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Marine Ecology Progress Series

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MEPS 653:167-179 (2020)  -  DOI: https://doi.org/10.3354/meps13488

Environmental conditions are poor predictors of immature white shark Carcharodon carcharias occurrences on coastal beaches of eastern Australia

Julia L. Y. Spaet1,2,*, Andrea Manica1, Craig P. Brand3, Christopher Gallen4, Paul A. Butcher2,3

1Evolutionary Ecology Group, Department of Zoology, University of Cambridge, Cambridge CB2 3EJ, UK
2National Marine Science Centre, Marine Ecology Research Centre, School of Environment, Science and Engineering, Southern Cross University, Coffs Harbour, New South Wales 2450, Australia
3Fisheries NSW, NSW Department of Primary Industries, National Marine Science Centre, Coffs Harbour, New South Wales 2450, Australia
4Fisheries NSW, NSW Department of Primary Industries, Port Stephens Fisheries Institute, Nelson Bay, New South Wales 2315, Australia
*Corresponding author:

ABSTRACT: 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.


KEY WORDS: Acoustic telemetry · New South Wales · Generalized additive model · GAM · Range test · Receiver performance · Seasonality · Spatial · Temporal


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Cite this article as: Spaet JLY, Manica A, Brand CP, Gallen C, Butcher PA (2020) Environmental conditions are poor predictors of immature white shark Carcharodon carcharias occurrences on coastal beaches of eastern Australia. Mar Ecol Prog Ser 653:167-179. https://doi.org/10.3354/meps13488

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