Statolith length and increment number for age determination in squid Illex illecebrosus (LeSueur, 1821) (Cephalopods: Ommastrephidae)

Abstract

A new method using a tracing to count increments in the statolith of the Ommastrephid Illex illecebrosus is described. The increments noted are true growth increments, i.e., they increase in number with statolith size, animal size, and time. However, statolith length is a more precise age indicator than is increment number. The increment-bearing portion of the statolith can be divided into three regions based on increment widths and variations of widths. These regions reflect different sta ges in the development of the animal. Retention of larval characteristics of gross morphology, change in growth constant of the statolith and change in configuration of the statolith, suggest that the larval condition extends beyond the rhynchoteuthion ( 8.5 mm dorsal mantle length) to include squid of dorsal mantle lengths from 50 - 70 mm.