Differences In Otolith Shape Research Articles

Asymmetrical individual both left and right otoliths of Tuna Scombrini collected from the Java Sea

Otolith can be used as a natural marker of fish stock or anomalies between individuals within fish stock. This research aims to study the relationships between fish length and otolith length and confirm differences in otolith shape between species in the Scombrini tribe and Carangidae family (Decapterus ruselli). Sample used in our analysis were collected around July - September 2023 from three different location, Rastrelliger brachysoma (Lekok waters, Pasuruan), Scomber australasicus (Bali Strait waters) and Decapterus ruselli (Sendang Biru, South Malang). Total 96 specimens were identified based on morphological character as Rastrelliger brachysoma, Scomber australasicus and Decapterus ruselli. Each of following samples were cut horizontally at the frontal head to open the skull and remove sagitta otolith below the hindbrain using dissecting set, then cleaned and stored dry in microtube 1,5 ml separately for left and right to further documented using Celestron Digital Microscope Pro Gray USB 44308. Otolith morphometric data collected includes maximum length using TpsDig and weight using analytical balance. The relationship between Forked Length (FL) and otolith length, length-weight relationship of otolith was determined using simple linear regression on software Statistical Product and Service Solutions (SPSS). Paired sample t-test was applied to determine asymmetrical size of left and right otoliths. In this study, it was found that the shape of the otoliths between species has differences in the rostrum, antirostrum, ventral and dorsal parts. FL-otolith length relationship of S. australasicus, R. brachysoma and D. ruselli are Y=0,725+0,164X, r2= 0,519; Y=0,191+0,230X, r2= 0,911; Y=3,156+0,075X, r2=0,071 respectively. The LW sagitta relationship shows that there is a very strong relationship (P<0,05) between L and W of otoliths. The results of the Paired Sample T-test showed that there was no significant difference in the size of the left and right otoliths (Sig>0.05). Otolith shape is influenced by fish behaviour, diet and environment and it may be used as additional information to distinguish between tribe or even species. Otherwise, its asymmetric relationship and LW relationship may be potential new methods for stock discrimination and have other implications such as stock assessment, understanding natural asymmetry, and its potential applications in fisheries management and conservation.

Türkiye’den Salmo cinsine ait iki türün karşılaştırmalı otolit morfolojisi

In this study, the morphology of the sagittal otolith of Salmo coruhensis Turan, Kottelat &amp; Engin, 2010 and Salmo fahrettini Turan, Kalayci, Bektaş, Kaya &amp; Bayçelebi, 2020 from Çam Stream (Artvin) and Terme Stream (Samsun) was described by images of scanning electron microscopy. Its shape and contour were also analyzed with shape indices, elliptic Fourier coefficients and wavelet transforms. As the study material, a total of 30 S. coruhensis sample and 20 S. fahrettini sample were obtained. Interspecies differences in otolith shape and morphometry were evaluated by principal components analysis, canonical discrimination analysis, and permutational multivariate analysis of variance. The two salmonid species studied were distinguished by both morphometric and shape analysis methods. However, wavelet transform was found to be more effective than shape indices and elliptic Fourier coefficients in species discrimination, with an overall classification success rate of 80%. Our results showed that saccular otolith morphology could be an additional diagnostic character for trout species differentiation.

Stock identification of the Mediterranean horse mackerel (Carangidae: Trachurus mediterraneus) in the Marmara and Black Seas using body and otolith shape analyses

