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close this bookGuidelines for the promotion of environmental management of coastal aquaculture development (1992)
View the document(introduction...)
View the documentPreparation of this document
View the document1. Introduction
View the document2. Guidelines for the promotion of environmental management of coastal aquaculture development
View the document3. Coastal aquaculture and the environment: The context
View the document4. Factors influencing environmental performance of coastal aquaculture
View the document5. Assessment of environmental hazards and impacts of coastal aquaculture
View the document6. Options for environmental management of coastal aquaculture development
View the document7. References
Open this folder and view contentsAnnexes

4. Factors influencing environmental performance of coastal aquaculture

79. An account follows on important factors which affect the environmental compatibility of coastal aquaculture, The perspective provided here is on factors which determine technical appropriateness, economic viability and social acceptability (Chong, 1990b). A consideration of these factors is crucial for coastal aquaculture in terms of sustainable development of the industry as well as for successful implementation of each aquaculture venture. These factors should not be considered in isolation but simultaneously since they are, in most cases, closely interrelated.

The site

80. Space is required, both on land and/or water. The most important site factors (Huguenin and Colt, 1989) are listed in Table 12. Seawater properties defining most water quality requirements for aquaculture purposes are listed in Table 13. 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. Lifespan, 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 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 may, therefore, vary from site to site.

The species

81. Coastal aquaculture organisms differ significantly in their biological and eco-physiological characteristics. Reproduction, feeding habits, food and nutritional requirements, behaviour, 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. Biological interactions between cultured organisms and wild communities may also be restricted to the immediate vicinity of the site, or affect wider areas.

The culture method

82. The choice of the culture method will, to some extent, depend on species and site selected. Availability and affordability of resources and inputs (land, water, seed, fertilizers/feeds, energy, skills) will also govern the ease or difficulty with which a site can be developed for extensive, semi-intensive or intensive aquaculture. Major factors in environmental performance of aquafarms are design and construction of facilities as well as the operative efficiency in the production process.

(a) Design and construction

83. Since “ideal” aquaculture sites may not always be available, it will be the ability for adaptive design and engineering which 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. Similarly important are the set-up of systems for 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. Unfortunately, the varying degrees of susceptibility of the environment to degradation are often not considered when planning and designing an aquafarm.

Table 12: Important bio-physical factors in aquaculture site selection (modified from Huguenin and Colt, 1989)

Biological Environment

* Primary Productivity: phostosynthetic activity.
* Local Ecology: number of trophic levels, dominant species.
* Wild populations of desired species: adults, sources of seed stocks.
* Presence and Concentrations of Predators: land, water, airborne.
* Endemic diseases and Parasites.

Locational Factors

* Watershed Characteristics: area gradients (elevations and distances), ground cover, runoff, up-gradient activities.

* Ground Water Supply: aquifers, water table depth, quality.

* Tides: ranges, rates, seasonal and storm variations, oscillations.

* Waves: amplitude, wave length, direction, seasonal and storm variations, storm frequency.

* Coastal Currents: magnitude, direction and seasonal variations.

* Existing Facilities and characteristics.

* Accessibility of site.

* History of Site: prior uses and experiences.

Soil Factors

* Soil Type. Profile, Subsoil Characteristics.
* Percolation Rate: coefficient of hydraulic permeability.
* Topography and distribution of soil types.
* Particle Size and Shape.
* Angle of Repose: wet, dry.
* Fertility
* Microbiogical Population
* Leachable Toxins: pesticides, heavy metals, other chemicals.

Meteorological Factors

* Winds: prevailing directions, velocities, seasonal variations, storm intensity and frequency.
* Light: total annual solar energy impingement, intensity, quality, photoperiod: diurnal cycle.
* Air Temperature and variations.
* Relative Humidity or Dew Point and variations.

* Precipitation: amount, annual distribution, storm maxima and frequency.

