Dr. P.S. Wong, Agriculture and Fisheries Department, Hong Kong.
Marine cage culture in Hong Kong.
Major constraints to aquaculture development in Hong Kong are shortages of suitable land and water space and pollution problems. Rapid urban development in the New Territories has increased land values leading to the conversion of freshwater fish ponds for residential development or their use as open storage sites for containers. To curb this rapid change in land use, two interim Amendment Bills for the Town Planning Ordinance were introduced in 1991. These amendments enabled the jurisdiction of the Ordinance to be extended to cover the whole territory and allowed for direct enforcement against unauthorised development in selected areas. Efforts are being directed to retain fish ponds, particularly those surrounding the Mai Po Marshes (a migratory bird sanctuary), for ecological and conservation purposes. Streams are so polluted by livestock and domestic waste discharges that the water cannot be used for fish culture. Farmers rely on rain or well water and adjust the composition of species stocked to minimise the need for water exchange. Since 1987, water control zones were gradually declared under the Water Pollution Control Ordinance to control discharges into inland and coastal waters. Control of livestock wastes also started with the enactment of the Waste Disposal (Amendment) Ordinance. This was further supplemented by the setting up of waste treatment demonstration plants, provision of a livestock waste collection service, as well as the introduction of an effluent-free pig-raising method. A feasibility study on the use of treated sewage effluent for fish culture is in progress.
In the 1970's, marine fish culture proliferated in Hong Kong to occupy 54 sheltered bays. To avoid conflicts between the various users of coastal waters, the Government enacted the Marine Fish Culture Ordinance in 1982 requiring all marine fish culture to be conducted under license in designated fish culture zones. Urban development had led to a deterioration in water quality in Tolo Harbour, causing red tide outbreaks and fish kills and, after implementation of the Water Pollution Control Ordinance, Tolo Harbour was the first Water Control Zone to be declared in 1987. This was followed by the Port and Junk Bay areas in 1989. For sewage discharges, the Environmental Protection Department (EPD) has drawn up a series of sewage master plans for different districts to be implemented in various stages. In the late 1980s, there was concern over the environmental impacts of marine fish culture and a study concluded that the polluting effect of marine fish culture was localised. Major sources of pollution included fish faeces, feed leachate, unconsumed feed, fouling organisms from cage cleaning and improper disposal of waste. Based on the recommendations made, the Government has taken action to reduce raft density in fish culture zones with limited tidal flushing, stepped up regulatory control over structures on rafts to prevent domestic dwellings, developed suitable pelleted feeds to replace trash fish and educated farmers on proper refuse and waste disposal. Trials in open sea fish farming are being conducted. A working group on mariculture zones, composed of the concerned departments, was formed to review the environmental condition of existing fish culture zones and oversee the selection of sites for any new fish culture zones.
Map of Hong Kong.
Since 1989, there has been large scale coastal land development throughout Hong Kong and three fish culture zones have been closed. Only one new fish culture zone was designated for relocation of the affected fish farmers. The associated widespread marine sand dredging and dumping are causing serious environmental impacts to the marine life in Hong Kong and impacts on marine fish culture are being monitored and assessed. Affected fish farmers were offered an ex-gratia allowance.
Oyster culture in Deep Bay is affected by land reclamation, pollution and contamination. Deep Bay was declared a Water Pollution Control Zone in 1991 and pollution control strategies for the bay are being considered.
The following is a review of environmental assessment and management of aquaculture development in Hong Kong, with emphasis on freshwater pond fish culture and marine finfish cage culture systems.
3. STATUS OF AQUACULTURE
3.1 Total aquaculture production
Although primary industry contributes less than 1% of the gross domestic product in Hong Kong, fisheries is the most important primary industry. It has an important economic role as a major component of the diet, particularly in a country chronically short of land. In 1992, for a population of 5.8 million, the consumption of fisheries products amounted to 287,930 tonnes which is equivalent to an average of 49.5 kg/person/year or 136 g/person/day. As such, most aquaculture production is for local consumption. Statistics for the aquaculture industry from 1987 to 1990 are shown in Table 1.
Table 1. Aquaculture production in Hong Kong, 1987–1992.
|Value (000s US $)||34,951||40,286||35,283||35,504||40,184||37,832|
|Production as % of GNP||0.00078||0.00076||0.00058||0.00052||nd||nd|
3.2 Inland and coastal resources
With limited land availability (total 1,074 km2) and a large population, the resources for inland and coastal aquaculture are very limited. There are 2,425 ha of reservoirs, but these are used purely for maintaining potable water supplies. Fish are kept in the reservoirs to control phytoplankton growth but no active fish culture operations are carried out there. There are approximately 600 streams in the New Territories. Characteristically, these are short streams having fast flowing upper reaches with rocky bottoms, becoming sluggish and silty bottomed in the lower reaches. Flows in these rivers are very variable responding rapidly to rainfall run-off. Around 70% of the river base flows from the upper reaches are channelled into reservoirs, while the lower reaches of most streams receive heavy loads of livestock wastes, domestic sewage and industrial discharges and are no longer a suitable resource for aquaculture.
The coastline of Hong Kong (including all the small islands) is about 800 km long, but as Hong Kong is a very busy port, the demand to use coastal waters for navigational purposes and related developments is great. In addition, with the huge population there are also heavy demands made on coastal waters for recreational purposes. All of these are competing for coastal waters and there is therefore very little suitable coastline left for aquaculture development The Port and Airport Development Project which started recently will lead to substantial changes in the coastline in the near future.
3.3 Aquaculture systems and species
Aquaculture in Hong Kong is comprised of three sectors: inland freshwater finfish pond culture, coastal marine finfish cage culture and oyster culture. The culture systems and major species involved in each sector are summarised in Table 2. There are currently around 600 inland freshwater finfish pond culture farms covering a total area of 1,350 ha, located mainly in the north-western New Territories (Figure 1).
Ninety percent of the farms practice polyculture of carps with tilapia or grey mullet and of these 76% are integrated with duck rearing.
Table 2. Aquaculture system, species and production in Hong Kong in 1990.
(US $ 000s)
|Channa maculatus||Snakehead||310||1,133||Pond, monoculture|
|Clarias fucus||Catfish||120||342||Pond, monoculture|
|Lates calcarifer||Sea bass||-||-||-|
|Ctenopharyngodon idella||Grass carp||860||1,433||Pond, polyculture|
|Hypophthalmichthys nobilis||Bighead carp||1,220||2,080||Pond, polyculture|
|Hypophthalmichthys molitrix||Silver carp||490||471||Pond, polyculture|
|Cyprinus carpio||Common carp||920||1,427||Pond, polyculture|
|Carassius auratus||Edible goldfish||-||-||Pond, polyculture|
|Mugil cephalus||Grey mullet||605||1,606||Pond, polyculture|
|Oreochromis niloticus/mossambicus||Tilapia||1,195||1,195||Pond, polyculture|
|Epinephelus tauvina||Green grouper||199||2,190||Floating netcages|
|Epinephelus areolatus||Spotted grouper||500||4,237||Floating netcages|
|Epinephelus akaara||Red grouper||166||2,266||Floating netcages|
|Mylio latus||Yellow finned seabream||130||1,541||Floating netcages|
|Rhabdosargus sarba||Goldlined seabream||830||5,091||Floating netcages|
|Chrysophrys major||Red pargo||80||539||Floating netcages|
|Lutjanus russelli||Russels snapper||227||1,874||Floating netcages|
|Lates calcarifer||Seabass||324||2,876||Floating netcages|
|Seriola purpurascens||Amberjack||167||1,207||Floating netcages|
|Crassostrea gigas||Oyster||805||811||Bottom/ raft culture|
For coastal marine finfish cage culture, there are some 1,650 licensed operators in 26 designated fish culture zones occupying a total sea area of 201.4 ha. Bottom culture of oyster, located in Deep Bay in the north-western New Territories, has diminished over the last decade due to increasing difficulties in spat collection. As a substitute, fattening of imported juveniles using the raft suspension method has increased in recent years. Presently, there are some 250 oyster culture operators occupying about 550 ha. of intertidal waters. This number is likely to decline in the near future.
