Mustelus Asterias Research Articles

Improving Marine Megafauna Knowledge with eDNA: A French Story

In the current context of large-scale biodiversity loss (Díaz et al. 2019), it is urgent to carry out biodiversity inventories in order to investigate spatial and temporal variations. Among the available methods, environmental DNA (eDNA) (Taberlet et al. 2018) combined with molecular metabarcoding (Valentini et al. 2009) bring new insights in drafting inventories of taxa present in an environment. Approaches based on eDNA facilitate the study of remote ecosystems and the detection of rare, cryptic or invasive species in a non-invasive way (Bohmann et al. 2014). In the marine realm, the study of mobile fauna, including mammals particularly, can greatly benefit from these new techniques. Here, we present a case study carried out in the northeast and northwest Atlantic, within the boundaries of marine protected areas. The Iroise Natural Marine Park*1 was the first French marine natural park created in France in 2007 (Fig. 1). The first campaign in the Iroise Natural Marine Park successfully detected several species of cetacean (e.g., Lagenorhynchus albirostris, Lagenorhynchus obliquidens) and four species of elasmobranchs (e.g., Scyliorhinus canicula, Torpedo marmorata, Raja undulata and Mustelus asterias). This study was extended to the Martinique Natural Marine Park*2, where similar analyses identified three cetacean species (Stenella attenuata, Lagenodelphis hosei and Tursiops truncatus) and 193 teleost taxa (Riou 2022), representing more than half of the species expected in Martinique. The analyses carried out in Martinique highlighted several remarkable sites for fish biodiversity. In Guadeloupe, in the heart of the Agoa Marine Mammals Sanctuary*3 (corresponding to the French Antilles exclusive economic zone), the taxonomic composition of different eDNA samples made in 2021 and 2022 was compared. The samples were analyzed using different primer sets, specific to vertebrates, teleosts and mammals. Comparison of the results obtained with vertebrate-specific primers and those specific to teleosts showed complementary results. For cetaceans, the analyses distinguished ten distinct cetacean taxonomic units and at least 3 distinct species from four samples. In addition, the eDNA samples were used to discriminate between the two recently recognised bottlenose dolphin ecotypes, based on the observation of a fixed nucleotide difference on the barcode targeted by the mammal-specific primers. New primers are currently being developed to make it easier to distinguish species of Delphinidae, which are still complex to identify. Environmental DNA and metabarcoding offer new possibilities for the inventories of marine megafauna and support adequate conservation decision-making processes. It is a major step towards better monitoring of marine mammal populations of the Atlantic Ocean. Moreover, our datasets will be freely available through open platforms following the FAIR (Findable, Accessible, Interoperable, and Reusable) principles.

Estimating the effects of recreational fisheries on sharks in the English Channel and adjacent seas using social networks

Recreational shark fishing in the English Channel and adjacent seas was analysed through the analysis of videos posted on social networks, which, for the first time, allowed us to assess which species in the area are the most affected by fishing techniques, the hotspots and the biological data of the species caught. Using this novel methodology, we found that recreational anglers target spotted and common smooth-hound sharks (Mustelus asterias and M. mustelus), particularly in French waters. Anglers also target the blue shark (Prionace glauca) and tope (Galeorhinus galeus), mainly in the waters of the United Kingdom (UK). Results show that recreational fishing has implications for the conservation of all these vulnerable species, and particularly for blue shark and tope since, respectively, 49% and 36% of the individuals of these two species caught were juveniles. Based on the results, we propose some recommendations to reduce fishing pressure on these species which should be implemented on a collaborative basis between France and UK for this shared resource.

