Deep-sea elasmobranchs (DSE) play a crucial role in marine ecosystems. However, they are poorly studied and face threats from overfishing, emphasizing an urgent need for improved scientific information, monitoring, and management strategies to reduce their bycatch. This study aimed to assess DSE bycatch from crustacean bottom trawling in southern Portugal, considering depths above and below 800 m (Regulation 2016/2336). Potential bycatch of deep-sea sharks was evaluated using in situ observations from the months of February and March and extrapolated for the fishing ban period (2017-2022). A total of 1559 specimens belonging to 18 DSE species were collected from 77 hauls between June 2020 and May 2022. Despite trawlers preferences for fishing above 800 m in the South, fishing below 800 m in the Southwest resulted in increased bycatch of DSE, including protected, uncommon, and endangered species such as Deania calceus, Mitsukurina owstoni, and Centroscymnus coelolepis. Furthermore, the areas and depth strata occupied by species like Galeus melastomus and Scymnodon ringens, suggested habitat flexibility, while others showed an apparent preference for specific depths and areas. These findings highlight the complexity of managing DSE populations amidst fishing pressures and depth restrictions. Despite the ban imposed to fishing below 800 m, bottom trawling persisted, leading to a potential elevated bycatch of deep-sea sharks for the months of February and March. This study emphasizes the urgency for improved enforcement of regulations in Portuguese waters and calls for the implementation of effective bycatch mitigation and fisheries management practices to safeguard DSE populations.

Chondrichthyans comprise a diverse group of vertebrate species with extraordinary ecological relevance. Yet, multiple members of this evolutionary lineage are associated with significant extinction risk. The sailfin roughshark Oxynotus paradoxus is a deep-water benthic shark currently listed as vulnerable due to population declines in parts of its range. Here we provide the first complete mitochondrial genome of O. paradoxus, comprising also the first record for the genus and family Oxynotidae. These data can facilitate future monitoring of the genetic diversity in this and related species. Genomic DNA was extracted from O. paradoxus collected in the eastern North Atlantic off western Portugal (37.59°N, 9.51°W) and sent for Illumina Paired-End (2 × 150 bp) library construction and whole genome sequencing on a Novaseq6000 platform. Trimmomatic (version 0.38) was used to remove adapters and MitoZ (version 3.4) to assemble and annotate the mitogenome. This mitogenome with 17 100 bp has a total of 38 genes, 13 of which are protein-coding genes, 23 transfer RNA genes, and 2 ribosomal RNA genes. Eight transfer RNAs and 1 protein-coding gene (NADH dehydrogenase subunit 6, NAD6) are in the complementary strand. In the provided phylogenetic inference, with all available and verified Squalomorphii mitogenomes, the four orders are well separated, and as expected, O. paradoxus is placed in the Squaliformes order. This data reinforces the need for more genomic resources for the Oxynotidae family.

Oxynotus paradoxus, documented in the Eastern Atlantic Ocean from Senegal to Scotland at depths ranging between 92 and 1044 m, has been a subject of limited scientific attention in Portugal. Despite its pres-ence in various Portuguese occurrence checklists, only two scientific studies have reported O. paradoxus, one off the mainland and the other off the Azores islands. In this study, conducted during fishing campaigns, four O. paradoxus specimens were caught off the southwest coast of Portugal (SW Iberian Peninsula) at depths rang-ing between 742 and 1238 m. Notably, an adult female achieved a new maximum depth record for this species, measuring 650 mm in total length. By examining this adult female, we provide novel insights into the ecology and biology of O. paradoxus. Morphometric measurements are compared with previous studies, revealing some intra-specific variability. The observed low hepato-, gonadosomatic, and ecophysiological indices suggest that the adult female had refrained from feeding for some time before collection. This individual-focused approach contributes significantly to the understanding of this poorly known species, especially considering its rarity. This study marks a noteworthy effort to enhance knowledge and emphasizes the importance of individual-based investigations when targeting rare species.

Deep-water sharks are among the most vulnerable deep-water taxa because of their extremely conservative life history strategies (i.e., late maturation, slow growth, and reproductive rates). Yet, little is known about their biology and ecology. Thus, this study aimed at investigating the trophic ecology of five deep-water shark species, the birdbeak dogfish (Deania calcea), the arrowhead (D. profundorum), the smooth lanternshark (Etmopterus pusillus), the blackmouth catshark (Galeus melastomus) and the knifetooth dogfish Scymnodon ringens sampled onboard a crustacean bottom-trawler off the southwest coast of Portugal. We combined carbon and nitrogen stable isotopes with RNA and DNA (RD) ratios to investigate the main groups of prey assimilated by these species and their nutritional condition, respectively. Stable isotopes revealed overall small interspecific variability in the contribution of different taxonomic groups to sharks' tissues, as well as in the origin of their prey. Scymnodon ringens presented higher δ15 N and δ13 C values than the other species, suggesting reliance on bathyal cephalopods, crustaceans, and teleosts; the remaining species likely assimilated bathy-mesopelagic prey. The RD ratios indicated that most of the individuals had an overall adequate nutritional condition and had recently eaten. This information, combined with the fact that stable isotopes indicate that sharks assimilated prey from the local or nearby food webs (including commercially important shrimps), suggests a potential overlap between this fishing area and their foraging grounds, which requires further attention.

Skates, Chondrichthyes fishes from order Rajiformes, are the most species-rich group of all Batoidea. However, their phylogenetic relationships and systematics is still a highly discussed and controversial subject. The use of complete mitogenome has shown to be a promising tool to fill this gap of knowledge. Here, the complete mitogenome of the Iberian pygmy skate Neoraja iberica (Stehmann, Seret, Costa & Baro 2008) was sequenced and assembled. The mitogenome is 16,723 bp long and its gene content (i.e. 13 protein-coding genes, 22 transfer RNA, and 2 ribosomal RNA genes) and arrangement are the expected for Batoidea. Phylogenetic reconstructions, including 89 Rajiformes and two outgroup Rhinopristiformes, recovered family Rajidae as monophyletic, and further divided in the monophyletic tribe Rajini, sister to tribes Amblyrajini and Rostrorajini. The newly sequenced N. iberica mitogenome is the first representative of the tribe Rostrorajini.