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Diving Physiology of
Marine Mammals
Fundamental Challenge
FOOD
NUTRIENTS
Separation of
Critical Resources
AIR / OXYGEN
Marine Mammals
Cetacea: odontocetes and mysticetes
Pinnipedia: otariids, phocids and odobenids
Sirenia: manatees and dugongs
Carnivora: sea otters & polar bears
Cetaceans
Odontoceti
Mysticeti
Pinnipeds
Otariids
Phocids
Odobenids
Sirenians
Manatee
Dugong
Carnivores
Sea Otter
Polar Bear
Special Adaptations
Anatomical and physiological adaptations in
the respiratory & cardiovascular systems,
blood, and peripheral tissues result in:
◦ Efficient ventilation
◦ Enhanced oxygen storage
◦ Regulated transport and delivery of
respiratory gases
◦ Extreme hypoxic tolerance
◦ Pressure tolerance
Diving Behavior
Dive duration
Dive depth
Diving Behavior: Cetaceans
BEAKED WHALES:
Routine dives:
◦ 800 m for 60 min
Maximum durations:
◦ 120 min
SPERM WHALES:
Routine dives :
400m for 40min
Maximum depths:
2000m
Diving Behavior: Cetaceans
Bottlenose dolphin
(Tursiops truncatus)
typically dive <5 min
& <20 m
Large baleen whales
typically dive <5 min;
can reach depths of
200 m
Diving Behavior: Pinnipeds
Large phocid seals are the longest-duration
divers among the pinnipeds
Maximum depths range: 600m to 1500 m
Diving Behavior: Pinnipeds
Routine dive durations of most other
phocid seals are less than 10 min.
Diving Behavior: Pinnipeds
OTARIIDS
Routine dives:
<3 to 4 min
ODOBENIDS:
Routine dives:
<4 to 6 min
Diving Behavior: Sirinians
Typical dives: 2 to 3 min, 12 m at most
Diving Behavior: Sea Otters
Average Dives: 1 to 3 min, <30 m deep.
Diving Fundamentals
Dive Response:
◦ Apnea
◦ Bradycardia
◦ Peripheral Vasoconstriction
Oxygen Stores:
◦ Lungs
◦ Blood
◦ Muscle
Researching Diving Physiology
Per Scholander (1905-1980)– observations
of cartilaginous reinforcement of airways
Hypothesis - more rigid airways would allow:
◦ Movement of air into those airways during
compression of the lungs at depth
◦ Alveolar collapse
◦ Cessation of gas exchange, and, in particular,
nitrogen absorption at depth
Researching Diving Physiology
Kooyman and colleagues documented the airway reinforcement of diving mammals in comparison to terrestrial mammals.
Most prominent in cetaceans and sea lions
◦ Cartilaginous reinforcement: trachea to alveoli
Less so in walruses and sea otters
◦ Distal airways reinforced by a mix of cartilage and muscular elements
Respiratory Mechanics
Reinforcement of the distal airways in
diving mammals allows for the movement
of air from the alveoli into the bronchi
during lung compression
Promotes collapse of the alveoli and
cessation of gas exchange at depth.
Respiratory Mechanics
Maximum expiratory flow rates:
◦ 162 liters s−1 in bottlenose dolphins
◦ 202 liters s−1 in young gray whales
Necessary in cetaceans since exhalation and inhalation occur in less than 1s
Such flows allow for a tidal volume as high as 88% of TLC in the pilot whale.
Respiratory Mechanics
High flow rates minimize the time for
exhalation/inhalation cycle
Rapid breaths allow animals to spend
most of their travel time below the
surface where drag is less
Lung Volumes
Lung volumes of diving mammals are in the
general range of terrestrial mammals.
Notable exceptions:
◦ small lungs of the deep-diving bottlenose whale
◦ large lungs of the shallow-diving sea otter.
Diving Lung Volumes
Diving lung volumes:
◦ lung volume at the start of a dive
◦ important determinants of the size of the respiratory O2 store during a dive.
