Marine Mammal
Energetics
MARE 390
Dr. Turner
Energetics
Employ a variety of methods to evaluate
costs & benefits of specific life processes
Involves costs of acquiring resources
evolution of adaptations to aquatic
existence - seawater
How resources are allocated
cost benefit interactions
energy-flow models
Energetics
Allocate energy across three uses:
- burned in metabolism
- allocated to growth
- used in reproduction
Metabolic Fuels
Substrates used in metabolism
fat, protein, carbohydrate, combination
2X energy metabolized from lipid than
amount from protein or carbohydrate
Lipids > proportion of metabolic fuel
Greater proportion of lipids in diet
Metabolic Rate
Cellular mechanics similar to other verts
Typically other mechanisms when diving
Standardized units
Biological state of an organisms can affect
metabolic rate
Basal Metabolic Rate (BMR)
Measure of the metabolic rate of mature
(sex & phys), postabsorptive individuals at
rest in a thermoneutral environment
BMR – used for comparison across groups
Most birds/mammals spend time in
environments that fall within the TNZ
Metabolic Rate
Lower
lethal
temp.
High and constant body temp
can be maintained at rest over a fluctuation
of temperatures of 5-10 C with little
Extra metabolic work—this is the TNZ.
Thermo neutral zone (TNZ)
Upper
lethal
temp.
BMR
Lower critical
temp.
Upper
critical temp.
Ambient Temperature
BMR & Body Mass
Kleiber Curve – BMR to body mass to the
0.75 power (BMR = aM0.75)
Do marine mammals have higher metabolic
rates??? – continues debate
Thermoregulation
Live in cold, highly conductive media
Heat capacity of water 25X air
Several adaptations to reduce heat loss:
large body size – reduced SVR
increased insulation
conserving counter-current systems
Provide broad thermoneutral zones
Body Mass – SAV Ratios
Marine mammals span a body-mass range
4X from sea otters (5kg) to blue whales
(10x104)
Surface area of a body ↑ proportionally to
the square of its length
Volume (≈mass) ↑ proportional to its cube
Marine mammals capable of producing
considerable heat with relatively little loss
Body Mass – SAV Ratios
SA/V Ratio
↑
↓
Body Mass – SAV Ratios
Reduce heat loss by streamlining body
form – reducing surface area
Surface area of pinnipeds, cetaceans, &
sea otters are 23% < terrestrial mammals
of similar body mass
Body Mass – SAV Ratios
Insulation
Use dense fur or blubber
Fur: depends upon capacity to trap air
Blubber functions: thermoregulation,
energy storage, buoyancy control,
streamlining
Non-shivering thermogenesis – brown fat
large amounts in pups
Fur
Fur – extreme sea otter (150,000 hairs/cm2)
In air: impedes thermoregulation
In water: works well in shallow water
environment
Deep divers – air squeezed out (pressure)
Blubber
Insulative value a function of thickness,
lipid content, & peripheral blood flow
Cetaceans – mostly lipid content
Very efficient in cetaceans & pinnipeds
less so in sirenians
manatees thinner than dugongs
Blubber
Sirenians – 2 blubber layers
Functionally cuts insulatory capability in
half
Skin
Skin
Blubber
Blubber
Muscle
Blubber
Muscle
Muscle
Cetacean
Manatee
Blubber
↓ Thermal Conductivity = ↑ Insulation
Peripheral Blood Circulation
Conserve heat in water (cold) – inhibits
heat dissipation on land (warm)
Counter current heat exchangers –
conserve heat by maintaining a heat
differential between oppositely directed
flows of blood
Counter Current Heat Exchangers
Heat is conserved before it is lost at the extremity
Parallel intermingling vessels (in contact)
= vascular bundles (rete)
39°C 37°C 35°C 33°C 31°C
29°C
27°C
28°C
38°C 36°C 34°C 32°C 30°C
Veins
Artery
Counter Current Heat Exchangers
Pinnipeds & cetaceans - Flippers & fins
(flukes)
Use hindflippers & forsal fin to cool gonads
Sirenians – vascular bundles throughout
body – expel heat in warm waters
Right & Gray whales – in mouths; when
feeding in cold waters
Counter Current Heat Exchangers
Counter Current Heat Exchangers
Energetics of Locomotion
Up to 80% of daily activity budget
Frictional resistance of water has large
effect – 800x more dense than air, 30x
more viscous
Must overcome hydrodynamic drag
What a Drag
Frictional & Pressure Drag – associated
with physical prcesses of water
surrounding the body surface
Induced Drag – associated with water flow
around the flippers, fins, & flukes
Wave Drag – moving at or near the surface
Body Streamlining
Drag reduced by streamlining body surface
Cost of Transport
Fitness ratio – measure of streamlining
Transport Adaptations
Wave Riding – large energetic savings
- bow or stern of ships & whales
Surfacing only to breathe
Porpoising – removes animal from high
drag environment at surface while
breathing; mammals < 10m
Crossover – velocity at which porpoising
becomes more efficient (5m/s)
Osmoregulation
Hyposmotic – body fluids have a lower
ionic content than surrounding water
losing water to hyperosmotic seawater
Larger kidneys than terrestrial mammals
Multi-lobed kidneys – reniculi
human & horses – single lobe
cetaceans – 450 to 3,000 reniculi
Osmoregulation
Osmoregulation
Cetaceans can concentrate urine to a
greater extent than any other mammals
Allow them a net-gain to drinking seawater
In cetaceans: 1L seawater = 0.5L water gain
In humans: 1L seawater = 0.5L water loss
Strategic Energetics Approach
Model of how marine mammals respond to
change