The Mediterranean horse mackerel (Trachurus mediterraneus) has been managed as a single stock in the Black Sea and adjacent regions, and its genetic structure has been under debate for decades, emphasising the necessity for additional research to validate the stock structure. This study used geometric morphometrics for body shape, shape indices, and elliptical Fourier analysis for otolith shape to explore their morphological differences in the Eastern Black Sea, Middle Black Sea, and Sea of Marmara. The findings revealed considerable differences in body and otolith shapes across the examined regions, suggesting the existence of three separate stocks. The geometric morphometrics revealed evident differences in the snout, followed by the caudal peduncle and body depths. Both otolith shape indices and elliptic Fourier analysis revealed significant directional bilateral asymmetry between the left- and right-sided otoliths. The elliptic Fourier analysis revealed a non-overlapping surface difference of 2.12% between the reconstructed left and right otolith outline shapes. However, no significant differences in otolith shape were observed between males and females using either otolith side. In addition, otolith shape analysis using shape indices and elliptic Fourier analysis reliably supported the presence of three distinct stocks of T. mediterraneus. This study provides evidence supporting the recognition of multiple phenotypic stocks of T. mediterraneus.

Otolith morphology as a tool for stock discrimination of three rockfish species in the East Sea of Korea

The shape and structure of otoliths play a vital role in studying fish populations because otolith shape indices are often applied to discriminate fish species. This study focused on examining inter- and intra-specific variations in otolith shape and size among three species of rockfish (Sebastes inermis, Sebastiscus marmoratus, and Sebastes zonatus) collected from the Dokdo and Ulleungdo regions of the East Sea in Korea. A total of 35 S. inermis specimens, 19 S. marmoratus specimens, and 59 S. zonatus specimens were collected between April 2021 and August 2022. The otolith shape was visualized using wavelet coefficients in the shapeR package. Otolith size indices, such as length, width, perimeter, and area, and shape indices, including form factor, aspect ratio, ellipticity, circularity, roundness, rectangularity, and squareness, were calculated for each species. Otolith size and shape indices significantly differed among the three rockfish species (p&amp;lt; 0.05). Compared with the other two species, S. marmoratus possessed more elongated otoliths, whereas S. zonatus had the largest otolith area, perimeter, and length. Average shape analysis based on wavelet coefficients revealed significant differences in otolith shape, particularly on the rostrum and posterior sides. A canonical analysis of principal components (CAP) confirmed the complete separation of otolith shapes among the three rockfish species, with 92.5% of the variation explained by the first axis (CAP1). The findings of this study enhance our understanding of the fish species in the Korean East Sea.

The utility of otolith-based methods for discriminating stock structure of the fishery important monacanthid, Nelusetta ayraud, over an intermediate scale

Connectivity and population structure of exploited fish species are critical to understand for effective assessment and management at appropriate spatial scales. We provide a first look at connectivity and population structure of a fishery-important monacanthid, Nelusetta ayraud, using otolith-based methods to compare among three locations (220–540 km apart) along the coast of New South Wales (NSW), Australia. Otolith elemental signatures sampled with laser-ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) revealed differences between two of the three locations during a recent period before capture, as well as differences between the two times examined, although spatial differences were consistent across these times. In contrast, elemental signatures in the juvenile core of the otolith did not differ among locations. Sr:Ca increased linearly with age, and Ba:Ca initially increased to age 1+ before declining in older age classes, consistent with previous observations of an ontogenetic movement into deeper offshore waters for N. ayraud. No differences in otolith shape were detected among locations using Elliptical Fourier Analysis. Our findings suggest there may be spatial structuring of the N. ayraud stock over an intermediate scale (100s km) within NSW, which will inform the design of a larger nation-wide investigation.

Comparing otolith shape descriptors for population structure inferences in a small pelagic fish, the European sardine Sardina pilchardus (Walbaum, 1792).

