Wednesday, 14 October 2009

A demersal trawl south of Grande Comore (Ngazidja)

Part of the cruise strategy is to assess the bottom (demersal) fauna and biodiversity of shallow shelf areas. This is typically done by demersal trawls in areas that are neither too steep and rough nor covered in vulnerable species such as corals. To date, around the Comoros, such habitat has only been found once as the volcanic origin of the islands have resulted in very steep and uneven slopes. To visualise the extreme of the slopes, imagine the ship anchored outside the port of Moroni. While the bow (front) anchor was in 35m of water, the stern (back) of the ship was floating 300m above the bottom.
Our first demersal trawl at 90m depth therefore caused much excitement. Highlights of this trawl were the capture of what appear to be six species of Unicorn fish (Naso sp). While some species such as the humpback unicornfish were easy to identify, others did not agree with all characteristics as provided by species keys. Are there more species in this genus than currently accepted? Only a closer examination of the specimen back at the museum will tell! Below are shown some examples.

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