Squalus Blainville Research Articles

Bioecological lessons learned from the neonate longnose spurdogs Squalus blainville (Squaliformes: Squalidae) suggest a potential nursery ground in the Marmara Sea

The capture of 176 neonate longnose spurdogs Squalus blainville (Risso, 1827), suggests a potential nursery ground in the eastern Marmara Sea (GFCM GSA28). Sampling was performed by means of a scientific bottom trawl hauled at a depth range of 121-126 m on 21 February 2024. Available data show that S. blainville may be captured in demersal fishery within their first year of life. Total length (TL) and total weight (TW) of the examined males ranged from 169 to 279 mm (238.4±20.7 mm) and from 21.4 to 117 g (66.5±19.8 g), respectively. The TL and TW of the examined females ranged from 187 to 292 mm (241.1±25.3 mm) and from 30.1 to 146 g (66.8±29.2 g), respectively. A male neonate (TL=169 mm) examined is believed to be the smallest free-swimming longnose spurdog caught to date. Under current fisheries regulations, S. blainville is a protected shark species in the waters of Türkiye and therefore should be released if caught as bycatch. However, in addition to reducing fishing pressure on the species by prohibiting targeted fishing, area-based conservation actions, which are based on closing areas that are critical for chondrichthyans (e.g., nurseries) to fishing either on a year-round or seasonal basis, should now be included in the conservation plans for S. blainville and other protected species in Turkish waters.

Abnormal hermaphroditic shark Squalus blainville (Risso, 1826) (Chondrichthyes: Squalidae) from the Aegean Sea

Eighty-six specimens of longnose spurdog Squalus blainville were examined for determination of some bio-ecogical features. During the study, one of the specimens was determined as a hermaphrodite with a clasper and yolk sac formation. This very rare case in elasmobranch is a report of hermaphroditism recorded from the Aegean Sea.

Biology and Ecology of Squalus Blainville (Risso, 1827) from the Eastern Mediterranean

Biology and Ecology of Squalus Blainville (Risso, 1827) from the Eastern Mediterranean

Biological parameters and spatial segregation patterns in sharks from the North Aegean Sea, Greece

Context Sharks are frequently caught as bycatch in trawl fisheries in the North Aegean Sea. However, very little information exists on their biology and ecology in the area. Aims Biological parameters and spatial segregation of sharks in relation to size class, sex, depth and geographic location were examined. Methods Morphological characteristics and generalised additive models were used to explore biological traits and aggregating behaviour respectively, by using data from the Mediterranean International Trawl Survey between 2014 and 2021. Key results Overall, 7761 specimens were measured, with Scyliorhinus canicula, Galeus melastomus and Squalus blainville being the most common species. Scyliorhinus canicula was found in shallow coastal waters, whereas the remaining species were detected in deeper waters. Conclusions Females were larger and heavier than males and the weight–length relationships corroborated size differences between sexes in all species, whereas allometric growth did not share the same patterns as those from the Mediterranean Sea. Generalised additive models showed that the distribution of dominant species is bathymetric and geographically dependent. Additionally, the depth and geographic segregation patterns are highly associated with ontogeny and not sex. Implications These findings highlighted the importance of incorporating elasmobranch behavioural characteristics in the poorly developed management regulations in the North Aegean Sea.

First description of Chloromyxum squali Gleeson and Adlard, 2012 (Myxozoa) in the Mediterranean Sea in a new host Squalus blainville (Chondrichthyes: Squalidae): morphological, ultrastructural and phylogenetic data.

