Extensive genetic population structure in the Indo–West Pacific spot-tail shark, <I>Carcharhinus sorrah</I>

Abstract

Carcharhinus sorrah (Mulle and Henle, 1839) is a coastal pelagic shark of the tropical and subtropical Indo?West Pacific, reaching 1.6 m total length. The species is widely harvested in line, net, and trawl fisheries over tropical continental shelves. We investigated mtDNA genetic differentiation in C. sorrah across the majority of the species' range, and examined the importance of six major historical and contemporary biogeographic features in shaping population genetic structure in this species. The present study includes dense sampling for a shark species across the Indo-West Pacific, with 349 specimens sampled from 21 collection locations from the northwestern Indian Ocean, Southeast Asia, New Caledonia, and to southerly distribution limits in Australia. Based on 469 base pairs of the control region, we found extensive genetic population structure, with allopatric lineages confined to Australia, New Caledonia, and the remaining surveyed area. Significant genetic subdivisions were observed over stretches of deep water dividing shelf habitat, particularly the Indonesian Throughflow-Timor Passage and Coral Sea, consistent with strong shelf habitat associated dispersal. Male length at maturity was consistent with a larger size throughout Southeast Asia and the Arabian Sea than known from Australia. Carcharhinus sorrah currently is assessed range-wide on the IUCN Red List (Near Threatened) based largely on Australian demographic data, which may under-represent overharvest risk in other parts of the species' range. The present study highlights the need for independent risk assessment and management for C. sorrah in Australia, Southeast Asia and the northwestern Indian Ocean, and New Caledonia.