to calculate predicted changes in suspended solids at the mouth of the rivers if peat mining is pursued.

The parameters identified to be of critical importance to this study were nutrients, chlorides, suspended solids, and biochemical oxygen demand (B.O.D.). Present pollution levels were reviewed, nutrient budgets were developed and an analysis of the possible enrichment of critical parameters in the hydrologic systems due to peat extraction was completed.

It is estimated from mass balance calculations that the Negril Morass is presently trapping as much as 73 percent of the phosphate and 77 percent of the nitrate which enters it. It is further estimated that B.O.D. is reduced by 54 percent and Total organic carbon (T.O.C.) by 50 percent. It is predicted from leaching experiments that if the extraction process were to spill 2–10 percent of dredged material, nitrate would increase from 0.16 mg/l to 0.17 mg/l, and suspended solids from 40 mg/l to 65 mg/l, increases of 6 and 65 percent respectively. These assumptions on dredge losses are based on no controls and, with proper engineering and management of the losses to the receiving streams and bays, the increases may be less (Jamaica, 1981).

Peat mining will result in the formation of brackish lakes which will naturally have little or no oxygen in the hypolimnion. The potential lake area (areas of peat depth greater that 3 m) has been determined from a peat contour map using a planimeter.

Total sulphide concentrations in both wetlands (Black River, Lower Morass and Negril) have been determined to be between 1 mg/1 and 3 mg/1 from spot examinations of well and surface water samples. It is expected that this high sulphide concentration will be reflected in the water quality of the resultant lakes, being worse in the bottom layers.

Heavy metals (specifically mercury, cadmium, copper, tin, lead, nickel and zinc) occur at low concentrations in the major outlets from both wetlands (less than 0.05 mg/1). There is not likely to be any significant change in their concentrations due to peat mining (Jamaica, 1981).

6.2 Present Status

Petrojam is presently investigating how to utilize the peat in the Negril swamps. The programme under consideration is to burn it in a power station for electricity generation. Simultaneously, plans are being made for the use of the area once the peat has been taken out. The plans for extraction are now being made. It seems likely that extraction will not be made so that one big lake is created, but rather in a pattern leaving a number of small lakes. Petrojam is now investigating how and if these lakes can be used in aquaculture production.

To this end two ponds, each of 2 500 m², were dug at the beginning of last year (finished in February 1982). They measure 50 × 50 m. One is slightly more than 5 m deep, and the other about 3 m. The depth of the peat varies between 8 and 15 m.

The following observations were made on the deeper pond: oxygen 6–7 mg/l at the surface, pH about 6.5; the surface of the water is fresh, but at the bottom salinity is about 4 ‰. The water is poor in phosphates. Possibly this has something to do with the fact that the waters running into the ponds come off limestone hills.

There has been a quick succession of plankton in the water and the plankton population now seems to have stabilized.

Fertilization experiments are being carried out in 10 ponds, each of 2 m². Different mineral fertilizers are used at different rates to evaluate their effectiveness in raising the nutrients in the water (nitrogen, phosphorus, etc.). The mangrove peat is said to have a pH of between 5.5 and 6.5.

No stocking of fish was undertaken in the larger ponds. However, after about six months, people were fishing for tilapia in the ponds. Some dead fish have been observed in the ponds occasionally. The hypothesis was advanced that their death may have been caused by oxygen deficiencies. Petrojam intends to continue these trials.

6.3 Recommendations

The fertilization trials should be pursued until adequate information on the technical and economical feasibility of the fertilization has been obtained. The resultant formula should then be applied in the two 2 500 m² experimental ponds.

The analysis of water should also be done regularly for the usual physico-chemical parameters.

The two experimental ponds should be stocked with T. nilotica male fingerlings. Stocking rate could be 2 fingerlings/m². The ponds should be fertilized according to the findings of the trials in the test ponds and the fish fed compounded feeds at a daily rate of 4 percent estimated body weight. The average fish weight should be estimated monthly to adjust the quantity of feed to be distributed.

7. THE CRATER LAKE, ST. ANN

The Crater Lake is a natural lake fed by springs or “blue holes”. The lake has a surface layer of fresh water one or two metres deep (1.25 m near shore and deeper towards the middle), below which there is water of a salinity of 19 to 21 ‰ which extends down to near the lake bottom. Fresh water springs issue from the limestone bed of the lake. Thus, a wide range of salinities is found in this system (Wiles, 1982).