Chloromyxum squali Gleeson and Adlard, 2012 originally described from Squalus acanthias Linnaeus, 1758 is reported for the first time from the gallbladder of Squalus blainville (Risso, 1827) caught from the eastern coast of Tunisia. In the present study, this chloromyxid was described based on morphological and ultrastructural features combined with molecular analysis of 18S rDNA. Young plasmodia were found attached to the gallbladder, while mature plasmodia and myxospores were observed floating free in the bile. Mature plasmodia were polysporic, subspherical in shape, measured 97.8 ± 0.5µm long and 63.4 ± 0.4µm wide. Mature myxospores were ovoid with a pointed anterior end, measuring 10.2 ± 0.5µm long and 8.3 ± 0.5µm wide. Two asymmetrical shell valves adhered together along an S-shaped suture line. Each valve has 5-7 elevated surface ridges parallel to suture line. A bundle of long caudal filaments extended from the basal end of shell valves. Four pyriform polar capsules equal in size, measuring 3.1 ± 0.4µm long and 2.5 ± 0.3µm wide, were situated at the same level in the anterior pole of the myxospore, each with a polar filament coiled in 7-8 turns. Pairwise comparisons among the SSU rDNA sequences revealed significant similarity between Chloromyxum squali infecting S. acanthias with the sequence obtained in this study. Phylogenetic analysis revealed that C. squali clustered in the clade of Chloromyxum species infecting the gallbladder of marine Chondrichthyes. Chloromyxum squali showed a seasonal variation of prevalence with significantly higher prevalence noted in summer and in autumn and absence of infection in winter.

Abundance, distribution and reproduction of the Data-Deficient species (Squalus blainville) around Sardinia Island (central western Mediterranean Sea) as a contribution to its conservation

Data-Deficient (DD) species are currently under threat because of the paucity of information regarding their abundance, distribution and biological traits. In this study we analysed temporal trends and bioecological features of the DD shark, Squalus blainville. Biological and fishery data were collected through two different scientific surveys spanning 1994–2018 and commercial hauls around Sardinia Island (central western Mediterranean) from 2008 to 2018. The analysis of temporal trends based on abundance data revealed a significant population decline over time. The late attainment of maturity and low fecundity of S. blainville are suspected to have contributed to making it highly vulnerable to overfishing. No bathymetric segregation by sex and size was found. However, the almost exclusive presence of pregnant females south-west of Sardinia could be due to sexual spatial segregation. This is also supported by histological findings showing long-term sperm storage to ensure the persistence of the species when females and males are separated. The documented decline of this species, its low reproductive potential and similarities in the depth distribution of immature and mature individuals indicate the need for urgent protection plans for S. blainville in Sardinian waters.

Spatial variability of Chondrichthyes in the northern Mediterranean

Thanks to the availability of the MEDITS survey data, a standardized picture of the occurrence and abundance of demersal Chondrichthyes in the northern Mediterranean has been obtained. During the spring-summer period between 2012 and 2015, 41 Chondrichthyes, including 18 sharks (5 orders and 11 families), 22 batoids (3 orders and 4 families) and 1 chimaera, were detected from several geographical sub-areas (GSAs) established by the General Fisheries Commission for the Mediterranean. Batoids had a preferential distribution on the continental shelf (10-200 m depth), while shark species were more frequent on the slope (200-800 m depth). Only three species, the Carcharhiniformes Galeus melastomus and Scyliorhinus canicula and the Torpediniformes Torpedo marmorata were caught in all GSAs studied. On the continental shelf, the Rajidae family was the most abundant, being represented in primis by Raja clavata and then by R. miraletus, R. polystigma and R. asterias. The slope was characterized by the prevalence of G. melastomus in all GSAs, followed by S. canicula, E. spinax and Squalus blainville. Areas under higher fishing pressure, such as the Adriatic Sea and the Spanish coast (with the exception of the Balearic Islands), show a low abundance of chondrichthyans, but other areas with a high level of fishing pressure, such as southwestern Sicily, show a high abundance, suggesting that other environmental drivers work together with fishing pressure to shape their distribution. Results of generalized additive models highlighted that depth is one of the most important environmental drivers influencing the distribution of both batoid and shark species, although temperature also showed a significant influence on their distribution. The approach explored in this work shows the possibility of producing maps modelling the distribution of demersal chondrichthyans in the Mediterranean that are useful for the management and conservation of these species at a regional scale. However, because of the vulnerability of these species to fishing exploitation, fishing pressure should be further incorporated in these models in addition to these environmental drivers.

