Theriologia Ukrainica (Dec 2022)
Winter records of killer whales (Orcinus orca) in the waters of the Wilhelm archipelago, West Antarctica
Abstract
Killer whales (KWs) are apex marine predators. In Antarctica, they have diverse trophic interactions and belong to five ecotypes that have differences in morphology, ecology, and acoustic repertoire. Around the Antarctic Peninsula (AP), two sympatric forms of Type B KWs are the most common. They have similar pigmentation patterns, but a larger form has been observed to feed mainly on seals (B1), and a smaller form feed on Pygoscelis penguins (B2). The waters of the West AP are experiencing ecosystem transformations caused by climate change at one of the fastest rates on Earth. Little is known about the austral winter distribution and ecology of KWs in this changing environment. The purpose of the study was to reveal the winter distribution and ecology patterns of KWs in the waters of the Wilhelm Archipelago. Boat-based visual observations and photo-identification were performed. The boat cruises were conducted within 14 nm of the Ukrainian Akademik Vernadsky Research Station, Galindez Island. In 2019, 10 surveys of a total of 194 nm were conducted, and in 2021 – 37 surveys of 605 nm. During both winters, three groups of KWs were recorded. A group of 7 KWs was encountered on 27 June 2019 near Hovgaard and Pleneau islands. It consisted of adults of both sexes and juveniles. In the same area, on 13 July 2021, another group of KWs was observed, consisting of at least 5 individuals (up to 7): 1 adult male, 2 adult females, a calf, and a juvenile of unknown sex. According to the external morphology patterns, it was determined that both groups belong to Type B, most likely of a smaller form (B1). Large gatherings of Pygoscelis penguins were observed in this area during both winters. On 22 July 2021, a group of KWs consisting of 2 adult males was observed in the Penola Strait. Observations of their joint feeding on a crabeater seal were performed. According to morphology and behaviour, they belong to the ecotype B2. As Antarctic krill move inshore during winter, penguins and crabeater seals likely took advantage of ice-free areas to feed on it, and their gatherings could attract KWs of both Type B ecotypes. Future work should include collecting photogrammetry data, skin biopsy samples, behaviour observations, and acoustic recordings to clearly differentiate between KW ecotypes and better understand their winter distribution and ecological patterns.
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