Browsing by Author "Andreotti, Sara"
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- ItemThe conservation of South African white sharks : population number, genetic distinctiveness and global connections(Stellenbosch : Stellenbosch University, 2015-03) Andreotti, Sara; Matthee, Conrad A.; Von der Heyden, Sophie; Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology.ENGLISH SUMMARY: The white shark (Carcharodon carcharias) is IUCN red listed as vulnerable, but the lack of basic biological information is arguably the biggest obstacle facing the conservation of the species. The aim of this project was to aid in the conservation of white sharks by producing various data sets that can be used in adaptive management. In doing so we estimated the South African white shark population number, their genetic connectivity along the coastline and investigate various behavioural aspects. We developed a categorization system to manage large photographic databases for individual identifications of white sharks by making use of dorsal fin images. The novel categorization system was developed by making use of 4398 photos taken over a 27 month period. A notches code method was produced and this proved to significantly reduce the search time associated to accurately identify individuals. From the photos we identified 426 individuals in the Gansbaai region of South Africa. By using a mark-recapture technique and the open population model POPAN, we estimated a range between 353 - 522 individuals (95% confidence). These data were confirmed by analyses of 14 polymorphic microsatellite markers for C. carcharias that revealed a contemporary effective population size (CNe) of 338 individuals (95% confidence, Pcrit = 0.01). Both estimates are in the same range but considerably less than a previously published estimate (e.g. N = 808 to 1008) that relyied on fin matching software (DARWIN) to automatically match the sharks’ dorsal fin. Through software validation, we provided evidence that DARWIN failed to produce accurate estimates and the discrepancy in population numbers are most likely due to the inclusion of false negatives in the published literature. To determine whether the Gansbaai population forms a unique evolutionary unit, the phylogeography of white sharks along the South African coastline was investigated by making use of mtDNA and microsatellite markers. A total of 238 unique individuals were sampled originating from five aggregation sites. Four mtDNA haplotypes were found for the entire range. One common mtDNA haplotype was shared by 89% of the individuals sampled, and a second haplotype (13 bp different) was present in 10% of the remaining sharks. No phylogeographic structure was found among aggregation sites. This finding was supported by microsatellite analyses and both data sets show a remarkably low level of genetic diversity (h = 0.02, π = 0.0027; Na = 7.6, Ho = 0.675). The genetic results suggest that the South African population is the result of a founder event or a severe bottleneck in the recent past. These data were combined with published mtDNA data at the global level and results suggest that at the continental scale three distinct mtDNA clades occur. These are confined to the Mediterranean and Indo-Pacific Oceans (Clade 1), the Atlantic and Indian Oceans (Clade 2) and a single haplotype restricted to the waters of South Africa (Clade 3). These clades are probably the result of allopatric speciation associated with the closure of the Isthmus of Panama as confirmed by dating analyses. By combining the mark-recapture analyses and genetic techniques, permutations test revealed that during scavenging situations, sharks associate with conspecifics in a non-random structure (Mean of pairwise associations = 728, mean of permutation test = 597, P = 0.00). Analyses of the nature of such associations were not statistically significant, but provided some insights (e.g. partial sexual segregation and different class size groupings) indicative of a complex social system which may rather mirror that of marine mammals. Based on the results of this study South African white sharks require more protection than previously thought and a long term management plan is needed to secure the future survival of the species, this will need to take into account the low genetic diversity and to include constant assessments of the population numbers.