The optimal management of the commercially important, but mostly over-exploited, pelagic tunas, albacore (Thunnus alalunga Bonn., 1788) and Atlantic bluefin tuna (BFT; Thunnus thynnus L., 1758), requires a better understanding of population structure than has been provided by previous molecular methods. Despite numerous studies of both species, their population structures remain controversial. This study reports the development of single nucleotide polymorphisms (SNPs) in albacore and BFT and the application of these SNPs to survey genetic variability across the geographic ranges of these tunas. A total of 616 SNPs were discovered in 35 albacore tuna by comparing sequences of 54 nuclear DNA fragments. A panel of 53 SNPs yielded FST values ranging from 0.0 to 0.050 between samples after genotyping 460 albacore collected throughout the distribution of this species. No significant heterogeneity was detected within oceans, but between-ocean comparisons (Atlantic, Pacific and Indian oceans along with Mediterranean Sea) were significant. Additionally, a 17-SNP panel was developed in Atlantic BFT by cross-species amplification in 107 fish. This limited number of SNPs discriminated between samples from the two major spawning areas of Atlantic BFT (FST  = 0.116). The SNP markers developed in this study can be used to genotype large numbers of fish without the need for standardizing alleles among laboratories.

The Atlantic bluefin tuna is a highly migratory species emblematic of the challenges associated with shared fisheries management. In an effort to resolve the species' stock dynamics, a genomewide search for spatially informative single nucleotide polymorphisms (SNPs) was undertaken, by way of sequencing reduced representation libraries. An allele frequency approach to SNP discovery was used, combining the data of 555 larvae and young-of-the-year (LYOY) into pools representing major geographical areas and mapping against a newly assembled genomic reference. From a set of 184,895 candidate loci, 384 were selected for validation using 167 LYOY. A highly discriminatory genotyping panel of 95 SNPs was ultimately developed by selecting loci with the most pronounced differences between western Atlantic and Mediterranean Sea LYOY. The panel was evaluated by genotyping a different set of LYOY (n = 326), and from these, 77.8% and 82.1% were correctly assigned to western Atlantic and Mediterranean Sea origins, respectively. The panel revealed temporally persistent differentiation among LYOY from the western Atlantic and Mediterranean Sea (F = 0.008, p = .034). The composition of six mixed feeding aggregations in the Atlantic Ocean and Mediterranean Sea was characterized using genotypes from medium (n = 184) and large (n = 48) adults, applying population assignment and mixture analyses. The results provide evidence of persistent population structuring across broad geographic areas and extensive mixing in the Atlantic Ocean, particularly in the mid-Atlantic Bight and Gulf of St. Lawrence. The genomic reference and genotyping tools presented here constitute novel resources useful for future research and conservation efforts.

In the present study we have investigated the population genetic structure of albacore (Thunnus alalunga, Bonnaterre 1788) and assessed the loss of genetic diversity, likely due to overfishing, of albacore population in the North Atlantic Ocean. For this purpose, 1,331 individuals from 26 worldwide locations were analyzed by genotyping 75 novel nuclear SNPs. Our results indicated the existence of four genetically homogeneous populations delimited within the Mediterranean Sea, the Atlantic Ocean, the Indian Ocean and the Pacific Ocean. Current definition of stocks allows the sustainable management of albacore since no stock includes more than one genetic entity. In addition, short- and long-term effective population sizes were estimated for the North Atlantic Ocean albacore population, and results showed no historical decline for this population. Therefore, the genetic diversity and, consequently, the adaptive potential of this population have not been significantly affected by overfishing.

