The genetic structure and population connectivity of the Mediterranean endemic speckled skate Raja polystigma were investigated in 10 population samples (N = 232) at 7 exonprimed nuclear ...microsatellites and at 3 mitochondrial DNA sequence markers. The phylogeographic and population genetic analyses revealed that R. polystigma in the western and central Mediterranean represents a near-panmictic population, with a subtle but significant mitochondrial divergence of the Adriatic deme. Nuclear genotypes revealed that 2.5% of the total individuals exhibited an admixed ancestry with the sibling species R. montagui (spotted ray). Individuals with admixed ancestry were detected along with purebred individuals in the Algerian, southern Tyrrhenian, Sicilian and Adriatic R. polystigma population samples, but they were absent or rare in Sardinian and northern Tyrrhenian ones. Since the 2 species co-occur in the southwestern Mediterranean, we suggested that this area may act as a secondary hybrid zone.
Elasmobranchs are a vulnerable group that has been overexploited for almost half a century in the Mediterranean. However, few elasmobranch species have been assessed because information on their ...basic biological parameters is lacking for most species. Raja polystigma is a poorly studied endemic skate in the Mediterranean. The aim of this work is to determine some basic life history parameters of this skate in the Balearic Islands. Data were collected from commercial catches and during MEDITS surveys. Total length varied from 17 to 59 cm for both sexes, with a higher proportion of females than males. Allometric and morphometric relationships differed between sexes, females being heavier for a given size. Females matured at a larger size than males (L50 47.7 cm and 38.4 cm, respectively). Potential fecundity ranged between 11 and 45 yolked oocytes per female, and spawning was observed mainly during winter and spring. Persistent hotspots of adults and juveniles were detected on the shallow shelf off the northwest of Mallorca and east of Menorca, with adults being found mainly in the shallow and juveniles in deeper areas. Time series of abundance and frequency of appearance showed stable trends throughout the study period (2003-2018).
The feeding ecology of eight demersal elasmobranchs, three sharks (Etmopterus spinax, Scyliorhinus canicula and Galeus melastomus) and five batoids (Myliobatis aquila, Leucoraja naevus, Raja ...polystigma, R. miraletus and R. clavata), from the Balearic Sea (western Mediterranean) was analyzed. For each species, the diet and feeding habits were characterized by depth strata using quantitative indices such as diet overlap, diet breadth and prey diversity. Diet variation with size and depth were also tested for the most abundant species. For shelf-living species, natantian and reptantian crustaceans together with teleosts were the most important preys. On slope bottoms, euphausiids were the preferential prey for S. canicula and G. melastomus, while E. spinax fed mainly on cephalopods. The most specialist and generalist diet corresponded to G. melastomus living on the upper slope and S. canicula from the continental shelf, respectively. High overlap was found between all the skates on the continental shelf and the sympatric sharks S. canicula and G. melastomus on the slope. Significant overlap was also found between S. canicula and R. clavata on the continental shelf. Size was found to significantly affect the diet of S. canicula, G. melastomus and R. clavata, whereas depth affected exclusively S. canicula.
Rare and poorly studied species, like the endemic skates of the Mediterranean Sea, are considered prone to high rates of extinction and threat because of non-optimal reporting and sampling, which ...reduce the power of analyses. In this regard, the goal of this study was to establish some basic life-history parameters, unknown to date, of one of these endemics, Raja polystigma, caught as by-catch from experimental and commercial hauls in the Mediterranean Sea. Sexes were equally distributed with no major differences in sizes. The age and growth were assessed through annuli counts of vertebral centra from a sub-sample of 184 individuals. Among different growth models applied to the length at-age-data, the logistic function provided the best fitting curve (L∞: 691.49; k: 0.26; IP: 4.03 years). The oldest female and male were aged 11 (590 mm LT) and 8 years (521 mm TL), respectively. The estimated longevity was 10.6–15.4 years for females and 7.7–11.2 years for males. Females and males matured at about the same size (L50 506.1 mm TL and 488.1 mm TL, respectively), showing an uncommon pattern among Rajidae. A clear reproductive seasonality was observed during spring and summer. Depth influenced the distribution pattern of R. polystigma which appeared to complete its life cycle in coastal waters, with mature adults found exclusively in the shallows and immature specimens in the whole bathymetric range. Given its dependence on the coastal environment and its peculiar life-history features, measures to alleviate anthropic effects on this habitat are urgently needed.
•Life-history traits identified R. polystigma as highly vulnerable to overfishing.•S-shaped models appeared to be more appropriate in describing R. polystigma growth.•Both sexes mature late at the same size showing an uncommon pattern among rajids.•Seasonal egg laying is unusual among Rajidae family.•Despite its wide depth range, life cycle is completed in impacted coastal waters.
Morphologic deformation in a ray: a case report Metin, G., Ege University, Faculty of Fisheries, İzmir (Turkey). Div. of Fishing and Processing Technology; İlkyaz, A.T., Ege University, Faculty of Fisheries, İzmir (Turkey). Div. of Fishing and Processing Technology; Kınacıgil, H.T., Ege University, Faculty of Fisheries, İzmir (Turkey). Div. of Fishing and Processing Technology
Turkish journal of veterinary & animal sciences,
(2009), 2009, Letnik:
33, Številka:
3
Journal Article
Recenzirano
Odprti dostop
This study presents the data from a morphologic deformation diagnosis of a speckled ray (Raja polystigma Regan, 1923) individual which was sampled from İzmir Bay. Deformation was located on the head ...part of the specimen and no deformation was observed in other body regions.
Bu çalışmada, İzmir Körfezi'nde örneklenen bir vatoz (Raja polystigma Regan, 1923) bireyinde gözlenen morfolojik deformasyona ait bulgular sunulmuştur. Deformasyon, bireyin baş bölgesinde olup vücudun diğer kısımlarında herhangi bir anormallik gözlenmemiştir.
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