Strong population genetic structure and contrasting demographic histories for the small-spotted catshark (Scyliorhinus canicula) in the Mediterranean Sea

Coastal and demersal chondrichthyans, such as the small-spotted catshark, are expected to exhibit genetic differentiation in areas of complex geomorphology like the Mediterranean Basin because of their limited dispersal ability. To test this hypothesis, we used a fragment of the mitochondrial cytochrome c oxidase subunit I gene and 12 nuclear microsatellite loci in order to investigate the genetic structure and historical demography of this species, and to identify potential barriers to gene flow. Samples were collected from the Balearic Islands, the Algerian Basin, the Ionian Sea, the Corinthian Gulf and various locations across the Aegean Sea. Additional sequences from the Atlantic and the Levantine Basin retrieved from GenBank were included in the mitochondrial DNA analysis. Both mitochondrial and nuclear microsatellite DNA data revealed a strong genetic subdivision, mainly between the western and eastern Mediterranean, whereas the Levantine Basin shared haplotypes with both areas. The geographic isolation of the Mediterranean basins seems to enforce the population genetic differentiation of the species, with the deep sea acting as a strong barrier to its dispersal. Contrasting historical demographic patterns were also observed in different parts of the species' distribution, most notably a population growth trend in the western Mediterranean/ Atlantic area and a slight decreasing one in the Aegean Sea. The different effects of the Pleistocene glacial periods on the habitat availability may explain the contrasting demographic patterns observed. The current findings suggest that the smallspotted catshark exhibits several genetic stocks in the Mediterranean, although further study is needed

Evidence of high genetic connectivity for the longnose spurdog Squalus blainville in the Mediterranean Sea

Squalus blainville is one of the least studied Mediterranean shark species. Despite being intensively fished in several locations, biological knowledge is limited and no genetic structure information is available. This is the first study to examine the genetic structure of S. blainville in the Mediterranean Sea. Considering the high dispersal potential inferred for other squalid sharks, the hypothesis of panmixia was tested based on a 585 bp fragment of the mitochondrial DNA cytochrome c oxidase subunit I gene from 107 individuals and six nuclear microsatellite loci from 577 individuals. Samples were collected across the Ionian, Aegean and Libyan Seas and off the Balearic Islands. Twenty three additional sequences of Mediterranean and South African origin were retrieved from GenBank and included in the mitochondrial DNA analysis. The overall haplotype diversity was high, in contrast to the low nucleotide diversity. Low and non-significant pairwise ΦST and FST values along with a Bayesian cluster analysis suggested high connectivity with subsequent genetic homogeneity among the populations studied, and thus a high dispersal potential for S. blainville similar to other squalids. The historical demography of the species was also assessed, revealing a pattern of population expansion since the middle Pleistocene. These findings could be considered in species-specific conservation plans, although sampling over a larger spatial scale and more genetic markers are required to fully elucidate the genetic structure and dispersal potential of S. blainville

Histochemical analysis of glycoconjugates in the domestic cat testis

The localization and characterization of oligosaccharide sequences in the cat testis was investigated using 12 lectins in combination with the ßelimination reaction, N-Glycosidase F and sialidase digestion. Leydig cells expressed O-linked glycans with terminal aGalNAc (HPA reactivity) and N-glycans with terminal/internal aMan (Con A affinity). The basement membrane showed terminal Neu5Aca2,6Gal/GalNAc, Galß1,3GalNAc, a/ßGalNAc, and GlcNAc (SNA, PNA, HPA, SBA, GSA II reactivity) in O-linked oligosaccharides, terminal Galß1,4GlcNAc (RCA120 staining) and aMan in N-linked oligosaccharides; in addition, terminal Neu5Aca2,3Galß1,4GlcNac, Forssman pentasaccharide, aGal, aL-Fuc and internal GlcNAc (MAL II, DBA, GSA I-B4, UEA I, KOH-sialidase-WGA affinity) formed both O- and N-linked oligosaccharides. The Sertoli cells cytoplasm contained terminal Neu5Ac- Galß1,4GlcNAc, Neu5Ac-ßGalNAc as well as internal GlcNAc in O-linked glycans, aMan in N-linked glycoproteins and terminal Neu5Aca2,6Gal/ GalNAc in both O- and N-linked oligosaccharides. Spermatogonia exhibited cytoplasmic N-linked glycoproteins with aMan residues. The spermatocytes cytoplasm expressed terminal Neu5Aca2,3Galß1,4 GlcNAc and Galß1,3GalNAc in O-linked oligosaccharides, terminal Galß1,4GlcNAc and a/ßGalNAc in N-linked glycoconjugates. The Golgi region showed terminal Neu5aca2,3Galß1,4GlcNac, Galß1,4GlcNAc, Forssman pentasaccharide, and aGalNAc in O-linked oligosaccharides, aMan and terminal ßGal in N-linked oligosaccharides. The acrosomes of Golgi-phase spermatids expressed terminal Galß1,3GalNAc, Galß1,4GlcNAc, Forssmann pentasaccharide, a/ßGalNAc, aGal and internal GlcNAc in O-linked oligosaccharides, terminal a/ßGalNAc, aGal and terminal/internal aMan in N-linked glycoproteins. The acrosomes of cap-phase spermatids lacked internal Forssman pentasaccharide and aGal, while having increased a/ßGalNAc. The acrosomes of elongated spermatids did not show terminal Galß1,3GalNAc, displayed terminal Galß1,4GlcNAc and a/ßGalNAc in N-glycans and Neu5Ac-Galß1,3GalNAc in O-linked oligosaccharides