Geometric morphometric methods were used to explore body shape morphology in 260 Atlantic bluefin tuna, Thunnus thynnus, collected in Sardinia (Western Mediterranean) during the breeding phase and in the Bay of Biscay (North Eastern Atlantic) during the feeding phase. The shape of each specimen was captured by high resolution digital images and recording the 2-D coordinates of seven morphological landmarks. A general procruste analysis (GPA) was applied in order to eliminate any morphological variations resulting from size, position or orientation of specimens. A thin plate-spline (TPS) method was then used to provide a graphical representation of the shape conformation between two sets of data. Results of the regression model between the direct and indirect measurements accounted for a R2 = 0.98. The Principal Components Analysis shows differences linked to the two sampling areas, accounting for 37% and 19.97% of the body shape variation in the first (PC1) and second (PC2) principal component, respectively. Specifically, the deformation grid projection highlights the major differences regarding the anterior-ventral part of the body (landmark 5-6-7). These differences might not necessarily be linked to an actual population substructure. Instead, it was hypothesized that such body shape differences were due to the diverse life phases during which specimens were collected, since the reproductive specimens show a 'potbellied' shape, which was larger than for the feeding specimens that showed a 'slimmer' shape. Analyses of likely sexual dimorphism conducted on Sardinian specimens did not reveal any significant differences; whereas body shape differences related to the pre- and post-reproductive sizes were detected

SUMMARY: To efficiently manage and maintain fish stock abundance and age structure, it is necessary to understand variability in its spatial distribution. The main objective of this study was to describe the demographic structure of the Bay of Biscay anchovy during the main spawning period based on adult samples from 15 daily egg production method surveys. The proportion of age-1 individuals was modelled using generalized additive models with a binomial distribution and a logit link in relation to geographical and environmental covariates. The possibility of obtaining different models depending on the average age-1 proportion (low or high) was also explored. In general, age-1 individuals were found in shallow waters close to the coast, especially associated with the Gironde and Adour river plumes, whereas older individuals were prevalent on the shelf break and in oceanic waters. However, in years with a high age-1 proportion the younger individuals were also dominant in oceanic waters. These results could be used for management purposes, such as defining protected areas for particular age groups.Keywords: spatial age composition, anchovy, Bay of Biscay, daily egg production method, generalized additive model, environmental effects.RESUMEN: Distribución espacio-temporal de la edad 1 de anchoa del golfo de Bizkaia (Engraulis Encrasicolus) en el momento de puesta. -Con el fin de gestionar eficientemente la abundancia y la estructura espacial de un stock es necesario entender su distribución espacial. El objetivo principal de este trabajo es describir la estructura demográfica de la anchoa del golfo de Bizkaia durante el periodo de desove a partir de las muestras de adultos recogidas en 15 campañas del método de producción diaria de huevos. La proporción de individuos de edad 1 se modeló en función de variables geográficas y ambientales por medio de un modelo aditivo generalizado con distribución binomial y función enlace logit. Además se estudió la posibilidad de obtener diferentes modelos dependiendo de si la proporción de edad 1 promedio es baja o alta. En general, los individuos de edad 1 se encontraron en aguas poco profundas cerca de la costa, especialmente en las plumas de los ríos Garona y Adur, mientras que los individuos de mayor edad prevalecieron en el cantil y en aguas oceánicas. Sin embargo, los años con una alta proporción de edad 1, los individuos jóvenes fueron también predominantes en aguas oceánicas. Estos resultados podrían utilizarse para fines relacionados con la gestión, tales como la definición de áreas protegidas para determinados grupos de edad.Palabras clave: composición de edad espacial, anchoa, golfo de Bizkaia, método de producción diaria de huevos, modelo aditivo generalizado, efectos ambientales.

There is an increasing trend upon adding a detailed description of the origin of seafood products driven by a general interest in the implementation of sustainable fishery management plans for the conservation of marine ecosystems. North Atlantic albacore ("Bonito del Norte con Eusko Label") and Bay of Biscay anchovy ("Anchoa del Cantábrico") are two commercially important fish populations with high economical value and vulnerable to commercial fraud. This fact, together with the overexploited situation of these two populations, makes it necessary to develop a tool to identify individual origin and to detect commercial fraud. In the present study, we have developed and validated a traceability tool consisting of reduced panels of gene-associated single nucleotide polymorphisms (SNPs) suitable for assigning individuals of two species to their origin with unprecedented accuracy levels. Only 48 SNPs are necessary to assign 81.1% albacore and 93.4% anchovy individuals with 100% accuracy to their geographic origin. The total accuracy of the results demonstrates how gene-associated SNPs can revolutionize food traceability. Gene-associated SNP panels are not of mere commercial interest, but they also can result in a positive impact on sustainability of marine ecosystems through conservation of fish populations through establishing a more effective and sustainable fishery management framework and contributing to the prevention of falsified labeling.