199
Chapter nine: Thermoregulation
interspersed with lipid depots known as adipocytes. Therefore, while a solid mass of beef
fat can be melted into an amorphous liquid, blubber can be heated and still maintain its
shape due to the protein matrix. Raw or heated, blubber can be sliced, very unlike the
material left over from heating regular animal fat.
Blubber is the product of evolutionary and adaptation pressures that go beyond
t hermal insulation capacity. It is a source of fuel and energy for fasting marine mammals
(see Chapters 6 and 10), and is laid on in very large amounts for animals preparing for the
low-food time of year. By the very process of metabolizing the lipid stored in the blubber,
marine mammals produce significant amounts of metabolically derived water, which is
then used for water balance during fasting or migration (see Chapters 7 and 10). It is also
buoyant, because of the high lipid content (over 90% lipid), and therefore influences hydrodynamic lift (see Chapter 1). The protein matrix provides shape, which comes into play
for hydrodynamic design and water flow. Finally, it also provides a significant and thick
shield for injury and damage caused by fighting (examples include male Steller sea lions,
elephant seals). All of these factors will influence the deposition and utilization of blubber
in addition to its needs for thermal insulation (Rosen et al. 2007).
The lipid composition and protein matrix of blubber can vary by species and within a
single animal. For the most part, cetacean blubber varies with depth, so that the chemical
and structural properties next to the skin are not the same as those next to the deep muscle
(Lowenstine and Osborn 1990; Haldiman and Tarpley 1993). The extremely thick blubber
of the Arctic bowhead whale can reach depths as great as 50 cm (Haldiman and Tarpley
1993). At the skin surface, the blubber is relatively cold, very structural, and firm. The cold
water tends to solidify the lipids and there is a high protein content to provide skin surface
structure (Haldiman and Tarpley 1993; Koopman 2007). Moving toward the warmer core
of the body, the blubber becomes more flexible and has a reduced protein matrix. By the
time the blubber contacts the muscle, it is extremely flexible and oily, with little or no
discernable structure remaining (Lowenstine and Osborn 1990; Haldiman and Tarpley
1993). Consequently, blubber samples taken from whales must be carefully calibrated to
the depth at which they were collected. Further, the blubber near the surface tends to be
metabolically stable and structural, while the blubber nearer to the muscle is more heavily
used for metabolic fuel and water production. This is an extremely important and highly
debated point for field methods that use dart biopsies on cetaceans to assess genetics, contaminant loads, and stable isotope status (Krahn et al. 2004). The outer skin covering of the
blubber is easily collected via dart for genetics analyses. However, the tissue near the skin
collected by the dart tends to be more structural blubber. Because of the high lipid content
of blubber and because many organo-chlorine (OC) contaminants (e.g., DDT and PCBs) are
highly lipophilic (dissolve easily in lipids), blubber should be a great sample tissue for contaminant load (see Chapter 14). However, if the cetacean sequesters ingested OCs in the
outer blubber layer where they are not metabolized and relatively harmless, then samples
from the surface blubber may be both relatively high in OC content, and yet not reflective
of OCs that could damage the animal if metabolized. Both the chapters on health and disease cover this issue in greater detail (see Chapters 13 and 14).
To add more complications, blubber depth, distribution and lipid content varies
d ramatically between otariids and phocids, and by species within each order. In general,
seals have thicker blubber with a relatively homogenous distribution across the body, and
high lipid content. The depth of the blubber layer in otariids can vary by a factor of 3 or
more depending on where on the body it is measured (e.g., Steller sea lions; Mellish et al.
2007). Blubber of both pinnipeds and cetaceans is also allocated for the various needs
of energy versus thermoregulation according to species-specific maps (Koopman 1998;
Chapter nine: Thermoregulation
interspersed with lipid depots known as adipocytes. Therefore, while a solid mass of beef
fat can be melted into an amorphous liquid, blubber can be heated and still maintain its
shape due to the protein matrix. Raw or heated, blubber can be sliced, very unlike the
material left over from heating regular animal fat.
Blubber is the product of evolutionary and adaptation pressures that go beyond
t hermal insulation capacity. It is a source of fuel and energy for fasting marine mammals
(see Chapters 6 and 10), and is laid on in very large amounts for animals preparing for the
low-food time of year. By the very process of metabolizing the lipid stored in the blubber,
marine mammals produce significant amounts of metabolically derived water, which is
then used for water balance during fasting or migration (see Chapters 7 and 10). It is also
buoyant, because of the high lipid content (over 90% lipid), and therefore influences hydrodynamic lift (see Chapter 1). The protein matrix provides shape, which comes into play
for hydrodynamic design and water flow. Finally, it also provides a significant and thick
shield for injury and damage caused by fighting (examples include male Steller sea lions,
elephant seals). All of these factors will influence the deposition and utilization of blubber
in addition to its needs for thermal insulation (Rosen et al. 2007).
The lipid composition and protein matrix of blubber can vary by species and within a
single animal. For the most part, cetacean blubber varies with depth, so that the chemical
and structural properties next to the skin are not the same as those next to the deep muscle
(Lowenstine and Osborn 1990; Haldiman and Tarpley 1993). The extremely thick blubber
of the Arctic bowhead whale can reach depths as great as 50 cm (Haldiman and Tarpley
1993). At the skin surface, the blubber is relatively cold, very structural, and firm. The cold
water tends to solidify the lipids and there is a high protein content to provide skin surface
structure (Haldiman and Tarpley 1993; Koopman 2007). Moving toward the warmer core
of the body, the blubber becomes more flexible and has a reduced protein matrix. By the
time the blubber contacts the muscle, it is extremely flexible and oily, with little or no
discernable structure remaining (Lowenstine and Osborn 1990; Haldiman and Tarpley
1993). Consequently, blubber samples taken from whales must be carefully calibrated to
the depth at which they were collected. Further, the blubber near the surface tends to be
metabolically stable and structural, while the blubber nearer to the muscle is more heavily
used for metabolic fuel and water production. This is an extremely important and highly
debated point for field methods that use dart biopsies on cetaceans to assess genetics, contaminant loads, and stable isotope status (Krahn et al. 2004). The outer skin covering of the
blubber is easily collected via dart for genetics analyses. However, the tissue near the skin
collected by the dart tends to be more structural blubber. Because of the high lipid content
of blubber and because many organo-chlorine (OC) contaminants (e.g., DDT and PCBs) are
highly lipophilic (dissolve easily in lipids), blubber should be a great sample tissue for contaminant load (see Chapter 14). However, if the cetacean sequesters ingested OCs in the
outer blubber layer where they are not metabolized and relatively harmless, then samples
from the surface blubber may be both relatively high in OC content, and yet not reflective
of OCs that could damage the animal if metabolized. Both the chapters on health and disease cover this issue in greater detail (see Chapters 13 and 14).
To add more complications, blubber depth, distribution and lipid content varies
d ramatically between otariids and phocids, and by species within each order. In general,
seals have thicker blubber with a relatively homogenous distribution across the body, and
high lipid content. The depth of the blubber layer in otariids can vary by a factor of 3 or
more depending on where on the body it is measured (e.g., Steller sea lions; Mellish et al.
2007). Blubber of both pinnipeds and cetaceans is also allocated for the various needs
of energy versus thermoregulation according to species-specific maps (Koopman 1998;