3.4 Supply of inputs
Limited seed supply is one of the major constraints to the aquaculture industry in Hong Kong. For inland freshwater finfish pond culture, although some farmers artificially breed fry of Chinese carps, tilapia, snakehead or catfish, most fish fry are purchased from China or Thailand. Seeds of some cultured marine finfish species e.g. Rhabdosargus sarba, Mylio berda, Chrysophrys major and Seriola purpurascens are obtained from local natural populations. However, the majority of grouper and snapper fry are imported from Thailand or the Philippines. In recent years, very little oyster spat could be collected from the wild and most of the young oysters were imported from China.
The other major input in finfish culture is feed. Many of the inland polycultured species feed on plankton in the pond water and feeds are normally applied as supplements to increase production. Common feeds include peanut cake, corn meal, wheat bran, bean meal or brewery waste. Integration with duck rearing makes use of the duck faeces to fertilise the pond water, increasing plankton growth and therefore increasing feed supply to the fish. Trash fish is used as feed in the monoculture of snakehead, catfish or seabass and also for coastal marine finfish cage culture, which involves mainly carnivorous fish species. Most of the trash fish for the fish culture zone on the eastern side of Hong Kong is supplied by purse seiners operating in nearby waters. The trash fish supplied are usually very fresh, but the supply is not constant and is declining with deterioration of inshore water quality due to pollution and increasing coastal development works. Some fish culture zones in the islands on the outskirts of Hong Kong (e.g. Lamma Island) use trash fish captured by trawlers as the supply is more constant. Generally, there is a shortage of trash fish during the winter months.
Figure 1: Aquaculture Production Sites in Hong Kong.
Key for Figure 1
Areas of fish pond production
Areas of oyster production
Designated Fish Culture Zones
3.5 Aquaculture species: quality, value and market
The quality and value of aquaculture species produced in 1990 is shown in Table 2. Due to the heavy demand from local markets, all locally produced aquaculture products are for domestic consumption.
3.6 Legal framework for aquaculture development
3.6.1 Access to aquaculture operations
Definition of aquaculture
There is no definition of the word “aquaculture” given in Government legislation. However, in the Marine Fish Culture Ordinance Cap. 353, there is a definition of “fish culture” which means any operation involving the maintenance, propagation or promotion of growth of any marine fish, crustaceans or molluscs (other than oyster) in captivity within waters in Hong Kong.
Aquaculture laws and regulations
A list of rules and regulations are shown below, but legislation of direct relevance to aquaculture are the Marine Fish Culture Ordinance (Chapter 353) and the Pearl Culture (Control) Ordinance (Chapter 307).
List of rules and regulations.
Animals and Plants (Protection of Endangered Species), Cap. 187.
Antibiotics Ordinance, Cap. 137.
Dumping at Sea Act 1974 (Overseas Territories) Order 1975.
Fisheries Protection Ordinance, Cap. 171.
Foreshore and Sea-bed (Reclamations), Cap. 127.
Marine Fish Culture, Cap. 353.
Marine Fish (Marketing) Ordinance, Cap. 291.
Pearl Culture (Control) Ordinance, Cap, 307.
Pharmacy and Poisons, Cap. 138.
Public Health (Animals and Birds) Ordinance, Cap. 139
Waste Disposal Ordinance.
Water Pollution Control (General), Cap. 358.
The Marine Fish Culture Ordinance protects and controls marine fish culture. This legislation requires that all marine fish culture operations be practised under licence and within designated fish culture zones. The licence specifies the size and location of the fish rafts, the size and use of structures permitted on the raft and regulations on moorings and installation of lights, licence number plate, refuse containers etc. The legislation also prohibits the release of pollutants and entrance of unauthorised vessels into the fish culture zone. There are also provisions to give instructions regarding fish culture operations, e.g. disposal of diseased fish or other wastes.
The Pearl Culture (Control) Ordinance conserves the resource of pearl oysters and controls the culture of pearls in Hong Kong. However, due to a deterioration in water quality in some sites and competition for water space, as well as changes in the pearl market, pearl farming is no longer practised in the territory. The Fisheries Protection Ordinance (Chapter 171) is also related to aquaculture as it promotes the conservation of all forms of aquatic life and turtles within Hong Kong waters. It prohibits the use of explosives and toxic substances for fishing and provides some protection for fish spawning grounds and oyster beds.
Lease and development planning permission
Unlike marine finfish cage culture, inland freshwater finfish pond culture and oyster culture have no direct legislative or licensing control. However, fish ponds and oyster beds involve lands which are either privately owned or on lease from the Government. The Lands Department is responsible for granting the lease of Crown Land. Recently, some control of land use in rural areas in the New Territories was provided by the Town Planning (Amendment) Ordinance in 1991. Development planning permission plans are prepared for each district and permission for any change in land use has to be approved by the Planning Department.
3.6.2 Environmental management of aquaculture
Water quality and water pollution control
Hong Kong's main water pollution management law is the Water Pollution Control Ordinance (Chapter 358) enacted in 1980. This ordinance empowers the government to declare water control zones. The whole territory is divided into ten Water Control Zones (Figure 2), and seven of these are already declared. Each water control zone has its own water quality objectives and its polluting discharges are controlled to maintain the desired beneficial uses of water, such as: irrigation; aquaculture; preservation of aquatic wildlife; active and passive recreation; transportation; and storm water channels. The areas of concern for water quality objectives include colour, bacterial count, dissolved oxygen, salinity, temperature, suspended solids, ammonia, nutrients and toxicants. The objectives form a basis for determining the standards for effluent discharge. Detailed standards for effluent discharge into inland and coastal waters are described in a Technical Memorandum issued under section 21(1) of the Water Pollution Control (Amendment) Ordinance 1990. The Environmental Protection Department is in charge of monitoring and enforcement of effluent discharge standards.
Some Water Control Zones include many existing fish culture zones, however, all fish culture zones were designated before the declaration of the Water Control Zones. Therefore the suitability of a site for marine finfish cage culture was assessed according to the criteria adopted by Agriculture and Fisheries Department which basically includes minimum depth, wave exposure, general water quality, distance from major urban or industrial centres as well as compatibility with the existing use of the coastal water. The Technical Memorandum on Effluent Standards issued under Section 21 of the Water Pollution Control Ordinance stipulates that no new effluent will be allowed within 200 m of the seaward boundaries of a marine fish culture zone and within 100 m of the landward boundaries. The Agriculture and Fisheries Department undertakes some monitoring of water quality within the fish culture zone. Some large fish farms undertake monitoring of water quality around the farm as a precautionary measure against oxygen depletion problems.
The majority of the inland finfish farms are in ponds with no water exchange and which have virtually no discharge. For monoculture of snakehead or catfish, which has very slow flow through of water, pond discharges are usually within the standards for irrigation, pond fish culture or general amenity use. For marine finfish cage culture, discharges from floating net cage culture operations are usually diffuse and in small quantities. There is no practical means of monitoring the effluents and efforts are directed towards improvement of husbandry and management practices to reduce pollution.
Environmental Impact Assessment (EIA)
In recent years, for developments which would result in significant changes to the physical environment or which were near to sensitive receivers, some EIA is normally required. Aquaculture is classified as a sensitive receiver and particular efforts are made to prevent or minimise pollution, which may be carried by tides or currents, affecting aquaculture operations. The EIA study usually includes an identification of the key sensitive receivers, the assessment of possible impacts both during the construction phase and operational phase, as well as recommendations for applicable mitigatory measures to minimise the impacts.
Since 1990, following a consultancy study on the environmental impact of marine finfish cage culture in Hong Kong, it has been agreed by concerned government departments, that in the process of determining whether a new site is suitable for designation as a fish culture zone, an EIA should be conducted. A detailed EIA on setting up a new fish culture zone north of Tung Lung Chau was conducted in 1991 for relocation of the mariculture operations in Tin Ha Wan fish culture zone, which had to be cleared for land development.
Figure 2: Water Control Zone Status as of December, 1992.
