Seamount coral reefs are egg case nurseries for deep-sea skates.

Egg case nurseries of the boreal skate (Amblyraja hyperborea) and Richardson's skate (Bathyraja richardsoni) were defined and mapped on a bathyal seascape (c. 500-1900 m depths) south of Tasmania, Australia, using 99 towed-camera transects (157 linear km; N = 50,858 images). In total, 738 skate egg cases were observed (present in 240 images, absent in 50,618); among 113 egg cases examined to identify parent species, 70% were A. hyperborea, 10% B. richardsoni and 20% unidentified Bathyraja species. "Recently laid" egg cases were differentiated from "aged" ones by classifying their colour and condition. The great majority (98%) of egg cases were observed in c. 1100-1400 m depths on seamounts (15 of 36 surveyed), not seamount bases or adjacent continental slope. Egg cases were associated with reefs formed by accumulated skeletal matrix of the stony coral Solenosmilia variabilis, with >90% egg cases (including most of those recently laid) observed on living S. variabilis that characterises a "coral zone" in c. 950-1350 m depths. Water in the coral zone is warmer (+0.66 to 2.37°C) than at the deep distributional limits of adult A. hyperborea and B. richardsoni (2000 and 3000 m, respectively), potentially providing for accelerated embryonic development. Co-occurrence with living coral infers an energetically favourable local-scale hydrodynamic environment for egg cases, particularly on seamount peaks, where increased water flow over egg cases would avert smothering by suspended sediment, and compensate for lower oxygen concentration compared to deeper depths occupied by adult skates. Criteria identifying egg case nurseries are strongly met for A. hyperborea at Seamount Z110 (468 egg cases of varied ages, maximum density of 5.47 m-2 ) and to a lesser extent on five others (Seamounts K1, Z16, Hill U, Z5 and Hill V). An abundance (density) criterion for defining nurseries needs to be flexible because it is a spatially scale-dependent measure that differs between surveys according to the tools and design employed. Off Australia, coral reef egg case nursery habitat is restricted to a narrow depth range in temperate latitudes where it is scarce and impacted by historical bottom trawl fishing in many locations. There has been effective conservation of nursery habitat, however, because four of the six nursery sites identified here and extensive coral reef areas are protected within marine parks.

Age, growth, maturity and extinction risk of an exploited and endangered skate, Atlantoraja castelnaui, from off Uruguay and northern Argentina.

The spotback skate Atlantoraja castelnaui (Arhynchobatidae) is a large and threatened skate species subjected to fishing pressure, endemic to the Southwest Atlantic that occurs from Rio de Janeiro, Brazil, to San Jorge Gulf, Argentina. The age, growth, age at maturity and the maximum intrinsic rate of population increase rmax of A. castelnaui were studied using 152 specimens collected from off Uruguay and north Argentina (35°-42° S), between June 2013 and February 2020. Vertebrae from 143 individuals were used for ageing (females: n = 83, size range 404-1300 mm total length, TL; males: n = 60, size range 400-1270 mm TL). Maximum ages determined for females and males were 30 and 28 years, respectively. To fit growth models, non-linear and Bayesian estimation approaches were considered. For the first approach, a set of four candidate growth (size-at-age) models were fitted: three-parameter von Bertalanffy, two-parameter von Bertalanffy with fixed L0 , Gompertz and Logistic. In the second approach, von Bertalanffy, Gompertz and Logistic were fitted. For non-linear estimation, model selection indicated that the entire set of candidate growth models were supported by the data. The von Bertalanffy was selected as the best model for Bayesian estimation. There were no differences in growth between sexes. For the sexes combined, the von Bertalanffy growth model by Bayesian method was considered the most adequate to describe the growth of A. castelnaui (growth mean parameters ± S.D.: L∞  = 1210.29 ± 40.68 mm; k = 0.12 ± 0.01 years-1 ; L0  = 179.20 ± 11.62 mm). The age at maturity was estimated at 16.21 and 14.04 years for females and males, respectively. The maximum intrinsic rate of population increase rmax was estimated as 0.252 years-1 . Life-history traits and rmax provided in the present study suggest that this species has a relatively low productivity and may be vulnerable to an intense fishing pressure.

