New research tracking yellow-eyed penguins behaviour on Stewart Island could help prevent them from becoming extinct.
Stewart Island is home to around a quarter of all yellow-eyed penguin breeding across their mainland range. Photo: AFP
Yellow-eyed penguins are endangered and the Rakiura population has dramatically declined in the last 15 years - falling from an estimated 154 pairs in 2008/2009 to 44 in the most recent breeding season.
University of Otago postgraduate student Thor Elley tracked the foraging behaviour and patterns of 19 adult yellow-eyed penguins across three Stewart Island locations, including Port Pegasus, Paterson Inlet, and Codfish Island.
The penguins were fitted with GPS dive data loggers during the 2020/21 breeding season, to track movements and diving behaviours, which resulted in the recording of a total of 25,696 dives across 91 foraging trips.
The study recently published in the journal Biology, shows that while foraging ranges and trip lengths were substantially different between the sites and dependant on a range of factors, the behaviour of birds from the same site were surprisingly predictable and consistent.
Elley said the predictability gives a robust estimation of the size and shape of ideal marine protection measures, and shows managing local fisheries could reduce overlap with where the penguins forage.
Stewart Island is home to around a quarter of all yellow-eyed penguin breeding across their mainland range, so the loss of one adult could significantly impact population numbers.
"Fisheries related mortality can have massive flow on effect during breeding seasons, such that if an adult dies, both dependant chicks usually starve, and the surviving breeding partner will likely skip the next breeding season."
Set netting restrictions in place adjacent to the South Island reduce the risk of entanglement and death within the four nautical mile exclusion zone, however no restriction on set netting is in place for Stewart Island and its outlying islands.
Elley said the set net effort peaked in summer, coinciding with the yellow‐eyed penguin breeding season.
"These fisheries overlap with the preferred foraging locations of yellow‐eyed penguins and current set netting practices both within Pegasus Inlet and in the waters along the coast could quite possibly mean local extinction is likely unless we re-think inshore fishing practices."
Co-author and supervisor for the study Professor Phil Seddon said new technology used in the study highlighted its potential in increasing our understanding of species behaviour.
"Not so long ago the at-sea distribution of yellow-eyed penguins was largely a mystery to us, but now, with miniature tracking devices, we are gaining a detailed picture of their marine distribution, a realm where the penguins spend most of their time."
"Improved understanding of the foraging range and feeding behaviour of yellow-eyed penguins will inform management, marine spatial planning, and other measures that can reduce the risks faced by this iconic living treasure."