COMMUNICATIONS

• CAGE CULTURE : NEAR-SHORE AND OFF-SHORE CULTURE
M.C.M. BEVERIDGE
INSTITUTE OF AQUACULTURE,
UNIVERSITY OF STIRLING

• ENVIRONMENTAL INTERACTIONS OF OFFSHORE AQUACULTURE
MICHEL MERCERON
IFREMER - FRANCE

• NUTRIENT LOADINGS
M.C.M. BEVERIDGE
INSTITUTE OF AQUACULTURE,
UNIVERSITY OF STIRLING
SCOTLAND

• BIOLOGICAL IMPACT OF AQUACULTURE ON THE ENVIRONMENT
MICHEL MERCERON
IFREMER - FRANCE

• GEOGRAPHICAL INFORMATION SYSTEMS (GIS) AND AQUACULTURE
M.C.M. BEVERIDGE
INSTITUTE OF AQUACULTURE,
UNIVERSITY OF STIRLING
SCOTLAND

• SOCIO-CULTURAL AND VISUAL IMPACTS
M.C.M. BEVERIDGE
INSTITUTE OF AQUACULTURE,
UNIVERSITY OF STIRLING
SCOTLAND

• AQUACULTURE SITE SELECTION
MARC KEMPF
IFREMER - FRANCE

• ENVIRONMENTAL IMPACT OF MARINE FINFISH CULTURE
IVAN KATAVIC
INSTITUTE OF OCEANOGRAPHY AND
FISHERIES - CROATIA

• SELECTED OPTIONS FOR ENVIRONMENTAL MANAGEMENT IN COASTAL AQUACULTURE
UWE BARG
FISHERY RESOURCES AND ENVIRONMENT
DIVISION FISHERIES DEPARTMENT
FAO

CAGE CULTURE
NEAR-SHORE AND OFF-SHORE CULTURE

By M.C.M. BEVERIDGE
SCOTLAND

INTRODUCTION

Cages, pens, floating tanks, and raceways are all water-based aquaculture systems. Cages are totally enclosed on all, or all but top, sides by mesh or netting, whereas in pen culture the bottom of the enclosure is formed by the lake or sea bed. Floating, submersible and submerged cage designs are used in mariculture. All consist of a collar or frame which supports the net bag.

Cages and pens probably first developed in Asia several hundred years ago, although it is only recently that they have become popular. Mariculture in cages began in Japan in the 1950s but developed largely as a result of the salmon farming industry in northern Europe and North America during the past two decades. However, whilst cages probably account for only 10–20% of world aquaculture production, they are the most important means of farming, in particular, sectors. Cages account for60% or more of global coastal fish culture and, if considering Mediterranean aquaculture, account for in excess of 90% of all seabass and seabream production.

The advantages of cages include low capital costs and simple management. Disadvantages can be summed up by the term «vulnerable» (weather;poachers and vandals), cages also more or less used only for monoculture.

DESIGN AND CONSTRUCTION

INTRODUCTION

There are a number of design principles common to all aquaculture facilities; they must hold stock securely, facilitate good growth and survivorship, be easy and safe to operate and be cost-effective. Cage designs have largely evolved by a process of trial and error and general design features such as shape and size have yet to be optimised for many species. In general, however, fish tend to grow better in larger cages, although handling difficulties with species such as seabass should be borne in mind. Cage bag depths greater than 10m are largely unnecessary.

INSHORE CAGES

In sheltered, inshore sites wooden collar cages are often sufficient. They are comparatively cheap and simple to build and can often be fabricated from locally-available materials using local labour. Frames are generally built from pressure treated softwoods, such as larch, with galvanised steel stanchions and reinforcing sections at the corners. They are typically square or rectangular in shape with dimensions of <100 m2 surface area by 5 m deep. Larger (100 – 150 m2) wooden collars designs are also used in sheltered sites in northern Europe, north America and Chile although they tend to be more costly and difficult to build. Proven commercial designs are also widely available.

Circular and rectilinear plastic cage designs are popular and widely used in both sheltered and moderately exposed locations. The styrofoam-filled, plastic pipe is cut into sections and welded into the appropriatte cage design. Commercial designs are widely available. Dimensions, similar to those given above for wooden cages, are typical.

Several prototype cages have been built to counteract problems such as fouling. These have not proved particularly successful, however.

OFFSHORE DESIGNS

There is an increasing trend towards development of offshore sites for cage aquaculture. Offshore sites are less exploited and, because there is less potential for conflict with other users, there are fewer planning restrictions. Water quality at offshore sites is often better and there are stronger currents and better water exchange. However, such sites are more exposed and there is increased risk of storm damage. Offshore sites are also arguably less secure. Capital and some operational costs are also considerably greater.

Two approaches have been taken to the development of offshore sites for aquaculture : improvement of the site or construction of cages which can withstand exposed conditions. In Japan, municipal authorities have sometimes invested in floating breakwaters in order to attract aquaculture activities, floating breakwaters are expensive to build and maintain and give only limited protection in shallow sites.

Three types of offshore cage have been designed : floating, semi-submersible and submerged for moderately exposed sites, conventional floating cage designs fabricated from steel have proved adequate in many instances. Large (6 000 – 12 500 m³) floating rubber-framed designs, such as the Bridgestone cage, have proved highly successful with rearing of salmonids at exposed sites. The cages operate on the principle that the cage frame absorbs energy which is dissipated through deformation of the frame members and through transmission to the moorings. Manufacture claim they are able to withstand 9 m wave heights. Such designs are expensive and much of the routine operations, such as feeding, are usually carried out from a boat.

Semi-submersible designs, also developed for salmonids, are proving increasingly popular. In such designs, the position of the cage in the water colum can be changed by modification of the buoyancy of the floatation system. Under normal operating conditions, the floatation system is located several metres below the water surface, where motion is only a fraction of that on the surface. Hence, the cages are relatively stable, even under extremely rough weather conditions. Such designs are somewhat smaller than flexible frame designs, but can be more expensive on a per unit volume basis.

Submerged cages have been developed for pilot scale operations only. The effects of isolation from the water surface is unknown for many species.

CONCLUSIONS

Offshore designs are a particularly attractive option for Mediterranean fish farmers, given the severe pressures on the coastal Zone and the poor currents and water quality in many inshore areas. However, it is only recently that offshore technology has begun to be used for seabass and seabream. It remains to be demonstrated that such large cages are appropriate for the culture of these species. Appropriate methods for handling fish will have to be developed.

BIBLIOGRAPHY

Beveridge, M.C.M. cage Aquaculture. Fishing News Books, Ltd., Oxford.

Heen, K, Monaghan, R L & Ulter, E 1993. Salmon Aquaculture, Fishing New Books, Oxford.

Institution of Chemical Engineers; 1988. Aquaculture Engineering Technologies for the Future I.

Chem. E. Symp. Series 111, Institution of Chemical Engineers, Rugby, England.

Institution of Civil Engineers. 1990, Engineering for Offshore Farming Thomas Telford, London

Reinersten, H, Dahle, L A, Jorgensen, L & Tvinnereim, K. 1993. Fish Farming Technology.
A A Balkema, Rotterdam.

ENVIRONMENTAL INTERACTIONS OF OFFSHORE AQUACULTURE

By Michel MERCERON
FRANCE

Faced with environmental pressure, the trend is towards moving coastal aquaculture further offshore. Apart from location, the main features of offshore fish farming are greater water depths (from 20 to 80 m), and the need for larger facilities and investments. To be economically realistic, it requires intensive rearing. Its running also makes specific tools necessary (e.g. to handle very large nets).

In environmental terms, some drawbacks are predictable :

-   the offshore environment is less known and harder to access than the nearshore one,

-   monitoring is more difficult,

-   unexpected events are more difficult to deal with,

-   hydrodynamics can be too strong on the surface and too calm near the bottom,

-   vertical stratification occurs more frequently,

-   the macrobenthos is less resistant to adverse conditions,

-   phanerogams (often protected species) may be present,

-   the predation risk from dolphins is increased.

The expected advantage of offshore conditions are :

-   larger sites,

-   fewer conflicts over use of space,

-   reduced visual impact,

-   waste-receiving water volume increased,

-   distance from chronic and man - caused pollution,

-   more stable physical and chemical parameters;

-   less discolored waters and partly less fouling.

Some models are available to quantify and predict project impact while others exist only as ongoing research. Remote sensing pictures provide another interesting tool particularly for finding surface temperature anomalies. They can reveal upwelling zones as well as poorly renewed ones.

An example of environmental study of an offshore aquaculture project is supplied by PRIMO, a French attempt at a quite comprehensive programme.

Due to investment costs, this type of aquaculture is mainly developing in countries where coastal space is scarce and already ;largely occupied or claimed for (e.g. Malta, Cyprus). Presently, we lack sufficient data to assess the validity of the above-stated ideas on impact. The results of ongoing monitoring programmes will be of great interest for extensive display and use.

«PISCICULTURE DE RECHERCHE INDUSTRIELLE EN MER OUVERTE»
«PRIMO» PROJECT
- Aim : demonstration of the technical and economical feasibility of offshore fish farming
- Project run by IFREMER between 1988 and 1991
- Site location : near Hyères and Toulon (French Mediterranean coast)
- Results : several files :
	technology
	animal husbandry
	environment*
	mediterranean potentialities*
- Realization postponed (for financial reasons)

Figure 3. Exemple de champs de SST à 2 km de résolution, calculé à partir des données de l'AVHRR des satelites NOAA : mois de Juillet 1989 sur la Méditerranée Occidentale.

NUTRIENT LOADINGS

M.C.M BEVERIDGE
SCOTLAND

INTRODUCTION

Wastes can be defined as that which is left over after use. In an open production system, such as an intensive aquaculture system, wastes are inevitable. They arise largely from uneaten food, faecal and urinary wastes. There are several approaches to the quantification of aquaculture wastes, including the use of models and direct measurement.

MODELLING NUTRIENT LOADINGS

SIMPLE MASS BALANCE MODELS

the origin of aquaculture waste nutrients is readily apparent :

c = a - b

Where c = nutrients into environment; a = nutrients supplied by the farmer in the diet; b = nutrients absorbed by the farmed fish.

