Understanding and predicting the distribution of organisms in heterogeneous environments is a fundamental ecological question and a requirement for sound management. To implement effective conservation strategies for white shark Carcharodon carcharias populations, it is imperative to define drivers of their movement and occurrence patterns and to protect critical habitats. Here, we acoustically tagged 444 immature white sharks and monitored their presence in relation to environmental factors over a 3 yr period (2016-2019) using an array of 21 iridium satellite-linked (VR4G) receivers spread along the coast of New South Wales, Australia. Results of generalized additive models showed that all tested predictors (month, time of day, water temperature, tidal height, swell height, lunar phase) had a significant effect on shark occurrence. However, collectively, these predictors only explained 1.8% of deviance, suggesting that statistical significance may be rooted in the large sample size rather than biological importance. On the other hand, receiver location, which captures geographic fidelity and local conditions not captured by the aforementioned environmental variables, explained a sizeable 17.3% of deviance. Sharks tracked in this study hence appear to be tolerant to episodic changes in environmental conditions, and movement patterns are likely related to currently undetermined, location-specific habitat characteristics or biological components, such as local currents, prey availability or competition. Importantly, we show that performance of VR4G receivers can be strongly affected by local environmental conditions, and provide an example of how a lack of range test controls can lead to misinterpretation and erroneous conclusions of acoustic detection data.

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 examined movements of 43 juvenile white sharks Carcharodon carcharias (1.7− 3.2 m total length) in eastern Australia via satellite-linked radio tags (SLRTs) 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 2 yr, the study registered approximately 182 000 detections of acoustic-tagged white sharks on 287 receivers over 7 yr, with individual tracking periods of up to 5 yr. Data reveal complex movement patterns over distances of thousands of kilometres and 13° 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 2-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 pro mise to examine movements over periods relevant to ontogenetic changes and at scales providing context to interannual variability.

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Habitat mapping is a useful method for understanding the complex spatial relationships that exist in the marine environment, and is used to evaluate the effectiveness of management strategies, particularly in regards to marine protected areas. This study explored the observed and predicted distribution of an uncommon soft coral species, Dendronephthya australis within the Port Stephens–Great Lakes Marine Park. Dendronephthya australis was mapped by video operated by a SCUBA diver towing a time synchronised GPS. A species distribution model was created to explore the possible occurrence of D. australis outside of the mapped area, using four environmental parameters: bathymetry, slope of seabed, velocity of tidal currents, and distance from estuary mouth. Dendronephthya australis colonies occurred along the southern shoreline in the Port Stephens estuary between Fly Point and Corlette Point, but no colonies were found within sanctuary (no-take) zones within the marine park. The model illustrated limited habitat suitability for D. australis within a larger section of the estuary, suggesting this species has specific environmental requirements survival. Owing to its current threats (anchor damage and fishing line entanglement), implications from these findings will assist future management and protection decisions, particularly in regard to its protection within a marine park.