Roberta Callicó Fortunato

Introduction: The Lebranche mullet (Mugil liza) is a commercially important fish species in southeastern and southern Brazil, which serves as the primary spawning ground for the Southern stock that supports the Brazilian industrial seine fleet. However, this stock’s distribution extends into Argentine waters (northern Patagonian shelf), and the connectivity between mullets caught in Brazil and their breeding areas across South America remains poorly understood. The authors hypothesized that adult mullets landed by the Brazilian fleet consist of two distinct groups: A local group originating in Brazilian waters (BR1) and a migratory group (BR2) that uses nursery areas in Argentina (AR). BR2 presumably returns to its original nursery grounds after spawning, to recover reproductive tissues, following a different migratory pattern than BR1. Objectives: To test this, the study analyzed the micro-chemical life history of 134 otoliths from mullets aged 0+ to 11 years using LA-ICP-MS. Methodology: Two elemental ratios (Ba/Ca and Sr/Ca) were measured from the otolith core to the edge and modelled using a generalized additive model for scale and shape (GAMLSS). Life history transitions were evaluated by pairwise comparisons of fitted values among ages. Results: GAMLSS showed that Ba/Ca ratios differed significantly among groups (AR ≠ BR1 ≠ BR2). In contrast, Sr/Ca ratios were similar between AR and BR2 during the first four years of life, significantly differing from those of BR1. Using empirically established thresholds for estuarine vs. marine habitats, the study determined that BR2 individuals leave nursery areas between ages 5 and 6, migrate back around age 8, and live there one last time after age 10 (the species’ maximum age). BR1 leaves nurseries after age 4 and returns between ages 5 and 6, exhibiting a shorter reproductive cycle. Importantly, the analysis of reproductive tissue mass showed that the weight after age 7 approximately matched the weight at age 3. After recovery, reproductive tissues doubled in weight before the second migration to spawn at sea. Conclusions: These findings provide crucial insights into M. liza’s life cycle, highlighting the need for shared stock management not only with neighboring nations (Argentina and Brazil) but also on a regional scale.

The streaked prochilod Prochilodus lineatus (Valenciennes) is a commercially freshwater species from South America, distributed in the Plata basin. In the present work the morphometry (circularity, rectangularity, form factor, OL/OW and ellipticity indices) and chemistry (Sr:Ca, Ba:Ca, Zn:Ca) of lapilli otolith, and geometric morphometry of scales of streaked prochilod juveniles, in two sites in the Plata basin (Uruguay River and Estrella Wetland), were compared to determine if they are area-specific and to identify possible breeding areas. Otolith Ba:Ca ratios was 0.017±0.003 mmol/mol for Uruguay River while for Estrella Wetland individuals was bellow the detection limits. Zn:Ca ratios tended to be higher for the latter (0.03±0.002 mmol/mol). Significantly high circularity and low rectangularity values were obtained for Estrella Wetland otoliths (p < 0.05), while no significant differences for form factor, OL/OW and ellipticity were observed between sampling sites. Considering all scale geometric morphometry variables, discriminant analysis showed a good percentage of classification of individuals (90.5% for Estrella Wetland and 85.7 % for Uruguay River). These results indicate that the otolith microchemisty and morphometry (circularity and rectangularity indices) and scale morphometry are good markers of habitat and represent a potential tool for identification of streaked prochilod nursery areas.

The aim of the present study was to evaluate the potential use of otolith microchemistry (Sr:Ca and Ba:Ca ratios) to identify silver mullet, Mugil curema, populations in Southeastern Caribbean Sea. Fish samples were collected in 7 areas of Nueva Esparta State (Venezuela). The otolith Sr:Ca and Ba:Ca ratios and water Sr:Ca were determined (by ICP-OES and EDTA volumetric method). Otoliths Sr:Ca and Ba:Ca ratios and Sr:Ca partition coefficient of mullets in Cubagua island (south of the State) were significantly different from ratios in La Guardia (north of the State). A discriminant analysis of otolith Sr:Ca and Ba:Ca ratios separated Cubagua Island from La Guardia values. These results suggest the existence of different mullet groups in the Southeastern Caribbean Sea. For this, the simultaneous use of Sr:Ca and Ba:Ca ratios could be a potential tool to identify populations in the study area.

The Mugilidae family is widely distributed all over the world. In the Mediterranean Sea there are 8 species of mullets (Thomson, 1997). Mugil cephalus is the most cosmopolitan one and has an important economic value in the region (Whitfield et al., 2012). It is a euryhaline species that migrates during some periods of the year from the sea to brackish or freshwater areas. The analysis of otolith morphology, morphometric and chemical composition has been used to identify stocks of important commercial species, and has facilitated the study of movements and migration. Particularly, the simultaneous use of Sr:Ca and Ba:Ca otolith ratios is used by several authors for stock and migration studies (Schuchert et al., 2010; Tabouret et al., 2010; Avigliano et al., 2014,2016). This research proposes the identification of Mugil cephalus stocks in two protected wetlands of the Valencian Community: Parque Nartural de l’Albufera de Valencia and Parque Natural Salinas de Santa Pola (Figure 1) using otolith microchemistry. For this, Sr:Ca and Ba:Ca ratios were obtained of 48 sub-adults (25 – 35 cm total length) from the selected areas. Otoliths were digested to obtain solutions from each individual. Using ICP-OES, Sr, Ba concentrations were obtained; Ca concentration was determined by titration with ethylenediaminetetraacetic acid (EDTA) (APHA 1993). Element:Ca relations were compared with ANOVA analysis with Bonferroni contracts between the selected places. A discriminant analysis was performed to test the accuracy of using that variable (element:Ca) for the localization of fish site. Significant differences (p < 0.0001) were observed among the ratios studied, having Albufera individuals smaller Sr/Ca and higher Ba/Ca ratios than Salinas de Santa Pola ones (Figure 2). The discriminant analysis separated 87.5% of individuals to the wetland where it was sampled (Table 1). Results might be suggesting that there are two sub-adult stocks associated with each wetland, consistent with knowledge of ecology of this species.