Abundance of &lt;i&gt;Octopus vulgaris&lt;/i&gt; on soft sediment

Stelios Katsanevakis,George Verriopoulos

doi:10.3989/scimar.2004.68n4553

Abstract

SUMMARY: 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/1000m 2 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 nothermocline period.

Highlights

The common octopus, Octopus vulgaris, is one of the most widely studied cephalopods
The distribution and abundance of O. vulgaris have been investigated in the main fishing areas of ABUNDANCE OF OCTOPUS VULGARIS 553
Small animals may pass through large-mesh nets the plasticity of the octopus body may allow even larger animals to escape

Summary

Introduction

The common octopus, Octopus vulgaris, is one of the most widely studied cephalopods. It is a species of great scientific and commercial importance and its culture is an area of increasing interest. It is a coastal and sedentary species, living mostly between 0 and 100 m depth; it is scarce at depths between 100 and 200 m and is only occasionally found at greater depths (Guerra, 1981; Belcari et al, 2002). The efficiency of a trawl depends on the type of dens that the octopuses use in the surveyed area. The relative proportion of the various den types varies in relation to depth, distance from shore, octopus size and sediment granulometry (Katsanevakis and Verriopoulos, 2004), so the catching efficiency of a trawl varies from area to area and reliable octopus density estimations are difficult

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Conclusion