Estimation of larval duration in Anguilla spp., based on cohort analysis, otolith microstructure, and Lagrangian simulations

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 degrees C in A. anguilla and 20.0 to 27.0 degrees 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.