The distribution of all larval stages of the Japanese eel, Anguilla japonica, were examined using historical catch records and original data in the western North Pacific (WNP) to evaluate existing information about the larval distribution and migration of this species. A total of 148 preleptocephali, 2547 leptocephali, 6 metamorphosing larvae, and 21 glass eels were collected during 37 cruises over a 52-year period . Sampling effort was spatio-temporally biased in latitude/longitude among seasons with sampling effort being concentrated near the western margin of the subtropical gyre near Taiwan in the winter season and extensive effort occurring near the spawning area to the east near the seamount chain of the West Mariana Ridge in summer during the spawning season. The distribution of preleptocephali (4.2-8.7 mm) was limited to a narrow area around 14°N, 142°E just west of the southern part of the seamount chain, while leptocephali (7.7-62.0 mm) were widely distributed at increasing size westward in the North Equatorial Current (NEC) to the region east of Taiwan. Metamorphosing larvae (52.7-61.2 mm) were collected only in the area 21-26°N, 121-129°E to the east of Taiwan, while glass eels (51.3-61.2 mm) occurred only within or west of the Kuroshio. These distributions suggest that leptocephali begin to

As the North Equatorial Current (NEC)-bifurcation is known to be related to El Niño-Southern Oscillation (ENSO) events, the influence of the position of the NEC bifurcation on transport success of the larval Japanese eel Anguilla japonica was investigated. Using a Lagrangian modelling approach, larval transport was simulated and the relative influence of El Niño and La Niña events and the NEC-bifurcation position on the success of particle transport analysed. The number of particles transported from the NEC to the Kuroshio tended to be lowest during El Niño years, and differences between La Niña and regular years were small. The transport success observed in simulations showed some relationships to annual A. japonica glass eel recruitment to Tanegashima Island over 1993 to 2001, but not in 2002. The study shows that particle tracking simulations can be used to improve knowledge of the oceanic migration of A. japonica but further studies are required, including comparisons with the effects on larval survival of fluctuations in temperature and food availability.

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The larval stage duration of fish species can be estimated by cohort analysis, otolith microstructure analysis, and Lagrangian simulations. A number of previous studies have indicated that age estimates based on otolith analysis may be underestimated in anguillid species, because increment deposition decreases at low ambient temperature. We used Lagrangian simulations to estimate the mean larval duration of the European eel Anguilla anguilla and the Japanese eel A. japonica and compared our estimates to the number of otolith increments, which is influenced by ambient temperature. Larvae are transported from the spawning grounds to recruitment areas, experiencing temperatures of 13.0 to 22.5°C in A. anguilla and 20.0 to 27.0°C in A. japonica. The simulated larval durations can be used to calculate the number of otolith increments, once corrected for the effect of ambient temperature of 313 and 208 d for A. anguilla and A. japonica, respectively. These estimates agreed well with those derived from otolith microstructure analyses in both species. We conclude that larval duration based exclusively on otolith microstructure analysis can be underestimated. The duration of the larval stage of A. anguilla and A. japonica confirmed by otolith increment counts corrected for the effect of ambient temperature, is approximately 2 yr and 7 mo, respectively.

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