This simple equation, which treats the aquaculture system as a black box, can be used to quantify nutrients released into the environment using data on nutrient content of the diet, food conversion ratio (FCR) and nutrient carcass content (see Box 1).

The advantage of this approach is that it is simple to perform and requires little information, other than data which is often available from feed manufacturers or from the literature. By manipulating variables such as the dietary content of a particular nutrient or FCR it also clearly shows the dependency of waste production on factors such as food and feeding.

The disadvantage of this black box model is that it is of little practical use since it doesn't indicate the source or what form the wastes are in (uneaten food/faecal/urinary products; solid/ dissolved; oragnic/ inorganic, etc) or when (diurnal/seasonal) the wastes are released.

PHYSIOLOGICAL MODELS

Much is known about the physiology of fish and other aquatic animals and this data can be useful in understanding in what form the wastes may be released into the environment. Data on diet digestiblilities can give information on faecal production and composition whilst data from studies of excretion can predict nitrogen excretion rates. When used in conjunction with assumptions in uneaten food, these can help explain what is happening within the animal and help identify ways to reduce wastes.

However, again such models are of limited value. Estimates of diet digestibilities based on digestibilitity data for individual dietary components are unlikely to be particularly accurate as they do not take account of the effects of interactions between dietary components on digestibility. Moreover, they cannot predict whether the wastes from fish farms will be solid or dissolved when they enter the environment, system and management being important determinants, and the models are not particularly good at predicting daily or seasonal fluctuations.

MEASURING NUTRIENT LOADINGS

Direct measurement may seem the best method of estimating nutrient loadings from aquaculture. However, there are a number of difficulties. Waste outputs fluctuate diurnally, depending upon feeding regime and management routines (cleaning, grading, etc,). There are also marked seasonal changes in waste production depending upon biomass, fish size and health status, and temperature.

It is not always easy to sample fish far effluents. In taking a sample from an effluent channel, for example, it must be borne in mind that solids will tend to be carried along the channel bottom. Sampling effluents from fish cages is also difficult because there is so much water movement and dilution that it is often difficult to detect any decrease in nutrient levels over background levels.

Considerable care must therefore be given, in the design of a sampling programme to quantify and determine the impacts of fish farm effluents and in carrying out such a programme. Consideration must also be given to the methods used in analysis of nutrient levels.

IMPACTS OF NUTRIENT LOADINGS

In summary, nutrient loadings from fish farms can cause hypernutrification (increase in environmental nutrient levels) which in turn can lead to eutrophication (an increase in phytoplankton standing crop and production). Increase nutrient loadings to sediments can stimulate benthic production particularly in the area immediately underneath cages or downstream from a discharge point. Impacts depend upon the relative sizes of the aquaculture operation and the environment into which the wastes are being released. More subtle effects of nutrients such as vitamins and trace minerals on aquatic ecosystems have been little explored.

BIBLIOGRAPHY

-   Barg, U. 1992. Guidelines for the promotion of environmental management of coastal aquaculture development. FAO Fish. Tech. Pap.(328) FAO, Rome.

-   Beveridge, M C M. 1984. Cage and pen fish farming. Carrying capacity models and environmental impact. FAO Fish. Tech.Pap.225.FAO, Rome.

-   Beveridge, M C M. 1987. Cage Aquaculture. Fishing News Books, Ltd., Oxford.

-   Brune, D E & Tomasso J R (eds.) 1991. Aquaculture and water quality, Advances in World Aquaculture Vol.3, World Aquaculture Society, Baton Rouge, Louisiana.

-   Nature Conservancy Council. 1989. Fish farming and the safeguard of the natural marine environment in Scotland. NCC, Scottish Headquarters, Edinburgh.

-   Pullin, R S V, Rosenthal, H & Maclean, J L, (eds.) 1993. Environment and Aquaculture in Developing Countries. ICLARM Conf.Proc 31., ICLARM, Manila

-   Rosenthal, H, Hilge, V & Kamstra, A (eds.).1993. Proc. Workshop on Fish Farm Effluents and their Control in EC Countries. Hamburg, Germay, 1991.

BIOLOGICAL IMPACT OF AQUACULTURE ON THE ENVIRONMENT

Michel MERCERON
FRANCE

Biological impacts on the environment are generally classified categories, but a common characteristic is that all of them are ruled by dispersal, the major regulating parameter. As regards enrichment, nitrogen mostly comes from gill excretion (soluble ammonia and urea). Apart from some very confined sites, its impact is generally regarded as negligible. Improving feed quality is the most common way of reducing this loading. Phosphorus is mainly supplied to the environment by faeces and wasted pellets. The impact of this particulate matter is much more obvious. Under sea cages, a decrease of the mean sediment grain size can be observed, as well as an increase of its content in organic matter and certain trace metals, some depletion of oxygen content and, in bad cases, hydrogen sulphide and methane production. How important the changes in living macro-fauna are depend on the ratio between particular organic matter flux and site dispersal. It can be a simple enrichment of existing communities, a change of some species, or decreased diversity, to the point of complete absence of the macrobenthos. Site selection is very important in limiting this impact, and better adjusted feed distribution seems effective. For land-based farms, lagooning or filtering of effluents is strongly recommended.

The veterinary products in question include antiparasitics and antibiotics. The risk arises from environmental toxicity of these components outside farms and, for antibiotics, the development of resistant bacteria strains rendering these products inoperative. Moreover, this antibioresistance may be transmitted to bacteria which are dangerous to man. The general trend is toward developping use of vaccines and using less noxious, more specific, treatments.

Another type of impact concerns wild populations. Their diseases can be aggravated by fish farming, due to the increase in global density of hosts for parasites and pathogenic agents. Limiting density of fish in farms, and of farms in the environment, can reduce this impact. Often aquaculture projects include the introduction of new species, or at least new strains for the region. These new species can proliferate in an uncontrolled manner, as can some subsidiary species potentially harmful for indigenous ones (e.g. a parasite which kills flat oysters in France, was imported with new Japanese oyster spat; this would not have occured if the recommendations of quarantine practices had been applied). Besides, when an allochtonous strain is cultivated (since escapes are unavoidable), an interbreeding with indigenous strains occurs. When escapes are too numerous (e.g.salmon in Norway), there is a risk of gene diversity loss. This can lead to a loss of resistance to certain adverse conditions. It can be local strains, use of sterile (triploid) fish and setting up gene banks are possible remedies. But the lack of basic knowledge of population genetics for farmed fish species and the rapid increase of gene mixing through aquaculture development are a concern.

Although water enrichment is not generally a problem, the impact on the bottom is quite obvious and is an accurate tool of assessment. The other impacts (veterinary treatments and influence on wild population) are less well known and require further investigation. Fish farmers must bear in mind that the pollution from their rearing facilities is often self-pollution to some extend. Public Authorities must remember that aquaculture's environmental quality is essential for its survival.

The fate of waste material released from intensive fish farming (redrawn from Gowen et al., 1988).

The average flux of carbon and nitrogen through a salmonid farm.

Phosphorus flow in a cage production in a Swedish lake. After Enell and Löf (1983).

Figure 1 : Etang de Thau, localisation.

Coupe 4 passant par les 3 zones conchylicoles.

Source: Poarson and Rosenberg 1978

S Number of Species

B Biomass

A Total Magrotaunal Abundance

Figure 6.5 Mean abundance (MEANAB) and median abundance (MEDAB) of sea lice infestation with linear sea distance from the nearest fish farm.

FIG. 1. Proportions of net-pen escapees among spawning Atlantic salmon from rivers in southern Nor-way during the autumns of 1987 and 1988. The data were compiled from Gausen (1988) and Moren and Gausen (1989), including only rivers where no Atlantic salmon have been released. Total sample sizes are N = 194 and N = 570 for 1987 and 1988, respectively.

CONCLUSIONS
	Predictable ecological impacts = enrichments
	Less known impacts = veterinary products and effects on wild populations
	Farming itself requires a good quality milieu
	Self-pollution self control of impact
	Some other impacts are also importrant:
		+ economic (e.g.:reducing fish price)
		+ social (employment, substitution to fishing)
		+ land use (conflict with tourism)
	We have to deal also with reverse impact.
	It is more complicated and diversified, but vital.

GEOGRAPHICAL INFORMATION SYSTEMS (GIS) AND AQUACULTURE

By M C M BEVERIDGE
SCOTLAND

INTRODUCTION

Maps are geographical representations of spatially related data sets. With the advent of powerful computers it is now possible to store, manage and manipulate huge, high resolution data sets.

GEOGRAPHICAL INFORMATION SYSTEMS

A GIS is essentially a database management system (DBMS) which allows the storage, retrieval, analysis and display of display-related data. Many GIS package also have modelling capabilities. GIS have advantages over maps in the easy, reliable and rapid manner in which they can perform these tasks. Physically, a Gis consists of an integrated computer hardware and software package. Today, many commercially available packages can run on a PC-based machine.

GIS can use data from a variety of sources-maps, tabular field data, remotely sensed data-which must be encoded so that it can be displayed in the form of a line, point or polygon. The computer displays the information in either vector or raster mode. The former, consisting of a series of x, y coordinates, is excellent for mapping of very small features, but requires complex routines and high processing power. The latter consists of cells (rows, columns) with values from which a composite map is built up. Raster-based packages are chapter, simpler and require less computing power.

Natural resources data are particularly suited to this type of process. However, not only biogeographic data can be entered, but also socio-economic data. Once entered, data should be verified before any operations are carried out. Once the data have been entered they can then be manipulated in various ways. Scale and orientation can be changed, for example. Data can be readily retrieved and printed out. Boolean logic, in which subjective scoring or preferences can be taken into account, can be used to identify sites with particular combinations of attributes. Hence, development alternatives can be rapidly evaluated.

GIS AND AQUACULTURE

GIS has been used over the past ten years or so for planning of aquaculture development. Uses range from the macro scale (e.g. regional, country) to micro-scale in which the technique has been used to optimise site selection within a small coastal area (Table 1).

