Tidal exchange of ichthyoplankton in the Swartkops estuary mouth, South Africa

Abstract

Tidal exchange of fish eggs, larvae and juveniles in the mouth of the Swartkops estuary was examined by plankton and seine-netting during two 24-h sampling sessions. Small larvae of resident estuarine species such as Caffrogobius multifasciatus, Psammogobius knysnaensis and Omobranchus woodi appear to be passively swept out of the estuary on the ebb-tide. Early juveniles of marine species which utilize the estuary as a nursery ground, such as Rhabdosargus holubi, Liza richardsoni and Heteromycteris capensis, enter the estuary on the flood-tide. Catches of these species near the bank during ebb-tide suggest that they actively migrate towards the banks to prevent being swept back out to sea.