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.

Genetic connectivity of the scalloped hammerhead shark Sphyrna lewini across Indonesia and the Western Indian Ocean.

Scalloped Hammerhead shark (Sphyrna lewini) is an endangered species which its populations have been declining globally including in Indonesia, the world's top shark fishing country. However, there is a lack of information on the recent population structure of this species to promote proper management and its conservation status. This study aimed to investigate the genetic diversity, population structure, and connectivity of the S. lewini population, in three major shark landing sites: Aceh (n = 41), Balikpapan (n = 30), and Lombok (n = 29). Meanwhile, additional sequences were retrieved from West Papua (n = 14) and the Western Indian Ocean (n = 65) populations. From the analyses of the mitochondrial CO1 gene, a total of 179 sequences of S. lewini, with an average size of 594 bp, and 40 polymorphic loci in four and eight haplotypes for the Indonesian population and the Western Indian Ocean population were identified. The overall values of genetic diversity were high (h = 0.717; π = 0.013), with the highest values recorded in Aceh (h = 0.668; π = 0.002) and the lowest in Papua (h = 0.143; π = 0.000). On the contrary, the overall value was fairly low in the Western Indian Ocean (h = 0.232; π = 0.001). Furthermore, AMOVA and FST showed three significant subdivisions in Indonesia (FST = 0.442; P < 0.001), with separated populations for Aceh and West Papua, and mixed between Balikpapan and Lombok (FST = 0.044; P = 0.091). In contrast, genetic homogeneity was observed within the population of the Western Indian Ocean (FST = -0.013; P = 0.612). The establishment of a haplotype network provided evidence of a significantly different population and a limited genetic distribution between the Indonesian and the Western Indian Ocean populations (FST = 0.740; P < 0.001). This study showed the presence of a complex population of S. lewini with limited connectivity only in Indonesia separated from the Western Indian Ocean and requiring specific management measures based on the population structure at the regional level.