Table 1 : Example of GIS applications in aquaculture

Source :Meaden and Kapetsky (1991), Aguillar and Ross (1993), Beveridge et al.(1994)

CONCLUSIONS

GIS is a useful tool, not only for planners trying to resolve conflicting aspirations in use of coastal resources but also for those interested in developing aquaculture. It can be used to explore possibilities and relationships. Various studies have shown that is a coast-effective way of carrying out such work.

However, aquaculture is still in its infancy and there is poor understanding of the relationship between production and environmental variables. Another problem relates to availability of data. Often the information that is required is not available, at least in the form or at the level of precision that is required. The maxim «rubbish in, rubbish out» s particularly apt with regard to GIS. It must also be remembered that once a GIS is established for a particular region that resources will be required to maintain an update the database.

Last, there are problems related to the GIS itself and the Boolean logic operations used to combine selection critera.

REFERENCES

Aguillar-Manjarrez, J & Ross, LG. 1993. Aquaculture development and GIS. Mapping Awareness & GIS in Europe, 7,49–52.

Ali, C, Ross, I.G & Beveridge, M C M, 1991. Microcomputer spreadsheets for the implementation of geographic information systems in aquaculture. A case study on carp in Pakistan. Aquaculture 92 : 199–205.

Beveridge, M C M & Ross, L G. 19914. Environment, site selection and planning : the role of Geographic Information Systems in aquaculture. In : Proc. IFS Workshop on Ecology of Marine Aquaculture. Osorno, Chile, November 18–23 1991. IFS, Sweden (in press).

Burrough, P A.1986. Principles of Geographic Information Systems for land resources assessment. Monograph on soils and resources surveys 12, Clarendon Press, Oxford, UK.

Kapetsky, J M.1989. Malaysia - A Geographical Information System for aquaculture development in Johore State. FI: TCP/MAL/6754, JANUARY 1989. FAO, Rome, Italy.

Kapetsky, J M, Mc Gregor, L & Nanne, H.1987. A Geographical Information System and satellite remote sensing plan for aquaculture development : a FAO - UNEP/GRID cooperative study of Costa Rica, FAO Fisheries Technical Paper 287. FAO, Rome Italy.

Kapetsky, J M, Wijktrom, U N, MacPherson, N J, Ataman, E & Chaponera, F.1990. Where are the best opportunities for fish farming in Ghana? The Ghana aquaculture Geographical Information System as a decision-making tool. FAO Field Technical Report 5 : FI/TCP/GHA/0051, FAO, Rome Italy.

Ibrekk, H O, Kryvi, H & Elvestad, S. 1992. Nationwide assessment of the suitability of the Norwegian coastal zone and rivers for aquaculture(LENKA). in : N.De Pauw & J.Joys (eds.) Aquaculture and the environment. European Aquaculture Society Special Publication 14, 413 -440.

Meaden, G.I. 1987. Where should trout farms be in Britain? Fish Farmer 10(2) : 33–35.

Meaden, G J. & Kapetsky, J M.1991. Geographical information systems and remote sensing in inland fisheries and aquaculture. FAO Fish. Tech. Pap. 318. FAO, Rome.

Muir, G F & Kapetsky, J M. 1988. Site selection decisions and project cost : the case of brackish water pond systems. l. Chem. E. Sump. Ser. 111 : 45–63.

Ross, L G, Mendoza, E A Q M & Beveridge, M C M. 1993, The application of Geographical Information Systems to site selection for coastal aquaculture : An example based on salmonid cage culture. Aquaculture 113 : 165–178.

SOCIO-CULTURAL AND VISUAL IMPACTS

By M C M BEVERIDGE
SCOTLAND

INTRODUCTION

Visual impacts should be considered as a type of environmental impact (see below). Socio-cultural impacts refer to the impacts on people and society and may stem directly from aquaculture or as a result of environmental impacts.

Both socio-cultural and visual impacts are important considerations in the development of aquaculture and failure to give these aspects due regard has resulted in problems in many parts of the world.

SOCIO-CULTURAL IMPACTS

Aquaculture creates jobs, usually in rural areas and often in remote, economically disadvantaged areas which have a history of de-population. Good data on employment in aquaculture is poor. However, a recent survey by the European Union of Fisheries Economists for the European Commission has shown that employment through aquaculture in the EU is rising. Jobs per tonne production are higher in the south of Europe than in the north. It is estimated that the aquaculture industry in the Mediterranean has probably created somewhere in the region of 1000–1200 jobs directly and a further 200–300 indirect jobs (transport, boat repair, etc.) Mediterranean aquaculture has also stimulated job creation in northern Europe where most equipment is manufactured.

It can be argued that job creation in rural, economically disadvantaged areas where traditional industries are in decline should be given an unqualified welcome. The creation of even a few jobs in such areas can secure the existence of shops and schools and ensure that vital services remain.

However, there can be problems, Fish farming unlike shellfish farming, requires daily commitments to ensure that stock are properly fed and looked after. This may not fit in with the prevailing lifestyles. In Scotland, for example, salmon farming has been established primarily in areas where the prevailing lifestyle is not suited to daily commitments of eight of ten hours work at a fish farm. Most prospective fish farm workers will own their own small farm and many also fish at certain times of the year. They must tend to their animals and crops and go fishing when time and season dictate.

Another problem is that many fish farming companies are multinational or owned by companies from outwith the area in which the fish farm is established. Skilled technical and managerial staff from to be brought in from outside, labouring staff being recruited locally. Incomers can be insensitive to local customs and culture and may not even speak the same language. Managerial and technical staff need accommodation and given their higher salaries, can push local house prices up in a situation where housing is limited. All these problems have been seen in western Europe, particularly in areas of Ireland, Scotland and France, and when allowed to carry on unchecked have led to labour problems and even vandalism of farm equipment. Problems can be overcome by a sensitive management approach.

There are also economic problems arising from the establishment of fish farms. Fish farms produce fish and the sale of farmed fish, either locally or transnationally, can depress market prices, In western Europe, the Atlantic salmon farming industry was established on the reputation of wild salmon, Atlantic salmon fisheries were, until 1980 or so, the principal source of the fish. Today, farmed salmon accounts for something like 80% of all Atlantic salmon traded. The massive increase in supplies caused by farming have depressed prices, severely affecting the livelihoods of salmon fishermen. The severity of the impact will depends on the extent to which farmed and wild products compete on the market and impacts are likely to be particularly acute during the exponential growth phase of the industry but may in part recover as markets become more sophisticated and diversified. Nevertheless, some impact of farming of seabass and seabream on prices is likely to be apparent in the Mediterranean region.

The establishment of aquaculture has also been implicated in the decline in recreational fisheries in many parts of Europe.

VISUAL IMPACTS

Fish and shellfish farms are not the most attractive of establishments. They are located in rural coastal areas, close inshore.

Landscape has an economic value. Houses and hotels are prepared to pay for visually attractive sites. The establishment of fish and shellfish burns can reduce that value, making houses of difficult to sell and hotels to fill with guests.

Problems relating to visual impacts of aquaculture developments have been one of the principle problems faced by the industry. Indeed, until recently, visual impact, and not socio-economic or environmental impacts, were the main factor behind restriction of developments in North America and the UK. In the Mediterranean where tourism is so important the problems posed by visual impacts are likely to be highly significant in dictating the availability of inshore sites and the size of farms. Much can be done to ameliorate impacts through sensitive planning and siting and landscaping of shore-based installation. Coastal management planning and GIS can be useful techniques. Cages designers are also increasingly aware that cages with low profiles and clean lines, and whose paint colour have been carefully chosen, are less likely to cause problems.

It is not only the farm installations but also the way in which they are running that can cause problems with visual impact. Many farms are an eyesore, as feed bags and other farm rubbish are not properly disposed off and allowed to litter the shoreline. Industry codes of practice, designed to minimise such impacts and to promote a positive image for the industry will be greatly needed in the Mediterranean where pressures on coastal areas are immense.

REFERENCES

Cobham Resource Consultant, 1987. An Environmental Assessment of Fish Farms. Final Report to the Country side Commission for Scotland, Grown Estate Commissioner, Highlands and Islands Development Board and Scottish Salmon Growers' Association. Cobham Associates, England.

EDAW Inc. 1986. Aquaculture siting study. State of Washington, Department of Ecology. Washington, USA.

Neiland, A., shaw, S A & Bailly, D. 1992. The social and economic impacts of aquaculture :a European review. In : N De Pauw & J Joyce (eds.) Aquaculture and the Environments. EAS Specl. Publ. 14, 469 – 482.

AQUACULTURE SITE SELECTION

By Marc KEMPF
FRANCE

Site selection is oriented in two main directions :(1) inventory of existing potentialities and their best use (depending on species and techniques available) ; this need is directly related to development planning and management schemes, (2) researching the most suitable site for a predetermined project, which is a more immediately-applicable task. Several illustrative examples are given here to illustrate this subject.

INVENTORY OF POTENTIAL SITES IN BRITTANY (FR)

Carried out in the late 70's and early 80's by CNEXO (later part of IFREMER), on request and with funding of regional authorities. The purpose was to establish a comprehensive inventory of all coastal sites suitable for aquaculture, and their best use for appropriate spices and techniques available. The final aim was development, and also coastal zone management, by intergrating aquaculture sites into existing schemes (POS = land use planning schemes on a municipal scale, SAUM = coastal management schemes on a local or regional scale).

The study consisted in setting out criteria and requirements for different kinds of mariculture, as well as inventorying sites, this including preselection on maps, field visits, bibliographic data analyses and some complementary measurements when required. The final report included a file of synthetic data sheets and maps for each site, easily transferable to planning documents.

PRIMO SITE IDENTIFICATION, TOULON-HYÈRES (FR)

Carried out in late 80's and early 90's by IFREMER, as an internal R & D project. The study aimed to identify an appropriate site for an experimental offshore indutrial fish farm (PRIMO), as per project requisites. After preliminary bibliographic screening of the French Mediterranean coast, attention was focused on the Toulon-Hyères area, where a comprehensive field and feasibility study was performed. Finally 4–5 suitable sites were identified, and their advantages/disadvantages compared. The final choice was left open to further logistic and socio-economic investigation, as well as to consultation of public authorities and local partners. But, in the end, financial reasons prevented the project from being achieved.

