Floating islands
ISLAND CONSERVATION SOCIETY - 01.06.2009
The rarest bird in Seychelles is not the magpie-robin nor the scops owl nor is it the white-eye. It is the Caspian tern. No more than ten pairs breed at Aldabra.
There may be a few more nesting at Astove and Cosmoledo, where they are occasionally seen, nobody knows for sure, but either way this is by far the tiniest breeding population of any species. Forty years ago a major study of the Aldabra colony found that breeding success for this, the only oceanic colony in the world, is extremely low. The study found that the biggest cause of nesting failure is high spring tides. The problem is that birds breed on low islands just above the high tide mark.
It only takes a high tide a little above the norm and the nest is lost. No one was concerned by the threat of rising sea levels at this time, but today it is a pressing problem.
Caspian terns are not the only birds of low coral islands threatened by rising sea levels. Black-naped terns (or Dyanman) breed across the Indian and Pacific Oceans. The entire known population of the African region, something in the region of 500 birds, is confined to Seychelles. One of the largest populations within Seychelles is on St François, only recently discovered following the opening of Alphonse Island Conservation Centre by Island Conservation Society (ICS). Last month, ICS staff discovered that the colony had suffered egg losses due to inundation by high tides.
Perhaps this is a sign of things to come. Are Caspian terns and black-naped terns doomed to be the first victims in Seychelles of global warming?
Not necessarily. A simple solution already tried in several countries might have applications in Seychelles. If an island is sinking, then float an island! Artificial floating islands can be made from a variety of materials including recycled plastic bottles. Anchored to the sea bed in a shallow lagoon and covered with sand and coral rubble they appear to birds little different than their normal nesting sites. Floating islands can be made in a variety of sizes. They can be small, but provide sufficient space for two or three pairs of terns or they can be much larger. In February this year, a massive 2,000 square metre floating island was launched in Dutchy Lake, in Oregon, USA to provide nesting habitat for Caspian terns. Singapore is currently planning an even larger floating island to provide wildlife habitat, about half the size of a football field to be launched on Punggol Reservoir.
Floating islands might also be useful at some islands where seabirds cannot nest due to the presence of predators. At Desroches and Poivre, for example, the task of getting rid of rats on these relatively large islands is a massive one and there are no immediate plans to do this. But Desroches and Poivre have large lagoons and a floating island in the shallow waters would instantly provide a rat free environment for birds.
Of course this is not a long term answer to the problem of rising sea levels, but in the short term, if the alternative is to see some of the rarest birds of Seychelles disappear, there may be no alternative.
The Island Conservation Society promotes the conservation and restoration of island ecosystems.
By Adrian Skerrett