Many cetaceans appear to dive on inspiration, while pinnipeds usually dive on expiration.
Consequently, the diving lung volumes of cetaceans are probably near TLC, while pinnipeds are closer to 40-50% TLC
Oxygen Transport - Hb
Marine mammals have exceptionally high [Hb]
values compared to terrestrial mammals.
O2 affinity of Hb not that different from
terrestrial counterparts
The P50, the O2 partial pressure at 50% Hb
saturation, is in the range of 26 to 30 mmHg
Hb is most elevated in long-duration divers.
Oxygen Transport - Mb
[Mb] in diving mammals are 10 to 30
times that found in terrestrial mammals.
High [Mb] have long been considered to
serve as an O2 store during diving.
High [Mb] also facilitate O2 diffusion
◦ Lung
◦ Blood
◦ Muscle
TOTAL OXYGEN STORES
Calculating O2 Stores
Total Body O2 Stores
Total body O2 stores of diving mammals
on a mass-specific basis range from two
to five times that of human O2 stores
Also notable is the change in the
distribution of O2 stores among species.
Distribution of Body O2 Stores
Species mL O2 kg-1 Lung % Blood % Muscle %
Human 20 24 57 15
Odontocetes 35 22 30 48
Otariids 40 13 54 33
Phocids 60 7 65 28
Sea Otter 55 55 29 16
Manatee 21 33 60 7
Circulatory Responses
Cardiovascular regulation is critical during
diving of all marine mammal species.
Changes in heart rate and cardiac output
contribute to:
(1) the rate of O2 uptake from the lungs
(2) the magnitude of O2 delivery and
consumption in tissues
Diving Heart Rate
The physiological hallmark of diving is a
decrease in heart rate during dives.
Bradycardia
Extreme example: 7 bpm average heart
rate of a gray seal during a 14 min dive
Circulatory Responses
Bradycardia ( HR)
Peripheral Vasoconstriction: blood
flow and blood O2 conserved for the heart
and brain, directed away from peripheral
tissues and other organs
HR and perfusion control the rate of
depletion of the blood and lung O2 stores.
Diving Heart Rate
Increase in heart rate during ascent = anticipatory tachycardia
Allows increased muscle blood flow and O2 extraction blood O2 is depleted by the end of the dive and increases Po2 gradient
Maximizes respiratory gas exchange, and minimizes duration of surface interval.
Aerobic Dive Limit
Oxygen stores and oxygen utilization
dictate the amount of time an animal can
spend underwater
Aerobic Dive Limit
Defined by Kooyman (1983) as the amount of time
an animal may spend diving before an increase in
blood lactate levels occurs.
Determining factor in the amount of time an animal
is capable of foraging underwater.
cADL= total body oxygen stores
oxygen demand
Blood
Muscle
Lung
Ecological Implications
Consequences for Immature
Animals
What does all of this mean
for immature marine
animals?
Increased Metabolic Rates
Limited Oxygen Stores
Harbor Seal
(Phoca vitulina)
California Sea Lion
(Zalophus
californianus)
Increased Metabolic Demand
Northern Elephant Seal
(Mirounga angustirostris)
Weddell Seal
(Leptonychotes weddellii)
Rea & Costa 1992
Thorson & LeBoeuf
1994
Ponganis et al. 1993 Liwanag et al. 2009
Burns et al. 2005
Limited Oxygen Stores
Emperor Penguins (Aptenodytes forsteri)
Blood Oxygen Stores:
6 mo = At/Near Adult Levels
Muscle Oxygen Stores:
6 mo = 31% adult values
Ponganis et al. 1999
Limited Oxygen Stores
Bottlenose Dolphins (Tursiops truncatus)
Total Body Oxygen Stores = >3 Years
Noren et al. 2002
Ecological Implications
19.1 min 9 min
cADL = TOTAL OXYGEN STORES
OXYGEN DEMANDS
Ponganis et al. 1993
Ecological Implications
