Distribution, abundance, reproduction and ageing of the common bobtail squid Sepietta oweniana (Sepiolidae, Cephalopoda) from the Portuguese Coast

Abstract

An investigation of the distribution and general biology (size, maturation and fecundity) of the sepiolid Sepietta oweniana off the Portuguese Coast is presented based on 594 specimens collected during research cruises between 1997 and 2008. Statolith microstructure was examined in 35 animals. S. oweniana was mainly encountered on the southwestern and southern continental slopes, while it was rare north of 38°N. Female mantle length (ML) ranged from 13.9 to 35.7 mm, male ML from 12.5 to 28.0 mm; specimens of both sexes being significantly larger in the southeastern area. Potential fecundity was 18–616 (mean 234±104) oocytes and mean mature oocyte diameter varied 2.3–3.4 mm. The year-round presence of mature animals, asynchronous ovulation, the presence of mature specimens over a range of different sizes and the occurrence of feeding activity throughout spawning are indicative of a continuous spawning strategy in this species. Growth increments were present in all statoliths, being narrow and nearly uniform in width. The total number of growth increments registered from the specimens sampled varied between 103 and 179; with a similar range in males (n=17) and females (n=18). Putative age estimates suggest an age approximation of 4.5–6 months for mature and spent females and 5–5.5 months for mature males.

Keywords:

• Ageing
• Portuguese coast
• reproductive biology
• Sepietta oweniana
• Sepiolidae

Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory, University of Copenhagen, Denmark

Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory, University of Copenhagen, Denmark

Notes

Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory, University of Copenhagen, Denmark