Influence of environmental factors On White Shark Behaviour.
Supervisor: Emilio Sperone (U Calabria)
The influence of environmental factors on Carcharodon carcharias has been target of research in the last decades. Considering the global distribution of this top predator, they can be found in a wide range of temperatures and depths. Different biotic factors as temperature, El Niño Southern Oscillation, bathymetry/water depth, water clarity, light, sun direction, lunar phase, cloud cover, tides, salinity, rainfall, swell, currents, wind, upwelling, chlorophyll, oxygen, barometric pressure and eddies have contributed to the understanding of white shark habitat use and distribution, along coastal and oceanic areas, as well to knowledge on predation activity in aggregation sites. These hotspots have been the main source of publications, however the lack of knowledge in the field of the influence of environmental factors on white shark behaviour is still large.

Dyer Island in South Africa is a well-known aggregation area for white sharks and a developed cage-diving ecotourism industry is established there. This tourism activity allows a safe and direct contact with these predators, and may act as a platform for scientific research. The ethological approach is a non-invasive method that provides an opportunity to study animal behaviour and it was used here to evaluate and prove the influence of the environmental factors on the complexity and the temporal sequences of C. carcharias behaviours. The biotic factors considered were time of the day, sea surface temperature, visibility, tides, El Niño Southern Oscillation, lunar phase, sea condition and cloud cover. When analysing individually the 720 records, excepting tides and time of the day, all of them showed an influence on the complexity of white shark behaviours. Visibility, lunar phase, sea condition and cloud cover may be related with the visual ability of detecting the bait. Sea surface temperature and El Niño Southern Oscillation may be related with physiological demanding and energy expenditure. As a complement, a generalised additive model was applied to consider the relationship between the factors while acting on these predators’ behaviour. 35.6% of the deviance of the number of behaviours was explained by sea surface temperature, visibility, tides, El Niño Southern Oscillation, lunar phase, sex and maturity stage.

The white sharks performed an average number of behaviours of 4 behaviours per ethogram. The association between the ethograms and the different environmental variables was significant for all the factors analysed. Commonly, behavioural units as parading, bait follow and visual inspection were performed in higher or smaller number than expected, showing an influence of the environmental factor. The first five behavioural units performed in an ethogram and the transitions between these behaviours demonstrate that parading and bait follow seem to be the standard behaviours of the white shark in relation to bait-attraction.

Often, white sharks swim over recreational waters or fishing areas. Knowledge about how white sharks respond to environmental factors is essential for managers and policy makers. Human encounters, fishing mortality and climate change are pressures that need to be addressed in order to protect and conserve this species.