Integument and Pelage

Phocid seals, like other pinnipeds, have a layer of hair and a specialized fat layer called blubber.  Blubber serves many functions but chief among them are providing thermal protection and serving as an energy storage depot.  

Perhaps more than any other marine mammals, many species of phocid seals rely on the blubber as an energy storage depot while undergoing extended periods of fasting.  For example, the Northern elephant seal spends several months fasting on shore during which time they lose a substantial amount of body mass, mainly from depletion of their blubber layer.  They also undergo significant changes in the amount of fat stored in the blubber layer while at sea.  Such changes cause changes in buoyancy as more low density lipid is added to the blubber layer.  These changes in buoyancy can be detected from dive records during periods when individuals are drifting up or down in the water column.

During necropsy, the thickness of the blubber layer should be measured at several body sites.  The most common sites are the ventral midline at the axilla and umbilicus although different facilities and researchers use different sites.  
Tips for measuring blubber thickness at necropsy:

•    Use a small metric with fine scale gradations
•    Make a clean slice through the blubber at the site that you want to measure
•    Insert the metric to the superficial surface of the deep muscle layer
•    Don’t push down too hard – try to do it the same each time
•    Get down at eye level and read the metric, noting both the blubber (fat layer) alone and with the pelage

Researchers also may request blubber samples.  Depending upon the study, the blubber may need to be collected using Teflon knives and film for contaminants or it may simply be frozen.  Blubber is best wrapped in two layers of plastic wrap and then double bagged to maintain maximum freshness.  One important tip is to use your scalpel to notch the dorsal, cranial margin of the blubber sample as this will provide the orientation of the sample relative to the body surface for the researcher.

 Detailed annotated images of the integument and pelage in two phocids, the harbor seal and elephant seal, are shown below.  CLICK on an image to see an enlarged view.