Distribution of blubber in the northwest Atlantic harp seal, Phoca groenlandica

Abstract

We examined blubber distribution in 50 mature harp seals (Phoca groenlandica) from the St. Lawrence River estuary, Canada, between December 1988 and April 1989. Blubber was thickest and most variable dorsally, becoming gradually thinner through the neck region and around the foreflippers. Blubber thickness relative to body radius was greatest dorsally at positions from 40 to 70% of standard length (measured back from the snout) and in the posterior region; it varied less topographically than blubber thickness alone, thereby increasing the insulating effectiveness of blubber stores. The largest sexual and seasonal differences in blubber were at the sites with the greatest relative blubber thicknesses. Pregnant females (winter) had thicker blubber than males (winter) or postpartum females (April) at corresponding body sites. Pregnant females had significantly thinner blubber ventrally in the abdominal region than at corresponding lateral positions, whereas males and postpartum females had a more uniform distribution. Blubber mass was highly correlated with estimated blubber volume (R2 = 0.9967, p < 0.0001), and can be approximated from maximum girth alone (R2 = 0.7847, p < 0.0001). Measured blubber density was 0.92 ± 0.01 g∙cm−3. We discuss the pattern of blubber distribution in harp seals with respect to the multiple functions of energy demands, thermal insulation, streamlining, and mobility.