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Modifying the design and selectivity of commercial fishing gears can reduce unwanted catches. Most gear selectivity research focusses on trawl gears, and there are relatively few examples of modified static nets, such as gill and trammel nets, which are used all over the world. Fishers operating in the southeast England’s common sole (Solea solea) static net fishery wanted to explore methods to try to reduce the unwanted catches of thornback ray (Raja clavata). In 2017, the fishery had common sole landings of 343 tonnes making it an important local fishery. The largest port, the beach launch port of Hastings, is the home port for 65 vessels. Here we describe the performance of a modified trammel net with reduced mesh size in the two outer walls, intended to reduce catches of thornback rays without reducing the landings of the target species of common sole. There no published studies on modifying the outer meshes of a trammel net. The fieldwork was undertaken onboard a vessel from Hastings, fishing over ten days. The catches from a standard gill net, a standard trammel net and a modified trammel net were compared. Six fleets of nets were fished, each made up of five different net sections. The three net designs were placed into the fleets in a random set design. All of the net designs had a minimum (inner) mesh size of 90 mm. There was no statistically significant difference in the number of thornback ray caught between the nets but the number of common sole was estimated at 87 % higher by value in the modified trammel net compared to the other nets. Therefore, when using the modified trammel net, considerably less fishing effort was required to catch the same quota of common sole, but with no increase in the rate of thornback ray catches. If this design were to be applied more widely in this fishery, it could reduce overall catches of thornback ray. The study shows the difference in selectivity towards common sole, plaice (Pleuronectes platessa), whiting (Merlangius merlangus) and thornback rays between a gill net and two trammel net designs.

Numerous studies over the last decades have focused on marine protected areas (MPAs) and their effects on fish communities. However, there is a knowledge gap regarding how species that live associated with soft-substrates (e.g., sand, mud) respond to spatial protection. We analyzed abundance, biomass and total lengths of the soft-bottom fishes in a multiple-use MPA in the north-eastern Atlantic, the Luiz Saldanha Marine Park (Portugal), during and after the implementation of its management plan. Data were collected by experimental fishing in areas with three different levels of protection, during the implementation period and for three years after full implementation of the MPA. Univariate analysis detected significant biomass increases between the two periods. Fish assemblages were mainly structured by depth and substrate, followed by protection level. Community composition analyses revealed significant differences between protection levels and between the two periods. Species exhibited a broad variation in their response to protection, and we hypothesize that factors such as species habitat preferences, body size and late maturity might be underlying determinants. Overall, this study provides some evidence of protection effectiveness in soft-bottom fish communities, supported by the significant increase in biomass in the protected areas and the positive trends of some species. project LIFE-BIOMARES [LIFE06 NAT/P/000192]; project BUFFER (ERA-Net BiodivERsA); company SECIL-Companhia Geral de Cal e Cimento S.A.; FCT-Foundation for Science and Technology [CCMAR/Multi/04326/2013, SFRH/BD/80771/2011]; Foundation for Science and Technology [SFRH/BD/80771/2011]; 2012 Sesimbra Scientific Prize

Predator avoidance is fundamental for survival and it can be particularly challenging for prey animals if physical movement away from a predatory threat is restricted. Many sharks and rays begin life within an egg capsule that is attached to the sea bed. The vulnerability of this sedentary life stage is exacerbated in skates (Rajidae) as the compulsory ventilatory activity of embryos makes them conspicuous to potential predators. Embryos can reduce this risk by mediating ventilatory activity if they detect the presence of a predator using an acute electrosense. To determine how early in embryonic life predator elicited behavioral responses can occur, the reactions of three different age groups (1/3 developed, 2/3 developed, and near hatching) of embryonic thornback rays Raja clavata were tested using predator-type electric field stimuli. Egg capsules were exposed to continuous or intermittent stimuli in order to assess varying predator-type encounter scenarios on the ventilatory behavior of different developmental stages. All embryos reacted with a "freeze response" following initial electric field (E-field) exposure, ceasing ventilatory behavior in response to predator presence, demonstrating electroreceptive functionality for the first time at the earliest possible stage in ontogeny. This ability coincided with the onset of egg ventilatory behavior and may represent an effective means to enhance survival. A continuous application of stimuli over time revealed that embryos can adapt their behavior and resume normal activity, whereas when presented intermittently, the E-field resulted in a significant reduction in overall ventilatory activity across all ages. Recovery from stimuli was significantly quicker in older embryos, potentially indicative of the trade-off between avoiding predation and adequate respiration. © 2015 Wiley Periodicals, Inc. Develop Neurobiol 76: 721-729, 2016.

Thornback ray muscle hydrolysates (TRMHs) prepared by treatment with proteases from Bacillus subtilis A26 (TRMH-A26), Raja clavata crude alkaline protease extract (TRMH-Crude), Alcalase (TRMH-Alcalase) and Neutrase (TRMH-Neutrase) were elaborated and their antioxidant properties and angiotensin I-converting enzyme (ACE) inhibitory activities were tested. TRMHs showed different degrees of hydrolysis (DH from 11 to 22%) and hydrophobic/hydrophilic peptide ratio. Protein content varied from 71 to 74%. Gly, Pro, Asp and Asn were the most prominent amino acids, while hypoxanthine was the major nucleotide related compound present. The antioxidant activity was assayed using various tests. TRMH-Neutrase exhibited the highest antioxidant activity in DPPH scavenging, reducing power and inhibition of β-carotene bleaching tests. However in the total antioxidative efficacy, TRMH-Crude exhibited the highest activity. TRMH-Crude and TRMH-Neutrase were the most potent to prevent DNA oxidation by Fenton reagent. Concerning anti-ACE activity, TRMH-A26 and TRMH-Neutrase exhibited the highest activity with 87% at 5 mg/ml. The results revealed that TRMHs could be employed as a protein source in food additive processing or diets for aquatic organisms and other farmed animals. Biological significance The present study explores for the first time the elaboration of enzymatic hydrolysates from thornback ray R. clavata . The hydrolysates are well characterized and showed an interesting protein content as well as the presence of nucleotide related compounds, essential amino acids and taurine, which make them an interesting source of fish meal in aquaculture feeds. The hydrolysates were found to exhibit ACE inhibitory activity and antioxidant activity. The hydrolysates could serve also as a potential protein source for functional foods.