Control of movement of fish
Presently there are no laws in Hong Kong requiring quarantine of imported live fish. Although the importance of quarantining fish is fully realised, such a system would be difficult to set up in view of the large volume of fish entering Hong Kong from different countries via different forms of transport. A quarantine service would not be cost-effective to run and is beyond the financial means of the industry.
There are also no regulations governing the export of live fish. However, depending on the importing countries, exporters may have to comply with certain requirements. When requested, the Agriculture and Fisheries Department (which includes a Fisheries Officer and a Veterinary Officer) will carry out inspections of the fish growing or holding facilities and issue certificate of health record of the fish premises and operations, as appropriate.
Control of toxic or hazardous substances or pharmaceutical preparations
The Antibiotics Ordinance controls the use of antimicrobial substances in aquaculture. Under this legislation, no person shall possess or administer by way of treatment, any antimicrobial substances (including antibiotics) or preparation unless he is a medical practitioner, dentist, veterinary surgeon or a holder of a valid permit for the purpose. The Antibiotics Ordinance does not, however, apply to antibiotic substances contained in food or food supplement for livestock. The Pharmacy and Poisons Ordinance governs the supply and possession of hormones and other scheduled poisons. At the moment, fish farmers do not routinely use antibiotics, hormones or other poisons as these are usually considered to be costly and there are also difficulties in administering to the fish as the fish are fed with trash fish.
Control of pesticides
The Agricultural Pesticides Ordinance registers and controls the import, packaging, labelling, storage, sale and transport of all agricultural pesticides. Hence, molluscicides such as tributyltin will be subject to control if it is imported as an active ingredient. There are no specific codes of practice for the use of biocides in aquaculture.
Protection of indigenous species
There is no legislation for the protection of indigenous species.
While official quarantine of imported live fish is not required, some progressive fish farmers keep imported fry separately from other fish and bath them with freshwater (for marine species), salt water (for freshwater species) or oxytetracycline. They also monitor the health condition of the fish for a convenient period of time. This practice is being actively encouraged by the Government.
Product quality control
The Public Health and Municipal Services Ordinance limits the maximum permitted concentration of metals in food and stipulates that no person shall sell any food items which contain stiboestrol substances. In addition, all shellfish and finfish destined for human consumption should not exceed the following standards, which are monitored and enforced by the Department of Health:
|Paralytic shellfish toxins||400 mouse units (mu)/100 gm|
|Ar||10 ppm (shellfish)|
|6 ppm (finfish)|
3.6.3 Institutional framework
The Agriculture and Fisheries Department is responsible for enhancing the productivity of the aquaculture industry through planning and improvement in culture and management techniques. It is empowered by the Marine Fish Culture Ordinance to protect and regulate marine fish culture activities in Hong Kong. In connection with this, the department is in charge of issuing and renewal of marine fish culture licences. The Aquaculture Fisheries Division, Fisheries Branch have a staff of 46 and is comprised of three sections:
The Aquaculture Regulatory and Management Section - regulating and licensing of marine fish culture.
The Aquaculture Technology Section - adaptive research into new culture techniques and investigations into aquaculture problems and constraints.
Aquaculture Development Section - inland finfish pond culture and oyster culture development.
There are three research sub-stations:
Au Tau Fisheries Sub-station concentrates on research related to inland finfish pond culture and is starting to study fish disease.
Kat O Fisheries Sub-station is mainly concerned with the improvement of marine fish culture techniques.
Aberdeen Fisheries Sub-station has facilities for water quality analysis, red tide identification and experimental environmental studies.
The Environment Protection Department is in charge of the protection of the environment as a whole. The groups which are related to aquaculture include Environmental Planning and Assessment, Water Quality Management and Waste Management. Details of the organisation and services provided by these groups are shown in Annex I. The Lands Department is in charge of land matters and is responsible for granting leases for oyster culture or pond fish rearing on crown land. Other non-governmental organisations which have concerns in these fields include tertiary education institutes, environmental pressure groups (e.g. Friends of the Earth, World Wide Fund for Nature) and fishermen and mariculturists associations.
Governing environmental activities related to aquaculture
The Environmental Protection Department is charged with implementing government environment policy over the whole region which includes water bodies where aquaculture activities are located, or involved. Tertiary institutes which are occasionally involved in research on environmental or technical issues related to aquaculture include the University of Hong Kong, Chinese University of Hong Kong, Hong Kong University of Science and Technology, City Polytechnic and Hong Kong Baptist College.
3.7 Government policy on aquaculture
A relatively low emphasis is placed on primary production in Hong Kong, and it is unlikely that much increased spending will be made in this area over the next few years. Although there are no direct subsidies to fish farmers, government assistance through free technical advice and services has done much to enhance the development of the industry. The Department of Agriculture and Fisheries is charged with undertaking adaptive research; environmental monitoring; developing and introducing new gear and equipment; and providing technical, managerial and financial advice to farmers. A general policy of free trade is adopted by the Hong Kong Government in which no trade barriers are imposed on imported primary products.
The priorities for aquaculture development may be defined as follows:
For inland pond finfish culture, interest is placed on culturing new exotic species with a higher market price.
For coastal marine fish cage culture, emphasis is placed on improving husbandry and management practices to minimise self pollution and on new culture schemes in the open sea.
Further development in coastal oyster culture in Deep Bay relies on drastic improvements in environmental conditions.
4. INTERACTIONS BETWEEN AQUACULTURE AND THE ENVIRONMENT
Coastal and inland fish culture in Hong Kong underwent rapid growth in the 1970s. At that time, coastal finfish cage culture proliferated in 54 coastal areas covering almost every sheltered bay. From 1980 onwards, Hong Kong experienced increasing land reclamation especially in the New Territories and inland areas devoted to fish culture gradually decreased. Fish culture is further constrained by the deterioration of water quality in both inland and coastal waters. Nevertheless productivity and competitiveness have been maintained through improved management and husbandry practices.
Oyster culture has been practised in the north-western waters of Hong Kong by the traditional bottom method for about 200 years. However, over the past few decades there has been a gradual decrease in oyster production due to increasing pollution of coastal waters and a deterioration in the condition of oyster beds arising from nearby land developments.
4.1 Impacts of external environment on aquaculture production
Land scarcity, water availability and pollution are major limiting factors affecting aquaculture development in Hong Kong. Land is very limited and there is competition among industrial, residential, recreational and inland aquaculture activities. Most streams are polluted and not suitable for fish culture. There is also heavy competition for coastal water areas for marine fish farming, navigation, recreation, land reclamation and as a sewage and waste discharge receiver.
Along with the increase in population in Hong Kong has come rapid urban development in the New Territories. Many fish ponds were reclaimed to allow for the development of residential sites, such as those at Tin Shui Wai. Fish farmers have had to face an increase in land prices in the New Territories, along with a decrease in the market price of pond fish. As a result, many fish ponds have been filled in and used as open storage sites for containers.
Extensive development and construction projects have also caused pollution problems for inland aquaculture. Invariably, drainage channels in low lands are blocked by construction work leading to frequent flooding of the ponds. Some fish ponds have also suffered limited damage due to storms and typhoons. Many land development projects have involved reclamation of sheltered shores where fish culture zones were located. Coastal reclamation has also destroyed many important areas that were once suitable breeding grounds for local fish species and contributed to the deterioration in the quality of surrounding water body. So far three fish culture zones were degazetted due to land reclamation with only one new fish culture zone set up for relocation of the mariculture operations. This resulted in the extinguishment of 11,513 m2 of mariculture rafts with an estimated annual production of 92 tonnes. In Deep Bay 3.35 ha. of oyster beds were reclaimed in Nim Wan to be used as a landfill site.
Many large scale development projects also require an enormous quantity of fill which up until now was mostly obtained from marine dredging. Excavated marine mud or construction waste materials were also dumped into designated marine dump sites. Some of the dredging and dumping activities are in close proximity to fish culture zones and invariably caused a deterioration in water quality, particularly the increase in suspended solids and turbidity. In addition, the proposed Lantau Port Peninsular Development will affect water quality in fish culture zones nearby.