Trophic partitioning between abundant demersal sharks coexisting in the North Aegean Sea

AbstractWe examined the feeding ecology (diet, trophic width and trophic position) of five demersal shark species (Mustelus mustelus Linnaeus, 1758, Galeus melastomus Rafinesque, 1810, Scyliorhinus canicula Linnaeus, 1758, Scyliorhinus stellaris Linnaeus, 1758, Squalus blainville, Risso, 1826) coexisting in the north-eastern Aegean Sea (around Gökçeda Island) by combining stomach content and stable isotope analyses. The results indicate clear differences in diet between the five sharks. Cephalopods were mainly found in diet of S. stellaris and M. mustelus and the stomachs of G. melastomus, S. canicula and S. blainville included fish. S. blainville showed the highest trophic position in respect of stable isotope analysis (TPsia = 4.89) around Gökçeada Island. It was followed by G. melastomus (TPsia = 4.57). Direct isotopic values (both stable nitrogen and carbon) and isotopic niche width based on the Standard Ellipse Area (SEA) clearly differed among the five shark species. In particular, S. blainville was isotopically segregated from the other shark species studied, showing a narrow isotopic trophic niche and higher trophic level. In contrast, M. mustelus had the widest trophic niche of the five species studied. The niche width of S. stellaris was narrower than M. mustelus and S. canicula but wider than S. blainville and G. melastomus. SEA showed that G. melastomus has a specialized feeding strategy in the area. There is no overlap between S. canicula and S. stellaris in trophic width.

Diet and trophic level of the longnose spurdog, Squalus blainville (Risso, 1826) in the 25-nautical mile Fisheries Management Zone around the Maltese Islands

The longnose spurdog, Squalus blainville (Risso, 1826), is reported to feed on bony fishes, cephalopods and crustaceans but misidentifications have resulted in ambiguities. This study describes and quantitatively analyses the diet of S. blainville in waters surrounding the Maltese Islands and compares the results with other Mediterranean populations to identify any regional or temporal variation. Additionally, variations in dietary composition with season, maturity, size and sex are investigated for the Maltese population.The diet of 255 individuals, collected from the 25-nautical mile Fisheries Management Zone around the Maltese Islands, was characterised using frequency of occurrence, wet weight and numerical occurrence of food items for sex, maturity, size and seasonal categories. Mediterranean International Trawl Survey (MEDITS) data for the period 2007–2015,which was derived from samples collected within the Food and Agriculture Organisation of the United Nations’s (FAO) General Fisheries Commission for the Mediterranean (GFCM) Geographical Sub-Area 15 (GSA 15), were analysed to identify any relationship between sex, maturity and depth. S. blainville fed on prey items belonging to four main groups: Crustacea, Mollusca, Teleostei and Sipuncula.Mollusca had the highest % IRI (Index of Relative Importance) for the total sample (52.5% of the IRI) and second were teleosts (% IRI=41.4). In terms of habitat, 63.51% of the identified prey categories were demersal, followed by benthic (28.65%) and then pelagic prey categories (7.84%). The highest dietary overlap was observed between seasons, and between immature and mature females; least overlap was between mature and immature males. An increase in size results in more predation especially on cephalopods. Mature and immature individuals were recorded at all depths. Our results indicate that there is some variation in diet between sexes and between maturity stages both in prey items and in the relative contribution of benthic, demersal, and pelagic prey.

Biology and fisheries aspects of Western Longnose Spurdog, Squalus edmundsi from the Eastern Indian Ocean, Indonesia

Fahmi, Sentosa AR. 2017. Biology and fisheries aspects of Western Longnose Spurdog, Squalus edmundsi from the Eastern Indian Ocean, Indonesia. Biodiversitas 18: 1714-1722. A research has been done to determine some biological aspects of Western Longnose Spurdog (Squalus edmundsi) from the Eastern Indian Ocean Fishing Region in Indonesia (WPP 573). A total of 1797 samples were recorded from bottom longline fisheries at Tanjung Luar, Lombok from July 2015 to November 2016 by a trained enumerator. The study revealed that Selat Alas and the south west of Sumbawa waters are the most fished areas in the region for this species, with the peak fishing season may occur from January to March. The average catch rate of S. edmundsi was about 8 individuals per boat. The size of sharks varied from 470 mm to 1150 m total length (TL), with average size was 723.6±111.5 mm. Size distributions and sex ratio between females and males were significantly different, indicating a sexual dimorphism. This study revealed a fact that there was no seasonal pattern in the reproductive cycle of S. edmundsi in this region, which means the parturition may occur throughout the year. Analysis on its population status showed that this species was very susceptible to overfishing. This condition should be responded by the government through management actions for its fishery.