Thornback ray skin gelatin has been hydrolyzed with two different proteases in order to obtain peptides with ACE inhibitory and antioxidant activity. Hydrolysates with protease from Bacillus subtilis A26 (TRGH-A26) displayed ACE inhibitory activity with an IC 50 value of 0.94 μg/μL whereas Neutrase® hydrolysate from Bacillus amyloliquefaciens (TRGH-Neutrase) showed an IC 50 value of 2.07 μg/μL. Regarding antioxidant activity, IC 50 values of 1.98 and 21.2 μg/μL in TRGH-A26 and TRGH-Neutrase, respectively, were obtained using the DPPH radical-scavenging assay. The most active fractions identified by size-exclusion chromatography were further purified by RP-HPLC and analysed using nanoESI-LC–MS/MS to identify the sequence of the peptides. APGAP was the most active peptide inTRGH-A26 for ACE inhibitory activity with an IC 50 value of 170 μM, whereas GIPGAP showed the best ACE inhibitory activity in TRGH-Neutrase sample with an IC 50 value of 27.9 μM. The highest antioxidant activity was identified in peptide AVGAT, showing a 33% of activity at 3 mg/mL using the DPPH radical-scavenging assay. The obtained results proved the potential of thornback ray skin gelatin hydrolysates as a source of bioactive peptides. Statement of significance This study describes a peptidomic approach for the identification of ACE-inhibitory and antioxidant peptides generated from thornback ray gelatin ( Raja clavata ) hydrolysates from Bacillus subtilis A26 and Bacillus amyloliquefaciens Neutrase® enzymes and expose the potential of thornback ray gelatin hydrolysate as a source of bioactive peptides. In this sense, the decrease of systolic blood pressure is one of the main measurements considered in public health for the treatment of cardiovascular diseases, stroke and even end-stage renal disease. Traditionally, synthetic drugs such as captopril and enalapril have been used as ACE inhibitors despite their secondary effects, but the finding of new sources for the generation of natural bioactive peptides such as thornback ray muscle results is very important in the knowledge of less hostile but highly effective antihypertensive peptides as well as the development of new uses for waste and by-products generated from marine products, helping to solve the already existing environmental problem affecting this industry.

Mature specimens of the cestode Echinobothrium typus van Beneden, 1849 from the thornback ray Raja clavata Linnaeus, 1758 that inhabit the Black Sea are found and described in detail for the first time. New details of the scolex armature and reproductive system structures of E. typus are revealed. Infection indices of this cestode in the thornback rays are analyzed. It is shown that the occurrence of E. typus in the definitive host Raja clavata depends not only on the presence and the population density of the intermediate host, presumably, amphipods Perioculodes longimanus Bate et Westwood, 1868, but also on the age-related changes in the food spectrum of the thornback rays.

This study provides a parasitological analysis of the elasmobranch species caught in the northern and central Adriatic Sea. Sixty-two marine leeches were recorded on 747 individuals of Raja clavata Linnaeus, 1758 (thornback ray), Myliobatis aquila Linnaeus, 1758 (common eagle ray), and Torpedo marmorata Risso, 1810 (marbled torpedo ray) caught in 56 hauls over a 5 yr period. All leeches were identified as Pontobdella muricata, which is a typical ectoparasite of benthic elasmobranchs. The prevalence of infection ranged from 7.11% on R. clavata to 12.00% on M. aquila. The intensity of infection, the preferential sites of attachment to the host, and the periodicity of infection were evaluated.

Discards survival probability in conventional commercial 80 mm pulse fisheries was assessed for undersized plaice (Pleuronectus platessa n=558), sole (Solea solea n=274), turbot (Scophthalmus maximus n=111), brill (Scophthalmus rhombus n=90), thornback ray (Raya clavata n=99) and spotted ray (Raya montagui n=23). In total nine sea trips were performed on three commercial pulse-trawlers with three trips per trawler. Sea trips were spread out over the year to account for potential seasonal variation in discards survival. All test-fish were randomly collected from the end of the sorting belt at both the start and end of the catch-sorting process from multiple hauls per sea trip. Reflex impairment and damages were assessed for all test-fish and summarized in a vitality index score indicating fish condition. Test-fish were housed in four custom-built monitoring units installed on board. Each unit contained 16 24L tanks. Numbers of fish housed per tank were five (plaice, sole), three (turbot, brill) and one (rays) fish per tank. Tank water was continuously renewed with sea water at a rate of at least one tank volume per hour to maintain proper water quality. Survival was monitored and dead fish were removed upon detection. Upon arrival in the vessel’s home port, monitoring units were taken from board and transported to and placed in a climate controlled room to continue survival monitoring for two more weeks. The total monitoring period ranged from 15 to 18 days among test-fish depending on the day of collection at sea. In the climate controlled room, tank bottoms were covered with coarse sand and fish were fed natural food. Control-fish, fish of the same species and in good condition collected in advance at sea, were deployed during all sea trips (30-35 control plaice, 10 control sole, 3 control turbot and brill, 2 control thornback ray, 2 control spotted ray per sea trip). Control-fish were treated equally as test-fish to separate fisheries related mortality from mortality caused by the experimental procedures. Discards survival probabilities were estimated from counts of surviving fish at the end of the monitoring period.Within all species, discards survival probabilities varied among sea trips. Discards survival probability estimates and their 95% confidence intervals (95%CI) based on all sea trips combined were 14% (95%CI 11-18%) for plaice, 19% (95%CI 13-28%) for sole, 30% (95%CI 20-43%) for turbot, 13% (95%CI 7-23%) for brill and 53% (95%CI 40-65%) for thornback ray. For spotted ray discards survival probabilities of 21% and 67% were observed during two sea trips. Given the agreement with a previous and comparable study and the large number of observations collected year-round, we consider the current results for plaice and for sole to represent the actual overall survival probability of undersized plaice and sole discards in the 80 mm pulse-trawl fisheries. The discards survival probability estimates for turbot, brill and thornback ray are based on limited numbers of observations per species. These estimates should therefore be considered and treated as a first indication of the actual discards survival probability for these species in the 80 mm pulse-trawl fisheries. Collection of more data should narrow down the current 95% confidence intervals and give more precise estimates for the survival probability. We expect however that these more precise estimates lie within the current 95% confidence intervals for the survival probability estimates.In all species tested, discards survival was strongly affected by fish condition, with large differences in survival probability between fish in best and worst condition. The proportion of fish in the best condition is small and their high survival probability has little effect on the survival probability of the entire population in the catches. We therefore recommend that measures aimed at increasing discards survival focus on improving the condition of discarded fish. Since catch-processing time seems to have no effect on fish condition nor discards survival, we recommend that measures aimed at improving the condition of discarded fish focus on the fish capture process rather than catch processing.

