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Occurrence, abundance and size trends of 25 demersal Chondrichthyes (10 Sharks: 3 Carcharhiniformes, 2 Hexanchiformes, 5 Squaliformes; 14 Batoids: 3 Myliobatiformes, 8 Rajiformes, 3 Torpediniformes and 1 Holocephalan: 1 Chimaeriformes) collected from 22 years (1994–2015) of Mediterranean International Trawl Surveys (MEDITS) around Sardinian seas, were given. Data relative to two strata, the continental shelf (10–200 m), the slope (201–800 m), and the overall (10–800 m), were analyzed in order to identify the general species distribution of their habitat preference. From the gathered data it appeared that the shelf was mostly inhabited by batoids while the slope by sharks. Only the small-spotted catshark Scyliorhinus canicula and the thornback skate Raja clavata were equally distributed with high values of occurrence and abundance both in the shelf and in the slope. All the other species showed a preferential distribution only in one stratum (shelf or slope). In general, temporal trends of abundance indexes were stable or increasing in all strata. GAM analysis also confirmed a stable trend. Almost all species displayed stable in size structure analysis, apart from R. brachyura and Dipturus oxyrinchus that showed a statistically increasing trend. Although the investigated chondrichthyan species seemed to display a not alarming status of conservation in Sardinian seas, more investigation should be done to assure a proper management of this threatened resource.

Sharks and rays (elasmobranchs) have the remarkable capacity to continuously regenerate their teeth. The polyphyodont system is considered the ancestral condition of the gnathostome dentition. Despite this shared regenerative ability, sharks and rays exhibit dramatic interspecific variation in their tooth morphology. Ray (batoidea) teeth typically constitute crushing pads of flattened teeth, whereas shark teeth are pointed, multi-cuspid units. Although recent research has addressed the molecular development of the shark dentition, little is known about that of the ray. Furthermore, how dental diversity within the elasmobranch lineage is achieved remains unknown. Here, we examine dental development and regeneration in two Batoid species: the thornback skate (Raja clavata) and the little skate (Leucoraja erinacea). Using in situ hybridization and immunohistochemistry, we examine the expression of a core gnathostome dental gene set during early development of the skate dentition and compare it to development in the shark. Elasmobranch tooth development is highly conserved, with sox2 likely playing an important role in the initiation and regeneration of teeth. Alterations to conserved genes expressed in an enamel knot-like signalling centre may explain the morphological diversity of elasmobranch teeth, thereby enabling sharks and rays to occupy diverse dietary and ecological niches.

Elasmobranchs (sharks, skates, and rays) are frequently captured as bycatch on a wide variety of fishing gears, such as pelagic longlines and hook-and-line fisheries, and therefore many species have experienced severe population declines. To reduce elasmobranch bycatch, scientists have begun exploring the effectiveness and potential application of elasmobranch-specific repellents, such as permanent magnets and electropositive metals. For the present study, the behavioural responses of captive small spotted catsharks ( Scyliorhinus canicula ) and thornback skates ( Raja clavata ) were observed in response to neodymium-iron-boron (Nd 2 Fe 14 B) permanent magnets. Results demonstrate that both R. clavata and S. canicula ; (1) significantly avoided the Nd 2 Fe 14 B magnets more often in comparison to the control and procedural control and (2) significantly fed from the control and procedural control more often in comparison to the Nd 2 Fe 14 B magnets. Data also suggests a relationship between water temperature and the avoidance distance by R. clavata , with closer approaches prior to avoidance occurring in association with water temperatures of ≤12 °C. Additionally, the tail beat frequency associated with the avoidance behaviour of S. canicula was significantly slower (≤9 beats/10 s) in water temperatures of ≤12 °C. The findings from this study agree with previous electrosensory repellent studies, in that elasmobranchs detect and are deterred by permanent magnets however, the present study also demonstrated that there is a correlation between avoidance speed and distance with water temperature. These findings suggest that water temperature may be correlated to magnetic repellent effectiveness and thus warrants further experimentation.

To access the final version, follow the next link. http://www.springerlink.com/content/t1809472211lk67q/, Aim Geographical (allopatric) speciation is a dynamic process whose footprints in the living world are a continuum of stages of increasing divergence. Geographical speciation can also contribute to the evolution of marine taxa. This study looked for two of these evolutionary stages (i.e. structured populations and sibling species) in the diversification patterns of two Atlantic skates (Raja, suborder Rajoidea) which exhibited high morphological and ecological conservativism, (undefined)

Hunter and Dauphinee1 demonstrated the presence of arginase in the voluntary muscle of the dogfish (Squalus sucklii) and also possibly in the muscle of the herring. In the course of another investigation, it has now been observed that this is not true of other elasmobranchs, since no arginase activity was found in the skeletal muscle of the common skate (Raja batis), thornback skate (R. clavata) or cuckoo ray (R. circularis) using the conditions of determination of Van Slyke and Archibald2 with the colorimetric procedure of Engel and Engel3. Activity was, however, observed in both the ordinary ‘white’ skeletal muscle (0.3 arginase units2/mgm. extract nitrogen) and ‘red’ lateral-band muscle (0.75 arginase units/mgm. extract nitrogen) of the lesser-spotted dogfish (Scyliorhinus caniculus) (cf. the observations of Matsuura et al. 4 on several non-elasmobranch species of fish).