The diving behaviour of the whale shark Rhincodon typus related to geographical and environmental conditions in the Galapagos Marine Reserve and the Eastern Tropical Pacific

Sofia Macarena Green

There is a gap in studies of whale shark diving behaviour on adult female whale sharks in pelagic environments, as prior research has been undertaken on juvenile whale sharks from coastal aggregations. This study aimed to investigate the diving behaviour of adult female whale sharks off the Galapagos Archipelago and in the open ocean of the Eastern Tropical Pacific using high location resolution data. Generalized additive models were used to determine the geographical and environmental conditions that drive diving behaviour. The variables tested were (1) Sea Surface Temperatures, (2) Chlorophyll-a concentrations, (3) lunar phases, (4) depth of the sea floor, and (5) distance to coast. Telemetry data from nine whale sharks: 8 adult females (10.5-12.5m) and one juvenile male (5m), indicate that SSTs were the most significant driver of maximum dive depths. Whale sharks demonstrated significant spatial/temporal differences in diving behaviour performing deeper dives when in warmer waters of the Equatorial Upwelling System than when in the colder waters within the Humboldt Current System. These results indicate that the adult female whale sharks change their diving patterns for maximum foraging efficiency, feeding at mesopelagic depths when in low productivity surface waters, and thermoregulation, for cooling purposes and lower metabolic activity.