Shrimp were collected from the Crater Lake in 1982 by Wiles and the lake was investigated by McQueen (York University, Toronto, Canada).

In Crater Lake a most interesting situation seems to prevail according to Wiles (1982). A large proportion (89.4 percent) of the benthic samples consisted of Macrobrachium carcinus, while only very few M. acanthurus and M. faustinum occurred in the collections. Of greatest interest is the presence in the plankton of phase II and later phases of Macrobrachium larvae and of juveniles. The existence of these early life cycle forms of Macrobrachium in the lake indicates that conditions are suitable for reproduction and growth of Macrobrachium. Copepod nauplii are abundant in the Crater Lake and could serve as a food source for developing Macrobrachium larvae (Wiles, 1982).

According to McQueen (1982) and as suggested by Wiles (1982), Macrobrachium, which require both fresh and salt water in order to complete their life cycle, could easily be cultured by establishing suitable substrate for the adults along the edge of Crater Lake. McQueen suggested that perhaps culture boxes would provide a refuge for shrimp but would exclude fish. The adult shrimp could be artificially fed and easily harvested. If the capepods turn out to be a major food source for larvae, perhaps their population could be augmented (McQueen, 1982).

8. THE DEANS VALLEY RIVER, WESTMORLAND

An irrigation scheme exists at Shrewberry, north of Petersfield, to supply water to a surgar cane plantation. The water is of excellent quality and in plentiful supply. Near the roadside, part of the irrigation canal has broken down, creating a small waterfall, and water flows into the river bed. Part of this water could be diverted from the irrigation canal and, making use of the fall of level, be used to supply water to raceways or to ponds to be constructed besides the sugar cane fields.

A detailed survey of the site should be carried out to evaluate the feasibility of raising M. rosenbergii in ponds or T. nilotica in raceways.

9. THE GREAT RIVER, HANOVER

The study group visited the Great River, some 200 m upstream from the bridge on which the coastal road crosses the river. This part of the river is apparently deep, with a slow current. Mullet and eel are said to occur in this part of the river. This site could probably be suitable for cage culture on a pilot scale.

10. USE OF MINED-OUT PITS FOR AQUACULTURE

10.1 Background

The Reynolds Jamaica Mines Ltd., with headquarters in Lydford, St. Ann, are mining bauxite in the Claremont-Moneague area. Jamaica has placed great emphasis on the reclamation and rehabilitation of the mined-out bauxite lands and the Reynolds Jamaica Mines are interested in using some of their mined out pits for aquaculture purposes.

Rainfall in this area of St. Ann (Lydford, about 5 miles (8 km) from Moneague) was said to be 70–80 in/year (between 1 780 and 2 030 mm/year), with a low evaporation rate. There is a 400 ft industrial well which provides 1 500 gal of water per minute.

Three study group members visited several pits in the Reynolds leased land. The pits surrounding the plant have a high silica clay content and, thus, have only been half mined. It is the Management's thinking that these silica clay could be used as a sealant for the bottom and the slopes of some of the mined-out pits. The pH of the topsoil is 6 and further down increases to 7.

The study group also visited the Moneague Lake which is split into several parts. One section, about 25 acres in extent, is fed by a river which disappears underground. The surrounding soils seem to be of a fine clay nature.

There are some fishermen on the lake using bamboo rafts, and it seems that they catch only African perch (Tilapia mossambica). This species was introduced by IFU in the late 1970s. It was thought by IFU personnel that there might be caustic soda intrusion into the aquifer in St. Ann, hence the poor growth of the fish and the relative lack of fertility of the lake.

10.2 Recommendations

It was agreed that a trial would be set up to test the use of silica clay as a sealant in one or two 100 m² ponds to be constructed by Reynolds Jamaica Mines Ltd. They should be 1 m deep. The seepage rates should be recorded. If silica clay proves to be a good sealant, the ponds should be stocked with T. nilotica male fingerlings at a stocking density of 2 fingerlings/m². Fingerlings will be provided by IFU. Ponds will be fertilized (with chicken manure if available), and fish will be fed compounded feeds.

The Moneague Lake could be stocked with T. nilotica fingerlings, but only if the results of the water analysis show that the water quality is suitable.