AQUACULTURE DEVELOPMENT SCHEME OF CORSICA (FR)

Carried out in the early 90's by IARE, University of Montpellier, on request and funding of the local authorities. The study was devoted to intensive fish culture in net cages, for small to medium sized farms, in fairly sheltered marine sites, between the 10–30 m isobaths. A series of criteria of was defined, as well as marketing and weighing system, allowing a final classification of the sites. The weighing considered primary criteria, eliminating those with a poor mark, and secondary ones.

OTHER EXAMPLES

SESECA, Sweden

result of the Swedish «Coastal Zone Project» (80–84) and «the Coast as a Natural Resource Project» (late 80's), conducted by the Swedish Evironmental protection Agency and devoted to identifying sensitivity to eutrophication.

- LENKA, Norway

a cooperative project between three Norwegian Ministries (Fisheries, Local Governments and Environment) between 1987 and 1990. It was designed as a planning tool to determine the suitability of the coast for aquaculture.

- Mapping of eutrophication-sensitive coastal zones : the case of Brittany (FR)

carried out between 1991 and 1993 by IFREMER and other partner, with EC, local authority and internal funding. It aimed at finding out the causes of eutrophication (mainly green algae mass production), mapping the eutrophication-sensitive zones, identifying the causes which determine the sensibility, and recommending measures to preserve or restore the water quality.

- Aquaculture development plan, Tunisia

(see national case study).

LESSONS DRAWN

The site selection must be adapted to the aim pursued. This is of vital importance to aquaculture activity, since the quality and characteristics of the site are essential for farming performance. Site selection is also closely related to development, coastal zone planning and management policy, especially in a climate of competition for coastal zone space and resources use. Aquaculture must be considered as a coastal activity with every right to exist, and necessary space must be preserved for its development.

ENVIRONMENTAL IMPACT OF MARINE FINFISH CULTURE CASE STUDY FROM CROATIA

By Ivan KATAVIC
CROATIA

INTRODUCTION

A growing concern for the possible adverse effects of mariculture activities on the environment has recently arisen in Croatia, as it is a case in the most of the Mediterranean countries. The interest to study such a problem vary according to the size of the farm, public pressure, and sensitivity of the sites which is determined by morphometry, water turnover, and bottom dynamic condition. Big farms, e.g. 200 tonnes production per year are measuring some basic hydrographic paremeters on their own, tending to obtain a suitable basis that can restrict expansion of production to safe level.

For the purpose of this report we have been provided with two years period hydrographical and biological data from one cage culture form producing 150 to 250 tons per year . These numerical data were completed by direct observation, aiming to get insight into eventual ecological changes which are likely to be associated with intensive farming in the cage during a 10 - yrs producing period. A complete review of the mariculture impact to the environment is beyond the scope of this paper. The problem in this context is lack of basic information before production was started. So our main interest was consequences on : (1) nutrient concentration in the water (nitrogen and phosphorus) as related to the feed loading in the cages; (20) productivity as related to transparency measured by Secchi disk; (3) oxygen level in both, cages and outside of the cages; (4) accumulation of the organic waste and its possible impact on benthic communities; and (5) changes in the wild fish stock in the area.

DESCRIPTION OF THE MARICULTURE SITE STUDIED

Farm is located in a relatively shallow, sheltered bay with the central parts from 10 to 15 m, while area bordering open waters is about 20 m in depth. The bay is in the central part 1 km wide and longitudinal axis is about 2 km. Pilot scale production started in 1980, progressively reaching production that vary from 150 to 250 tons/year in the last decade. Main fish produced in the number of 500 m³ cages is sea bass (Dicentrarchus labrax) which represent about 85% of the population. Other species are gilthead sea bream (Sparus aurata), sheep nose bream (Diplodus puntazzo), and read sea bream (pagrus major). The production of the molluscs,Mytilus galloprovincialis and Ostrea edulis has never exeeded 50 tons per year.

MATERIAL AND METHODS

In our case, data on fish production, and on the type and amount of feed used were provided from the farm manager. The nitrogen and phosphorus concentration in the feed were obtained from the manufactures' specifications. The main nitrogen content was treated as equivalent to raw protein content divided by 6.25.

Water samples for the nitrogen and phosphorus components were collected once per months at two locations: one was cage site and second was control station which is 1 km away from the most exposed cage. Measurements of temperature, salinity and Secchi depth were made at the same times as nutrients, starting from July 92 to December 93. Samples were collected from the surface water (3) m depth) and from deep water (1 m above the bottom).

The water samples for nitrogen and phosphorus analysis were preserved by freezing and thawed rapidly before standard N and P analysis in the laboratory.

The Secchi depth was measured on the shady side of the boat with a white-painted 30 - cm in diameters.

Salinity was measured by means of optical refractometer, while oxygen-probe was used to measure oxygen saturation in the water.

RESULTS AND DISCUSSION

Estimated nutrient loading

Based on the average yearly production which was in the last ten years period about 200 tonnes and amount of the feed used as a second parameter, the feed coefficient is set to 3, which is an average value for the most Croatian farms. Such a production need an annual average feed usage of 600 tons. From the begining of production, the preference has been given to dry feed, either localy produced, or more frequentely, improved one. The annual nutrient load was calculated by using the next equation :

L = p × (FC × C_feed - C_fish) (Person, 1988)

where:

The annual load for fish farm studied was calculated to be 24 600 kg of nitrogen (ranging from 18 450 to 750 kg within the 10-yrs period)

An average phosphorus load is 4 140 kg varying from 3 100 to 5 180 kg for the same period of the time. Further calculation of the nutrient load from such a fish farm gives an average of 123 kg/N and 21 kg/P per tonnes of fish produced.

Based on the above calculation one can imagine how the load from fish, together with the diffuse load is high, particularly in view of the water volume and restricted water exchange. Our question was to which extent such a nutrient load will be generation ecological changes in this environment? Whether such a development of intensive mariculture in this bay is still in harmony with the eco-system ? What are measures to be taken to reduce possible risks of negative effects to the natural environment ?

In a comprehensive field work which was done in Swedish and Finnish coastal areas with a number of finfish farm, mean value for feed coefficient was reported to 1.5 only (Wallin and Hakanson, 1991). The nutrient load from such a fish farm was calculated to 81 kg of N and 11 kg P per ton of fish produced.

Compared to our 123 kg N and 21 kg P per ton of fish produced, it is evident that the nutrient load from a fish farm can be significantly reduced by lowering the feed coefficient and/or by using feed with lower N and P concentration. This will ask optimization of the feed and fedding methods which must be based on Knowledge of the real requirements of fish in different circumstances rather than feed fish untill satiation ?.

The load of nutrients (both nitrogen and phosphorus) from a fish farm can be separated in a dissolved fraction (fish excretion) and a particulate fraction (feed waste and faeces).

Studies of Person (1985), Ackefors and Enell (1990) show that about a quarter of the supplied nitrogen and phosphorus is incorporated into the fish for their growth. About quarter of phosphorus is excreted in dissolved form and about 50% sinks to the bottom in particulate form. In contrast to the phosphorus, about 50% of the nitrogen load is in dissolved form and a minor proportion is in particulate form (about a quarter of supplie N). Eventhough this figures may vary greatly from farm to farm, but in general could be considered as averages for fish cage (Wallin and Hakanson, 1991).

The negative eutrophication effects are generally greatest in summer (June–September) and thus the mean values of N and P for this period were expected to be highest. However, there were no correlations between nutrient supply during that period and nutrient concentration (phosphorus, nitrate, nitrite) in the water. Surface and bottom water concentration of the nutrients were not significantly different, and no significant difference with control station were found. One hypothesis is that in this case the assimilative capacity of the ecosystem is still balanced with dose of nutrients discharges.

Deposition of faecal matters and unconsumed food pellets in the intensive cage culture production may lead to the self pollution which is associated with three important metabolic compounds in water: ammonia (NH3), nitrite (NO2), and hydrogen sulfide (H2S). These compounds are produced as a result of protein metabolism of the fish or of the decomposition of organic matter such as faeces, plankton, or uneaten feed.

Ammonia is produced directly by plants, animals, and microbes in aquatic system. It is subsequently oxidized to nitrite and then to nitrate (NO3) by bacteria. Ammonia can be highly toxic in its free (unionized) from. Ammonia toxicity increases directly with pH and water temperature. Nitrite is formed from oxidation of ammonia by bacteria. In warm weather, nitrite is normally not a problem because bacteria quickly convert it to relatively nontoxic nitrate. Regardless of its source and the time of year it accumulates, nitrite is a serious problem, it complexes with the hemoglobin in fish blood to form metahemoglobin.

Hydrogen sulphide can be expected in the enclosure in which fish are heavily feed. It develops when uneaten feed, faeces and phytoplankton decomposes in a oxygen-free environment, primarily in bottom sediments. Any concentration that can be smelled is excessive and may be dangerous to an aquatic animals.

Hydrogen sulfide also accumulates in feeding areas with high concentration of organic matter. Accumulation of hydrogen sulphide can be identified by the presence of black sediments with the rotten-egg smell. Concentrations are expected to be highest in summer and lowest in winter.

Primary productivity

Excessive nutrient loading may lead to the several of the eutrophication effects. In our case Secchi depth has decreased almost twice as compared to control station.The most expressed difference in Secchi depth were recorded from June to September.

It has been frequently suggested to use Secchi depth measurement to obtain direct information on coastal trophic status. Our experience are supporting arguments to use Secchi depth as important nutrient effect parameter because of:

-   It has high degree of explanation where nutrient load is included;

-   It is simple and inexpensive to measure;

-   It is a collective parameter, expressing transparency, plankton density, sedimentation/resuspension, and nutrient recirculation in culturing areas.

