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The foraging ecology, diet, and mass estimation of an apex predator, the leopard seal (Hydrurga leptonyx), at Livingston Island, Antarctic Peninsula


Describing the foraging dynamics of apex predators is crucial to understanding ecosystem function and to effective conservation and management. Leopard seals are conspicuous apex predators in Antarctic coastal ecosystems; however, their foraging ecology is poorly understood. Likely due to a geographical redistribution driven by pack-ice habitat reduction in the western Antarctic Peninsula, leopard seals have been hauling out at Cape Shirreff with increasing frequency in recent years. Utilizing that rare access we implemented an integrated sampling design including morphometrics, biological samples, and bio-logger deployments in January and February between 2008 and 2014. Subsequently, we quantified foraging behavior using: k-means cluster (diving), time-local convex hulls (movement), Bayesian stable isotope mixing models (diet), and linear regression (mass estimation) analyses. While they are typically described as generalist apex predators, video, dive, and movement data suggest they employ specialized foraging patterns. They affect coastal ecosystems through pathways beyond direct predation, including intraspecific kleptoparasitism, predator-induced stress effects, facultative scavenging and food caching. Leopard seal diving behavior is concentrated at night, is both shallow and coastal, and is composed of four distinct dive types. Haul-out probabilities were highest near midday and were positively correlated with available daylight. Video, scat and stable isotope analyses indicate that their summer diet contains four prey groups: Antarctic fur seals, pygoscelid penguins, krill, and demersal notothen fishes. Finally, measurements of body size and mass are fundamental to pinniped population management and research. The recent proliferation of unmanned aerial systems (UAS) in wildlife monitoring has provided a promising new platform for the photogrammetry of free-ranging pinnipeds. Photogrammetric measurements from a single, vertical image obtained using UAS were as accurate as ground measures, and provide a noninvasive approach for estimating the mass and body condition of pinnipeds. This dissertation provides substantial insight into the hunting tactics, foraging behavior, and diet of large adult female leopard seals and provides a viable option for future monitoring.

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