Abstract
The demersal brown banded bamboo shark Chiloscyllium punctatum is a major component of sharks landed in Malaysia. However, little is known about their population structure and the effect of high fishing pressure on these weak swimming sharks. Both mitochondrial DNA control region (1072 bp) and NADH dehydrogenase subunit 2 (1044 bp) were used to elucidate the genetic structure and connectivity of C. punctatum among five major areas within the Sundaland region. Our findings revealed (i) strong genetic structure with little present day mixing between the major areas, (ii) high intra-population genetic diversity with unique haplotypes, (iii) significant correlation between genetic differentiation and geographical distance coupled with detectable presence of fine scale geographical barriers (i.e. the South China Sea), (iv) historical directional gene flow from the east coast of Peninsular Malaysia towards the west coast and Borneo, and (v) no detectable genetic differentiation along the coastline of east Peninsular Malaysia. Genetic patterns inferred from the mitochondrial DNA loci were consistent with the strong coastal shelf association in this species, the presence of contemporary barriers shaped by benthic features, and limited current-driven egg dispersal. Fine scale population structure of C. punctatum highlights the need to improve genetic understanding for fishery management and conservation of other small-sized sharks.
Highlights
Sharks are generally highly vulnerable to overexploitation due to their life history strategies, such as late maturity and low fecundity[1,2,3,4,5]
A total of 70 unique haplotypes and 63 polymorphic sites were detected, in which 40 sites were found in the Control region (CR) region and the rest were found in the NADH dehydrogenase subunit 2 (ND2) region (Supplementary Tables S1 and S2)
Evidence from this study showed some support for selective directional population expansion for C. punctatum the demographic history may not be shared for all the populations in Malaysia
Summary
Sharks are generally highly vulnerable to overexploitation due to their life history strategies, such as late maturity and low fecundity[1,2,3,4,5]. Studies on small-sized benthic coastal sharks have increased in recent years in part due to their catch prominence and importance in coastal fisheries, both globally and in Southeast Asia, e.g. whitespotted bambooshark Chiloscyllium plagiosum[16], nurse shark Ginglymostoma cirratum[17], whitetip reef shark Triaenodon obesus[18], leopard shark Triakis semifasciata[19] and common smoothhound Mustelus mustelus[20]. One such group of sharks is the longtail carpet shark or bamboo shark from the family Hemiscyllidae (order Orectolobiformes). Despite growing concerns of shark exploitation in Malaysia as one of the top shark-fishing nation globally[40], genetic studies of local shark populations, including C. punctatum are almost non-existent (see Dudgeon et al.[41] for exception)
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