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International audience; Skates are characterised by conservative body morphology which hampers identification and leads to frequent taxonomic confusion and market mislabelling. Accurate specimen classification is crucial for reliable stock assessments and effective conservation plans, otherwise the risk of extinction could be unnoticed. The misclassification issue is evident for the genus Dipturus, distributed worldwide, from the continental shelf and slope to the deep sea. In this study, barcode cytochrome oxidase I gene (COI) sequences were used along with species delimitation and specimen assignment methods to improve taxonomy and zoogeography of species of conservation interest inhabiting the Atlantic Ocean and Mediterranean Sea. In this study, we provided new evidence of the occurence of D. nidarosiensis in the Central-Western Mediterranean Sea and the lack of Atlantic-Mediterranean genetic divergence. The Atlantic endangered species D. laevis and D. batis clustered together under the same molecular operational taxonomic unit (MOTU) with any delimitation methods used, while the assignment approach correctly discriminated specimens into the two species. These results provided evidence that the presence of the barcode gap is not an essential predictor of identification success, but the use of different approaches is crucially needed for specimen classification, especially when threshold-or tree-based methods result less powerful. The analyses also showed how different putative, vulnerable, species dwelling across SouthWestern Atlantic and SouthEastern Pacific are frequently misidentified in public sequence repositories. Our study emphasised the limits associated to public databases, highlighting the urgency to verify and implement the information deposited therein in order to guarantee accurate species identification and thus effective conservation measures for deep-sea skates.

Despite being commonly recognized by the general public, knowledge about the biology and life-history of electric rays is still scarce. Globally, according to the International Union for Conservation of Nature, more of the 80% of the species belonging to the Torpedinidae family are, indeed, classified as Data Deficient, so as, in most of the cases, no proper management measures are available for the conservation of these species. For this reason, the main goal of this study is to provide new information on life-history traits of three species inhabiting the Mediterranean Sea. Age and growth were estimated through direct annuli count of 146 vertebral centra sections of Torpedo marmorata. Females’ growth pattern was found to be better described by a S-shaped function (Gompertz L∞ = 622 mm TL; k = 0.15; IP = 2.75 years), while males’ by a logarithmic one (von Bertalanffy L∞ = 485 mm TL; k = 0.14; t0 = -2.28). The oldest female and male were aged 17 (560 mm TL) and 11 (432 mm TL), respectively. Females (L50 = 379 mm TL and A50 = 5.5 years) appeared to mature later than males (L50 = 272 mm TL and A50 = 3.8 years), also attaining bigger sizes. Despite the observation of late-pregnant females being found only in autumn and regressing ones in autumn and winter, the presence of juveniles during the whole year may indicate a longer reproductive period. The stomach content analysis identified T. marmorata as a top predator (TROPH = 4.38) with a very narrow trophic niche (Bi = 0.22), extremely specialized in feeding on bony fishes. In addition, this work provides new and updated information on T. torpedo and the rare Tetronarce nobiliana growth, reproductive features and diet. Therefore, offering new essential data to assess the population conditions of all Torpedinidae species that inhabit the Mediterranean Sea, will lead to effective conservation plans.

As far as is known, in this paper the first case of lacking of skin-related structures (epidermis, stratum laxum, dermal denticles and teeth) in a free-swimming elasmobranch, the blackmouth catshark, Galeus melastomus, is reported. The individual was caught by trawl in Sardinian waters (central-western Mediterranean) in July 2019 at a depth of 500 m. Although this kind of morphological abnormality is potentially fatal, the observations suggested that the specimen was in good health and well developed.

The aim of the present study was to evaluate, through a Collaborative Fisheries Research (CFR) project, the efficacy of artificial dens as a possible integrative action for the management of O. vulgaris in the wild. Artificial dens, anchored on rocky substrates at a depth of 38–42 m in a temporary Fully Protected Area (FPA) off the western coast of Sardinia (central western Mediterranean Sea), showed their effectiveness as a temporary and/or safe site for Octopus vulgaris spawning. The suitability of these artificial dens was demonstrated by the presence of egg strings and females in parental care, and by the fact that all of the brooding-phases until the hatching had taken place inside. The presence of abundant cobbles, appeared to be a key factor in the building of a solid barrier for protection at the entrance of the spawning artificial dens, similar to those seen in natural dens. In addition, our results demonstrate the potential coexistence of artificial dens with natural ones, suggesting their potential use as integrative tool for the management of O. vulgaris. Close collaboration with fishermen in the framework of a CFR project within FPA may increase the success of this management action, through the enforcement of the area. Brooding details and laid egg features revealed by the monitoring are reported and discussed.

