River modelling to better manage mammalian predator access to islands in braided rivers

Abstract

The South Island of New Zealand has many classical braided gravel-bed rivers where vulnerable or endangered endemic birds breed and nest of gravel bars devoid of vegetation. Their endangered status arises both from reduced habitat caused by changes in flow regime and river bed narrowing, and predation by introduced mammals such as rats, cats, hedgehogs and mustelids. Successful breeding now only occurs on islands within the braided system because flowing channels deter mammalian predators. The water is in demand for irrigation and hydroelectricity generation. The paper reports on the nature of flows that need to be retained in the rivers to enable successful breeding of the endangered birds, based on an IFIM approach using suitability index curves and outputs from a 2-D hydrodynamic model.