Underwater visual census (UVC) techniques using SCUBA have been rarely employed to evaluate fish diversity associated with oil and gas offshore platforms. These techniques can be particularly useful since traditional methods such as fishing surveys are not able to give information about fishes strictly associated with high complex habitats such as off-shore platforms. Therefore ISPRA and Eni E&P Division, from 2003 to 2008, carried out a research program with the aim to test the appropriateness of UVC techniques using scuba in describing the fish diversity associated with off-shore platforms and to understand the ecosystem role of these artificial structures. UVC techniques, allowed an accurate description of the fish assemblage associated with off-shore platforms and the acquisition of a big amount of data if compared to the sampling effort. In particular, these underwater techniques allowed the exploration of the inner areas of the platforms where the cryptobenthonic species represent most of the total fish diversity: in Adriatic platforms blennids species represented 22% of the total fish diversity. These species hide inside the oil rigs internal structures and escape normally to captures. For these reason species richness resulted higher than that of previous studies carried out, in the Adriatic Sea, through traditional fishing surveys. The use, for the first time in Mediterranean Sea, of these techniques in off-shore platforms located in different areas allowed the introduction of an investigation protocol also replicable in other areas. However, underwater visual census techniques provided important information and hence should be employed in studies aimed at investigating fish assemblages associated with oil and gas platforms

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