Stage
1 - Preparation Stage
10.32 Drying out of pond - During harvesting the ponds are totally drained and allowed to dry out over the winter months by sunlight. Organic detritus which has accumulated at the bottom of the pond during the previous growing season is broken down and consolidated. This procedure also reduces pathogenic bacteria and parasites within the system (Pers. Comm., HKNTFAA).
10.33 Some fish ponds do not require complete drying every year, more specific details regarding such decisions were not elaborated on by aquaculturists. Under such circumstances, following harvesting, eutrophic water from the nearby operating fish ponds is pumped into the pond before restocking.
10.34 Liming - Once the bottom of the pond has dried out, lime (Calcium oxide) is applied to the bottom of the pond to:
· neutralise the acidity of the sediment;
· increase the ponds buffering capacity to changes in the pH;
· accelerate the decomposition rate of the organic matter; and
· act as a sterilising agent to kill bacteria.
Where adverse pond conditions warrant it, a second application of lime is applied later in the year (Pers. Comm. Prichard/Lai).
10.35 Exclusion of predators - Depending on the preferred management techniques adopted by each aquaculturists and the requirements of each individual pond, traditional teaseed cake may be added to the pond to eliminate predators (e.g. eel, snake head or cat fish) that bury into the soft substrate at the pond bottom. However, this technique is now rarely applied (Pers. Comm. Prichard/Lai). Such predatory fish species prey on fingerlings released into the pond leading to a substantial fall in landed catch when harvested, and hence income. No figures are available to substantiate losses in catch.
10.36 Application of fertilisers - The application of lime is sometimes preceeded with dressing the base of the pond with an organic fertiliser. This may include:
· poultry manure;
· decaying dead fish left over from last harvest; and
· peanut cake is applied to the base of ponds which are stocked predominantly with grey mullet.
10.37 As the organic fertilisers decompose, inorganic nutrients are released into the water column which:
· encourage prolific of growth of phytoplankton;
· provide a direct organic food supply for small invertebrates, zooplankton and insect larvae which are a food source for species of fish reared in polyculture systems.
10.38 For example, midges (Chironomids) lay their eggs into the ponds and subsequently their larva (blood worms) proliferate, which are consumed by cultured fish. Blooming of a type of zooplankton (rotifer) is nutritionally important food source consumed by Bighead.
Re-Watering
of Ponds
10.39 No large river systems with unpolluted water or large quantities of groundwater exist in Hong Kong to directly supply clean water to the fish ponds. Hence aquaculturists are dependent on rain water to fill ponds. However, water may also be pumped from full ponds or from less polluted water courses. Under such circumstances nets will placed over the water inlet to preclude or minimise the number of predatory fish which enter the fish pond that could lead loss of stock via predation over the season. Table 10.5 summarises the recommended water quality for initial commencement of culturing at the beginning of the season (the Water Quality Chapter describes water quality in the fish ponds). Pond water at pH below 6.5 or higher than 8.0 will have adverse effect on the growth and reproduction of fish, however, this can be effectively managed by the application of lime.
Table 10.5
Recommended Water Quality Standard for Refilling Fish
Ponds
|
Parameters |
Units |
|
Ammonia
(as nitrogen) |
< 0.1 mg/L |
|
BOD5 |
< 10 mg/L |
|
Chlorine |
< 0.1 mg/L |
|
Chlorophyll
a |
< 1 mg/L |
|
Dissolved
Oxygen |
> 1 mg/L |
|
Oxidised
Nitrogen (as nitrogen) |
< 5 mg/L |
|
PH |
6-8.5 |
|
Phosphate
(as phosphorus) |
< 1 mg/L |
|
Salinity |
< 2 0/00 |
|
Suspended
solids |
< 20 mg/L |
(Source: AFD, 1995)
10.40
Step 2 – Fish Fry
· Historical View – Fish fry are the tiny newly hatched fish less than <1cm in length. Historically fish ponds in Hong Kong were stocked with wild fry (e.g. Grey Mullet) caught from the coastal shores of Hong Kong. However, rapid coastal reclamation throughout the territory together with deterioration in water quality has led to the rapid demise of spawning and nursery grounds of commercially important fish within the territory. These combined factors have led to a rapid decline of a reliable supply of adequate quantities of fish fry required by local commercial fish rearing purposes. Consequently, alternative sources are now sought.
· Commercial Rearing - Rearing of fish fry to supply commercial aquaculture ventures requires comprehensive fish hatchery equipment, intensive management, and an extensive scientific knowledge of fisheries biology. Whilst a few local aquaculturists breed and rear fry of Catfish, Common Carp and Snake head, such setups are scarce in Hong Kong. No specific details regarding these establishments and associated costs are available for inclusion in this report.
· Importation from Overseas - To meet the high local demand of commercial fish fry, local aquaculturists are forced to import fry from overseas such as mainland China, Japan, Taiwan and elsewhere in South East Asia e.g. Thailand (AFD, 1999). Table 10.6 summarises the countries from which specific species of fish fry and fingerlings are imported.
Table 10.6
Countries from
which Fish Fry and Fingerlings are Imported
|
Species of Fish |
Country Supplied From |
|
Carp (different species) |
China Taiwan |
|
Grey Mullet |
China Hong Kong Japan Taiwan |
|
Sea Bass |
United States of America |
|
Yellow Croaker |
Fujian, China |
(Source:
Pers. Comm. Prichard/Lai)
10.41
Step 3 –Stocking
· Time of Year – More recently local aquaculturists have tended to stock ponds with fingerlings or juvenile fish (15cm in length) as they have a higher rate of survival and hence ultimately result in a more lucrative financial returns (Pers. comm. Prichard/Lai). The ponds are stocked with fry or fingerlings in Spring (February to April) to correspond with the commencement of the growing season of fish. This provides adequate time for fish to reach a marketable size by autumn, when they are harvested.
Stocking
Regimes
The stocking density and species composition vary according to the proposed culture technique, the fry that are available from suppliers and the market demand for particular species. With respect to the fish ponds within the Study Area ponds located closer to the sea are used to raise higher value fish (marine species), whilst ponds further inland are used to raise more hardy species of fish e.g. Catfish and Snakehead (Pers. comm. Prichard/Lai).
