Sex Differences in the Individual Behaviour of Bait-Attracted White Sharks (Carcharodon carcharias, Linnaeus, 1758) Are Linked to Different Environmental Factors in South Africa

Abstract

The white shark (Carcharodon carcharias) is a charismatic species and, consequently, one of the most studied and protected sharks. This species can be found in a wide range of temperatures and depths, showing site fidelity and migrating across the oceans. This offers a challenge to understanding the processes influencing their lifecycle and, more importantly, assessing anthropogenic disturbances to their populations. These predators' behaviour has been linked to diverse abiotic factors. Here, an ethological approach was used to understand the influence of environmental variables on white shark behaviour. A different environmental impact was found between the activity of females and males toward the bait. Females performed a higher number of behaviours under daylight, lower sea surface temperatures, short wavelets, clear and cloudy skies, under La Niña events, elevated moonlight and high tides. Males behaved with more complexity at dawn, medium sea surface temperatures, large wavelets, few clouds, high tides, and elevated moonlight. The world's aquatic habitats are experiencing significant physiochemical shifts due to human-induced climate change. Knowledge about how white sharks respond to environmental factors is essential to guide management and conservation actions.

Keywords: environmental influences; ethograms complexity; sexual differentiation; white shark.

Figure 1

Study area in Dyer Island, South Africa.

Figure 2

Generalised additive model functions of female white shark behaviour complexity in relation to the explanatory variables. Tick marks above the x-axis indicate the number of observations. The dashed lines represent the 95% confidence intervals of the spline functions. SST = sea surface temperature; ENSO = El Niño Southern Oscillation.

Figure 3

Generalised additive model functions of male white shark behaviour complexity in relation to the explanatory variables. Tick marks above the x-axis indicate the number of observations. The dashed lines represent the 95% confidence intervals of the spline functions. SST = sea surface temperature; ENSO = El Niño Southern Oscillation.