Abstract
The Norwegian skate Dipturus nidarosiensis (Storm, 1881) has only recently been recorded in the western-central Mediterranean Sea. It was hypothesized a more ancient presence of the species, which has not been detected due to a misidentification with other species of the same genus. This situation could lead to underestimate the risk of a dramatic decline of the spawning stock. In the IUCN Red List, the species is listed as near threatened and considered rare in both the northeast Atlantic and the Mediterranean areas. In the Mediterranean Sea, Norwegian skates were repeatedly caught mostly in two areas between 2005 and 2020: Sardinia Seas and Adriatic-Ionian Seas. In total, 58 specimens were caught, and 28 morphological length measurements were taken on all specimens. The Canonical Discriminant Analysis proved the presence of significant differences only for assemblages made on the basis of the specimen’s area of capture, but not on the basis of sex or ontogenetic development. This analysis could be the first step to highlight the differences between the populations of Norwegian skate in the Mediterranean basin. Moreover, a preliminary analysis of depth of capture was performed as a first step to study this species vertical distribution.
Highlights
The Norwegian skate Dipturus nidarosiensis (Storm, 1881) is geographically distributed along the Northeast Atlantic, from Iceland, the Faroe Islands and northern Norway to Madeira and northern Mauritania [1]
The species presence has been frequently observed in the Northeast Atlantic and in Bay of Biscay [2,3,4], recently, it has been recorded in Mediterranean basin, mainly in the northwestern part, in particular along the southern Sardinia coast [5,6,7,8,9,10,11], off Algeria [7] and in the Alboran Sea [12]
In consideration of the above, the present study aims in describing and characterizing from morphological points of view for the first time, the Norwegian skate specimens caught in two area: the South Adriatic-Ionian Sea (Central Mediterranean) and Sardinia waters (Western Mediterranean)
Summary
The Norwegian skate Dipturus nidarosiensis (Storm, 1881) is geographically distributed along the Northeast Atlantic, from Iceland, the Faroe Islands and northern Norway to Madeira and northern Mauritania [1]. On the bases of the abovementioned studies, two hypothesis on the origin of the species presence in the Mediterranean Sea were formulated: either a recent entry of this species across the Atlantic via the Strait of Gibraltar [5] or an ancient presence of the Norwegian skate, which had not been detected due to a misidentification between D. nidarosiensis and D. batis [13]. The latter hypothesis could be supported by the fact that the Norwegian skate is an often-misidentified species both in the Atlantic Ocean and in the Mediterranean basin [5,7,12,16,17]. As with most elasmobranchs, D. nidarosiensis shows a k-selected life strategy, characterized by a slow growth rate, long life spans, late-age at sexual maturity, and low fecundity [6]
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