The age, growth and maturation of the purpleback flying squid, Sthenoteuthis oualaniensis, were determined by statolith analysis using data from April–June 2013 surveys in the equatorial eastern tropical Pacific Ocean (ETPO). Three distinct growth zones with different width increments (postnuclear, dark and peripheral zones), checks and aberrant microstructures were found in the statoliths. The longevity of the species was a maximum of 0.5 years. Hatching dates were from November to March, with a peak between January and February. The high percentage of mature females (69.5%) suggested that there was at least another peak after April–June, and the study area might be a potential spawning ground for the species. Size and age at first maturity were 192-mm mantle length (ML) and 114 days for females, whereas males began to mature at 137mm ML and 87 days.
The sclerotised beaks of cephalopods have emerged as useful material to track their habitat and trophic ecology by using stable isotope analysis, because beaks grow continuously throughout their life without replacement. Here, stable isotopes of δ13C and δ15N in five continuous sections along the crest were measured to investigate the potential ontogenetic habitat shift and foraging-ecology change of Dosidicus gigas from the oceanic waters off Ecuador. In total, 90 sections from 18 upper beaks were examined with δ13C values of −18.99 to −17.49‰ and δ15N values of 0.69 to 7.09‰. Kruskal–Wallis test showed that there were significant differences in both isotopes between sections. The result of generalised additive models showed a significant overall decrease in both δ13C and δ15N values across the beak crest. The corrected standard ellipse area (SEAc) of the beak sections was 0.48 to 0.93‰2, with no high overlap between the two sections, with values ranging from 0.00 to 0.57. High individual variation of δ15N values in most beak sections indicated that D. gigas in our study area appears to have a generalist food spectrum in most of its life history, except for the stage just before being captured.
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