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The pros and cons of the spread of cage aquaculture in Africa

13 May 2020, at 5:08pm

Concerns over the spread of fish farm cages in Africa’s inland waterways have been expressed in a new study which gives a valuable overview of the extent of the continent’s freshwater cage culture.

The researchers note that, as recently as 2006, the only commercial cage aquaculture taking place on Africa’s inland waterways was in Lake Kariba, although there were also small-scale pilot projects underway in lakes Malawi, Volta and Victoria.

Harvesting Nile tilapia at a farm run by Source of the Nile fish farm in Uganda
Harvesting Nile tilapia at a farm run by Source of the Nile fish farm in Uganda

The extent of freshwater cage culture

Their research – which was based on painstaking examination of images obtained via Google Earth Engine, combined with verification by ground truthing and phone surveys – revealed that this number has now increased to 263 installations, with more than 20,000 cages between them.

The study, which was led by researchers in Uganda, confirmed the presence of cage aquaculture on a total of 18 water bodies. These were divided between eight countries: Ghana having 36.1 percent of the installations, Uganda 17.9 percent, Kenya 16.4 percent, Tanzania 13.3 percent, Rwanda 8 percent, Zimbabwe 3.8 percent, Zambia 3 percent) and Malawi 1.5 percent.

With 39.9 percent of all the installations, Lake Victoria had the highest number of cage aquaculture installations of all the water bodies. They also ascertained that lakes Victoria, Kariba, and Volta, as well as the River Volta host 82.9 percent of cage aquaculture installations on the African inland waters.

Although the study provided a unique overview of the extent of cage culture the authors admit that they were unable to identify cage aquaculture in a number of water bodies where cage aquaculture reportedly occurs – including Lake Tanganyika in Zambia, and some lakes in Nigeria and the Ivory Coast.

The researchers note that the use of cage-based systems in inland waters has the “potential to close the fish supply deficit in the region and provide other social benefits such as employment and income”.

“However,” they warn, “if not appropriately guided and regulated, cage aquaculture could become unsustainable, causing conflicts with other water uses, environmental degradation and economic losses to aquaculture enterprises.”

Best practice, in practice?

The researchers’ analysis found “partial adherence to best practices” at the cage aquaculture installations they investigated. Some of the key issues uncovered included 138 installations being located within 200m of the shore, contrary to best practice. This included 61 installations on rivers such as the Volta (Ghana), the Nile (Uganda) and small water bodies which do not offer the possibility of the buffer because of their shape or size.

They also found 27 cage aquaculture installations – all in Uganda or Zimbabwe – located entirely within protected areas or <1 km away from the protected areas, which were designated as forest reserves, community wildlife management areas or Ramsar sites.

Cages in eutrophic and hypertrophic waters, shallow water bodies and sites (≥5 m average depth) were also noted.

“Depending on the scale, these impacts could devastate the biodiversity attributes of African inland lakes and dependent fisheries resources useful for food security, employment, and revenue generation,” they said.

The hazards of allowing the sector to develop without greater regulation were noted by the authors, who looked to examples from outside Africa to illustrate the perils of unregulated growth.

“Ignoring best practices during establishment of cage aquaculture is not only detrimental to the environment but could also disrupt cage aquaculture investments. This possibility should be recognized as an incentive for promoting best practices among fish farmers and prospective farmers. In several instances, farmers have been forced to remove cage aquaculture installations from lakes and rivers for environment reasons such as fish kills. In China, farmers were forced to remove cages from lakes and rivers in response to a new directive for proper zoning. Similar decisions have been experienced in Philippines on Taal lake and River Pansipit and in Indonesia on Jatiluhur Reservoir,” they explained.

Although they concede that they uncovered “no reports of adverse or catastrophic impacts of cage aquaculture on African inland water bodies” they note that “it has been associated with loss of nutrients to water on Lake Malawi, low dissolved oxygen, increased ammonia concentration around cages and eutrophication of Lake Victoria.”

They also point to the escape, from farms in Lake Volta, of non-native strains of tilapia originating from Asia which are now interbreeding with native strains.

Looking ahead

The researchers reflect that the level of cage culture impacts on African waters is still minimal, probably because area under cage aquaculture is still negligible compared to the size of the water bodies. For instance, their results indicated that only 176.9 hectares of Lake Victoria are under cages, which is a mere 0.0026 percent of the lake’s total surface area.

In order to ensure this remains the case the authors recommend a series of measures, including the establishment of aquaculture zones which exclude shallow lakes such as Kyoga and George in Uganda.

“Just as there are plans to transfer marine coastal aquaculture to offshore areas, zoning on African waters should consider prohibiting cage aquaculture near the shoreline and exclude water bodies such as rivers, small lakes and reservoirs,” they recommend.

Other best practices they suggest include “encouraging the farming of native fish species, use of appropriate stocking rates, maximizing feeding efficiency, minimizing contamination, disease surveillance, maintaining production information, environmental monitoring and farm decommissioning. The development of the best practices should engage and train farmers not only to promote best practices but also to equip them with skills and knowledge for implementation. Engaging farmers is critical as good farm management can avoid adverse impacts of cage aquaculture.”

“Development of regulatory frameworks and producer organizations should also be strengthened to minimise negative impacts on the environment,” they add.

Summing up his research lead author Laban Musinguzi told The Fish Site: “The need for more nutritious food in Africa makes it inhumane to reject cage aquaculture development on her inland waters for the sake of conservation. However, proponents of the development have to fully adhere to best practices to sustain other water uses, particularly capture fisheries production.”

Further information

An abstract of the study, which was published under the title, "The extent of cage aquaculture, adherence to best practices and reflections for sustainable aquaculture on African inland waters", can be accessed in the Journal of Great Lakes Research.