32
Marine Mammal Physiology: Requisites for Ocean Living
Lung volumes of diving mammals are in the general range of terrestrial mammals (Kooyman 1973; Fahlman et al. 2011; Piscitelli et al. 2013). Notable exceptions are the
small lungs of the deep-diving whales and the large lungs of the shallow-diving sea otter.
Bottlenose whales (Hyperoodon ampullatus), sperm whales (Physeter macrocephalus), and pygmy
and dwarf sperm whales (Kogia breviceps, Kogia sima) have lung volumes of 21–28 ml kg −1
(Scholander 1940; Miller et al. 2004; Piscitelli et al. 2010). Allometric analyses of lung mass in
cetaceans revealed that kogiids, physeterids, ziphiids, and mysticetes all had relative lung
masses similar to terrestrial mammals, while delphinids, phocoenids, and monodonts had
relatively larger lung masses (Piscitelli et al. 2010, 2013). Sea otter lung volume has been
measured at 345 ml kg −1 (Lenfant et al. 1970). The high lung volume in the otter presumably
contributes to its buoyancy at the surface, where it feeds, grooms, and cares for its young.
Such buoyancy in the otter also elevates more of the body out of the water while the animal
is at the surface; this should reduce body heat loss due to conduction in water (Chapter 9).
The percentage of the total body O 2 store provided by the respiratory store is shown in
Table 2.1. While total lung capacity is often necessary to calculate the respiratory O 2 store,
the respiratory store is not equivalent to the quantity of O 2 in the total lung capacity. This is
because many marine mammals dive with lung volumes that are much less than the total
lung capacity (see Section 2.3.1).
2.2.1.2 Blood O 2 stores
The blood O 2 store is the largest O 2 store in many marine mammals. Almost all pinnipeds
store 50% or more of their O 2 in the blood (Table 2.1). The blood O 2 store is also highest in
both walruses and manatees; however, in sea otters the respiratory O 2 store is the highest
at 45%. In Cetacea, blood is the largest O 2 store in deep, long duration divers, such as the
sperm whale (P. macrocephalus) (Table 2.1).
Blood O 2 stores are calculated using three parameters: (1) blood volume (one-third is
assumed to be arterial and two-thirds venous), (2) hemoglobin (Hb) concentration, and
(3) the amount of oxygen extracted from hemoglobin during a dive (net Hb desaturation) (Lenfant et al. 1970; Kooyman 1989) (see Section 2.3.2). Many marine mammals have
elevated values of these parameters when compared to terrestrial mammals. The typical
human Hb concentration of 15 g dl −1 and blood volume of 70 ml kg −1 are 50%–70% lower
than Hb concentrations and blood volumes of marine mammals. The greatest elevations
in both Hb and blood volume are in the longest-duration divers and in highly active species (Ridgway and Johnston 1966; Ponganis 2011). This is exemplified in the phocid seals.
The northern elephant seal and the gray seal (Halichoerus grypus) have blood volumes of
216 and 213 ml kg −1 and Hb concentrations of 25 and 20 g dl −1 , respectively. In general, Hb
and blood volume are not as high in otariids as in phocid seals, but some otariid species
have hemoglobin concentrations up to 23 g dl −1 and blood volumes up to 186 ml kg −1 . Hb
concentration and blood volume span a wide range in cetaceans, from the shallow-diving
bottlenose dolphin with values similar to standard human values to the sperm whale,
with an Hb concentration of 22 g dl −1 and a blood volume of 200 ml kg −1 (Sleet et al. 1981;
Ridgway 1986). Consequently, the bottlenose dolphin only stores 33% of total body O 2 in
the blood store, while the sperm whale’s blood store accounts for 64% of the total O 2 store
(Table 2.1). Manatee and walrus values are not particularly high, but the sea otter’s values
are within the otariid range at 19 g dl −1 and 174 ml kg −1 (Thometz et al. 2015).