Studying demographic and genetic connectivity can help assessing marine meta-population structure. Rays and skates have no larval phase hence population connectivity can only result from active movement of individuals. Using thornback ray (Raja clavata) in European waters as a case study, demographic and genetic connectivity were studied for 11 putative populations for unequal population abundances and two hypotheses of dispersal rates. Genetic simulation results highlighted three large meta-populations: in the Mediterranean, around the Azores and on the Northeast Atlantic shelf. Demographic results highlighted a finer population structure indicating that several pairs of putative populations might be demographically linked. Results were highly sensitive to dispersal assumptions and relative population abundances, which provided insights into the potential magnitude of genetic and demographic connectivity differences. Accounting for demographic connectivity appears to be crucial for managing and conserving rays and skates while genetic connectivity provides a longer term perspective and less subtle spatial structures. Moreover, accounting for heterogeneity in population abundances is a key factor for determining or interpreting meta-population connectivity.

This investigation aims to fill gaps in our understanding of the intestinal immune cells of elasmobranchs. Whole digestive tracts of fifteen thornback ray Raja clavata were provided by a trawl fleet from the Gulf of Asinara (Sardinia, western Mediterranean Sea). Histochemical, immunohistochemical and ultrastructural observations were conducted on the spiral intestine. Three types of granular cells were identified; type I in epithelium, types II and III in lamina propria-submucosa, with each of them containing cytoplasmic granules with different ultrastructural characteristics. Data on size and density of each granular cell type are provided. Immunostaining of intestinal sections showed the reactivity of the granular cells: type I cells were positive for lysozyme, mast cell tryptase and tumor necrosis factor-ɑ based on antibody staining; type III cells were immune-reactive to anti-interleukin 6 antibody, whilst type II cells were negative to all the antibodies used. Comparison of each granular cell type with immune cells of teleosts or mammals and an hypothesis on their nature and function are reported. A potential role for granular cells in intestinal cellular immunity is also discussed with respect to type I and type III cells having similarities to Paneth cells and neutrophils, respectively.

Using living animals in school lessons makes it possible for students to have an emotionally charged learning experience. With the example of Thornback rays (Raja clavata), the emotional affects of sea animals on students are investigated. Theoretical aspects can be found in the explanation of activity-oriented teaching, which is organised holistically and student-active. The preparation for and confrontation with the thornback ray was successfully adjusted to the individual needs of the students. The students collectively worked on research issues and the ray was presented as a research object. Besides the emotional adventures of touching a living ray, the students took notes of the most important growth characteristics of the ray. Hence the students encounter the ray as a living animal on different levels. To check the hypotheses of how a living animal influences the students’ emotional state, the PANAS questionnaire is applied. PANAS serves as a snap-shot of the students’ emotional state. Whilst there are no differences found concerning the negative affects, the positive affects show a significant difference between a lesson with and a lesson without a real object. If the lesson comprises a real object, the item attentive is chosen significantly more often than in a lesson without real objects. Additionally, the data was analysed with a t-test, whereat the students in the framework of an activity-oriented lesson show significantly more positive affects compared to a lesson without real objects. The study gives a comprehensive insight into the different emotions of students when confronting them with a real object.

The diet of Raja clavata (Thornback Ray) was studied in 2008–2009 in Sigacik Bay in the eastern Mediterranean, based on 187 stomach contents obtained by commercial trawl operations. 40 different prey species were found. Mysidacea, Parapenaeus longirostris and Plesionika sp. were the most abundant prey items. The results indicate that the main prey varies considerably depending on the ecological characteristics of the habitat.

Potential utilization of skin by-product from thornback ray ( Raja clavata ) was investigated. Gelatin from alkali-pretreated skin was extracted without or with pepsin at pH 2.0 in 0.2 M acetic acid or 0.1 M glycine-HCl buffer. The addition of pepsin increased the yields of gelatin. Indeed, the yields of gelatin from thornbach ray obtained with pepsin treatment was about 30%, while those obtained in acetic acid or glycine-HCl buffer were 18.32% and 23.01%, respectively. The characteristics and functional properties of thornback ray gelatin (TRGP), obtained by treatment with 5 units of pepsin/g of skin in glycine-HCl buffer, were investigated and compared with halal bovine gelatin (HBG). TRGP had high protein content (90 g/100 g) similar to halal bovine gelatin (HBG). TRGP had a molecular weight (170 kDa) lower than HBG (226 kDa) and imino-acids content lower than HBG (10 and 22 residues per 100 residues, respectively). Its gel strength (140 g) was lower than that of HBG (260 g), possibly due to lower hydroxyproline content. Textural properties showed that the values hardness, elasticity, cohesiveness and chewiness of TRGP were lower than those of HBG. The functional properties of TRGP were examined in comparison to HBG. TRGP showed stronger ability to clarify apple juice than bovine gelatin. The nutritional component of clarified apple juice was practically not changed. As expected, the different origin and extraction process of HBG and TRGP influenced the properties of the corresponding gelatin solutions.

Abundance trends and distribution patterns from 1902 to 1932 for 7 elasmobranch species in the German Bight (eastern central North Sea) were analyzed and compared to survey trends for 1991 to 2009. Abundances of thornback ray Raja clavata, common skate Dipturus batis, smoothhound Mustelus spp., tope shark Galeorhinus galeus, and spiny dogfish Squalus acanthias declined and common skate was extirpated, while abundances of starry ray Amblyraja radiata and lesser spotted dogfish Scyliorhinus canicula increased. A meta-population approach was devel- oped to analyze connectivity in terms of the surrogate parameter Crepresenting donor population Nj, separation distance Di,j, and migration range parameter α. As populations declined, connectiv- ity between sub-populations was lost before resident populations finally collapsed. The loss of connectivity was caused by both a loss of sub-populations and a subsequent increase in the dis- tance separating the remaining sub-populations. For lesser spotted dogfish, an increase in the donor population fostered the establishment of a local sub-population after 2000. For starry rays, an apparent increase in Nj due to a concentration of the donor population near the study area increased connectivity with the local sub-population. The interpretation of local abundances in terms of meta-population dynamics demonstrates the importance of seasonally resolved survey information for conservation planning.

