Citizen Science Data Reveals Environmental Influence on Sightings of Great White Sharks in Mossel Bay, South Africa

Whilst previous studies have described the impact of various environmental conditions on behaviour and abundance of great white sharks (GWS), existing knowledge gaps must be addressed in order to turn the tide on their population declines. This study used data collected by a diving tour operator, to investigate how environmental and anthropogenic variables affected the rate of GWS sightings. Observation data were collected by trained crew and volunteers alongside tourists, and combined with externally sourced environmental data. Hurdle modelling identified that the probability of sighting at least one GWS fluctuated seasonally (peaking during winter), but was also correlated with minimum running air temperature, water visibility and the length of time the boat stayed at anchor. The rate GWSs were sighted also rose in winter, and was associated with maximum running air temperature, the arrival time, seal activity, and the wind direction and speed. These findings indicate that environmental conditions directly impacted upon the sighting frequency, but also influenced habitat selection on a fine spatial scale. This study emphasises that collaboration with ecotourism companies could represent a valuable, inexpensive alternative for scientific data collection, as long as powerful statistical methods are used, the influence of human activity is considered and results are interpreted with consideration of the data collection methodology.