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Sevengills on the Move

PhD student: Tammy Engelbrecht (UCT)

Supervisors: Prof Justin O’Riain (UCT), Dr Alison Kock (Shark Spotters, UCT, SAIAB), Dr Adam Barnett (James Cook University)

Funded by:
 UCT, Two Oceans Aquarium, Ocearch


This study aims to investigate the distribution, behaviour and spatial ecology of sevengills in southern Africa using data derived from fisheries combined with acoustic and satellite telemetry. Although the project is in its early stages, we have already made some interesting discoveries.

Long-term tag-and-recapture data for sevengills from recreational angling in southern Africa has shown them to be wide-ranging, capable of large-scale migrations of up to 600 kilometres (370 miles)!


coastal_movements

Broad scale (>400 km) coastal movements of sevengill sharks in South Africa. Minimum coastal distance between sites is indicated, as well as the direction of movement.

Yet even though they can travel long distances, sevengills commonly return to specific coastal areas seasonally, a characteristic known as site fidelity. In one particular case a sevengill tagged by an angler in Namibia was recaptured in the exact same fishing spot more than four years later. Furthermore, despite the species’ wide-ranging capability, no sevengills tagged in Namibia were reported recaptured in South African waters (or vice versa), which may indicate that populations are regionally segregated. These preliminary findings provide a glimpse into the complexities of sevengill behaviour and show that we have a long way to go before we understand this enigmatic species.


sevengill_distributionMap showing catch locations (blue icons) for broadnose sevengill sharks in Southern Africa.

In the next phase of this research we will use acoustic and satellite telemetry to dig more deeply into the mysterious movements of sevengills and investigate what drives these patterns – on a fine scale in False Bay and more broadly along the South African coastline.

So, how does this research fit into the mandate of Shark Spotters? Over the past 10 years Shark Spotters, with the support of the Save Our Seas Foundation, have focused research on the well-known white sharks of False Bay. Through this work we have gained an understanding of the white shark presence and how this varies over space and time, but we still have limited insight into the greater role of large, predatory sharks in coastal ecosystems and what drives their behaviour. The Shark Spotters’ research programme has therefore expanded from studying a single species in isolation to investigating the interactions between white sharks, other predatory sharks like the sevengills, their prey and the environment. This will enable us to improve our understanding not only of the apex predators that live in False Bay, but also of the complex and dynamic ecosystem that these sharks are a pivotal part of. Through this research, we can gain the necessary knowledge to foster a balance between the needs of people and sharks in the bay.

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