Applying isotopic clocks to identify prior migration patterns and critical habitats in mobile marine predators

Large-scale migrations present challenges to management of exploited or at-risk marine species. Our understanding of predator movements has greatly improved, but data are often inadequate to understand patterns on population scales. The chemical composition of predator tissues, most often stable isotope ratios of carbon and nitrogen (δ‎13C and δ‎15N), provides markers of movement as predators incorporate discrete regional isotopic signatures throughout their migratory pathways. These signals can be analysed from small quantities of various tissues (e.g. muscle, liver, blood, hair, feathers) all of which provide different timescales of movement. Predator physiology mediates the assimilation and turnover rates of stable isotopes in tissues, providing a temporal element to interpretation of predator isotopic signatures. Combining physiology-mediated isotopic turnover rates and geographic ‘isoscapes’ of regional isotopic gradients allows for isotopic clock estimates of predator migration timing, which can be used to generate population-scale estimates of retrospective movements using large datasets across targeted regions and sampling periods. This allows for improved regional and international management and conservation of mobile species across their migratory ranges.