Sharks caught in the protective gill nets off KwaZulu-Natal, South Africa. 11. The scalloped hammerhead shark Sphyrna lewini (Griffith and Smith)

  • P de Bruyn Department of Zoology, Nelson Mandela Metropolitan University, PO Box 77000, Port Elizabeth 6000, South Africa, and Natal Sharks Board, Private Bag 2, Umhlanga Rocks 4320, South Africa; current address: Oceanographic Research Institute, PO Box 10712, Mari
  • SFJ Dudley Natal Sharks Board, Private Bag 2, Umhlanga Rocks 4320, South Africa
  • G Cliff Natal Sharks Board, Private Bag 2, Umhlanga Rocks 4320, South Africa
  • MJ Smale Port Elizabeth Museum, PO Box 13147, Humewood 6013, South Africa
Keywords: cpue, distribution, embryos, gill nets, length frequency, length-weight relationships, maturity, nursery grounds, reproduction, seasonality, stomach contents

Abstract

Between 1978 and 1998, a total of 3 385 scalloped hammerhead sharks Sphyrna lewini was caught in the protective nets off KwaZulu-Natal. The mean annual catch was 166 sharks (range 60–279). There was a significant decrease in catch rate with time, but the relationship with the population size in KwaZulu-Natal waters is unknown. Size and sex segregation is indicated. Sizes-at-50% maturity were 161.5cm (males) and 183.1cm (females). Most of the catch (91%) was immature, but neonates are poorly sampled by the 51-cm meshed nets. In small animals (<160cm precaudal length, PCL), males significantly outnumbered females by 2.2:1, and in large animals by 3.6:1. The length-mass relationship differed between sexes. Catches of both small and large animals were highest in summer. Most of the large males were caught in November and December, consistent with an inshore movement of mature animals to breed in summer, but no evidence of recent mating was observed in either sex. Females pregnant with term embryos (median embryo length per litter 30.4–36.2cm) were caught between October and March. These females tended to have maximum ovarian follicle diameters of ≥30mm, indicating that mating would occur shortly after parturition. The median size of 11 litters was 10 embryos. The Tugela Bank to the north of the netted region appears to be a nursery ground. Teleosts, comprising 42 families and 60 identified species, dominated the diet in terms of frequency of occurrence (77%), followed by cephalopods (25%).

Keywords: cpue, distribution, embryos, gill nets, length frequency, length-weight relationships, maturity, nursery grounds, reproduction, seasonality, stomach contents

African Journal of Marine Science 2005, 27(3): 517–528
Published
2006-01-09
Section
Articles

Journal Identifiers


eISSN: 1814-2338
print ISSN: 1814-232X