An integrated approach towards conservation management of hammerhead sharks in the southwestern Indian Ocean.

Clemo, N. J.*¹, Klein, J. D.¹, Bennet, R.², Dicken, M. L.³, Jaquemet, S.⁴, Bester-van der Merwe, A. E.¹

¹ Molecular Breeding and Biodiversity Research Group, Department of Genetics, Stellenbosch University, Stellenbosch, South Africa.
² Wildlife Conservation Society, Western Indian Ocean Shark and Ray Conservation Program, Bronx, NY, USA.
³ KwaZulu-Natal Sharks Board, Umhlanga Rocks, South Africa.
⁴ UMR Entropie, Université de La Réunion, La Réunion 97744, France.

Coastal communities in the southwestern Indian Ocean (SWIO) rely heavily on fisheries for both income and sustenance. The majority of fisheries in this region are small-scale artisanal fisheries, many of which catch sharks for both local consumption and export. One of the most important sharks caught in these fisheries is Sphyrna lewini (scalloped hammerhead shark), which is currently categorised as Critically Endangered on the International Union for the Conservation of Nature’s Red List of Threatened Species. Very little is known about the population dynamics and diversity of this species within the SWIO, information that is vitally important for the implementation of conservation measures. For a more holistic approach to conservation, it is important to consider how local fishers view sharks, and hammerhead sharks in particular. This study aims to generate genetic data from S. lewini specimens obtained in the SWIO to assess the genetic diversity and population connectivity of the species in this region. A 552bp section of the control region (a highly variable, non-coding region of mitochondrial DNA) has been successfully sequenced for 108 samples, sourced from four nations in the SWIO, namely: South Africa, Mozambique, Tanzania, and Réunion Island (France). Preliminary results show a single large haplogroup has been observed containing many individuals from all four sampling nations, as well as several smaller haplotypes containing individuals from multiple sampling nations. These results suggest the presence of minimal genetic structure within the SWIO, suggesting there is ample admixture within the population and supporting the notion that S. lewini is a semi-oceanic species.The sequences produced in this study will also be used to augment an existing baseline database used for DNA zip-coding. DNA zip-coding is used to identify the source population of samples collected from shark fin markets, and thereby pinpoint geographic locations where increased conservation measures are needed. The inclusion of these sequences in the database will increase the accuracy of these assays for samples originating from the Indian Ocean. Finally, interviews will be conducted with local fishers in the region to assess a variety of metrics regarding their intent and knowledge regarding shark fishing. These data will be essential for formulating conservation measures at the ground level, enabling effective conservation actions to be implemented from both the top-down and bottom-up.

Keywords: Elasmobranchs, Sphyrna, conservation management, population genetics, control region, zip-coding