Status of Southeast Asia's marine sharks and rays.

In Southeast Asia, elasmobranchs are particularly threatened. We synthesized knowledge from the peer-reviewed and gray literature on elasmobranchs in the region, including their fisheries, status, trade, biology, and management. We found that 59% of assessed species are threatened with extinction and 72.5% are in decline; rays were more threatened than sharks. Research and conservation is complicated by the socioeconomic contexts of the countries, geopolitical issues in the South China Sea, and the overcapacity and multispecies nature of fisheries that incidentally capture elasmobranchs. The general paucity of data, funds, personnel, and enforcement hinders management. Reduced capacity in the general fishery sector and marine protected areas of sufficient size (for elasmobranchs and local enforcement capabilities) are among recommendations to strengthen conservation.

En el sureste de Asia, los elasmobranquios se encuentran particularmente amenazados. Sintetizamos el conocimiento a partir de la literatura gris y revisada por pares sobre los elasmobranquios en la región, incluidos sus pesquerías, estado, mercado, biología y manejo. Nuestra evaluación incluyó x especies de tiburones y y especies de rayas. Descubrimos que el 59% de las especies evaluadas están bajo amenaza de extinción y 72.5% están en declive; de estas, las rayas estuvieron más amenazadas que los tiburones. La investigación y la conservación son complicadas debido al contexto socioeconómico de los países, los temas geopolíticos en el Mar del Sur de China y la sobrecapacidad y naturaleza multiespecie de las pesquerías que capturan accidentalmente a los elasmobranquios. La escasez general de datos, financiamiento, personal y aplicación limita el manejo. La capacidad reducida en el sector generalizado de la pesquería y las áreas marinas protegidas de tamaño suficiente (para los elasmobranquios y las capacidades de aplicación local) se encuentran entre las recomendaciones para fortalecer la conservación.

DNA-based species identification of shark fins traded in thai markets.

Shark fins are among the most highly prized seafood products in the world with massive consumption in Asia over the past several decades. The demand for shark fins is a major driver of the enormous population declines of elasmobranchs that are generally vulnerable to overexploitation. This study aims to better understand the species composition of shark fin products in Thailand and their conservation statuses by using DNA-based species identification. Various types and sizes of shark fins were collected from 4 locations in Thailand. DNA barcoding method based on a fragment of the cytochrome c oxidase subunit I (COI) gene was applied to species identification. Fins from at least 15 shark species were found from Thailand's markets. The spottail shark (Carcharhinus sorrah) and the night shark (Carcharhinus signatus) were the two dominant species presented in this study. 34% of identifiable samples are the species that have not been record in this region. 62% of species detected from the fin samples are categorized under the threatened categories of IUCN Red List. Species composition reported in shark fin products potentially helps indicate the appropriate conservation action and increases awareness from monitoring the trade in elasmobranch products. Supplementary Information: The online version contains supplementary material available at 10.1007/s10592-023-01519-0.

Citizen science reveals the population structure and seasonal presence of whale sharks in the Gulf of Thailand.

The whale shark Rhincodon typus is a broadly distributed and highly mobile planktivorous shark species. The sharks form predictable aggregations in many areas, providing the opportunity for cost-effective scientific monitoring through divers and other marine resource users. Sightings of individuals outside of these aggregate zones elsewhere in their range are typically rare. We used a citizen science-based approach to shed light on occurrence and seasonality in the waters around Koh Tao, Thailand and neighbouring islands in the Gulf of Thailand. Although there is a paucity of quantitative data, anecdotal reports suggest substantial declines in sightings in the early 2000s. We identified a total of 178 individual whale sharks (from 249 sightings) between 2004 and 2019, with most of these (84%) from the 2015-2019 time period due to an increase in sighting reports facilitated by social media and direct marketing. Size estimates were reported for 102 of the sightings, with a range of 2-6 m and mean of 3.7 m overall. Sex was reported for 27% of sightings, with a 2:1 female-to-male ratio. Modified maximum likelihood methods suggest whale sharks are transient to Koh Tao and surrounding areas, with whale shark sightings following the regional monsoon cycle. One international resighting was obtained from Malaysian waters (~700 km away). Encouraging citizen science participation is particularly useful in data-poor regions like the Gulf of Thailand, despite limitations in size and sex estimation reliability, which can play an important complementary role in dedicated research programs.

Integrated Taxonomy Revealed Genetic Differences in Morphologically Similar and Non-Sympatric Scoliodon macrorhynchos and S. laticaudus.

Previous examination of the mitochondrial NADH2 gene and morphological characteristics led to the resurrection of Scoliodon macrorhynchos as a second valid species in the genus, in addition to S. laticaudus. This study applied an integrated taxonomic approach to revisit the classification of the genus Scoliodon based on new materials from the Malaysian Peninsula, Malaysian Borneo and Eastern Bay of Bengal. Mitochondrial DNA data suggested the possibility of three species of Scoliodon in the Indo-West Pacific, while the nuclear DNA data showed partially concordant results with a monophyletic clade of S. macrorhynchos and paraphyletic clades of S. laticaudus and S. cf. laticaudus from the Malacca Strait. Morphological, meristic and dental characteristics overlapped between the three putative species. Collective molecular and morphological evidence suggested that the differences that exist among the non-sympatric species of Scoliodon are consistent with isolation by distance, and Scoliodon macrorhynchos remains as a valid species, while S. cf. laticaudus is assigned as S. laticaudus. The Malacca Strait acts as a spatial delineator in separating the Pacific S. macrorhynchos (including South China Sea) from the Northern Indian Ocean S. laticaudus. Future taxonomic work should focus on clarifying the taxonomic status of Scoliodon from the Indonesian waters.

Complete mitochondrial genome of the blacktip reef shark Carcharhinus melanopterus (Carcharhiniformes: Carcharhinidae).

The complete mitochondrial genome of the blacktip reef shark Carcharhinus melanopterus is determined for the first time in this study. The gene composition and order in the mitogenome of C. melanopterus is identical to most vertebrates. The overall base composition is 31.3% A, 25.3% C, 13.3% G and 30.1% T. There are 29 bp overlaps and 21 bp short intergenic spaces in the mitogenome. Two start codons and three stop codons were found in protein-coding genes. The dihydrouridine arm of tRNA-Ser2 was replaced by a simple loop and the other tRNAs could be folded into the typical cloverleaf structure. The termination associated sequence (TAS) and the conserved sequence blocks (CSB1-3) are found in the control region.

Complete mitochondrial genome of the mangrove whipray Himantura granulata (Myliobatiformes: Dasyatidae).

In this study, the complete mitogenome of mangrove whipray Himantura granulata was first determined. It is 17,657 bp in length and consists 22 tRNA genes, 2 rRNA genes, 13 protein-coding genes and 1 putative control region with the typical gene arrangement and transcriptional orientation in vertebrates. Two start codon patterns and two stop codon patterns were found in the protein-coding genes. The tRNA-Ser2 (GCU) could not form the typical clover-leafs structure for lacking the dihydrouridine arm. The control region is 1914 bp in length with poor G (14.9%) and high A + T (59.1%) content.