Conservation implications for post-fledging dispersal of yellow-eyed penguins/hoiho

Abstract

With the extinction of yellow-eyed penguins Megadyptes antipodes on mainland New Zealand predicted within the next few decades, identifying preventable causes of mortality during the juvenile dispersal period is critical. Between 2017 and 2019, we tracked 30 juvenile yellow-eyed penguins during their post-fledging dispersal to determine their dispersal trajectory, marine habitat use, and to identify overlap with commercial gillnet fishing operations, a known cause of yellow-eyed penguin mortality. Using k-nearest neighbour local convex hulls, we identified core foraging hotspots (50% isopleths) and main marine habitats (95% isopleths). We identified environmental covariates that influenced penguin habitat use during separate stages of the dispersal journey. After fledging, juvenile yellow-eyed penguins from the Otago coast dispersed and foraged 140 to 692 km (mean ± SD = 359.9 ± 129.3 km) from their natal locations, north-north-east into the Canterbury Bight, a region where penguin bycatch in commercial gillnet fishing operations has been recorded. There was a 51.6% overlap between core juvenile foraging hotspots and known commercial gillnet fishery locations (from 2017 to 2019). Less than 12.6% of the core foraging hotspots occurred within the 4 nautical mile gillnet prohibition zone implemented in 2008. A recent extension in the size of the gillnet prohibition zone in 2020 increased this spatial overlap to cover 36.9% of core foraging hotspots and 28.9% of main marine habitats. These findings highlight the vulnerability of juvenile yellow-eyed penguins at this critical life-stage, but there is opportunity to amalgamate marine protection measures with other endangered species with overlapping distributions that are also at risk of gillnet-related mortality.