In vivo ultrasonic attenuation was estimated for extracranial soft tissues of two Tursiops truncatus and one Delphinapterus leucas. Backscatter data was non-invasively collected as part of routine health-based ultrasound examinations using a transducer operating in the 1.6-3.7 MHz frequency range. Data collected over the proximal mandible and temporal regions was processed to yield attenuation estimates using a reference tissue phantom whose properties had been independently determined. The estimated attenuations were at the low end of the range of literature-reported values for mammalian fatty and connective tissues. A companion model-based analysis quantified errors arising from tissue composition and sound speed uncertainties.