Mitigating slipping-related mortality from purse seine fisheries for small pelagic fish: case studies from European Atlantic waters

The release of unwanted catches (UWC) from purse seines, while the catch is still in the water, is known as “slipping”. Once thought to be a benign process, compared to discarding UWC overboard from the fishing vessel, it is now recognised that “slipping” can lead to significant mortality in the released fish if done inappropriately. In this chapter, we examine purse seining and slipping operations, and discuss what drives slipping and potential mitigation measures to reduce slipping mortality. We use three examples of purse seine fisheries for small pelagic species in the North-east Atlantic; from Norway, Portugal and Spain. The ideal solution (identifying and avoiding UWC before the net is set) requires the development of tools to enable fishers to better characterise target schools in terms of key selection criteria, e.g., with respect to species, individual size and catch biomass. Such tools are being developed, based primarily on hydro-acoustic technology. However, some UWC in purse seine catches are inevitable, and operational improvements in slipping practices have been shown to significantly reduce stress and mortality in the released UWC. We conclude with a discussion on the challenges currently facing the implementation of the European Union (EU) Landing Obligation with regards to minimising slipping related mortality.info:eu-repo/semantics/publishedVersio

Report of the 2006 ICCAT workshop for bluefin tuna direct ageing

This report provides the presentations, discussions and conclusions from the ICCAT bluefin tuna workshop for direct ageing held in Santander, Spain, in April 2006. The report summarizes the ageing criteria used in the past and the agreements on future age determination based on otoliths, vertebrae and spines. Advantages and disadvantages of each calcified structure for ageing and border interpretation were discussed. It was considered that bluefin tuna age interpretation becomes very difficult from age ten onwards using the whole vertebra and the spine sections methods, but this last technique continues to be useful for older ages. Otolith sections can be used for the whole age range. Participants agreed that none of these three structures could be excluded from routine ageing because otoliths are not easily available. Age estimations within the same structure and between different structures of the same specimen were compared for several readers. Better precision was found between spine readers compared to vertebra and otolith readers. Good age agreement was also achieved between readers of spines and vertebrae from the same bluefin for ages less than 12 years. Preliminary results from radiocarbon assays on otoliths were presented at the workshop and gave promising outcomes for bluefin tuna age validation. Also, these suggested that bluefin tuna can live longer than had previously been established and that a review is needed of the currently used asymptotic size and growth rate for both stocks. Another important contribution of the workshop was a manual for age interpretation.Le présent rapport recueille les présentations, discussions et conclusions de l’Atelier de l’ICCAT chargé de la détermination directe de l’âge du thon rouge, tenu à Santander (Espagne) au mois d’avril 2006. Le rapport résume les critères employés par le passé pour interpréter l’âge et les accords pour la détermination future de l’âge à partir des otolithes, vertèbres et épines. L’Atelier a discuté des avantages et des inconvénients de chaque structure calcifiée pour déterminer l’âge et l’interprétation du type de bord. On a abordé la difficulté de l’interprétation de l’âge des thons de plus de 10 ans au moyen de la vertèbre entière et des sections des épines, bien que cette dernière méthode continue d’être utile pour les âges avancés. Les sections d’otolithes peuvent être employées pour toute la gamme d’âges. Les participants ont convenu qu’aucune de ces trois structures ne doit être exclue pour l’interprétation de l’âge parce qu’il n’est pas toujours possible d’obtenir des otolithes. On a comparé les lectures de l’âge à l’intérieur de la même structure et entre différentes structures du même exemplaire pour divers lecteurs. On a obtenu une plus grande précision parmi les lecteurs d’épines que parmi les lecteurs de vertèbres et d’otolithes. On a également obtenu un bon accord