Morphological Traits and Capture Depth of the Norwegian Skate (Dipturus nidarosiensis (Storm, 1881)) from Two Mediterranean Populations

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.

Ontogenetic Shifts in Body Morphology of Demersal Sharks’ Species (Order: Squaliformes) Inhabiting the Western-Central Mediterranean Sea, with Implications for Their Bio-Ecological Role

“…Nonetheless, while information on the feeding behaviour and trophic level are usually available for many species [ 2 ], little is known regarding how ontogenetic growth affects their environmental role. In this context, shifts in body proportions during growth have been observed in several species of elasmobranchs, e.g., as found in [ 6 , 7 , 8 , 9 , 10 , 11 ]. Since such shifts may be linked to changes in, e.g., the species’ interaction with the habitat, diet composition, or locomotion, expanding our understanding of the ontogenetic trajectories of sharks will allow for a more precise evaluation of stock conditions as well as enabling the implementation of appropriate measures for protection and management [ 12 ].…”

To Be, or Not to Be: That Is the Hamletic Question of Cryptic Evolution in the Eastern Atlantic and Mediterranean Raja miraletus Species Complex

“…Among elasmobranchs, skates and rays exhibit highly effective modulation of electro-sensory signals depending on behaviour ([ 16 ] and references therein). At the same time, they display a marked conservation of ecological and morphological traits [ 17 , 18 , 19 , 20 , 21 , 22 , 23 ], especially between recently diverged species [ 12 ]; a strong evolutionary success in terms of resilience at the evolutionary scale [ 24 ] and a high degree of endemism [ 25 , 26 ] and species richness [ 27 , 28 , 29 ].…”

Protection from fishing improves body growth of an exploited species

“…Contrary to our findings, theoretical work on MPAs has assumed reduced body growth in MPAs due to density dependence, and therefore reduced fisheries yields outside MPAs due to spill-over of slow-growing (and smaller) individuals [35,61]. Although it is well documented that individual growth can be affected by compensatory density dependence in exploited populations [62–65], the effects of protection on body growth of aquatic animals have been shown to both be positive [33,66–69] (also this study) and negative [34,36,70,71]. These mixed results illustrate that it is difficult to generalize how protection can affect body growth, because the outcome may depend on the interactions of many factors, such as the life histories of the species in question, the selectivity and intensity of the fishery, and the age, size and location of the reserve.…”