-   Such measurement can indicate fish farmers to minimise discharger of nutrients by reducing feed waste and by using high-energy feeds with low nitrogen and phosphorus concentration. At the same time this will give an opportunity for larger fish production at the farm without increasing eutrophication.

Impact in the cage

Oxygen depletion in the fish farm studied in the Croatia was usually associated with heavy fouling. Saturation of the oxygen during the summer time, occasionaly may drop in the cage below 70% while at the same time the surrounding water was saturated at near 90 to 95% In order to avoid such oxygen depletion risk in the summer, cage nets were changed twice per months succeeding to maintain oxygen level in most the time close to saturation.

There are several factor that influence oxygen in the cage. First is temperature, time of day as a consequence of photosynthesis, as well as mixing of the water; not only already mentioned fouling but physical presence of the cage and other farm related structure (moorings, floaters, predators nets etc.) and even the presence of fish themselves interfere with the flow and can reduce import of the oxygenated water outside of the cage.

Depletion of the oxygen is probably the most frequent event in the cage itself. These effects are generally on a scale of at most a few hundered meters and fluctuated over time. Sensitivity to oxygen differs between species, life stages, and between the different life processes. A number of the studies has shown that Do effect on growth rate, food conversion, and feeding. However, exposure to fluctuating levels of DO impaired growth and appetite almost as much as continues low Do (Cuenco et al, 1985). They pointed importance of avoiding variation in DO for small fish. For salmonids DO should be above 7 mg 02/1 (Davis, 1975) and for successful life cycle of the most of the fish suggested DO is above 5 mg 02/1.

A tendency among cage farmers to overload the system by the increasing the stocking density is a risky practice, especially under certain circumstances. This farm has stocking density of sea bass in cages from 6 to 8 kg/m³in average, that gives 3 to 4 tonnes of fish in a single 500 m³ in average. However, some fish farmers are increasing production almost twice as this. Such an increased density from 12 to 15 kg/m³ (7 to 8 tonns of fish per cage) is coupled with new approach; cages are located towards more exposed site to minimise risk of oxygen depletion and to optimise culturing conditions.

A very short time is required for the effects of oxygen depletion since it takes a few minutes for fish to asphyxiate. Usual condition such as abnormally low currents or pollution that stress the fish cause increase in their oxygen demand. When the feed is given and not eated by the fish and the organic matter reaches a certain level, the following scenario can be expected:

1. accumulation of the waste material and organic detritus results in a further decreases of DO in the water;

2. At the sites with poor replacement of bottom water such as well protected bay, fjord etc. reduced oxygen is usually associated with increased levels of ammonia;

3. A decreases of DO in the water by the time will results in anoxic sediments wich produce both methane gas and hydrogen sulphide; H2S is extremely toxic to all leaving organisms;

4. Most of the fish aggregated in the restricted areas of the cage, and such behaviour could led to suboptimal leaving conditions that reducing feeding and increases further accumulation of unconsumed food;

5. Next that can be expected is sudden mortality and accumulation of dead fish at the bottom of the cage.

6. Occurence of pathogenic bacteria, viruses and parasites, some of which are resistance to antibiotics.

Effects on the Macrobenthos

After ten - years of intensive fish production significant changes in the benthic flora and fauna are observed. From the sandy bottom, extremely abundant phanerogamic flora (Cymodocea nodosa) has disappeared below the cages. Marine algae growing at the bottom are very scarce. Fauna is represented mostly with echinoderm of the class Echinoidea (sea urchin) Holothuroidea (sea cucumbers), and there are some ascidians (Thaliacea);

These changes of the benthic communities in the immediate environment of the studied area should be subjected to the increased attention in the next coming years. It would be interested to get insight into the macrofauna that is present in the sediment and compared it with the transects from the reference station; Unfortunately, this research has not yet been done; In any case, these observations are clear indications that depositional rates caused by the accumulation of organic matters is overwhelming the carrying capacity of the benthos.

To conclude, bottom fauna which is regularly used as an indicator in fish farming monitoring studies has been indicative in our case. It would be highly recommended to undertake studies on the community structure, the species diversity (function of the number of species present and the evennes with which they are distributed), and the bottom fauna biomass as compared with the reference areas. It would be an advantage to have a sufficient number of localities to be compared.

Effects on wild fish stocks

Fish stocks in the surrounding area have been studied in greater detail. The studies concerned small fish species. the fishing was done mainly with a small bottom seine. In the reference areas the best represented fish of commercial interest belonged to Mugilidae family (most abundant are Chelo labrosus and Liza saliens and occasionally Oedachilus labeo and Liza aurata were recorded. Five species represented Sparidae farm. (most abundant were Diplodus annularis, Diplodus sargus, and after that Diplodus puntazzo, Sarpa salpa, and Oblada melanura) and Mullidae with Mullus barbatus only.

An increase in total abundance and biomass together with different species composition towards a greater number of grey mullets at the surface, and as a bottom feeder striped sea bream, Lithognathus mormyrus in particular.

Abundant shoals of commercial size grey mullets is dominating in the uper layers. Biomass is estimated up to 30 tonnes. Fish recruitment is thought to occur near the farm where small fish are attracted to the farm by the unusually rich food supply available. The explanation for such an abundance is the load from fish farming, together with the diffuse load is rather high in view of water volume and restricted water exchange. This has caused eutrophication in the water area (Secchi depth) and low oxygen concentration in the cage from time to time.

An attempt was made to estimate the density of the striped sea bream. This species was most abundant near the farm bottom, and seems to be the species that makes the best use of the greater quantity of food available. The food choice of striped bass was studied by Jardas (1985) showing Chyronomus as an important food item of striped seabream. The biomass of subadults and commercial size (100 to 200 grams) was estimated to be several tonnes in the immediate cage areas. Fish quantity and its species composition are of particular interest in environmental impact studies because fish rank high in food chains and also integrate with lower levels of the food chain. Significant changes in the quantity of fish stocks were observed in an immediate water area.

CONCLUSION

It is in the interest of mariculture to develop its activities in harmony with the environment. This asks for the use of careful site selection which may be one of the most effective ways of avoiding negative impact of intensive finfish farm to the environment. Certain conditions in selecting sites must be taken into account: (1) the currents strong enough to spread and mix the nutrient loading, (2) the recipient capacity of the area should be large enough, (3) depth of the water bellow cage must be as large as possible (4) area should not show any sign of eutrophication, (5) and the area with a large proportion of erosion and transportation bottoms is the most tolerant to fish farming.

In addition to the location, better feeding methods and adequatly balanced feed is a reasonable way to avoid the negative effects to the environment.

There was no a significant relationship between the supply of nutrients and the concentration of inorganic nitrogen, neither in the surface nor bottom water in the areas investigated.

Bottom fauna and flora and Secchi depth could be good indicators in fish farming monitoring.

LITERATURE CITED

Ackefors, H. and Enell, M., 1990. Discharge of nutrients from Swedish fish farming to adjacent sea areas. Ambio, 19, 28 – 35.

Cuenco, M.l., Stickeney, R.R., Grant, W.E, 1985. Fish bioenergetics and growth in aquaculture ponds: IT. Effects of interaction among size, temperature, dissolved oxygen, unionized ammonia and food on growth of individual fish. Ecological Modelling 37, 191 – 206.

Davis, J.C., 1975. Minimal dissolved oxygen requirements of aquatic life with emphasis on Canadian species: a review. J.Fosh. Res. Board Can. 32, 2295 – 2332.

Jardas, l., 1985. The feeding of juvenile striped seabream, Lithognathus mormyrus (L., 1958) (Pisces, Sparidae). Rapp. P.- V.Reun. CIESM, 29:107–8.

Persson, g., 1988. Relationship between feed, productivity and pollution in the farming of large rainbow trout (Salmo gairdneri).

National Swedish Environmental Protection Agency, Stockholm, Report, no 3534, 48 p.

Wallin, m. and Hakanson L., 1991. Nutrient loading models for estimation the environmental effects of marine fish farm. Proceedings of a Nordic symposium on the theme : Marine Aquaculture and Environment T.Makinen (ed). Vol. 22, 39/57.

SELECTED OPTIONS FOR ENVIRONMENTAL MANGAGEMENT IN COASTAL AQUACULTURE

UWE BARG
Fishery Resources and Environment Division
Fisheries Department
FAO

Scope of this working paper

In view of the workshop topic and the expected contributions by the participating experts, this working paper has been prepared to focus mainly on options for environmental management at the farm-level. An attempt has been made to highlight the range of possible management responses by the farmer, with particular emphasis to waste released by aquaculture operations. Some possible measures by public authorities to promote environmental management in coastal aquaculture are summarized.

Introduction

Aquaculture interacts with the environment. In utilizes resources and causes environmental changes. Most interactions have beneficial effects. There has been substantial socio-economic benefits arising from the expansion of aquaculture. These benefits include increased income, employment, foreign exchange earnings and improved nutrition. So far, most aquaculture practices have had no or little significant adverse effects on ecosytems.

However, aquaculture operations in many temperate and tropical countries still can be improved. Current aquaculture development efforts need to be strenghened to further improve the management and operation of many aquafarms to ensure their durability and environmental compatibility. It is also important to recognize that aquaculture developments in many cases are increasingly subject to a range of resource-use and market constraints. Resources used by aquaculture are limited, and very often have to be shared with other activities.

Also, there is concern about the potential environmental implications of aquaculture development, comprising the adverse effects of aquaculture operations on the environment as well as the consequences of increasing aquatic pollution affecting feasibility and sustainable development of aquaculture. Unfortunately, environmental problems have resulted from conversion of wetland habitats, nutrient and organic waste discharges, introduction of exotic species, chemical usage, as well as from deterioration of water quality and decreasing availability of suitable sites for aquaculture.

Approaching environmental management of aquaculture

Environmental management of aquaculture implies the management of the interaction between aquaculture and the environment, one of its purposes being the reduction of unwanted impacts from these interactions; managing the impacts implies achieving control over their magnitude and nature.

