Kororā/Little Blue Penguins (Eudyptula minor) as marine ecosystem indicators - comparing stress physiology and foraging ecology

Abstract

Using three study sites in the Hauraki Gulf, this study aimed to determine whether changes in foraging ecology and stress physiology were observed in kororā populations over time and space and whether these measurements could be used as indicators of marine ecosystem health. Kororā are inshore foragers and do not migrate following breeding, therefore they are reliant on local marine resources year-round and may act as a high-resolution marine indicator over a small spatial scale. GPS tracking from Motu Muka during the breeding season revealed a foraging range of < 25 km. The tracking of kororā in the wider Hauraki Gulf provided insight into how individuals foraged in a marine environment with high human impact. Feather stable isotope analysis revealed kororā from Motu Muka foraged on a lower trophic level prey than the Otata or Tāwharanui populations during pre-moult foraging trips. This study was the first to extract the stress hormone corticosterone from kororā feathers and to identify differences in the stress experienced by populations in the region. This method could provide a less-invasive monitoring tool in the conservation of kororā colonies. The combination of feather corticosterone with stable isotope analysis revealed nutritional stress may have been the reason behind elevated corticosterone in the Motu Muka population. Feather corticosterone was lower in contemporary kororā than in museum specimens collected in the region since 1934 but was irrelative to the prey trophic level. The use of museum specimens showed further trends in diet and broad foraging location over 113 years and indicated changes have occurred in the Hauraki Gulf marine food web over time. Both temporal and spatial differences in physiology and foraging ecology reflected the contrasting environmental conditions experienced by each of the three colonies. This validated the integrated use of feather corticosterone, stable isotopes and tracking of kororā populations as measurements to monitor changes in marine ecosystem health. Further studies should seek to determine the causes behind the differences in stress physiology and foraging ecology among the colonies and over time through a regionwide monitoring program to link foraging ecology and stress physiology to breeding success.