Evaluating fish assemblages associated with gas platforms: Evidence from a visual census technique and experimental fishing surveys

Abstract

Fish assemblages associated with extractive platforms were surveyed, for the first time, using traditional fishing surveys (bottom gill net) and an underwater visual census (UVC) technique in order to test the effectiveness and to identify strengths and weaknesses of both methods. The study was carried out during three seasons at two offshore gas platforms (Eleonora and Squalo C) located in the central Adriatic Sea. Both methods recorded a similar number of fish species although with only eight species in common, thus supplying complementary information and a good estimate of the total fish species richness (39) associated with these gas platforms. The use of innovative techniques, such as UVC, to explore the inner part of the platforms, allowed the censusing of several cryptobenthic species, mostly Blennidae (8 species), never recorded during previous studies. Even if both methods were able to detect temporal variability, only the UVC technique was able to highlight spatial changes between platforms, demonstrating their high efficiency regarding the quality of the scientific information supplied. The innovative method of studying biodiversity presented in this study appears to be highly reproducible and suitable for monitoring fish diversity in artificial and very complex habitats like gas platforms.