· Polyculture - Stocking densities of the fingerlings in the carp polyculture ranges from 10,000-35,000 fingerlings/ha (Wilson, 1992). Typical species stocked include: Bighead, Grass Carp and Common Carp. In addition Silver Carp are added to maintain adequate water quality. The market demand and hence value of Grey Mullet has increased in recent years, hence this species is frequently reared with species of Carp.
· Monoculture - Stocking densities of fingerlings in monoculture ponds are much higher, in the range of 150,000-300,000 fingerlings/ ha. Species reared include Catfish, Sea Bass, Snakehead (refer to Table 10.4).
· Vulnerability to Predators - Rearing of fry to fingerlings (juvenile fish 2-3cm in length) is the most critical stage of the pond management, as the juvenile fish are critically vulnerable to predation by aquatic predators e.g. dragonfly nymph, catfish and various species of birds, notably heron, egret and cormorant.
· Nutrient Enrichment - At this stage of the life cycle juvenile fish consume plankton, consequently aquaculturists frequently add fine grains of wheat or soya to the ponds to enhance the nutrient levels within the pond water and thereby increase production of plankton which is consumed by the fish.
· Continuous Stocking - More recently, to generate quicker cash return some local aquaculturists have adopted a continuous stocking regime of juveniles fish, and correspondingly continuously harvest the ponds throughout the year.
10.42
Step 4 - Rearing Stage
Polyculture
· Feeding Regimes - During February-October when fish growth is rapid, within the polyculture system the fish are fed once to twice a day, once being the norm (Pers. comm. Prichard/Lai). Feed is typically cereal based products as summarised in Table 10.7. Low protein feeds (e.g. rice barn) are typically added to the pond at the beginning of the growing season when the fish are small and a large amount of natural food is available. Whilst at the later stage of the growing season as fish become larger, a switch is made to feeding fish higher protein food (e.g. peanut cake). It is uncommon for commercial feeds to be added to polyculture fish ponds in Hong Kong.
Table 10.7
Feed Types Added to
Polyculture Fish Ponds
|
|
Feed |
|
Common Cereal Based Feed |
Corn meal Peanut cake Wheat bran Rice bran |
|
Other Types of Feed |
Biscuit Bread Brewery
waste Instant
noodle Sorghum Soya bean |
|
Ponds in which Grass Carp are Reared |
Grass clippings |
· Monitoring Behaviour of Fish - The appetite of the fish depends on environmental temperature, oxygen levels in ponds and the quality and quantity of feed applied. However, temperature is the predominant factor influencing the appetite of the fish. When the temperature rises, fish consume more feed, whilst for fish that remain in the ponds over winter their food intake is considerably less. Consequently to maintain a careful nutrient balance within the pond the aquaculturist must observe the daily feeding behaviour to determine the amount of feed that should be added to the pond. A considerable amount of feed remaining at the pond bottom eight hours after feed application indicates overfeeding. Overfeeding should be avoided as left-over feed increases the biological oxygen demand (BOD) of sediment and result in an anoxic condition at the pond bottom. This leads to fish dying and hence loss in revenue.
Monoculture
· Similar feeding regimes and management principles are applied to monoculture ponds, with the exception that high protein commercial feeds are applied to these ponds.
Addition of Fertilisers
·
Requirement for Fertilisers - The dynamics of polyculture pond system is heavily dependent upon
autotrophic and heterotrophic food production. During the growing season
fertilisers are applied to the ponds approximately every fortnight to maintain
the nutrient content. Organic fertilisers added to the pond include cattle, pig
and poultry manure and peanut cake; inorganic fertilisers are rarely applied.
· Monitoring Water Quality - The amount of fertilisers added to the pond is critically important and therefore must be carefully managed. During day light, plankton (microscopic free floating plants) photosynthesise and produce oxygen. At night when photosynthesis ceases the oxygen is consumed by living aquatic organisms within the pond. In ponds where excessive quantities of fertilizer have been added, excess nutrients will collect at the bottom of the pond causing prolific growth and multiplication of bacteria that reside in the detritus. The increasing bacteria will rapidly consume the dissolved oxygen within the pond water resulting in the production of methane and hydrogen sulphide which are highly toxic to fish. By dawn high biological oxygen demand (BOD) by the bacteria will result in insufficient dissolved oxygen within the pond and therefore lead to fish mortality.
· Ammonia (NH3) – Ammonia in the pond water is produced by fish during excretion and the decomposition of the nitrogenous compounds of the organic fertilisers. When dissolved oxygen levels are adequate, nitrifying bacteria convert ammonia to non-toxic nitrites and nitrates (i.e. nitrification). However, in high density fish culture regimes combined with the addition of large quantities of feed and organic fertilisers, ammonia concentrations may increase to levels that are toxic to fish. This causes osmoregulatory imbalance, damage to kidneys and gill epithelium leading to suffocation. Sub-lethal levels cause poor growth and reduction in tolerance to pathogens and parasites. This problem can be resolved by continuous aeration.
· Observation – Daily monitoring of fish behaviour by aquaculturists is the most effective method to maintain optimum water quality. The gills of fishes are very sensitive to environmental stresses and infection. Since fish breathe via their gills, any abonormalities experienced e.g. low oxygen levels in the pond, will cause the fish to congregate at the pond surface where the dissolved oxygen level is highest. By regularly observing the colour and visibility of the water, and the behaviour of fish, aquaculturists can implement corresponding treatment. These can include temporary termination of feeding and addition of fertilizers, initiating aeration, removal of some water which is replaced with less nutrient rich water to effectively dilute the phytoplankton.
Monitoring Water Levels
· Flooding – Flooding periodically occurs in the North West New Territories including within the Study Area. Elevated water levels can cause the fish ponds to overflow leading to loss of fish. During flooding episodes attempts may be made to reduce risk of flooding by pumping water out of ponds. However, this is fruitless if adjacent water courses also flood. Some aquaculturists place temporary mesh fences around the perimeter of the pond in effort to retain fish within ponds during flooding episodes (Pers. Comm., Deacon/Everitt).
· Low Water Levels – If during the dry season the water levels become unacceptably low in active ponds, expensive tap water is used to replenish water levels.