Storms and typhoons have, occasionally, caused physical damage of mariculture structures. There are also limited problems of floating garbage and other solid matter. Temperature and salinity changes were linked to a massive mortality of oysters in Deep Bay during 1979, although over-utilisation of the oyster beds undoubtedly also contributed to the problem.
Toxic industrial wastes
Although industrial waste has been accused of contributing to the gross pollution of Hong Kong's water courses, there are no reports of toxic industrial effluent affecting aquaculture.
Human and agricultural wastes
A great proportion of the rural areas in the New Territories remain unsewered. Domestic effluent and waste from pig or poultry farms are all discharged into the few available streams and rivers. These are so polluted that the water is no longer suitable for fish culture. Most pond farmers therefore use rain water, underground well water or tap water.
Sewage from urban centres established in the New Territories in recent decades are insufficiently treated, if at all, before discharge into nearby coastal waters. This is one of the contributing factors causing eutrophication of waters with limited tidal flush (e.g. Tolo Harbour) and serious environmental deterioration, as well as microbial contamination of some shores (e.g. Deep Bay). In Tolo Harbour, red tides have occurred frequently and about 50% of the annual reported red tide incidents were found in Tolo (Table 3). In 1988, a toxic bloom caused by Gonyaulax polygramma spread throughout Tolo Harbour and lasted for about three months. Oxygen depletion caused by the collapse of phytoplankton blooms has been a continual problem for fish culture zones within Tolo Harbour. Economic losses from fish kills due to oxygen depletion in fish culture zones in Tolo over the past five years amounted to about US $ 1 million.
Deep Bay is the most important oyster production area, but environmental conditions have deteriorated drastically, resulting in heavy microbial contamination of the oyster beds and a great reduction in oyster spat settlement. Production of oysters decreased from 200 tonnes valued at US $ 1 million in 1987 to 120 tonnes valued at US $ 0.7 million in 1991. Nowadays, very little spat can be collected from the wild in local waters and oyster farmers have shifted to fattening of young oysters purchased from China.
Table 3. Number of Red Tide incidents in the coastal waters of Hong Kong.
|Year||Total||Western||Southern||Junk Bay & Port Shelter||Eastern||Tolo||North Eastern|
Oil spills are not considered a significant source of pollution in inland waters. For coastal waters, in October 1987 and September 1989, used oil (probably bilge water discharged from vessels), affected the Yim Tin Tsai and Sok Kwu Wan fish culture zones respectively. As only small amounts of oil were discharged, the impacts on fish culture activities as well as the environment were insignificant.
With the construction of the nuclear plant at Daya Bay, about 40 km north-east of Hong Kong, there are some worries about the possibility of radioactivity contaminating fisheries products.
4.2 Contamination of aquaculture products
So far, there have been no reports of heavy metal or biocide contamination problems in cultured finfish in Hong Kong. Incidents of ciguatera poisoning have been recorded through ingestion of marine finfish such as humphead wrasse, coral trout, red snapper and grouper (Epinephelus fugoguttatus). These species are not cultured but captured from coral reefs in the Philippines or Indonesia and occasionally kept in fish culture zones for a short period before going to the market. Human parasitic diseases associated with fishery products are not a problem in Hong Kong. Infestation of Opisthorchidea has been reported in the territory, presumably as a result of ingesting under-cooked freshwater fish.
The environment in Deep Bay has been polluted by domestic and agricultural wastes as well as industrial wastes. The majority of oysters produced locally are from the Deep Bay area and these oysters are found to be highly contaminated with coliform bacteria and occasionally Vibrio bacteria. Although viral hepatitis has never been isolated from oysters, outbreaks of viral hepatitis A in Hong Kong are often associated with the consumption of shellfish, particularly oysters. With regard to heavy metal content, some oysters in Deep Bay have been found to contain cadmium at a level exceeding the maximum permitted level according to the Food Adultery (Metallic Contamination) Regulations, Cap. 132.
The green lipped mussel (Perna viridis) commonly attaches to fish rafts or wharf piles. This organism is not cultured in Hong Kong, but collected for sale as by-products of the fish culture zone. Although mussels from wharf piles in Victoria Harbour are highly contaminated with PCBs, mussels from fish culture zones have no serious contamination problem as yet.
In March 1898, high levels of toxins that cause paralytic shellfish poisoning (PSP) (=20,000 mu/kg) were detected in the green mussels in Junk Bay, in association with a bloom of Alexandrium catenella. Later levels of PSP toxin in green mussels from fish culture zones in Lamma Island and Sha Tau Kok were also found to exceed the WHO recommended standard of 4,000 mu/kg. This led to a temporary ban on harvesting of green mussels from these areas. The public was advised through the mass media not to eat shellfish until the situation was cleared. The ban was lifted in early April when PSP in shellfish from the affected area had decreased to well below 4,000 mu/kg. In 1990 and 1991, Alexandrium catenella was again detected in Hong Kong coastal waters during March to May, but PSP levels in shellfish remained well below the WHO recommended standard.
4.3 Impacts of aquaculture on the environment
Poor management of inland finfish ponds can result in problems of self-pollution, but effects on the outside environment are not considered significant. Marine fish culture zones are mostly restricted to coastal sheltered areas where flushing is not adequate. In addition, fish farmers tend to overstock their cages. This has led to incidents of oxygen depletion causing fish kills, and a general deterioration in water quality within fish culture zones (e.g. fish culture zones in inner Tolo Harbour and inner Port Shelter).
The lack of freshwater available for pond culture often means that water exchange is inadequate, especially for monoculture of snakeheads and catfishes which requires frequent water exchange. Some farmers also tend to overstock and overfeed their fishes, resulting in high ammonia levels inside the ponds and leading to serious fish disease outbreaks.
Coastal marine finfish culture activities have been shown to have some polluting effect on the environment. Feed conversion rates are poor and food wastage is high. Other sources of pollution come from fouling organisms following cage cleaning and improper disposal of refuse and waste, including dead fish. This smothers the seabed beneath the fish cages and results anoxic conditions in the sediment, the production of toxic gases and an increase in nutrient loading to the water. The polluting effect is more significant in fish culture zones with limited tidal flush, such as in Tolo Harbour. The effects, however, are fairly localised and become insignificant beyond 1–1.5 km away from the fish culture zone.
Presently chemotherapeutants are used only occasionally in aquaculture operations in Hong Kong and do not create any significant impact on the environment and human health. Table 4 shows some of the chemotherapeutants used in Hong Kong.
Table 4. Chemotherapeutants used in Hong Kong.
|Formalin bath||100ppm for 30–60 mins||Parasite control..|
|Acriflavine||100ppm for 1 min||Surface bacteria control (Myxobacter, Vibrio).|
|Dipterex (for addition to freshwater)||0.2 – 0.4 ppm||Control of parasites e.g. Lerneae sp; Argulus sp.|
|Oxytetracycline||50mg/kg fish||Aeromonas; Streptococcus; Edwardsiella infections.|
Impacts on mangroves
Small patches of mangroves can be found scattered throughout the Territory, the most extensive mangrove community is found in NW Hong Kong at Mai Po in inner Deep Bay. In the past, “tambaks” or “gai-wais” were constructed within the mangrove for shrimp culture, thus removing part of the mangrove trees. At present, the area has been designated as a nature reserve with restricted access and is managed by World Wide Fund (Hong Kong) in view of its importance as a major feeding and resting ground for migrating seabirds.
Interactions between aquaculture and native species
Fry for inland freshwater pond fish farms are imported from China or Thailand, but there are no recorded interactions between cultured fish and the natural stocks. Reservoirs in Hong Kong are not used for aquaculture and the fish stock they contain are mostly artificially introduced to control water quality. Streams and rivers are very small and are seriously polluted by domestic and agricultural waste, which has a much greater effect on the natural fish stock. Fry of some cultured marine finfish species e.g. Rhabdosargus sarba, Chrysophys major, Seriola purpurascens are obtained from the natural populations and there is probably some impact on the wild fish stock. However, there is no available information on the interaction of mariculture with natural fish stocks in the coastal waters of Hong Kong.
