African Journal of Marine Science

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

PD Cowley, SE Kerwath, A-R Childs, EB Thorstad, F Økland, TF Næsje


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
AJOL African Journals Online