Abstract
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.
Highlights
The scalloped hammerhead shark, Sphyrna lewini is considered a coastal species because of its need for nursery areas
All sequences of S. lewini obtained were deposited in the BOLD System with the Barcode Index Number (BIN) registry of BOLD: 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
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
Summary
The scalloped hammerhead shark, Sphyrna lewini is considered a coastal species because of its need for nursery areas. It is distributed in tropical waters as well as on the mainland, islands, and near the coastal region [1, 2]. Around one to three million sharks are killed each year because of fishing and the shark fin trade around the world [7, 8] This species was considered to be underexploited in 1999. The Convention on International Trade in Endangered Species (CITES) listed hammerhead sharks in Appendix II, and in 2019 the status was upgraded to Critically Endangered (CR) [10]
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