| Summary: | 204 pages This Ph.D. Dissertation deals on the study of several aspects of the ecology of the horned octopus Eledone cirrhosa (Lamark, 1798) in the NW Iberian Peninsula, from western gulf of Biscay to north Portugal. The horned octopus is a benthic octopod distributed along the continental shelf and slope throughout the Mediterranean and northeast Atlantic from Morocco to Norway, including the British Isles and Iceland. In the NW Iberian Peninsula this species is considered as a by-catch of trawling fishery, mainly targeting hake (Merluccius merluccius), monkfish (Lophius sp.) and Norway lobster (Nephrops norvegicus). Horned octopus landings show a cyclical pattern consistent with its life cycle, and its commercial interest considerably varies throughout its geographic range. According to ICES reports, landings of E. cirrhosa in VIIIc and IXa north subareas reached 1145 t in 2013. In terms of both body size and main reproductive parameters (such as maturation, fecundity, and eggs/spermatophores size), specimens of E. cirrhosa from northwest Iberian Peninsula have intermediate characteristics to those exhibited by individuals from the north-eastern Atlantic Ocean and those from the Mediterranean Sea, suggesting some gradation on environmental conditions. This gradient, in turn, was also found in our study area. During the sampling, carried out over two years, a significant bias was observed in the relative abundance between sexes, always favourable to females. The spawning season of the species also varies throughout its range. Specifically, in the northwest Iberian it concentrates in May and June. Similarly to the maximum size, the size-at-maturity increased with latitude. This population parameter ranged from 100 to 134 mm mantle length (ML) for females and between 91 and 108 mm ML for males, depending on the fishing ground The analysis of catches per unit effort (CPUE) obtained from scientific surveys and carried out at different times of the reproductive cycle of the species shows the existence of ...
|
|---|