Statistical modelling reveals spatial, temporal, and environmental preferences for white sharks

Statistical modelling reveals spatial, temporal, and environmental preferences for white sharks at an oceanic aggregation site

Edgar E. Becerril-García, Raúl O. Martínez-Rincón, Felipe Galván-Magaña, Omar Santana-Morales, Mauricio Hoyos-Padilla

Marine Ecology Progress Series 655: 171-183 (2020)

DOI: https://doi.org/10.3354/meps13528

Abstract

Guadalupe Island, Mexico, is one of the most important white shark (Carcharodon carcharias) aggregation sites in the Eastern Pacific. In the waters surrounding Guadalupe Island, cage diving has been carried out since 2001 during August-November; however, there is scarce information regarding the factors associated with this seasonal aggregation. The purpose of this study was to describe the probability of occurrence of white sharks relative to spatial, temporal, and environmental factors in Guadalupe Island. Generalized additive models (GAMs) were used to describe the effect of sea surface temperature, water visibility, tide, moon phase, cloud cover, time of day, and location on white shark occurrence. GAMs were generated from a data set of 6266 sightings of white sharks, classified as immature males, mature males, immature females, and mature females. A sexual segregation related to month was observed, where females arrived after males during late September. GAMs evidenced a segregation of white sharks according to the analysed variables, which is consistent with previous observations in this locality. Environmental preferences for each white shark category are potentially influenced by feeding habits, sexual maturation, and reproduction. This study constitutes a baseline of the effect of the environment on the occurrence of white sharks in Guadalupe Island, which can be used in further studies regarding management and conservation in future climatic and anthropogenic scenarios. Its relevance is related to the understanding of its ecology in oceanic environments and the presence of this threatened species during the ecotourism season.

Keywords: Generalized additive models, environmental factors, protected species, conservation, Ecology