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Habitat selection by Octopus vulgaris in the Cíes Islands archipelago (NW Spain)

AutorGuerra, Ángel ; Hernández-Urcera, Jorge; Garci, Manuel E. ; Sestelo, M.; Regueira, Marcos ; González, Ángel F. ; Cabanellas-Reboredo, Miguel ; Calvo-Manazza, Matías; Morales-Nin, Beatriz
Fecha de publicación13-nov-2015
CitaciónCephalopod International Advisory Council (2015)
ResumenThe selection of spawning habitat of a population of Octopus vulgaris that is subject to a small-scale exploitation was studied in the Cíes Islands within the National Park of the Atlantic Islands of Galicia (NW Spain). The technique used was visual censuses by scuba diving. We conducted 93 visual censuses from April 2012 to April 2014. The total swept area was 123.69 ha. Habitat features (season, depth, zone, bottom temperature, swept area, bottom substrate type, and creels fishing impact) were evaluated as predictors of the presence/absence of spawning dens using GAM models. O. vulgaris has a noteworthy preference for spawning in areas with hard bottom substrate and moderate depth (approximately 20 m).The higher density of spawning dens (1.08 ha¿1) was found in a surveyed area of 50.14 ha located in the northeastern part of the northern Cíes Island. We propose to protect the area comprised from Punta Escodelo to Punta Ferreiro between 5 and 30 m depth. This area has a surface of 158 ha equivalent to 5.98%of the total marine area of the Cíes islands. The strengths and weaknesses of a management strategy based on the protection of the species¿ spawning habitat are discussed. Moreover, censuses targeting Octopus vulgaris living in dens on sandy bottoms showed that there were no significant differences between octopus presence in dens during open and closed fishing seasons. Depth had a significant negative relationship with occupancy. The average number of dens per 1000 m2 was 3.84±0.84 in June and 3.89 in October. The area per den was 260 m2. Den number estimations varied between 1586 and 2057. The largest number of dens (76.5%) was found between 5 and 10 m depth. Den distribution was clumped. No significant differences were found between octopus size classes (small, medium and large) and den diameter. Associate dens were observed. There were no significant differences in den diameter and shell types found around the middens. Many dens could be ¿permanent¿. The surveyed area had around 1100 individuals, mainly small specimens. No significant differences were found between octopus size and depth. Substrate, den type and food abundance and availability (especially razors Ensis arcuatus) seem to be the main factors influencing dens and octopus density and distribution. Den availability does not appear to be a limiting factor in this case. Temperature, den availability, predators and fishing pressure influencing density and distribution are discussed. Rodas inlet may be a preferential habitat for O. vulgaris individuals ranging from 200 to 2000 g, but especially small specimens (¿1000 g). 85
DescripciónTrabajo presentado en el Cephalopod International Advisory Council, celebrado en Hakodate, Japón, del 6 al 14 de noviembre de 2015
URIhttp://hdl.handle.net/10261/150170
Aparece en las colecciones: (IMEDEA) Comunicaciones congresos
(IIM) Comunicaciones congresos
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