Oxynotus Centrina Research Articles

First description of leucism in the deep-sea angular rough shark (Oxynotus centrina) and the first documented pigment disorder in family Oxynotidae Gill, 1912.

The capture of a rare, critically endangered adult angular rough shark, Oxynotus centrina (Linnaeus, 1758), with abnormal coloration is reported in this paper. The shark exhibited a partial reduction in pigmentation, resulting in an overall pale appearance with white-greyish patches. Since the retinal pigmentation appeared normal, the shark was considered leucistic. This represents the first documented case of leucism in this species and the first colour disorder reported in the family Oxynotidae Gill, 1912. Despite the atypical appearance, the physical health of the shark seemed unaffected, supporting the notion that pigment disorders in deep-sea sharks do not inherently impair survival and growth. Full morphometric characteristics are presented and compared with those of a normal individual of the same sex caught in the same area, showing no differences.

Distribution and diversity of elasmobranchs in the Sea of Marmara: A 2023 status report

Abstract Elasmobranchs, encompassing an array of sharks and rays, confront a threat of extinction on a global scale. The Sea of Marmara (SoM) stands out as a critical refuge for these endangered species. This study harnesses data derived from comprehensive trawl surveys, representing the first area‐based evaluation of the elasmobranchs inhabiting the SoM. Sampling protocols were carried out at 10 separate stations along the 980‐km coastline of the SoM, each bounded by different ecological characteristics and anthropogenic influences. A total of eight shark species and six ray species were caught in the towed area of the entire the SoM. Notably, Scyliorhinus canicula and near‐threatened Raja clavata constitute more than 50% of the total abundance. Additionally, rare, and critically endangered species, including the Oxynotus centrina, Squatina squatina, Dipturus batis, and Myliobatis aquila, were documented, expanding our knowledge of their presence in the region. Spatial distribution heterogeneity was pronounced within species. Size distributions were species‐specific, and the presence of both juvenile and adult individuals suggested successful reproduction and growth. Records expand the known size range in the SoM for six shark and three ray species. It also provides first‐size information based on the total length of the S. stellaris and D. batis. Additionally, the urgent need for field‐based conservation efforts is highlighted, citing a previously unidentified important sensitive areas located in the southern part of the SoM.

Some Population Parameters of Picked Dogfish (Squalus acanthias L. 1758) Incidentally Captured in Commercial Fisheries in Southern Black Sea Shores and a First Record of Angular Roughshark (Oxynotus centrina, L. 1758) for Black Sea

The study, which aimed to determine some population parameters of picked dogfish (Squalus acanthias L. 1758) distributed in the Black Sea, was carried out in the five fishing seasons (between 2016 and 2023 years). The sharks draw attention as a bycatch for all fishing gear used in the Black Sea. In the study, total length (cm), weight (g) and sex (female/male) data were obtained from the sharks captured with all fishing gears (demersal trawl, midwater trawl, gillnets purse seine, turbot gillnets, trammel nets and bottom) used in commercial fishing activities in the Black Sea of Türkiye. A total of 576 specimens were collected all fishing gears during the sampling period. Length-weight relationship (LWR) was founded as W=0.0097L2.8521 (R2 =0.9854) for all the picked dogfish. Also, mean total length 48.9±0.707 cm respectively. In addition, the first record of the angular roughshark (Oxynotus centrina, L. 1758) species was given for the Black Sea coasts, which originated in the western Atlantic, was seen in the Mediterranean, Aegean Sea and the Marmara Sea of Türkiye. The shark, which was accidentally caught with a purse seine net, measured as 33.5 cm in total length and weighed 585 g.

Morphometric Analyses of the Angular Roughshark, Oxynotus centrina (Oxynotidae), with Biological Notes on Specimens from the Sea of Marmara

Morphometric measurements as percentages of total length of 6 specimens of Oxynotus centrina (Linnaeus, 1758), captured in the Sea of Marmara were reported. All of the analyzed proportions of landmark measurements as percentage of total length show allometry. Although, slight differences were seen between the morphometrics of Marmara specimens of O. centrina and those reported for the angular roughsharks captured in several geographical subregions of the Mediterranean Sea, these variations can be considered admissible based on allopatry. Regarding the mouth morphology in particular, the proportion of head length/mouth width to total length showed negative allometry, indicating O. centrina is a small-mouthed shark compared to increasing body size. A partly digested shark embryon and vitellus like slurry were found in the stomach content of one specimen captured in the Sea of Marmara, which provided supporting evidence for the predation on elasmobranch eggs by O. centrina in the wild.

