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Fish farms: Emerging threats coming ashore

MAURITIUS - The prospect of implementing fish farms inside and outside of the lagoon is arousing concern among those who care for the environment. The main one is the fate of our reefs and future of our beaches.

"We have to be very careful. It is because of corals that there are beaches. They are so important in the whole functioning and protection of the shores," says Dr Deolall Daby, associate professor for Marine and Environmental Sciences at the University of Mauritius. His reaction comes in the wake of the presentation of the Aquatic Business Activities Bill. The authorities are already considering the implementation of fish farms in the lagoon. Proposed sites have been identified by Idéeaquaculture, a French consultant firm that assessed the start-up of red drum (Sciaenops ocellata) and tropical sea-bream (Rhabdosargus sarba) in 2005 at the Ferme Marine de Mahébourg.

The proposed sites are found in the lagoon of Tamarin, Bambous-Virieux, Trou-aux-Biches, Cap-Malheureux, Mahébourg and Poste-Lafayette, some in the open sea, near Le Morne and Flat Island. Three other farms would operate inland. It is those found in the sea that are causing concern among environmentalists.

Dr Daby contributed to studies on the Environmental Impact Assessment of human activity on corals with fellow scholars from the University of Wales. While being not necessarily against the development of aquatic business, he questions the exact location of the sites: “Each lagoon has its specifications. Some sites may be appropriate, some not at all. Once we add nutrients to water, we have rapid disruption,” he explained.

So it is not clear from what has been carried out in Mahébourg how the new sites will react to the farms. Dr Daby says that one essential aspect is the current patterns. Currents dictate the direction of everything that flows in the water. Nutrients used to feed the fish in the farm can propagate with the flow and accumulate on corals.

This accumulation may have effects on temperature, transparency, salinity of water or its pH, that are associated with polyp development, and whose disturbance may threaten, or kill, corals. Since the public is not aware of important details of the projects, Dr Daby recommends close assessment studies before the beginning of any activity and scrupulous technical monitoring of the quality of water if anything is implemented.

Another threat is algae blooms. A view shared by Ian Watt, marine biologist and director of Reef Conservation Mauritius, a non-governmental organisation.

The algae proliferate by devouring the nutrients and their presence affects the level of oxygen that conditions life in the lagoon. “There is reasonable flushing in most of our lagoons to prevent the algae from choking completely other forms of life. But the whole system will be affected,” he said.

Identification of sites

Of more concern are the sharks that may be attracted by the concentration of fish and food. “The presence of farms may work as the Fish Aggregating Devices that were once put in the sea. Even if the lagoons are mostly protected by their natural barrier, baby sharks may first pass through and come back at adult age through passes”, observes Dr Deolall Daby.

Mr Watt agreed and said that as aquatic farms needed fairly deep water to develop properly, then sharks would have no trouble to come in their vicinity.

Questions are also being asked about how these potential sites were identified. At this stage, it appears that it was Idéeaquaculture an organisation that specialises in technical and socio-economical feasibility studies, technical surveys, economic and financial analysis.

Environmentalists say that the intensive fish farming that seems to be emerging may not be so bad. However they want to see more local community involvement in projects. People must be able to express their views, which may be possible provided there is more transparency.