How much is too much? A carrying capacity study of white shark cage diving in Guadalupe Island, Mexico

Abstract The Guadalupe Island Biosphere Reserve is one of the main aggregation sites for the white shark Carcharodon carcharias and is considered to be the best place in the world for white shark cage diving. From 2014 to 2019, the number of cage diving vessels in Guadalupe Island grew from 6 to 10, with an estimated 2800 tourists participating in white shark cage diving during the 2019 season. In 2016, the National Commission of Protected Natural Areas of Mexico requested a carrying capacity in which current regulations, white shark behavior, and the management capacity of the reserve were considered. To characterize the movement patterns of the white shark, 12 individuals were acoustically tracked. Based on the critical habitat of the white shark determined by an analysis of kernel densities, three carrying capacity scenarios (i.e., critical, optimal, and expanded) were calculated in which 1, 6 or 12 vessels, respectively, could operate simultaneously. It is important to consider that as the number of simultaneously operating cage diving vessels increases, the probability of sighting a white shark decreases [> 0.9 (critical scenario), > 0.5 (optimal scenario), and > 0.1 expanded scenario]. The results of this study may act as a baseline for the management of other white shark tourism and aggregation sites in the world. However, future studies should also include other variables, such as the energy budget, due to the use of attractants in cage diving that may potentially affect individual behavior.