First documented record of neonate angular roughshark Oxynotus centrina from the eastern Adriatic Sea

Many biological aspects of deep-water sharks are poorly known due to their rarity and difficulties in conducting detailed research on them. The angular roughshark (Oxynotus centrina) is a rare species, critically endangered in the Mediterranean Sea, of which records are scarce across this region. Here we present a record of a female neonate O. centrina from the south-eastern Adriatic Sea, caught by a Montenegrin commercial trawler. Scientific observers were present on-board and collected the specimen, which was subsequently analysed in the laboratory. The specimen was 225 mm long (TL), weighed 59.6 g and had an unhealed umbilical scar. To date, records of this species in the Adriatic Sea have comprised of both adult and older juvenile individuals, but no records of neonates were found in the published literature. In this work, the basic biological observations of the specimen are reported.

Length-Weight Relation of the Angular Rough Shark, Oxynotus centrina (Linnaeus, 1758) in the Mediterranean Sea

Oxynotus centrina is considered a rare or uncommon shark species throughout its distribution range. Because of this reason, it is one of the 46 uncommon elasmobranchs in the Mediterranean Sea, which requires filling the knowledge gaps, such as length-weight relations. Based on the analysis of 34 angular rough sharks, the length-weight relations (LWR) of males, females and combined sexes of O. centrina were described as W = 0.216L2.686, W = 0.134L3.041 and W=0.102L3.173, respectively. Total lengths (TL) of females and combined sexes were strongly correlated with total weights (TW); while TL of males was moderately correlated with TW. The b values of LWRs of females and combined sexes (3.041 and 3.173, respectively) were not significantly different from 3.0 (t-test, p>0.10) and indicated positive allometric growth for the examined TL and TW range of O. centrina in the Mediterranean Sea.

The occurrence and feeding of a critically endangered shark species, Oxynotus centrina in the Sea of Marmara.

The angular roughshark, Oxynotus centrina (Linnaeus, 1758), is a rarely encountered deep-sea demersal shark species. It is listed as "Critically Endangered" in the IUCN's regional assessment for the Mediterranean. Like other sharks and rays, the angular roughshark is subject to by-catch in demersal trawl and longline fisheries. This study contributes new knowledge on (a) its occurrence, size and sex information; and (b) its feeding ecology in the Sea of Marmara. Data were collected on total length (TL), total weight (TW) and sex from unpublished research survey reports performed intermittently from 1994 to 2020. According to the data, O. centrina was mainly recorded from the muddy sand bottom type in the southwest region of the Marmara Sea, which has higher biodiversity of macrobenthic species than other regions. Different methodological approaches were conducted to understand its feeding, such as DNA metabarcoding and isotope analysis to identify its prey spectra and assign a trophic level. Sampled specimens were full of liquid in their stomachs without any discernible visually identifiable prey items. The metabarcoding analyses were also unsuccessful in identifying any prey items. Trophic position calculation based on nitrogen isotope in muscles highlighted that O. centrina has the highest trophic position compared to the other sharks and rays in the Sea of Marmara. Although it was found mainly feeding on polychaetes and sipunculids species from previous studies, the δ15 N values made the authors cautious about the possibility of this species feeding on low trophic-level benthic invertebrates. Because the authors could not observe the presence of shark vitellus in the stomachs and could not succeed in DNA identification for prey, this study highlights high δ15 N values similar to top predators for O. centrina. The authors conclude that this species strategically feeds mainly on shark eggs to fulfil its nutritional requirements with minimum energy expenditure in line with its slow-moving behaviour and mouth morphology.

Marmara Denizi'nde Fanyalı Uzatma Ağlarına Yakalanan Kritik Tehlike Altındaki Domuz Köpek Balığının (Oxynotus centrina (Linnaeus, 1758) Bazı Morfometrik Özellikleri

Angular rough shark is a rare occurrence and one of the critically endangered species. In this study, angular rough shark caught as bycatch with trammel nets was investigated in the Southern coasts of the Marmara Sea, Turkey. The weight of this species, which was caught in these nets, was measured as 212 gr due to the degradation by parasites. The actual weight before degradation was determined as 2623 gr from the length-weight relationship formulation. Morphometric measurements of the species were performed and compared with previous studies. As a result, the population structure and biology of critically endangered species, such as limited information about angular rough shark as bycatch in fisheries should be investigated. Fishing methods will prevent catching angular rough sharks are improved and their survival should be ensured through appropriate protective measures.

