Habitat selection and population spreading of the horned octopus Eledone cirrhosa (Lamarck, 1798) in Galician waters (NW Atlantic)

Distribution and abundance of Eledone cirrhosa, a benthic octopus inhabiting the NE Atlantic and Mediterranean Sea, were studied in north-western Iberian waters. Capture data collected during two series of surveys, carried out during summer–autumn in Galician waters (NE Atlantic Ocean), were analyzed. “Galicia” series (G1, G2 and G3) extended along the Galician continental shelf from Ribadeo Ría to Miño Estuary in 1974, 1975 and 1976, and “Cigala” series (C 06, C 07 and C 08) were recorded from Finisterre Cape to Miño Estuary in 2006, 2007 and 2008. Data from a total of 276 trawls, ranging from 50 to 500m, and corresponding environmental parameters were transferred to a Geographic Information System (GIS), providing a platform for a spatial–temporal analysis. Bathymetric distribution, variations in abundance, biomass and average body size of the octopus Eledone cirrhosa were analyzed through depth strata and seasons. Higher abundances were obtained in the intermediate strata and in autumn, most likely due to new recruits. Largest sizes of E. cirrhosa were collected in summer and average weight increased with depth throughout the sampling period. These variations of biomass and abundance suggest the existence of segregation by size and agree with the landings pattern of the trawlers fishery, in which E. cirrhosa is not a target species. No significant differences were found between G1 and G2 surveys or between C ones, performed at the same dates, suggesting that the polled data of surveys are useful tools for representing phenological stages of the species. Collected data and developed models illustrate a migratory behaviour during the reproductive period. Among the eight environmental variables considered, only the latitude remained significant in all developed models, suggesting an effect of photoperiod over the species distribution.