Food and feeding strategy of the thornback ray, Raja clavata, were studied from stomach contents analysis of specimens caught monthly in the Gulf of Gabes. The data were analysed according to sex, size and season. At total of 1280 stomachs was examined, from specimens ranging from 14 to 110 cm total length (TL), of which 1076 (83.98%) contained food. Thornback ray feed mainly on teleosts, crustaceans and cephalopods, whereas gastropods and polychaetes are occasionally consumed. Significant differences were found between the diets of males and females; however, ontogenetic changes were also detected, with crustaceans constituting the greatest proportion of the diet of smaller rays. Both teleosts and cephalopods increased in importance with growth of the skates. Prey diversity increased with size; large and mobile prey species were more commonly found in the diet of larger skates. Diet composition showed seasonal variations. Quantitative analyses and graphical methods indicate that the thornback ray is a generalist feeder.

The thornback ray Raja clavata is one of the most abundant bycatch species of trawl fishing in the waters of the Gulf of Gabes, but little is known about its life history in this area. The present study provides the first data on age and growth of this species in Tunisian waters, as well as additional data on its reproduction. The age of individuals was estimated by counting growth bands on central vertebral sections. Marginal increment and edge analysis supported the hypothesis of annual deposition of growth bands, with the opaque band formed during autumn. The parameters estimated from von Bertalanffy and Gompertz growth functions showed differences between sexes. The oldest thornback ray female was aged 15 years (104 cm TL), whereas the oldest male was 12 years (89 cm TL). Variations in the gonadosomatic and hepatosomatic indices of both sexes and the presence of vitellogenic activity in mature females during the year indicated that the species cannot be considered to be a continuous spawner. Males were found to mature between 55 and 75 cm TL, whereas females matured between 72.4 and 85 cm TL. The TL at which 50% of the population reached maturity was 67.44 and 81.42 cm for males and females, respectively. Males and female thornback rays mature, respectively, at approximately 5.3 and 7 years old.

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).

An exceptionally well-preserved specimen of a batoid from the Turonian (Late Cretaceous) of Morocco has been named as †Tingitanius tenuimandibulus, sp. nov. The fossil has been identified as a member of the Platyrhinidae and represents the oldest known example of a thornback ray. Mechanical and acid preparation of the ventral surface has revealed the general body form of the specimen and permitted teeth and three morphotypes of dermal denticles to be extracted. Computed tomographic (CT) scanning of the chondrocranium and thoracic region has allowed the detailed study of the skeletal elements concealed within the rock. The phylogenetic position of the new specimen and implications for the phylogenetic positions of the ‘rhinobatoids’ are discussed. †Britobatos, gen. nov., is erected to accommodate †Raja primarmata which is here shown to be a sister taxon to the Platyrhinidae including †Tingitanius. It is likely that reassessment of isolated batoid teeth from the Cretaceous and Paleogene will confir...

Three albino skate specimens (Rajidae) were captured from the North Sea and English Channel between 2008 and 2011. Using DNA barcoding (COI gene) and morphometric analyses, species were identified as a spotted ray Raja montagui, a blonde ray Raja brachyura and a thornback ray Raja clavata. This finding represents the first record of full albinism (a lack of skin and retinal pigmentation) in rajid species.

Proximate chemical composition and fatty acid (FA) profile of different parts and sexes of ray (Raja clavata) were compared. The proximate values of liver samples significantly differed from other body parts (p < 0.05). Pectoral fin had the highest moisture, protein, and ash contents (78.6, 20.5, and 1.2%, respectively). The highest fat content (39.7%) was observed for liver samples. A significant variation was also observed between sexes in terms of proximate and FA values (p < 0.05). The levels of saturated (SFA), monounsaturated (MUFA), and polyunsaturated fatty acids (PUFA) varied between 27.1–32.1, 14.9–19.0, and 34.3–39.5%, respectively, in total fatty acid methyl esters (FAME). The highest total PUFA and docosahexaenoic acid (DHA) values were observed in the edible portion of liver for both sexes due to high contents of fat, despite the low values of % total FAME in comparison with other body parts. Significant variations among FA levels were observed for different body parts (p < 0.05). The highes...

The abundance, occurrence, biological features, growth and mortality parameters of the thornback ray, Raja clavata L. 1758 (Rajformes, Rajidae), coming from two contiguous areas of the Strait of Sicily (Central Mediterranean Sea) were analysed in order to discriminate the stocks. The two investigated areas include bottoms off southern Sicily (I-G16) and bottoms further at large (O-G16). The density indexes, biomass indexes and occurrences were substantially lower in I-G16 than O-G16. On the contrary, the biological traits were more similar, although significant differences were detected in the sex ratio, in the median total length of all specimens, in the length frequency distribution, in the estimated maximum length and in the female length-weight slope parameter. The median length of fully mature specimens did not significantly differ between the two areas. The von Bertalanffy’s asymptotic length and the ratio of total mortality/von Bertalanffy’s curvature parameter suggest a total mortality higher in the I-G16 than the O-G16 populations. This article supports the hypothesis that the investigated populations, in spite of a similar original life cycle, have evolved in two distinct unit stocks as a consequence of the different fishing efforts and the low-intermingling rate between the two areas.

In Portuguese waters, thornback ray Raja clavata spawns mainly between May and January, although females and males in spawning condition are found throughout the year. The maturation process can be divided into three main phases by using information on gonad weight, oviducal gland and uterus width in females and on gonad weight, clasper length and sperm duct width in males. Females attain length-at-first-maturity at 784 mm and males at 676 mm, at ages of 7.5 and 5.8 years, respectively. In females larger than length-at-first-maturity, a resting stage was identified characterized by low gonadosomatic index and well-developed oviducal glands and uteri. These results along with the low proportion of adult females that are effectively reproducing per month demonstrated that the thornback ray cannot be considered a continuous spawner as described in other studies. Fecundity was determinate with about 35 eggs released per batch. During the spawning season, a total of four batch episodes occur indicating that the total fecundity was approximately 136 eggs per female. Regional differences may exist in the reproductive strategy of the species, namely on the duration of the spawning season, length-at-first-maturity, and fecundity, which can be related to a more intense fishing pressure in northern European waters.

