Spatiotemporal distribution patterns of immature Australasian white sharks (Carcharodon carcharias)

Abstract

In Australian and New Zealand waters, current knowledge on white shark (Carcharodon carcharias) movement ecology is based on individual tracking studies using relatively small numbers of tags. These studies describe a species that occupies highly variable and complex habitats. However, uncertainty remains as to whether the proposed movement patterns are representative of the wider population. Here, we tagged 103 immature Australasian white sharks (147-350 cm fork length) with both acoustic and satellite transmitters to expand our current knowledge of population linkages, spatiotemporal dynamics and coastal habitats. Eighty-three sharks provided useable data. Based on individual tracking periods of up to 5 years and a total of 2,865 days of tracking data, we were able to characterise complex movement patterns over ~45° of latitude and ~72° of longitude and distinguish regular/recurrent patterns from occasional/exceptional migration events. Shark movements ranged from Papua New Guinea to sub-Antarctic waters and to Western Australia, highlighting connectivity across their entire Australasian range. Results over the 12-year study period yielded a comprehensive characterisation of the movement ecology of immature Australasian white sharks across multiple spatial scales and substantially expanded the body of knowledge available for population assessment and management.

Effective number of white shark (Carcharodon carcharias, Linnaeus) breeders is stable over four successive years in the population adjacent to eastern Australia and New Zealand

“…In this study, we trialed a sampling and genotyping protocol aimed at estimating Nb over time (four breeding seasons; 2010–2013) in a population of C. carcharias of conservation concern. We focus on the east Australia–New Zealand population (EAP) of C. carcharias which, due to patterns of coastal residency and site fidelity (Bruce et al., 2019; Spaet et al., 2020), is genetically distinct from other identified populations in the North‐Pacific, South‐West Australia, Atlantic, South Africa, and Mediterranean (Andreotti et al., 2016; Blower et al., 2012; Gubili et al., 2010; O’Leary et al., 2015; Tanaka et al., 2011). The EAP has experienced a large (>90%) decline during the 20th century due to targeted fishing and mortalities associated with bather protection programs (Reid et al., 2011; Roff et al., 2018); however, recovery is now anticipated due to protection through international conventions and jurisdictional legislation [i.e., International Plan of Action for the Conservation and Management of Sharks (FAO, 2000) and the Environment Protection and Biodiversity Conservation (EPBC) Act of 1999 (EPBC, 1999)].…”

Oceanographic conditions associated with white shark (Carcharodon carcharias) habitat use along eastern Australia

“…There is an approximate demarcation between the south-western and eastern populations from around Wilsons Promontory in Bass Strait (Fig. 1) to approximately 142° E (see Spaet et al 2020). Both of these populations are genetically distinct from the South African population (Pardini et al 2001).…”

“…In Australia, 3 species of sharks (white shark Carcharodon carcharias, tiger shark Galeocerdo cuvier and bull shark Carcharhinus leucas) account for the majority of serious or fatal shark attacks on humans (West 2011, Mcphee 2014. Of the 3 species, white sharks have the widest distribution, ranging from Papua New Guinea to sub-Antarctic Islands (Bradford et al 2020, Spaet et al 2020, and have been responsible for the largest number of human deaths and injuries. The abundance of adult white sharks has remained relatively stable up to 2018 following protection (classified as Vulnerable, IUCN; Rigby et al 2019) that was put in place in the 1990s (Hillary et al 2018).…”

“…Predicting the distribution of top predators that are able to span a large range of oceanic conditions (Spaet et al 2020) is challenging, as sharks most likely rely on evolved migration strategies and distribute at fine scales according to local distribution of prey resources. However, there has been little examination of the regional distribution of white sharks in eastern Australian waters in relation to ocean conditions (e.g.…”

Operational Protocols for the Use of Drones in Marine Animal Research

“…The error incurred in drone-based detections of sharks relative to true densities largely depends on water depth, sea conditions, water clarity, and the animal's position in the water column [39][40][41][42]. However, unlike surveying air-breathing marine species, many shark species are far less prone to swimming at the surface and spend considerably more time at depth [43]. The clear exception to this might be whale sharks and basking sharks [41,44].…”