First fossil record of Mustelus aff. punctulatus Risso, 1826: new evidence for a smooth-hound shark population in the Late Miocene North Sea Basin

Mustelus is a problematic genus in palaeoichthyology. Due to the scarcity of fossil teeth, relative homogeneity in tooth morphology and the lack of published extant dentitions, the early history of smooth-hound sharks remains poorly understood. Recently, two teeth were collected in the Tortonian Deurne Member (Diest Formation) near Antwerp (Belgium). Surprisingly, a detailed SEM-based comparison with the extant North-Eastern Atlantic species (Mustelus mustelus, Mustelus asterias, Mustelus punctulatus) allowed assigning the fossil teeth to Mustelus aff. punctulatus. Today, this species is largely restricted to the Mediterranean and lies at the very base of the placental Mustelus clade evolution. Until now, this species remained unrecognized in the existing fossil record. By (re)evaluating isolated teeth from other upper Miocene localities in the southern North Sea Basin, the existence of a widely distributed population of Mustelus aff. punctulatus for the late Serravallian and the Tortonian can now be postulated. Thereafter, the species disappeared from the North Sea. Until today, no single record of Mustelus punctulatus is known from the Mediterranean predating the Messinian Salinity Crisis. Therefore, it is hypothesized that the current populations have their origin in southward migration from northern, Atlantic populations, and this probably after the “Zanclean Flooding”.

Historical trophic ecology of some divergent shark and skate species in the Dutch coastal North Sea zone

Over the last century the fish community of the Dutch coastal North Sea zone has lost most its shark and skate species. Whether their disappearance has changed the trophic structure of these shallow waters has not been properly investigated. In this study historical dietary data of sharks and skates, being in the past (near)-residents, juvenile marine migrants and marine seasonal visitors of the Dutch coastal North Sea zone were analyzed for the period 1946–1954. Near-resident and juvenile marine migrant species were demersal while all marine seasonal visitors species were pelagic. Based on stomach content composition, the trophic position of four of the various shark and skate species could be reconstructed. The (near)-resident species, the lesser spotted dogfish, the marine juvenile migrant, the starry smooth hound, and the benthopelagic marine seasonal visitor, the thornback ray, had a benthic/demersal diet (polychaetes, molluscs and crustaceans), while the pelagic marine seasonal visitor, the tope shark, fed dominantly on cephalopods and fishes. Diet overlap occurred for fish (tope shark and lesser spotted dogfish), for hermit crabs (lesser spotted dogfish and starry smooth hound) and for shrimps (thornback ray and starry smooth hound). Trophic position ranged from 3.2 for thornback ray preying exclusively on crustaceans to 4.6 for the tope shark consuming higher trophic prey (crustaceans and fish). The analysis indicates that most of the shark and skate species were generalist predators. The calculated trophic positions of shark and skate species indicate that those species were not necessarily at the top of the marine ecosystem food web, but they might have been the top predators of their particular ecological assemblage.

Evaluation of the comprehensive feeding strategy and trophic role of overexploited mesopredator species in the Sea of Marmara (northeastern Mediterranean)

Mesopredator species play an essential role in balancing and sustaining ecosystems through their interactions with various species and with their habitats. In ecosystems that have been subjected to overfishing, it is essential to obtain information on the trophic ecology of such predators. Based on this motivation, this study aimed to investigate the feeding strategies and trophic roles of four demersal sharks (e.g., Mustelus mustelus, Mustelus asterias, Squalus acanthias, and Scyliorhinus canicula) by analyzing their stomach contents and using stable isotope (δ13C and δ15N) analysis. These shark species are subject to overfishing, and their landings have decreased by 98% over the last 18 years in the Sea of Marmara. The results demonstrated that interspecific differences in the main prey resources exist among those sharks. Mustelus mustelus and Mustelus asterias feed mainly on crustaceans, and their diets are very similar. However, Mustelus asterias utilizes a specialist feeding strategy while Mustelus mustelus utilizes a medium-state generalist strategy. Squalus acanthias occupies a high trophic level and mainly feeds on teleosts over both short and long time scales. The probability of isotopic niche overlap of Scyliorhinus canicula with the isotopic niches of S. acanthias was the highest (70.7%), which indicates that both species exploit similar food resources within the same environment. These results contribute to the knowledge of the ecological role of these highly vulnerable cartilaginous species and may help to improve conservation programs in the Sea of Marmara, a lesser-known part of the northeast Mediterranean.