New technologies can support data collection on endangered shark species in the Mediterranean Sea

In the last 50 yr, shark populations showed steep declines in the Mediterranean Sea. The IUCN lists most Mediterranean species as threatened (55%), while considering 27.5% of them Data Deficient. Here, sharks are currently one of the rarest and more elusive groups of animals, and data from fisheries and scientific monitoring still insufficiently support robust abundance and distribution assessments. New technologies can fill this data gap by linking people and scientists through new monitoring strategies. SharkPulse, an international collaborative project, aims at creating a large world database of shark occurrence records by mining images on the web, social networks, and private archives. Here we analyzed 1186 sharkPulse records from the Mediterranean Sea. We collected records to characterize spatio-temporal patterns on 37 species, highlighting distribution changes for 5, and, by using generalized linear models, estimating trends in sighting for the most abundant species. With 273 records, Hexanchus griseus had the most sighting records since the beginning of the series. We identified pupping areas and aggregation sites for immature Prionace glauca and Isurus oxyrinchus; pinpointed strongholds of the Critically Endangered Squatina squatina to focus conservation efforts; and identified broader than previously reported regional distribution ranges for Alopias superciliosus, Dalatias licha, Heptranchias perlo, H. griseus, Oxynotus centrina, and P. glauca. We confirmed that fishing is still the major threat for Mediterranean sharks and call for a greater effort in controlling the emerging patterns with efficient conservation effort indexes. If properly standardized, opportunistic data can efficiently and cost-effectively advance our understanding of shark abundance, distribution, and conservation status.

Contemporary records of the rare and critically endangered angular rough shark, Oxynotus centrina (Linnaeus, 1758), from the eastern Adriatic Sea.

The angular rough shark, Oxynotus centrina (Linnaeus, 1758), is a poorly known and rare bathydemersal shark inhabiting continental shelves and upper slopes with a significant lack of data and rarely published records in the Adriatic Sea in this century. In this paper, we present 20 new occurrences recorded from May 2015 to September 2021, of which 19 are in Croatian and one in Montenegrin territorial waters. Records of juveniles, subadults and adults are reported. Higher number of records off the Kornati archipelago in the central Adriatic Sea suggest that this area is of particular importance for this species. Furthermore, habitats in the Southern Adriatic might have lower density. Due to the nonsystematic research and nonprobabilistic data collection, it is difficult to establish whether the greater number of records in the continental shelf is just an ostensible phenomenon.

Bio-Ecological Features Update on Eleven Rare Cartilaginous Fish in the Central-Western Mediterranean Sea as a Contribution for Their Conservation.

Cartilaginous fish are commonly recognized as key species in marine ecosystems for their fundamental ecological role as top predators. Nevertheless, effective management plans for cartilaginous fish are still missing, due to the lack of knowledge on their abundance, distribution or even life-history. In this regard, this paper aims at providing new information on the life-history traits, such as age, maturity, reproductive period, in addition to diet characteristics of eleven rare cartilaginous fish inhabiting the Central-Western Mediterranean Sea belonging to the orders Chimaeriformes (Chimaera monstrosa), Hexanchiformes (Heptranchias perlo and Hexanchus griseus), Myliobatiformes (Aetomylaeus bovinus and Myliobatis aquila), Rajiformes (Dipturus nidarosiensis and Leucoraja circularis), Squaliformes (Centrophorus uyato, Dalatias licha and Oxynotus centrina) and Torpediniformes (Tetronarce nobiliana), useful for their assessment and for future management actions. Particularly, the present paper provides for the first time the age estimation of D. nidarosienis and L. circularis which were both found capable of becoming older than ten years. In addition, the present study updates the sizes of first maturity of C. uyato and D. licha, which appeared to be capable of reproducing earlier than what was previously hypothesized, representing very valuable information for a better understanding of these rare species populations status and, eventually, their conservation. On the basis of the stomach content analysis, it was possible to identify five different predator groups.

Oxynotus centrina (Oxynotidae) from the Tunisian coast (Mediterranean Sea)

The authors report in the present paper the capture of two specimens of a rare shark, angular rough shark Oxynotus centrina (Linnaeus, 1758), from the northern coast of Tunisia. A first specimen was a juvenile female caught off Ras Jebel, the second specimen was a juvenile male caught off Kelibia. These captures occurred after two decades in the area where it appears that the species is not totally exctincted. The Mediterranean distribution of O. centrina appears to be different according to the region, absent from the coast of France, specimens were still sporadically caught in the Adriatic Sea, and mainly in the Aegean Sea and the eastern Basin.

