Stable isotopes in otoliths: what have we learned so far?

Stable isotopes in otoliths are increasingly used to understand life history and movement patterns of fish. Due to the variability of isotopic values found in estuarine and marine ecosystems, and the inert nature of otoliths that keep a life-long record of the environment of a fish, isotopic analysis of otoliths can be used for a wide variety of purposes. We reviewed the current understanding of how measurements of carbon, oxygen and nitrogen stable isotopes in otoliths are used. Here, we specifically discuss advances in stock discrimination, and quantification of movement and contribution of juvenile habitats to adult populations. Classification of fish stocks yielded significantly higher success rates when carbon and oxygen isotopes were combined with elemental markers. The limited number of studies that successfully used isotopes to track actual fish movement showed unequal contributions from different juvenile habitats to adult stocks, which is crucial information for the sustainable management of fisheries. Based on our findings, we outline guidelines for successfully using stable isotope studies in different geographical regions. Overall, our analysis provides an imperative overview of the progress in this field, and directions for future research