ACCURACY AND PRECISION OF AGE AND HATCH DATE ESTIMATES FROM OTOLITH MICROSTRUCTURE EXAMINATION

Known-age herring and cod larvae, reared in an outdoor mesocosm and the laboratory, respectively, were distributed to 18 study participants representing 10 different countries as part of an international otolith microstructure study. All details of rearing and sampling protocol were withheld from study participants, who were asked to estimate the age of multiple samples (aged 1-65 days) based only on the otolith microstructure. On average, age differences among samples were accurately estimated, while absolute ages (hatch dates) were underestimated. Otoliths from herring larvae less than 14 days old were the most difficult to interpret. Estimates of hatch date and measurements of the hatch check diameter differed significantly among readers, implying that differences in skill and/or increment interpretation among researchers could result in misleading differences among both collaborators and published results. The experience of the investigator and the degree of preparation of the larger otoliths were among the sources of the interinvestigator differences in ageing accuracy. With the possible exception of SEM, equipment type was not correlated with either accuracy or precision. The coefficient of variation (C.V.) of the age estimates decreased with larval age to a level of about 10-15%, and did not differ significantly among age readers. This study confirmed the utility of otolith microstructure examination for high-resolution age determination of young fish under quasi-natural conditions. Although the accuracy and precision levels characteristic of the herring otolith microstructure are probably somewhat lower than those of most other species, resolution of ± 1 day may be beyond the capabilities of the technique for a number of species. © 1991 Conseil International pour l'Exploration de la Mer.