entre les lecteurs d’épines et de vertèbres originaires du même exemplaire pour les âges inférieurs à 12 ans. Les résultats préliminaires des essais de radiocarbone dans les otolithes ont été présentés à l’Atelier, offrant de bonnes perspectives pour son utilisation dans la validation de l’âge. Ces résultats indiquent aussi que le thon rouge a une plus grande longévité que ce qui avait été auparavant établi et qu’il est nécessaire de réviser la longueur asymptotique et le taux de croissance actuellement utilisés. L’élaboration d’un manuel aux fins de l’interprétation de l’âge a constitué une autre contribution importante de l’Atelier.Este informe recoge las presentaciones, discusiones y conclusiones del congreso de ICCAT para la determinación directa de la edad de atún rojo, celebrado en Santander, España, en abril de 2006. El informe resume los criterios empleados en el pasado para interpretar la edad y los acuerdos para la determinación futura de la edad a partir de otolitos, vértebras y espinas. Se discutieron las ventajas y los inconvenientes de cada estructura calcificada para determinar la edad y la interpretación del tipo borde. Se planteó la dificultad en la interpretación de la edad de atunes mayores de 10 años utilizando la vértebra entera y las secciones de espinas, no obstante este último método continúa siendo útil para edades mayores. Las secciones de otolitos pueden ser empleadas para todo el rango de edades. Los participantes acordaron que ninguna de estas tres estructuras deben excluirse para la interpretación de la edad porque no siempre es posible obtener los otolitos. Se compararon las lecturas de edad dentro de la misma estructura y entre diferentes estructuras del mismo ejemplar para varios lectores. Se obtuvo una mayor precisión entre lectores de espinas comparada con las obtenidas por los lectores de vértebras y otolitos. También se obtuvo un buen acuerdo entre lectores de espinas y vértebras procedentes del mismo ejemplar para edades menores de 12 años. Los resultados preliminares de las pruebas de radiocarbono en otolitos fueron presentados en el congreso, proporcionando buenas expectativas para su uso en la validación de la edad. Estos resultados también indican que el atún rojo es más longevo de lo que se consideraba y que es necesaria una revisión de la longitud asintótica y de la tasa de crecimiento empleadas actualmente. Otra importante contribución del congreso fue la elaboración de un manual para la interpretación de la edad

Fin Spine Bone Resorption in Atlantic Bluefin Tuna, Thunnus thynnus, and Comparison between Wild and Captive-Reared Specimens

Bone resorption in the first spine of the first dorsal fin of Atlantic bluefin tuna (ABFT) has long been considered for age estimation studies. In the present paper spine bone resorpion was assessed in wild (aged 1 to 13 years) and captive-reared (aged 2 to 11 years) ABFT sampled from the Mediterranean Sea. Total surface (TS), solid surface (SS) and reabsorbed surface (RS) were measured in spine transverse sections in order to obtain proportions of SS and RS. The spine section surface was found to be isometrically correlated to the fish fork length by a power equation. The fraction of solid spine bone progressively decreased according to a logarithmic equation correlating SS/TS to both fish size and age. The values ranged from 57% in the smallest examined individuals to 37% in the largest specimens. This phenomenon was further enhanced in captive-reared ABFT where SS/TS was 22% in the largest measured specimen. The difference between the fraction of SS of wild and captive-reared ABFT was highly significant. In each year class from 1- to 7-year-old wild specimens, the fraction of spine reabsorbed surface was significantly higher in specimens collected from March to May than in those sampled during the rest of the year. In 4-year-old fish the normal SS increase during the summer did not occur, possibly coinciding with their first sexual maturity. According to the correlations between SS/TS and age, the rate of spine bone resorption was significantly higher, even almost double, in captive-reared specimens. This could be attributed to the wider context of systemic dysfunctions occurring in reared ABFT, and may be related to a number of factors, including nutritional deficiencies, alteration of endocrine profile, cortisol-induced stress, and loss of spine functions during locomotion in rearing conditions.Versión del editor4,411

