An otolith-based back-calculation method to account for time-varying growth rate in rainbow smelt (Osmerus mordax) larvae

This study develops a new back-calculation method, based on the larvae of r ainbow smelt (Osmerus mordax), that takes into account the variation of gro wth rate over time. Known-aged larvae were reared in four 60-L microcosms d uring 49 days in order to obtain a large range of individual growth traject ories. We first validated the daily nature of the otolith increment deposit ion rate. The proposed time-varying growth (TVG) method weights the contrib ution of each increment in the length calculation using a growth effect fac tor. A small growth increment contributes less to the length increase of la rvae than its relative importance in total otolith growth. On the other han d, a large growth increment contributes more to the length increase of larv ae in comparison with its relative importance in total otolith growth. This method provided significantly better estimates of previous length-at-age t han the biological intercept (BI) method at the individual level. In additi on, the TVG method tended to provide more accurate estimates of previous le ngth-at-age than the BI method at the population level, but the difference was not significant. The importance of using the TVG method instead of the BI method to back-calculate individual and population growth trajectories i ncreases with the magnitude of the growth effect and the variation in growt h rates over time.