Horizontal and vertical movements of starry smooth-hound Mustelus asterias in the northeast Atlantic.

Commercial landings of starry smooth-hound Mustelus asterias in northern European seas are increasing, whilst our knowledge of their ecology, behaviour and population structure remains limited. M. asterias is a widely distributed demersal shark, occupying the waters of the southern North Sea and Irish Sea in the north, to at least the southern Bay of Biscay in the south, and is seasonally abundant in UK waters. There are no species-specific management measures for the northeast Atlantic stock, and the complexity of its population structure is not yet fully understood. To address this issue, we deployed both mark-recapture and electronic tags on M. asterias to gain novel insights into its horizontal and vertical movements. Our data suggest that the habitat use of M. asterias changes on a seasonal basis, with associated changes in geographical distribution, depth utilisation and experienced temperature. We report the first direct evidence of philopatry for this species, and also provide initial evidence of sex-biased dispersal and potential metapopulation-like stock structuring either side of the UK continental shelf. Investigations of finer-scale vertical movements revealed clear diel variation in vertical activity. The illustrated patterns of seasonal space-use and behaviour will provide important information to support the stock assessment process and will help inform any future management options.

Sex differentiation in seasonal distribution of the starry smooth‐hound Mustelus asterias

This mark-recapture study of starry smooth-hound Mustelus asterias tagged during the summer months near the Dutch coast demonstrates a large-scale spatial sex differentiation in their circannual migration patterns and small-scale spatial sex differentiation during summer. Overwintering occurs in the North Sea, English Channel and Bay of Biscay, with significantly more males in the Northern North Sea and more females in the Bay of Biscay. During summer, sheltered sea arms off the Dutch coast were almost exclusively used by adult females. In subsequent summers post-release, both sexes were mostly confined to the Southern North Sea, suggesting philopatry.

Using Local Ecological Knowledge of Fishers to Reconstruct Abundance Trends of Elasmobranch Populations in the Strait of Sicily

Fishers “local ecological knowledge” (LEK) can be used to reconstruct long-term trends of species that are at very low biomass due to overfishing. In this study, we used historical memories of Sicilian fishers to understand their perception of change in abundance of cartilaginous fish in the Strait of Sicily over the last decades. We conducted interviews with 27 retired fishers from Mazara del Vallo harbour (SW Sicily) working in demersal fisheries, using a pre-defined questionnaire with a series of open and fixed questions related to the abundance of sharks and rays. The questionnaire included specific questions about the trends they perceived in catch or by-catch of cartilaginous fish abundance between the 1940s and 2000s compared to the present. Information was gathered for 18 species, including Carcharhinidae, mesopredatory demersal sharks (Squalidae, Hexanchidae, Centrophoridae, Oxynotidae, Triakidae, Scyliorhinidae and Squatinidae) and batoids. Overall shark catches were perceived to have diminished since the early 1940s: about 95% of fishers reported the decline of commercially important species (e.g. Mustelus spp.) and indicated species that could have been depleted or locally extinced (e.g. Squatina spp., Sphyrna lewini, Mustelus asterias, etc.). Our study shows that LEK of fishers can be beneficial for reconstructing long-term population trends of exploited species when traditional standard data on fisheries catch or species relative abundance from surveys is limited or only available for recent periods. The results obtained clearly indicate the rapid and alarming decline of elasmobranchs in the Strait of Sicily highlighting the need for urgent conservation measures to be adopted.

