Area-use Patterns and Diel Movements of White Steenbras Lithognathus Lithognathus in a Temporarily Open/Closed South African Estuary, Inferred from Acoustic Telemetry and Long-term Seine-netting Data

摘要

Acoustic telemetry and long-term seine-netting data were used to assess distribution, area use, home range dynamics and movement patterns of estuarine-dependent juvenile white steenbras Lithognathus lithognathus in the temporarily open/closed East Kleinemonde Estuary. Using 15 years of biannual seine-netting data, it was shown that white steenbras abundance was highest in the mouth region and decreased with distance from the mouth. Fifteen fish equipped with acoustic transmitters were monitored for eight months using an array of stationary acoustic receivers, while five of these fish were also manually tracked for two months. Results from both telemetry methods indicated that activity was greatest in the mouth region and lower reaches of the estuary. All individuals exhibited site fidelity and remained resident near their sites of capture. The mean length of estuary used by the 15 individuals was 1 888 m (SD 666). There was a distinct diel activity pattern, with certain individuals utilising deeper parts of the estuary during the day and shallow regions at night. The results indicate that the shallow littoral zone is a critical habitat for juvenile white steenbras.