Combining microvolume isotope analysis and numerical simulation to reproduce fish migration history

Tracking the movement of migratory fish is of great importance for efficient conservation, although this has been technically difficult to achieve in small fish to which artificial tags cannot be attached. We show that migration history can be reproduced by combining high-resolution otolith stable oxygen isotope ratio (delta O-18) analysis and numerical simulation. High-precision micromilling and microvolume carbonate analysing systems had the remarkable capability of extracting the otolith delta O-18 profiles with 10-30 days resolution. Furthermore, reasonable movements were reproduced by searching the routes consistent with the otolith delta O-18 profile, using an individual-based model with random swimming behaviour. This method will be a valuable alternative to tagging and electronic loggers for revealing migration routes in early life stages, thereby providing crucial information to understand population structures and the environmental cause of recruitment variabilities, and to validate and improve fish movement models.