Growth, age structure and environmental history in the cephalopod Martialia hyadesi (Teuthoidea: Ommastrephidae) at the Antarctic Polar Frontal Zone and on the Patagonian Shelf Edge
Martialia hyadesi were collected from fishing vessels at the Antarctic Polar Frontal Zone (APFZ) and the Patagonian Shelf Edge (PASE) during the 1989 austral autumn and winter. Squid were measured, weighed, assigned a maturity stage and the paired statoliths were removed. Statolith sections revealed concentric growth rings using light and scanning electron microscopy. Counts of these putative daily micro-growth increments were made directly and by an estimating procedure. Energy dispersive (ED) and wavelength dispersive (WD) x-ray analyses of Sr and Ca content were made on subsamples of statolith sections. Estimated increment counts, which were generally higher than direct counts, were adopted for routine application. Back calculated hatching dates showed that a single cohort, with a relatively narrow size range, was sampled in each geographical area. Back calculations suggested that M. hyadesi at the APFZ had hatched in the austral winter and those at the PASE had hatched in the spring. At the PASE, growth rate was estimated to be some 30% higher than at the APFZ and PASE squid were more mature at a given age. The hypothesis that the Sr:Ca ratio along the growth axis of the statolith contains information on thermal history was examined. Sr:Ca ratios in the statolith fell in the range 0.009–0.017 and varied systematically but this variation did not apparently relate to season and ratios were not significantly different between geographical areas. A consistent feature was a relatively low Sr:Ca ratio at the time of hatching. According to the Sr:Ca thermometer hypothesis this is consistent with spawning in relatively warm water but it could equally be due to depositional differences during early statolith growth. The Sr:Ca thermometer hypothesis could neither be confirmed nor rejected by the data but there is evidence that strontium varies systematically with age in the squid statolith.
Authors: Rodhouse, Paul G., Robinson, K., Gajdatsy, S.B., Daly, H.I., Ashmore, M.J.S.