Coastal swimming patterns of white sharks (Carcharodon carcharias) at Mossel Bay, South Africa

Abstract

Between June and December 2005, active and passive acoustic telemetry was used to examine fine scale movements of 13 white sharks (Carcharodon carcharias) (ten passive, three active) at Mossel Bay. A total of 24 active trackings (ranging from 2 h to 103 h in duration) were conducted. Patterns of rate of movement (ROM), swimming linearity (LI), swimming bearing, and instantaneous swimming speed (ISS) were assessed. A conversion quotient (Q) of 1.21 between ISS and ROM (10 min sample interval) was calculated suggesting ROM is a good indicator of white shark activity. The mean ROM for tracked sharks was 0.52 m·s −1 , with a greatest sustained ROM of 1.33 m·s −1 (4.8 km·h −1 ).Sharks displayed greatest LI and ROM during directional travels between the three persistent aggregation sites. The majority of the shark movement was, however, non-linear as the sharks repeat patrolled at the three aggregation sites. Two of these sites were not associated with pinniped presence, and sharks typically patrolled back and forth parallel to the shore line at a comparatively low ROM which suggested resting. The third aggregation site was adjacent to Seal Island, and despite low LI, sharks displayed a high ROM, indicating high activity levels. We propose that the high ROM is related to maximising search area when patrolling to hunt Cape fur seals (Arctocephalus p. pusillus).

Marine predator–prey contests: Ambush and speed versus vigilance and agility

“…For example, on 25 August 2000, a 3.4-m white shark swimming at 0.5 m/s fled a larger conspecific, moving across the length of our 8-m observation vessel in 90.8 s. This corresponds to a burst speed of 11.9 m/s. This value is comparable with reported burst speeds of 6 m/s and 7 m/s for white sharks hunting pinnipeds at other sites (Johnson et al 2009). During initial strike on a Cape fur seal, white sharks breach the waters' surface (Martin et al 2005).…”

White Sharks (Carcharodon carcharias) Scavenging on Whales and Its Potential Role in Further Shaping the Ecology of an Apex Predator

“…Furthermore, both of these whale species are known to come within <1 km of the coastline during the winter months (June – December), subjecting them to higher risks of boat collisions, stranding, and entanglement with fishing gear [49], [50]. The hypothesis that white sharks may track, harass, and prey on inshore whales is consistent with white shark tracking studies revealing a high degree of “on-and-offshore” patrolling movements parallel to the South African coastline [51], [52]. In free-ranging predators, random-walk Lévy movement has been attributed to searching for prey that are randomly or widely distributed, whereby consumers will alternate between periods of highly-tortuous movement and longer-distance, straight-line movement [53].…”

Travelling light: white sharks (Carcharodon carcharias) rely on body lipid stores to power ocean-basin scale migration

“…Similarly, the mean track linearity (calculated as the ratio of the straight-line distance to the curvilinear distance) was 0.96 ( n = 5 migrations; s.d. = 0.026), demonstrating that the migration trajectories were highly directional towards a distant destination and were markedly different from area-restricted search (ARS) behaviour such as is characteristic of foraging [39]. Track linearity during coastal periods, by contrast, showed a strong ARS imprint (mean = 0.27; s.d.…”