Adélie penguins as ecosystem indicators : foraging behaviour and habitat

Understanding the foraging movements and behavioural strategies of animals is a fundamental aim in ecology. Movement ecology underpins foraging success, which can have significant implications for an animal’s fitness, survival, and reproductive performance, and ultimately drive population-level trends and characteristics. This is particularly relevant for marine predators which make foraging and movement decisions in dynamic ocean environments where prey are patchily distributed.
In the Southern Ocean, understanding animal foraging ecology can play an important role in ecosystem monitoring and assessment. Information about foraging behaviour, and associated intrinsic and extrinsic drivers, can be used to guide spatially-explicit conservation and precautionary fisheries management through the Convention for the Conservation of Antarctic Marine Living Resources (CCAMLR) and its Ecosystem Monitoring Program (CEMP).
This thesis is concerned with the foraging behaviour and habitat use of Adélie penguins, a key indicator species monitored by CCAMLR through CEMP. The specific interactions between Adélie penguin vertical [underwater] and horizontal movements and their marine environment are investigated using long-term satellite telemetry, dive data, satellite-derived environmental products and krill acoustic surveys. This thesis work focuses on the Béchervaise Island Adelie penguin colony, an important long-term monitoring site in East Antarctica. In this thesis, I present the following:
1) Seasonal patterns in dive behaviour – multi-year dive data available from the Béchervaise Island Adélie penguin colony are used to examine how underwater foraging activity varies through the chick-rearing period. Using 10 years of time-depth recorder (TDR) data, I examine diving activity at multiple scales (i.e. foraging trips, dive bouts and individual dives), and how these behaviours vary between sex and the guard and crèche period. This work represents the first account of Adélie penguin diving activity at this important colony in East Antarctica. In this chapter, I demonstrate substantial variation in diving effort between guard and crèche, and differential sex-specific foraging strategies over the chick-rearing period.
2) Horizontal-vertical movement relationships – multi-year dive and spatial location data for penguins at the Béchervaise Island colony are quantitatively integrated to test optimal foraging theory expectations regarding horizontal-vertical movement relationships. I examine horizontal move persistence along movement trajectories, and the relationship with underwater dive effort and a range of abiotic environmental variables. Results show Adélie penguin foraging behaviour does not conform with area-restricted search expectations, challenging the traditional interpretation of horizontal-vertical movement relationships and habitat use for this colony.
3) Spatial overlap between predator foraging and prey distribution – krill swarm data at Béchervaise Island collected during acoustic surveys over two seasons and contemporaneous horizontal-vertical movement information for Adélie penguins are spatially integrated. I examine the spatial overlap between predator foraging effort and krill swarm abundance and distribution. Results show penguins concentrate foraging activity in areas with a high number of krill swarms rather than areas with a high swarm biomass.
This thesis significantly advances our understanding of Adélie penguin movement behaviour and foraging strategies at Béchervaise Island, and East Antarctica more broadly. It provides important knowledge regarding the spatial distribution of underwater foraging effort throughout the chick-rearing period, and the relationship with static and dynamic oceanographic features and krill prey-field characteristics. The work of this thesis can be used to inform spatially-explicit fisheries management in East Antarctica and can contribute to ecosystem models which predict likely impacts and responses under future krill harvesting and climate scenarios