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The spotted catshark (Scyliorhinus canicula) and the blackmouth catshark (Galeus melastomus) are demersal sharks showing a distinct bathymetric distribution in the western Mediterranean. Together, both species represent more than 85% of the total abundance of demersal chondrichthyans in this Mediterranean basin. Our study provides a complete analysis of the genetic population structure, connectivity and demographic history of both species. Sampling was performed across four geographical subareas (GSAs) established by the General Fisheries Commission for the Mediterranean in the western Mediterranean: the northern Alboran Sea (GSA01), Alboran Island (GSA02), Balearic Islands (GSA05) and northern Spain (GSA06). Three mitochondrial fragments were analyzed for both species, and 12 microsatellite loci for S. canicula. We found contrasting patterns of population structure and connectivity in both species. Scyliorhinus canicula displayed significant genetic differences and low connectivity between some GSAs corresponding to different sub-basins (Alboran vs. Balearic). In contrast, G. melastomus showed absence of a population structure and high connectivity between GSAs. These findings are in accordance with the fact that both species exhibit different dispersal behaviors, which leads to distinct bathymetric distributions. Contrasting demographic histories were also identified: Scyliorhinus canicula revealed a recent stable population, with evidence of bottlenecks in the past, which may be related to Pleistocene glacial periods; whereas G. melastomus showed a recent population expansion. Altogether, our findings indicate a mismatch between fishery subareas and population structure for both sharks, which must be considered for fisheries management purposes.

To investigate the ability of elasmobranchs to distinguish between differing prey-type electric fields we examined the electroreceptive foraging behaviour of a model species, Scyliorhinus canicula (small-spotted catshark). Catshark preferences were studied by behaviourally conditioning them to swim through narrow tunnels, and on exit presenting them simultaneously with two different electric fields. Their subsequent choices of the following paired options were recorded; (i) Two artificial electric fields (dipole electrodes) with different magnitude direct current (D.C.), (ii) Two artificial electric fields, one D.C. and the other alternating current (A.C.), of the same magnitude, and (iii) similar magnitude, natural and artificial D.C. electric fields associated with shore crabs and dipole electrodes respectively. We found a highly significant preference for the stronger D.C. electric field and a less pronounced, but still significant, preference for the A.C. electric field rather than the D.C. electric field. No preference was demonstrated between the artificial and natural D.C. electric fields. The findings are discussed in relation to the animal’s diet and ecology and with regard to anthropogenic sources of electric fields within their habitat.

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.

Movements and habitat selection of male and female dogfish, Scyliorhinus canicula, in a tidal sea lough in south-west Ireland were determined over two temporal scales. Continuous acoustic tracking of four individuals (two males, two females) for 6 days was used to monitor fine-scale changes in behaviour patterns and extent of home ranges. Mark-recapture by number-tagging dogfish captured at sampling stations during August-September in consecutive years was used to reveal long-term philopatric behaviour. Transmitter-tagged male dogfish showed very similar behavioural patterns of low activity during the day in deep water (12–24 m depth) followed by more rapid movements into shallow areas (

Zinc and copper levels in the gills, kidney and intestine of the dogfish Scyliorhinus canicula L. collected in a 80 to 120 m deep zone close to Barcelona (Spain) during the months of February–March 1981 were measured by atomic absorption spectrophotometry after subacute (10 ppm Zn for 3 wk) and acute (80 ppm Zn for 24 h) treatment with ZnSO4. Individuals exposed to 80 ppm Zn accumulated Zn in the gills, whereas no significant increase in Zn content was found in the kidney or intestine. No differences in the Cu content of any of these tissues were found. Dogfish exposed to 10 ppm Zn for 3 wk displayed an increase in Zn content of the gills, kidney and intestine. An increase in the Cu concentration of the gills was also recorded which may suggest that Cu, and hence Zn and other heavy metals, are excreted via the gills when the kidney and intestine are overloaded. A light-microscopic study of the gill epithelium was carried out on dogfish treated with 10 ppm Zn for 3 wk, 80 ppm Zn for 24 h and 175 ppm Zn for 14 h, and chloride cell response was quantified. Chloride cells increased in number after each treatment, even appearing in the secondary lamellae following treatment with 175 ppm Zn. It is suggested that the chloride cell may excrete bivalent ions when dogfish are exposed to an excess of bivalent salts.

The surface morphology of the gill epithelium of the dogfish Scyliorhinus canicula L. (collected near Barcelona, Spain, in February–March, 1981) was studied by scanning electron microscopy. Pavement cells exhibited either surface microvilli or microridges, which were randomly distributed on both the primary (afferent and efferent sides and interlamellar spaces) and secondary epithelium. Chloride cell apical regions on the afferent side displayed characteristics closer to freshwater than to marine teleosts: no apical pits were detected; chloride cells displayed longer microvilli than those of adjacent cells. Two morphologically different cell types were identified: a large chloride cell and a smaller cell (probably a chloride cell too), measuring 4 to 7 μm and 1 μm, respectively, the latter being dominant in the interlamellar spaces. Apart from pavement cells, the mucous cell was the prevalent cell type on the efferent region. The respiratory epithelium consisted of a mozaic of typical epithelial cells; some chloride and mucous cells were present, mainly located at the base of the secondary lamellae. Surface morphological changes were monitored after exposing the dogfish to subacute zinc treatment: 10 ppm Zn (ZnSO4) for 3 wk. The chloride cell was the only cell type that underwent any modifications: microvilli became longer and tips were swollen following Zn treatment. The results are discussed in relation to a previous study on the effects of zinc sulphate on chloride cell response and heavy metal distribution in excretory organs of the dogfish.