Energetics forelæsning. week 3

Question 1

Intended learning outcomes

Answer 1

• Describe the main energetic requirements of marine mammals, and their anatomical and behavioural adaptations to conserve energy

Question 2

Food resources and hence energy is limited, so the body have to “choose” what to use it for…

Answer 2

– Metabolism
* Basal metabolic rate
* Thermoregulation
* Osmoregulation
* Activity
– Growth of body
– Repair of damaged cells
– Build energy storage (e.g. for winter or reproduction)
– Reproduction

Question 3

How allocate resource to maximize own fitness?

Answer 3

– R-strategy: Reproduce early, short life
– K-strategy: Maintain body, late reproduction, long life

Question 4

Why does it matter? Energy allocation

Answer 4

• Any change in behaviour (foraging, breeding, resting, travelling, etc) will affect energy use!
• Health and body condition
  – Individual fitness
  – Population/species trends and viability
  – Energy acquisition and use defines chance of survival
• Implications for management and conservation
  – Intra- and interspecific competition
  – Recovery from whaling, sealing, etc.
  – Cumulative effect of by-catch, diseases, contaminant loads, noise, habitat disturbance, climate change, etc.

Question 5

Population consequences of disturbance

Answer 5

• Hunting and ship-strike have direct lethal effects
  *…but most disturbances are more subtle and long-term

Question 6

Effect of disturbance on haul-out behaviour?

Answer 6

Effects of cruise ships in Alaska on harbour seal pups?
* 1.4 million cruise passengers visit Alaska each year
* Study observed behaviour of seals when ships approach, and estimated thermal budget of pups at different levels of age, activity and disturbance (Jansen et al 2010)

Effect of disturbance on haul-out behaviour?
* Pups jump into water when ships approach…
* Large increase in disturbance (hazard) when ships are closer than approximately 500 m!

Effect of disturbance on energy budget?
* Seal pups use more energy when in water
* Negative energy budget if young seals (<13 days) spend a large proportion of time (>60%) in water
* Seals that are more active can stay longer in the water without heat loss (but then needs to eat more)

Management implications
* Current guidelines for ships to stay >100 m away, however at that distance >90% of pups jump in water
* The study suggest that guidelines should be >500 m to avoid thermal stress in harbour seal pups

Question 7

Metabolic rates

Answer 7

• Basal metabolic rate (BMR): mature, resting animals in a thermo-neutral environment
• Resting metabolic rate (RMR): not in thermo-neutral environment
• Field metabolic rate (FMR): measured in the field, so
  reflect the actual metabolic rate of the animal
• Rates difficult to measure in marine mammals!
  – Ventilation rate (box)
  – Heat loss (infrared photo)
  – Doubly labelled water (DLW)
  – Heart rate monitor (tags)
  – Accelerometer (tags)

Question 8

Surface-to-volume ratio

Answer 8

• You can conserve energy by having:
  – Small surface-to-volume ratio
  – Large body and short/reduced extremities

Ratio much higher in calves than adults

Question 9

Blubber

Answer 9

All* marine mammals have blubber

• Insulation with blubber (and fur)
• Also functions as energy storage, buoyancy control and streamlining, so crucial to maintain blubber layer
• Whales: large variation in blubber thickness (1-40 cm)
• Pinnipeds: Phocids and walrus > sea lions > fur seals
  *Sea cows:Thin blubber layer (living in tropics)
  *Sea otters : very thin blubber layer (use fur)

Question 10

Blubber lipid content

Answer 10

• High lipid content = low conductivity = good insulation

Question 11

The lanugo fur

Answer 11

• Phocid pups are born with a white lanugo fur
  – Thermoregulation and camouflage, but bad for swimming! – Pups change to adult fur after a few weeks
• Lanugo fur lost in uterus in some seals
  – Due to sufficient blubber, unstable environment, escape from
  predators, and/or pupping during summer
• Otarid pups born with adult-like (dark) fur

Question 12

Countercurrent system

Answer 12

• All marine mammals
• Blood vessels go out to epidermis
• Conserving heat, and getting rid of it
• Gray whales (and right whales) have countercurrent system in mouth to minimise heat loss during feeding
• Perhaps also present in other cetaceans??
• Trade-off in pinnipeds: adaptations to conserve body temperature when in water makes it harder to get rid of body heat when on land…
• Is pinniped distribution limited by temperature?

Question 13

Osmoregulation

Answer 13

• Body fluid has lower ionic content than seawater, resulting in constant loss of water to the environment
• Mechanisms for conserving water
  – Minimize loss by large kidneys; excrete concentrated urine
  – Obtain water through diet
  – Drinking sea water (all sirenians and otters; some pinnipeds and odontocetes)

Question 14

Activity

Answer 14

• Activity is costly; up to 80% of total energy budget!
• Sea water
  – Water is much denser than air = higher friction!
  – Propulsion is easier = greater momentum/power
  – Neutrally buoyant = no need to use energy to support body
• Hydrodynamicdrag

Question 15

Hydrodynamicdrag

Answer 15

– Frictional drag (body surface texture and area)
– Pressure drag (form/size of cross-sectional area)
– Induced drag (caused by flippers and flukes)
– Wave drag (from production of waves)

Question 16

Surface drag

Answer 16

• Increased drag towards surface due to waves
• Some species can minimise drag by jumping out of water when surfacing to breath

Question 17

Example 2: Energy use by seals during haul-out on ice and land?

Answer 17

Heat loss during haul-out on ice
* Estimating heat loss in Weddell seals on sea ice
* Heat sensors placed on seals for 1-13 days
* Additional measurements of blubber thickness, size, outside temperature, etc
* Blubber thickness main determinant of heat loss

Heat loss during haul-out on land
* Heat loss during lactation and moult (change of fur) estimated by thermal infrared cameras in two captive female harbour seals (Paterson et al. 2012)
* Haul-out frequency is high during lactation and moult
* Heat loss during moult (change of fur) correspond to doubling of RMR (resting metabolic rate)

Question 18

Regulation of heat loss in seals?

Answer 18

• Thermal imagery suggest flexible “thermal windows” in seals controlled by regulation of blood flow to surface
• …so seals can conserve energy by only changing small patches of fur at the time

Question 19

Example 3: Energy use during foraging at sea?

Answer 19

Energy use during foraging at sea
* Jeanniard-du-Dot et al. 2017
* Can we use accelerometers to estimate energy use during foraging trips in otarids?
* Study to compare accelerometer data from tags with metabolism estimated by doubly labelled water (DLW)
– 20 northern fur seals and 20 Antarctic fur seals
– Tags use GPS, Time/depth recorders (TDRs) and accelerometers

• Field metabolic rate estimates
  – Metabolism can be calculated from O-in and CO2-out
  – Doubly labelled water (DLW; 2H2 18O) is traceable hydrogen (2H) and oxygen (18O) which is infused in the body of the animal and measured at several time points to estimate CO2 production (respiration) and hence energy use
• Some correlation between energy use and acceleration when looking at foraging trip overall…
• …but good correlation when foraging split into behaviour categories based on GPS and time-depth recorder data
• So tag acceleration data is a good proxy of energy use!