Speaker: Emeritus Professor Colin Townsend, University of Otago

You may not be surprised to learn that if New Zealand’s rivers were to be placed end to end they would total 9,471 km in length. But did you know that the streams that feed those rivers total more than 400,000 km! Did you know that the beds of such streams that have been reached by the introduced brown trout tend to be more slippery than those still occupied by native fish? Or that an ancient whitebait species became ‘landlocked’ into headwater streams of the South Island and evolved into 12 or more new non-migratory species? Or that streams whose beds are disturbed at an intermediate rate have a higher biodiversity than streams turned over by more frequent spates or not disturbed at all? Or which of the human-caused impairments (nitrogen, sediment, water abstraction, increased temperature) is most harmful to stream ecosystems? Well nor did I - until my research team started work three decades ago.