Spatial and trophic preferences of jumbo squid Dosidicus gigas (D'Orbigny, 1835) in the central Gulf of California: ecological inferences using stable isotopes.

RATIONALE

The jumbo squid Dosidicus gigas is a fishery resource of considerable economic and ecological importance in the Mexican Pacific. Studies on its habitat preferences are needed to understand recent fluctuations in the abundance and availability of the species. Stable isotope analysis allows us to infer ecological aspects such as spatial distribution and trophic preferences.

METHODS

We used an isotope ratio mass spectrometer, automated for carbonate analysis, and coupled to an elemental analyzer, to determine the isotopic composition of statoliths (δ O and δ C values) and beaks (δ C and δ N values) from 219 individuals caught over two fishing seasons (2007 and 2009) off the coast of Santa Rosalía, in the central Gulf of California. We used these isotopic ratios to assess variation in spatial and trophic preferences by sex, size, and fishing season.

RESULTS

In the 2009 group, we observed significant differences in statolith δ C values and beak δ C and δ N values between males and females. Between size groups, we observed significant differences in statolith δ O and δ C values in 2007 and in beak δ C and δ N values during both seasons. Both seasons were characterized by high overlap in δ O and δ C values between sexes and in 2009 between size groups. We observed low trophic overlap between sexes in 2009 and between size groups during both seasons.

CONCLUSIONS

The isotopic ratios from statoliths and beaks indicate that D. gigas has changed its spatial and trophic preferences, a shift that is probably related to changes in the species' diet. This intraspecific variation in preferences could be related to characteristics such as size, which may influence squid distribution preferences.