Estuarine habitat use by juvenile dusky kob Argyrosomus japonicus (Sciaenidae), with implications for management

  • PD Cowley South African Institute for Aquatic Biodiversity (SAIAB), Private Bag 1015, Grahamstown 6140, South Africa
  • SE Kerwath Marine and Coastal Management, Department of Environmental Affairs and Tourism, Private Bag X2, Rogge Bay 8012, South Africa
  • A-R Childs South African Institute for Aquatic Biodiversity (SAIAB), Private Bag 1015, Grahamstown 6140, South Africa
  • EB Thorstad Norwegian Institute for Nature Research (NINA), Tungasletta 2, NO-7485 Trondheim, Norway
  • F Økland Norwegian Institute for Nature Research (NINA), Tungasletta 2, NO-7485 Trondheim, Norway
  • TF Næsje Norwegian Institute for Nature Research (NINA), Tungasletta 2, NO-7485 Trondheim, Norway

Abstract

The spatial and temporal area-use patterns of estuarinedependent juvenile dusky kob Argyrosomus japonicus in the Great Fish Estuary, South Africa, were examined using acoustic telemetry. In all, 29 individuals (307–400 mm total length) were surgically equipped with individually coded transmitters and monitored for a period of up to 195 days using an array of 11 moored data-logging acoustic receivers. Tagged dusky kob spent most time in the estuary (84%), compared with neighbouring marine (13%) and riverine (4%) environ ments. Tagged fish made extensive use of the estuary from the mouth to between 6.4 km and 10.3 km upstream, and spent approximately equal proportions of time at each of the seven receivers located between 0.5 km and 6.5 km from the mouth. A total of 18 fish undertook sea trips of a mean duration of 3.5 days, whereas three individuals made riverine excursions (mean duration = 7.3 days). A total of 12 (41%) tagged fish was captured in the estuary prior to, during or after the monitoring period. These findings highlight the importance of estuaries as critical nursery areas, and that the use of these habitats by dusky kob should be better reflected in the management arrangements for this fishery species.

Keywords: acoustic telemetry; Argyrosomus japonicus; fisheries management; movement behaviour; nursery habitat; South Africa

African Journal of Marine Science 2008, 30(2): 247–253
Published
2008-10-20
Section
Articles

Journal Identifiers


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