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 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. Metabolic Rate 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 38°C 36°C 34°C 32°C 30°C 28°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) Movie Movie

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