Diversity of Empruthotrema Johnston and Tiegs, 1992 parasitizing batoids (Chondrichthyes: Rajiformes and Myliobatiformes) from the Southwest Atlantic Ocean, with description of three new species.

During an extensive research project involving 519 specimens of batoids, including 13 species of Rajiformes and Myliobatiformes (Chondrichthyes) from the Argentine Sea, three new species of Empruthotrema were found and are described using morphologic characteristics and two molecular markers: LSU rDNA and COI mtDNA. The new species can be distinguished from their congeners by the number and distribution of the marginal loculi, the length and morphology of male copulatory organ, and the presence of eyespots. Additionally, multivariate analysis identified the dimensions of the pharynx and ejaculatory bulb as diagnostic features. Host specificity and previous records of the genus in the region are discussed. This is the first description of new species in this genus for the Southwestern Atlantic Ocean, as well as for arhynchobatid hosts.

Description of a new species of rhinebothriidean tapeworm from the skate Dipturus batis in the Mediterranean Sea.

Examination of rajid skates off the Algerian coast in the Mediterranean Sea revealed that three of the 33 Dipturus batis Linnaeus, 1758 examined harboured a new tapeworm species: Echeneibothrium algeriensis n. sp. This new species, collected from the anterior half of the spiral valves, is described on the basis of morphological data from light and scanning electron microscopy. The new species differs from previously described Echeneibothrium species by details of the scolex and loculi, total length, the length of the myzorhynchus, the number of proglottides, and the number of testes. Comparison of the diets of the ten skate species common in the Mediterranean basin indicates some varying degree of overlap, suggesting that host specificity in this host-parasite system is determined by other host and/or ecological variables such as adaptations of the parasites to their respective hosts, either on the morpho-anatomical level, in physiological characteristics of the parasite's habitat, in the trophic requirements for the successful transmission of the parasite, or in adaptations to the behavioural characteristics of the host. Furthermore, restricted overlap of E. algeriensis n. sp. with congeners in parasite assemblages of D. batis indicates some structuring according to attachment-site preferences. However, attachment-site preferences are not explained solely by morphological compatibility between bothridia and villi. This study reiterates the need to examine multiple factors synergistically in studies on host specificity of parasites, and the need to examine the parasite fauna of hosts across their entire geographical range in order to truly appreciate the biodiversity they harbour.

At-vessel mortality of skates (Rajidae) taken in coastal fisheries and evidence of longer-term survival.

Data on the vigour and at-vessel mortality (AVM) of 6798 skates (comprising Raja clavata n = 6295; R. brachyura n = 208; R. undulata n = 185, R. montagui n = 98 and R. microocellata n = 12) captured by commercial fishing vessels in the inshore waters of the southern North Sea and English Channel were recorded. AVM in longline fisheries averaged 0·44% across five vessels (0-1·47%), although skates were usually unhooked manually and did not usually pass through a bait-stripper. AVM in otter trawls averaged 0·76% (0-2·35%), from four vessels fishing with tow durations of <1·5 h (southern North Sea) or 1-4 h (English Channel). No AVM was noted for skates taken as a by-catch in drift trammel nets (soak times <4 h). Anchored tangle nets resulted in an overall AVM of 2·0-2·7%, but increased from 1·47% (13-28 h soak time) to 6·16% (42-53 h soak time). There were significant differences in the vigour of skates between gears, with R. clavata caught by longline and tangle nets in better condition than those captured by otter trawl or drift trammel net. Similarly, R. undulata caught by tangle net were in better condition than those caught by otter trawl. The vigour of R. undulata was also found to be higher than other skate species for both trawl and tangle net. In total, 5283 skates were tagged with Petersen discs and released, with recapture rates for the various combinations of vessel and gear ranging up to 24·8% for R. clavata. Whilst confirming a degree of post-release survival, quantitative estimates of post-release mortality for skates remain unknown.

A review of elasmobranch catch-and-release science: synthesis of current knowledge, implications for best practice and future research directions.

