First annulus formation in the European anchovy; a two-stage approach for robust validation

Abstract

the age determination in fast-growing short-living species, such as european anchovy (Engraulis encrasicolus), has been widely recognized as a difficult task and bias introduced by readers leads to bias in reconstructing the population age structure. in this context, it is worth to note that age structure of fish population represents key information in fishery ecology and for stock assessment models. The uncertainty in estimating the age of the European anchovy by otolith reading is linked to the number of false-growth increments (checks) laid down before the annulus formation. While direct validation methods (e.g. mark-recapture, rearing, radiochemical dating) are difficult to implement specially for this short living species, the use of different indirect methods, supported by a coherent statistical approach, represents a robust and easier validation tool. A statistical modeling approach has been here adopted to assess the coherence of two well-known methods, namely Edge Analysis and Marginal Increment Analysis, in order to validate the first annulus formation in European anchovy. Both methodologies in two different yearly cycles converged toward the same result, thus confirming the annulus identification for the first year class. In addition, the completion dates of the checks and the first annulus were computed in order to gain a better insight into otolith growth dynamic. According to the species spawning period, the completion date of the first annulus falls in the summer period, while the first and second checks completion dates were mostly found in summer and winter respectively. General additive models using marginal increments as dependent variable showed a significant effect of the month, highlighting the presence of only one clear minimum in July/August, as well as specific relationships with condition factor and gonadosomatic index. Modeling the otolith edge morphology, the probability to find a hyaline band displayed in both years a similar shape, characterized by a minimum in July/August and higher values between november and January. the obtained results evidenced temporally coherent patterns providing a better insight in the otolith growth dynamic as well as a more robust validation of the first annulus formation in the European anchovy. Otolith annual growth increments, composed of alternating opaque and translucent zones, are commonly used to determine the age of fishes since 1899 1. However, counting annuli was sometime misleading in estimating the age of tropical or deep-sea adult fishes, mainly due to a more stable environment leading to more constant growth, thus resulting in less certain annulus formation 2. Erroneous age estimates can negatively affect management of marine resources, since several biological variables such as growth-rate, mortality rate and productivity are obtained by the age structure of the population 3-5. Age determination in short living species, such as anchovies, is further complicated because of the predominance of young fishes (0, 1 or 2 years old), which often ...

Accuracy and Precision of Otolith‐Derived Age Interpretations for Known‐Age Lake Trout

“…For example, the tendency of R1 to overestimate the age of fish in this study may indicate a greater propensity to mistakenly include checks in age interpretations. Translucent zone formation in the otoliths of fish has been associated with rapid growth rates and high temperatures (Beckerman and Wilson 1995;Neat et al 2008;Fablet et al 2011;Basilone et al 2020), although there is considerable variation both within and among species (Beckerman and Wilson 1995;Williams et al 2005;Høie et al 2009). Although the seasonal timing of zone formation in Lake Trout otoliths was not confirmed in this study, it is likely that the transparent zones, associated with the putative true annuli in this study, form in the spring or early summer as a result of rapid growth and increased metabolism as water temperatures return to the thermal optimum for growth in this species (10°C; Edsall and Cleland 2000).…”

Length-Weight Relationships and Otolith-Based Growth Curves for Brushtooth Lizardfish off Taiwan With Observations of Region and Aging–Material Effects on Global Growth Estimates

“…The analysis is considered as a complementary method to MI analysis in that edge analysis is a qualitative approach and MI analysis is a quantitative approach (Carbonara et al, 2018). In this regard, additional comparison with edge analysis for verification in the future is recommended (Basilone et al, 2020).…”