Cephalopod prey of two demersal sharks caught in the Aegean Sea (eastern Mediterranean)

This study concerns the cephalopod species that are part of the diet of the small-spotted catshark Scyliorhinus canicula and the longnose spurdog Squalus blainville sampled by commercial trawlers in the Aegean Sea from 2005 to 2012. Based on the examined cephalopod beaks, 15 species were identified belonging in six families of Teuthida, one of Sepiida and two of Octopoda. The diversity of cephalopod prey species was higher for S. canicula (N = 15) than for S. blainville (N = 10). Nektonic cephalopods comprised the majority (>72%) of the preyed species by both sharks, among which about 55% inhabit the demersal zone and 45% the mesopelagic. In the diet of S. canicula, the demersal squid Illex coindetii and the pelagic sepiolid Heteroteuthis dispar were equally represented composing 20% of prey specimens, followed by the small-sized squid Abralia veranyi and the demersal sepiolid Rossia macrosoma. The latter species was substituted in the diet of S. blainville by the demersal medium-sized octopod Scaeurgus unicirrhus, which with the equally represented three other species, composed 50% of the cephalopod prey. Differences observed between S. canicula and S. blainville in the condition of beaks retained in their stomach contents and in the variation of prey species diversity by predator specimen size, may imply differences in their foraging tactics (hunting for prey vs scavenging on the bottom), habitats and stomach evacuation frequency.

Diet and trophic level of the longnose spurdog Squalus blainville (Risso, 1826) in the deep waters of the Aegean Sea

Knowledge of the diet and trophic level of marine predators is essential to develop an understanding of their ecological role in ecosystems. Research conducted on the trophic ecology of the deep-sea sharks is rather limited. The purpose of this study was to examine the diet of the longnose spurdog Squalus blainville, a deep-sea shark categorized as “data deficient” within its distribution range, with respect to sex, maturity, age, season and sampling location. The stomach contents of 211 specimens, captured in the Aegean (off Skyros and the Cyclades Islands) and Cretan Seas, using commercial bottom-trawlers from 2005 to 2012, were analysed. The cumulative prey curve showed that the sample size was adequate to describe the species’ diet. The identified prey items belonged to five major groups: Teleostei, Crustacea, Cephalopoda, Annelida and Phanerogams. Higher diet diversity was observed in females compared to males, in immature individuals compared to mature ones, regardless of sex, and in spring and winter compared to other seasons. Age and sampling location seemed to influence both the diet diversity and trophic spectrum of the species. Feeding intensity based on the vacuity index was not significantly influenced by any of the factors examined, while the stomach filling degree was significantly influenced by all factors, except sex, showing significantly higher values in mature females compared to immature ones, in older individuals, in autumn compared to winter, and a significantly lower value in the Cyclades Islands compared to other locations. Females showed a significant larger mouth length compared to males of the same length, while no between-sex differences were found in gut morphometrics. The estimated fractional trophic level (TROPH=4.41) classified the species as carnivore with a preference for Teleostei and Cephalopoda, confirming its high trophic position.

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

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

Aging and life history traits of the longnose spiny dogfish in the Mediterranean Sea: New insights into conservation and management needs

Aging chondrichthyans has been characterized as a slow and difficult process, but at the same time it is considered of fundamental importance for the holistic management and conservation of their populations. This study aims to assess the age and growth of the longnose spurdog S. blainville, to correlate the results to the species’ biological features and to compare them with those reported in previous studies that used different aging methods. By counting the growth bands on the enamel surface of the dorsal fin spines, age was estimated in 569 out of 810 individuals that were taken as by-catch from commercial fisheries in the Mediterranean Sea during an 8-year period. Spine morphometrics revealed sexual dimorphism as far as spine length, spine base width and spine weight are concerned. The between-sex differences were also reflected in the length-weight relationships, in the gonadosomatic (GSI) and hepatosomatic (HSI) indices, and in the condition factor (K). All three somatic indices differed significantly among maturity stages, seasons or age classes. The reproducibility of the age readings was considered high based on the estimated CV and APE precision indices. Age bias plots also indicated no significant intra- and small inter-reader variation. The estimated VBGF parameters were: L∞=1097.3mm, k=0.03 yr−1 and t0=−5.58 yrs for females, and L∞=665.5mm, k=0.08 yr−1 and t0=−3.35 yrs for males. Likelihood ratio tests showed that all growth parameters were statistically significantly different between sexes (χ2=38.26, df=3, P<0.001). Females reached higher longevity (28 yrs) than males (22 yrs) and attained maturity at higher age and larger size (T50=17 yrs and L50=568.1mm) than males did (T50=11.3 yrs and L50=460.6mm). S. blainville seems to be a long-lived shark of slow growth and late maturity, a combination of traits indicating a species of great vulnerability to fishing pressure that can only sustain a low harvest rate.

