Search

Genetic effective population size (N) estimators are useful as applied conservation tools. Many elasmobranch (shark and ray) species are threatened at local and global scales, and tools to monitor these populations are greatly needed. This study investigates contemporary N and its relationship with census size (N) in a population of zebra sharks ( Stegostoma fasciatum). Our N using the linkage disequilibrium method, 377 (95 % CI 274-584) was found to closely approximate the mark-recapture N for this population of mature sharks (458, 95 % CI 298-618), with an N/N ratio of 0.82 (SE = 0.33). Furthermore, we conducted a series of sensitivity analyses to examine how the numbers of samples and loci affect the precision and accuracy of the estimators. We demonstrate that for this species robust and precise estimates are obtainable with a minimum of 91 samples (approximately 20 % of the census population) and 10 microsatellite loci. These findings contribute important information to the greater body of N and N/N relationships in elasmobranchs and wildlife populations as well as provide important guidelines for implementing genetic monitoring in elasmobranch conservation efforts. [ABSTRACT FROM AUTHOR]

Since the first investigation 25 years ago, the application of genetic tools to address ecological and evolutionary questions in elasmobranch studies has greatly expanded. Major developments in genetic theory as well as in the availability, cost effectiveness and resolution of genetic markers were instrumental for particularly rapid progress over the last 10 years. Genetic studies of elasmobranchs are of direct importance and have application to fisheries management and conservation issues such as the definition of management units and identification of species from fins. In the future, increased application of the most recent and emerging technologies will enable accelerated genetic data production and the development of new markers at reduced costs, paving the way for a paradigm shift from gene to genome-scale research, and more focus on adaptive rather than just neutral variation. Current literature is reviewed in six fields of elasmobranch molecular genetics relevant to fisheries and conservation management (species identification, phylogeography, philopatry, genetic effective population size, molecular evolutionary rate and emerging methods). Where possible, examples from the Indo-Pacific region, which has been underrepresented in previous reviews, are emphasized within a global perspective. [ABSTRACT FROM AUTHOR]

The Indo-West Pacific (IWP), from South Africa in the western Indian Ocean to the western Pacific Ocean, contains some of the most biologically diverse marine habitats on earth, including the greatest biodiversity of chondrichthyan fishes. The region encompasses various densities of human habitation leading to contrasts in the levels of exploitation experienced by chondrichthyans, which are targeted for local consumption and export. The demersal chondrichthyan, the zebra shark, Stegostoma fasciatum, is endemic to the IWP and has two current regional International Union for the Conservation of Nature (IUCN) Red List classifications that reflect differing levels of exploitation: ‘Least Concern’ and ‘Vulnerable’. In this study, we employed mitochondrial ND4 sequence data and 13 microsatellite loci to investigate the population genetic structure of 180 zebra sharks from 13 locations throughout the IWP to test the concordance of IUCN zones with demographic units that have conservation value. Mitochondrial and microsatellite data sets from samples collected throughout northern Australia and Southeast Asia concord with the regional IUCN classifications. However, we found evidence of genetic subdivision within these regions, including subdivision between locations connected by habitat suitable for migration. Furthermore, parametric FST analyses and Bayesian clustering analyses indicated that the primary genetic break within the IWP is not represented by the IUCN classifications but rather is congruent with the Indonesian throughflow current. Our findings indicate that recruitment to areas of high exploitation from nearby healthy populations in zebra sharks is likely to be minimal, and that severe localized depletions are predicted to occur in zebra shark populations throughout the IWP region. [ABSTRACT FROM AUTHOR]