MEPS 399:187-198 (2010)  -  DOI: https://doi.org/10.3354/meps08383

ABSTRACT: Cephalopods play an important role in marine food webs, but their feeding ecology has been mostly examined by traditional methods. In this study, δ¹³C and δ¹⁵N values were measured along the proostracum (a morphological part of the gladius) to reconstruct squid feeding variations. Gladii or the internal shell of jumbo squid Dosidicus gigas was collected at 6 sites from the eastern Pacific Ocean to evaluate trophic shifts as a function of size. The results showed that C- and N-isotopic values varied throughout proostracum length for all squid; changes that could be determined by temporal variation in prey consumption. Both δ¹³C and δ¹⁵N significantly increased with length and supported ontogenic shifts in diet. Detectable differences in δ¹⁵N values were found at all sites. This δ¹⁵N-oceanic variation may be associated with variations in squid assimilated diet, but may also be due to differences in the biochemical cycle among areas. Isotopic values only overlapped among the nearest sites. These results suggest that D. gigas did not migrate over large geographic areas, but rather moved within narrower latitudinal ranges. We recommend the use of stable isotopic analyses along the gladius as an effective approach to tracing foraging variations and also in geographically differentiating subpopulations.

KEY WORDS: Gladius · Squid · Stable isotopes · Trophic variation · Geographic variation