Growth Zones within the Statolith Microstructure of the Deepwater Squid Moroteuthis ingens (Cephalopoda: Onychoteuthidae): Evidence for a Habitat Shift?

Abstract

Within the statoliths of the onychoteuthid squid Moroteuthis ingens captured off the southeast coast and the Chatham Rise (New Zealand} between 500 and 1239 m depth, there were conspicuous zones consisting of an inner opaque and outer translucent zone; these strikingly resembled zones observed in some teleost fish otoliths. There was no relationship between the number of increments within the opaque zone among individuals of different length and age, but the width of the opaque zone was negatively related to both mantle length and age. The smallest juveniles captured in bottom trawls had a narrow translucent zone relative to the opaque zone which suggested that the translucent zone is laid down after settlement and that settlement takes place probably at or before 160 mm mantle length in this species. This study suggests that the transition observed within the statolith microstructure of M. ingens represents a habitat change from an epipelagic habitat to a demersal habitat. Evidence for the hypothesis is drawn from analogous features observed within teleost otolith microstructure and from available information on Moroteuthis and Onykia.