Diet composition of starry smooth‐hound Mustelus asterias and methodological considerations for assessing the trophic level of predatory fish

The stomach contents of 640 starry smooth-hound Mustelus asterias from the north-east Atlantic were examined. The diet was dominated by crustaceans (98.8% percentage of index of relative importance, %IRI), with the two main prey species being hermit crab Pagurus bernhardus (34% IRI) and flying crab Liocarcinus holsatus (15% IRI). Ontogenetic dietary preferences showed that smaller individuals [20-69 cm total length (LT ) n = 283] had a significantly lower diversity of prey than larger individuals (70-124 cm LT , n = 348); however, 18 prey species were found exclusively in smaller individuals and eight prey taxa were found exclusively in larger individuals. Larger commercially important brachyurans such as edible crab Cancer pagurus and velvet swimming crab Necora puber were more prevalent in the diet of larger individuals. Specimens from the North Sea ecoregion had a lower diversity of prey types for a given sample size than fish from the Celtic Seas ecoregion. Whilst cumulative prey curves did not reach an asymptote, this was primarily due to the high taxonomic resolution utilized and 95% of the diet was described by just seven crustacean taxa. The trophic level (TL) was calculated as 4.34 when species-level prey categories were used. This fine-scale taxonomic resolution resulted in a TL estimate close to a whole level above that estimated using wider taxonomic groupings. This large bias has important methodological implications for TL studies based on categorized prey data, particularly those of predatory fish.

Bycatch and discarding patterns of dogfish and sharks taken in English and Welsh commercial fisheries.

At-sea observer programmes can provide spatio-temporal data on the sizes and quantities of fish being either discarded or retained, including for species and size categories that may not be sampled effectively during scientific surveys. Such data were analysed for English and Welsh fisheries operating on the continental shelf of the North Sea ecoregion (ICES Divisions 4a-c and 7d) and Celtic Seas ecoregion (ICES Divisions 6a, 7a-c, e-k) for the period (2002-2016). These data were collated for four main gear types: beamtrawl, nephrops and otter trawls, and nets (including gillnets, tangle nets and trammel nets). Beamtrawlers caught proportionally more smaller individuals than otter trawlers, whilst nets were the most size-selective gear for larger sharks. Size-related discarding was observed, with smaller spurdog Squalus acanthias and starry smooth-hound Mustelus asterias (< 60 cm total length, LT ) usually being discarded. Such size-based selection was not evident for lesser-spotted dogfish Scyliorhinus canicula, which was generally landed as bait. Temporal changes in the discard-retention patterns were evident for S. acanthias and porbeagle Lamna nasus, with increased regulatory discarding as management measures became restrictive. A corresponding increase in the proportion of the non-quota M. asterias retained was also observed over the study period. Knowledge of the size-based discard-retention patterns by métier can also help inform on where future studies on discard survival could usefully be undertaken.

Long-term temporal and spatial changes in the richness and relative abundance of the inshore fish community of the British North Sea Coast

Changes in temporal and spatial composition of the British inshore North Sea fish community are reviewed. Sampling from the cooling water filter screens of power stations bordering the North Sea commenced in the early 1960s. To date, a total of 112 marine fish species have been recorded, a high proportion of the total inshore fish species complement of shallow North Sea British waters. The unrecorded top predators, such as large sharks, swordfish and tuna are not regularly observed in waters <20m deep. The greatest species number (92) is reported from fully marine waters in East Anglia. A group of 18 ubiquitous, high abundance, taxa form a core inshore community throughout the region in both estuarine and marine waters. They show a high level of concordance in relative abundance along the British east coast from the 1970s to the present. A second group of 20 species are abundant, but more restricted in habitat. Where they do occur, this group are usually always present and form together with the ubiquitous taxa the local core community. The third group of 67 species, are never abundant and are restricted in occurrence both spatially and temporally. Total species richness declines between 50 and 56°N, probably because high summer temperatures allow the southern North Sea to support summer migrants entering via the English Channel. Since the 1960s there has been a notable recovery in fish diversity and abundance in large industrialised estuaries such as the Thames and the Firth of Forth. Linked to spawning and nursery habitat gain, smelt, Osmerus eperlangus, and bass, Dicentrarchus labrax, have greatly increased in abundance. There is no evidence for a decline in species richness since the 1970s. However, elasmobranch species number has declined while two species Raja clavata and Scyliorhinus canicula have remained abundant and one, Mustelus asterias, has increased in abundance. It is argued that overexploitation and habitat destruction remain, as they have been for the last 300years, the most serious threats to the health of North Sea inshore fish communities. There are no clear signs that climate change is causing species loss, although it may be influencing relative species abundance as species at the southern edge of their range such as the viviparous blenny, Zoarces viviparous, have declined in the southern British North Sea. Power station water temperature records do not show a warming trend, in some estuarine locations temperature has declined with reduced thermal pollution; the temperature record cannot explain the observed major changes in fish relative abundance observed since the 1970s.