Until relatively recently commercial fisheries have been considered the main driving factor for elasmobranch population declines. However, this belief has begun to shift with the realization that recreational elasmobranch catches may equal or exceed commercial catches in some regions. Many recreational angling fisheries for elasmobranchs involve high participation in catch-and-release angling practices. However, high release rates may not necessarily equate to high survival rates. Therefore, to assist accurate assessment of the potential impact of recreational angling on elasmobranchs, we attempted to summarize and integrate currently available information on specific risk factors associated with recreational angling, alongside associated mortality rates, as well as information on angler behaviour as it relates to identified risk factors. We categorized the major angling-related effects into two groups: injury-induced effects; and biochemical disruption-induced effects; providing a summary of each group and outlining the main lethal and sub-lethal outcomes stemming from these. These outcomes include immediate and delayed post-release mortality, behavioural recovery periods (which may in-turn confer increased predation risks), chronic health impacts and capture-induced parturition and abortion. Additionally, we detailed a range of angling practices and equipment, including hook-type, hook removal and emersion (i.e. air exposure), as well as inter- and intra-specific factors, including aerobic scope, respiratory mode, body size and species-specific behaviours, which are likely to influence injury and/or mortality rates and should therefore be considered when assessing angling-related impacts. We then utilized these data to provide a range of actionable recommendations for both anglers and policymakers which would serve to reduce the population-level impact of recreational angling on these enigmatic animals.

Morphological and Molecular Evidence Reveals the Longnose Skate Zearaja brevicaudata (Marini, 1933) to be a Senior Synonym of Dipturus lamillai Concha, Caira, Ebert & Pompert 2019.

Longnose skates have great economic importance in South American fisheries, and in order to preserve them, it is important to have a well-defined taxonomic status of their species. Dipturus lamillai was recently described for Malvinas Islands waters based on morphological and molecular comparisons with Zearaja chilensis. Although D. lamillai has been compared with several congeneric species, it was not properly compared with the morphologically similar Zearaja brevicaudata, the most abundant longnose skate in the Southwest Atlantic. Here, these species were compared by morphological and molecular analyses in order to evaluate their conspecificity. Linear morphometric variables of holotype and paratypes of D. lamillai and 69 specimens of Z. brevicaudata were compared and investigated using Principal Component Analysis. In addition, thorn patterns, denticle distributions, color, and clasper morphology were compared. No body proportions or other single character that could differentiate D. lamillai from Z. brevicaudata were found. Molecular analyses comprised of the comparison of the Cytochrome oxidase subunit I (COI) and the NADH dehydrogenase subunit 2. The results of the Maximum Likelihood (ML) carried out for each molecular marker showed that sequences from D. lamillai clustered together with those of Z. brevicaudata, and the molecular distance determined by Kimura two-parameter were lower than the expected for different species. Additionally, the Automatic Barcode Gap Discovery method and the Bayesian implementation of the Poisson tree processes were carried out with COI sequences to explore species limits, and their results were consistent with ML analyses. In summary, the results obtained showed that there are no morphological or molecular differences between these nominal species of the valid skate genus Zearaja, leading to the conclusion that they are conspecific. Therefore, we designated Z. brevicaudata as a senior synonym of D. lamillai.

Complete mitochondrial DNA sequence of Norwegian skates (Raja brachyuran Lafont, 1871) imported to Korea.

In this study, the complete mitochondrial genome of Norwegian skates imported to Korea was sequenced with a circular molecule of 17,121 bp, which consisted of 13 protein-coding genes (PCGs), 2 ribosomal RNAs, 22 transfer RNA genes, and a control region (D-loop). And among these sequences, 193 bp sequence in the D-loop of the genus Raja suggested the possibility of being used as a genetic marker for classification of Raja and Dipturus species. The BI phylogenetic tree by using the nucleotide sequences of 13 PCGs from 15 available mitogenomes of family Rajidae confirmed also that Norwegian skates imported to Korea form a group with Raja brachyura species with high branch value, and that this was a species of Raja brachyura. As above, these results would be expected to provide for the further understanding on the phylogenetic relationship, taxonomic classification and phylogeography of the family Rajidae.

