Research at the KZN Sharks Board
The Board employs three biologists whose primary aim is to analyse information taken from catches in the shark nets. This information is used to:
||Improve our understanding of the biology of those species of sharks and other animals caught in the shark safety gear.
||Assess the impact of mortalities on local stocks.
||Reduce mortalities in the shark safety gear without jeopardising the safety of beach users.
Every animal caught is identified, sexed, measured and recorded. Live sharks found in the shark safety gear are now not only tagged and released but many are also injected with tetracycline to validate age and growth studies. Dead sharks that are not badly decomposed are brought into the laboratory, where they are weighed and measured. They are then kept frozen until they are dissected by technical staff, who record various biological data. A section of the vertebral column is removed for ageing studies and some jaws are kept for the KZNSB reference collection. Additionally, various tissues are sampled for a variety of different studies.
The KZNSB is publishing, in the African Journal of Marine Science Volume 7 (1988) et seq., a series of papers on the biology and catch statistics of the shark species commonly caught in the nets. These and many other KZNSB publications (view list) are available on request.
The KZNSB has been an active member of the South African National Tagging Program since 1984. The Tagging Program is administered by the Oceanographic Research Institute (ORI) and since its inception in 1984, 4689 registered members have tagged over 219 000 fish of about 350 species. Most of the participants are volunteer anglers, but several research institutes and universities also participate.
The overall recapture rate of sharks released from the nets and drumlines is about 4%. It is interesting to note that the recapture rate of free-swimming raggedtooth sharks tagged by divers, where there is no capture stress, is higher (10.2%) than that of raggies tagged from the nets and drumlines (4.7%). Recapture rates for other net-tagged species vary, e.g. 4.8% for the blacktip and 4.6% for the tiger shark.The overall recapture rate for injected sharks is 4.6% and 6.5% for the giant guitarfish. To date none of the other tagged rays has been recaptured. Here are some recapture highlights.
Ageing of sharks
The conservation, management and rational utilisation of shark stocks are receiving increasing global attention. In a local context it is essential to have accurate information on the biology and life history of the various species being exploited in the shark nets to understand the impact of the netting program on these shark populations. Knowledge of shark age and growth is fundamental to these processes.
Opportunities for visiting researchers and students
The KZNSB is always seeking ways of obtaining as much scientific information as possible from any animals caught in the shark nets and on the drumlines. It is therefore receptive to requests from other scientists for material. For example tissue samples are collected, on request, for genetic or pollution studies by scientists, who supply sample vials and cover all postage/freight costs. Researchers are welcome to visit the KZNSB to collect their own material, but laboratory and office space are extremely limited. One PhD student has collected a wide variety of copepod and helminth parasites from sharks and rays caught in the nets.