Abundance of Octopus vulgaris on soft sediment
Keywords:cephalopod, visual census, population density, fishing gear efficiency, thermocline, Octopus vulgaris
Until now the distribution and abundance of Octopus vulgaris had been investigated in the main fishing areas of the species only by fishing surveys. The catching efficiency of fishing gear is variable and depends on several aspects of the animal´s behaviour and life history as well as on the type of the gear and the environmental characteristics of the area surveyed. A good alternative for studying the abundance of octopus is by visual census. The population density of O. vulgaris was measured by visual census with scuba diving. The survey was conducted in coastal areas of Greece and on soft sediment. O. vulgaris density ranged from 0 to 6.88 individuals/1000 m2 and the mean density values of this study were much higher than those mentioned in other papers. Octopus density was significantly associated with season. Densities of octopuses lower than 500 g were higher in coarse sediments than in finer ones. The density of large octopuses (> 500 g) increased with depth. Octopuses larger than 200 g tended to dwell deeper during the period of intense thermocline than during the no-thermocline period.
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