Reports of marine litter pollution first appeared in scientific literature of the early 1970s; yet, more than 40 years later, no rigorous estimates exist of the amount of litter existing in the marine environment. To cope with this global urgency, this study reports the status of marine litter abundance along fishing grounds surrounding the island of Sardinia (CW Mediterranean Sea; FAO Geographical Sub-Area 11) through three years of trawl surveys. A total of 302 hauls, covering a total of 18.4 km2 of trawled surface were carried out in the framework of the MEDITS campaign, at depths comprised between 0 and 800 m. A total of 918 items were collected and sorted, with the highest concentration observed above 200 m depth. Overall, plastic was the dominant component of litter, followed by glass and metal. Comparing our results with other areas from the Mediterranean basin, Sardinian waters showed a lower impact, possibly as a consequence of multiple factors such as the lower human population density and the low flow of the main rivers, among others. In addition, fishermen behaviour with respect to marine litter was investigated by mean of anonymous questionnaires, emphasizing the necessity to further develop management policies and infrastructures supporting litter disposal.

Knowledge of the mechanisms that allow coexistence among sympatric species is fundamental to understand ecosystem functioning. Resource partitioning among seven elasmobranchs inhabiting the Sardinian continental shelf (40°07′N, 9°00′E): Dasyatis pastinaca; Raja asterias; R. brachyura; R. clavata; R. miraletus; R. polystigma and Scyliorhinus canicula, was investigated through stomach content analysis. Data from 1680 samples collected between 2005 and 2014, in 26–200 m depth, were analysed with respect to population, sex, season (winter and summer) and size groups. Species living in shallower waters (characterized by a narrower bathymetric range) had the most specialized diets. All species appeared to be mesopredators, feeding mainly on Crustacea, Actinopterygii, Mollusca and Polychaeta. Despite shared common morphological features, from the high ecological diversity of prey items, we hypothesized the presence of different predatory behavior among the species studied: some species were able to feed on endobenthic and/or epibenthic organisms, while others had made limited movements in the water column. Non-parametric Multi-Dimensional Scaling analysis highlighted the presence of five predator groups, confirming strong resource partitioning, as also demonstrated by low levels of interspecific niche overlap. The observed variations in feeding habits could be ascribed only to size and not to sex or season. Generally, diet changed from small Crustacean prey, to larger prey, like Actinopterygii and Mollusca. Some species became more generalist during development, others restricted their prey range. Shifts in feeding habits affected species’ roles in the food web, with different species occupying different functional trophic groups over the course of their life cycles.

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.

This study reports data on benthic litter abundance, composition and distribution obtained during deep-sea trawl surveys conducted along the Sardinian continental margin down to the bathyal plain, at depths comprised from 740 to 1740 m. None of the investigated sites was litter free. Density ranged from a minimum of 4 to a maximum of >1300 litter items per km2, with a mean value of 258 ± 59 items. Plastic accounted for 56% of the total collected items, followed by glass (24%), metal (10%). Most items, irrespectively of the category, were single-use items. Fish abundance in all of the investigated catches was significantly higher than the number of litter items, the weight of which was similar to the reared fish biomass. Our results confirm that anthropogenic waste has reached the deep Mediterranean Sea, and that the most recent EU legislation banning single-use plastic tools represents a timely and necessary measure.

The uncertainty in age estimation by otolith reading may be at the root of the large variability in red mullet (Mullus barbatus) growth models in the Mediterranean. In the MEDITS survey, red mullet age data are produced following the same sampling protocol and otolith reading methodology. However, ageing is assigned using different interpretation schemes, including variations in theoretical birthdate and number of false rings considered, in addition to differences in the experience level of readers. The present work analysed the influence of these variations and the geographical location of sampling on red mullet ageing using a multivariate approach (principal component analysis). Reader experience was the most important parameter correlated with the variability. The number of rings considered false showed a significant effect on the variability in the first age groups but had less influence on the older ones. The effect of the theoretical birthdate was low in all age groups. Geographical location had a significant influence, with longitude showing greater effects than latitude. In light of these results, workshops, exchanges and the adoption of a common ageing protocol based on age validation studies are considered fundamental tools for improving precision in red mullet ageing.

The oocyte maturation and spawning pattern of European hake Merluccius merluccius, one of the most important species in the Mediterranean fishery, were investigated using data collected in a scientific trawl survey (Mediterranean International Trawl Survey, MEDITS) as well as commercial landing data collected in several geographical sub-areas (GSAs): the Southern and Central Tyrrhenian Sea (GSA10), Sardinia (GSA11), the Southern Adriatic Sea (GSA18) and the Western Ionian Sea (GSA19). The lack of the validation of macroscopic maturity scales is one impediment to obtaining reliable estimates of the reproductive parameters used to assess a fish stock. The MEDITS maturity scale was validated for female European hake by histological analysis of the oocyte diameter frequency distributions and according to the gonadosomatic index. The oocyte diameter frequency distributions and histological analysis confirmed that the ovarian organisation of hake was asynchronous, including a batch spawning pattern and indeterminate fecundity. Females in spawning condition were recorded throughout the year in all GSAs although the main peaks of spawning activity were in winter and in late summer and early autumn. The L50 estimated for GSA10, GSA11, GSA18, GSA19 were 33.03 cm, 30.03 cm, 31.95 cm and 32.95 cm, respectively. Moreover, no significant trends in the annual estimate of L50 from 2007 to 2015 in any of the study areas were observed. Mean batch fecundity and relative fecundity (360,687 eggs/fish, 281.6 eggsg−1 in GSA10, 361,311 eggs/fish, and 262.2 eggs g−1 in GSA18) were higher than those reported in other Mediterranean areas.

