Explorative analysis on red mullet (<em>Mullus barbatus</em>) ageing data variability in the Mediterranean

Abstract

The uncertainty in age estimation by otolith reading may be at the root of the large variability in red mullet (Mullus barbatus) growth models in the Mediterranean. In the MEDITS survey, red mullet age data are produced following the same sampling protocol and otolith reading methodology. However, ageing is assigned using different interpretation schemes, including variations in theoretical birthdate and number of false rings considered, in addition to differences in the experience level of readers. The present work analysed the influence of these variations and the geographical location of sampling on red mullet ageing using a multivariate approach (principal component analysis). Reader experience was the most important parameter correlated with the variability. The number of rings considered false showed a significant effect on the variability in the first age groups but had less influence on the older ones. The effect of the theoretical birthdate was low in all age groups. Geographical location had a significant influence, with longitude showing greater effects than latitude. In light of these results, workshops, exchanges and the adoption of a common ageing protocol based on age validation studies are considered fundamental tools for improving precision in red mullet ageing.

Age, growth and mortality of the striped seabream Lithognathus mormyrus (Linnaeus, 1758) in the Gulf of Tunis (Central Mediterranean Sea)

“…Hydrological parameters and productivity are different in these two regions (Azouz, 1971; Ben Othman, 1973) and the fishing pressure is known to be higher in the Gulf of Gabes. Geographic variations in the estimated growth parameters of fishes may be attributed to several factors, such as gear selectivity, methodologies of study (reader experience), fishing exploitation and geographic location of samples (Carbonara et al ., 2019); however, they generally represent epigenetic responses to environmental conditions (Ibrahim et al ., 2008).…”

“…The variable age ranges may be attributed to geographic and environmental differences, as well as differences in sampling. According to Carbonara et al (2019) geographic location was the most important factor significantly correlated to age variability in Mullus barbatus in the Mediterranean, with the longitudinal (west-east) sample geographic component influencing more than the latitudinal (north-south) one.…”

Growth and Age Validation of the Thornback Ray (Raja clavata Linnaeus, 1758) in the South Adriatic Sea (Central Mediterranean)

“…The estimated growth parameters are obviously model-dependent; therefore, ignoring the model selection uncertainty may introduce substantial bias (Katsanevakis and Maravelias, 2008). This has serious implications for stock status assessments (Carbonara et al, 2019b). The AIC allows the selection of the "best model" (or models) from a set of candidate models (Katsanevakis, 2006), minimizing the risks associated with an a priori selected growth model (Katsanevakis and Maravelias, 2008).…”

“…This is reasonable, considering the wide geographic area of origin. However, several other factors may be responsible for higher variability of age estimation, apart from the geographic area (Carbonara et al, 2018) and genetic origin (Matić-Skoko et al, 2018): differences in sampling methodologies (Coggins et al, 2013); age schemes/criteria (International Council for the Exploration of the Sea [ICES], 2008;Hüssy et al, 2016;Carbonara et al, 2018); preparation methods (Smith et al, 2016); and reader experience (Kimura and Lyons, 1991;Carbonara et al, 2019b).These combined factors can thus lead to considerably greater differences than those observed in R. clavata. Then, it could be needful, taking in account the results obtained by the present work, considering the use of thin sectioned vertebra as suggested preparation method.…”

Does fish growth respond to fishing restrictions within Marine Protected Areas? A case study of the striped red mullet in the south‐west Adriatic Sea (central Mediterranean)

“…Age was assigned to each back‐calculated TL, following the criteria reported in Carbonara, Zupa et al (2019) for the congeneric Mullus barbatus . Considering that the transparent growth increments are deposited on the otolith during the winter months and considering the spring spawning period (Kousteni, Anastasopoulou & Mytilineou, 2019), for each back‐calculated length an age to these growth increments was assigned as follows: 1° growth increment 0.5 years, 2° growth increment 1.5 years, 3° growth increment 2.5 years and so on (Carbonara et al, 2018).…”