Population-scale habitat use by school sharks Galeorhinus galeus (Triakidae) in the Southwest Atlantic: insights from temporally explicit niche modelling and habitat associations

Abstract

Population-scale information on the spatial ecology of threatened mobile sharks is required to design more effective management measures. Using an exhaustive collection of presence-only records and relevant predictors, we applied temporally explicit environmental niche modelling to study habitat use by a school shark Galeorhinus galeus population in the Southwest Atlantic. As a complementary tool, we developed randomized habitat association curves to assess both the representation of data with biological information and possible intra-population variation in habitat use. Seasonal niche models supported a core area of distribution between southern Brazil and southern Argentina. Marginal seasonal variation in suitability at the northern and southern extremes of its distribution supported the hypothesis that the G. galeus population behaves to some degree as a niche shifter on an annual cycle. Habitat associations revealed regional bias in the collection of records with biological information, and suggested a complex intra-population segregation pattern between sexes and between maturity stages during the cold half of the year. Overall, results supported large-scale partial migrations (i.e. some individuals migrate while others remain resident) of the G. galeus population. This study demonstrates the significance of future regional efforts that focus on producing more and better databases to derive relevant information at a low cost for the management of threatened sharks and their relatives.