Marine and Freshwater Research Marine and Freshwater Research Society
Advances in the aquatic sciences
RESEARCH ARTICLE

Population status of 14 shark species caught in the protective gillnets off KwaZulu–Natal beaches, South Africa, 1978–2003

Sheldon F. J. Dudley A C and Colin A. Simpfendorfer B
+ Author Affiliations
- Author Affiliations

A Natal Sharks Board, Private Bag 2, Umhlanga Rocks, 4320, South Africa.

B Center for Shark Research, Mote Marine Laboratory, 1600 Ken Thompson Parkway, Sarasota, FL 34236, USA.

C Corresponding author. Email: dudley@shark.co.za

Marine and Freshwater Research 57(2) 225-240 https://doi.org/10.1071/MF05156
Submitted: 22 August 2005  Accepted: 17 January 2006   Published: 10 March 2006

Abstract

Shark nets have been set off the beaches of KwaZulu–Natal, South Africa, since 1952 to reduce the risk of shark attack. The nets fish in fixed localities 400 m from shore and both directly affect local shark populations and act as fisheries-independent monitoring devices. Reliable catch information at the species level was available for the period 1978–2003. Trends in catch rate and size were used to assess the population status of 14 commonly caught shark species. In addition, a demographic modelling approach was used in conjunction with the catch information to assess the potential effect of the nets on populations. Catch rates of four species (Carcharhinus leucas, C. limbatus, Sphyrna lewini and S. mokarran) showed a significant decline, as did the mean or median length of three species (Carcharhinus amboinensis, C. limbatus and female Carcharodon carcharias). For three species that showed declining catch rates or length the potential effect of the shark nets was assessed to be low, suggesting that other sources of catch were responsible for the declining status. The potential effect of the shark nets was assessed to be high for two species (Carcharhinus obscurus and Carcharias taurus, neither of which showed declines in catch rate or length), because of very low intrinsic rates of population increase.

Extra keywords: catch, CPUE, demographic modelling, maturity, size.


Acknowledgments

The operations staff of the NSB maintain the KZN shark nets and record all catches. Catch, effort and dissection data are captured by staff in the research department of the NSB. Geremy Cliff and Sabine Wintner contributed unpublished life history information. We are grateful to Ken Goldman (Jackson State University, Jackson, MI) for providing von Bertalanffy growth data on Carcharias taurus. Mote Marine Laboratory hosted SD in 2004 and permitted CS to participate in this project.


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