Strongly structured populations and reproductive habitat fragmentation increase the vulnerability of the Mediterranean starry rayRaja asterias(Elasmobranchii, Rajidae)

Abstract

1. The Mediterranean starry ray (Raja asterias) populations within the Mediterranean Sea are susceptible to high rates of bycatch in the multispecies trawl fisheries.Understanding its population structure and identifying critical habitats are crucial for assessing species vulnerability and setting the groundwork for specific management measures to prevent population decline. 2. To assess the population structure of R. asterias in the Mediterranean, the genetic variation in nine population samples at one mitochondrial marker and eight nuclear microsatellite loci was analysed. Moreover, 172 egg cases collected in the Strait of Sicily were identified at species level using integrated molecular and morphological approaches. 3. Genetic analyses revealed that the Mediterranean starry ray comprises three distinct units inhabiting the western, the central-western, and the central-eastern areas of the Mediterranean. An admixture zone occurs in the Strait of Sicily and the Ionian Sea, where individuals of the central-western and central-eastern population units intermingle. 4. The joint morphometric-genetic analyses of rajid egg cases confirmed the presence of more than one species in the admixture area, with a predominance of egg cases laid by R. asterias. DNA barcoding revealed that egg cases and embryos of R. asterias shared several haplotypes with adult individuals from the centralwestern and central-eastern Mediterranean Sea, revealing that females of both populations laid numerous eggs in this area. 5. According to these findings, detailed taxonomic determination of egg cases, when combined with seasonal migration studies, could improve the capability to Giusy Catalano, Valentina Crobe, and Alice Ferrari contributed equally to this work.

I Like This New Me: Unravelling Population Structure of Mediterranean Electric Rays and Taxonomic Uncertainties within Torpediniformes

“…In particular, the role of oceanographic discontinuities has been invoked in several elasmobranch studies as the main factor responsible for geographically isolating and hence genetically differentiating the populations. This pattern has been reported for the differentiation of the easternmost Mediterranean locations of the Levantine Sea, with the Strait of Sicily potentially representing a barrier limiting the genetic exchanges between the Eastern and the Western Mediterranean basins [1,7,[84][85][86][87].…”

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

“…The combination of these features could have limited gene flow between western and eastern populations and driven the differentiation of the Eastern Mediterranean samples (ADR, ISR and LEV; Figure 1 ). The specific habitat and depth preferences, the less pronounced migratory behaviour and the limited dispersal capability of taxa belonging to the R. miraletus species complex are rather common characteristics among skates [ 62 , 73 , 113 , 114 ], although other congeneric species did not show such evidence of deep differentiation at both nuDNA and mtDNA markers [ 10 , 56 , 72 , 110 ]. In detail, the Mediterranean starry ray R. asterias showed a strongly structured population with three geographical clades corresponding to the western, central–western and central–eastern Mediterranean areas [ 62 ].…”

“…The specific habitat and depth preferences, the less pronounced migratory behaviour and the limited dispersal capability of taxa belonging to the R. miraletus species complex are rather common characteristics among skates [ 62 , 73 , 113 , 114 ], although other congeneric species did not show such evidence of deep differentiation at both nuDNA and mtDNA markers [ 10 , 56 , 72 , 110 ]. In detail, the Mediterranean starry ray R. asterias showed a strongly structured population with three geographical clades corresponding to the western, central–western and central–eastern Mediterranean areas [ 62 ]. R. clavata showed a weak but detectable phylogeographic structure in the Levantine Sea [ 73 ] and a finer structuring located off the Algerian coasts and Tyrrhenian basins, suggesting the occurrence of additional barriers to dispersal [ 113 ].…”

“…Detailed protocols used for DNA extraction, PCR amplification, DNA sequencing and genotyping of mitochondrial and nuclear markers [ 56 , 58 , 61 , 62 ] are described in the Supplementary Material Text S1 .…”

Looking into the prevalence of bycatch juveniles of critically endangered elasmobranchs: a case study from pelagic longline and trammel net fisheries of the Asinara Gulf (western Mediterranean)

“…The literature gives several examples about the limited contact between shark and ray populations at both large and small scales. For example, recent studies applying the molecular approach have highlighted the main role of water circulation and temperature in sharks (Di Crescenzo et al, 2022;Melis et al, 2023a) and rays (Catalano et al, 2022;Melis et al, 2023b). Similarly, evidence based on molecular data showed how biotic and abiotic features such as bathymetry, hydrological constraints, and prey abundance can influence the presence, movement, and dispersion of sharks and rays (Catarino et al, 2015;Di Crescenzo et al, 2022).…”