Otolith shape analysis has been one of the most used approaches to study population structure in the past decades. Currently, two sets of shape descriptors are used to perform otolith shape analysis, namely, Elliptic Fourier descriptor (EFd), which focuses on the overall otolith shape differences, and Discrete Wavelet descriptor (DWd), which is sensible to local differences along the otolith contour. Here, the authors conducted a comparative analysis of the performance of both the descriptors in reconstructing the population structure and connectivity patterns in a small pelagic fish species with a wide geographical distribution and fast growth rate, the European sardine Sardina pilchardus (Walbaum, 1792), for the first time. A combination of each otolith shape descriptor and shape indices was explored using multivariate statistical methods. The two otolith shape descriptors showed similar, although limited, overall classification success associated with the population dynamic characteristics of the species. Both descriptors point to migration among adjacent areas, such as northern Atlantic locations, eastern Mediterranean and even across well-defined physical obstacles, such as the Strait of Gibraltar, among Atlantic and western Mediterranean locations. Both descriptors supported the division of the populations of Mediterranean waters into three main groups but slightly differed in the group limits of the Atlantic waters. A comparison of the present results with those from previous otolith shape analysis studies using EFd on a decadal time scale revealed differences in the population structure and connectivity patterns compared to the earlier period. These differences not only may be attributed to changes in environmental variables leading to changes in population dynamics but can also be the result of the sardine biomass sharp decrease that occurred in the past decade.

Morphologic, morphometric and contour shape variations of sagittal otoliths of Lepidorhombus spp. in the Aegean Sea.

Otoliths are calcareous anatomical structures in the inner ear of fishes, and they can be used in the discrimination of fish species and stocks due to their species-specific shape. Sagittal otoliths in the Lepidorhombus whiffiagonis and Lepidorhombus boscii, two flatfish species of the same genus distributed in the Aegean Sea, were compared using morphology, morphometry and contour shape analyses. Blind and eyed side otoliths of Lepidorhombus species were evaluated separately due to their morphological features and statistical differences in morphometric measurements (p < 0.05). Four analysis groups were formed: blind side otolith of L. whiffiagonis, eyed side otolith of L. whiffiagonis, blind side otolith of L. boscii and eyed side otolith of L. boscii. Morphometric differences in otolith shape were performed by canonical discriminant analysis, and the first discriminant axis explained 97.4% (Wilks λ=0.270) of the variance between the groups, and the second axis explained 2.3% (Wilks λ=0.620). Classification success between Lepidorhombus species based on CDA is 100%, and the overall CDA classification score between groups is 76.5%. The wavelet functions obtained in the contour analysis showed high variability in the anterior, posterior-dorsal, antero-dorsal and ventral regions of the otoliths among these four analysis groups. Consequently, it is thought that this study will contribute to the taxonomic classification of fish with the morphological and morphometric differences in the blind and eyed side otoliths and the analyses made with the high discrimination success obtained in Lepidorhombus species.

A new species of Astronotus (Teleostei, Cichlidae) from the Orinoco River and Gulf of Paria basins, northern South America.

Based on morphological and molecular analysis of Astronotus species, a new species is described from the Orinoco River and Gulf of Paria basins in Venezuela and Colombia. Morphologically, it differs from Astronotuscrassipinnis and Astronotusocellatus in pre-orbital depth, caudal peduncle depth, head width, and caudal peduncle length, with significant differences in average percentage values. Osteologically, it differs from the two described species by lacking a hypurapophysis on the parahypural bone (hypural complex) and having two or three supraneural bones. Another characteristic that helps diagnose the new species is the morphology of the sagitta otolith, which is oval with crenulated dorsal and ventral margins and a rounded posterior edge. Genetically, the new species is distinct from all the other lineages previously proposed for the genus, delimited by five single locus species delimitation methods, and also has unique diagnostic nucleotides. Phylogenetic analyses support the monophyly of the new species as well as all other species/lineages. Astronotus species have considerable genetic, anatomical, and sagitta otolith shape differences, but have few significant traditional morphometric and meristic differences, because there is high variability in counts of spines, soft dorsal-fin rays, and lateral-line scales. It is clear that this new species is genetically and anatomically differentiated from all other species within the genus, and deserves recognition as a new valid species.

