By Dr Ryan Daly
During winter on the KZN coast there is an influx of sharks associated with the sardines. These include dusky sharks (Carcharhinus obscurus), blacktip sharks (Carcharhinus limbatus), spinner sharks (Carcharhinus brevipinna) and others. We know they make the most of winter in KZN to feed on the sardines but it’s still unclear what all these sharks do for the rest of the year. In order to find out more about these shark’s migration and habitat use, we have been making the most out of one of the best sardine runs on record in KZN to tag these sharks.
In order to investigate the movements of these sharks, we fit them with acoustic tags that ping a unique coded ID to underwater receivers located along our coastline from Cape Town to the Mozambique border. We are then able to follow their movements for over 6-8 years as they make annual migrations along our coast. For some sharks like the Endangered dusky shark, we will hopefully be able to improve their conservation by understanding more about areas that are critical for them. The KZN coastline remains an important nursery area for juvenile dusky sharks but we don’t know much about their movements as they mature which may take up to 25 years. We hope that by tagging a range of juveniles and adult sharks we are able to find out more about this species and discover which areas on our coast are most important from juvenile to adult sharks so that we can design effective conservation strategies for the species.
As sharks are increasingly under threat from fisheries globally, South Africa remains an important shark “hotspot” and we need to ensure that these top predators continue to thrive and support healthy, balanced marine ecosystems. As such, we hope that by studying their movements along the South African coast we are able to promote their conservation.