Predation
· Fish commercially reared in ponds provide concentrated feeding opportunities for birds. Species include ardeids (i.e. Herons, Egrets), however, as their beak size is relatively small they are only able to feed on the small fingerlings at the beginning of the season. As the commercial fish increase in size Ardeids then feed primarily on the ‘trash fish’ which are of no commercial value. Ardeids therefore do not have significant impact on predating on commercial species. However, Cormorants frequent Hong Kong between October-April, during which they feed extensively on fish ponds. In addition many of the birds feed at night or near day break, and are therefore more difficult to control. The Hong Kong New Territories Fish Aquaculture Association (HKNTFAA) state that aquaculturists within the Study Area annually loose 10% of their commercial catch, which accounts for approximately 120kg per acre to predation by birds. However, the HKNTFAA do not retain records to account for the financial losses attributed to this loss (Pers. comm., Prichard/Lai).
· Historically aquaculturists shot birds as a method to control predation, however, new legislation was introduced to outlaw this. Since the designation of Mai Po Nature Reserve in 1994 and implementation of corresponding management techniques to protect and enhance wetland habitats and minimise disturbance, members of the HKNTFAA have observed a distinct increase of birds frequenting ponds within the study area. Many ponds are covered with netting to minimise predation of commercial fish by birds. As an intermediate measure to manage this issue, the World Wildlife Fund for Nature (WWF) currently purchase fish from members of the HKNTFAA to stock ponds managed by WWF at Mai Po to alleviate the problem (Pers. Comm, Prichard/Woo). Both WWF and Agriculture and Fisheries Department are currently investigating longer term mutually acceptable management regimes to address this issue.
10.43
Step 5 -Harvesting Stage
Factors
Influencing Harvesting
A number of factors influence the time at which fish are harvested including:
· Fish reaching a marketable size i.e. Fish that reach the optimum market size will achieve a higher market rate than fish which are either to big or too small.
· Market prices – When market prices are high, more fish will be harvested, whilst if prices fall aquaculturists will retain fish in ponds e.g. after a flooding event the market price for fish may increase.
·
Market demand – Supply more fish when demand dictates.
· Time of Year – Harvesting typically occurs between October and March (autumn - winter) for several reasons defined in the preceeding text. However, many local aquaculturists have more recently adopted a continuous stocking/harvesting regime throughout the year hence harvesting may last 6-12 months in duration. Table 10.8 summarises the typical production period and market size of fish commonly reared in polyculture systems. During winter the water temperature falls causing fish to loose their appetite and correspondingly growth becomes minimal. With the exception of ponds subjected to continuous stocking, local aquaculturists believe that there is no merit in retaining fish in ponds over winter if no significant increase in body size and hence market revenue is achieved. Thirdly, pond maintenance can only be carried out during the dry season once the ponds have been drained.
Table 10.8
Production Period and Typical Market Size of Fish
Reared in
Polyculture Systems*
|
Species |
Production Duration
(Months) |
Market Size Weight (kg) |
|
Bighead Carp |
9 – 14 |
1.0 – 2.0 |
|
Common Carp |
6 – 9 |
0.3 – 0.6 |
|
Grass Carp |
20 – 24 |
1.0 - 2.5 |
|
Grey Mullet |
7 – 12 |
0.2 – 0.6 |
|
Silver Carp |
9 – 14 |
1.0 – 2.0 |
|
Tilapia |
4 – 9 |
0.2 – 0.6 |
|
Yellow
Croaker |
24** |
No data available |
(Source: Wilson, 1992; ** Pers. Comm. Prichard/Lai)
Note: * No comparable information available
for species cultured in monoculture systems
· Draining Ponds – At the commencement of harvesting, ponds are drained. Fish are harvested by gradually reducing the water level of ponds. This is achieved by either pumping water into an adjacent pond or alternatively discharging it into a water course. The reduced amount of water in the pond increases the density of fish in the pond thereby making them easier to catch. Draining is usually conducted during the autumn to early winter. Wth the adoption of continuous stocking/harvesting draining of ponds may occur every two years (Pers. comm. Prichard/Lai).
· Netting - A seine net is inserted into the pond and dragged by two individuals from either side of the banks along the length of the pond. The two ends of the net are then pulled together thereby trapping the fish. The fish are then removed from the pond and placed in holding tanks where they are transported in lorries to market. All fish are transported live to market, with the exception of Grey Mullet that die once they are caught (Pers. comm. Prichard/Lai).
· Harvesting Duration – Aquaculturists employ temporary staff to assist during harvesting of the fish. The duration of harvesting varies according to each individual aquaculturist, whether the pond is stocked annual or continuously, the market demand for fish and the availability of casual staff. Fish are harvested from ponds gradually, as an influx of fish to the market will result in a drop in price. More recently harvesting is being undertaken more gradually over a duration of between 6-12 months (Pers. Comm, Prichard/Lai).
· Feeding Opportunities of Birds – As the water is drained out of the pond, trash fish become exposed in the low water levels which create excellent feeding opportunities for birds (Refer to Section 8.45)
10.44 Step 6 - Pond Maintenance
· Drying Out - Over the duration that the pond is actively used, a large amount of detritus accumulates at the pond bottom which significantly reduces both the depth and volume capacity. Therefore following harvesting during the autumn, the pond is drained completely. Water is pumped either into adjacent water courses or alternatively into adjacent ponds. The base and sides of the ponds are then allowed to dry under the sun, thereby consolidating the bottom detritus.
· Dredging - Once dry, these areas are then worked over with a bulldozer to redistribute the bottom detritus allowing the organic matter to be oxidised completely. Less frequently the base of the ponds are dredged out to increase the depth of the pond by 0.30m to increase volume capacity. The dredged material is used to build up the bunds around the perimeter of the ponds. These works are conducted on a rotational basis i.e. not all ponds are dredged in the same year. Works are typically undertaken in September onwards. Such maintenance works were formerly conducted every two to three years. However, due to the increased operational costs ponds are now dredged every 3-5 years (Pers. Comm., Deacon/Everitt).
· Maintenance Works – Approximately every three years a range of maintenance work of ponds are carried out which include reconstruction of bunds around the circumference of ponds using a bulldozer.
Creation of Feeding
Opportunities of Birds During Draining of Ponds
10.45 As stated in Section 108.43 as ponds are drained down during
harvesting, trash fish become exposed which provide feeding opportunities for birds.