Otolith shape as a tool for species identification of the grenadiers Macrourus caml and M. whitsoni

Accurate species identification of harvested fishes is a central, yet often overlooked, component of fishery monitoring. This study examined the efficacy of using otolith shape to differentiate between the morphologically similar grenadiers Macrourus caml and M. whitsoni and validate species identifications by fishery observers within and adjacent to the Ross Sea region, Antarctica. Otolith shape information was collected from 610 M. caml and 329 M. whitsoni otoliths from research collections, where confidence in species identification was high, and 2558 samples collected by fishery observers from commercial longline catches. Univariate and linear discriminant analyses of research-collected samples revealed consistent differences in otolith shape between the two species, with otoliths of M. caml being larger and more elongate than those of M. whitsoni. No significant effect of collection depth or fishing season on otolith shape was evident for either species, and no significant effect of sampling location on otolith shape was evident for M. caml. Otolith shape of M. whitsoni varied slightly among sampling regions, although the extent of these differences was less than those between species. To validate observer identifications, a random forest (RF) model was trained using otolith shape data of 75% of the research collection samples, validated on the remaining 25%, and used to predict the species of fishery observer-collected samples. The RF model achieved high classification success for individuals from the research collections, with an Out-Of-Bag error rate of 5.97% for the training dataset. Overall classification success of individuals in the validation dataset was 96.2%, with 96.8% of M. caml and 94.8% of M. whitsoni correctly classified. Using this model, 90.6% of M. caml and 85.7% of M. whitsoni sampled by fishery observers were predicted as being correctly identified. Individual observer identification success ranged from 50.5% to 98.2%. The reliable and predictable differences in otolith shape observed between the two species indicates that our approach can be applied to ongoing or archived otolith collections to confirm species identification of fishery-sourced samples to improve the accuracy of fisheries monitoring, facilitate assignment of previously collected material to species level, develop high-confidence datasets for further biological analyses, and to understand and prioritise observer training needs. More broadly, our results highlight the potential for using otolith shape as an effective tool for assessing the accuracy of species identifications in fisheries sampling programs.

Assessing the Speciation of Lutjanus campechanus and Lutjanus purpureus through Otolith Shape and Genetic Analyses

Based on their morphological and genetic similarity, several studies have proposed that Lutjanus campechanus and Lutjanus purpureus are the same species, but there is no confirmed consensus yet. A population-based study concerning otolith shape and genetic analyses was used to evaluate if L. campechanus and L. purpureus are the same species. Samples were collected from populations in the southwestern Gulf of Mexico and the Venezuelan Caribbean. Otolith shape was evaluated by traditional and outline-based geometric morphometrics. Genetic characterization was performed by sequencing the mtDNA control region and intron 8 of the nuclear gene FASD2. The otolith shape analysis did not indicate differences between species. A nested PERMANOVA identified differences in otolith shape for the nested population factor (fishing area) in morphometrics and shape indexes (p = 0.001) and otolith contour (WLT4 anterior zone, p = 0.005 and WLT4 posterodorsal zone, p = 0.002). An AMOVA found the genetic variation between geographic regions to be 10%, while intrapopulation variation was 90%. Network analysis identified an important connection between haplotypes from different regions. A phylogenetic analysis identified a monophyletic group formed by L. campechanus and L. purpureus, suggesting insufficient evolutionary distances between them. Both otolith shape and molecular analyses identified differences, not between the L. campechanus and L. purpureus species, but among their populations, suggesting that western Atlantic red snappers are experiencing a speciation process.

