Effects of Age Validation on Biomass- and Yield-Per-Recruit of the Arabian Yellowfin Seabream, Acanthopagrus arabicus, in Kuwait

Growth estimation using fish otoliths is integral to assessing and managing fishery resources. Otolith annuli are generally assumed to deposit annually, although deposition time varies among species. Inaccurate determination of annuli deposition time affects estimates of key population parameters, such as growth and natural mortality, that affect estimates of fishery reference points. We estimated the absolute age from the number of annuli (opaque zones in otolith sections) and actual age from validated deposition of the first annulus in juveniles, birth date, and capture date. Arabian seabream (Acanthopagrus arabicus) otoliths were examined to (i) validate the age of young fish at the first annulus deposition and determine its formation periodicity and (ii) assess effects of absolute age and actual age on estimated biomass-per-recruit (BPR), yield-per-recruit (YPR), and fishing mortality reference point (F_0.1) subject to growth- and maximum age-based natural mortality (M) estimators. Estimated von Bertalanffy growth parameters differed between the two age-estimation procedures. Growth parameters estimated from actual age suggested the species reached a much smaller asymptotic length but at a faster growth rate than from absolute age. Higher levels of YPR were estimated from absolute age than actual age across all fishing mortality rates when M was also based on growth parameters. At F_0.1, YPR was overestimated by more than 50%, whereas BPR estimates differed little among age-estimation methods and M estimators. We conclude that estimating growth parameters from actual age can avoid overestimating YPR and associated F_0.1.