The effects of different processing methods (marinated and smoked) on proximate compositions and fatty acids of thornback ray (Raja clavata) and spiny dogfish (Squalis acanthias) were investigated. Total lipid content was 3.39% in thornback ray and 5.90% in spiny dogfish. The lipids of raw fish consisted mainly of polyunsaturated fatty acids in thornback ray and saturated fatty acid in spiny dogfish. The n−3/n−6 ratio of thornback ray (3.78) was higher compared to spiny dogfish (2.87). After processing, water content decreased significantly while crude protein, lipid, and ash contents increased in both fishes. In general, processing techniques significantly (p < 0.05) affected fatty acid fractions; in both species, SFA content increased, MUFA and PUFA content decreased. In addition, after processing n−3/n−6 ratios increased although total n−3 and n−6 contents decreased. The results indicated that heat treatment and acidic medium during processing had considerable affects on the proximate and fatty acid composition of the final products. Marinated and smoked products prepared from both fish species offer a balanced fatty acid composition for human nutrition. In terms of fresh and processed products, while the spiny dogfish appears to have a higher PUFA content, the thornback ray is a richer source of EPA + DHA.

Specimens of Raja clavata were monthly collected at the coast of Havaalani (Trabzon/Turkey) from January 2009 to December 2009 at depths between 20 and 40 m. A total of 230 individuals of thornback ray (131 females and 99 males) were collected by bottom trawls during research cruises. Using logistic regression, it was determined that TL at 50% maturity of males was 718 mm TL and of females 746 mm TL. The ovarian fecundity ranged from 27 to 60 yellow follicles in both ovaries. Females carrying egg cases were found in July and October. Variations in the gonadosomatic and hepatosomatic indices indicated a continuous reproductive cycle during the year.

There is a need for a unified terminology to describe reproductive phase assignment across fish taxa, regardless of the reproductive strategy involved. Reproductive terminology already adopted for teleosts has been applied to oviparous elasmobranchs of both sexes. A historical review of the terminologies used by previous authors and how these correspond to the new terminology is presented. Five reproductive phases are considered: immature, developing, spawning capable (which includes an actively spawning subphase), regressing, and regenerating. By using an oviparous elasmobranch, the thornback ray Raja clavata, as an example, the different phases are described based on both macroscopic and microscopic features of the reproductive tract, including the ovaries, oviducal glands, and uterus in females and the testes, claspers, and sperm ducts in males. The regressing phase was observed in females, but the regenerating phase was not; neither of these two phases was observed in males. Records from othe...

The marine leech, Stibarobdella moorei was collected from dorsal parts of the thornback ray (Raja clavata) and angelshark (Squatina squatina) (Elasmobranchii) captured by commercial trawl vessels as non-target species from depth of 50 meters of Antalya Bay which is located in the eastern Mediterranean coast of Turkey on April and July, 2013. The leeches caused two typical lesions on epidermal tissues of both hosts: the major lesion by oral sucker and a minor one by caudal sucker. The leeches were identified as Stibarobdella moorei which has not been reported from elasmobranches in the Turkey’s Mediterranean shores. This study represents new host and geographical records.

The most frequently caught skate species around Jersey include blonde ray Raja brachyura, undulate ray Raja undulata, small-eyed ray Raja microocellata and thornback ray Raja clavata. Between September 2006 and December 2008, a total of 814 individuals were tagged and released, of which 64% were small-eyed ray, 22.6% blonde ray and 12.4% undulate ray. The size distribution, sex-ratio and maturity of these samples are summarized. There were 138 reported recaptures (return rate = 17.1%), with most fish recaptured from the study area. Indeed, many of the tagged skates were recaptured within the same release area or within 20 km, indicating high site fidelity, with the longest distance travelled only 61 km. Thirteen fish were recaptured on multiple (2–4) occasions. To date the longest time at liberty has been 754 days. These results are discussed in relation to our current knowledge of the stock structure and exploitation of skates in the western English Channel.

The reproductive processes of chondrichthyans are complex. Knowledge of the development and maturation of the oviducal gland is vital for understanding the reproductive biology of a species. This study represents the first contribution of this subject for skates. In the oviparous thornback ray, Raja clavata, oviducal gland development begins early in the developing stage with the formation of gland tubules and the distinct lamellae of each zone: club, papillary, baffle and terminal. Oviducal development is complete by the end of the developing stage when the storage and secretion of products is evident within the gland tubules of each zone. Periodic acid-Schiff and alcian blue histological staining showed that the secretory mucous cells of the club and papillary zones produce neutral and sulfated acid mucins. The last row of gland tubules of the papillary zone stains intensely for sulfated acid mucins. The baffle zone, which is responsible for the production of the egg capsule, represented 60–80% of the glandular zone of the oviducal gland. Sperm bundles were observed in the deeper recesses of the baffle zone during the maturation process, and during capsule extrusion, sperm were detected near the lumen. The terminal zone was composed of two types of gland tubules: serous (producing protein fibres) and mucous glands (producing sulfated acid mucins).

Due to the impacts of commercial fishing on elasmobranchs, future research and management necessitates reliable and accurate information on life history. For females, maturity assessment is limited to dissection, and it is not desirable to be removing large numbers in order to assess the reproductive characteristics of a population. The present study evaluated ultrasonography as a potential, non-lethal method for assessing the maturity status of two oviparous elasmobranchs, the thornback ray (Raja clavata) and small-spotted catshark (Scyliorhinus canicula). Ultrasound permitted visualisation and measurement of the ovary in R. clavata, and the shell gland, ovarian follicles and egg capsules within the oviducts for S. canicula. With the exception of the ovary in R. clavata, the dimensions of these structures on the sonograms were directly corroborated by in situ measurements, and ultrasound was verified as an accurate and reliable method of making quantitative and qualitative assessments of these internal reproductive structures.

The effects of frozen storage of surimi produced from thornback ray and the washing of mince on the chemical composition were investigated. The crude ash content which was initially found as 1.38% in raw thornback ray decreased approximately 12 and 80% after the first and second washing, respectively. After the third washing, crude ash content increased to 207% of the amount in the second washing because of addition of salt to the last washing water. The crude protein content of mince also decreased approximately to 28 and 20% after the first and second washing, respectively. After the third washing, the decrease in the lipid levels was approximately 30%. At the end of 6 months of frozen storage at−23.8 ± 2C, dry matter, crude ash and crude protein contents increased in a greater ratio in surimi containing 4% sorbitol, 4% sucrose and 0.3% Na-tripolyphosphate than surimi prepared with 8% sorbitol and 0.3% Na-tripolyphosphate. PRACTICAL APPLICATIONS In the present study, the effects of frozen storage of surimi produced from thornback ray and the washing of mince on the chemical composition were investigated. Washing procedure significantly decreased crude ash, crude protein and crude fat content of mince. There were significant differences in moisture, crude ash, and crude protein contents during the 6 months storage period of frozen surimi obtained by using different cryoprotectant mixtures. The folding test scores were highest in fresh surimi and during the first two months of storage. Thornback ray can be used for the production of surimi.

