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Abstract:

The advent of electronic tagging has seen vast advances in our understanding of marine top-order predator movements over broad spatial scales. However, most studies are restricted to short temporal scales. We examine movements of 43 juvenile white sharks (1.7 to 3.2 m total length) in eastern Australia via satellite linked radio tags (SLRT) and internally implanted long-life acoustic tags, the latter monitored by receiver arrays spanning a continental-scale and across international boundaries. Although SLRT data were restricted to less than two years, the study registered approximately 182,000 detections of acoustic-tagged white sharks on 287 receivers over seven years, with individual tracking periods of up to five years. Data reveal complex movement patterns over distances of thousands of kilometres and 13 degrees of latitude, with sharks ranging from the southern Great Barrier Reef, Queensland, to Tasmania and across the Tasman Sea to New Zealand. Sharks showed a variety of movement patterns including annual fidelity to spatially restricted nursery areas, directed seasonal coastal movements, intermittent areas of temporary nearshore residency and offshore excursions into the Tasman Sea. Movements east to west through Bass Strait were restricted, further supporting the two-population model for the species in Australian waters. The latitudinal range of movements increased with years at liberty and female sharks were more commonly encountered than males in nearshore waters. Long-term monitoring of acoustic-tagged sharks via data sharing through collaborative national and international receiver arrays offers future promise to examine movements over periods relevant to ontogenetic changes and at scales providing context to interannual variability.

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