Temporal dynamics of demersal chondrichthyan species in the central western Mediterranean

Event Abstract Back to Event Temporal dynamics of demersal chondrichthyan species in the central western Mediterranean Martina F. Marongiu1, Cristina Porcu1, Andrea Bellodi1, Alessandro Cau1, Antonello Mulas1 and Maria C. Follesa1* 1 University of Cagliari, Department of Life and Environmental Sciences, Italy The rapid expansion of fisheries and globalized trade are emerging as the principal drivers of coastal and ocean threat. Considering the important role of Chondrichthyes as predators at the top of food chain in marine ecosystems, knowledge on their biology remains scarce in the Mediterranean. In this regard, our objective is to give information on their spatial distribution, abundance and population structure. Data were collected for 25 demersal species, including batoid species, sharks and holocephalans from 1994 to 2013 during scientific bottom trawl surveys (MEDITS project) carried out around the Sardinian seas. The total frequency of occurrence (f%), the Biomass Index (BI, kg/km2), and the Density Index (DI, N/km2) were estimated for the continental shelf (10-200 m), slope (200-800 m), and overall (10-800 m) depth strata. Size trends were also calculated for the most abundant species considering all depth strata. The correlation among MEDITS figures (f%, BI, DI, size structure) and years were assessed by species computing the Pearson linear coefficient. From f% and abundance indexes investigation, only the small spotted catshark Scyliorhinus canicula and the thornback ray Raja clavata were ubiquitous in all strata investigated, instead, all the other species showed a preferential distribution for the shelf or the slope. In general, the temporal trends of BI and DI were stable or positive for both macro-strata, except for the longnose spurdog Squalus blainville which seemed to show a statistically significant decreasing trend. All analyzed species displayed temporal stable trends in size structure analysis, apart from Raja brachyura and Dipturus oxyrinchus that showed a statistically significant increase. Despite the time series analysis revealed stable or positive trends, it appears clear the need of urgent management measures to protect the demersal chondrichthyan species extending the monitoring over time and implementing the data collected by scientific and commercial trawl surveys. Keywords: chondrichthyans, distribution, abundance, population structure, Mediterranean Sea Conference: XV European Congress of Ichthyology, Porto, Portugal, 7 Sep - 11 Sep, 2015. Presentation Type: Poster Presentation Topic: Ecology, Conservation and Invasive Species Citation: Marongiu MF, Porcu C, Bellodi A, Cau A, Mulas A and Follesa MC (2015). Temporal dynamics of demersal chondrichthyan species in the central western Mediterranean. Front. Mar. Sci. Conference Abstract: XV European Congress of Ichthyology. doi: 10.3389/conf.FMARS.2015.03.00194 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 16 Nov 2015; Published Online: 02 Dec 2015. * Correspondence: Prof. Maria C Follesa, University of Cagliari, Department of Life and Environmental Sciences, Cagliari, 09126, Italy, follesac@unica.it Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Martina F Marongiu Cristina Porcu Andrea Bellodi Alessandro Cau Antonello Mulas Maria C Follesa Google Martina F Marongiu Cristina Porcu Andrea Bellodi Alessandro Cau Antonello Mulas Maria C Follesa Google Scholar Martina F Marongiu Cristina Porcu Andrea Bellodi Alessandro Cau Antonello Mulas Maria C Follesa PubMed Martina F Marongiu Cristina Porcu Andrea Bellodi Alessandro Cau Antonello Mulas Maria C Follesa Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

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.

