Abstract
Blubber has many functions, among which energy storage, thermoregulation, buoyancy, and hydrodynamic streamlining are the most frequently cited. Within and between taxa, variations in its structure and distribution likely reflect different adaptations of a species to its life history requirements, environment, health, and function. Here, we use ultrasound to describe the distribution of blubber in the finless porpoise (Neophocaena asiaeorientalis sunameri) based on examinations of 34 fresh cadavers recovered as accidental fisheries bycatch. Measurements of blubber depth determined by ultrasound positively correlated with conventional measurements using a scalpel and calipers. Whereas conventional surgical incision and visual examination revealed two layers of blubber, ultrasound revealed up to three layers; thus, ultrasound reveals additional structural detail in blubber while crude necropsy techniques do not. Across life history categories, ultrasound revealed the distribution of inner blubber to be topographically consistent with that of full-depth blubber. Blubber in the dorsal region was stratified into three layers and was significantly thicker than that in the lateral and ventral regions, in which a middle layer was normally absent. Ultrasoundprovides a fast, effective, and accurate means to determine blubber thickness and structure, and thus, assessment of the health of fresh finless porpoise carcasses. Blubber depth is determined largely by the thickness of the inner and middle layers, wherein lipids are concentrated. The thickening of blubber in the dorsal thoracic-abdominal region suggests multiple roles of thermal insulation, lipid storage, and, we speculate, to facilitate vertical stability in the complex shallow and estuarine waters in which this animal absent of a dorsal fin occurs.
Highlights
Blubber has many functions, among which energy storage, thermoregulation, buoyancy, and hydrodynamic streamlining are the most frequently cited
Blubber in the dorsal region posterior to the head was stratified into three layers (Figure 2B), in contrast to that blubber in lateral and ventral regions, which was normally absent of the middle layer and consisted of two layers only (Figure 2C,D)
Topographic distribution of full-depth and inner blubber Across life history groups, finless porpoise full-depth blubber was distributed in a similar manner to that of the inner blubber layer, and full-depth blubber was significantly thicker in the dorsal region than that in the lateral and ventral regions where an obvious middle layer was absent
Summary
Among which energy storage, thermoregulation, buoyancy, and hydrodynamic streamlining are the most frequently cited. Blubber performs a variety of functions in aquatic mammals, such as acting as an energy reserve, for thermal insulation, providing buoyancy, and streamlining the body (Ryg et al 1988). In ringed seals (Pusa hispida), blubber from the posterior region has been deemed over-insulated and to function primarily as a fat reserve; it is from this region that blubber depth should, preferably, be measured to assess body condition (Ryg et al 1988). Koopman (1998) determined sites of energy storage in harbor porpoises (Phocoena phocoena) to occur predominately in the thoracicabdominal region, whereas that blubber in the tailstock region performed a hydrodynamic role, streamlining the peduncle. Biochemical and histological findings in harbor porpoises and bottlenose dolphins (Tursiops truncatus) have further demonstrated fat deposition and mobilization to
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