Blubber serves as an insulator and is key in the thermoregulation of cetaceans. Changes in blubber thickness were investigated to compare between bottlenose and rough-toothed dolphin species and to assess the diagnostic use of blubber thickness measurements as an indicator of body condition by monitoring individual variations.
Blubber thickness in dolphins was measured using a scanoprobe ultrasound machine, which uses interfaces to distinguish between layers within the body. Four bottlenose and two rough-toothed dolphins at Dolphin Quest French Polynesia (DQFP) were sampled at quarterly intervals for a 2-year period. Blubber thickness measurements were recorded from three positions, results presented are from measurements obtained in front of the dorsal fin.
Blubber thickness varied between bottlenose and rough-toothed dolphin species. The juvenile rough-toothed dolphin studied had the thinnest blubber layer with an average of 12 mm. The adult rough-toothed dolphin had an average blubber layer of 16 mm, which was less than that of juvenile bottlenose dolphins, which had a blubber layer of 18 mm. Adult bottlenose dolphins had the thickest blubber layer of all dolphins studied, averaging between 25 and 30 mm.
Individual dolphins at DQFP were monitored for changes in the thickness of their blubber layer. Over the study period the blubber layer of a female adult bottlenose dolphin almost doubled; although length of this animal did not change and her weight did not proportionately increase. In a juvenile male bottlenose dolphin that experienced an infection lasting a few weeks, a blubber thickness decline from an established baseline of 18 mm to 13 mm was evident. The blubber thickness of this animal had returned to baseline values when measured 3 months later. These examples illustrate the potential to use blubber thickness measurements as an indicator of body condition when monitoring dolphins.