Shark and skate egg-cases cast up on two South African beaches and their rates of hatching success, or causes of death

  • Craig Smith
  • Charles Griffiths

Abstract

Collections of chondrichthyan egg-cases cast ashore at two sites along the South African coastline were identified and examined for cause of mortality. A total of 574 egg-cases collected from False Bay could be attributed to five species of scyliorhinid shark. two skates and the elephantfish or chimaera, while the 538 egg-cases collected from Port Alfred belonged to four scyliorhinid sharks and two skate species. At both sites eggs of shysharks of the genus Haploblepharus made up more than 70% of the samples, followed by skates (5% in False Bay and 19% in Port Alfred) and then catsharks of the genus Porodenna (1 and 7% respectively). Haploblepharus egg-cases generally displayed relatively high rates of hatching success of over 60% and predation rates of 18-30%. Haploblepharus fuscus was the exception with a low hatching success of 37% and a predation rate of 40%. Porodenna egg-cases suffered predation losses of 43%. and had a hatching success of 47%. Skate egg-cases displayed non-predator induced egg mortalities of up to 35%, but predation rates of less than 14%. Hatching success was moderate at 57%. The holes found in egg-cases could be categorised into five types, of which four were clearly predator boreholes. The most abundant of these was shown to be caused by whelks of the genus Bumupena.

S Afr. J. Zool 1997, 32(4)

Author Biographies

Craig Smith
Marine Biology Research Institute and Zoology Department, University of Cape Town, Rondebosch, 7701 South Africa
Charles Griffiths
Marine Biology Research Institute and Zoology Department, University of Cape Town, Rondebosch, 7701 South Africa
Published
2017-04-10
Section
Articles

Journal Identifiers


eISSN: 2224-073X
print ISSN: 1562-7020