Redescription of Tripaphylus musteli (van Beneden, 1851) (Copepoda: Sphyriidae) and the relegation of Paeon Wilson, 1919 to synonymy with Tripaphylus Richiardi in Anonymous, 1878

Tripaphylus musteli (van Beneden, 1851) (Copepoda, Siphonostomatoida, Sphyriidae) is redescribed from an adult female collected from the branchial chamber of a starry smooth-hound, Mustelus asterias Cloquet (Carcharhiniformes, Triakidae), captured in the English Channel off Portland, UK. The new account of T. musteli is the first based on a complete adult female and highlighted the lack of a robust distinction separating Tripaphylus Richiardi, in Anonymous, 1878 and Paeon Wilson, 1919 prompting us to relegate Paeon to a junior subjective synonym of Tripaphylus. In the light of this synonymy the eight former species of Paeon are transferred to Tripaphylus as follows: T. ferox (Wilson, 1919) new combination, T. elongatus (Wilson, 1932) new combination, T. vassierei (Delamare Deboutteville & Nuñes-Ruivo, 1954) new combination, T. lobatus (Kirtisinghe, 1964) new combination, T. asymboli (Turner, Kyne & Bennett, 2003) new combination, T. versicolor (Wilson, 1919) new combination, T. australis (Kabata, 1993) new combination, and T. triakis (Castro Romero, 2001) new combination. Comparisons between terminology used in this report and that in the literature indicate that all transformed adult females of Tripaphylus probably possess a full complement of cephalic appendages and maxillipeds. All limbs, with the exception of the maxillae share a general morphological similarity to the corresponding appendages of conspecific males. The maxilla of the transformed adult female of Tripaphylus is a small digitiform protuberance associated with a swelling in some species.

Seasonal migration of the starry smooth-hound shark Mustelus asterias as revealed from tag-recapture data of an angler-led tagging programme.

The primary aim of this long-term angler-led tagging programme was to gain information about seasonal changes in distribution of the starry smooth-hound shark Mustelus asterias, along the Dutch coast for management and conservation purposes. Between 2011 and 2014, M. asterias comprised 92·6% (n = 2418) of the total elasmobranch catch (n = 2612) by the licenced group of taggers within the Dutch Delta of which 2244 M. asterias were fin-tagged with plastic rototags. Sex and total length (LT ) composition inside the eastern tidal basin (Oosterschelde) were significantly different, i.e. more females and larger individuals, than outside indicating a pupping ground, which was confirmed by the capture of 30 newborn pups (≤32 cm). The distribution pattern of reported recaptured M. asterias (return-rate 3·6%, n = 80) showed a circannual migration between summering in the southern North Sea and wintering in the English Channel and the Bay of Biscay, and suggests that M. asterias is philopatric. The Dutch angling season for M. asterias runs from approximately mid-May to mid-October when the water temperature is above 13° C. Recaptures of eight mature females, but no males in the Bay of Biscay, indicate partial spatial segregation by sex, where mature females migrate over larger distances than immature females and males. These observations, with the absence of recaptures in other known summering areas (i.e. the Irish Sea and Bristol Channel), suggest that the southern North Sea is used by a separate population. Implications for management and recommendations to improve and expand the study approach are discussed.