2.2.1.3 Muscle O 2 stores
In all marine mammals except the manatee, muscle is a significant component of the
total O 2 store in comparison to their non-diving counterparts (Table 2.1). A large muscle
Marine Mammal Physiology: Requisites for Ocean Living
Lung volumes of diving mammals are in the general range of terrestrial mammals (Kooyman 1973; Fahlman et al. 2011; Piscitelli et al. 2013). Notable exceptions are the
small lungs of the deep-diving whales and the large lungs of the shallow-diving sea otter.
Bottlenose whales (Hyperoodon ampullatus), sperm whales (Physeter macrocephalus), and pygmy
and dwarf sperm whales (Kogia breviceps, Kogia sima) have lung volumes of 21–28 ml kg −1
(Scholander 1940; Miller et al. 2004; Piscitelli et al. 2010). Allometric analyses of lung mass in
cetaceans revealed that kogiids, physeterids, ziphiids, and mysticetes all had relative lung
masses similar to terrestrial mammals, while delphinids, phocoenids, and monodonts had
relatively larger lung masses (Piscitelli et al. 2010, 2013). Sea otter lung volume has been
measured at 345 ml kg −1 (Lenfant et al. 1970). The high lung volume in the otter presumably
contributes to its buoyancy at the surface, where it feeds, grooms, and cares for its young.
Such buoyancy in the otter also elevates more of the body out of the water while the animal
is at the surface; this should reduce body heat loss due to conduction in water (Chapter 9).
The percentage of the total body O 2 store provided by the respiratory store is shown in
Table 2.1. While total lung capacity is often necessary to calculate the respiratory O 2 store,
the respiratory store is not equivalent to the quantity of O 2 in the total lung capacity. This is
because many marine mammals dive with lung volumes that are much less than the total
lung capacity (see Section 2.3.1).
2.2.1.2 Blood O 2 stores
The blood O 2 store is the largest O 2 store in many marine mammals. Almost all pinnipeds
store 50% or more of their O 2 in the blood (Table 2.1). The blood O 2 store is also highest in
both walruses and manatees; however, in sea otters the respiratory O 2 store is the highest
at 45%. In Cetacea, blood is the largest O 2 store in deep, long duration divers, such as the
sperm whale (P. macrocephalus) (Table 2.1).
Blood O 2 stores are calculated using three parameters: (1) blood volume (one-third is
assumed to be arterial and two-thirds venous), (2) hemoglobin (Hb) concentration, and
(3) the amount of oxygen extracted from hemoglobin during a dive (net Hb desaturation) (Lenfant et al. 1970; Kooyman 1989) (see Section 2.3.2). Many marine mammals have
elevated values of these parameters when compared to terrestrial mammals. The typical
human Hb concentration of 15 g dl −1 and blood volume of 70 ml kg −1 are 50%–70% lower
than Hb concentrations and blood volumes of marine mammals. The greatest elevations
in both Hb and blood volume are in the longest-duration divers and in highly active species (Ridgway and Johnston 1966; Ponganis 2011). This is exemplified in the phocid seals.
The northern elephant seal and the gray seal (Halichoerus grypus) have blood volumes of
216 and 213 ml kg −1 and Hb concentrations of 25 and 20 g dl −1 , respectively. In general, Hb
and blood volume are not as high in otariids as in phocid seals, but some otariid species
have hemoglobin concentrations up to 23 g dl −1 and blood volumes up to 186 ml kg −1 . Hb
concentration and blood volume span a wide range in cetaceans, from the shallow-diving
bottlenose dolphin with values similar to standard human values to the sperm whale,
with an Hb concentration of 22 g dl −1 and a blood volume of 200 ml kg −1 (Sleet et al. 1981;
Ridgway 1986). Consequently, the bottlenose dolphin only stores 33% of total body O 2 in
the blood store, while the sperm whale’s blood store accounts for 64% of the total O 2 store
(Table 2.1). Manatee and walrus values are not particularly high, but the sea otter’s values
are within the otariid range at 19 g dl −1 and 174 ml kg −1 (Thometz et al. 2015).
2.2.1.3 Muscle O 2 stores
In all marine mammals except the manatee, muscle is a significant component of the
total O 2 store in comparison to their non-diving counterparts (Table 2.1). A large muscle