Otolith ageing of white seabass (Atractoscion nobilis): Known-age validation, reader performance and sex-specific...

The sciaenid white seabass (Atractoscion nobilis) is stocked in California (U.S.) where it supports commercial and recreational marine fisheries. Despite its importance, age and growth remains incompletely understood (e.g., differences between females and males) and has not been validated using known-age fish. In this study, the sectioned sagittal otoliths of 196 hatchery-reared white seabass were analysed. These known-age fish, recaptured after up to 14 years at liberty, allowed reader age interpretation to be validated and reader performance to be quantified. Reader age was not biased relative to true age in hatchery-reared fish, and among-reader precision was high [74.5% agreement, 5.1% average coefficient of variation (ACV)]. Otoliths from wild white seabass were subsequently analysed to develop sex-specific von Bertalanffy growth models, showing that females (age 0-24, n = 355) grow faster and are older than males (age 0-15, n = 381). Otolith morphometric-true age regressions were developed from an expanded dataset of 365 hatchery-reared white seabass to assess an alternative age determination technique for wild conspecifics. Relative to reader age interpretation, age predicted from otolith morphometrics (weight, length, width and thickness) had highly variable agreement (9.5%-68.8%) and ACV (9.5%-44.2%), depending on the age range examined. This study is the first to provide validated, sex-specific age and growth for this moderately long-lived marine fish species, and demonstrates how stocking programmes can serve as an ecological tool to help manage wild populations.