Table 10.9 summarises the common residual trash fish found in both monoculture
and polyculture ponds. The combined average weight per hectare of fish pond is
261.88kg/ha. Hence with approximately 73.74ha of active ponds within the study
area 19,311.03kg/yr of trash fish are produced annually within the study area
which provide feeding opportunities for a variety of species of birds including
Ardeids and Commerants (Aspinwall & Co, Unpublished data).
Table
10.9
Species
of Trash Fish that are Commonly Found in Fish Ponds
|
Common Name |
Scientific Name |
|
Mosquito
Fish |
Gambusia affinis |
|
Pawn |
Macrobrachium nipponense |
|
Tilapia |
Oreochromis mossambicus |
(Source: Aspinwall & Co., Unpublished data)
Water Quality &
Quantity
10.46 Water quality of fish ponds is principally determined by acidity and alkalinity (pH), oxygen, nutrients and salinity as described below.
· Acidity and alkalinity (pH) - The acidity and the alkalinity of the water is influenced by the underlying geology and soils of the catchment area, the quantity of rainfall as well as biological activities such as anaerobic respiration by bacteria in the water. Most organisms including fish being reared in ponds can only tolerate a limited pH range (pH 6 - 8.5) (Refer to Table 10.5) (AFD, 1995).
·
Dissolved Oxygen Level - Photosynthesis by phytoplankton and other submerged aquatic
plants produces oxygen. This is subsequently absorbed by fish via the gills and
other living organisms within the pond during respiration. Dissolved oxygen is
quantified in terms of Biochemical Oxygen
Demand (BOD) which represents the potential oxygen demand due to the
breakdown of organic matter in the water. The breakdown of organic matter
requires oxygen and the higher the level of BOD, the lower the amount of oxygen
available for plants, and invertebrates
and fish. (e.g. fish).
Unlike the flowing environment of a water course where gas exchange occurs, water in fish ponds is quiescent, hence gas exchange with the water is limited. At night when photosynthesis stops, oxygen may be depleted as a result of respiration, while the level of oxygen may only build up slowly during the day time. In addition, the capacity of the water to hold dissolved oxygen decreases with increasing temperature. Consequently by carefully monitoring the behaviour of fish aquaculturists can implement active aeration in ponds to increase the dissolved oxygen levels in ponds and hence minimise fish kills attributed to oxygen deficits in the pond.
· Nutrients - The concentration of dissolved nitrogen and phosphorous in the water column can control the development of living organisms in ponds. Phosphorus forms insoluble salts which are unavailable to plants and therefore can restrict growth of organisms in ponds.
Water quality can be classified according to the concentration of nutrients:
· Eutrophic - Nutrient rich water
· Oligotrophic - Low nutrient levels
By the addition of nutrients to the fish pond, the water body is maintained in a eutrophic state resulting in algal blooms which give the water a green tinge. However, as stated in section 10.42 the addition of nutrients to the pond must be carefully managed otherwise the biomass of algal will become too dense, resulting in turbidity thereby preventing light from penetrating the water column. If this occurs other submerged plants such as algae are unable to photosynthesis, and consequently die and decay. The organic matter rapidly reduces the dissolved oxygen concentration in the water, leading to fish suffocating.
· Chemical pollutants - Toxic pollutants include heavy metals (e.g. mercury, lead and cadmium) and inorganic compounds (e.g. ammonia, cyanide, fluoride, acids and alkalis and organic micropollutants). In sub lethal or lethal concentrations they can cause negative impacts upon aquatic organisms. In solution, these chemicals may be absorbed passively by plants and animals resulting in negative impacts. If various pollutants are present simultaneously, synergistic effects (combined effects) may occur. In addition, environmental factors may also influence the impact of chemical pollutants. For example:
· the pH of the water may influence the toxicity;
· increasing temperature increases toxicity; and
· increasing salinity decreases toxicity.
When organisms at the bottom of the trophic food web consume contaminated food, the pollutant bioaccumulates through the food chain. Whilst there may not be obvious evidence of changes sub-acute impacts may occur. In addition, organisms at the beginning of the life cycle are more sensitive to pollutants.
· Saline Intrusion – As a component of environmental monitoring undertaken for the Fish Pond Study, the potential of saline intrusion was investigated due to the proximity of ponds to the coastal area of Inner Deep Bay. However, no saline intrusion was found (Aspinwall & Co, 1997).
·
Groundwater Intrusion – Similarly, monitoring water levels of drained ponds indicated
that ground water intrusion of fish ponds does not occur, hence fish ponds are
effectively a ‘closed loop system’.
· Water budget – Fish ponds are effectively self-contained entities and therefore are not subjected to the dynamic water budgets of other open system wetland habitats. Hence the water levels are dependent on rainfall, the transfer of water from one pond to another or, in extreme cases, when water levels drop, to the addition of tap water.
Correspondingly water will be lost from the fish pond via:
· evaporation and evapo-transpiration;
· filtration through permeable substrate; and
· artificial draining during harvesting.
Water levels will change with the season due to rainfall and variable evaporation /evapotranspiration rates.
Socio
Economic Aspects of Aquaculture Management in Hong Kong
Land
Ownership
10.47 A preliminary investigation of the land ownership where ponds are located within the study area has indicated that all the land on which fish ponds are located is government land. However, in communication with the HKNTFAA, the chairman Mr Lai informed the study team that whilst the majority of the land within the vicinity of Lok Ma Chau is government land, small areas are privately owned (Pers. comm. Prichard/Lai). These private areas are outside the proposed area of the Lok Ma Chau Station and the ecological mitigation area.
Leasing
10.48 Ponds located on government or privately owned land are typically leased for a 5-10 year contract, the actual duration of the contract is dependent upon each individual lease holder. Following the expiry of the lease the majority are renewed. Other than increased annual costs no additional clauses are added to the lease contract, nor are any specific conditions regarding management regimes, conduct etc cited in the lease contract.
Costs
of Leases
10.49 Ten years ago the cost of an annual lease was in the range of $7400 – 11,840/ha/annum, considerably lower than costs today. However, as the demand for land for development in the region of the study area has risen sharply, together with a correspondingly rapid boom in the local aquacultural industry over the last 5-10 years lease costs have risen sharply.
10.50 During 1999 aquaculturists that manage ponds within the Study Area lease land at the cost of $14,800-16,280/ha/annum. This sum is paid to the appropriate individual as a lump sum once a year.
