Sharks caught in the KwaZulu-Natal bather protection programme,South Africa. 14. The smooth hammerhead shark Sphyrna zygaena (Linnaeus) |
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| Authors: | ML Dicken H Winker MJ Smale G Cliff |
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| Institution: | 1. KwaZulu-Natal Sharks Board, Umhlanga Rocks, South Africa;2. Department of Development Studies, School of Economics, Development and Tourism, Nelson Mandela Metropolitan University, Port Elizabeth, South Africa;3. Branch: Fisheries Management, Department of Agriculture, Forestry and Fisheries (DAFF), Cape Town, South Africa;4. Centre for Statistics in Ecology, Environment and Conservation, Department of Statistical Sciences, University of Cape Town, Cape Town, South Africa;5. Port Elizabeth Museum, Port Elizabeth, South Africa;6. Department of Zoology and the Institute for Coastal and Marine Research, Nelson Mandela University, Port Elizabeth, South Africa;7. School of Life Sciences, University of KwaZulu-Natal, Durban, South Africa |
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| Abstract: | The current study provides long-term catch-rate, biological and feeding data for smooth hammerhead sharks, Sphyrna zygaena, caught in South Africa’s KwaZulu-Natal bather protection programme. In total, 2 512 S. zygaena were caught in net installations between 1978 and 2014, and 72 S. zygaena were caught on drumlines between 2007 and 2014. There was no significant log-linear year trend in the net catch rate over time (slope = 0.0054, t = 1.808, p = 0.07). However, there was a significant temporal increase in mean size of the captured sharks (slope = 0.0012, t = 3.502, p < 0.001). A quasi-Poisson generalised additive mixed model showed that increasing latitude, winter months, colder sea temperatures and the deployment of drumlines all had a significant positive effect on the catch rate of sharks in nets. The size frequency of the catch was unimodal, with significantly more females caught in the nets and more males on the drumlines. The majority (93.1%) of all sharks caught were immature and measured between 80 and 120 cm precaudal length. Teleosts and cephalopods dominated the sharks’ diet in terms of all dietary indices. The prey species consumed indicate that immature S. zygaena are feeding primarily within the pelagic zone of shallow coastal habitats. |
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| Keywords: | CPUE drumlines generalised additive mixed model length frequency sex ratio shark nets stomach contents |
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