counting methods used are reliable. This study suggests that the RSS of the upper beak is an appropriate tool for estimating the age of D. gigas, O. bartramii and perhaps S. oualaniensis, although erosion of the rostral region may result in an underestimation of squid ages.

No abstract

No abstract

No abstract

No abstract

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.