The distribution and abundance of the endangered Knysna seahorse Hippocampus capensis (Pisces: Syngnathidae) in South African estuaries

  • Jacqueline F Lockyear Department of Ichthyology and Fisheries Science, Rhodes University, PO Box 94, Grahamstown 6140, South Africa
  • Thomas Hecht Department of Ichthyology and Fisheries Science, Rhodes University, PO Box 94, Grahamstown 6140, South Africa
  • Horst Kaiser Department of Ichthyology and Fisheries Science, Rhodes University, PO Box 94, Grahamstown 6140, South Africa
  • Peter R Teske Molecular Ecology and Systematics Group, Botany Department, Rhodes University, PO Box 94, Grahamstown 6140, South Africa

Abstract

The occurrence, distribution and abundance of the endangered Knysna seahorse Hippocampus capensis in 10 estuaries on South Africa's warm temperate south coast, were investigated. Seahorses were found only in the Knysna, Swartvlei and Keurbooms estuaries. Sex ratios were even and, in most cases, more adults were found than juveniles. During the first year of study, seahorse densities were higher in the Swartvlei and Keurbooms estuaries than in the comparatively larger Knysna Estuary but, during the second year, seahorses were absent from the Keurbooms estuary, and the population size in the Swartvlei Estuary had decreased by more than 80%. These results suggest that, although the two smaller estuaries are able to support comparatively high densities of seahorses, population sizes may fluctuate considerably. Population size estimates for the Knysna Estuary were similar to those obtained in a previous study, suggesting that this estuary may represent a more stable environment and may thus be particularly important for the survival and conservation of this species.

Keywords: freshwater floods; Keurbooms Estuary; Knysna Estuary; Swartvlei Estuary; patchy distribution; population size fluctuation; submerged vegetation

African Journal of Aquatic Science 2006, 31(2): 275–283
Published
2006-12-04
Section
Articles

Journal Identifiers


eISSN: 1727-9364
print ISSN: 1608-5914