Population Structure of Indian Mackerel (Rastrelliger kanagurta) in Java and Bali Island, Indonesia Inferred from Otolith Shape

The Indian mackerel, Rastrelliger kanagurta, is a commercially important resource across Indonesia's archipelagic waters. Despite its essential role in the fisheries industry, information regarding its population structures for management purposes is still limited. The present study investigates the variability of otolith shape as an efficient tool for stock discrimination. A total of 159 pairs of sagittal otolith were sampled at four localities along the southern Java-Bali coastal waters. Otolith outline was modeled by using Wavelet coefficients and was compared between localities using ANOVA-like permutation test, Canonical Analysis of Principal Coordinates (CAP), and classification test performed using linear discriminant analysis. The results showed significant differences in the shape of otolith between populations, reflected explicitly in the morphological feature of the excisura major. The differences in otolith shape were examined from all localities (ANOVA-like, p&lt;0.001, and CAP p&gt;0.05), except those otoliths between Palabuhanratu and Pacitan, thus, a mixed stock may occur in these two locations. These findings were also confirmed by the low classification success rate using LDA 44.26%. These results suggested that at least two distinct stocks potentially contributed to the fishery, impacting species management and conservation.

Use of otolith morphology and morphometry for species discrimination of megrims Lepidorhombus spp. in the Central Eastern Adriatic Sea

AbstractSagittal otolith morphology and otolith shape of two megrim species, Lepidorhombus boscii and Lepidorhombus whiffiagonis, were compared using descriptive morphological characters and Wavelet shape coefficients. Differences in otolith shape were examined by linear discriminant analysis (LDA). The first discriminant axis explained 66.6% of the variation between the groups, and the second axis 28.5%. Otolith classification based on LDA showed that in 79.5% of cases an otolith can be correctly classified based only on its shape. Relationships between otolith morphometric parameters (length and width) and fish size (total length) were described by fitting simple linear regression models. For L. boscii the highest positive correlation was found between right otolith width and total body length (R2 = 0.82), and for L. whiffiagonis between left otolith length and total body length (R2 = 0.39).

Stock separation of the shallow-water hake Merluccius capensis in the Benguela ecosystem using otolith shape analysis

The fishing industry is an important economic sector in Namibia and South Africa, with the shallow-water hake Merluccius capensis being an important target species. Recent genetic studies of M. capensis found two stocks in the Benguela Current Large Marine Ecosystem, one in the north (17–29° S) and one in the south (29–36° S), and a proposed mixed stock in the Orange River area (around 29° S). The present study investigated the use of otolith shape analysis for purposes of stock-structure analysis of M. capensis. Merluccius capensis otolith samples were collected during demersal-trawl surveys along the Benguela, for the years 1992, 2004 and 2005. Different years were selected to investigate temporal stability in otolith shape in the northern Benguela. A total of 1 628 otolith images were analysed using the shapeR library in R. Otolith shape was analysed using wavelet transformation, and ANOVA-like permutation tests indicated no significant differences between the northern (17°31′–25°29′ S) and central (25°30′–29°05′ S) Benguela for all years but showed significant differences between the northern and southern (29°05′–35°50′ S) Benguela. This study therefore demonstrated that otolith shape could be used for stock discrimination of M. capensis. It confirmed one stock of M. capensis in the northern and central Benguela and another in the southern Benguela, which supports the current, separate management approach for this species. It also showed some differences in otolith shape from the 1990s to the 2000s, which could be explained by increased movement of the southern Benguela stock to the northern Benguela and increased hybridisation in the later years.

Differences in otolith shape and fluctuating-asymmetry between reared and wild gilthead seabream (Sparus aurata Linnaeus, 1758).

Otolith structure is a useful tool in discrimination among fish populations as it is a permanent record of the influence of endogenous and exogenous factors. In the present study we examined otolith morphology and fluctuating asymmetry (FA) for differences between wild-caught (by bottom trawl) and reared specimens of Gilthead seabream (Sparus aurata). Based on the frequency of regenerated scales (degree of scale regeneration, SRD) on each specimen, a threshold of 30% SRD was used to assign wild-caught fish individuals as wild (≤30% SRD, LR group) or as possible aquaculture escapees (>30% SRD, HR group). Based on the analysis of elliptic Fourier descriptors, significant differences were found in otolith shape between reared (Rr) and the wild-caught groups (LR, HR). Reared fish had otoliths with significantly larger perimeter (OP ) than wild-caught fish. Furthermore, FA was significantly higher in the Rr than the LR group for OP and all except one shape descriptors (harmonics 2-7). The HR group exhibited intermediate levels of FA between the low and high FA levels observed in the LR and Rr groups. Results are discussed in terms of the value of combining otolith and scale morphology for the identification of escapees in wild Gilthead seabream stocks.