Social conflicts and aquaculture
The major problem in Hong Kong is the lack of land and water space to cater for the needs of the huge population. Due to the rapid urban development and the increasing price of land, more and more inland fish ponds have been sold for developmental projects (e.g. Tin Shiu Wai) or filled in for container storage sites. There is also competition between pond fish farmers for water supplies. In coastal waters, suitable areas for fish culture are also usually suitable for recreational purposes such as yachting and water-sports (e.g. Port Shelter and Double Haven), and often interfere with navigational fairways (e.g. Lamma Channel, Kap Shiu Mun) or are close to nearby coastal reclamation, domestic or industrial developments (e.g. Tolo Harbour). There is also competition between fish farmers for sites within a fish culture zone. The working group on mariculture zones with representatives from various concerned government departments was established to resolve problems between mariculture and different coastal water users.
Some fish farmers have also attracted adverse public criticism for living in structures built on fish rafts. The waste and debris released from such domestic dwellings contributed significantly to bad water quality in the fish culture zones and nearby areas. In 1990, there were 471 dwelling structures on rafts and 1,960 people recorded as living aboard rafts, but this practice is now prohibited by the Marine Fish Culture Ordinance and strictly enforced by licensing control.
5. INTERACTIONS BETWEEN AQUACULTURE AND THE ENVIRONMENT IN-DEPTH STUDY
5.1 Inland finfish semi-intensive pond culture in Hong Kong
5.1.1 The culture system
Inland finfish ponds are mainly located in the lower reaches of rivers and streams occupying unused paddy fields and swamp areas. Large ponds with sizes ranging from 1 to 4.5 ha each are enclosed by earthen bounds and filled with rain water or well water. Species cultured include various carps with tilapia or grey mullet. Fry are stocked in early spring (February to March) and grow to marketable size of about 600 to 800g in eight to nine months. For optimum production of this polyculture system a balanced composition of fish species, which utilise different niches, as well as careful control of nutrient levels in the water are important. Feeds such as peanut cake, corn meal and wheat bran are applied once a day. Occasionally, brewery waste is also used. Nowadays, the majority of these polyculture farms are integrated with duck rearing and the duck droppings go directly into the water as fertiliser.
5.1.2 Environment's influence on inland finfish pond culture
Since the 1980s, inland aquaculture has been seriously affected by the increase in land development to cope with graded increases in population and the shortage of available land in the urban area for further development in Hong Kong. In the process of setting up new urban centres in the New Territories, the government has “consumed” numerous fish ponds. Large areas of fish ponds on private land were also filled up for other uses like residential development. This usually affected the price of the surrounding land and gradually increased the pressure for further development of the neighbourhood, leading to a spreading effect. Further, with the increase in trade with mainland China, there is a heavy demand for goods storage sites. As a result, many fish ponds near the border were illegally filled up to become open storage sites for containers. The decrease in the area of fish ponds, together with the decrease in number of culturists and production over the years are shown in Table 5.
Table 5. Inland finfish pond culture: Production, pond area and number of culturists.
(US $ million)
|Number of culturists|
Land development for residential or industrial use increases the economic value of the land substantially (approximately US $ 500/m2 for a residential flat). When compared with the gross output of a polyculture farm of approximately US $ 7/m2, this is totally out of proportion. Owing to the fast and enormous economic gain in land development, there is no incentive for the fish pond owner to resist the pressure of land development. To curb the rapid and undesirable change in land use, the Government enacted two interim amendment bills for the Town Planning Ordinance in 1991. The amendments enabled the extension of the jurisdiction of the ordinance to cover the whole territory as well as the direct enforcement against unauthorised development in special areas. Development Permission Area (DPA) plans are prepared for various parts the rural areas in the New Territories by the Town Planning Board. Unless in conformity with the DPA plans or with the required planning permission, any development other than the existing use, undertaken or continued on after the gazettal of the DPA plans may be subject to enforcement proceedings under the ordinance.
Discharge of sewage and livestock waste
Most rural areas remain unsewered. Domestic effluent and wastes from pig or poultry farms are all discharged into the nearby streams and rivers. Many of the pig or poultry farms are small scale and isolated and, as such, setting up treatment facilities for either the domestic sewage or livestock farms would be costly. Flushing in most streams is also very limited as 70% of the base flow is directed into reservoirs. Past surveys have revealed that over two thirds of these water courses are grossly polluted with low dissolved oxygen levels, high BOD and high ammonia levels such that they are no longer suitable for aquaculture purposes.
Most inland finfish pond farmers, particularly those practising polyculture of carps, employ special management practices to deal with the lack of water supply. The ponds are filled by rainwater during the early spring. The composition of the stocked population is controlled such that the nutrient levels of the pond water are maintained at a certain level to enable growth of phytoplankton, which is food for many of the cultured carps. There is no change of water in the pond throughout the year. Any water loss due to evaporation is normally refilled by rainwater or well water, or even tap water during droughts. Ponds in each farm are drained in rotation once every two to three years for decomposition of the organic waste accumulated on the pond bottom. The water in the ponds is not discharged, but pumped to the other ponds within the farm.
Monoculture of catfish and snakehead requires frequent water exchange as the fish are fed with trash fish. These farms are usually located in sites with available source of suitable water supply (e.g. in upstream areas). The ponds are usually small (0.2 ha) and fish are kept at high density. Water is channelled to flow through a number of ponds. In places where water flow is limited, mass mortalities have occurred occasionally.
The Government's effort to combat pollution in water courses was initiated in 1983 with the establishment of a central Steering Group on Water Course Maintenance and Management. The core environmental legislative provisions for protecting Hong Kong's watercourses are represented by the Water Pollution Control Ordinance (Cap. 311) and the Waste Disposal (Livestock Waste) Regulations 1988 under the Waste Disposal Ordinance (Cap. 354). Under the Water Pollution Control Ordinance, the Government is empowered to declare water control zones. The whole Hong Kong territory is divided into ten water control zones (see Figure 2). To date seven water control zones have been declared. In water control zones, polluting discharges are controlled to maintain the desired beneficial uses including: irrigation; aquaculture; preservation of aquatic wildlife; active and passive recreation; as a means of transport; or as storm channels. Previously there were two ways in which discharge of effluent could be allowed. The first was by licensing, which specifies the permitted volume, quality and rate of discharge of the effluent to a public foul sewer or the environment. The second allowed an existing discharge in operation to be exempted from licensing subject to its compliance of the Crown lease. These exemptions were revised in 1990 by an amendment to the Water Pollution Control Ordinance to give more stringent control of polluting effluents. Exemptions were phased out in 1992 and no exemptions are granted in new water control zones gazetted after 1990. Control now involves licensing discharges to the foul sewer or directly to the environment. The 1990 amendments of the Water Pollution Control Ordinance included the introduction of a new set of effluent standards published in 1991 in a technical memorandum “Standards for Effluent Discharge into Drainage and Sewerage System, Inland and Coastal Waters”. This provides a set of concise water quality standards for discharges to comply with and act as a guide for the Environmental Protection Department (EPD) in issuing licences. Compliance with licence conditions is monitored and any non-compliance with a licence or any discharge without a licence are to be prosecuted.
The livestock waste control legislation was passed in 1987 and the first phase of control was implemented in June 1988. With this, the keeping of livestock in all urban and new town areas was banned and legislative control over waste disposal was effected in the remaining areas in phases over a 10 year period. Disposal of livestock waste effluents is required to meet the standard of 50 mg/l BOD5 and 50 mg/l suspended solids. If a farmer wishes to continue in business in the control areas, he is eligible for a capital grant and loan for the installation of the necessary pollution control facilities. If he chooses to cease business, he is eligible for an ex gratia allowance. The financial allowance totalled HK $ 600 million (1 US $ = 7.8 HK $).
The EPD provides free livestock waste collection services to assist farmers in the proper disposal of livestock wastes. A total of 150 collection points have been set up in the control areas and some 9,000 tonnes of livestock waste were collected in 1991. The collected waste is converted into compost which is sold as fertiliser for gardening and landscaping. Presently, there are two composting plants with a total capacity of 75 tonnes/day. Privatisation of the livestock waste collection service and composting facilities is being considered.
