193
chapter nine
Thermoregulation
Michael A. Castellini and Jo-Ann Mellish
9.1 The big picture challenge
One of the first questions when seeing a seal or a whale in the ocean is to ask “How do
they stay warm in that cold water?” As humans, we cannot survive for long in the ocean
because it is much cooler in absolute terms than our body temperature, and it also carries
heat away from our bodies faster than air. Yet, many marine mammals spend their entire
lives in this environment. The obvious answer to this dilemma is that they often have very
thick fur or blubber that insulates them from the colder water. While this may be true in
many cases, it creates another challenge that is usually not considered: How do they cool
off if they are exercising very hard, come into very warm water, or haul out on a hot sandy
beach? If the fur and blubber are so effective that they can protect them from water as
much as 40°C colder than their core body temperature, then it must be a problem for them
to cool off or dump heat.
The answer to this apparent conflict is that marine mammals have developed highly
evolved thermoregulatory systems that not only allow them to conserve heat under cold conditions, but to release heat under warm conditions. Of course, a species’ ability to conserve
Contents
9.1 The big picture challenge ................................................................................................. 193
9.2 Basics of heat flow .............................................................................................................. 194
9.2.1 Heat flow applied to marine mammals .............................................................. 195
9.2.2 What is insulation? ................................................................................................ 196
9.3 Insulation in marine mammals ....................................................................................... 196
9.3.1 Fur ............................................................................................................................ 196
9.3.2 Blubber ..................................................................................................................... 198
9.4 Heat generation in marine mammals ............................................................................. 201
9.5 Heat balance versus other metabolic demands ............................................................. 203
9.6 Toolbox ................................................................................................................................ 204
9.6.1 Measuring blubber................................................................................................. 204
9.6.2 Infrared thermography ......................................................................................... 205
9.6.3 Heat flow underwater ........................................................................................... 206
9.6.4 Designer temperature telemetry ......................................................................... 209
9.7 Unsolved and future questions ....................................................................................... 209
9.7.1 Steller’s sea cow ...................................................................................................... 209
9.7.2 Climate change ....................................................................................................... 210
9.8 Conclusions ......................................................................................................................... 210
Glossary ........................................................................................................................................ 211
References ..................................................................................................................................... 211
chapter nine
Thermoregulation
Michael A. Castellini and Jo-Ann Mellish
9.1 The big picture challenge
One of the first questions when seeing a seal or a whale in the ocean is to ask “How do
they stay warm in that cold water?” As humans, we cannot survive for long in the ocean
because it is much cooler in absolute terms than our body temperature, and it also carries
heat away from our bodies faster than air. Yet, many marine mammals spend their entire
lives in this environment. The obvious answer to this dilemma is that they often have very
thick fur or blubber that insulates them from the colder water. While this may be true in
many cases, it creates another challenge that is usually not considered: How do they cool
off if they are exercising very hard, come into very warm water, or haul out on a hot sandy
beach? If the fur and blubber are so effective that they can protect them from water as
much as 40°C colder than their core body temperature, then it must be a problem for them
to cool off or dump heat.
The answer to this apparent conflict is that marine mammals have developed highly
evolved thermoregulatory systems that not only allow them to conserve heat under cold conditions, but to release heat under warm conditions. Of course, a species’ ability to conserve
Contents
9.1 The big picture challenge ................................................................................................. 193
9.2 Basics of heat flow .............................................................................................................. 194
9.2.1 Heat flow applied to marine mammals .............................................................. 195
9.2.2 What is insulation? ................................................................................................ 196
9.3 Insulation in marine mammals ....................................................................................... 196
9.3.1 Fur ............................................................................................................................ 196
9.3.2 Blubber ..................................................................................................................... 198
9.4 Heat generation in marine mammals ............................................................................. 201
9.5 Heat balance versus other metabolic demands ............................................................. 203
9.6 Toolbox ................................................................................................................................ 204
9.6.1 Measuring blubber................................................................................................. 204
9.6.2 Infrared thermography ......................................................................................... 205
9.6.3 Heat flow underwater ........................................................................................... 206
9.6.4 Designer temperature telemetry ......................................................................... 209
9.7 Unsolved and future questions ....................................................................................... 209
9.7.1 Steller’s sea cow ...................................................................................................... 209
9.7.2 Climate change ....................................................................................................... 210
9.8 Conclusions ......................................................................................................................... 210
Glossary ........................................................................................................................................ 211
References ..................................................................................................................................... 211