A new genus of Rhinebothriidea from species of Psammobatis (Rajiformes: Arhynchobatidae) off Argentina.

Two species of a new genus of Rhinebothriidea have been collected from species of Psammobatis Günther along the coast of Argentina. Semiorbiseptum gen. nov. is considered a rhinebothriidean for the presence of facially loculated bothridia borne on stalks and cirrus covered with spinitriches. The genus is unique in the arrangement of loculi and septa on the distal bothridial surface, including semicircular septa in the middle region. Despite the anterior-posterior orientation of bothridia, Semiorbiseptum gen. nov. fits well in the description of the family Rhinebothriidae by lacking a myzorhynchus at the adult stage and postvaginal testes, and by having vitelline follicles that are not interrupted at the level of the ovary. The two new species differ from each other in the number of facial bothridial loculi and in the microthrix pattern on the proximal bothridial surface. Unlike the majority of rhinebothrideans in the marine environment, which show high specificity for their definitive host, Semiorbiseptum mariae sp. nov. was found in two species of Psammobatis, the smallthorn sand skate Psammobatis rudis Günther and shortfin sand skate Psammobatis normani McEachran. These species have a sympatric distribution, similar to the hosts of most rhinebothrideans that parasitize more than one host. On the contrary, Semiorbiseptum alfredoi sp. nov. was found only in P. normani. This study shows that some of the characters previously proposed as possible synapomorphies for the order have interspecific variability or can be equivocally interpreted (e.g. the entrance of the vas deferens into the cirrus sac, bothridial stalk shape).

A new Miocene skate from the Central Paratethys (Upper Austria): the first unambiguous skeletal record for the Rajiformes (Chondrichthyes: Batomorphii).

A new fossil skate, Ostarriraja parva gen. et sp. nov., represented by a single partial articulated skeleton collected from the early Miocene fish-bearing strata of Upper Austria, is described here in detail. This taxon exhibits a unique combination of skeletal and dental features (e.g. nasal capsules broad and oval; presence of pectoral arch; compound radial articulated with single radial segments in serial fashion; separated pelvic girdle condyles; reduced catenated calcification of radials; about 86 pectoral radials; 20-21 pelvic-fin radials; 65-70 predorsal vertebrae) that clearly support its assignment to a new genus of the order Rajiformes, and the phylogenetic analyses reveal its basal position within the group. The comparison between Ostarriraja and the holomorphic batoids from Late Cretaceous of Lebanon traditionally aligned with skates concurs to suggest that this Neogene occurrence represents unquestionably the first known skeletal record for the group. The morphological and phylogenetic affinities of Ostarriraja with the living skates suggest a close association of this taxon with the temperate-cold water environments hypothesized for the Central Paratethys during the early Miocene. http://zoobank.org/urn:lsid:zoobank.org:pub:8BB8F0F3-35C5-47FA-AE3C-2CBF445C4BCA.

Almost a century of oblivion: Integrative taxonomy allows the resurrection of the longnose skate Zearaja brevicaudata (Marini, 1933) (Rajiformes; Rajidae).

Zearaja chilensis has been reported from Southern Brazil in the Southwest Atlantic (SWA) to northern Chile in the Southeast Pacific (SEP), and it was listed as vulnerable by the IUCN. Recent molecular studies have called into question the conspecificity between specimens from these opposite coasts of South America, which can have implications for the conservation status of the species. To verify the identity of specimens identified as Z. chilensis, 47 individuals from SWA and 22 from SEP were examined. By comparing external morphology, spinulation pattern, clasper, egg cases, and mitochondrial cytochrome c oxidase I (COI) sequence data, differences between groups were found. Adults from SWA presented longer snout length and shorter tail than those from SEP. Dermal denticles were restricted to the rostral area in SWA skates, whereas in SEP skates most of the dorsal surface was covered with denticles. Marked differences in the morphology of several components of clasper were noticeable. Egg cases of SWA skates had thinner lateral keels than those of SEP. Molecular analysis revealed two well-defined cohesive clusters, corresponding to SWA and SEP specimens, respectively. Average K2P distance between groups was 3.4%, higher than expected for intraspecific differences, and sequences were assigned to different BINs. These integrative approaches strongly support that specimens from SWA known as Z. chilensis correspond to a different nominal species than those from SEP. Herein, Z. brevicaudata (Marini 1933) is resurrected from synonymy with Z. chilensis.