The development of aquaculture is heavily dependent on the quality and quantity of available resource. The major resources required include:

Environmental management of aquaculture should consider aquaculture as part of the whole resource system upon which i9t relies. Ideally, environmental management of aquaculture should give consideration both to:

-   internal (on-farm) management of resources (e.g. in maintaining suitable conditions for the culture stock for optimal production, and reduction of environmental impacts), that is mainly by the aquaculturists;

-   external (off-farm) management of resources, mainly by public authorities.

In the following sections major factors and possible farm management responses are highlighted. Last, a brief overview is given on selected measures which may be necessary to be implemented by public authorities.

Factor which may need to be considered in environmental farm management

There are several factors which may generated adverse interactions between aquaculture and the environment:

Type of aquaculture system

Considered «openness» of the aquaculture system, i.e a) the extent to which the culture system relies on ‘external’ off-farm inputs, and b) the extent to which the siting of the aquaculture farm exposes it to environmental change.

-   greater openness implies greater environmental interaction, e.g. seaweed and mollusc farms are vulnerable to environmental change, intensive farms relying heavily on external inputs (and where waste material are not recycled) have greater potential for environmental impact.

-   closed system, involving recycling of water, organic matter and nutrients, with the aquaculture system, or where aquaculture is part of a large agricultural system, are likely to give rise to less environmental impacts, and be less vulnerable to environmental changes taking place outside of the farm.

-   in more open systems, more attention should be given to environmental management, particularly in relation to the ‘external’ environment.

Degree of intensification

Aquaculture production levels have been increased through expansion (increase in culture area) and intensification of culture operation or inputs. Both factors, expansion and intensification, carry an enhanced potential for adverse ecological effect. Consider changes in the degree of intensification, in particular two aspects:

-   the culture system, e.g. with increasingly intensive use of inputs (e.g.water, feed, seed), the potential for environmental impacts increase, particularly related to wastes released. Also, with intensification, stress may be increased, disease problems my become serious, and disease control and water quality management become more important. Experience shows that each culture unit has a finite capacity for development (e.g. pond, tank, culture area).

-   the aquaculture environment. Each aquaculture environment also has a finite capacity for development. Often, environmental problems have arisen because the ‘intensity of resources use’ by the aquaculture operation has exceeded the capacity of the environment, either to supply feed (e.g. nutrients and particulate matter for seaweed and molluscs), to flush waste materials away from culture sites (e.g. cage culture, shrimp culture areas), or to absorb the wastes released with negligible ecological consequences.

The environmental capacity for aquaculture will also depend on the intensity or resources use, such as water and land, by other competing sectors - which will also affect the level of acceptable environmental change. For example, the capacity for aquaculture development will be less if there are many other competing users of land or water, or the environment is viewed by society as a whole as being of particular value.

Species Characteristics

Reproduction, feeding habits, food and nutritional requirement, behaviours, growth capacities, water quality requirements, stress tolerance and susceptibility to parasites and disease characterize suitability of a species to be cultured. The very specific characteristics of the cultured organisms also determine type, magnitude and range of ecological implications. Some characteristics may be particularly important, e.g.:

-   environmental tolerance of the culture species, e.g. temperature, dissolved oxygen, salinity and tolerance to toxins. Such tolerance will determine the suitability of culturing species at particular sites, and the response of species to environmental changes.

-   food and nutritional requirement will determine the use of feeds and fertilizers, and the amount of metabolites, excreta, and uneaten food released.

-   ecological characteristics, such as filter feeding habits, e.g. molluscs are prone to public health problems because of their filter feeding behavior, also important.

-   interaction with wild stocks; concerns which have arisen over the actual and potential impact of introductions and transfer of new species include: a) loss of indigenous species or reduction in the productivity or diversity of indigenous stocks, due to harmful side effect of the new species, either through competition with indigenous stocks, or introduction of new parasites or pathogens.

The Site

The Site will determine availability of water, of which considerable volumes (both sea and fresh-water) may be needed to maintain water quality. Hydrographic and topographic site characteristics are very important, in particular for sea based and land-based farms relying on natural water movements (currents, tides) for adequate water exchange and waste dispersal. Life span, possibilities for expansion and intensification, and the ecological effect of an aquafarm are often determined by physical characteristics of the site selected. However, the ecological effect of an aquafarm are often determined by physical characteristics of the site selected. However, the ecological characteristics of the site, e.g., diversity, structure, dynamics and interrelationships of benthic and pelagic communities may be quite distinct. The level and extent of ecological change, therefore, vary from site to site.

Location of aquaculture facilities

The location of the aquaculture facilities is also important, particularly in relation to existing pattern of land and water use, in terms of current ‘value’ of existing resources, and their human social and economic use or potential.

Design and construction of aquaculture facilities

Design and engineering will significantly determine productivity and environmental compatibility of an aquafarm. Technical soundness of construction and setting of holding units, type and amount of materials used, disposal of removed soil and vegetation, are important factors of ecological relevance. Similarity important are the set-up of systems of water renewal and waste water discharge in land-based aquafarms. For water exchange in sea-based farms, anchorage, size of nets and their meshes, seabed coverage, distance between stakes, etc., have to be considered in relation to water depth, bottom slope and exposure to prevailing currents. Clearly, the expected biomass of a farm will determine the magnitude of waste output and water exchange requirements.

Operation of aquaculture facilities

The operational practices of aquaculture farms also plays an important role in environmental impact particularly water, soil, seed and feed management. Farms operating similar culture systems, in similar environments may have different environmental impacts, e.g. through difference in the operational management of soil, water and other sources.

Preparation and maintenance of holding units, technical installation (e.g. sluice gates, pumps), equipment (e.g., aerators, feeders) and gear (e.g., harvesting nets, boats) is essential. Fluctuation in the availability of good quality seed for stocking often result in inefficient use of farm facilities. In constant, over-stocking i.e., high stocking density combined with low water exchange, may, however, reduce growth and create water quality and health problems. Inadequate farm operation often directly affects stress level and required water-(and soil-) quality. Ensuing increased susceptibility to disease and parasites may then lead to excessive use of prophylactic drugs.

Similar problem can be expected with over-use of fertilizers and feeds. Of importance is also the type (physico-chemical characteristics) of fertilizers applied and feeds given. Further, feeding methods, (in particular frequency, timing, dispersal of food) and particle size determine the amount of food eaten as well as adequate timing and phasing of farm operations, can significantly influence magnitude and extent of ecological effects, and costs.

Environmental management involving the private sector

Within the private sector, which includes farmers and supporting industries, environmental management may be implemented:

-   at farm level, particularly in relation to the location and management of individual farms.

-   through farmer groups/cooperative actions. Cooperative action may be required where farmers are sharing common resources. Increasingly, farmers are cooperating to solve common problems, e.g. in controlling water pollution through cooperative water management.

It should be recognized that there are some increasingly serious «incentives» for improved environmental management within the private sector, particularly where farmers are growing crops, e.g. shrimps, for export markets. These ‘incentives’ incllude:

-   non-tariff trade barriers, which are sometimes being created because of environmental concerns. For exemple, some pressure groups within some importing countries have tried to implement bans on aquaculture commodities which have been produced through ecologically-degrading practices.

-   Market acceptability. If there is unacceptable contamination with antibiotics or other material such as pollutants (e.g. public health concerns related to molluscs) (real or imaginary), then this will affect the marketability of aquaculture products and profitability of aquaculture enterprises. As water pollution problems increase, and as consumer awareness over ‘clean’ or ‘organic’ food increase, aquaculture production will need to give increasing attention to culture environments.

-   Economic losses from disease. Disease outbreaks, and ensuring economic losses to farmers.

-   Seen particularly in shrimp culture - many of which are related to some form of environmental deterioration - provide a strong incentive to improve the environmental management of farms. Where environmental problems arise from outside of the farm, e.g. through self-pollution of culture areas then these problems provide incentive for far mers to cooperate, or seek assistance from government in confronting problems.

Private sector (farm) management options

The following details some of the farm management options which may be considered in improving the environmental management of aquaculture.

Aquaculture system potentials:

As ‘open’ system are more ‘vulnerable’ to environmental problems, there are possibilities to reduce environmental impacts, by moving towards more closed systems. Closed systems are usually less vulnerable to many of the environmental impacts on aquaculture, and environmental impacts of aquaculture may sometimes be reduced by reliance on less external input and recycling of potentially damaging materials (e.g. pond effluent) within the farming system. Examples are:

-   in small-scale integrated aquaculture-agriculture farming systems, where potentially polluting materials are recycled within the farming system.

-   through promotion of polyculture and integrated forms of culture, in inland and coastal aquaculture, involving recycling of nutrients, organic matter, Considerable scope exists for such systems in marine environments, where much monoculture occurs.

-   on farm recycling of water

Species characteristics

The selection of species which are will adapted to the culture environments is important, e.g. water polluted with organic discharge will be less suitable for mollusc than fish. Alternatively, some species have a higher tolerance to poor environmental conditions than others. There may also be some merit in promoting the use of indigenous fish species, rather than relying on exotic species, which have potential for negatives impacts on both indigenous culture and capture fisheries

Degree of intensification - environmental capacity

In terms of management, consider two aspects:

-   intensification within the aquaculture system, e.g. ensuring intensity, in terms of stocking, production and feeding, is matched to the capacity of the culture system. Obviously, effluent problems are normally less serious in semi-intensive culture than in intensive culture; and

-   Aquaculture environment. In practical terms, this means that the culture intensity is matched to the capacity of the recipient environments to flush or absorb the waste released.

Location desing and operation

Clearly the location, design characteristics and operational features of aquaculture systems, all play a very important role in environmental management:
For land resources, consider:

-   the use of lower value land resources for aquaculture (e.g. land which will not be used by agriculture or tourism). Choices related to land use will depends to some extents on the ‘values’ assigned to different land types by society;

-   the siting of farms in relation to other users, both in terms of the environmental impact on aquaculture (e.g. siltation) and possible conflicts with other users.

For water resources, consider:

-   the siting of farms in relation to other users, both in terms of the environmental impact on aquaculture (e.g. water pollution) and possible conflicts with other users, e.g. through effluent discharge, water use conflicts;

-   design of water supplies and drainage systems, to avoid self-pollution problems, as well as conflicts, e.g. proper design of drainage systems to avoid salinization of fresh water resources.

