Dams, ducks and DNA: identifying the effects of a hydro-electric scheme on New Zealand's endangered blue duck

Abstract

Blue duck are conspicuous inhabitants of headwatersections of many rivers in the central North Island of NewZealand. These rivers are also home to a number ofhydro-electricity dams. One scheme in particular – the TongariroPower Development (TPD) involves the reduction and diversion ofwater flow from the headwaters of the Whakapapa, Whanganui andTongariro Rivers in the central North Island of New Zealand. Numbers of the endangered blue duck (Hymenolaimus malacorhynchos)on the Tongariro River have declined markedly in the last decade. Opinions have differed as to whether this indicated a reductionin the `health' of the population or simply a reduction in thecarrying capacity of the river. The issue centered aroundwhether the Tongariro River population was still self-sustaining,or reliant upon immigration from other source rivers. DNAmarkers were used to estimate the relative contributions tooverall recruitment of production from within the population andmigration from external sources. Up to 11 birds were collectedfrom one unmodified population, two stable modified populationsand one declining population. DNA fingerprinting results from twomultilocus probes were analysed using a one-way ANOVA and showedthat mean bandsharing among individuals from the Tongariro River(0.19) was significantly lower than values recorded from thethree other rivers (0.37–0.39). Discovery curves alsoindicated that the Tongariro population contains more geneticvariation than the other three. These results suggest that theTongariro River population is a `sink' dependent upon immigrationfrom a number of different source populations, rather than localproduction.