Can the bathymetric distribution of cephalopods be studied with commercial fishing gears?

Abstract

The species composition and bathymetric distribution of cephalopods close to the island of Fuerteventura (Canary Islands, Central-eastern Atlantic) were investigated. The cephalopods were caught in 27 trawls carried out in March 2002, including two trawl series of 4 tows at four discrete depth levels during day and night times, using a commercial fishing gear. Fishing depths ranged between 0-1000 m. A total of 28 cephalopods species belonging to 15 families were identified; the samples swere dominated by Oegopsida, being Sepiida and Octopoda less numerous (2 and 3 species, respectively). Cephalopods were mainly represented by their early life stages, post-larvae and juveniles; captured adults were of species reaching short maximal sizes (i. e. the genus Spirula, Abraliopsis, Abralia, Pterygioteuthis and Pyroteuthis). The families in highest number and frequency of occurrence, were Pyroteuthidae and Enoploteuthidae with a relatively low diversity (3 and 2 species, respectively). Cephalopods concentrated in deeper waters during the day. The two fishing series let us verify the vertical migration of several cephalopod species. Both, the number of species (from 13 to 20) and total number of specimens (from 44 to 91) were larger for the night hauls. The later suggests a considerable potential of the technique used to study cephalopod populations.