Movements and residency of juvenile white steenbras Lithognathus lithognathus in a range of contrasting estuaries

• We assess estuarine movements of juvenile white steenbras using acoustic telemetry.
• Diel and tidal movements are the primary and secondary cyclical behaviours.
• Hypersalinity caused by excessive water abstraction restricted fish movements.
• Strong site fidelity and long-term residency in estuaries (in sandy lower reaches).
• Estuaries represent critical nursery habitats for juvenile white steenbras.

Acoustic telemetry was used to assess estuarine area use and movements of an overexploited, endemic fishery species in three South African estuaries; two permanently open systems with contrasting salinity gradients and an intermittently open system. Forty juvenile white steenbras Lithognathus lithognathus (215–379 mm FL) were surgically equipped with acoustic transmitters and tracked for up to 355 days. Tagged fish exhibited high levels of site fidelity and long-term residency within each estuary. Most of their time was spent in the lower reaches of all three estuaries and hypersalinity restricted movements into the upper reaches of the freshwater-deprived estuary. All tagged fish exhibited a distinct diel movement pattern. Most individuals (91%) in the two permanently open estuaries also exhibited a tidal-associated pattern, which comprised mainly small-scale (tens to hundreds of metres) transverse movements between deep channels and shallow banks. Observed behaviour was consistent across a range of estuary sizes, types and physico-chemical conditions. This study has identified critical habitats for juvenile white steenbras across a range of estuarine environments. Estuarine management initiatives need to consider these critical habitats, in order to enhance abundance of juveniles and ultimately recruitment to the marine (adult) population.

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