Figure 3. Relationship between sighting frequency of sharks in surveyed 1 km² cells and the log of the number of people within a 10 km radius of each cell for A) all shark species combined, B) all sharks excluding nurse sharks (Ginglymostoma cirratum), and C) nurse sharks only.

Data on the number of people was obtained from the Socioeconomic Data and Applications Center at http://sedac.ciesin.columbia.edu/gpw/global.jsp. Trends (solid red lines) were fitted using inverse power models to define the relationship between sighting frequency of sharks (y) and log of human density (x). The models were A) y = 1/[6.8*(x+1)^0.09], p<0.0001; B) y = 1/[20.6*(x+1)^0.11], p = 0.0002; C) y = 1/[10.2*(x+1)^0.09], p<0.0001. The graded colours on the figure are used to identify the density of cells on the plots where red = high, green = intermediate, white = low. Dashed lines show human population density = 1000 and sighting frequency = 0.10.