Age and Growth of Nototodarus sloanii (Cephalopoda: Oegopsida) Based on Daily Increment Counts in Statoliths.

Abstract

Statoliths of Nototodarus sloanii collected around New Zealand were examined to determine age. By comparing the increase in number of increments in statoliths with the number of days elapsed between sampling dates, the periodicity of the increment formation was validated. Estimated hatching month ranged from January to December. This result suggests that spawning occurs throughout the year. The relationship between statolith radius and dorsal mantle length suggests daily increment width must reflect squid growth well. Back-calculation was applied to compensate for the short sampling period. The differences in size at age are significant between the seasonal groups. The winter group is larger than the summer one between about 100 and 230 days old. This difference became smaller and finally the summer group became larger than the winter one at around 250 days old and after. It is suggested that differences in growth between the groups are consistent with seasonal changes in water temperature.