Inter-annual variability in trophic patterns of jumbo squid (Dosidicus gigas) off the exclusive economic zone of Peru, implications from stable isotope values in gladius

The jumbo squid Dosidicus gigas plays an important role in marine food webs in the eastern Pacific Ocean, as not only a voracious predator but also a valuable prey source. In this study, the proostracum (a morphological part of the gladius) from 45 samples were selected over three years and were serially sampled based on growth information obtained from the statolith. The δ13C and δ15N values along the proostracum were used to reconstruct the feeding variations of D. gigas and to evaluate the potential effects of 2009-10 El Niño event on the variability of their trophic patterns. The results show a strong variation in δ13C and δ15N values along the proostracum for all the squid; changes that could be determined by temporal variation of foraging as well as migration among regions with distinct baselines. An El Niño event could decrease the variation of trophic patterns of squid through compressing the space and time for foraging and migration. These results support our general hypothesis that a time-based consecutive sampling of the gladius can back-calculate an ontogenetic shift and the possible migration patterns of squids more precisely and comprehensively and suggest that the isotopic values of D.gigas might be influenced much more by their migration behavior.