In addition to all of these, the Agriculture and Fisheries Department has successfully developed a new effluent-free pig raising method known as “Pig on Litter” system. The technique involves the use of sawdust as litter bedding mixed with a bacterial product and the pig excrement deposited thereon is decomposed in situ, rendering the pig sties effluent-free and odourless. The method is being extended to pig farmers and so far 8 commercial farms have adopted this system. With all of these efforts, at the end of 1991 the amount of pollution load due to livestock waste, measured as BOD, had been reduced from 96,000 kg/day to 55,000 kg/day. There has been a modest but steady improvement in river and stream water quality; 52% of the rivers were classified as fair as compared with 32% in the early eighties.
In view of the above achievement, a review of the control scheme began in 1991 to further improve the control efficiency. During this review, the Government has agreed not to extend enforcement action against livestock farmers beyond the Phase I Stage I areas (see Figure 3).
Figure 3: Livestock Waste Prohibition and Control Areas introduced in a phased programme.
It is also proposed that livestock farming will be licensed with installation and proper maintenance of waste treatment facilities or the effluent-free system as the licence requirement.
5.1.3 Study of the influence of inland finfish culture on the environment
Due to water shortages, inland finfish pond culture farms are operated more or less under closed culture systems, apart from the few farms undertaking monoculture of catfish and snakehead. There is, therefore, no significant polluting effect on the outside environment.
Fry for freshwater finfish culture are either imported or artificially bred by farmers. There is no evidence of interactions between the cultured fish species and natural fish stocks. The freshwater fish fauna, although affected seriously by channelisation and pollution in the lower reaches of the rivers and streams, is still diverse. There are 96 species of indigenous fish recorded in Hong Kong, of which 32 species spend their entire lives in freshwater. Introduced tilapias from Africa and poecilids from America threaten the local stream communities especially the local endemic minnow, which has not been recorded since 1986. Aquaculture was usually blamed for the introduction of tilapia, but according to records tilapia was introduced into reservoirs in the early seventies while polyculture with tilapia began in the late seventies. The poecilids on the other hand were introduced as ornamental fish.
In recent years, with the uncontrolled filling up of many inland fish ponds, there have been repeated incidents of serious flooding. The number of significant floods and the estimated losses are shown in Table 6. It is now realised that fish ponds, particularly those on the flat plains near the lower reaches of rivers and streams, serve as buffers for strom-water during heavy rain. In addition, the mangrove area at the Mai Po Marshes, one of the stopping over sites for migratory birds, is located at the edge of a large stretch of fish ponds. With Mai Po designated as a bird sanctuary, it is now recognised that the fish ponds surrounding the Mai Po mangrove are vital in maintaining the ecology of the marshes and are now categorised as the Buffer Zone for Mai Po by the Planning Department. Changes of land use not in line with conservation of Mai Po will not be permitted. Therefore inland fish ponds in Hong Kong in fact have a positive influence on the environment helping to conserve the environment and controlling floods.
Table 6. Estimated loss as a result of flooding of inland fish ponds, 1983–1992.
|No of incidents||2||0||1||1||0||1||2||1||1||2|
|No of affected farms||250||0||25||22||0||142||206||2||7||124|
|Area of fish ponds||161||0||12.5||13||0||99||176||1.7||5.9||120.9|
|Estimated loss (tonnes)||375||0||30||30||0||217||283.6||-||8.4||502.9|
|Estimated loss (US $ '000)||507.5||0||42.3||33.8||0||325.5||420.0||12.8||31.8||652.5|
5.2 Coastal finfish cage culture
5.2.1 The culture system
Coastal marine finfish cage culture in Hong Kong involves the rearing of prime species of groupers, sea breams, snappers or sea bass from fry or fingerlings to marketable size, in cages suspended from floating wooden rafts in coastal waters. As the wooden raft cannot withstand exposed conditions, this type of culture has to operate in sheltered seas. Most fish culture zones are, therefore, located in relatively sheltered coastal areas with adequate water depth away from urban centres, navigational fairways and sites of development.
Fish fry are usually stocked in early spring and, depending on the species, they take about 1.5 to 2 years to attain marketable size. Traditionally the fish are fed with trash fish, which is minced into paste or fine pieces for fry and fingerlings and chopped into pieces for adults. Fouling of the nets is quite rapid in the summer necessitating net changing about once every two weeks. The nets are dried and cleaned with a pressurised water jet. Many fish culture zones do not have nearby land based support facilities. In these fish culture zones, all farm operations including feed preparation, net cleaning and watch keeping have to be conducted on the fish raft. The majority of the farm units are small sized and family based, consisting of 1–2 rafts with an average total raft area of about 230 m2. Presently, there are 24 large scale company-run farms occupying about 21.7% of the total raft area in Hong Kong.
5.2.2 Study of environment's influence on coastal finfish cage culture
In the late 1970s, coastal finfish cage culture was practised in 54 bays in Hong Kong. To avoid conflicts with other coastal water users, the Marine Fish Culture Ordinance was enacted in 1980 and 24 fish culture zones were designated. These fish culture zones were mostly near to traditional fishing villages, sufficiently sheltered, with adequate depth and yet far away from urban and industrial centres. In 1984, with the heavy demand for farm development for the mariculture industry, 4 more fish culture zones were designated making up a total of 28 fish culture zones. However, during the early 1980s, there was also rapid development of urban centres in the New Territories to cope with the fast population growth. Consequently, some urban and industrial areas gradually encroached close to some gazetted fish culture zones. Later in 1989, with the commencement of the Airport and Port development, a number of sheltered bays where fish culture zones were located had to be reclaimed. Three fish culture zones were degazetted. Details of mariculture operations affected by these degazettals are shown in Table 7.
Table 7. Fish Culture Zones degazetted and cleared for land development.
|Year||Fish culture zone||Relocation||Extinguishment|
(US $ '000s)
(US $ '000s)
|1990||Tai A Chau||0||0||0||12||740||190.2|
|1991||Tin Ha Wan||47||11,167||8.8||31||4,840||220.3|
For clearance of the Tin Ha Wan fish culture zone, a nearby site suitable for fish culture (Tung Lung Chau north) was designated as a new fish culture zone for relocation of the operations in the Tin Ha Wan fish culture zone. Tin Ha Wan mariculturists, therefore, were offered options to either relocate to the new fish culture zone or to extinguish their business. For the other two fish culture zones, no suitable nearby sites could be found, therefore all the mariculture operations had no choice but to extinguish. For relocation to new fish culture zone, ex-gratia allowances based on the expenses required for towing the fish rafts were paid. As for total extinguishment, ex-gratia payment including notional loss of income for one average crop and the capital investment in raft, and cages was provided.
In connection with large scale land development works, marine sand is dredged to provide the enormous quantity of fill material required at an economic rate. It is estimated that the cost of such marine fill amounts to only US $ 2.5–3.8/m3. Also, special sea areas are designated for the dumping of dredged marine mud or construction spoil (Figure 4). Both dredging and dumping would inevitably destroy nabitats in the area, thereby removing the associated communities. This would greatly reduce natural fry production and therefore affect fry supply to the finfish cage culture operation. How long the bottom communities take to re-establish once dredging and dumping ceases is not known, but it is likely that this will be in terms of a number of years. Also, during the dredging and dumping operations, turbid plumes are produced and accumulated organic matter/contaminants in the bottom sediments can be released, which may cause some deterioration in surrounding water quality. Information on the likely impact of this water quality deterioration on the growth of cultured fish and therefore aquaculture production is lacking.
Figure 4: Reclamation, dredging and dumping sites in Hong Kong.
For most dredging and dumping operations close to sensitive receivers such as fish culture zones, gazetted swimming beaches or sea water intakes, the EPD would required a full EIA to be conducted. The EIA is expected to identify the sensitive receivers and assess the likely impact as well as providing recommendations on appropriate mitigatory measures. To protect fish culture zones from the likely impacts of dredging/dumping activities, comprehensive water quality monitoring is included as a contractual requirement for dredging/dumping operations near to fish culture zones. Close monitoring of dissolved oxygen levels, turbidity and suspended solids at flood and ebb tide conditions at a frequency of a minimum of five times per week are imposed. Based on data from a literature review, a level of 80 mg/l of suspended solids is adopted as a target level which should not be exceeded at the fish culture zone.