Table 13: Seawater properties important in aquaculture water quality management (modified from Huguenin and Colt, 1989)

Physical Parameters

* Temperature Range (daily and seasonal variability)
* Salinity Range (tidal and seasonal variability)
* Particulates (solids)

- composition (organic and inorganic)
- size
- concentration

* Color
* Light

- artificial or natural
- total annual incident energy
- intensity of radiant energy
- quality of light
- photoperiod (daily cycles)

Chemical Parameters

* pH and Alkalinity
* Gases

- total gas pressure
- oxygen
- nitrogen
- carbon dioxide
- hydrogen sulfide

* Nutrients

- nitrogen compounds
- phosphorus compounds
- trace metals and speciation

* Organic Coumpounds

- biodegradable
- non-biodegradable

* Toxic Coumpounds

- heavy metals
- biocides

Biological Parameters

* Bacteria (type and concentrations)
* Virus
* Fungi

* Others


(b) Operation

84. Preparation and maintenance of holding units, technical installations (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 results in inefficient use of farm facilities. In contrast, 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 diseases and parasites may then lead to excessive use of prophylactic drugs. Similar problems 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 method, (in particular frequency, timing, dispersal of food) and particle size determine the amount of food eaten. In short, efficient farm management, which includes rational choice and utilization of inputs as well as adequate timing and phasing of farm operations, can significantly influence magnitude and extent of ecological effects, and costs.

(c) Production level

85. It may be expected that individual, small-scale aquaculture practices with comparatively low yields have little or no significant effect on the surrounding ecosystem. However, production levels have been increased through expansion (increase in culture area) and intensification of culture operations or inputs. Both factors, expansion and intensification, carry an enhanced potential for adverse ecological effect.

Skills

86. In some cases, aquaculturists lack technical, managerial and practical skills to efficiently operate their aquafarms. Skilled labour is sometimes imported. Appropriate aquaculture manpower is an important factor determining farm productivity.

Technological standard

87. Present aquaculture technologies are, in many cases, far from complete and still require substantial improvements to ensure reliability, efficiency and easy application. Application of appropriate and adaptive technology can improve environmental performance of aquafarms.

Access to financing and credit

88. Small-scale farms often do not have the financial resources to afford improvements in farm management efficiency and productivity through appropriate technology, including adequate quality of seed, fertilizers/feed and equipment. Moreover, small-scale investors facing serious problems in obtaining credit have little flexibility in selecting and developing appropriate sites.

Economic viability

89. Long-term economic viability is often restricted due to increasing costs of required resources or inputs available in the area where the aquafarm is sited. As a result, it becomes increasingly difficult for the aquafarmer to optimize the utilization of inputs, to improve the quality of products, to lower production costs, and to reduce adverse ecological effect. Marketing costs (including costs of transportation of products) can be considerable. Fluctuations in prices of aquaculture products seem to particularly affect profitability of extensive (low-input, low-productivity) systems as well as intensive systems with high capital investment and production costs. Frequent collapse and abandonment of aquafarms due to financial and economic feasibility constraints, may lead to sceptcism about social acceptability and environmental compatibility of coastal aquaculture practices.

Legal status

90. Many aquafarmers and aquaculture investors often face legal uncertainties about the utilization of land and water resources required. Often, there are many authorities having direct and indirect jurisdiction over the use of land and water for aquaculture, which causes confusion and heavy bureaucratic burdens to the aquafarmer. The type of tenurial arrangements, such as short-or long-term leases of land or water surface, can influence development and lifespan of aquafarms. Uncertainties in the allocation of land and water resources under public domain in many cases result in social conflicts with other users. Environmental legislation, if existing, often does not cover specific requirements and characteristics of the various coastal aquaculture practices.

Coordination

91. Coordination of coastal aquaculture development supported by adequate information bases and planning capacities, is lacking in many countries. Even though aquaculture development may be prioritized in national development plans, technical assistance to the sector and enforcement of supportive regulations is frequently not being carried out due to lack of financial resources. Inadequate institutional cooperation between government authorities in charge of planned development of the various activities in the coastal zone (agriculture, fisheries, urban and industrial development, sanitation, etc.) may significantly hamper both overall development as well as environment protection efforts.