Conservation Genetics 1: 103–113, 2000. © 2000 Kluwer Academic Publishers. Printed in the Netherlands. 103 Dams, ducks and DNA: identifying the effects of a hydro-electric scheme on New Zealand’s endangered blue duck Tania M. King 1 , Murray Williams 2 & David M. Lambert 1,∗ 1 Molecular Ecology, Institute of Molecular BioSciences, Massey University, Private Bag 11-222, Palmerston North, New Zealand; 2 Department of Conservation, PO Box 10420, Wellington, New Zealand ( ∗ Corresponding author: E-mail: D.M.Lambert@massey.ac.nz) Received 15 November 1999; accepted 11 February 2000 Key words: blue duck, conservation genetics, hydro-electric power, Hymenolaimus malacorhynchos, minisatellite DNA fingerprinting Abstract Blue duck are conspicuous inhabitants of headwater sections of many rivers in the central North Island of New Zealand. These rivers are also home to a number of hydro-electricity dams. One scheme in particular – the Tongariro Power Development (TPD) involves the reduction and diversion of water flow from the headwaters of the Whakapapa, Whanganui and Tongariro 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 reduction in the ‘health’ of the population or simply a reduction in the carrying capacity of the river. The issue centered around whether the Tongariro River population was still self-sustaining, or reliant upon immigration from other source rivers. DNA markers were used to estimate the relative contributions to overall recruitment of production from within the population and migration from external sources. Up to 11 birds were collected from one unmodified population, two stable modified populations and one declining population. DNA fingerprinting results from two multilocus probes were analysed using a one-way ANOVA and showed that mean bandsharing among individuals from the Tongariro River (0.19) was significantly lower than values recorded from the three other rivers (0.37–0.39). Discovery curves also indicated that the Tongariro population contains more genetic variation than the other three. These results suggest that the Tongariro River population is a ‘sink’ dependent upon immigration from a number of different source populations, rather than local production. Introduction Formerly widespread in rivers of New Zealand’s North and South islands, the endangered blue duck (Hymen- olaimus malacorhynchos) is presently distributed in remote and forested headwaters of rivers in the central North Island and the west coast of the South Island (Marchant and Higgins 1990). Blue duck are dispersed year-round as pairs that defend exclusive territories of approximately one km of river (Williams 1991). Blue duck are a ‘top predator’ within riverine ecosys- tems, feeding almost exclusively on aquatic inverte- brates (Collier 1991). Their presence is widely taken to indicate ‘intactness’ and ‘quality’ of a particular river ecosystem, especially for conservation advocacy purposes (Adams et al. 1997). Recent studies estimate a total breeding population of 1200 pairs (Adams et al. 1997). As an exclusively river-dwelling species, blue duck are vulnerable to changes in water flow. The principal method of power generation in New Zealand is hydro-electric (Allen 1976). Most major rivers carry one or more dams and significant power schemes have arisen from the reduction and diver- sion of water flow from smaller rivers. One such diversion scheme is the Tongariro Power Development (TPD). The TPD reached full production in 1983 and redirects water from several rivers flowing from the flanks of volcanoes in central North Island (Figure 1).