Tracking ecosystem changes in Western Antarctic Peninsula to inform CCAMLR decision-making: insights from the ongoing ecosystem monitoring programme in Ardley Island’s CEMP site

In western Antarctic Peninsula (WAP), one of the polar areas most affected by global warming, Adelie (Pygoscelis adelie) and Chinstrap (P. antarticus) penguin populations have declined since the 1970s. In contrast, Gentoo penguin (P. papua) populations are stable and even increasing. Population declines in the WAP have been linked to the reduction of total biomass and size of available Antarctic krill caused by regional declines in sea-ice extent and duration, fishing, and the population increase of natural competitors. In recent years, Bransfield Strait and the South Shetland Islands have become a hotspot for the krill fishery. Identifying foraging areas that are regularly used by penguins would provide valuable information for the small-scale management of the krill fishery and the design of a Marine Protected Area in WAP, currently under discussion in CCAMLR. Ardley Island, in the Fildes Region, southwest of King George Island/Isla 25 de Mayo is one of the few areas in Antarctica where the three Pygoscelis penguin species breed sympatrically. Due to its geographical position in the rapidly changing WPA, the establishment of a continuous monitoring programme in Ardley Island is relevant to understand the effects of long-term climate change and other sources of anthropogenic pressure such as tourism or fishing. In 2019 Uruguay initiated a monitoring programme of the breeding colonies of Gentoo and Adelie penguins in Ardley Island using standard CCAMLR methods. Since 2022 it is a CEMP site. In addition to standard population parameters, the programme aims to track changes in individuals’ foraging ecology, use of space, trophic ecology, energy budgets, and physiological conditions. The most remarkable observation during the monitored period, is the sharp decline in the number of Adelie breeding pairs, and contrasting values for both Adelie and Gentoo penguins, in proxies of feeding energetic investment and individuals’ conditions between seasons. This is likely linked to changes in krill availability. The consequences of these variations in resource availability, the carry-on effects of these variations, and the way the different species (with different ecological plasticity) respond to these changes, require further exploration. Understanding the predator-prey interactions at small scales is critical for ecosystem conservation planning and resource management. Using an accelerometry-data-based approach we identified the areas where Adélie penguins from Ardley Island forage. The core foraging area is located within Maxwell Bay, 10 km off the colony, with this area being systematically used by more than 60% of the population throughout the summer seasons and across seasons. Nearly 20% of the population also uses the area close to Orca Seamount for foraging (35 km from the colony), mainly during the late guard stage. Vessel movements in Maxwell Bay have increased significantly since the early 2000s during the summer season. This activity overlaps in space and time with the foraging areas of the Pygoscelid species that breed in Ardley Island. Our results emphasize the relevance of Maxwell Bay and Orca Seamount as critical foraging areas during the breeding season for Adélie and the other Pygoscelid penguins. Adelie penguins have also been tracked during the winter season since 2021. Areas used throughout the annual cycle are widely distributed across the region. During the breeding stage, penguins exploit resources available in subarea 48.1, while they depend on resources available in subarea 48.5 for the post-breeding and moulting stage, and resources distributed across subareas 48.1, 48.2 and 48.5 during wintering. Their dependence on resources from different subareas in different times of the year in order to sustain their colonies also emphasizes the need of incorporating the temporal dimension of resources utilization when designing conservation measures for this region.