It has been amply demonstrated that trawl fishing affects overall biomass, size and species structure of demersal fish communities, and an increasing number of studies are proving that this could have even greater unexpected effects on biological diversity. The aims of this study are: (1) to examine the temporal trends of several ecological diversity indices for middle-slope communities in specific locations within the Sardinian seas, which have been recently subject to increasing fishing capacity; and (2) to simulate the Shannon's entropy (H′) temporal trend, using a multiple linear regression, in order to investigate about the relationships between fishing effort and species diversity. The data come from 11 MEDITS trawl surveys (1994 to 2004). Temporal trends in fishing effort were analysed and ecological diversity indices were measured. Analysis was conducted for four areas (NW, NE, SE, SSW). Significant variations over time in both fishing pressure and ecological diversity indices were found for the southern zones. More precisely, the SE zone showed an increase in fishing effort (+120% in 2004), and a decrease of Shannon–Weiner's diversity. The SSW zone exhibited a 22.6% increase of fishing effort and a decrease of species richness. The best model of H′ incorporates species richness and fishing effort expressed as number of boats per trawling area. Our results seem to indicate that fishing pressure affected the species richness and the abundance of middle-slope species and that variation in ecological diversity indices differed with different levels of fishing effort.

This work focuses on the species associations of the Baronie Seamount (north-eastern Sardinia, Italy), according to variations in depth and time of day. The aim was to highlight the potential vertical movements of the species and to compare these results to existing data from a submarine canyon. Twenty-two samples were taken at different depths and times along two trawl lines over the seamount. A total of 94 species were caught; among these, 48 bony fish, 9 cartilaginous fish, 13 molluscs and 24 crustaceans were selected for analysis. Cluster analysis showed 3 groups in which both depth and time of day play an important role in grouping. Nine species showed some daily and nocturnal movement, probably linked to trophic requirements. The daily movements according to size and sex of the shrimps Aristaeomorpha foliacea and Aristeus antennatus were also studied. For these two populations, the analysis showed an uneven distribution and the diel cycle appears to involve only the females. These species seem to adapt their life cycle to the geomorphology of the sea bottom. The diurnal movements from the base of the seamount to the edge of the continental shelf increase the range of the species distribution. In fact, the seamount, due to its geomorphological conformation, offers these species the opportunity to very quickly span a considerable range of depths. These movements are known to occur in the continental shelf and slope, but in the seamount they are broadened and can be studied more easily.

This study quantifies the main reproductive features of the long-lived red coral Corallium rubrum, an octocoral endemic to the Mediterranean Sea and neighboring Atlantic areas and one of the most valuable of all marine species, at different depths (38-40 m versus 96-115 m) in north-western Sardinian waters (Central-Western Mediterranean Sea). Different population structures between depths were observed with shallow colonies smaller (in basal diameter and height) than deeper ones. Both populations were all gonochoric at polyp and colony level and fertile. The sex-ratio was balanced in the deep red corals while in the shallow ones it was significantly biased towards female probably in response to perturbations such as mass mortality events more common at shallow levels. Deep and shallow colonies were found to have a synchronous female sexual products development in the two depths investigated. C. rubrum produced large female sexual products in both depth intervals in relationship with its reproductive mode, confirming a long oogenic development. In contrast to reproductive timing, the volume occupied by female sexual products per polyp was different between the populations, being higher in the deep than in the shallow populations. C. rubrum exhibited a reproductive strategy characterized by a relative low number of female sexual products per polyp revealing significant differences among the two depth ranges analyzed with a lower mean value of sexual products in the shallow colonies (mean fecundity per polyp: 1.14) than in the deeper ones (mean fecundity per polyp: 2.09). These results indicate differences in reproductive parameters such as sexual products distribution and reproductive output (fecundity) were observed between shallow and deep populations of C. rubrum, in particular within deep dwelling populations.

In the Mediterranean Sea, in addition to the two historically known species belonging to the Squalus genus, a third species, Squalus megalops, has been reported. Considering the high level of morphologic similarity of this species with the native species S. blainville, this study aims to evaluate the Central-Western Mediterranean spurdog population in order to test the hypothesis of the presence of two distinct species S. blainville and S. megalops. A total of 137 spurdogs, caught in the Sardinian waters, were analyzed morphologically and genetically after their subdivision into two groups depending on the number of the lateral processes in the chondrocranium basal plate. The CAP analysis, employing all body and chondrocranial measurements, revealed no clear segregation among the a priori assigned groups with a high misclassification percentage. Besides, no evident dissimilarities in teeth and dermal denticle morphology between the two groups were observed. All the 18 specimens which were genetically analyzed, by sequencing of the mtDNA marker COI, clustered together resulting to be S. blainville. All the obtained results indicated the presence, in the study area, of only one species, ascribable to S. blainville.