10.51 Within the vicinity of the Study Area ponds range in size from 0.67-2.02ha, with ponds typically falling within the 1.0-1.35ha size range. The number of hectares of pond leased by each aquaculturist varies considerably.
Cost of Pond Management
10.52 Figure 10.4 summarises the overall costs, revenue and profit associated with managing fish ponds within the Study Area (Pers. comm. Prichard/Tam/Lai (HKNTFAA)). The costs associated with aquaculture practices applicable to management of ponds that will be effected by the proposed Spur Line, have been quoted in the proceeding text are essential to demonstrate the annual costs of operating such pond management practices. All quoted costs have been provided by members of the Hong Kong New Territories Fish Culture Association, and were correct in September 1999.
10.53 The actual costs associated with each pond will vary according to the species being reared and the culture technique. Since marine fish are fed predominantly artificial feed, costs of rearing marine fish are approximately 60-70% higher than freshwater and brackish species (refer to Table 10.10).
10.54 Table 10.109
summarises the initial costs for stocking ponds. Whilst costs for the purchase of
fry have been cited in Table 10.9, more recently as fish hatchery techniques
improve and suppliers stocks become more reliable and are able to supply a
greater number of fish, local aquaculturists have increasingly chosen to
purchase and stocking fingerlings (approximately 7cm in length) and juvenile
fish (approximately 12-15cm in length) as they have a higher survival rate than
fry and very juvenile fish. In addition, by initially stocking ponds with
larger fish these are less susceptible to predation by birds, hence harvest
yields and profits are proportionally higher.
10.55 The costs of purchase of fish fingerlings from fish hatcheries are dependent upon the species of fish and the length available. General costs are cited below, specific information for additional species is currently being sought and if available will be quoted in the final report.
· Marine Fish - $2-2.5/fish (7.5cm in length)
· Grey Mullet - $0.05-1.0/fish (2.5cm in length)
· Other freshwater fish - $0.5/2.5cm of fish
10.56 As stated in Section 108.45, approximately 10% of the fish
annually stocked in ponds are subsequently eaten by birds. The last column of
Table 10.10 equates the approximate annual financial losses per hectare
attributed to bird predation. As stated in Figure 10.4,
the typical annual profit achieved following the annual harvest of a fish pond
(per hectare) is HK$44,400, consequently the losses attributed to predation by
birds and other losses e.g. flooding
are relatively high. Poaching of cultured fish does not occur in the Lok Ma
Chau area (Pers. comm. Prichard/Lai).
Table 10.10
Summary of the Potential Financial Loss per Hectare
due to
Predation by Birds
|
|
Cost Stocking Pond/Ha (HK$) |
Equivalent
10% in Revenue/Ha (HK$) |
|
Fry* |
20,000 |
2000 |
|
Grey Mullet (fingerlings)** |
10,000 – 35,000 |
1000 |
|
Marine Fish (fingerlings) |
25000 – 87,5000 |
2500 |
|
Other Fresh Water Fish (Fingerlings |
60,000 –
210,000 |
6000 – 21,000 |
* Species
specific information is currently not available
** Costs
are based on the higher value previously quoted
(Source: Pers. Comm.
Prichard/Lai)
Annual Production of Fish
10.57 In 1994, 5,500
tonnes ,000kg (4,900 tonnes) of fresh fish
were produced within fish ponds from the whole of Hong Kong. More up to date
information is currently not available (Aspinwall & Co., 1997). As the
aquaculture industry booms worldwide, competition with other suppliers who can raise
fish at far lower costs than in Hong Kong, notably in mainland China, has
resulted in local aquaculturists’ profits declining rapidly. In the early 1990s
local aquaculturists where making 60% more profit on harvested fish than they
are currently receiving in 1999.
10.58 Table 10.11 summarises the typical weight of fish harvested per acre of fish pond and the corresponding market value. The variation in values of typical live weight of fish harvested in the polyculture environment varies according to the amount of fish initially stocked in the pond, management factors (e.g. feeding) and other factors that account for losses (e.g. flooding, predation by birds). The HKNTFAA state that for the last three years market prices have been relatively stable.
10.59 Based on 73.74ha of active fish ponds within the study area, between 1320 and 2640 tonnes of fish are produced annually within the study area[1]. Whilst no up-to-date figures are currently available for the total fisheries production within Hong Kong, for comparative purposes in 1994, 5,500 tonnes of fish were produced from all fish ponds within Hong Kong.
Table 10.11
Typical Weight of Fish
Harvested per hectare of Fish Pond and Corresponding Market Value of Fish
|
Common Species Name |
Typical Annual Harvest Live
Weight of Fish (kg/ha/yr) |
Typical Market Wholesale
Value (HK$/kg/yr) |
|
SPECIES REARED IN POLYCULTURE SYSTEMS |
||
|
Big Head |
13,430 – 17,902 |
4.8 - 6.0 |
|
Common Carp |
13,430 – 17,902 |
4.8 - 6.0 |
|
Grass Carp |
13,430 – 17,902 |
4.8 - 6.0 |
|
Grey Mullet |
13,430 – 17,902 |
4.8 - 6.0 |
|
Mud Carp |
13,430 – 17,902 |
4.8 - 6.0 |
|
Silver Carp |
13,430 – 17,902 |
4.8 - 6.0 |
|
Talapia |
13,430 – 17,902 |
4.8 - 6.0 |
|
SPECIES REARED IN MONOCULTURE SYSTEMS |
||
|
Catfish |
26853 – 35,804 |
12.1 |
|
Snakehead |
35,804 |
6.1 – 9.1 |
|
Seabass |
17,902 |
12.1 – 18.1 |
(Source:
Pers. Comm. Prichard/Tam/Lia, HKFNTAA)
Social Aspects of
Aquaculture
10.60 The majority of the aquaculturists who manage the ponds present within the Study Area have the following characteristics:
· Received no formal education.
· Do not possess any other marketable skills.
· Choose to work as an aquaculturists due to the traditional subsistence way of life which is relatively unique to Hong Kong.
· Many aquaculturists are at least 50-60 years old.
· They do not receive either a private or state pension or government subsidy.