Fish farmers have repeatedly complained about the increase in fish mortalities alleged to be caused by the dredging/dumping activities. Water quality data from the monitoring programme and specific investigations, however, did not provide any evidence of drastic deterioration of water quality so as to lead to mass mortality of cultured fish at the fish culture zone. Generally it is observed that for fish culture zones very near to dredging/dumping activities, there is a significant increase in suspended solids (20–30 mg/l), but the levels are well below those which would have an adverse effect on the fish. However, considering the possibility of stress created by the repeated fluctuations in suspended solids in the water, a special ex-gratia arrangement was designed and approved by government in July 1993. Fish farmers at fish culture zones where more than 100% increases in suspended solids have been detected, or where the highest background level exceeds 50 mg/l, are required to decide the future of their operations. Those who opt to continue at their risk are paid half the notional loss of income for one crop. These who opt to suspend their operation would be paid the notional loss of income while those who decide to extinguish their operations would be paid the full ex-gratia allowance for clearance including notional loss of income for one crop and capital investment in rafts and cages.
Human and agricultural wastes
The coastal waters of Hong Kong receive considerable discharges of domestic sewage, livestock waste and industrial effluents. These water-borne wastes contribute to eutrophication, particularly in enclosed bays. To a lesser extent the discharges from the Pearl River, which carry a substantial quantity of nutrients, also contribute to the eutrophication problems in western territorial waters. Ideally, fish culture zones should be located far away from known urban and industrial areas. Therefore the majority of fish culture zones are located in the eastern waters. However, with limited land and high populations, various large urban centres were established in the New Territories in the early 1980s and some of these centres were fairly close to fish culture zones. The wastes from these urban centres, though secondarily treated when discharged, increase nutrient levels in the water and may lead to eutrophication. Four fish culture zones were located within Tolo Harbour, a poorly flushed water body in the north-eastern part of New Territories. With the establishment of Sha Tin and Tai Po urban Centres, water quality in Tolo Harbour, particularly the inner Tolo, deteriorated. Red tides became more frequent and some caused fish kills in the fish culture zones through depletion of oxygen in the water. The main red tide events over the past 5 years that have impacted on mariculture all occurred in Tolo (Table 8). The total economic loss amounts to about US $ 1 million.
Table 8. Red tides associated with fish kills in Hong Kong (1987–1993).
(US $ 000s)
|July 1987||Yung Shue Au:|
|April 1988||Yim Tin Tsai (east)|
|May, 1988||Tai Po Hoi:|
To prevent a further deterioration of water quality, Tolo Harbour was declared the first Water Control Zone. The Tolo Harbour Action Plan aims to reduce nutrient loadings by improving sewage treatment, removing livestock waste pollution and reducing industrial effluents. With all these efforts, the frequency of red tides in Tolo has fallen drastically since 1991.
To minimise fish losses caused by oxygen depletion, the Department of Agriculture and Fisheries has developed an efficient system of aeration and the technique was being extended to fish farmers in fish culture zones prone to suffer oxygen depletion problem. Fish farmers were also encouraged to undertake dissolved oxygen monitoring so that aeration could be started in time. With these techniques, Yung Shue Au fish farmers were able to prevent fish kills during the serious red tide outbreak in 1988.
5.2.3 Study of the influence of coastal finfish cage culture on the environment
In 1990, a consultancy study on assessment of the environmental impact of marine fish culture in Hong Kong was conducted. It surmised that the polluting load from fish farms exerts its effects on the receiving water in three principal ways:
Organic wastes accumulate and decay on the sea bed adjacent to the cages. The effect of the deposited solids is to blanket the seabed resulting in anoxic conditions and the production of toxic gases. The scale of the problem arising from solid deposition is quite small, affecting the seabed immediately beneath the cages and diminishing to no effects within 1.0–1.5 km.
Wastes from fish farms consume oxygen which, in areas with restricted water circulation, may lead to oxygen depletion of the water. This again is a very localised problem which can be alleviated with improved fish husbandry.
The addition of nitrogen loading to the water may result in phytoplankton blooms. Since nitrogen is released in soluble forms (ammonia/urea) by excretion from the fish stocks, it is the most difficult pollutant to reduce.
The study identified that the environmental impact of coastal finfish cage culture arises largely from feed wastage, dead fish, dwellings on fish rafts, improper disposal of refuse and wastes as well as the lack of flushing in many fish culture zones. As for the estimates of nitrogen loading and oxygen demand from coastal finfish cage culture provided by the consultancy study, recently it was found that there were gross errors and over-estimations and more detailed studies to assess the actual pollution loading by fish culture are needed to clarify the situation.
Fish farmers often think that they are the victims of pollution rather than the polluter themselves. Therefore there are difficulties in arousing their awareness for the need for better husbandry practices, particularly the older farmers. The Agriculture and Fisheries Department has undertaken to promote environmentally friendly culture practices so that coastal finfish cage culture can be continued in Hong Kong. To eliminate pollution due to dwellings on fish rafts, since 1990 the department has specified the size and use of structures permitted on the fish rafts as licence conditions. Assistance from the Housing Department was obtained to arrange for housing for farmers with no land accommodation. In 1990, there were 471 domestic dwellings but with strict licence control the size and use of these structures was all rectified. Research on pellet feeds to replace trash fish has been carried out since 1989. Presently, a moist pellet feed composed of trash fish mixed with fish meal, vitamins, binders has been shown to produce better growth than trash fish with a lower feed conversion ratio (3:1 as compared to 8:1 for trash fish). The moist pellet feeds also reduced feed leachate and wastage. In addition, fish fed with the moist pelleted feed have been shown to have better resistance to cold stress. The use of this moist pellet feed is now being extended to the fish farmers through farm trials.
To improve the condition of fish culture zones with limited flushing, where possible, actions have been taken to expand the zone to enable the spacing out of the rafts. There is also a temporary moratorium on issuing of new fish culture licence such that raft density in problematic fish culture zones could be gradually reduced. There are also education programmes and liaison work with fish farmers to make them realise the importance of farm hygiene and environmentally-friendly husbandry practices. The formation of fish farmers associations is also encouraged to facilitate communication and co-operation amongst fish farmers as well as with government departments.
Experiments on open sea cage culture have been initiated. Results have shown that open sea cage culture is feasible but to make it economically sustainable, the operation has to be fairly large scale and a nearby land based site or attached platform, is needed for feed preparation and for watch keeping purposes. The open sea cage culture may not be an alternative to relocate fish culture operations from sheltered sites, but it should help to reduce raft density from the traditional fish culture zones. Efforts are being devoted to choosing suitable sites for such operations.
6. PRIORITIES FOR DEALING WITH ENVIRONMENTAL PROBLEMS
6.1 Prevention and cure of the detrimental effects to aquaculture of man-made changes to the environment
To curb undesirable changes in land use in fish culture areas, amendment bills for the Town Planning Ordinance were introduced in 1991 enabling the extension of jurisdiction of the ordinance to cover the whole territory; the introduction of direct enforcement against unauthorised development in selected areas and the delegation of authority by the Town Planning Board (TPB). Development Permission Area (DPA) plans are prepared for some rural areas in the New Territories by TPB under the provision of the Town Planning (Amendment) Ordinance 1991. Unless in conformity with the DPA plans or with the required planning permission, any development undertaken after the gazetting of the DPA plans may be subject to enforcement proceedings under the ordinance. Ex-gratia allowance is made available for farmers affected by land development projects.