Summary Population structure and distribution of the thornback ray, Raja clavata, L. 1758, in the northern and central Adriatic Sea were described based on data from bottom trawl surveys conducted in the area between 1996 and 2006 within the scope of the ‘MEDITS’ project. R. clavata was caught at depths between 23 and 270 m; highest abundance and density indices were recorded at a depth stratum 50–100 m. The sex ratio was close to 1 : 1. Length at first sexual maturity for both sexes was calculated. Length–weight relationships were obtained for males, females and the whole sample. Calculated parameters of the length–weight ratio showed a positive allometry for both sexes. The recent state of the population was compared with data from the 1948–49 ‘Hvar’ expedition. The comparison revealed that significant changes have occurred in distribution and abundance of R. clavata in the Adriatic Sea since the time of the ‘Hvar’ expedition. During the 1948–49 ‘Hvar’ expedition R. clavata was distributed throughout the entire continental shelf; during the 1996–2006 MEDITS expedition the species was found only in restricted areas and with much lower abundances. Significant changes also occurred in the demographic composition of the population. All described changes indicate an over-fishing of the thornback ray in the Adriatic Sea, a result of the high fishing intensity to which the species has been exposed for the past 60 years.

Species distribution maps are needed for ecosystem-based marine management including the development of marine spatial plans. If such maps are based on predictive models then modelling procedures should aim to maximise validation success, and any uncertainty in the predictions needs to be made explicit. We developed a predictive modelling approach to produce robust maps of the distributions of selected marine species at a regional scale. We used 14 years of survey data to map the distributions of plaice, sole and thornback ray in three hydrographic regions comprising parts of the Irish Sea, Celtic Sea and the English Channel with the help of the hybrid technique regression kriging, which combines regression models with geostatistical tools. For each species–region combination we constructed logistic Generalized Linear Models (GLMs) based on presence–absence data using the environmental variables: depth, bottom temperature, bed shear stress and sediment type, as predictors. We selected GLMs using the mean squared error of prediction (MSEP) estimated by cross-validation then conducted a geostatistical analysis of the residuals to incorporate spatial structure in the predictions. In general, we found that species occurrence was positively related to shallow areas, a bed shear stress of between 0 and 1.5 N/m 2 , and the presence of sandy sediment. Predicted species occurrence probabilities were in good agreement with survey observations. This modelling framework selects environmental models based on predictive ability and considers the effect of spatial autocorrelation on predictions, together with the simultaneous presentation of observations, associated uncertainties, and predictions. The potential benefit of these distribution maps to marine management and planning is discussed.

The feeding ecology of the thornback ray, Raja clavata, was studied based on the analysis of the stomach contents of specimens caught in the south-eastern Black Sea, Turkey, between May 2003 and January 2004. A total of 198 thornback rays were analysed to describe food habits and investigate the effect of sex, size and season on diet. Thornback rays fed mainly on teleost fish (especially red mullet, Mullus barbatus ponticus) and mud shrimp (Upogebia pusilla). Other prey included harbour crab, whiting, shrimp larvae and others. No differences were observed between dietary composition of males and females, but significant differences were found between size classes and seasons.

Serra-Pereira, B., Figueiredo, I., Farias, I., Moura, T., and Gordo, L. S. 2008. Description of dermal denticles from the caudal region of Raja clavata and their use for the estimation of age and growth. – ICES Journal of Marine Science, 65: 1701–1709. This work is a response to a lack of knowledge of the biology of Raja clavata in southern European waters, particularly in terms of age and growth. Two structures were analysed: dermal denticles and vertebral centra. Six types of dermal denticle were identified in the tail. Among those, small thorns were the most suitable for age determination owing to their fixed position, persistence throughout their lifespan, and defined growth-band pattern. Caudal thorns were more accurate than vertebral centra for age determination and were therefore selected as the most appropriate structure for ageing R. clavata. Based on edge analysis, annual band deposition was verified. The birthdate was established as 1 June based on the prevalence of hyaline edges in age-0 class specimens: prevalence peaked in May and June. Both von Bertalanffy and Gompertz growth models were fitted to age-at-length data, but the former was considered more appropriate based on similarity between the estimated L∞ and the maximum size recorded for the species. No significant differences in growth parameters were observed between sexes. The estimated growth parameters were L∞ = 1280 mm, k = 0.117 year−1, and t0 = −0.617 years. The maximum age estimated for R. clavata was 10 years, for a female of length 835 mm.

Edible marine species (fish, cephalopod molluscs, crustaceans) from the Adriatic Sea were analyzed for content in heavy metals (Hg, Cd and Pb) and polychlorinated biphenyls (PCBs). Health risks to human via dietary intake of seafood were assessed by the target hazard quotients (THQs) and the toxic equivalent factors (TEFs). Mercury maximum concentrations corresponded to fish (0.07-1.56 microg g(-1)w.w.), followed by cephalopod molluscs (0.10-0.55 microg g(-1)w.w.), and crustaceans (0.27-0.33 microg g(-1)w.w.). Cadmium levels in cephalopods (0.18-0.59 microg g(-1)w.w.) were higher than those in fish (0.01-0.05 microg g(-1)w.w.) and crustaceans (0.02-0.04 microg g(-1)w.w.), while for Pb the concentrations were generally low (fish: ND-1.18 microg g(-1)w.w., cephalopods: ND-0.17 microg g(-1)w.w., crustaceans: ND-0.03 microg g(-1)w.w.). For PCBs, concentrations in fish, cephalopods and crustaceans ranged between 141 and 3,406 ng g(-1)l.w., 190 and 542 ng g(-1)l.w., and 202 and 429 ng g(-1)l.w., respectively. Cd and Pb THQ values as well as estimates of PCB TEQ exposure indicated the absence of health risks through consumption of the various seafood. In contrast, mercury TEQs values due to consumption of certain fish species (albacore, rosefish and thornback ray) indicated that human health risk might be of concern.