Detecting Mugil curema (Perciformes: Mugilidae) phenotypic stocks in La Paz Bay, Baja California Sur, Mexico, using geometric morphometrics of otolith shape, growth, and reproductive parameters

In a holistic approach it is important to identify potential fishing units to better understand population structure and dynamics. The objective of this work was to evaluate the potential existence of a Mugil curema population structured in stocks in La Paz Bay. For this, a total of 709 specimens were collected between 2010 and 2013. Two fish groups were identified (G1, n = 212, and G2, n = 178), and the otolith shape was compared using geometric morphometrics, L50% was estimated, age was assigned, and a multi-model approach was used to evaluate individual growth. Eight age groups were assigned for G1 (3-10) and 5 for G2 (3-7). The most adequate model to describe growth for both groups was the von Bertalanffy growth model (G1: L∞ = 421.77, k= 0.32, t0 = -0.05; G2: L∞ = 406.5, k = 0.36, t0 = -0.02). Differences in otolith shape and growth parameters between groups were significant; opposite, L50% estimates (G1 = 325 mm LT; G2 = 330 mm LT) were not significant. Results suggest the presence of a M. curema population structured in at least 2 stocks in La Paz Bay: one stock reproduces in Spring (G1) and the other in the Fall (G2).

Ontogenetic and interpopulation differences in otolith shape of the European perch (Perca fluviatilis)

Fish otoliths are conservative structures that are widely used on fishery science for multiple purposes. Despite its relevance in the research field, little is known about the ontogeny and inter-population effects on the otolith of freshwater fish. In this study we used otoliths from 1800 European perch (Perca fluviatilis) individuals from 9 different populations to analyze the ontogenetic and inter-population differences on the otolith shape using six morphometric indices. The relationship between fish and otolith length was fitted using three different regression models (linear, power and logistic) to identify the best allometric relationship. Our results show that there are strong ontogenetic and interpopulation differences in P. fluviatilis otolith shapes. We also show that the relationship between the fish and otolith length follows a logistic curve. The ontogenetic differences on otolith shape might be related to extrinsic factors (diet shift and intra and interspecific competition) in each ecosystem, given that the reservoirs are different and no clear pattern on the otolith shapes can be distinguished among populations. Our results imply that the available back-calculation models may not always provide accurate estimates of P. fluviatilis length and that a model that takes into account the real allometric relationship for the species can improve the fish length estimations of back-calculated fish lengths for the European perch.

Ecomorphological patterns in otoliths of tropical fishes: assessing trophic groups and depth strata preference by shape

The morphology and morphometry of otoliths have emerged as powerful indicators of ecological characteristics of fishes. However, shape descriptors that can accurately predict well-documented functions played by species in tropical ecosystems are either restricted to a few groups or poorly known. Therefore, we evaluated the power of two otolith shape descriptors (ecomorphological indexes and Fourier harmonics) in discriminating trophic and depth strata preference groups of tropical fish species. Differences in otolith shape of ecological groups were visualized by linear discriminant analysis (LDA), and tested by a jack-knife cross-validation method and permutational multivariate analysis of variance (PERMANOVA) for both methods. Visually and statistically, both descriptors were good predictors of trophic groups and depth preference categories (PERMANOVA, p < 0.05). Overall jack-knifed classification success between both descriptors were very similar, with harmonics correctly classifying 90.38% of assigned trophic groups and 75.96% of given depth preference categories, against 82% and 56.25% of ecological indexes, respectively. Our results suggest that Fourier descriptors and ecomorphological indexes of otoliths should be used as functional traits in future studies, as otolith shape provides a wider range of ecological information regarding feeding habitat, mobility, substrate association and water column use.

