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|Benthos and habitat characterization under different fishing pressures off Portugal (Western Iberian Margin)|
Córdova, E.A. (2014). Benthos and habitat characterization under different fishing pressures off Portugal (Western Iberian Margin). MSc Thesis. Universiteit Antwerpen/Universiteit Gent/VUB: Antwerpen, Gent, Brussel. 14, 72 pp.
The seabed of the Western Iberian Margin (WIM) off Portugal has been exposed to bottom trawl fishery for decades. Fishing vessels are permanently operating in the Southeast area above 6 nm from the coast, between 200 and 500 m depth. Impacts of bottom trawling on benthic environments implies alteration on seabed morphology, sediment resuspension, changes in biogeochemical cycles, as well as destruction of megafauna. However, fishing impact studies have been mainly focused on shallow- water ecosystems, leaving a gap of information about the effect of trawling on deep-sea environments. This study characterized benthic habitats and its associated epifauna and endofauna in an area off the WIM subjected to different levels of fishing pressure. Two transects, between 200 and 400 m depth, were surveyed based on video footage using a Remotely Operated Vehicle (ROV). Habitats along both bathymetric transects were classified according to seabed morphology, while trawl marks were counted and abundances of groups at high taxon level of epifauna analysed. Sediment samples for metazoan meiofauna and environmental analyses, were taken at three stations under different fishing pressures. Groups of meiofauna, as well as pigment composition and sediment granulometry, were analysed. Fishing activity in the area was monitored through online marine traffic system during 30 days and correlated with integrated traffic density maps. Eight habitats were characterized along the transects. Epifauna was composed by 15 groups dominated by polychaetes and anemones, showing abundance and diversity variations among the habitats. Meiofauna was composed by 19 groups dominated by Nematoda, Copepoda and nauplii. There were no significant differences in meiofauna densities between stations. Meiofauna densities were highly concentrated in the first 2 cm of the sediment, and this was apparentlys rather related to food availability than to sediment granulometry, despite the low phytopigment concentrations found at the stations. Trawling marks showed a patchy distribution with higher concentrations west of the transects. Additionally, density maps of navigation and online vessel monitoring showed similarities with the trawl marks observed at the video footage, except for the eastern portion (habitat 8) of transect II. Variability of specific epifauna groups could be also related to trawling activity while analysis on meiofauna suggested no effect from fishery. However, further studies should be made in order to clarify the observations.