Toni Johnston


Past M Sc student

Toni’s research was intended to provide information on the effects of willows and riprap on invertebrates, fish and habitat in a large river and help inform future bank stabilisation management decisions. Willows (Salix sp.), an exotic tree, and riprap are used as bank stabilisation measures on the Waikato River. Few studies on the effects of willows and riprap on large river ecology exist in New Zealand. The few studies in small streams in New Zealand and studies overseas have found the effects of willow and riprap can be harmful as well as beneficial to native freshwater life. Limited information means the effects of current river management techniques involving the removal of willow and the addition of riprap are unclear. The objectives of Toni’s research were to determine habitat characteristics, invertebrates and fish at willowed and riprap sites on the Waikato River in Hamilton. She compared five paired sites of willow and riprap in close proximity (site pairs within 1 km). Physical habitat conditions were assessed in relation to different river flows, including velocity, depth, wetted habitat, chainage and substrate. Assessment of fish populations were carried out with the aid of backpack and boat electrofishing, Gee Minnow trapping and spotlighting. Invertebrate populations were measured quarterly, for seasonal comparison, by kick netting and/or coir sampling depending on the results of a pilot study to test methods.


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Johnston, T. 2011. Comparison of riparian willows and riprap as habitat for fish and invertebrates in the Waikato River. Unpubl. MSc thesis, The University of Waikato. 145 p.

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