The IUCN/SSC Shark Specialist Group
Shark News 7: June 1996
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Tagging at the Natal Sharks Board
Sabine Wintner, Natal Sharks Board, South Africa
The South African National Tagging Program is administered by the
Oceanographic Research Institute (ORI). Since its inception in 1984
it has recorded over 100,000 fish (more than 350 species) tagged by
3,350 registered members. The Natal Sharks Board (NSB) joined the
programme in 1984, tagging free swimming raggedtooth sharks
Carcharias taurus. A pole sling is used by NSB snorkel divers to insert
a yellow "Hallprint" dart tag with stainless steel head and plastic
streamer. By the end of 1995, 535 C. taurus had been tagged this way.
Of the annual average of 1,440 sharks caught in the nets, 15% are
found alive, and since 1978 the percentage of sharks released has
increased steadily. This development was a result of a gradual
acceptance that many sharks caught pose little threat to swimmers and
the increasing reluctance of those servicing the nets to kill live sharks
(Cliff and Dudley 1992). From 1978 to 1986, 462 netted sharks were
marked with NSB rototags. In 1987 the NSB changed to dart tags, and
over 1,300 sharks from 14 species have been tagged to the end of
1995. The majority of these sharks were C. taurus (over 670), followed
by the tiger shark Galeocerdo cuvier (over 160) and dusky shark
Carcharhinus obscurus (over 100) and including 37 white sharks
Carcharodon carcharias. The NSB tags only one batoid species, the
giant guitarfish Rhyncobatus djeddensis; 330 have been marked.
Average annual recapture rate of sharks is around 3% and for
R. djeddensis over 6%. It is interesting to note that the recapture rate
of C. taurus tagged by divers, where there is no capture stress, is higher
(5%) than that of C. taurus tagged in the nets (3.4%).
Opportunistic tagging by NSB staff has increased the number of
tagged C. carcharias to over 50. Based on the combined ORI and NSB
tagging databases, first estimates of mortality and population size for
C. carcharias on the South African coast were calculated. The overall
estimate was 1,279 sharks, F = 0.055 yr -1 and Z = 0.53 yr -1 (Cliff et al.
in press). Based solely on the NSB tagging data, analysis commissioned
by the Board has estimated netting mortalities for various species:
C. carcharias 0.07-0.15 yr -1 , Carcharhinus leucas 0.02-0.03 yr -1 ,
C. taurus 0.03-0.06 yr -1 and G. cuvier 0.02-0.04 yr -1 , given different
scenarios of natural mortality, tag loss, tagging mortality and under-reporting
of recaptures.
In 1993 an additional programme was started, the Tetracycline
Tagging Program. In addition to being tagged the sharks are injected
with the chemical oxytetracycline and marked with an orange tag,
instead of the conventional yellow one. The NSB offers a 'reward' of
R 100 (23 US$) for the return of such a shark. Between 1993 and May
1996 nearly 400 sharks were injected, both in the nets and through
opportunistic tagging. The majority are again C. taurus (over 160),
followed by G. cuvier (over 55) and C. obscurus (over 35), and 18
C. carcharias have also been injected. Recapture rate to date is 2%,
with most sharks caught within the first month after tagging. The NSB
is continuing with this project and it is hoped that the future will see
more valuable recaptures of tetracyclined sharks.
References:
Cliff, G., and Dudley, S.F.J. 1992. Protection against shark attack in South
Africa. Australian J. Marine and Freshwater Research, 43: 263-272.
Cliff, G., van der Elst, R.P., Govender, A., Whitthuhn, T.K., and Bullen,
E.M. In press. Tagging of white sharks provides first estimates of
mortality and population size on the South African Coast. In:
Klimley, A.P. and Ainley, D.G. (eds.). Great White Sharks: the
Biology of Carcharodon carcharias. Academic Press, San Diego.
Sabine Wintner, Natal Sharks Board, Private Bag 2,
Umhlanga Rocks, 4320, South Africa. Tel: +27 31 561-1001,
fax: +27 31 561-3691, email: wintner@shark.co.za
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