Plastic debris ingested by deep-water fish of the Ionian Sea (Eastern Mediterranean)

Debris has been recognized as a global environmental problem including within deep habitats. From 26 fish species (1504 specimens) caught in the Eastern Ionian Sea during deep-water long-line surveys, plastic debris was found in 24 individuals of Galeus melastomus (3.2%) and single individuals of Pteroplatytrygon violacea, Squalus blainville, Etmopterus spinax, and Pagellus bogaraveo. The occurrence of debris among their food was infrequent. Ingested debris included primarily plastics (86.5%) and to a lesser extent pieces of metal and wood. Among ingested plastics, fragments of hard plastic material constituted the highest proportion (56.0%), followed by plastic bag fragments (22.0%), fragments of fishing gears (19.0%) and textile fibers (3.0%). Among the species with ingested debris, G. melastomus swallowed all debris categories; P. violacea and S. blainville ingested plastic bag fragments, whereas pieces of hard plastics were found in E. spinax and P. bogaraveo.

Age, growth, longevity, natural mortality and maturity of the longnose spurdog, Squalus blainvillei (Chondrichthyes: Squalidae), in the Gulf of Gabes (Central Mediterranean Sea)

Age, growth, longevity, natural mortality and size and age at maturity of the longnose spurdog, Squalus blainvillei, in the Gulf of Gabes (Tunisia, Central Mediterranean Sea) are reported. Marginal increment suggested annual band formation. Age estimates ranged from 3 to 15 and 4 to 19 years for males and females, respectively. Von Bertalanffy growth parameters derived from length at age data were: L-infinity = 105.7 cm, K = 0.11year(-1), t(0) = -1.12 year for females and L-infinity = 91.1 cm, K = 0.14 year(-1), t(0) = -1.42 year for males. Males and females reached maturity at 52.3 cm and 62.5 cm TL corresponding to 4.97 and 7.44 years, respectively. Longevity estimates were 24.75 and 31.50 years for males and females, respectively. Based on life history parameters, natural mortality estimation M ranged from 0.16 to 0.33.

Taxonomic research on &lt;i&gt;Squalus megalops&lt;/i&gt; (Macleay, 1881) and &lt;i&gt;Squalus blainvillei&lt;/i&gt; (Risso, 1827) (Chondrichthyes: Squalidae) in Tunisian waters (central Mediterranean Sea)

Two species of spurdog of the genus Squalus occur in the Gulf of Gabes (southern Tunisia, central Mediterranean): the longnose spurdog Squalus blainvillei (Risso, 1827) and a short-snout spurdog of the Squalus megalops-cubensis group. Morphometric and meristic data as well as a genetic analyses (DNA inter-simple sequence repeat markers and molecular barcoding methods) support the assignation of this short-snout spurdog to Squalus megalops (Macleay, 1881). Squalus megalops occurs commonly in temperate and tropical Australian waters, and is also thought to occur in the eastern Atlantic, southern Indian Ocean and western North Pacific although these records need to be confirmed. Our study confirms that it occurs in the Mediterranean Sea. Populations of both S. blainvillei and S. megalops are described based on Tunisian material.

Squalus formosus, a new species of spurdog shark (Squaliformes: Squalidae), from the western North Pacific Ocean

A new species of spurdog, Squalus formosus n. sp., from the lower continental shelf and upper continental slope off the coast of Taiwan and southern Japan, is described. It belongs to the 'highfin megalops group', the members of which share a short snout, high dorsal fins, robust dorsal spines, tricuspid denticles and a white posterior caudal margin. Squalus formosus is most similar to Squalus albifrons, a recently described species from eastern Australia, but differs in some morphological characters and fin colouration. Squalus formosus is sympatric with three other species of Squalus in Taiwanese waters, i.e. Squalus brevirostris, Squalus japonicus and Squalus mitsukurii, and can be readily distinguished from these in the following combination of characters: tall and upright first dorsal fin, with a tall and robust spine, short and bluntly pointed snout, white caudal-fin posterior margin and first dorsal fin with a white anterior margin parallel with dorsal spine. This new species was considered by some authors to be conspecific with Squalus blainville from the eastern Atlantic Ocean, but the results of this study reveal that it is probably endemic to Taiwan and southern Japan.