Telemetry validated nitrogen stable isotope clocks identify ocean-to-estuarine habitat shifts in mobile organisms

1. Throughout their life history, many animals transition among heterogenous environments to facilitate behaviors such as reproduction, foraging, and predator avoidance. The dynamic environmental and biological conditions experienced by mobile species are integrated in the chemical composition of their tissues, providing retrospective insight into movement.

2. Here, we present a unique nitrogen stable isotope clocks (‘isotopic clocks’), which integrate tissue turnover rates, consumer stable isotope ratios, and habitat-specific isotope baselines and can be used to predict time-since-immigration and the timing of habitat shifts in migratory animals. Isotope values of blood plasma to derive time-since-immigration estimates and timing of seasonal habitat shifts for juvenile sand tiger sharks (Carcharias taurus); a species known to perform seasonal movements between ocean and estuarine environments.

3. Isotopic clocks estimated for 65 individuals sampled across six years illustrated th...