Diversity, phylogenetic relationships and host associations of Calliobothrium and Symcallio (Cestoda: ‘Tetraphyllidea') parasitising triakid sharks

The laciniate, relatively large-bodied tetraphyllidean tapeworm genus Calliobothrium van Beneden, 1850 parasitises triakid sharks with all but one species found parasitising sharks of the genus Mustelus Linck, 1790. Historically, species of this genus were thought to exhibit a relaxed degree of host specificity relative to species of their sister genus Symcallio Bernot, Caira, &amp; Pickering, 2015. However, several more recent studies have begun to question this difference and, in particular, the conspecificity of specimens identified as the types species, C. verticillatum (Rudolphi, 1819) van Beneden, 1850, from multiple host species. Our results suggest that diversity in the genus Calliobothrium has been under-reported. To explore this situation, specimens previously identified as C. verticillatum were collected from Mustelus asterias Cloquet, 1819 off the United Kingdom and Mustelus canis (Mitchell, 1815) off Connecticut, USA; these sharks each were found to host distinct species both of which are described here. Mustelus asterias was also confirmed to host Symcallio leuckarti (van Beneden, 1850) Bernot, Caira &amp; Pickering, 2015, which is redescribed. In combination with newly collected material from Mustelus palumbes Smith, 1957 off South Africa and data available from GenBank, molecular phylogenetic analyses based on 28S rDNA data for four of the seven known species of Calliobothrium, including both new species and five of the 11 known species of Symcallio, were conducted. The resulting phylogeny supports the mutual monophyly of the two genera, which are readily distinguished based on whether they exhibit proglottid laciniations, and supports subclades of Symcallio with and without hook accessory pieces. These subclades of Symcallio appear to exhibit an intriguing congruence with two known subclades of their host genus, Mustelus.

Reproductive characteristics and life-history relationships of starry smooth-hound Mustelus asterias in British waters.

The reproductive biology and other life-history parameters were investigated for Mustelus asterias in British waters, with specimens caught from both commercial fisheries and research-vessel surveys. In total, 504 specimens [238 males, 24-99 cm total length (LT) and 266 females, 28-124 cm LT] were examined, with further information collected from 238 uterine pups. The lengths at 50% maturity were estimated as 70·4 and 81·9 cm LT for males and females, respectively. Ovarian fecundity ranged from one to 28, and uterine fecundity from four to 20. The number, mass and LT of pups were positively correlated with maternal LT. Full-term pups ranged from 205 to 329 mm LT, and the smallest free-living fish caught was 24 cm LT . Parturition occurred in February in the western English Channel and during June to July in the eastern English Channel and southern North Sea, indicating either protracted spawning or asynchronous parturition for the stock as a whole. The reproductive cycle is thought to extend beyond 1 year. Developmental abnormalities observed included atresia in oocytes, uterine eggs that failed to develop, a partly developed pup and an abnormal male with a single aberrant clasper. Data relating to conversion factors, oocyte numbers and diameter and gonado-somatic and hepato-somatic indices are presented, and the seasonality of the reproductive cycle is discussed.

New Mediterranean Biodiversity Records (April, 2014)

