Hoiho/yellow-eyed penguins have undergone significant declines on the New Zealand mainland since the late 1990s. Ongoing ocean warming has been identified as a main cause, although it only partially explains observed reduction in penguin numbers. Particularly fisheries impacts are suspected to contribute significantly to the decline. Besides degradation of the benthic habitat because of bottom trawling, incidental mortality in set net fisheries is known to pose a substantial threat to the species. However, assessing the actual impact of fishing activities is difficult due to the lack of comprehensive data on the penguins’ at-sea distribution and utilisation of the marine habitat.
Between December 2018 and August 2020, a total of 73 hoiho were fitted with tracking devices (GPS dive loggers, GPS-GSM dive transmitters, satellite transmitters) to examine the penguins’ at-sea movements and diving behaviour across their core mainland range. Deployments occurred at 12 different sites ranging from North Otago and the Otago Peninsula to the Catlins and Paterson Inlet, Rakiura/Stewart Island. Of the 73 deployments, 11 units could not be recovered, and five deployments yielded no or severely fragmented data due to device malfunction. The remaining 57 deployments resulted in foraging data from 42 different penguins.
Data recorded covered the chick-guard and post guard stages of breeding (October-January), the critical pre-moult phase (February-March) and the winter period (April-August). Data comprised a total of 33,290 at-sea locations representing 370 individual foraging trips, or 6,417 at-sea hours. A total of 118,698 dive events were determined from the depth data highlighting the species’ principally benthic foraging strategy across its mainland range. The data indicate that the existing 4-nautical mile set net restriction zone is only marginally beneficial for hoiho, if at all. Across their mainland range, large portions of the penguins’ marine habitat are located outside the restriction zone. Especially hoiho in North Otago and the Foveaux Strait area are exposed to substantial set netting activity.
GPS and dive data recorded over the course of this project complement data recorded by studies using similar methodologies carried out by University of Otago researchers between 2003 and 2018. It provides a solid basis for the development of advanced hoiho habitat preference models, essential to quantify the potential and actual impact of set net fishing and other benthic fisheries. Further tracking information will be collected from Stewart Island/Rakiura birds under project POP2020-05.