Bull Shark (Carcharhinus leucas) Occurrence along Beaches of South-Eastern Australia: Understanding Where, When and Why

Abstract

Unprovoked shark bites have increased over the last three decades, yet they are still relatively rare. Bull sharks are globally distributed throughout rivers, estuaries, nearshore areas and continental shelf waters, and are capable of making long distance movements between tropical and temperate regions. As this species is implicated in shark bites throughout their range, knowledge of the environmental drivers of bull shark movements are important for better predicting the likelihood of their occurrence at ocean beaches and potentially assist in reducing shark bites. Using the largest dataset of acoustically tagged bull sharks in the world, we examined the spatial ecology of 233 juvenile and large (including sub-adult and adult) bull sharks acoustically tagged and monitored over a 5.5-year period (2017–2023) using an array of real-time acoustic listening stations off 21 beaches along the coast of New South Wales, Australia. Bull sharks were detected more in coastal areas of northern NSW (<32° S) but they travelled southwards during the austral summer and autumn. Juveniles were not detected on shark listening stations until they reached 157 cm and stayed north of 31.98° S (Old Bar). Intra-specific diel patterns of occurrence were observed, with juveniles exhibiting higher nearshore presence between 20:00 and 03:00, whilst the presence of large sharks was greatest from midday through to 04:00. The results of generalised additive models revealed that large sharks were more often found when water temperatures were higher than 20 °C, after >45 mm of rain and when swell heights were between 1.8 and 2.8 m. Understanding the influence that environmental variables have on the occurrence of bull sharks in the coastal areas of NSW will facilitate better education and could drive shark smart behaviour amongst coastal water users.

Global genetic diversity and historical demography of the Bull Shark

“…As C . leucas inhabits areas with water temperatures down to 18°C (Brunnschweiler et al., 2010; Lea et al., 2015; Matich & Heithaus, 2012; Smoothey et al., 2016, 2019, 2023), sea surface temperature changes during the LGM did not significantly reduce its distribution in the tropics (Monteagudo et al., 2021). Additionally, long‐range movements (Espinoza et al., 2016; Lea et al., 2015; Lee et al., 2019) may have facilitated colonization of newly emerged areas.…”

From little things big things grow: enhancement of an acoustic telemetry network to monitor broad-scale movements of marine species along Australia’s east coast

“…within marine reserve boundaries; 16 ], to arrangements that encircle geomorphological features such as offshore reefs or seamounts [ 17 , 18 ], and large-scale arrays that incorporate receiver gates or curtains to record movements among embayments, estuaries [ 19 ], or along coastlines [e.g. 20 , 21 , 22 ]. Large-scale networks of acoustic receivers are increasingly expanding across the world’s oceans, forming regional- to continental-scale arrays that can address a broader range of ecological questions, including the identification of long-range movements or population connectivity [ 10 , 23 , 24 ].…”