According to reports, the following 16 species have extended their distribution to other Mediterranean areas or have made a new appearance in other regions. The first category includes the following organisms: The rare and common Indo-Pacific seaweed Codium arabicum (Lebanese coasts), the acari Thalassarachna affinis (Marmara Sea), and the non-indigenous nudibranch Flabellina rubrolineata, which has also been found in many other areas of the Aegean Sea. In addition, the rare sea slug Thecacera pennigera (Piccolo of Taranto), the fangtooth moray Enchelycore anatina (National Marine Park of Zakynthos, Ionian Sea), the carangid Seriola fasciata (Gulf of Antalya), Lagocephalus sceleratus (SE. Ionian Sea), the reticulated leatherjacket Stephanolepis diaspros (Slovenia, N. Adriatic Sea), the marbled stingray, Dasyatis marmorata (NE Levantine), the starry smooth-hound Mustelus asterias (Iskenderun Bay, NE Mediterranean), the cephalopod Ommastrephes bartramii (Ionian Sea) have also been reported. The Atlantic crab Dyspanopeus sayi has expanded to many Italian areas and the blue crab Callinectes sapidus to a lake in N. Greece and in the S. Adriatic Sea. Finally, Farfantepenaeus aztecus has been found in the Ionian Sea, thus showing its wide expansion in the Mediterranean. The larval stages of Faccionella oxyrhyncha have been found, after many years, in the Aegean Sea and the first report of an existence on intersexual acari Litarachna duboscqi in Split(Adriatic Sea) was reported.

Multiple paternity in the starry smooth-hound sharkMustelus asterias(Carcharhiniformes: Triakidae)

Multiple paternity was investigated in the starry smooth-hound shark, Mustelus asterias Cloquet, 1821. Analysis of 12 pregnant females and their embryos, at four microsatellite loci, showed that at least 58% carried multiply-sired litters. Paternal skew was observed, with one male siring most of the embryos within a litter, although no patterns of association were detected between the identity of the father and the size or the uterine position of the embryos. Sperm storage was observed in the oviducal glands of all twelve females. Results shed light on the complexity of reproductive strategies and selective processes in M. asterias. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 111, 119–125.

The First Documented Record of Genus Mustelus (Chondrichthyes: Triakidae) in the Black Sea

Two specimens of Starry smoothhound, Mustelus asterias Cloquet, 1821 were captured from three miles off the coast of Sile (south-western Black sea) on 19 November 2000 at a depth ca. 90 m. This paper is on the presence of M. asterias in the Black Sea.

Concentration of DL-PCBs in fish from market of Parma city (north Italy): Estimated human intake

The concentrations of 12 congeners of non-ortho and mono-ortho dioxin-like polychlorinated biphenyls (ΣDL-PCB) were measured in 30 fish samples from Parma markets by GC/MS technique. The samples were randomly purchased, choosing the species commonly found in supermarkets. The concentration of DL-PCBs estimated remained under the fixed Italian limit of 4 pg g −1 ww WHO-TEQ (World Health Organization–Toxic Equivalent) in the major part of the samples, so the situation seems to be not at a level sufficient to pose a risk to human health of the Parma population. The medium daily intake for DL-PCBs for Italian consumers (Parma) was also estimated. This value generally resulted minor than 2 pg g −1 ww WHO-TEQ kg −1 body weight, exceeding only in four cases: eel, smooth hound, starry smooth hound and tuna.

Reproductive biology of the starry smooth‐hound shark Mustelus asterias: geographic variation and implications for sustainable exploitation

Examination of the reproductive biology of Mustelus asterias in the north-east Atlantic Ocean highlighted apparent geographical variation in maturity, fecundity and ovarian cycle between Atlantic and Mediterranean populations. The stretch total length (L(ST) ) and age at 50% maturity for Atlantic males and females were estimated at 78 cm L(ST) and 4-5 years and 87 cm L(ST) and 6 years, respectively. Size at maturity of females was considerably smaller than in Mediterranean specimens (96 cm L(ST) ). Ovarian fecundity ranged from eight to 27 oocytes and uterine fecundity from six to 18 embryos. The gestation period was c. 12 months, followed by a resting period of c. 12 months, resulting in a biennial cycle. Females stored sperm in the oviducal gland and, unlike Mediterranean specimens, no uterine compartments were observed in Atlantic specimens. This study reveals the existence of strong, possibly adaptive, divergence in life-history traits in an elasmobranch, whose northern populations may be more susceptible to overexploitation than previously believed.