Female reproductive traits of a commercially exploited skate: Atlantoraja platana (Günther, 1880) (Chondrichthyes, Rajidae). Ovarian morphology, gametogenesis and microscopic verification of maturity criteria.

Atlantoraja platana is an endemic species of the Southwest Atlantic Ocean, and is one of the most captured by the local bottom trawl industrial fisheries. In this work, the microscopic architecture of mature female's gonads and the dynamics of follicle development are studied as a contribution to raise awareness of reproductive biology of the species. Folliculogenesis depicts the same histologic pattern as in other Elasmobranchs. Follicles in different degrees of maturation coexist in mature animals. The oogonia were only found in immature individuals. Likewise, atretic follicles were recorded in ovaries of all sexual maturity stages. The microscopic size recorded from the beginning of yolk input is smallest than the detected with the necked eye. This study provides valuable information about female's gametogenesis that could be taken into account in the development of fisheries management.

Complete mitochondrial genome of the Yellow-spotted skate Okamejei hollandi (Rajiformes: Rajidae).

The complete mitochondrial genome of the Yellow-spotted skate Okamejei hollandi was determined in this study. It is 16,974 bp in length and contains 13 protein-coding genes, two rRNA genes, 22 tRNA genes, and one putative control region. The overall base composition is 30.5% A, 27.8% C, 14.0% G, and 27.8% T. There are 28 bp short intergenic spaces located in 12 gene junctions and 31 bp overlaps located in nine gene junctions in the whole mitogenome. Two start codons (ATG and GTG) and two stop codons (TAG and TAA/T) were used in the protein-coding genes. The lengths of 22 tRNA genes range from 68 (tRNA-Ser2) to 75 (tRNA-Leu1) bp. The origin of L-strand replication (OL) sequence (37 bp) was identified between the tRNA-Asn and tRNA-Cys genes. The control region is 1311 bp in length with high A + T and poor G content.

Complete mitochondrial genome and the phylogenetic position of the Borneo leg skate Sinobatis borneensis (Rajiformes: Anacanthobatidae).

In this study, the complete mitochondrial genome of the Borneo leg skate Sinobatis borneensis (Rajiformes, Anacanthobatidae) was determined. It had circular molecules (16,701 bp), consisting of 37 genes with a typical gene order in vertebrate mitogenome. In the whole mitogenome, there were 28 bp short intergenic and 31 bp overlaps, respectively, located in 12 and 7 gene junctions. The nucleotide composition was 31.1% A, 26.0% C, 13.9% G and 29.1% T. Two start codons (GTG and ATG) and two stop codons (TAG, TAA/T) were used in the protein-coding genes. The 22 tRNA genes ranged from 66 bp (tRNA-Cys) to 75 bp (tRNA-Leu1 and tRNA-Lys). The phylogenetic result showed that S. borneensis was clustered with the Atlantoraja castelnaui and Pavoraja nitida.

Complete mitochondrial genome and the phylogenetic position of the Leadhued skate Notoraja tobitukai (Rajiformes: Arhynchobatidae).

In this study, the complete mitochondrial genome of the Leadhued skate Notoraja tobitukai (Rajiformes: Arhynchobatidae) was determined. It was a circular molecule (16, 799 bp), consisted of 37 genes with a typical gene order in vertebrate mitogenome. In the whole mitogenome, there were 24 bp short intergenic and 26 bp overlaps. The nucleotide composition was 32.3% A, 22.6% C, 13.1% G and 32.0% T. Two start codons (GTG and ATG) and two stop codons (TAG, TAA/T--) were used in the protein-coding genes. The 22 tRNA genes ranged from 65 bp (tRNA-Cys) to 75 bp (tRNA-Leu1). The phylogenetic result showed that N. tobitukai was clustered with the Pavoraja nitida.