-   Water quality management, e.g. appropriate adjustment of water exchange and aeration rates

For waste management, consider:

-   Treatment of effluents may be required, particularly in intensive aquaculture systems. Treatment technologies are being developed based on sedimentation, decantation biological oxidation and filtration. Often, treatment techniques are designed for «high-tech» system, based on water-recycling approaches, including nitrification and biofilters, foam fractionation, carbon adsorption, ion exchange, algal system and ozone.

-   Treatment facilities must be efficient, yet economically feasible to install and to operate. Use of suitably designed sedimentation ponds appears to be a cost-efficient practice in many commercial farms. The sludge accumulated in sedimentation ponds or in culture ponds should be disposed off safely.

-   Removal of suspended matter from ponds may also be achieved in sedimentation ponds stocked with filter-feeding organisms, such as oysters or mussels. Nutrient loads can be reduced when seaweeds such as Gracilaria and Caulerpa are polycultured with shrimp or milksfish in ponds or cultivated in exit canals. Integrated practices, for examples, off-bottom polyculture of bivalves and seaweeds, salmonid cage culture combined with mussel culture, use of mullets in bottom cages underneath seabream cages, or shrimp/oyster co-production systems may proves very successful in reducing effects of waste loads from sea-based farms.

-   Changing culture sites is an approach which may be used with sea-based aquafarms to avoid excessive accumulation of organic sediments. Site rotation may contribute to sediment recovery through natural dispersal and disintegration of wastes during periods where farming areas are left to lie fallow. Additional trawling of sediments is sometimes applied to assist oxygenation and mineralization of wastes. Sediments loading per unit area may be reduced through single point mooring system in cage farms.

For land and water resources, consider:

-   In practical terms, both require the proper identification and consideration of potential environmental problems during site selection. An alternative is to zone aquaculture enterprises (with consideration of environmental capacity), a management technique which can reduce conflicts between different users, by concentrating aquaculture in selected areas.

For feed (and fertilizer) resources, consider:

-   diet type (wet, moist, dry pellet);

-   source of feed;

-   feeding intensity and methods;

-   alternatives uses of the feed or fertilizer, both on and off-farm.

Since inputs of fertilizers and, in particular, feeds are often the main cause of deterioration of environmental quality within and outside the culture unit, improvements are required in the management (i.e. choices, storage, handling and application) of these inputs.

Excessive use of inorganic and organic fertilizers should be avoided. Under farm conditions, it is difficult to precisely predict or adjust the degree of fertilization required. Monitoring of pond water quality should be carried out regularly. It is suggested to record time, frequency and mode of application as well as the type and amount of fertilizers be well dispersed or diluted.

Feeding regimes need to be adapted to specific feeding habits and behaviours of cultured species, particularly in intensive (feed-lot) farming system. Ideally, feed inputs should be determined based on knowledge of species-specific feeding behaviours and nutritional requirements as well as on estimates of biomass in the culture units.

In many cases, feed wastage, due to over-feeding can be reduced by careful hand-feeling. Feed supply by automatic feeders should be closely monitored. It may be required that feeds be evenly dispersed over the culture unit, or feeding strategy may have to be adjusted according to territorial behaviour of cultured stock or water currents prevailing in the culture unit.

Meticulous recording is suggested of amount and type (e.g. trash fish, Compound feeds, water content, chemical composition, particle size, etc) of feeds given, of feeding methods and devices (hand-feeding, demand/automatic feeders, boat feeding, feed blowers, etc) as well as of feeding time and frequency per day or of any change in feeding strategy, such as position of operator/feeder as related to the culture unit. Feeding response of cultured stock should, where possible, also be observed.

For seed resources, consider:

-   the origin of stocks(e.g. wild or hatchery);

-   pathogen/disease status of stocks

-   stocking density

-   stress avoidance

As a final remark, attention is drawn to the fact that environmental interactions of aquaculture can be described as: a) environmental impacts of aquaculture; b) environmental impacts on aquaculture, and c) environmental impacts of aquaculture on aquaculture.

Farm Level environmental management options have been summarized in following table:

Some general options for environmental management by public authorities

There is a range of possible measures which may be undertaken by public authorities to promote environmental management in relation to coastal aquaculture development:

-   Encourage national policy which ensures equitable use of natural resources for aquaculture; and which protects aquaculture environments.

-   Evaluate economics benefits of aquaculture and economic of environment, and protection of aquaculture resources/environments.

-   Review and strengthen aquaculture policy giving due consideration of environment, and related food security, social, economic, and legal considerations.

-   Promote integrated approaches to planning of aquaculture development, within the broader framework of natural resources management, and dialogue (involving government and resources users) in avoiding and/or resolving conflicts.

-   Clarify responsibilities for aquaculture/resources management, to avoid conflicts, inefficiencies, and implementations difficulties.

Government may consider to support human resource development

There may be a need for human resource development at different levels, to encompass the skills required for the planning and operation of aquaculture in relation to the environment, with emphasis on farm management practices and resources protection. Consider:

-   Farmers, and private sector organisations, particularly in sensitizing farmers to the issues involved, and in avoiding and dealings with farm level problems;

-   extension workers, and others involved (government and non-government personnel) involved in assisting farmers at local levels.

-   policy makers and planners, involved with the planning of aquaculture development, and in natural resources management, to increase awareness of the issues involved, and of mechanisms and choices involved in dealings with problems in the major aquatic resource systems; and

-   research scientists - strengthening of human resources in national research institutions to properly deal with the various environmental issues related to aquaculture development, and integrated aquatic resource management.

Major options of a legislative framework for the environmental management of aquaculture

Review/formulate/strengthen aquaculture legislation, with option for:

-   definition of aquaculture

-   aquaculture licence(incl. information, EIA, environmental monitoring, introduction of exotics, flexibility)

-   creation of awareness

-   protection of aquaculture environment (e.g. effluent discharge controls, marine and land zoning)

-   enforcement (e.g; public participation, monitoring, penality provision)

-   financial incentives/disincentives

Formulating an appropriate legal and institutional framework

The preparation of an appropriate legal framework requires close collaboration with scientists, the producers, the competing users, etc. and last but not least the government authorities.
Furthermore it is important to consider following elements:

-   the purpose of the industry: food production and market, employment, research or recreation;

-   the resources used i.e. water, land, specie, feed, energy, labour, etc.;

-   the system or methods used for production

-   the environment in which the production is conducted;

-   the technical capacity of the government to implement and enforce the measures.

With regards to the institutional framework is important to consider that;

-   the control of environmental impacts of aquaculture has not always an institutional identify i.e. the responsible institution or network of institutions are difficult to identify. They are not specifically linked together by functions and management strategies;

-   as aquaculture is touching upon various natural resources, an environmental management plan for aquaculture must necessarily involve coordinated action concerning different matters in areas already included within the sphere of authority of many agencies;

-   the division of function between the central management agency and the various less centralized institutions and authorities, though of critical importance, are not always clear.

Documentation consulted/used for preparation of this Working Paper

-   Draft report of Workshop of Environmental Assessment and Management of Aquaculture Development in Asia-Pacific. FAO TCP/RAS/2253. (1994)

-   Draft technical report «Aquaculture management in Asia: Approaching the environmental concerns», by TCP team (Philips, Wijkstrom, Van Houtte). FAO TCP/RAS/2253.

-   GESAMP (1991): Reducing environmental impacts of coastal aquaculture. FAO (1991)

-   Guidelines for the promotion of environmental management of coastal aquaculture development. FAO Fish.Tech.Paper (328). FAO (1992).

-   Environmental planning for aquaculture development: integrating aquaculture in coastal zones, draft paper by J.Muir. MEDRAP II Seminar on Planning of Aquaculture Development (June 1992); unpublished.

RECENT PUBLICATION ON THE ENVIRONMENT

Institute of Aquaculture, University of Stirling, STIRLING FK9 4LA

Aquatic resources and their management

Ali C, Ross I.G & Beveridge M C M (1991) Microcomputer spreadsheets for the implementation of geographic information system in aquaculture.

A case study on carp in Pakistan. Aquaculture 92, 199–205

Aguillar-Manjarrez, J&Ross L G (1993) Aquaculture development and GIS. Map Aware. GIS Europe, 7, 49–52.

Burbridge P, Gavine F M & Kelly L A (1994) Regulating wastes from aquaculture production. United Kingdom: Scotland. Proc. Workshop on fish farm Effluents and their Control in Ec. Countries. Hamburg, Germany, 1992. (in press).

Chacon-Torres A, Ross L G, Beveridge M C M & Watson, A (1992) Chlorophyll and suspended solids: observation in Lake Patzcuaro, Mexico, using SPOT multispectral imaging. Int. J. Mexico, using SPOT multispectral imaging.Int. J.Remote Sensing, 13, 587–603

Chacon-Torres A, Ross L G & Beveridge M C M (1989) Lake Patzcuaro, Mexico, Results of a new morphometric study and its implication for productivity assessments.Hydrobiologia, 184, 125–134.

Chacon-Torres A, Ross L G & Beveridge M C M (1988) The use of remote sensing for water quality investigation for aquaculture and fisheries. proc. Int. Chem. Eng.Symp., 111, 21–44

Kelly L A (1992) Estimating sediment yield variation in a small forested upland catchment. Hydrobiologia, 235/236, 199–203

Macintosh D J et al (1991) Final Report of the Integrated Multidisciplinary Survey and Research Programme of the Ranang Mangrove Ecosystem. UNDP/UNESCO Regional Mangroves Project RAS/86/120, 183 PP.

Ross L G, Mendoza E A & Beveridge M C M (1993) The application of Geographical Information Systems to site selection for coastal aquaculture: an example based on salmonid cage culture.Aquaculture, 112, 165–178.

Murphy K j, Tippet & Beveridge M C M (eds.) (1994) Loch Lomond: The catchment ecology and limnology of a temperate lake. Developments in Hydrobiology Series. Kluwer, Netherlands. (in press).

