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Abstract
The effects of coastal floodgates on fish distribution are largely unknown. In this study, we used Dual-frequency Identification Sonar (DIDSON) to assess the effect of tidal floodgates on movement of diadromous juvenile galaxiids in a New Zealand estuarine system and test the suitability of DIDSON as a tool for monitoring behaviour of small fish. DIDSON allowed observations of juvenile galaxiid movements over 24 h through contrasting gated and un-gated culverts. More than twice as many fish were recorded passing the un-gated culvert than the gated culvert. Movement occurred during the day and night and was highest at the un-gated culvert just before high tide. By contrast, movement past the gated culvert was highest during low tide, when the gate was open. DIDSON is suitable for discretely observing in situ behaviour of small fish at night or in turbid water and will assist to identify design and operational needs for fish-friendly floodgates.
Acknowledgements
We thank Rob Holmes for assistance with the fieldwork, Martin Rutledge (DoC) for assistance with site selection and the landowner (M Staples) for access to the sites. Comments from Rowan Strickland helped improve an earlier version of this manuscript. This project was funded by the New Zealand Foundation for Research Science and Technology as part of the Integrated Catchment Management Project (Contract No. C09X0214).
