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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 (δ18O) analysis and numerical simulation. High‐precision micromilling and microvolume carbonate analysing systems had the remarkable capability of extracting the otolith δ18O profiles with 10–30 days resolution. Furthermore, reasonable movements were reproduced by searching the routes consistent with the otolith δ18O 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.

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Shoji, J., Toshito, S., Mizuno, K., and Kamimura, Y., Hori, M., Hirakawa, K. 2011. Possible effects of global warming on fish recruitment: shifts in spawning season and latitudinal distribution can alter growth of fish early life stages through changes in daylength. – ICES Journal of Marine Science, 68: 1165–1169. Changes in growth rates, shifts in the spawning season, and shifts in the spawning area (latitude) are expected after an increase in sea temperature resulting from global warming. Fish can avoid higher temperatures by a poleward shift in the spawning area and a temporal shift in spawning timing. However, these shifts will include changes in daylength experienced during their early life stages. To understand comprehensively the possible effects of global warming on fish recruitment, effects of temperature and daylength on growth, daily ration, and growth efficiency of black rockfish, Sebastes cheni, a dominant species in coastal waters of the western North Pacific, were examined under wild and laboratory conditions. The growth rate was elevated at higher temperatures between 11.1 and 21.3°C. Growth efficiency was highest at 16°C. The effect of photoperiod on growth was also significant, with enhanced growth resulting from the longer daylength. The effect of shifts in spawning season and spawning area would differ among fish species and spawning season. Comparison of early growth under different daylength conditions between S. cheni and ayu, Plecoglossus altivelis altivelis, indicated that the shifts in spawning season and spawning area would have different effects on fish early life stages (FELSs) related to changes in daylength. Changes in daylength resulting from a poleward shift in the spawning area will have opposite effects for summer- and winter-growing FELSs, and the effects are more prominent at higher latitudes.

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