Revisiting daily age determination in juvenile anchoveta Engraulis ringens

Abstract

Recent studies using otolith microstructure analysis have suggested that the duration of the juvenile stage in anchoveta (Engraulis ringens) is shorter than previously suspected, which suggests that the ages being entered into the traditional age-based stock assessment are incorrect. However, the interpretation of young pelagic fish otoliths remains problematic. To clarify the age interpretation of larval and juvenile E. ringens, newly hatched larvae were reared in a quasi-natural environment for periods of up to 103 days. The sagittal otoliths were subsequently examined and measured by international otolith experts in a double-blind workshop study. The young anchovy could be aged both accurately and precisely using otolith microstructure, after measures were taken to correct for unresolvable increments formed immediately after hatch. The presence of a fast-growth transition zone characterised by either considerable splitting or subdaily increments or both was confirmed. This study confirms the hypothesis of rapid growth and young age through the juvenile stage for anchoveta, suggesting that a critical appraisal of the annual age determinations used as the basis for anchoveta stock assessment is warranted. The otolith interpretation principles outlined in this study may apply broadly across many small pelagic fish species.

Temperature and prey density drive growth and otolith formation of the world's most valuable fish stock

“…However, our study demonstrates that, even under high prey concentrations, 40% of the daily rings were not formed at a water temperature of 14.5 °C, producing a two-fold underestimation of age. This effect has been previously reported in larvae of several species of small pelagic fish such as Atlantic herring, Clupea harengus 26 , 51 , 52 , European anchovy 50 as well as for adults and juveniles of Peruvian anchovy 27 , 53 . Similarly, daily increment formation was not observed in Japanese anchovy during winter when larvae experienced cold temperatures and exhibited slow rates of somatic growth 54 .…”

“…As suggested by the “growth-effect theory”, slow-growing larvae have larger otoliths compared to fast-growing larvae of the same age 47 – 49 . Nonetheless, under extreme conditions of starvation and low temperature, the daily deposition can be interrupted or altered, resulting in a 20 to 40% 27 , 50 underestimation in the real age of larvae.…”

“…Moreover, understanding how temperature and prey may affect growth as depicted in otoliths is needed to buttress science-based advice on the processes controlling survival and recruitment strength. Although the deposition of the first ring in the larvae of most anchovy species has been associated with the onset of the exogenous feeding, yolk sac absorption or eye pigmentation 24 , 25 , otolith development (e.g., the frequency of increment formation and increment widths) and somatic growth can be decoupled when feeding and growth conditions are suboptimal 26 , 27 . Research has started to examine the growth and development of Peruvian anchovy larvae under controlled (e.g.…”