Influences of selected geophysical and environmental drivers on the movement patterns of Rhabdosargus holubi in a southern African estuary
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A total of 21 juvenile Cape stumpnose (Rhabdosargus holubi) were tagged with internal acoustic transmitters in the lower, middle and upper reaches of the Kowie Estuary, South Africa. The movements of all fishes were continually monitored for five months using 22 stationary data-logging acoustic receivers, positioned along the length of the estuary. Diel and tidal cycles were identified in the movements of several individual R. holubi; however the lack of extensive movements for most individuals emphasised high residency of the species to particular sections of the estuary. River inflow and water temperature significantly affected the movement behaviour of most tagged R. holubi. Periods of increased freshwater inflow and rising riverine temperatures prompted certain individuals to shift their position downstream, while reduced sea temperatures in the lower reaches prompted certain individuals to shift their position further upstream from the mouth. Given the predicted effects of climate change in the study region, which include increased river inflow due to catchment rainfall and decreased sea temperatures due to ocean upwelling, these results suggest that R. holubi may be sensitive to the environmental effects of global warming and that the distribution and movement behaviour of this species in southern African estuaries is likely to be affected as climate change proceeds.
KeywordsAcoustic telemetry Estuarine fish Physico-chemical parameters Kowie estuary
We thank the National Research Foundation (NRF) of South Africa for funding that made this study possible. We are also grateful to two anonymous reviewers of the original manuscript for their useful comments and queries that enabled us to improve the final version of the paper.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
All applicable international, national, and/or institutional guidelines for the care and use of animals were followed. The research conducted on Rhabdosargus holubi in this study was approved (Code 2014/02) by the Animal Ethics Committee of the South African Institute for Aquatic Biodiversity. This article does not contain any studies with human participants performed by any of the authors.
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