Foraging movement of short-tailed shearwater in the Southern Ocean

Abstract

**Abstract:** Short-tailed shearwater (STSH) breeding in Tasmania employs a dual foraging strategy and they feed in the Southern Ocean during long trips. In the Southern Ocean, Antarctic krill (krill) is a key species, while myctophids can be one of alternatives. In the Indian sector, where krill abundance is relatively low compared to the Scotia-Weddell Sea, krill-independent food web may be developed regionally. In this sector krill-dependent food web may be dominant over the continental slope while krill-independent food web may be in oceanic zone. To understand how does STSH move in these two habitats in the Indian sector, we tracked individuals using GPS logger and identified prey species of tracked individuals using fatty acid signature of stomach oils. We collected 14 long trip tracks and two oil samples from STSH breeding on Wedge Island in Tasmania in Jan- Feb 2019. Two core-use areas (50% kernel density) were recognized. One (named "core-2") was in 160°E 67°S l in the continental slope zone and the other ("core-3") was in 120°E 57°S in the oceanic zone. 93% of birds used Core-2 during the long trips. We analyzed fatty acid composition of stomach oil in two birds spending 7 days in 2core area before visiting the colony. The fatty-acids profile indicated that the two birds fed on myctophids. Core-3 might also be important to some extent but no diet samples were available at this moment. This study indicates that at least some individuals fed on myctophids even over the continental slope. This study indicate the importance of myctophids in the Southern Ocean ecosystem. **Authors:** Sarara Azumi¹, Yutaka Watanuki¹, Akinori Takahashi², Nobuo Kokubun², Yasuhiro Ando¹, Masato Moteki³, Fernando Arce Gonzalez⁴, Mary-Anne Lea⁴, Mark Hindell⁴ ¹Hokkaido University, ²National Institute of Polar Research, ³Tokyo University of Marine Science and Technology, ⁴University of Tasmania