Search

A total of 255 longnosed skate Dipturus oxyrinchus caught in Sardinian waters (central-western Mediterranean Sea), was analysed with respect to fish total length ( LT), season and depth, in order to provide information on diet and feeding behaviour. Specimens ranging from 93 to 1153 mm LT, were collected at depths between 121 and 671 m, during experimental trawl surveys carried out from 2005 to 2010. The diet comprised crustaceans [prey specific index of relative importance (% IPSRI) = 72·69], teleosts (% IPSRI = 10·28) and molluscs (% IPSRI = 10·94). Levins' index ( Bi) showed a narrow niche breadth ( Bi = 0·35). The mean ± s.e. trophic level ( TL) was 3·63 ± 0·50. The analysis showed major ontogenetic changes in the feeding behaviour. Early life stages were characterized by a benthic diet, which changed to benthopelagic during growth. Mysids, particularly Lophogaster typicus (% IPSRI = 34·51), were the main prey items of immature individuals, replaced by euphausiids, mainly Meganyctiphanes norvegica (% IPSRI = 13·19), in maturing fish. Crustaceans became less important in mature specimens, being replaced by molluscs (% IPSRI = 28·99) and teleosts (% IPSRI = 24·56). A concomitant increase of the TL was recorded (mean ± s.e. = 3·41 ± 0·44, 3·75 ± 0·54 and 4·28 ± 0·61 for immature, maturing and mature individuals). These feeding patterns ensured low levels of intraspecific competition. This study provides new information about the role that the D. oxyrinchus plays in the marine food chain and data now essential to formulate new and effective management plans for this species. [ABSTRACT FROM AUTHOR]

Copyright of Cybium: International Journal of Ichthyology is the property of Societe Francaise d'Ichtyologie (SFI) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Fourteen specimens of the Norwegian skate, Dipturus nidarosiensis (Rajiformes, Rajidae), were caught off the Sardinian coasts (Central Western Mediterranean Sea) in 2005-2008 between 600 and 1420 m of depth. Their identification has been confirmed by the sequencing of three regions of the mtDNA (16SrDNA, control region and cytochrome c oxidase subunit 1) and comparison of the obtained sequences with that of three species of Dipturus (D. batis, D. oxyrinchus and D. nidarosiensis) from the Mediterranean Sea and the adjacent North-eastern Atlantic Ocean. A simple PCR-RFLP assay has been developed for an easy, reliable and robust identification of these skate species. A morphological comparison of the Norwegian skate with congeneric species is given in order to help future identifications. This is the first record of D. nidarosiensis in the Mediterranean Sea; the possibility of recent or ancient but unnoticed occurrence of the Norwegian skate in the region is discussed. [ABSTRACT FROM AUTHOR]

We present the first data on the population structure, reproduction, and feeding ecology of Polycheles sculptus S. I. Smith, 1880 from the Sardinian sea. Samples were collected during experimental trawl surveys carried out in 2006-2007 in Sardinian waters, at depths between 1037 and 1598 m. A total of 72 specimens of P. sculptus, 31 males, 40 females, and 1 specimen of undetermined sex, was examined. The sex ratio of the whole sample showed a slight preponderance of females. No significant deviations from the expected 1 : 1 relationship were, however, found along the investigated depth range. A clear seasonality in reproduction was not determined. The species showed a high value of the stomach vacuity index (Cv). The diet was based on eight broad categories of preys, but no dominant prey was recognized. Females showed the greatest width in their diet, though Morisita's index indicated a large overlap between sexes. [ABSTRACT FROM AUTHOR]

The spotfin burrfish Chilomycterus reticulatus (405 mm standard length) is recorded for the first time on the shoreline of the Mediterranean Sea. The adult specimen was found dried on a beach near the south Sardinian Sea (S. Antioco’s Island). Photographs and morphometrics of the specimen are given. [ABSTRACT FROM AUTHOR]

Eggcases of eight rajiform skates (Dipturus nidarosiensis, D. oxyrinchus, Leucoraja melitensis, Raja asterias, R. brachyura, R. clavata, R. miraletus and R. polystigma) present in the central-western Mediterranean are described, based on specimens obtained from fishery surveys. Eggcase features such as dimensions, horns and apron lengths, and presence/absence of lateral keels were crucial to discriminate the eggcases of the various species. Morphological and morphometric data, confirmed by the multivariate analysis, indicated that the eggcase of R. miraletus and L. melitensis were distinct from those of the other species for being unkeeled. Within the species having keeled eggcases, those of the genus Dipturus and R. brachyura were discriminated from the remaining group by having the largest dimensions and aprons. Sandy bottoms (<100–150 m depth) were identified as egg-laying sites (i.e. sites with females bearing eggcases in uteri) for many species belonging to genus Raja Raja asterias, R. brachyura, R. miraletus and R. polystigma). The finding of R. asterias and R. miraletus carrying eggcases yearly on the same sites, seems to confirm the theory that many rajid species demonstrate site fidelity, returning to the same depositional area on an annual basis. Some remarks on reproductive biology of these skates are also provided. The eggcase identification key reported here represents the first for the Mediterranean and may be useful, in the future, to identify egg-laying grounds of skates with a nonlethal method. [ABSTRACT FROM AUTHOR]