Growth and otolith morphology vary with alternative reproductive tactics and contaminant exposure in the round goby Neogobius melanostomus

Round goby Neogobius melanostomus sagittal (saccular) otolith morphology was compared between males of the two alternative reproductive tactics (termed guarder and sneaker males) and between males captured from sites of high or low contamination. Otolith size increased with fish size and also displayed an ontogenetic shift in shape, becoming relatively taller as otoliths grew in size. Despite a considerable overlap in age between males adopting the two reproductive tactics, size-at-age measurements revealed that guarder males are significantly larger than sneakers at any given age and that they invest more into somatic growth than sneaker males. Controlling for body size, sneaker males possessed heavier sagittal otoliths than guarder males. Subtle otolith shape differences were also found between the two male tactics and between sites of high and low contaminant exposure. Sneaker males had relatively shorter otoliths with more pronounced notching than guarder males. Fish captured at sites of high contamination had otoliths showing slower growth rates in relation to body size and their shapes had more pronounced caudal points and ventral protrusions when compared with fish captured at sites of low contamination. The results are discussed in relation to life-history tradeoffs between the male tactics in terms of reproductive and somatic investment as well as the putative metabolic costs of exposure to contaminants. Overall, this study reveals that male alternative reproductive tactics and environmental contaminants can have small, yet measurable, effects on otolith morphology and these factors should be accounted for in future research when possible.

Size-effect, asymmetry, and small-scale spatial variation in otolith shape of juvenile sole in the Southern North Sea

While otolith shape analysis can provide a valuable tool for discriminating between fish populations, factors which may influence otolith shape, such as the effect of size, directional asymmetry in growth, and local environmental conditions, are often unknown. Here, we analyzed differences in otolith shape across three size classes of age-0 common sole Solea solea L. from nursery grounds off the Belgian coast and in the Wadden Sea. Across size classes, form-factor decreased and roundness remained consistently high in both nursery grounds, while ellipticity increased in the Belgian nursery. Directional asymmetry between left and right otoliths measured by Fourier coefficients accounted for 0.96 and 7.2% of the variance when comparing otoliths overall, and for each size class, respectively. Within the Belgian nursery, results were consistent across sampling years and locations. In addition, otolith shape was marginally different between nursery grounds, but highly variable within nursery grounds. A small divergent group, which seems partly related to fish size, was noted at both spatial and temporal scales. Based on these results and before embarking on a study of population structure using otolith shape in age-0 common sole, we recommend testing for directional asymmetry and fish size effects across the entire region of interest.

Otolith shape analysis as a tool for stock separation of albacore tuna feeding in the Northeast Atlantic

For management purposes, albacore tuna (Thunnus alalunga, Bonnaterre 1788) in the North Atlantic are considered to be from one homogenous stock. However, multiple lines of evidence suggest that there is some degree of stock complexity. In this study, the stock structure of North Atlantic albacore tuna is investigated using otolith shape analysis. Juvenile albacore tunas were collected from the commercial fishery in the Bay of Biscay region over a three-year period (2012–2014). Catches were concentrated in two main areas: within the Bay of Biscay (East) and off the western shelf edge (West). Otolith shape was defined using Elliptical Fourier analysis and was compared between albacore from these two catch locations using generalised canonical discriminant analysis. The results show significant differences in otolith shape between albacore from the Eastern and Western locations using Elliptical Fourier descriptors. The discriminant analysis and jack-knifed cross-validation classification correctly classified East and West samples with a success rate of 72% and 75% respectively. The results suggest that two components with distinct environmental life histories contribute to the fishery in the Northeast Atlantic. It also implies that albacore juveniles display some degree of fidelity to their feeding areas.