Rays and skates are an unavoidable part of the by-catch in demersal fisheries. Over the past 40 years, the thornback ray (Raja clavata) has decreased in numbers and even disappeared in some areas, leading to concerns about genetic risk. For this reason, the effective population size (N-e), the migration rate (m) and temporal changes in the genetic diversity were estimated for the population of thornback rays in the Irish Sea and Bristol Channel. Using genotyped, archived and contemporary samples (1965 and 2003-2004), N-e was estimated at 283 individuals (95% CI = 145-857), m at 0.1 (95% CI 0.03-0.25) and the N-e/N ratio between 9 x 10(-5) and 6 x 10(-4). Although these results must be treated with caution, due to the small sample sizes, this is the first attempt to estimate N-e in an elasmobranch species. The low N-e/N ratio suggests that relatively few individuals contribute to the next generation. The combined effect of sex bias, inbreeding, fluctuations in population size and, perhaps most important, the variance in reproductive success may explain the low N-e/N ratio. In addition, the relatively high gene flow between Irish Sea population and other source populations is likely to have had an impact on our estimate, which may be more relevant at the metapopulation scale. No significant loss of genetic diversity was found over the 40-year timeframe and long-term maintenance of the genetic diversity could be due to gene flow.

A new cestode, Macrobothridium sinensis n. sp., is described from the spiral intestine of Platyrhina sinensis from coast of Xiamen, China. It is the first record of the order Diphyllidea in China. The new species can be distinguished from the 3 previously described species of Macrobothridium by the testes number (16-24 vs. 29-37, 27-46, and 5-6, in M. rhynchobati, M. euterpes, and M. syrtensis, respectively) and a single-row arrangement of testes; M. sinensis is most similar to M. euterpes in strobila length (1.77-6.23 vs. 2-4.5 mm) and number of segments (6-8 vs. 5-9). In addition, M. sinensis differs from M. rhynchobati and M. syrtensis in the strobila length, ovary shape, and number of apical hooks. The uterine pore is the first described in the Diphyllidea; thus, the present uterine pore can now be used to distinguish Macrobothridium from Echinobothrium and Ditrachybothridium in the Diphyllidae.

Summary The sensory determination of ammonia in raw, steamed and boiled ray wings using a scoring system appeared to be a valuable method of quality assessment. The borderline of acceptability was reached after 10 (±1) days in ice. A combination of the steaming and boiling tests (with addition of acetic acid and salt) was useful to confirm definite spoilage or to indicate the approach to the borderline of acceptability. The chemical determination of ammonia appeared to be a useful objective method in addition to the organoleptic tests. Thornback ray was borderline at a concentration of 60–70 mg N. From the other related parameters determined (urea, pH, redox potential, total bacterial count, α-amino nitrogen) only pH appeared to be of value.

The fatty acid and proximate composition in the flesh of thornback ray (Raja clavata, L. 1758) collected in the coast of Sinop in Turkey were evaluated. Proximate analyses of thornback ray are rich in protein (20.02%) and low in lipid (0.51%). The crude ash and moisture contents were found as 1.38% and 77.47%, respectively. The total SFA, MUFA and PUFA content were 48.27%, 13.98% and 24.10% of total fatty acids, respectively. Palmitic acid (C16:0, 26.45%) and stearic acid (C18:0, 10.62%) were the dominant saturated fatty acids. The major unsaturated fatty acids were determined as docosahexaenoic acid (C22:6 n3, 12.21%), oleic acid (C18:1, 8.88%) and linoleic acid (C18:2, 3.43%). The results of this study have showed that thornback rays are good sources of protein. The atherogenic index (AI) and index of throm- bogenicity (IT) were calculated as 2.37 and 0.63, respectively.

WOS: 000251083600007 PubMed: 17852470 Surimi was prepared from the thornback ray (Raja clavata L. 1758) and divided into two groups. The first group was prepared with 4% sorbitol, 4% sucrose and 0.3% sodium tripolyphosphate as a cryoprotectant, while surimi in second group was prepared with 8% sorbitol and 0.3% sodium tripolyphosphate. The frozen surimi samples were stored at -23.8 +/- 2 degrees C for 6 months. The total volatile basic nitrogen (8.40 mg/ 100 g for group A, 6.30 mg/100 g for group B), trimethylamine nitrogen (2.55 mg/ 100 g for group A, 2.38 mg/ 100 g for group B), thiobarbituric acid (1.29 mg malondialdehyde/100 g for group A, 1.17 mg malondialdehyde/100 g for group B), and pH values (7.34 for group A, 6.98 for group B) of surimi increased during frozen storage but remained within the acceptable limits. Total psychrophilic aerobic bacteria counts and sensory evaluation points in both groups decreased during frozen storage. The results of this study showed that thornback ray was found to be suitable for surimi production and the surimis were still acceptable at the end of the 6-month storage period.

How have North Sea skate and shark assemblages changed since the early 20th century when bottom trawling became widespread, whilst their environment became increasingly impacted by fishing, climate change, habitat degradation and other anthropogenic pressures? This article examines long-term changes in the distribution and occurrence of the elasmobranch assemblage of the southern North Sea, based on extensive historical time series (1902–2013) of fishery-independent survey data. In general, larger species (thornback ray, tope, spurdog) exhibited long-term declines, and the largest (common skate complex) became locally extirpated (as did angelshark). Smaller species increased (spotted and starry ray, lesser-spotted dogfish) as did smooth-hound, likely benefiting from greater resilience to fishing and/or climate change. This indicates a fundamental shift from historical dominance of larger, commercially valuable species to current prevalence of smaller, more productive species often of low commercial value. In recent years, however, some trends have reversed, with the (cold-water associated) starry ray now declining and thornback ray increasing. This shift may be attributed to (i) fishing, including mechanised beam trawling introduced in the 1960s–1970s, and historical target fisheries for elasmobranchs; (ii) climate change, currently favouring warm-water above cold-water species; and (iii) habitat loss, including potential degradation of coastal and outer estuarine nursery habitats. The same anthropogenic pressures, here documented to have impacted North Sea elasmobranchs over the past century, are likewise impacting shelf seas worldwide and may increase in the future; therefore, parallel changes in elasmobranch communities in other regions are to be expected.

One way to understand the mechanics by which angular movements of the head are transduced by the cupula-endolymph system of the semicircular canals is to monitor the output of this transduction as close to its site of origin as possible. This fact has led several vestibular neurophysiologists over the years to record the activity to a prescribed set of stimuli from primary neurons in the frog, the thornback ray, the cat, the squirrel monkey and, in the case of the present communication, the white king pigeon.