10.61 As a component of the Wetland Compensation Study (WCS) currently being undertaken on behalf of the Agriculture and Fisheries Department, several community consultation sessions are being undertaken to facilitate the public and other interested parties to contribute ideas regarding the future management of wetland habitats (including fish ponds) in Hong Kong. During a recent consultation exercise it was stated that aquaculture management in Hong Kong is a traditional way of life which historically has been practised in Hong Kong since circa 1900s. Local aquaculturists purposely choose to pursue this profession as they wish to follow the traditional lifestyle and would like to continue do so.
10.62 As demonstrated by the figures in Table 10.3, during a seven year period between 1987 and 1994 a total of 530ha of fish ponds were lost. In addition, as education is now available to all of the younger generation in Hong Kong, employment and career prospects have improved considerably. Consequently, very few young people choose to work as aquaculturists, particularly as typical overall annual income is relatively low (approximately $3700/month/ha of active pond[2]). This has resulted in a permanent loss of this lifestyle for numerous local aqauculturists, and ongoing development, notably in the north west New Territories where the majority of the fish ponds exist, continues to contribute to the gradual demise of this traditional unique cultural way of life.
10.63 Local aquaculturists do not posses any formal qualifications or alternative skills, are of the older generation and have purposely chosen this profession as they enjoy the traditional lifestyle and do not want to work in other professions. If they are no longer able to practise their livelihood, due to their age, lack of academic qualifications and skills, they may encounter difficulties in finding alternative jobs.
10.64 Where ponds are to be lost or partially lost to accommodate the construction of the Spur Line and associated wetland compensation area, local aquaculturists expect:
· financial compensation for current and future projected loss of earnings;
· loss of livelihood;
· potential forthcoming changes to their traditional way of life which is considered by many as an important component of the cultural heritage of Hong Kong and therefore every effort should be made to retain it; and
· the aquaculturists that operate in the Sheung Shui to Lok Ma Chau area wish to continue working as aquaculturist and would welcome the opportunity of continuing practising their profession elsewhere in the vacinity of the study area if they are forced to permanently vacate their leased land within the Study Area.
Evaluation of Importance of Fish Pond Aquaculture
10.65 On the basis of the information cited in this chapter regarding fish pond management and associated socio economic issues, an overall evaluation has been prepared in Table 10.12 using the criteria listed in Annex 9 of the EIA Ordinance Technical Memorandum as guidance.
Table 10.12
Evaluation of the Environmental
and Socio-Economic Importance of Fish Pond Aquaculture Practices in the Sheung
Shui – Lok Ma Chau Area
|
Criteria |
Evaluation |
|
Size |
73.74ha of active fish ponds 12.04ha of inactive fish ponds |
|
Typical Aquaculture Resources/
Production within Study Area |
Typical annual revenue generated by fish pond is
circa $192,400ha/yr whilst profit is in the range of $44,400/ha/yr. Average production and financial
value of fisheries in the area varies according to the species. For
polyculture species live weight ranges from 13,430-17,902kg/ha/yr, whilst the
market value ranges between HK$4.8-6.0kg/ Whilst depending on the species reared in the
monoculture system corresponding values range from 17,902 – 35,804kg/ha/yr; typical market
values range from HK$6.1-18.1 Based on 73.74ha of fish ponds being present within
the study area between 1100-2640 tonnes of fish are possibly produced
annually within the study area. |
|
Typical Aquaculture Production in Hong Kong as a whole |
In 1994 the 5,500,000kg (5,500 tonnes) of freshwater
fish were produced in Hong Kong from fish ponds. |
|
Number of Operating
Aquaculturists with Study Area |
At this stage of the study no specific information is currently available regarding the number of aquaculturists who are currently actively operating ponds within the boundaries of the study area. |
|
Impact on Aquaculture
Activity |
A total of 73.74ha of active fish ponds and 12.04ha
of inactive fish ponds exist within the boundaries of the study area. |
|
Overall Evaluation |
Moderate |
Identification of Potential Impacts
10.66 The area of fish ponds to be lost due to the proposed development
was calculated by superimposing, the construction
phase footprint (i.e. land directly and
permanently altered by the project) over the habitat map. GIS software was
utlitised to calculate the area of fish pond to be lost (refer to Table 10.12).
Figure 10.1 illustrates the location of fish ponds to
be lost to accommodate construction of the station at Lok Ma Chau and
supporting viaduct structures. As indicated by Figure
10.1 the fish ponds located at Lok Ma Chau and San Tin are located within
the boundaries of the WCA. In addition, one abandoned fishpond will be used
as a temporary compensation area for potential impacts in the marsh area in
Long Valley during the
construction stage. This pond is shown in Figure 10.1 west of the River Beas, and
within the Scheme Boundary for the railway. It is shown in more detailed in Figures
4.10 and 4.12 of the eEcology chapter. This pond will be temporarily modified to become a marsh area, and will be reinstated after construction of the Spur
Line is complete.
10.67 Table 10.13 summarises the direct loss of habitats including active and inactive fish ponds within the study area. These include:
· Lok Ma Chau – 9.5 ha of active fishponds and 0.04 ha of inactive fish ponds will be lost to accommodate construction of the station, vertical columns to support the viaduct and a temporary works area; a further two currently active ponds will be lost at Ha Wan Tsuen to facilitate construction of a permanent works area;
· Chau Tau – 0.62ha of inactive fish ponds will be lost to accommodate both permanent and temporary works areas; and
· Long Valley - 0.01ha of an active pond will be lost to accommodate construction of a vertical column to support the viaduct.
10.68
As the
project engineering designs are still being formulated and revised, area
specific information regarding the temporary loss of fish ponds attributed to
construction activities e.g. works
areas and access routes are currently not available.
