Variability in the foraging range of blue penguins
The little or blue penguin Eudyptula minor is primarily an inshore forager generally feeding within 30 km of breeding sites during the nesting period. The Trust’s GPS foraging study is part of a wider research project and results have just been published.
Led by Tim Proupart and Dr Sue Waugh of the Museum of New Zealand Te Papa Tongarewa, the paper published in the NZ Journal of Zoology included data from three sites, Wellington, Motuara Island (Marlborough) and our West Coast study. Data has been collected over the last five years and, for three of those years, the West Coast Penguin Trust have carried out the field work at Charleston and Cape Foulwind. Altogether the study includes tracks gathered on 68 individuals in three regions of central New Zealand between 2011 and 2016.
Foraging patterns varied between sites and between years. Tracks revealed that penguins can rely on distant foraging areas while incubating, with nesting birds from Motuara Island travelling up to 214 km to feed. Isotope analyses of blood samples showed that this distant food from deep waters (0–200 m deep) is likely to be squid dominated, which has a low nutrition value. During the chick rearing period, birds undertook a diet shift to a higher trophic level while foraging closer to their colony, and possibly near river plumes.
These findings highlight the need to consider much larger potential foraging ranges when assessing and managing threats to the penguins. The research team, including the Trust’s Kerry-Jayne Wilson and Reuben Lane, advise that conservation efforts need to take this variation into account to protect these penguins, which are currently in decline across New Zealand.
Variable foraging ecology may expose blue penguins to threats much further from colonies than the 30 km previously considered important. Thus blue penguins may be exposed to dredging or seabed mining on foraging habitat far from known colonies. Penguins at the colonies studied in Wellington, Buller and Marlborough all feed in areas where seabed mining and dredging activities are currently under consideration. Proposals for significant seabed disturbance are currently being assessed in the South Taranaki Bight, the West Coast including Buller and in Wellington Harbour and Cook Strait; all areas used by the penguins. Benthic disturbance increasing water turbidity and disrupting marine food webs may affect the penguins’ foraging efficiency, survivorship and breeding.
Figure: Inter-annual variability of Buller blue penguin foraging areas between 2013, 2015 and 2016. The light grey area represents the home range the dark grey the focal area. Study colonies are shown by the circles: grey for Nile River, white for Cape Foulwind. Tracks not included in kernel calculation due to small samples sizes are shown: in 2015, incubation track from Nile River (dotted line) and chick-rearing stage track from Cape Foulwind (black line), and in 2016 an incubation track from Nile River (dotted line). The black circle shows the Buller River mouth. The dashed line is 50 m bathymetric contour; the solid line is 100 m.
The West Coast Penguin Trust is grateful for support for this project from the JS Watson Trust managed by Forest & Bird, and the support of and collaboration with the Museum of New Zealand Te Papa Tongarewa.