Habitat-based BART models for cetaceans in the western South Atlantic: current and future distribution under climate...

The Santos Basin, Southwestern Atlantic Ocean, is a region of high cetacean diversity. We analyzed the largest systematic ship-based cetacean sightings dataset for the area, collected between 2015 and 2019, to assess current distributions and potential responses to climate change for major taxonomic groups: migratory whales, Bryde's whales, small delphinids, large delphinids, and sperm and beaked whales. Bayesian Additive Regression Trees (BART) were employed to model species occurrence as a function of static and dynamic environmental covariates. Models demonstrated good predictive performance (AUC = 0.76-0.96; TSS = 0.40-0.86), highlighting the importance of depth, isobaths, rugosity, SST, and chlorophyll-a in driving habitat suitability. Predicted distributions indicate that migratory whales are concentrated in the northern SB and along the continental slope, whereas Bryde's whales occupy shallow coastal areas. Small delphinids favor shallow waters and the outer shelf, whereas large delphinids, sperm and beaked whales occur mainly along the 1000-m isobath and in deeper offshore areas. Future projections under medium- (SSP2-4.5) and high-emission (SSP5-8.5) scenarios suggest a coastal shift and contraction of suitable habitat for migratory whales, a potential range expansion for Bryde's whales and small delphinids, and relative stability for large delphinids, sperm and beaked whales. Our results provide a robust, group-level assessment of cetacean habitat preferences and potential climate-driven distributional changes, thereby informing adaptive conservation and management strategies in the SB under future climate scenarios.