Pelagic cephalopods of the Arabian Sea with an emphasis on Sthenoteuthis oualaniensis

Abstract

Taxonomic composition, vertical and horizontal distribution, and the biology of cephalopods were studied during the 30th cruise of the Soviet research vessel PROFESSOR VODYANITSKY in the Arabian Sea from February to April 1990. Small planktonic cephalopods were collected by midwater trawl down to 500 m depth, while large nektonic species were captured by jiggers and hand nets during night drift stations from the surface to 120 m depth. Nineteen species of 13 families were recorded. Mainly early life stages and small-sized planktonic oceanic species were present in trawl samples, with Sthenoteuthis oualaniensis, Abralia marisarabica, Abraliopsis lineata, Ancistrocheirus lesueurii, Onychoteuthis banksii, Chtenopteryx sicula, and Liocranchia reinhardti prevailing. The nektonic squids S. oualaniensis, O. banksii, Thysanoteuthis rhombus and pelagic octopuses Tremoctopus violaceus and Argonauta argo were recorded on the surface. Among all cephalopods, S. oualaniensis absolutely dominated numbers and biomass in the epipelagial of the Arabian Sea. Juveniles (3-10 cm ML) and middle-sized specimens (10-30 cm ML) were observed at night, hunting on lantern fishes and flying fishes around the drifting vessel. The giant females (30-62 cm ML) were caught mainly close to the thermocline. The mean biomass of S. oualaniensis on studied area was estimated as 4.5 t km.2, and the most productive sites were identified.