Molecular and morphological evidence for the identity of the blackspot shark, Carcharhinus sealei , and the Indonesian w
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Molecular and morphological evidence for the identity of the blackspot shark, Carcharhinus sealei, and the Indonesian whaler shark, C. tjutjot, with notes on their population structures Azie Azri & Hussein Taha & Takaomi Arai
Received: 27 April 2020 / Accepted: 6 September 2020 # Springer Nature B.V. 2020
A b s t r a c t The requiem sharks of the genus Carcharhinus are captured as bycatch in the IndoPacific region. The lack of morphometric data due to the common practice of head and fin removal of sharks, hinders the implementation of shark management measures. Carcharhinus specimens found in the waters of Brunei Darussalam were identified using morphological analysis, and their identification was further validated by mitochondrial cytochrome c oxidase subunit I (COI) gene sequence analysis. This study successfully identified twenty-seven specimens as either the blackspot shark, Carcharhinus sealei, or the Indonesian whaler shark, Carcharhinus tjutjot, by molecular genetic analysis, although the difficulty of accurately identifying these sharks solely on morphology was encountered. Mitochondrial COI gene sequence analysis also suggested that C. tjutjot has two genetically distinct populations/groups, while C. sealei had a single panmictic population in the Indio-Pacific region. The findings suggest that C. sealei could be a more highly migratory species than C. tjutjot in the region. Keywords Carcharhinus . Genetic identification . Migration . Population structure . Sharks . South China Sea . Tropical waters
A. Azri : H. Taha : T. Arai (*) Environmental and Life Sciences Programme, Faculty of Science, Universiti Brunei Darussalam, Jalan Tungku Link, Gadong, BE 1410, Brunei Darussalam e-mail: [email protected]
Introduction There is growing worldwide concern that an increase in demand for shark fins will have a catastrophic impact on shark populations and stocks. Many shark species are highly vulnerable to fishing pressure as they are slow to mature and have low fecundity and long gestation periods (Hamlet 2005). Historical and long-term catch data are less reported in sharks than in teleosts due to the lower com mercial value of shark fisheries. Morphologically similar species are often grouped together in catch records, and carcasses processed at sea can be misidentified on landing if their characteristic body parts have been removed. The lack of catch statistics makes it difficult for stock assessment and fisheries management for sharks. The requiem sharks of the genus Carcharhinus are among the most economically important groups of sharks in tropical regions of the world (White and Sommerville 2010). Since many of these species are morphologically similar, accurate identifications are often difficult, particularly when ontogenetic changes may lead to misidentification issues, e.g., C. sealei has often been listed as C. tjutjot due to morphological similarities between them (Compagno 1984). Sharks landed without fins makes identification using traditional field characters particularly difficult. Molecula
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