Williamson R B & Beveridge M C M (1994) Fisheries and aquaculture. In P S MAITLAND, P J Boon & D S McLusky (eds.) The freshwater resources of Scotland. John Wiley and Sons Ltd., Chichester (in press).

Ecotoxicology

Baird D J (1992) Predicting population response to pollutants: a reply to Forbes & Depledge. Funct. Ecol., 6, 616–619.

Baird D J, Barber I, Bradley M C, Soares A & Calow P (1991) A comparative study of genotype sensitivity to acute toxic stress using clones of Daphnia magna straus. Ecotox. Env. Safety, 21, 257–265.

Baird D J, Barber I, Soares A & Calow P (1991) An early life stage test with Daphnia magna straus: an alternative to the 21-day chronic test?. Ecotox. Env. Safety, 22, 1–7.

Beveridge M C M, Baird D J, Rahmatullah S M, Beattie K A & Codd G A (1993) Grazing rates on toxic and non-toxic cyanobacteria by Hypophthalmichthys molitrix and Orecochromis niloticus. J.Fish Biol., 43, 901– 907.

Birchall D, Exley C, Chappell J & Philips M J (1989) Control of aluminum toxicity by silica. Nature (London),338, 146–148.

Bradley M, Naylor C, Baird D J, Barber I, Soares A & Calow P (1994) Reducing variability in Daphnia toxicity tests: a case for further standardisation. IN: A Soares & P Calow (eds.) Progress in standardisation of aquatic toxicity tests. Lewis Publishers, Michigan (in press).

Exley C, Chappel J S & Birchall J D (1991) A mechanism for acute aluminium toxicity in fish. J.Theor.Biol., 151, 417–428.

Noguiera A, Baird D J &Curtis A (1994) A new approach to individual-based dynamic modelling with application in ecotoxicology. In: A Stebbing, P Mathiessen & K.Travis (edd.) Ecotoxicology the next 10 years. SETAC-Europe Publication (in Press).

Philips M J & Saleh M A M (1988) Aluminium to tropical aquatic environments and its toxicity to Oreochromis aureus. In Pullin R S V, Bhukuswan T, Tonguthai K, & Maclean J L (eds.) The second Int Symp. on Tilapias in Aquaculture.ICLARM Conference Proceedings, 15. Department of Fisheries, Thailand & ICLARM, Manila, Philippines. pp.489–496.

Siriwardena P P G S N, Rana K J &Baird D J (1993) Importance of juvenile life-history strategy to pollutant resistance in the tilaopias: a sub family of African Cichlids. In: L C Wrobel & C A Brebbia (eds.)Water pollution II: modelling, measuring and prediction. Computational Mathematics Publications, Southampton. pp.692–700.

Soares A, Baird D J & Calow P (1992) Interclonal variation in the performance of Daphnia magna Straus in Chronic bioassays. Env. Tox. Chem., 11, 1477–1483

Biology and ecology of aquatic systems

Beveridge M C M, Begum M, Frerichs G N & Millar S (1989) The ingestion of bacteria in suspension by the tilapia Oreachromis niloticus. Aquaculture, 81, 373–378.

Beveridge M C M, Briggs M R P, Northcott M E & Ross L G (1988) The occurrence, structure and development of microbranchios-pines among the tilapias (Cichlidae:Tilapiini) Can.J.Zoo., 66, 2564–2572.

Beveridge M C M, Sikdar P K, Frerichs G N & Miller S (1991) The ingestion of Bacteria in suspension by the common carp cyprinus carpio L.J.Fish Biol., 39,825–831.

Beverdge M C M, Wahab Md A, & Dewan S (1994) Effects of daily harrowing on pond soil and water nutrients levels and on rohu fingerling production. Prog.Fish Cult. (in press).

Bradley M C, Baird D J & Calow P (1993) Maternal provisionning and the control of fecundity in Daphnia magna Straus. Biol.J. Linn.Soc., 44, 325–333.

Dempster, P W, Beverige, M C M & Baird, D J (1993) Produccion de peces hervioros en sistemas semi-intensivos. Cien. Invest. Agrar., 20 (2), 224–244.

Dempster P W, Beveridge M C M & Baird D J (1993) Herbivory in the tilapia Orechromis niloticus(L): a comparison of feedings rates on phytoplankton and periphyton. J.Fish Biol., 43, 385–392.

Keshavanath, P, Beveridge, M C M, Baird, Baird, D J, Nimmo, A & Codd, G. (1994) The functional grazing response of a phytoplanktivorous fish Oreochromis niloticus to mistures of toxic and non-toxic strains of the cyanobacterium Microcystis aeruginosa. J.Fish Biol. (in press)

Macintosh D J (1988) The ecology and physiology of decapods of mangrove swamps. Proc.Symp.Zoo.Soc.London, 59, 315–341

Martinez Cordero F J, Beveridge M C M, Muir J F, Mitchell D & Gillespie M (1994) A not on the behaviours of adults Atlantic Hailbut, Hippoglossus hippoglossus, (L.) in cages; Aquacult.Fish.M.gmt.(in press).

Martinez-Palacios C A & Ross L G (1988) The feeding ecology of the central American cichlid Cichlasoma urophthalmus (Gunther) J. Fish Biol., 33, 665–670.

Northcott M E & Beveridge M C M (1988) The development and structure of pharyngeal apprauts associated with filter feeding in tilapias (Oreochromis niloticus L).J.Zool., 215,133–149.

Northcott M E, Beveridge M C M & Ross L G (1991) A laboratory investigation of the filtration ingestion rates of the tilapia Oreochromis niloticus feeding on two species of blue-green algae. Env.Biol.Fishes, 31,75–85.

Phillips M J (1989) Feeding sounds of rainbow trout, Salmo gairdneri Richardson.J.Fish Biol., 35, 589–592.

Rahmatullah S M & Beverige M C M (1993) The ingestion of bacteria in suspension by fry of planktivorous Indian major carps (Catla catla, Labeo rohita) and chinese carps (Hypophthalmichthys molitrix, Aristichthy snobilis). Hydrobiologia, 264, 79–84.

Aquaculture and environmental impact

Baird D J (1994) Pest contro in tropical aquaculture: an ecological hazard assessment of natural and synthetic control agents. Mitt.Int verein.Limnol. (in press)

Bergheim A, Kristiansen R & Kelly L A (1993) Treatment and utilization of sludge from landbased farms for salmon.In:J_K Wang (ed.) Techniques for modern Aquaculture. ASAE, Michigan.PP; 486–495.

Beveridge M C M (1987) Cage Aquaculture. Fishing New Books, Oxford. 352p.

Beveridge M C M (1988) Problems caused by birds at inland waters and fresh water fish farms.In Bungenberg de Jong C M (ed;) Report of the working party on the prevention and control of bird predation in auquaculture and fisheries operations. EIFAC Tech; Pap. 51, FAO, Rome, 34–73.

Beverige, M c M & Muir, J F (1994) Environmental impacts and sutainability of cage culture in Southeast Asian lakes and reservoirs.In: W van Dessen, T Saidin and M Verdegem (eds.) Ecological Aspects of Fish Production in SE-Asian Lakes and Reservoirs University of Wageningen (in press).

Beveridge M C M & Phillips M J (1993) Environmental impact of tropical inland aquaculture. In: R S V Pullin, H Rosenthal & J L Maclean (eds.) Environment and Aquaculture in developing Countries. ICLARM Conf. Proc. 31, 213–236.

Beveridge M C M, Phillips M J & Clarke R M (1991) A quantitative and qualitative assessment of wastes from aquatic animal production. In: D E Brune & Tomasso J R (eds.) Aquaculture and water quality, Advances in World Aquaculture Vol.3, World Aquaculture Society, Baton Rouge, Louisiana, pp. 506–533.

Beveridge, M C M, Ross, L G & Kelly, L A (1994). Aquaculture and biodiversity. Ambio (in press).

Kelly L A (1992) Dissolved reactive phosphorus release from sediments beneath a fresh water cage aquaculture development in West Scotland. Hydrobiologia, 235/236, 569–572

Kelly L A (1993) Biological availability of phosphorus released from aquaculture wastes determined by Selenastrum capricornutum bioassay. Hydrobiologia, 253, 367–372.

Kelly L A & Karpinksi A W (1994) Measuring BOD output from fish farms; proc. workshop on Fish Farm Effluents and their Control in EC countries. Hamburg, Germany, 1991. (in Press)

Kelly, L A, Bergheim, A & Hennesy, MM (1994) Estimating ammonium outputs from fish farms. Wat. Res. (in press).

Nature Conservancy Council (1990) Fish farming and the Scottish freshwater environment. NCC, Scottish Headquarters, Edinburgh.

Nature Conservancy Council (1989) Fish Farming and the safeguard of the natural environment in Scotland. NCC, Scottish Headquarters, Edinburgh.

Phillips, M J, Beveridge, M C M & Macintosh, D J. 1990. The impact of aquaculture on the coastal environment. In: R.Meie (ed) Proceedings of the international Symposium on the Coastal Zone. China Oceans, Press, Beijing. p.537–545

Phillips M J, Beveridge M C M & Clarke R M (1991) Impact of aquaculture on water resources. In: D E Brune & Tomasso J R (eds.) Aquaculture and water quality, Advances in World Aquaculture Vol. 3, World Aquaculture Society, Baton Rouge, Louisiana, pp. 568–591.

Phillips M J, Clarke R & Mowat A (1993) Phosphorous leading from Atlantic salmon diets. Aqua.Eng.,12, 47–54.

Phillips M J, Kewei-Lin C & Beveridge M C M (1993) Shrimp culture and the environment lessons from the world's most rapidly expanding warm water aquaculture sector. In: R S V Pullin, H Rosenthal & J L Maclean (eds.) Environment and Aquaculture in Developing countries.ICLARM Conf. Proc.31, 171–197. Weston D P, Phillips M J & Kelly L A (1994) Environmental impact of salmonid culture.In: Salmonid culture. Elsevier, Amsterdam (in press).