Table 10.13
Long-term Estimated Direct Habitat Loss (ha) as a Result of the
Construction of the Spur Line
|
Section |
Sheung Shui |
Long Valley |
Kwu Tu |
Chau Tau |
Lok Ma Chau |
Total loss |
Total present within 500 m |
% Loss within 500 m |
|
Fung Shui wood |
0.00 |
0.00 |
0.00 |
0.00 |
0.00 |
0 |
17.81 |
0.0% |
|
Lowland secondary forest |
0.00 |
0.00 |
0.07 |
0.00 |
0.00 |
0.07 |
15.11 |
0.5% |
|
Plant. Forest |
0.60 |
0.00 |
0.07 |
0.01 |
0.01 |
0.69 |
32.89 |
2.1% |
|
Orchard |
0.00 |
0.00 |
2.46 |
0.00 |
0.00 |
2.46 |
10.91 |
22.5% |
|
Dry Agric. land |
0.01 |
0.40 |
0.00 |
0.00 |
0.00 |
0.41 |
13.02 |
3.1% |
|
Wet Agric. land |
0.00 |
0.83 |
0.00 |
0.02 |
0.00 |
0.85 |
28.31 |
0.2% |
|
Inactive Agric. land |
0.00 |
0.00 |
0.03 |
0.58 |
0.00 |
0.61 |
38.27 |
4.3% |
|
Active Fishpond |
0.00 |
0.01 |
0.00 |
0.00 |
9.5 |
9.5 |
73.74 |
12.9% |
|
Inactive Fishpond |
0.00 |
0.00 |
0.00 |
0.62 |
0.04 |
0.66 |
12.04 |
5.5% |
|
Pond |
0.00 |
0.00 |
0.00 |
0.00 |
0.00 |
0 |
2.31 |
0.0% |
|
Marsh |
0.00 |
0.00 |
0.00 |
0.00 |
0.01 |
0.01 |
5.17 |
0.2% |
|
Water courses |
0.00 |
0.00 |
0.00 |
0.01 |
0.00 |
0.01 |
8.05 |
0.1% |
|
Grass/shrub mosaic |
0.00 |
0.00 |
0.06 |
0.00 |
0.01 |
0.07 |
54.27 |
0.1% |
|
Wasteland |
0.90 |
0.00 |
1.00 |
0.01 |
0.00 |
1.91 |
35.52 |
5.4% |
|
Developed areas |
8.50 |
0.01 |
6.80 |
2.40 |
0.07 |
17.78 |
432.03 |
4.1% |
10.69 An ecological impact assessment has previously been undertaken for fish ponds in terms of ecology (Chapter 4 of this report). Consequently this impact assessment focuses on the socio- economic impacts attributed to the impacted and loss of fish ponds within the study area. These include:
· Loss of fish ponds – As stated earlier, 9.5 ha of active ponds and 0.66ha of inactive fish ponds will be lost from the study area.
· Fisheries Production – Approximately 9.6 ha of fish ponds are scheduled to be lost to accommodate construction of the Spur Line. Since the status of abandoned ponds may change to active during the year and vice versa, for consistency purposes to facilitate an estimate of the annual losses and revenue abandoned ponds have been treated as active ponds in this context.
· Table 10.14 summarises the estimated annual loss of production of fisheries from the impacted area which amounts to:
· Polyculture ponds – 136 - 181 tonnes of live weight of fish
· Monoculture ponds – 271 - 362 tonnes for Catfish, 362 tonnes for Snakehead, 181 for Seabass.
10.70 The actual loss will be dependant upon species reared in particular ponds, ponds which are managed under a monoculture system will result in a substantially higher loss of revenue than ponds that are reared under a polyculture system. Since specific information is currently not available as to what species, stocking densities and cultured systems are practiced in the proposed impacted ponds, detailed estimates can not be provided.
·
Compensation Area - As stated in the Ecology Chapter of this report, to mitigate for
the loss of habitats to accommodate construction of the proposed Spur Line and associated
works, a total of approximately 28.5 ha of fish ponds in the Lok Ma Chau
area located to the south west area of the proposed station have been
proposed to compensate for habitat
lost. As a component of the proposed management regime a number of management
regimes have been recommended that include enlarging the ponds, reprofiling
bunds, planting of marginal emergent plants, reducing the water depth,
increased drain down periods and manipulating aquaculture management regimes to
optimise food availability for birds. The proposed compensation area is
currently not leased out for fishfarming activities. For effective management
of the compensation habitat, the specialist contractor contracted by KCRC to
manage the fishponds within the compensation area (until the wetland trust management organisation is
established) is likely to employ local aquaculturists to implement the proposed
management regime. As stated in the Ecology Chapter, the proposed modification
of aquaculture management practices are not anticipated to cause any
significant detrimental effects on fish production or financial viability of
aquaculture management. However, more specific details are currently not
available, hence an estimate of potential socio economic impacts for the proposed
compensation area cannot be fully evaluated.
· Loss of Livelihood – The number of aquaculturists who currently manage the scheduled impacted ponds along the Spur Line route is currently not known, therefore it is not feasible to assess how many local aquaculturists will be affected by the development.
·
Decline in availability of
Seasonal Work – As stated in Figure
10.4, during harvest time approximately 8 casual staff are hired over a 10
day duration to assist in harvesting each pond. With approximately 9.6 ha
of fish ponds within the study area this will result in a decline in the
availability of casual seasonal work within the Lok Ma Chau area.
Table 10.14
Summary of the Potential
loss of Production and Revenue Attributed to the
Loss of Fish Ponds within
the Study Area.
|
Common Species Name |
Typical Annual Harvest Live
Weight of Fish (kg/ha/yr) |
Approximate Loss in
Production of Live Weight Fish
(tonnes)[3]
|
Typical Market WholesaleValue(HK$/kg/yr) |
Indicative Market Wholesale
Values for the 10.2ha of Impacted Fish Ponds (HK$) [4] |
|
POLYCULTURE MANAGEMENT SYSTEM |
||||
|
Big Head |
13,430 – 17,902 |
136 – 181 |
4.8 - 6.0 |
816,000 – 1,086,000 |
|
Common Carp |
13,430 – 17,902 |
136 – 181 |
4.8 - 6.0 |
816,000 – 1,086,000 |
|
Grass Carp |
13,430 – 17,902 |
136 – 181 |
4.8 - 6.0 |
816,000 – 1,086,000 |
|
Grey Mullet |
13,430 – 17,902 |
136 – 181 |
4.8 - 6.0 |
816,000 – 1,086,000 |
|
Mud Carp |
13,430 – 17,902 |
136 – 181 |
4.8 - 6.0 |
816,000 – 1,086,000 |
|
Silver Carp |
13,430 – 17,902 |
136 – 181 |
4.8 - 6.0 |
816,000 – 1,086,000 |
|
Talapia |
13,430 – 17,902 |
136 – 181 |
4.8 - 6.0 |
816,000 – 1,086,000 |
|
MONOCULTURE MANAGEMENT SYSTEMS |
||||
|
Catfish |
26853 – 35,804 |
271 – 362 |
12.1 |
3,279,000 – 4,380,200 |
|
Snakehead |
35,804 |
362 |
6.1 – 9.1 |
3,208,200 – 3,294,200 |
|
Seabass |
17,902 |
181 |
12.1 – 18.1 |
2,190,100 – 3,276.100 |
(Source: Pers. Comm. Prichard/Tam/Lia, HKFNTAA)
Construction Phase Impacts
10.71 The predicted short term impacts of the construction phase of the Spur Line project are likely to be:
· Permanent loss of 9.5 ha of active fish ponds and 0.66ha inactive fish ponds. Additional areas may be lost temporarily e.g. in the Ha Wan Tsuen area to accommodate temporary works access and storage areas;
· Loss in production of fisheries and associated live weight (refer to Table 10.14); and
· Loss of permanent employment and livelihood of full time aquaculturists and temporary casual work.
