Abstract
Understanding the habitats that seabirds use, and their connection to marine food-webs is key to answering questions about their ecology. Knowledge of trophic connections and foraging patterns is invaluable for making conservation decisions for animals that have high threat classifications; such as penguins. If it is known where individuals forage and what prey they rely on, these areas and resources can be safeguarded to ensure endemic biodiversity thrive.
The present study used GPS/dive and video loggers to better understand the foraging ecology of breeding Fiordland crested penguins/Tawaki (Eudyptes pachyrhynchus) in Doubtful Sound, New Zealand. Comparisons are made of dive behaviour, spatial use and prey capture between a mid-fjord colony and an outer-fjord colony in 2020 and 2021. Core foraging areas of the two colonies did not overlap: outer-fjord Tawaki foraged coastally and at the fjord entrance; mid-fjord Tawaki almost exclusively foraged within the fjord. Dive strategies contrast: outer-fjord Tawaki made longer, deeper dives with faster decent velocities, taking advantage of a larger epipelagic zone in coastal waters and occasionally diving to the benthos; mid-fjord Tawaki made shorter and shallower dives, foraging in the upper 20m of the water column just below the low salinity layer in the fjord. Video logger observations found that Tawaki in Doubtful Sound specialised in foraging for fish larvae with high capture success rates.
Isolated populations are influenced by patterns in autochthonous food sources and by subsidies from allochthonous resources. The difference in organic matter flow creates resource refuges for small populations. The study investigates stable isotopes δ13C, δ15N and δ34S to determine the relative importance of local resources produced within the fjord to the diet of three colonies of Tawaki across the fjord’s environmental gradients. Whole blood is analysed from penguins at outer-fjord, mid-fjord and inner-fjord colonies in Doubtful Sound. Results demonstrate that isotopes could be used to discriminate diet and trophic levels of penguins among the three colonies. The present study compares isotopic values of the colonies and fishes associated to different marine habitats in the fjord using a multiple-source mixing model. Results demonstrate that locally produced resources from the fjord were important to each of the colonies. Mesopelagic resources were most important for the outer- fjord colony while pelagic and estuarine resources were most important for colonies in the mid and inner fjord. The current study highlights the importance of locally produced resources in the New Zealand fjords to diet of Tawaki, as well as the extent of foraging plasticity that Tawaki employ to access resources in different marine environments.