206
Marine Mammal Physiology: Requisites for Ocean Living
transfer modeling, it was possible to estimate that radiation contributed more than half of
the total heat loss in dry animals resting on the ice, regardless of the size of the individual.
Conduction to the ice surface accounted for about one-third, and convection came in last
place with about 15% of total heat loss. Further, the studies were able to estimate how
environmental conditions could impact heat loss in these animals, providing an example
of how drastic changes in energy budgets can occur with changes in an animal’s environment. For example, a small 120 kg Weddell seal (or other similarly sized seal) in low
wind conditions of 4 m/s will lose 52 W, however, if you increase the wind to a moderate
(for Antarctica) wind speed of 17 m/s, the heat loss jumps to 124 W.
This is just a small sample of the species-specific information that we can now model
due to the improvement of two types of imaging tools—infrared (thermal) and ultrasound. These technologies have a multitude of diverse applications that we only expect
to grow, given their no or low-contact requirements, high portability, and increasingly
affordable prices. However, caution must be exercised in that these images are providing the combined effect of the anatomy (insulation), physiology (metabolic state), and
environment. A major limitation of thermal imaging cameras is that they can only be
used in air.
9.6.3 Heat flow underwater
Throughout this section, we have brought up the issue that because the heat capacity of
water is so high, heat will flow out from the warm marine mammal to the cold water at
elevated rates. We have also noted that diving will reduce metabolic rate, and therefore
reduce internal heat generation. However, we have mostly discussed the characteristics
and measurements of heat flow in air. How can one measure heat flow in marine mammals while underwater?
The Fick equation provides some background for this problem. In general, the surface area, inside to outside temperature differential, and the thickness of a material
are usually the easiest values to obtain. However, the thermal conductivity is usually
very difficult, especially in living tissue (such as blubber) given the dynamic nature
of blood flow. Early in the study of potential impacts of oil development in Alaska,
research teams investigated the impact of oil on the thermal properties of sea otter,
walrus, and seal pelts. They used a Fick device where a pelt was put in a water bath
with the skin side of the pelt sealed directly on a hot plate set to 37°C, and water flowing over the pelt above held at 1°C–2°C. They used a device that measured how much
electrical energy was needed to keep the hot plate at 37°C. Conduction and convection
were accounted for by maintaining the water at a constant temperature of 1°C–2°C,
and the hot plate was stabilized at 37°C. The SA was measured as was the depth of the
pelt. All the Fick variables were known, except for the thermal conductivity of the pelt,
which could then be solved using simple algebra (Kooyman et al. 1977). More modern
versions use computer-aided analyses of pelts using suites of thermocouples and standard reference materials with known heat conductance (Liwanag et al. 2012b). While
this method works well in the laboratory for pelts, it was not useful for studies of live
animals, either in air or in water.
The invention of electronic heat flow disks was a breakthrough in the field of thermoregulation for both cetaceans and pinnipeds. These small disks can measure the
temperature difference between the skin surface where they are attached, the water
temperature surrounding them, they are of a precise thickness and their thermal
conductivity is accurately known. Therefore, using Fick theory, they can be used to
Marine Mammal Physiology: Requisites for Ocean Living
transfer modeling, it was possible to estimate that radiation contributed more than half of
the total heat loss in dry animals resting on the ice, regardless of the size of the individual.
Conduction to the ice surface accounted for about one-third, and convection came in last
place with about 15% of total heat loss. Further, the studies were able to estimate how
environmental conditions could impact heat loss in these animals, providing an example
of how drastic changes in energy budgets can occur with changes in an animal’s environment. For example, a small 120 kg Weddell seal (or other similarly sized seal) in low
wind conditions of 4 m/s will lose 52 W, however, if you increase the wind to a moderate
(for Antarctica) wind speed of 17 m/s, the heat loss jumps to 124 W.
This is just a small sample of the species-specific information that we can now model
due to the improvement of two types of imaging tools—infrared (thermal) and ultrasound. These technologies have a multitude of diverse applications that we only expect
to grow, given their no or low-contact requirements, high portability, and increasingly
affordable prices. However, caution must be exercised in that these images are providing the combined effect of the anatomy (insulation), physiology (metabolic state), and
environment. A major limitation of thermal imaging cameras is that they can only be
used in air.
9.6.3 Heat flow underwater
Throughout this section, we have brought up the issue that because the heat capacity of
water is so high, heat will flow out from the warm marine mammal to the cold water at
elevated rates. We have also noted that diving will reduce metabolic rate, and therefore
reduce internal heat generation. However, we have mostly discussed the characteristics
and measurements of heat flow in air. How can one measure heat flow in marine mammals while underwater?
The Fick equation provides some background for this problem. In general, the surface area, inside to outside temperature differential, and the thickness of a material
are usually the easiest values to obtain. However, the thermal conductivity is usually
very difficult, especially in living tissue (such as blubber) given the dynamic nature
of blood flow. Early in the study of potential impacts of oil development in Alaska,
research teams investigated the impact of oil on the thermal properties of sea otter,
walrus, and seal pelts. They used a Fick device where a pelt was put in a water bath
with the skin side of the pelt sealed directly on a hot plate set to 37°C, and water flowing over the pelt above held at 1°C–2°C. They used a device that measured how much
electrical energy was needed to keep the hot plate at 37°C. Conduction and convection
were accounted for by maintaining the water at a constant temperature of 1°C–2°C,
and the hot plate was stabilized at 37°C. The SA was measured as was the depth of the
pelt. All the Fick variables were known, except for the thermal conductivity of the pelt,
which could then be solved using simple algebra (Kooyman et al. 1977). More modern
versions use computer-aided analyses of pelts using suites of thermocouples and standard reference materials with known heat conductance (Liwanag et al. 2012b). While
this method works well in the laboratory for pelts, it was not useful for studies of live
animals, either in air or in water.
The invention of electronic heat flow disks was a breakthrough in the field of thermoregulation for both cetaceans and pinnipeds. These small disks can measure the
temperature difference between the skin surface where they are attached, the water
temperature surrounding them, they are of a precise thickness and their thermal
conductivity is accurately known. Therefore, using Fick theory, they can be used to