Human and livestock wastes
The Government is taking a series of actions to combat the problem of water pollution. In 1980, the Water Pollution Control Ordinance was enacted for controlling discharges. The territory was separated into ten water control zones which were declared in phases. A series of comprehensive sewerage master plans for all sewerage catchments is being prepared. In terms of long-term planning, a comprehensive sewage disposal strategy for the whole territory was proposed in 1989. A major part of the proposed strategy involved the construction of large tunnels linking the main urban areas to treatment plants where chemical treatment and high speed sedimentation will be provided. Further tunnels will be used to discharge the treated effluent. Details for the implementation of this project are still under consideration. In relation to the acute shortage of freshwater for aquaculture, a study to investigate the feasibility of re-using biologically treated sewage effluent for fish culture is being carried out.
Control of livestock waste discharges started with the enactment of the Waste Disposal (Amendment) Ordinance in 1987. All farms within areas declared as livestock waste control zones have to be equipped with proper waste treatment facilities. To assist farmers to understand and comply with the new controls the EPD published a code of practice and set up waste treatment demonstration plants including the dry-muck-out and wet-muck-out methods. A livestock waste collection service is also provided. In addition, the Agriculture and Fisheries Department has introduced an effluent-free pig raising method to the farmers.
A red tide reporting network, with the Agriculture and Fisheries Department (AFD) as the co-ordinating centre, was established in 1983. All government staff conducting routine duties around Hong Kong coastal waters (i.e. staff of Marine Police, Marine Department, Environmental Protection Department, Auxiliary Airforce, Agriculture and Fisheries Department) are requested to report sightings of red tides immediately to AFD, providing details on the location, extent, colour and whether fish kills were observed. If convenient, water samples would be collected and forwarded to the AFD. The AFD identifies the causative species of the red tide and assesses possible effects of the red tide. Depending on the loaction of the red tide, a site investigation may be conducted. In the case of a suspected toxic red tide, fish and shellfish samples would be collected from nearby waters to assess toxicity levels and whether toxicity exceeds the WHO recommended limit. If necessary, the Department of Health would be informed to impose a ban on sale of shellfish/fish for human consumption. Where applicable, fish farmers would be advised to two their fish rafts to waters away from the red tide. When it is assessed that the red tide will cause oxygen depletion of the water, fish farmers would be advised to aerate the water.
An oil spill contingency plan co-ordinated by the Marine Department was established in 1987. The plan provides fast information exchange and enables immediate and appropriate action to be taken to minimise the impact of the oil spills. Guidelines for protective measures for different sensitive areas are provided, e.g. no oil dispersant to be used in fish culture zones or within 1 km of the fish culture zones.
Contamination of aquaculture products
At present, the Department of Health carries out a monitoring programme analysing the presence of contaminants in food items from markets and restaurants. Any food items confirmed to be contaminated with substances detrimental to human health would be banned or confiscated and those responsible for selling the contaminated products would be prosecuted.
The red tide reporting network also helps to minimise health risks due to red tide toxins. When a toxic red tide is detected, the Agriculture and Fisheries Department assesses toxicity levels in the shellfish and fish collected from nearby areas. If the toxicity level exceeds 4,000 mu/kg, the Health Department is informed. Health Department officials undertake further tests to confirm the dangers and, if necessary, sale of the contaminated seafood is suspended. Medical practitioners are alerted to look out for cases with symptoms of intoxication and the Agriculture and Fisheries Department advises culturists and fishermen to refrain from harvesting shellfish from the affected area.
Liaison with fish farmers
The formation of “Fish Farmer Associations” in fish culture zones is being encouraged by the Government. It is intended that an intimate communication network be established among the mariculturists and the staff of the Department of Agriculture and Fisheries. It is hoped that these will form part of an overall warning system against sudden changes in water quality, particularly the occurrence of red tides, as well as outbreaks of acute fish diseases.
6.2 Prevention and cure of the detrimental effects of environmental change caused by aquaculture activities
Environmentally-friendly husbandry practices
Staff of the Agriculture and Fisheries Department frequently visit fish farms to give technical advise on farm management and proper husbandry techniques. Emphasis is placed on educating farmers on the consequences of overstocking and overfeeding, thereby reducing the risks of self-pollution in intensive pond and raft culture. The Department also conducts water quality monitoring programmes in several fish culture zones with the aim of collecting information of use to the fish farmers. Practical training courses on subjects such as low oxygen remedial measures are provided as necessary. In addition, studies are being undertaken in particular areas that would reduce the impact of aquaculture on the environment, such as the development of artificial pelleted feeds to replace the traditional trash fish and investigations into the possibility of open sea fish farming.
The government is considering relocating some of the problematic fish culture zones (the inner end of Tolo Harbour, Port Shelter and Long Harbour) or reducing raft density within these zones. The aim is to reduce total fish stocks and pollution loadings to the environment, particularly in areas prone to oxygen depletion. In addition to these measures, regulatory controls would be stepped up in areas such as proper refuse and waste disposal.
To prevent the unrestrained development of inland areas, including those previously utilised for fish culture, an amendment of the Town Planning Ordinance was passed requiring developers to apply for permission to change the usage of the land. With regards to coastal aquaculture, a “Working Group on Mariculture Zones” was established to resolve conflicts among different users. A feasibility study of fish farming in the open-sea is also being undertaken. This would help avoid the strong competition between users of inshore coastal marine waters.
7. FUTURE AQUACULTURE DEVELOPMENT
In Hong Kong, with extremely limited land and heavy demands for land development, it seems inevitable that inland finfish pond culture activities will be further reduced. The Government, however, has initiated actions to retain a stretch of fish ponds in the north-western New Territories for the protection of the Mai Po Marshes Nature Reserve. Coastal finfish cage culture, although suffering environmental impacts from land development and sewage discharge, is also blamed as a polluter. Emphasis for further development is placed on improving husbandry practices and relocating some of the activity to the open sea such that the industry becomes environmentally harmonious and economically sustainable.
Government structure for waste management.
|Policy.||Secretary for Planning and Lands.|
|Planning, Environment and Lands Branch, Environment Division.|
|Policy development planning and monitoring.||Environmental Protection Department, (Waste Management Policy Group).|
|Provision of services.|
Solid waste collection.
|Urban Services Department.|
|Regional Services Department.|
|Environmental Protection Department.|
Waste treatment and disposal.
|Civil Engineering Services Department.|
|Electrical and Mechanical Services Department.|
|Environmental Protection Department.|
|New works||Environmental Protection Department (Solid Wastes Project Group).|
|Various Works Department (Implementation).|
|Environmental Protection Department (Livestock Waste Control Group).|
|Environmental Protection Department (Solid Wastes Control Group).|
Oils, chemicals and refuse from vessels and ports.
|Urban Services Department.|
|Regional Services Department.|
Domestic waste storage and collection.
|Urban Services Department.|
|Regional Services Department.|
Government structure for water management.
|Policy.||Secretary for Planning, Environment and Lands.|
|Planning, Environmental and Lands Branch, Environment Division.|
|Policy development, planning and monitoring.||Environmental Protection Department (Water Policy Group).|
|Provision of services.||Environmental Protection Department.|
Sewerage and sewage treatment.
Drainage Services Department.
Sewerage in new towns
Territory Development Department.
Domestic and industrial waste water discharges.
|Environmental Protection Department.|
|Buildings and Lands Department.|
Effluent in water gathering grounds.
|Water Supplies Department.|
Supervision of marine fish culture industry.
|Agriculture and Fisheries Department.|
Bathing beach management
|Urban Services Department.|
|Regional Services Department.|
Government structure for environmental planning and assessment.
|Policy.||Secretary for Planning, Environment and Lands.|
|Planning, Environment and Lands Branch, Environment Division.|
|Policy development, planning and monitoring.||Environmental Protection Department (Environmental Assessment and Planning Group).|
|Provision of services|
Land use planning standards and guidelines.
|Environmental Protection Department|
Land use planning - engineering feasibility studies.
|Territory Development Department|
|Civil Engineering Services Department.|
Land use plans and land use amendments.
|Buildings and Lands Department.|
Project reviews and impact assessment studies.
|Environmental Protection Department.|
Liaison, complaints and enquiries.
|Environmental Protection Department.|
|Various Government Departments.|
Land use planning.
|Building and Lands Department (Lease/allocation conditions, building approval).|
|Building and Lands Department (Lease allocation conditions, building approvals).|