16
Marine Mammal Physiology: Requisites for Ocean Living
Semi-aquatic mammals operate primarily at the water surface. Possession of large,
low-density air-filled spaces provides positive buoyancy and decreases the effort needed
to float. Sea otters maintain buoyancy in part with lungs that are two times larger than
that of other similarly sized mammals (Kooyman 1973; Tarasoff and Kooyman 1973). The
non-wettable fur of the sea otter is extremely dense (1008–1573 hairs/mm 2 ) entrapping a
large volume of air for buoyancy (Kenyon 1969; Tarasoff 1974; Williams et al. 1992a). The
density of hairs in the pelage of semi-aquatic mammals is high in comparison with terrestrial and aquatic mammals (Tarasoff 1974; Sokolov 1982; Fish et al. 2002). However, the
amount of buoyancy afforded by fur becomes proportionately smaller as the body size
increases (Fish et al. 2002).
Although the positive buoyancy afforded by fur will reduce energy costs at the surface, buoyancy is a major determinant of locomotor costs when diving (Lovvorn and
Jones 1991). To submerge, a positively buoyant animal can expend at least 95% of its total
mechanical energy to work against the buoyant force (Stephenson et al. 1989). The buoyancy of a diving sea otter can be 20 times greater than the drag on the body (Lovvorn and
Jones 1991). At depth, fur has serious limitations. The air in the fur will compress reducing buoyancy at depth and reduce the insulation value of the fur. Reduction of insulation
performance is also attributed to water infiltration. Furthermore, maintenance of the air
layer requires a large fraction of the daily energy budget devoted to grooming (Kenyon
1969; Williams 1989). However, specialized fur structures on some areas of the body may
enhance insulation as well as drag reduction (Erdsack et al. 2015).
Blubber offers a structure for aquatic mammals, which requires lower maintenance
costs than fur, is not prone to fouling, is an effective thermal barrier in water, can be
used as an energy reserve, facilitates streamlining, has spring-like properties to reduce
locomotor effort, and provides buoyancy (Lang 1966; Kooyman 1973; Brodie 1975; Pabst
1996). Buoyancy from blubber is not depth-sensitive. The lipid composition of blubber
makes it essentially incompressible relative to air, but not as buoyant (Lovvorn and
Jones 1991). Without large lungs (Kooyman 1973; Tarasoff and Kooyman 1973), aquatic
mammals offset the high density of the body tissues (i.e., bone, muscle) with a thick
layer of blubber. Approximately 20%–30% of the total mass of marine mammals is blubber (Kooyman 1973).
The distribution of buoyancy is associated with the maintenance of trim (i.e., fore and
aft angle of a vessel). Having longitudinal trim provides streamlining to reduce drag. For
sea otters, the elongate shape of the lungs can keep the body in trim on the water surface. The diaphragm is oriented diagonally in pinnipeds and longitudinally in the mantee
to extend the lungs and their buoyancy of a large portion of the body to maintain trim.
Mysticete whales of the family Balaenopteridae feed by engulfing large volumes of water
and prey in a distended throat pouch (Pivorunas 1979; Shadwick et al. 2013). This engulfment would produce increased drag and a torque that would pitch the whale downward
when the mouth is opened. The flippers of the minke whale (Balaenoptera acutorostrata) are
canted at an angle to produce a lift that would produce an opposing torque to trim the
body during the feeding maneuver (Cooper et al. 2008).
1.3.6 Maneuverability
The ability to maneuver (i.e., turn) with speed becomes imperative in the acquisition and
capture of prey. Maneuverability is defined as the space required to execute a turn, and
agility is defined as the rapidity that direction can be changed and is measured as the
rate of turn (Norberg 1990; Walker 2000). Small animals have an advantage with respect
Marine Mammal Physiology: Requisites for Ocean Living
Semi-aquatic mammals operate primarily at the water surface. Possession of large,
low-density air-filled spaces provides positive buoyancy and decreases the effort needed
to float. Sea otters maintain buoyancy in part with lungs that are two times larger than
that of other similarly sized mammals (Kooyman 1973; Tarasoff and Kooyman 1973). The
non-wettable fur of the sea otter is extremely dense (1008–1573 hairs/mm 2 ) entrapping a
large volume of air for buoyancy (Kenyon 1969; Tarasoff 1974; Williams et al. 1992a). The
density of hairs in the pelage of semi-aquatic mammals is high in comparison with terrestrial and aquatic mammals (Tarasoff 1974; Sokolov 1982; Fish et al. 2002). However, the
amount of buoyancy afforded by fur becomes proportionately smaller as the body size
increases (Fish et al. 2002).
Although the positive buoyancy afforded by fur will reduce energy costs at the surface, buoyancy is a major determinant of locomotor costs when diving (Lovvorn and
Jones 1991). To submerge, a positively buoyant animal can expend at least 95% of its total
mechanical energy to work against the buoyant force (Stephenson et al. 1989). The buoyancy of a diving sea otter can be 20 times greater than the drag on the body (Lovvorn and
Jones 1991). At depth, fur has serious limitations. The air in the fur will compress reducing buoyancy at depth and reduce the insulation value of the fur. Reduction of insulation
performance is also attributed to water infiltration. Furthermore, maintenance of the air
layer requires a large fraction of the daily energy budget devoted to grooming (Kenyon
1969; Williams 1989). However, specialized fur structures on some areas of the body may
enhance insulation as well as drag reduction (Erdsack et al. 2015).
Blubber offers a structure for aquatic mammals, which requires lower maintenance
costs than fur, is not prone to fouling, is an effective thermal barrier in water, can be
used as an energy reserve, facilitates streamlining, has spring-like properties to reduce
locomotor effort, and provides buoyancy (Lang 1966; Kooyman 1973; Brodie 1975; Pabst
1996). Buoyancy from blubber is not depth-sensitive. The lipid composition of blubber
makes it essentially incompressible relative to air, but not as buoyant (Lovvorn and
Jones 1991). Without large lungs (Kooyman 1973; Tarasoff and Kooyman 1973), aquatic
mammals offset the high density of the body tissues (i.e., bone, muscle) with a thick
layer of blubber. Approximately 20%–30% of the total mass of marine mammals is blubber (Kooyman 1973).
The distribution of buoyancy is associated with the maintenance of trim (i.e., fore and
aft angle of a vessel). Having longitudinal trim provides streamlining to reduce drag. For
sea otters, the elongate shape of the lungs can keep the body in trim on the water surface. The diaphragm is oriented diagonally in pinnipeds and longitudinally in the mantee
to extend the lungs and their buoyancy of a large portion of the body to maintain trim.
Mysticete whales of the family Balaenopteridae feed by engulfing large volumes of water
and prey in a distended throat pouch (Pivorunas 1979; Shadwick et al. 2013). This engulfment would produce increased drag and a torque that would pitch the whale downward
when the mouth is opened. The flippers of the minke whale (Balaenoptera acutorostrata) are
canted at an angle to produce a lift that would produce an opposing torque to trim the
body during the feeding maneuver (Cooper et al. 2008).
1.3.6 Maneuverability
The ability to maneuver (i.e., turn) with speed becomes imperative in the acquisition and
capture of prey. Maneuverability is defined as the space required to execute a turn, and
agility is defined as the rapidity that direction can be changed and is measured as the
rate of turn (Norberg 1990; Walker 2000). Small animals have an advantage with respect