New information on distribution of marine leech, Pontobdella muricata (Linnaeus, 1758) is given here. One leech was observed on the dorsal surface of Thornback Ray, Raja clavata (Linnaeus, 1758) that was caught in 2013 in the Antalya, Turkey. This is a new record for the eastern Mediterranean coast of Turkey.

Population genetic structure of the thorny skate (Amblyraja radiata) was surveyed in > 300 individuals sampled from Newfoundland, Iceland, Norway, the Kattegat and the central North Sea. A 290-bp fragment of the mt cytochrome-b gene was first screened by SSCP. Sequences of SSCP haplotypes revealed 34 haplotypes, 14 of which were unique to Iceland, 3 to Newfoundland, 1 to Norway and 3 to the Kattegat. The global F-ST was weak but significant. Removal of the two Kattegat locations, which were the most differentiated, resulted in no significant genetic differentiation. Haplotype diversity was high and evenly distributed across the entire Atlantic (h = 0.8) with the exception of the North Sea (h = 0.48). Statistical parsimony revealed a star-like genealogy with a central widespread haplotype. A subsequent nested clade analysis led to the inference of contiguous expansion with evidence for long distance dispersal between Newfoundland and Iceland. Historical demographic analysis showed that thorny skates have undergone exponential population expansion that started between 1.1 million and 690,000 years ago; and that the Last Glacial Maximum apparently had little effect. These results strongly differ from those of a parallel study of the thornback ray (Raja clavata) in which clear structure and former refugial areas could be identified. Although both species have similar life history traits and overlapping ranges, the continental shelf edge apparently does not present a barrier to migration in A. radiata, as it does for R. clavata.

Many marine fish stocks worldwide are reported to be in decline and participants in recreational fisheries commonly complain that their catches are declining in size and number as a result. In many fisheries, however, it is difficult to investigate such claims because established data collection programmes are lacking. We sought to investigate perceived and actual trends in anglers’ trophy fish catches within a marine recreational fishery, and to investigate whether catches bore any relationship to abundance trends in target stocks. Temporal changes in catches, as perceived by participants in the recreational fishery, were assessed qualitatively using a structured survey. Subsequently we investigated two previously unused sources of sea anglers’ trophy fish catch data available for Wales, UK (national angling club and angling magazine reports) and extracted reports for a 27-year period. We assessed species-specific trends in the numbers and sizes of trophy fish reported, and found strong temporal declines in the numbers of trophy thornback ray Raja clavata and cod Gadus morhua reported, as well as a decline in total reported trophy fish. The weight of the heaviest thornback ray reported each year had also declined significantly with time. These trends also were most frequently mentioned by participants in the recreational fishery. Significant declines in cod and thornback ray stocks in the region have been reported, which would explain the reduction in anglers’ catches of trophy-sized individuals. As fishing pressure has been shown to reduce the numbers and sizes of individuals in a population we hypothesised that the numbers and sizes of trophy fish caught by anglers would correlate positively with stock abundance. In the absence of stock assessment data we used commercial landings-per-unit-effort (LPUE) figures to give a relative indication of stock abundance trends for the region. However, few correlations of trophy fish catch data with commercial LPUE were found, which is likely attributable to limitations of the LPUE data. Nevertheless, the negative trends in catches of trophy fish by anglers are striking and provide an additional means to monitor gross changes in populations of species vulnerable to over-exploitation.

The phylogeography of thornback rays (Raja clavata) was assessed from European waters, using five nuclear microsatellite loci and mitochondrial cytochome b sequences. Strong regional differentiation was found between the Mediterranean basin, the Azores and the European continental shelf. Allelic and haplotype diversities were high in Portuguese populations, consistent with the existence of a refugium along the Iberian Peninsula. Unexpectedly, high diversity was also found in the English Channel/North Sea area. The lowest genetic diversity was found in the Black Sea. Populations sampled from the Mediterranean, Adriatic and Black Seas were characterized by a single mitochondrial haplotype. This haplotype was also the most ancestral and widespread outside of the Mediterranean basin except for the Azores. Populations from the Azores were dominated by a second ancestral haplotype which was shared with British populations. Results from multidimensional scaling, amova and nested clade analysis indicate that British waters are a secondary contact zone recolonized from at least two refugia--one around the Iberian Peninsula and one possibly in the Azores. Links to a potential refugium known as the Hurd Deep, between Cornwall and Brittany, are discussed. Finally, a historical demographic analysis indicates that thornback ray populations started to expand between 580,000 and 362,000 years ago, which suggests that the Last Glacial Maximum (20,000 years ago) had mainly affected the distribution of populations rather than population size.

Sharks and rays are vulnerable to fisheries exploitation because of late maturation and low fecundity, highlighting the need for effective conservation strategies. Area closures have been proposed as an appropriate management option for thornback rays in the southern North Sea, where they appear to form local subpopulations between which there is limited mixing. To gain a fishery-independent estimation of stock distribution, 197 thornback rays Raja clavata tagged with electronic data storage tags (DST) were released in the Thames Estuary in 1999 and 2000. The tidal location method was used to estimate the positions of individual fish between time of release and recapture. The fishery-independent seasonal stock distributions were integrated with landings data and a simple model was developed to estimate monthly fishing effort per International Council for the Exploration of the Sea (ICES) rectangle by different fleets and gear types. The potential impacts of closed area management, in terms of reducing thornback ray mortality in the southern North Sea, were calculated. Spatial closures were applied either (i) as permanent closures of individual ICES rectangles or (ii) seasonally, at the level of the Thames Estuary. Catch reductions were calculated allowing for the redistribution of fishing effort. The results confirmed the importance of the Thames Estuary for thornback rays. However, 77% of rays moved outside the estuary over winter, with seasonal migration into the Thames to spawn between March and August. The effects of closures varied between areas and gear types. Permanent closures of individual ICES rectangles were less effective at reducing fishing mortality on rays than a spring or summer closure of the Thames Estuary as a whole, which would have a major impact on the commercially more valuable sole fishery. Synthesis and applications. The results presented illustrate the potential impacts of a range of closure scenarios, prior to their implementation, as a basis for advice on sustainable exploitation of thornback rays. These models could be further refined by additional studies of juvenile behaviour and of other ray subpopulations in the southern North Sea.