Swordfish or Shark Slice? A Rapid Response by COIBar-RFLP.

Market transparency is in strong demand by consumers, and the authentication of species is an important step for seafood traceability. In this study, a simple molecular strategy, COIBar–RFLP (cytochrome oxidase I barcode–restriction fragment length polymorphism), is proposed to unveil commercial fraud based on the practice of species substitution in the swordfish trade. In particular, COI barcoding allowed the identification of the species Prionace glauca, Mustelus mustelus, and Oxynotus centrina in slices labeled as Xiphias gladius. Furthermore, the enzymatic digestion of COI amplicons using the MboI restriction endonuclease allowed the simultaneous discrimination of the four species. Interestingly, an intraspecific differential MboI pattern was obtained for the swordfish samples. This pattern was useful to differentiate the two different clades revealed in this species by phylogenetic analyses using several molecular markers. These results indicate the need to strengthen regulations and define molecular tools for combating the occurrence of fraud along the seafood supply chain and show that COIBar–RFLP could become a standardized molecular tool to assess seafood authenticity.

Occurrence and tissue distribution of perfluoroalkyl substances (PFASs) in sharks and rays from the eastern Mediterranean Sea

Persistent organic pollutants (POPs), including Perfluoroalkyl substances (PFASs), enter into the marine ecosystem, raising questions on possible adverse effects caused to the health of marine organisms and especially of top predators. Thus, there is an urge to assess the occurrence and the tissue distribution of PFASs in apex predators. To this end, the current study examines concentrations and distribution of 15 PFASs among 85 samples of different tissues from 9 shark and ray species collected in Greece. The results showed a similar PFAS pattern among the different tissues, with long carbon chain PFASs being the most frequently detected compounds. PFTrDA was the most predominant compound in terms of concentration and frequency of detection, followed by PFUnDA and PFOS. PFTrDA concentrations ranged between < LOQ and 27.1 ng/g ww, while PFUnDA and PFOS levels ranged from <LOQ to 16.0 and < LOQ to 21.6 ng/g ww, respectively. Regarding their frequency of detection, PFTrDA and PFUnDA were detected in 98% and 91% of the samples, respectively, while PFOS was detected in 79%. ΣPFAS concentrations in each analysed tissue ranged from 0.3 to 85 ng/g ww, with the latter being detected in the liver of angular roughshark (Oxynotus centrina). On average, PFASs were found to be accumulated in tissues in the following order: gonads > heart > liver ≈ gills > muscle. Relative contribution (%) of individual compounds to ΣPFAS concentration varied among the different shark tissues, and also among the different shark species. No correlation between PFASs levels in tissues and sharks’ gender, length and geographical origin was observed.

Observations on the biological traits of the rare shark Oxynotus centrina (Chondrichthyes: Oxynotidae) in the Hellenic Seas.

New records of the rare angular rough shark Oxynotus centrina from the Hellenic Seas are presented. Its occurrence is reported for the first time in the Corinthian Gulf. Some aspects of the species' biology are described and compared with previous studies.

Angular roughshark Oxynotus centrina (Squaliformes: Oxynotidae) in captivity feeding exclusively on elasmobranch eggs: an overlooked feeding niche or a matter of individual taste?

A specimen of angular roughshark Oxynotus centrina has been kept successfully in captivity for the first time. Over a period of 24 months, the specimen preyed exclusively on the contents of elasmobranch egg cases, suggesting a specialized trophic niche.