Population Genomics of the Blue Shark, Prionace glauca, Reveals Different Populations in the Mediterranean Sea and the Northeast Atlantic

Populations of marine top predators have been sharply declining during the past decades, and one-third of chondrichthyans are currently threatened with extinction. Sustainable management measures and conservation plans of large pelagic sharks require knowledge on population genetic differentiation and demographic connectivity. Here, we present the case of the Mediterranean blue shark (Prionace glauca, L. 1758), commonly found as bycatch in longline fisheries and classified by the IUCN as critically endangered. The management of this species suffers from a scarcity of data about population structure and connectivity within the Mediterranean Sea and between this basin and the adjacent Northeast Atlantic. Here, we assessed the genetic diversity and spatial structure of blue shark from different areas of the Mediterranean Sea and the Northeast Atlantic through genome scan analyses. Pairwise genetic differentiation estimates (FST) on 203 specimens genotyped at 14,713 ddRAD-derived SNPs revealed subtle, yet significant, genetic differences within the Mediterranean sampling locations, and between the Mediterranean Sea and the Northeast Atlantic Ocean. Genetic differentiation suggests some degree of demographic independence between the Western and Eastern Mediterranean blue shark populations. Furthermore, results show limited genetic connectivity between the Mediterranean and the Atlantic basins, supporting the hypothesis of two distinct populations of blue shark separated by the Strait of Gibraltar. Although reproductive interactions may be limited, the faint genetic signal of differentiation suggests a recent common history between these units. Therefore, Mediterranean blue sharks may function akin to a metapopulation relying upon local demographic processes and connectivity dynamics, whereby the limited contemporary gene flow replenishment from the Atlantic may interplay with currently poorly regulated commercial catches and large-scale ecosystem changes. Altogether, these results emphasise the need for revising management delineations applied to these critically endangered sharks

MEDLEM database, a data collection on large elasmobranchs in the Mediterranean and Black Seas

The Mediterranean Large Elasmobranchs Monitoring (MEDLEM) database contains more than 3,000 records (with more than 4,000 individuals) of large elasmobranch species from 21 different countries around the Mediterranean and Black seas, observed from 1666 to 2017. The principal species included in the archive are the devil ray (1,868 individuals), the basking shark (935 individuals), the blue shark (622 individuals), and the great white shark (342 individuals). In the last decades, other species such as the thresher shark (187 individuals), the shortfin mako (180 individuals), and the spiny butterfly ray (138) were reported with increasing frequency. This was possibly due to increased public awareness on the conservation status of sharks, and the consequent development of new monitoring programs. MEDLEM does not have homogeneous reporting coverage throughout the Mediterranean and Black seas and it should be considered as a database of observed species presence. Scientific monitoring efforts in the south-eastern Mediterranean and Black seas are generally lower than in the northern sectors and the absence of some species in our database does not imply their actual absence in these regions. However, the available data allowed us to analyse the frequency and spatial distribution of records, the size frequencies for a few selected the available data allowed us to analyse the frequency and spatial distribution of records, the size frequencies for a few selected species, the overall area coverage, and which species are involved as bycatch by different fishing gears

Spatial and Sex-Specific Variation in Growth of Albacore Tuna (Thunnus alalunga) across the South Pacific Ocean

Spatial variation in growth is a common feature of demersal fish populations which often exist as discrete adult sub-populations linked by a pelagic larval stage. However, it remains unclear whether variation in growth occurs at similar spatial scales for populations of highly migratory pelagic species, such as tuna. We examined spatial variation in growth of albacore Thunnus alalunga across 90° of longitude in the South Pacific Ocean from the east coast of Australia to the Pitcairn Islands. Using length-at-age data from a validated ageing method we found evidence for significant variation in length-at-age and growth parameters (L∞ and k) between sexes and across longitudes. Growth trajectories were similar between sexes up until four years of age, after which the length-at-age for males was, on average, greater than that for females. Males reached an average maximum size more than 8 cm larger than females. Length-at-age and growth parameters were consistently greater at more easterly longitudes than at westerly longitudes for both females and males. Our results provide strong evidence that finer spatial structure exists within the South Pacific albacore stock and raises the question of whether the scale of their “highly migratory” nature should be re-assessed. Future stock assessment models for South Pacific albacore should consider sex-specific growth curves and spatial variation in growth within the stock