ALCOM identified the following aspects of aquaculture that can have a possible environmental impact:
aquaculture systems may significantly alter the environments;
aquaculture may create environments for human disease vectors;
genetic quality of the cultured fish is important to the surrounding environment, due to the risks or accidental release of fish.
The aquaculture system and intensity determine the type and scale of environmental effects in combination with the physical, chemical, and biological characteristics of the area in question. Intensive aquaculture systems cause eutrophication of the environments through release of effluents loaded with waste products. Large scale systems can seriously after the environment.
The culture systems adopted by small-scale farmers in southern Africa did not have a significant effect on the environment. The small ponds with extensive or semi-intensive management, operated with stagnant water, and even when drained the amounts of water and the concentrations of nutrients in the effluents were too small to cause an adverse effect.
Aquaculture can cause ecological change, destroy wetlands habitats and disturb wildlife. In the areas where fish farming was introduced by the Programme no situation occurred where large number of ponds had been constructed and had impacted the local ecology. In most cases farm land or areas adjacent to farm land had been used for pond construction, and as a result the total area of cultivated land had only marginally increased.
The aquaculture systems, as adopted through the intervention of ALCOM had no significant impact on the environment.
It is possible that water-related projects such as irrigation schemes and aquaculture increased the prevalence of schistosomiasis by providing the vector snail with favourable habitats, and by increasing people's contact with water. Privately owned fish ponds, however, do not necessarily increase the prevalence of schistosomiasis. Properly constructed and well managed ponds offered little habitat for the vector snails while the restricted access to ponds by other people limited the risk of the transfer of parasites.
Larger ponds and reservoirs with open access do offer a serious risk for spreading the disease. The prevalence of schistosomiasis in people who are in regular contact with water from reservoirs is high in the region. ALCOM started some activities to investigate the possibility of biological control of the vector snails, but this activity never went beyond the first phase of an experiment. No results were obtained and conclusions could not be drawn from this experiment.
Aquaculturists are interested in maximising production from the culture of fish. Species for which culture systems and techniques have been developed and with known production potential are therefore preferred by culturists. These species are not always indigenous to the areas where they are proposed to be used, and are often introduced from other areas. Aquaculture is conducted in controlled systems, but even if fish are used in strictly confined areas, there is still a risk of the fish escaping and entering into natural waters.
Whether or not these escaped individuals establish viable populations in natural waters depends on many factors. Their impact on the local ecosystem and biodiversity again depends on the system in which they are introduced and on the characteristics of the species. However, the introduction of alien species should be seen as a serious form of pollution, and unlike other forms of pollution, biological pollutants have the ability to reproduce and disperse in all directions, and when they do, they are virtually impossible to eradicate. The introduction of alien species should therefore be treated with the utmost care.
ALCOM addressed this issue on various occasions. It initiated a study on species introductions in Zambia, that revealed significantly more introductions than previously reported and made recommendations to the government on controlling introductions.
In Mozambique ALCOM reviewed the potential impact of Chinese carps, and initially concluded that it was unlikely they could establish wild populations in southern Africa. The use of Chinese carps in Mozambique was therefore continued. Later, this conclusion proved incorrect since Silver carps managed to establish breeding populations in the Olifants river in South Africa and spread further into Mozambique and the Limpopo river. ALCOM conducted an Environmental Impact Assessment after it became apparent that Silver carps had been stocked in coastal barrier lakes in Mozambique. This study concluded that there was no justification for the introduction, and that further stocking should be prevented.
ALCOM organised a Technical Consultation on species for small reservoir fisheries and aquaculture in southern Africa, which was attended by 52 participants from within and outside the region. This consultation concluded that the effects of any introduction are extremely difficult to predict due to limited knowledge of the dynamics of the various ecosystems. It also showed that due to the diversity of culture systems and resource ownership, the changes in economies, and wide variety of purposes of culturing fish made it impossible to predict what species are most likely to be introduced in the future. The consultation made several recommendations on how the region could develop a system that would improve the evaluation of any proposed introduction and would ensure the collaboration between countries in the region.
ALCOM organised, with the assistance of IUCN, a review of the inter-country co-operation regarding introduction of aquatic species in the Limpopo river system. It reviewed the present legal institutional situation in the four countries sharing the river, as well as international and regional institutions relevant for improving the co-operation. The consultation concluded that information exchange between countries, as well as between the various national departments and organisations within countries, was critical for the establishment of rules and regulations to harmonise mechanisms to authorise and control introductions of aquatic species. The consultation further came up with a strategy and action plan to achieve this harmonisation. Due to the cessation of the project funding and uncertainty regarding the future of ALCOM, the Programme could not follow up on this action plan.
Already in 1992, ALCOM realised that activities on environmental aspects should be elaborated within the conceptual framework of water resources management. This was based upon the recognition of increasing problems with water scarcity, competition among water users and concern about water quality.
The most recent consultation on species introductions revealed that even for the issue of introductions and translocations of aquatic species an approach based on water shed management should be adopted.
Both findings called for an integrated and holistic approach towards water management and encompasses much more than fish alone. The ALCOM component dealing with reservoir fisheries produced an inventory of the reservoirs in southern Africa to estimate potential production and scope for enhanced fisheries management. This data base will be extended to include more data and aspects of water resource management. There is a clear need for including data on species distributions, potential for aquaculture, integrated water management and use, etc. to enable planners to determine the possibilities for optimal use of this limited resource.
