Alberto Teodorico Correia

Understanding the population structure of highly migratory marine species is essential for effective fisheries management and conservation. The bluefish, Pomatomus saltatrix, is a widely distributed pelagic fish of great ecological and economic importance in the Southwest Atlantic; however, its population structure in this region remains poorly understood. This study investigated the population structure of P. saltatrix along the southeastern and southern coasts of Brazil using a landmark-based truss network morphometrics approach. A total of 109 adult individuals were sampled at three sites along the Brazilian coast—Rio de Janeiro, São Paulo and Santa Catarina—between August and October 2024. Body morphology was assessed using a truss network system composed of 25 morphometric transformed distances derived from 12 landmarks. One-Way ANOVA or Kruskal–Wallis tests revealed significant differences among sampling sites for 18 of the 25 transformed morphometric distances. PERMANOVA revealed significant overall differences in body morphology among the three sampling sites, with all pairwise comparisons being significant. Moreover, the FDA showed a clear spatial structure, despite partial overlapping between the three sampling-site groups. Overall jackknife reclassification success was 87.2%, with the highest accuracy achieved for Rio de Janeiro, followed by São Paulo and Santa Catarina. Despite the high reclassification accuracy, the observed morphometric differences may be compatible with a shared stock exhibiting site-specific phenotypic variation, although stock boundaries cannot be established from morphometric evidence alone. Overall, these findings demonstrate that landmark-based truss network morphometrics is an effective tool for detecting spatial phenotypic structuring in P. saltatrix, providing valuable information to support future studies and fisheries management in the Southwestern Atlantic.

Otolith shape has been widely used as a tool to investigate the population structure of marine fish, as it reflects environmental, physiological, and genetic influences throughout the lives of individuals. The morphological variability of Pomatomus saltatrix sagittal otoliths along the southeastern–southern coast of Brazil was assessed using Elliptic Fourier Descriptors (EFDs) and Wavelet Transform Descriptors (WTDs). A total of 74 individuals from Rio de Janeiro (RJ, N = 25), São Paulo (SP, N = 24), and Santa Catarina (SC, N = 25) were analyzed. The coefficients obtained from both methodologies were subjected to multivariate analyses, including Permutational Multivariate Analysis of Variance (PERMANOVA) and Flexible Discriminant Analysis (FDA), combined with Jackknife Cross-Validation (JKC). The results showed high similarity in otolith shape among the sampled locations. Overall, PERMANOVA detected significant spatial differences for both EFD and WTD, although the proportion of variation explained by sampling location was low for both descriptors (P. saltatrix along the southeastern–southern coast of Brazil. Although subtle morphological heterogeneity was detected among the analyzed locations, the evidence does not support the existence of completely isolated stocks. The observed patterns indicate weak spatial phenotypic differentiation and may be consistent with population connectivity; however, connectivity cannot be directly inferred from otolith shape alone and represents only one possible interpretation, as similar environmental conditions, shared growth histories, or limited discriminatory power of otolith morphology could also contribute to the observed scenario. Thus, the study reinforces the utility of otolith morphometry as a complementary tool for population studies and highlights the importance of integrating it with other phenotypic and genotypic approaches for a more comprehensive understanding of the structure of the species’ stocks.

Introduction: Understanding population structure is essential for effective fishery management, and otolith shape analysis provides a robust framework for detecting spatial variation in marine fish populations. The bluefish (Pomatomus saltatrix), a commercially important and widely distributed species along the southeastern and southern Brazilian coast, may exhibit subtle population structuring that is still not fully resolved. Methodology: Otolith contour variation was analyzed using two complementary approaches: Elliptical Fourier Descriptors (EFD) and Wavelet Transformed Descriptors (WTD). A total of 75 individuals (25/site) were sampled from Rio de Janeiro, São Paulo, and Santa Catarina, with total lengths ranging from 33.2 to 45.5 cm. Multivariate analyses included Permutational Multivariate Analysis of Variance (PERMANOVA), pairwise Hotelling’s t-tests (HT²), Flexible Discriminant Analysis (FDA), and jackknife reclassification matrices (JKC). Results: For the EFD approach, PERMANOVA showed no significant differences among localities, while FDA revealed partial overlap among groups and a JKC overall reclassification accuracy of 46%. In contrast, the WTD approach detected significant spatial differences, with PERMANOVA indicating overall variation among localities and HT² identifying significant differences between Santa Catarina and the other regions. FDA improved visual separation of Rio de Janeiro samples, although the JCK accuracy decreased to 35%. Conclusion: The combined results suggest the presence of weak to moderate spatial structuring in P. saltatrix along the studied coastline. However, inconsistencies among analytical approaches and relatively low reclassification success rate to the original site indicate that the observed differentiation is insufficient to conclusively define distinct population units, remaining compatible with either a single stock exhibiting spatial heterogeneity or weakly differentiated subpopulations.