Complete mitochondrial genome and the phylogenetic position of the Leadhued skate Notoraja tobitukai (Rajiformes: Arhynchobatidae).

In this study, the complete mitochondrial genome of the Leadhued skate Notoraja tobitukai (Rajiformes: Arhynchobatidae) was determined. It was a circle molecular (16, 799 bp), consisted of 37 genes with a typical gene order in vertebrate mitogenome. In the whole mitogenome, there were 24 bp short intergenic and 26 bp overlaps. The nucleotide composition was 32.3% A, 22.6% C, 13.1% G and 32.0% T. Two start codons (GTG and ATG) and two stop codons (TAG, TAA/T) were used in the protein-coding genes. The 22 tRNA genes ranged from 65 bp (tRNA-Cys) to 75 bp (tRNA-Leu1). The phylogenetic result showed that N. tobitukai was clustered with the Pavoraja nitida.

Complete mitochondrial genome and the phylogenetic position of the Bowmouth guitarfish Rhina ancylostoma (Rajiformes, Rhinobatidae).

In this study, the complete mitochondrial genome of the Bowmouth guitarfish Rhina ancylostoma (Rajiformes, Rhinobatidae) was first determined. The total length of this circle DNA was 17 217 bp, consisted of 37 genes with a typical gene order in vertebrate mitogenome. It had 42 bp short intergenic spaces and 40 bp overlaps. The nucleotide composition in R. ancylostoma was as follows: A, 33.0%; C, 25.1%; G, 12.6% and T, 29.3%. Two start codons (GTG and ATG) and two stop codons (TAG and TAA/T) were used in the protein-coding genes. The 22 tRNA genes were ranged from 67 bp (tRNA-Ser2) to 75 bp (tRNA-Leu1). The phylogenetic result showed that R. ancylostoma was clustered with the Rhinobatos.

Complete mitochondrial genome and the phylogenetic position of the White-spotted guitarfish Rhynchobatus australiae (Rajiformes, Rhinobatidae).

We first determined the complete mitochondrial genome of the White-spotted guitarfish Rhynchobatus australiae (Rajiformes, Rhinobatidae). The complete mitogenome was 16,804 bp, with a base composition of 32.3% A, 27.5% T, 26.9% C and 13.3% G, containing 13 protein-coding genes, two rRNAs, 22 tRNAs and a control region (D-loop). It had 35 bp short intergenic spaces and 39 bp overlaps between genes. The gene order and composition of R. australiae was similar to most other fishes. The codon usage followed the typical vertebrate mitochondrial pattern (ATG or GTG for start codon and TAA or T for stop codon). The phylogenetic result showed that R. australiae was clustered with the Rhinobatos.

Long-PCR based next generation sequencing of the whole mitochondrial genome of the peacock skate Pavoraja nitida (Elasmobranchii: Arhynchobatidae).

We determined the complete mitochondrial genome sequence (16,760 bp) of the peacock skate Pavoraja nitida using a long-PCR based next generation sequencing method. It has 13 protein-coding genes, 22 tRNA genes, 2 rRNA genes, and 1 control region in the typical vertebrate arrangement. Primers, protocols, and procedures used to obtain this mitogenome are provided. We anticipate that this approach will facilitate rapid collection of mitogenome sequences for studies on phylogenetic relationships, population genetics, and conservation of cartilaginous fishes.

Mitochondrial genome of the ringstraked guitarfish Rhinobatos hynnicephalus (Elasmobranchii: Rajiformes).

The complete mitochondrial genome of the ringstraked guitarfish Rhinobatos hynnicephalus is firstly presented in this study, which is also the first representative in the family Rhinobatidae. It is 16,776 bp in length and contains 37 genes and one control region as the typical gene arrangement and transcriptional direction in vertebrates. The overall base composition is 31.7% A, 26.8% C, 13.5% G and 28.1% T. The 22 tRNA genes ranged from 67 bp (tRNA-Ser2) to 75 bp (tRNA-Leu1). The origin of L-strand replication (OL) sequence was identified between tRNA-Asn and tRNA-Cys genes. The termination associated sequence (TAS) and the conserved sequence blocks (CSB 1--3) were recognized in the control region.