Droplet Formation and Transport during Exhalation and Aspiration of Bottlenose Dolphins*

Advancement in understanding of exposure of marine mammals to surface crude oil after a spill is necessary for evaluating risks and responses. In this study, we characterize the airflow and airborne water droplets generated by trained bottlenose dolphins during exhalation and inhalation. Data is obtained for various dolphins’ size, sex, levels of prior activities, chuffs, and normal breaths. Test performed in the National Aquarium involve acquisition of high-speed holograms of a sample volume with a cross section of 68x68 mm² covering the exit from the dolphins’ blowhole at a resolution of 33 μm/pixel. Upon reconstruction, we obtain a record of the droplet generated by the breathing. In some cases, the air is also seeded by externally generated mist for evaluating the velocity field after accounting for the settling velocity of the droplets. The evolution of the droplets size and spatial distributions are processed using a machine learning algorithm. Cross-correlation based analysis is used for mapping the velocity distributions in a series of volume slabs. Ongoing data analysis shows that for normal breathing events the exhalation occurs for 200-300 ms with speeds exceeding 5 m/s, and that the most probable droplet diameter is about 130 μm.