Introduction: Understanding population structure is essential for the effective management of marine resources. The bluefish (Pomatomus saltatrix) is a widely distributed and commercially important species along the Brazilian coast, yet its population structure in the South–Southeastern region remains unclear. Objectives: This study aimed to assess the body morphological variation and to infer the population structure of P. saltatrix along the South and Southeastern coasts of Brazil using a landmark-based geometric morphometrics method. Methodology: Individuals were collected between August and October 2024 from artisanal fisheries in Rio de Janeiro (n = 46), São Paulo (n = 37), and Santa Catarina (n = 29). A total of 12 landmarks were used to derive a truss network and extract 25 transformed distances (DTs). Data were analyzed using univariate (one-way ANOVA, followed by Tukey’s test if needed, or Kruskal–Wallis followed by Dunn’s test if needed) and multivariate statistics (PERMANOVA and Flexible Discriminant Analysis (FDA)). Results: Significant regional differences were detected for most DTs, except DT3, DT4, DT6, DT9, DT13, DT24, and DT25. PERMANOVA revealed significant differences among all sampling locations, including pairwise comparisons (p < 0.05). FDA achieved an overall reclassification success of 93% of individuals to their original location. Conclusion: Despite the high reclassification accuracy, the results support the existence of a single stock with spatial structuring rather than completely distinct population units, indicating that P. saltatrix in this region is not homogeneous.

Introduction: Understanding population structure is essential for fisheries management and stock identification. In marine species, spatial differentiation may arise from environmental conditions and biological factors, even when populations appear continuous. Otolith shape and body analyses have been widely used as effective tools to detect such differences, as they reflect both genetic and environmental influences. Objectives: The main objective of this study was to assess the population structure of Sarpa salpa in three fishing grounds in the Northeast Atlantic using two geometric morphometric approaches. Methodology: A total of 133 individuals collected between November 2025 and March 2026 from Santa Maria (n = 48), Peniche (n = 36), and Olhão (n = 49) were analyzed using two geometric morphometric approaches. The first involved otolith contour analysis using Elliptical Fourier Descriptors (EFD), with 12 descriptors explaining 90% of the cumulative variance. The second approach used truss network analysis based on 11 body landmarks, corresponding to 22 transformed distances (TD). Statistical analyses included multivariate analysis of variance (MANOVA), Hotelling’s T-square tests (HT2) for multiple comparisons, and linear discriminant function analysis (LDFA), with reclassification success assessed using a jackknifed (leave-one-out) classification matrix (JKM). Results: EFD analysis showed significant differences for MANOVA, with significant HT2 between all locations, but LDFA indicated considerable overlap, with a global JKM reclassification rate of 60%. In contrast, TD also showed significant MANOVA results, with significant HT2 across all comparisons. However, LDFA demonstrated clear separation among the three groups, achieving a JKM overall reclassification success of 98%. Conclusions: The results indicate that geometric morphometrics based on body landmarks provides greater discriminatory power than otolith contour analysis for identifying population structure. These results suggest the existence of distinct population units of Sarpa salpa in the Northeast Atlantic, highlighting the importance of spatially explicit approaches for fisheries assessment and management.

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.