Operation Phase
10.72 The predicted long term impacts associated with the operation of the Spur Line project are likely to be:
· Permanent loss of fish ponds (i.e. for works access and storage areas);
· Permanent loss of fisheries production; and
·
Permanent loss of livelihood and hence
contribute to the demise of traditional of this local cultural heritage and way
of life.
Mitigation
10.73 A number measures could be implemented to mitigate for the anticipated loss of fish ponds and socio-economic fisheries impacts which will be the responsibility of KCRC. These are described below.
Habitat Loss
· To minimise habitat loss and for compatible engineering reasons, slight realignment of the proposed track route has already been taken into consideration. Further adjustments to the alignment to reduce remaining loss of fish ponds are not feasible.
·
Any fish ponds that are scheduled to
be lost temporarily during the works should be reinstated on-site following
completion of all works. Temporary occupation areas for construction works do
not contain any fish ponds. One fishpond west of the River Beas will be
constructed as a temporary compensation area to mitigate for construction
impacts in the Long Valley marsh. This fishpond is shown within the Scheme Boundary
for Spureline on Figure 10.1, west of River Beas, and in more
detail in Figures 4.10 and 4.12 of the Ecology Chapter. It is
currently an abandoned fishpond. This temporary compensation area will be
reinstated after the end of the construction period and implementation of the
long-term mitigation areas for permanent ecological impacts.
· A total of 9.6 ha of fish ponds are scheduled to be permanently lost or disturbed within the study area. These have been compensated for through provision of an area to the southwest of the proposed station terminus at Lok Ma Chau. Details of the mechanism of implementation of this compensation area are described in the Ecology Chapter of this report. As this compensation area is currently not licensed for fishfarming activities, the socio-economic impacts on the fisheries of the area cannot be specified.
Fisheries Production & Loss of Revenue
· The loss of fisheries production and associated income will be dealt with during the resumption of temporary land during the Spur Line construction. The fishponds which are within the Spur Line Scheme Boundary and which are not required for compensation at a later stage, will be reinstated and returned to the original owners after construction is complete.
Involvement
in Management of Compensation Area
·
To gain community support and hence a
higher success of the proposed management regime planned for the wetland
compensation area, local aquaculturists should be actively involved in the
modification of the fish ponds and offered the first choice of managing these
fish ponds.
·
As stated in Section 10.423, currently 10% of
the annual stocks are lost to predation by birds. Mitigation measures could be
developed in conjunction with WWF and the HKNTFAA, to integrate management
techniques that optimise feeding opportunities for birds within the proposed
wetland compensation area. Management techniques to enhance feeding
opportunities at specific times could include stocking of commercial ponds with additional fingerlings, and reducing water levels to expose more
fish. Such management regimes could be manipulated to coincide when other local
commercial aquaculturalists are stocking ponds with fingerlings, to encourage
birds to feed in the compensation area and thereby lessen predation on
commercial ponds.
Summary
10.74 This chapter describes fish pond aquacultural practices undertaken within the Study Area, including current aquacultural locations, practices and quantification of resources, and related socio-economic issues. An assessment of impacts from the Spur Line is followed by appropriate mitigation measures. A total of 73.74ha of active fish ponds and 12.04ha of inactive ponds occur within the 1km corridor of the study area. In addition, a further 28.5ha of fishponds located to the south west of the proposed station complex have been proposed as compensation for the fish ponds impacted by the station complex.
10.75 Anticipated impacts attributed to the construction phase of the proposed works include the permanent loss of 9.5 ha of active ponds and 0.66ha of inactive ponds. Anticipated loss of annual fish production from the directly impacted area is in the range of 136 – 181 tonnes using the polyculture system, or between 181 – 362 tonnes for monoculture. The equivalent commercial market value for fisheries resources cultured using the polyculture technique in this 9.6 ha fishpond area ranges from HK$816,000 – 1,086,000, whilst for those cultured under the monoculture system, the market value ranges from HK$2,190,100 – 4,380,200 depending on the species reared. The area proposed for compensation area is currently not licensed for fishfarming activities and therefore no socio-economic impacts can be specified.
10.76 Mitigation measures include reinstatement of fish ponds temporarily
lost during works. The management of the ecological compensation fishponds area
in the Lok Ma Chau area will be by the Wetland Trust Management Organisation which
is in the process of being established. Financial support will be by a lump sum
donated by KCRC, which will be invested by the trustees to cover recurrent
costs of the wetland management organisation. Income from the fishpond
operation will also be used in the management process.
References
AFD (1999) Website: http://www.info.gov.hk/afd/fish/aquac.htm
Anon., (1995) Focus on Fish Ponds : VI Porcupine ! 18:19-26.
Everitt, S.. & Cook, J. (1997) Regional Study and Workshops on Aquaculture: Sustainability and the Environment. Hong Kong Study Report. Asian Development Bank
Personal Communication Susannah Everitt (Au Tau Fisheries Dept. AFD)/ Richard Deacon (BBV)
Personal Communication Anna Prichard (Ecoscope) / Mr Lai Loy Chau (Hong Kong New Territories Fish Culture Association)
Personal Communication Kenneth Tam (BBV) / Mr Lai Loy Chau (Hong Kong New Territories Fish Aquaculture Association)
Wilson, K.D. (1992) Pond Fish Culture in Hong Kong. Unpublished AFD Paper.
Bibilography
Aspinwall & Co. (1997) Study on the Ecological Value of Fish Ponds in Deep Bay. Executive Summary/ Final Report. Planning Department Hong Kong.