Size at maturity of Mediterranean marine fishes

In this review we collected data on the length at maturity (Lm) and maximum reported total length (Lmax) of 565 Mediterranean marine fish stocks, representing 150 species, 68 families, 24 orders and 3 classes. Overall, Lm ranged from 2 cm, for the males of the toothcarp Aphanius fasciatus, to 350 cm, for the females of the bluntnose sixgill shark Hexanchus gris- eus .L m was positively linearly related with Lmax for Actinopterygii (logLm =- 0.123 ? 0.92 9 logLmax; r 2 = 0.87, n = 471, P \ 0.001) and Elasmobranchii (logLm =- 0.008 ? 0.922 9 logLmax; r 2 = 0.90, n = 92, P \ 0.001) with the two slopes being signif- icantly different (ANCOVA: F = 2,904, P \ 0.001). The reproductive load (Lm/Lmax) ranged between 0.23 (sand steenbras Lithognathus mormyrus) and 0.94 (angular roughshark Oxynotus centrina and thornback ray Raja clavata). The mean Lm/Lmax was signifi- cantly (ANOVA, F = 34.14, P \ 0.001) lower for Actinopterygii (mean = 0.59, SD = 0.122, n = 471) compared to Elasmobranchii (mean = 0.70, SD = 0.132, n = 92) and Holocephali (mean = 0.77, SD = 0.077, n = 2). The Lm/Lmax was significantly (ANOVA, F = 43.80, P \ 0.001) higher for species providing some form of parental care, i.e. guarders, bearers, nesters (mean Lm/Lmax ± SD = 0.68 ± 0.141, n = 111) compared to non-guarders (mean Lm/Lmax ± SD = 0.59 ± 0.123, n = 454). The mean Lm/Lmax displayed a remarkable constancy with longi- tude (northern and southern Mediterranean coastline: ANOVA, F = 0.01, P = 0.93), latitude (western, cen- tral and eastern regions: ANOVA, F = 1.25, P = 0.29) and habitat (ANOVA, F = 0.85, P = 0.51).

Abundances of Demersal Sharks and Chimaera from 1994-2009 Scientific Surveys in the Central Mediterranean Sea

Bibliographic and data gathered in scientific bottom trawl surveys carried out off the Southern Coasts of Sicily (Mediterranean Sea), from 1994 to 2009 and between a depth of 10 and 800 m, were analysed in order to prepare a checklist of demersal sharks and chimaera, which are species sensitive to fisheries exploitation. Out of the 27 previously reported demersal shark and chimaera taxa in the Mediterranean, only 23 were found in literature and 20 sampled during the surveys in the investigated area. Among the species sampled in the surveys, only 2 ubiquitous ( Squalus blainville and Scyliorhinus canicula ) and 3 deep-water ( Chimaera monstrosa , Centrophorus granulosus and Galeus melastomus ) species showed a wide geographical distribution with a consistent abundance. Excluding the rare (such as Oxynotus centrina ) or uncommon shark (e.g. Squalus acanthias ), the estimated frequencies of occurrence and abundance indexes show a possible risk of local extinction for the almost exclusively (e.g. angelshark, Squatina spp.) or preferential (e.g. Scyliorhinus stellaris ) neritic species.

Classification of Sharks in the Egyptian Mediterranean Waters Using Morphological and DNA Barcoding Approaches

The identification of species constitutes the first basic step in phylogenetic studies, biodiversity monitoring and conservation. DNA barcoding, i.e. the sequencing of a short standardized region of DNA, has been proposed as a new tool for animal species identification. The present study provides an update on the composition of shark in the Egyptian Mediterranean waters off Alexandria, since the latest study to date was performed 30 years ago, DNA barcoding was used in addition to classical taxonomical methodologies. Thus, 51 specimen were DNA barcoded for a 667 bp region of the mitochondrial COI gene. Although DNA barcoding aims at developing species identification systems, some phylogenetic signals were apparent in the data. In the neighbor-joining tree, 8 major clusters were apparent, each of them containing individuals belonging to the same species, and most with 100% bootstrap value. This study is the first to our knowledge to use DNA barcoding of the mitochondrial COI gene in order to confirm the presence of species Squalus acanthias, Oxynotus centrina, Squatina squatina, Scyliorhinus canicula, Scyliorhinus stellaris, Mustelus mustelus, Mustelus punctulatus and Carcharhinus altimus in the Egyptian Mediterranean waters. Finally, our study is the starting point of a new barcoding database concerning shark composition in the Egyptian Mediterranean waters (Barcoding of Egyptian Mediterranean Sharks [BEMS], http://www.boldsystems.org/views/projectlist.php?&#Barcoding%20Fish%20%28FishBOL%29).

Historical and contemporary records of the angular rough shark Oxynotus centrina (Chondrichthyes; Oxynotidae) in Turkish waters

During the last 58 years, only 12 angular rough sharks were recorded in Turkish waters. Rare captures of the species in the area needs an immediate action for the conservation of O. centrina. To protect the habitat of O. centrina, strict regulations should be implemented for diving in the localities, where the angular rough sharks occur regularly. Protecting the habitat of the angular rough shark is an urgent need before subjecting O. centrina to 100% protection in the seas of Turkey.