Mesoscale eddies in the Southern Ocean influence foraging trip behaviour of multiple penguin species

Mesoscale eddies are rotating vortices of water that perturb the local physical, chemical, and biological environment. In the Southern Ocean, penguins inhabit regions characterised by intense eddy activity, which can offer foraging opportunities. To better understand relationships between penguins and eddies, we collated tracking data for five species (emperor, king, chinstrap, Adélie, and macaroni penguins), totalling 3189 individuals from 59 colonies. Data were subset by colony and breeding stage to create 74 case studies. We then fitted Hidden Markov Models to penguin tracks to identify Area-Restricted-Search (ARS) behaviour (a proxy for foraging) and used Generalised Additive Mixed Models to relate behaviour to the presence of eddies. In 28 case studies, penguins displayed a pronounced increase in ARS within specific parts of eddies. All five species exhibited an association between ARS and eddies in several case studies, though substantial regional differences in association strength were observed. In life history periods when penguins experienced central place constraints, ARS was more frequently associated with eddies. By studying five extensive case studies in greater detail, we found that eddies possibly influenced trip trajectories by aggregating prey at submesoscale filaments around their peripheries, interacting with the distribution of sea ice, and potentially by transporting key prey species in their interiors. In these case studies, eddy maturity, amplitude, and intensity also differed between eddies collocated with ARS and the background eddy field. When eddy abundance varied, foraging trip durations also varied, though with opposing trends depending on the colony and breeding stage. Eddy activity is projected to increase in the Southern Ocean, which in isolation would have mixed impacts on penguins, though the negative impacts of broad-scale changes in prey availability and sea ice concentration are likely to outweigh any impacts of changing eddy fields.