Introduction: Fish stock identification and delineation are fundamental requirements for preventing local depletion and promoting the sustainable exploitation of marine resources. The blackspot seabream, Pagellus bogaraveo, is the most commercially valuable sparid species across the Northeast Atlantic and the Mediterranean Sea. To effectively discriminate fish stocks, researchers increasingly rely on the use of natural tags, which reflect both environmental and genetic influences, providing critical information regarding fish movements and population structure. Objective: To broaden the understanding of P. bogaraveo stock structure, samples originally obtained for a parasite-based discrimination study were used to provide complementary insights through otolith shape and geochemical signatures. Methodology: A subset of 150 individuals (30 per location) collected across five Portuguese locations (Portugal mainland: Matosinhos, Figueira da Foz, and Sagres; and Archipelagos: Azores and Madeira) was selected for otolith analyses. Otolith contour phenotypic variation was quantified through Elliptical Fourier Descriptors (EFDs) and Shape Indices (SIs), while elemental signatures (element: Ca) were analyzed using solution-based inductively coupled plasma mass spectrometry (SB-ICP-MS). Statistical analyses involved both univariate (one-way ANOVA, followed by Tukey tests, if needed) and multivariate approaches (MANOVA and LDFA), considering both individual and combined datasets. Results: EFDs + SIs yielded the lowest discriminatory power, with an overall reclassification accuracy of 38%. In contrast, Ca signatures provided the highest discrimination at 79%. The combination of both markers resulted in a slightly lower overall accuracy of 75%, likely due to the higher variance associated with the morphological data. Conclusions: In agreement with the previous parasite assessment, these otolith-based approaches confirm that the Macaronesian archipelagos consist of distinct stocks, separate from the Portuguese continental shelf. Furthermore, significant differences in otolith geochemical signatures between Sagres and Figueira da Foz point to a further subdivision of stocks. These findings are consistent with recent genetic data identifying three distinct stocks along the western and southern Iberian Peninsula, reinforcing the need for localized management of P. bogaraveo populations to ensure long-term fishery sustainability.

The South American silver croaker, Plagioscion squamosissimus, holds significant importance for the artisanal fisheries operating in the sub-middle and lower courses of the São Francisco River, located in northeastern Brazil. Its complex horizontal movement patterns and habitat-use preferences are not fully understood in the waters of hydroelectric dam reservoirs, raising important questions for the rational and sustainable management of this species. This study aimed to identify the habitat use of P. squamosissimus individuals captured in three fishers’ associations (Olho D’água do Casado, Petrolândia and Rodelas). Individuals were collected between September 2023 and March 2024. A selection of 25 individuals per location from the same age group (+2 years) was used, following annual age estimation based on existing growth curves. Element-to-calcium (element/Ca) ratios in the otolith cores and edges were determined using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The data were analyzed using univariate and multivariate statistics to assess the degree of separation between individuals in relation to natal origin (otolith cores) and time of capture (otolith edges) from the three sampling sites. Significant differences in element/Ca ratios between core and edges of the otolith were observed for Ba/Ca, Mg/Ca, Mn/Ca and Sr/Ca ratios. These results indicate an ontogenetic change in the habitat use, in which similarity in core signatures suggests a common natal origin, likely influenced by shared environmental conditions of the individuals investigated in this study.

Understanding the life-history strategies of deep-sea fishes is essential for improving ecological knowledge and informing conservation efforts. Using otolith microchemistry, this study reconstructed the ontogenetic movement patterns of four grenadier species (Nezumia aequalis, Hymenocephalus billsam, Coelorinchus marinii, and Malacocephalus occidentalis) caught in the continental slope off southern Brazil (Southwestern Atlantic). Elemental signatures (Ba:Ca, Sr:Ca, Li:Ca, Mg:Ca, Mn:Ca, Ni:Ca, Cu:Ca, and Zn:Ca) were quantified along core-to-edge transects of sagittal otoliths using Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS). Ontogenetic shifts were identified using change-point detection (PELT). A general decline in elemental incorporation with age was observed across species, consistent with ontogenetic physiological regulation. Species-specific multi-elemental patterns suggest distinct ecological strategies. Nezumia aequalis exhibited an abrupt decline in Ba:Ca, indicating an early-life environmental shift. Hymenocephalus billsam showed increasing Ba:Ca and Sr:Ca profiles, consistent with continued use of pelagic-associated water masses. Coelorinchus marinii and Malacocephalus occidentalis displayed more complex patterns, with the latter showing pronounced Ba:Ca and Zn:Ca peaks that may reflect mid-life habitat shifts or physiological events. Mn:Ca ratios differed between pelagic and demersal species. Otolith microchemistry combined with change-point analysis could provide insights into deep-sea fish ontogeny, although interpretations should consider both environmental and physiological influences.