Inter- and intra-regional patterns of stable isotopes in Dosidicus gigas beak: biological, geographical and environmental effects

Abstract

We analysed stable carbon (δ13C) and nitrogen (δ15N) isotopes of 478 Dosidicus gigas specimens collected outside the Ecuadorian, Peruvian and Chilean exclusive economic zones in the south-eastern Pacific Ocean during 2009 to 2013. There were significant spatial differences both in δ13C and δ15N values across regions, with the lowest values off Ecuador and the highest values off Chile. A small intra-regional range of isotope values indicates that squid off Ecuador feed at the same trophic level with similar primary production. In contrast, a large intra-regional range of isotope values suggests that squid off Chile, especially Peru, migrate over a large geographic range and occupy a wide range of trophic levels. A generalised additive model was used to estimate the biological (mantle length and age), geographical (latitude, and distance to the shelf break) and environmental (sea-surface temperature and chlorophyll-a) effects on isotope values. Best fitted generalised additive models explained 54.0% of the variability in δ13C and 93.1% of the variability in δ15N. The yield relationships between isotopes and explanatory variables increase our understanding of D. gigas habitats, movement and feeding ecology in the south-eastern Pacific Ocean.