## 4 Discussion
### Diving Behaviour
Archival data of YOY and juvenile white sharks in the eastern Pacific revealed diel patterns opposite to those described in our study, with sharks conducting high frequency oscillations during the day, while occupying surface mixed layers during the night [48; 57]. In our study, nocturnal high frequency oscillatory movements and relatively constant depth during the day (including occasional ascents to the surface followed by surface swimming periods of up to 3 h) were characteristic of the entire tracking period in all sharks and did not noticeably change even during across-ocean migrations (see shark 180, Figure 4). The consistency in this behaviour across individuals and tracking periods might indicate that individuality in dietary preferences and foraging behaviour, as observed in adult white sharks [58; 59], may develop later in life. In our study, deep-diving behaviour was observed infrequently in six sharks, suggesting that individual sharks employ diverse strategies for deep pelagic habitat use, which varies across space and time. Mesopelagic excursions or occupation of deep pelagic habitats are common features of nearly all oceanic taxa studied with electronic tags [60]. Although direct evidence remains sparse, most shark tracking studies suggest deep-diving behaviour to be largely related to foraging, often within and below sound scattering layers e.g., [28; 61; 62]. The importance of mesopelagic prey for white sharks has recently been established in the Mexican Pacific using mercury isotopes yet considering that sharks could potentially access mesopelagic prey that migrate to the surface, direct evidence for the consumption of mesopelagic prey currently does not exist [63]. To clearly link mesopelagic excursions and successful foraging, future studies should leverage innovative tag technologies alongside emerging tools for studying food webs, e.g., ecological tracers such as Amino-Acid Compound-Specific Isotope Analysis (AA-CSIA) [63], trace elements [64], or radiogenic isotope analysis [65], The most likely alternative explanation for deep-diving behaviour suggests that large marine predators use occasional forays into the deep to probe the water column for navigational cues, e.g., geophysical gradients such as magnetic field intensity and/or inclination [66]. Such gradients may be up to 25 times stronger vertically than horizontally [60; 67]. While in reality, it is still unknown whether sharks use information from the Earth's field for navigation, results of several studies indicate that migratory sharks have the sensory capabilities to detect geomagnetic elements and use deep dives to orient to a change in geomagnetic intensity gradient [68; 69]. Deep dives occurred in offshore waters along the eastern coasts of Australia and Tasmania (Figure S4). The angle of geomagnetic inclination contour lines in this region intersects at 30\({}^{\circ}\) (in the NE direction). Although the majority of deep-dive locations in our dataset are subjected to the limitations of light-based geolocations, most of them either align with the major contour lines or build clusters around them (Figure S4). If sharks are able to detect magnetic declination, predictable variation in inclination angle may allow them to maintain a steady compass heading and to determine whether their position is north or south of a particular area [70]. However, the infrequent occurrence of deep dives suggests that navigation via geomagnetic topotaxis is likely only a response to exceptional circumstances, e.g., before the onset of a directed migratory movement or a change from the current course of travel. Deep dive initiation times peaked in the early morning hours after dawn, suggesting that at least a portion of deep-dives might be triggered by environmental cues or a circadian clock.