Spatial Dynamics and Fine-Scale Vertical Behaviour of Immature Eastern Australasian White Sharks (Carcharodon carcharias)

SIMPLE SUMMARY: To understand how ecosystems function and to be able to better protect large marine predators, like sharks, it is important to understand how these animals move and navigate through their ocean environment. For white sharks in Australian and New Zealand waters, horizontal movement has been relatively well studied, but their diving behaviour is less well understood. We tagged 27 immature white sharks with three different tag types that collect positional, temperature and depth data. Tagged sharks travelled from southern Queensland to southern Tasmania and New Zealand. All sharks frequently dove up and down the water column (0–632 m) and experienced temperatures ranging from 7.8–28.9 °C. Importantly, there was a noticeable difference in the sharks’ diving behaviour between day and nighttime. During the day, white sharks remained at relatively constant depths, while at night, they constantly moved vertically through the water column in a high frequency. These findings help us to better understand how Eastern Australasian (EA) white sharks navigate through the ocean and provide new information on the ecology of juvenile white sharks. ABSTRACT: Knowledge of the 3-dimensional space use of large marine predators is central to our understanding of ecosystem dynamics and for the development of management recommendations. Horizontal movements of white sharks, Carcharodon carcharias, in eastern Australian and New Zealand waters have been relatively well studied, yet vertical habitat use is less well understood. We dual-tagged 27 immature white sharks with Pop-Up Satellite Archival Transmitting (PSAT) and acoustic tags in New South Wales coastal shelf waters. In addition, 19 of these individuals were also fitted with Smart Position or Temperature Transmitting (SPOT) tags. PSATs of 12 sharks provided useable data; four tags were recovered, providing highly detailed archival data recorded at 3-s intervals. Horizontal movements ranged from southern Queensland to southern Tasmania and New Zealand. Sharks made extensive use of the water column (0–632 m) and experienced a broad range of temperatures (7.8–28.9 °C). Archival records revealed pronounced diel-patterns in distinct fine-scale oscillatory behaviour, with sharks occupying relatively constant depths during the day and exhibiting pronounced yo-yo diving behaviour (vertical zig-zag swimming through the water column) during the night. Our findings provide valuable new insights into the 3-dimensional space use of Eastern Australasian (EA) white sharks and contribute to the growing body on the general ecology of immature white sharks.