Energetics and Temperature Regulation
|J. Craig George, Ph.D.
|AEWC, Bob Elsner and Eric Follmann (UAF), Tom Albert
These studies investigated the thermoregulation capabilities and the metabolic rate (or energetics) of the bowhead whale. With the permission of the AEWC, subsistence-harvested bowhead whales were examined providing a rare opportunity to collect unusual data. Deep body temperatures are low, as compared with other whales, at about 33.8 Celsius. Metabolic rates appear low, as do heat transfer rates, due to their thick blubber. Growth rates appear accordingly slow. The tongue, flukes, and skin of the thorax (main body) appear to be important thermoregulatory organs.
Previous observations of bowhead thermoregulation:
Herman Melville (1851) in Moby Dick:
For the whale is indeed wrapt up in his blubber as in a real blanket…What would become of a Greenland Whale [bowhead whale], say, in those shuddering, icy seas of the North, if unsupplied with his cosy surtout?
J.E.I. Hokkanen (1990):
The insulation of the bowhead is good enough to allow it to swim in liquid oxygen! The blubber coats for large whales are obviously not dimensioned for thermal demands…
… [to avoid overheating] in those species [with] thicker insulation, metabolism would have to be lowered to the reptilian level.
…for large whales, blood circulation to the dermal layer is essential for heat loss…if blood flow is decreased below a critical level, the animal will overheat…
blubber is primarily a food reserve.
John Burns (1993):
The question of why are bowhead whales so fat requires further inquiry…[thick blubber] enables…whales to survive the occasional year when food is virtually lacking, or, more likely, back-to-back years of low food availability.
Inupiat whaling captains knew about the ability of bowheads to thermoregulate and told scientists that “the bowhead is like a thermos bottle.”
Postmortem Body Temperatures
“Postmortem temperatures were measured at several locations on freshly harvested bowhead whales. Strong temperature gradients were observed through the blubber at all sites examined.” (George, 2009) Bowhead whales have regional heterothermy which means that different parts of the body can be at different temperatures at the same time. This allows for the conservation of heat, or energy, in cold climates. See the photo below labeled with the different body temperatures that were measured.
This picture shows the post-mortem body temperatures that were measured from a subsistence-harvested bowhead whale. The tongue is relatively warm likely due to its huge size and layers of fat providing insulation. (Photo: NOAA, NMFS)
Thermal Conductivity through Blubber and Muscle
The thermal conductivity (TC) of the blubber is important in understanding heat loss to the environment for bowhead whales. This device has a heated plate inside of an insulated box with a cooled top. The TC can be estimated by measuring temperature difference across the blubber sample that is placed in the box.
This graph shows the thermal gradient measured through the blubber of a bowhead whale. Note that the gradient continues to the muscle. (Source: Craig George)
Thermoregulation in Flukes
Flukes are an important thermoregulatory structure. There are large arteries in the flukes, surrounded by a network of veins, called arteriovenous anastomoses or AVAs. These AVAs provide for countercurrent heat exchange allowing for the loss of heat through the flukes or the conservation of core body heat, as needed.
This x-ray of a bowhead fluke shows the network of arteries fanning out to the tips of the flukes. This photo done by injecting contrast media into the fluke arteries
This drawing shows a cross-section through the network of blood vessels in the flukes. Drawing by Craig George
This is a cross-section of a bowhead whale fluke. Note the “vascular rosette” and the “arterio-venous anastomoses loops” or AVA bypass
Heat Loss Model suggests:
The head and thorax showed the highest amount of heat loss overall due to its much larger surface area. However, when corrected for size, the flukes have the highest heat flux (amount of heat lost per second). The measurements for heat loss were used to estimate resting metabolic rates which appear to be quite low for these animals.
The heat loss measurements confirm the “Inupiat Thermos Bottle” hypothesis. The bowhead whale heat loss and likely metabolic rates appear to be very low compared with other whales. Bowhead whales are very good at conserving heat; in fact, they probably have to use various mechanisms (like the flukes) to ‘dump’ excessive heat, even in extremely cold water, when they exercise.
- Deep body temperatures were low, ~33.8 C, as compared to other whales.
- Metabolic rates were low as compared to other whales.
- Blubber thermal conductivity values similar to other cetaceans; but “thermal resistance” much higher because of blubber thickness.
Are bowhead whales “overheating”?
- Probably not since they have low metabolic rates, but they are ‘over-insulated’ and probably need to lose heat when exercising.
- Bowhead whales have good mechanisms to regulate heat loss via flukes, flippers, and probably their tongue.
- Blubber thickness is likely mainly a “fuel storage” mechanism providing bowheads with the ability to endure long periods of low prey abundance, maybe even a year or more.
From George’s (2009) abstract:
“All harvested whales examined showed strong thermal gradients through their blubber and through the muscle, the latter being atypical of most mammals. The deep body temperature averaged 33.6 degrees Celsius which is lower than in other non-hibernating…mammals. Resting metabolic rates for whales were estimated using a heat-loss technique. The thermal conductivity of the blubber averaged 0.23 W/meter-K, similar to that of other whales and marine mammals. Heat flux rates were highest for the palatal rete, flukes and tongue, and lowest in the thorax. The estimated metabolic rates were considerably lower than predicted. Their thick blubber likely buffers bowheads against high variability in primary and secondary productivity in arctic seas.”
George, J.C. 2009. Growth, morphology and energetics of bowhead whales (Balaena mysticetus). (Dissertation). University of Alaska Fairbanks, Fairbanks, Alaska.
- Elsner, R., J. Pirie, Kenney, D. D. & Schemmer, S. 1974. Functional circulatory anatomy of cetacean appendages. In R. J. Harrison (ed.) Functional Anatomy of Marine Mammals, Volume 2. Academic Press, London. Pp. 143–159.
- Hokkanen, J.E.I. 1990. Temperature regulation in marine mammals. Journal of Theoretical Biology 145: 465-485.
- Elsner, R., et al. 2004. Temperature-viscosity relations of bowhead whale blood: a possible mechanism for maintaining cold blood flow. Marine Mammal Science 20(2):339-344.
- Elsner, R., et al. 2004. Vasomotor responses of isolated peripheral blood vessels from bowhead whales: thermoregulatory implications. Marine Mammal Science 20(3):546-553.
- Werth, A.J. 2007. Adaptations of the cetacean hyolingual apparatus for aquatic feeding and thermoregulation. The Anatomical Record 290:546-568.
- Ball, H.C. et al. 2015. Seasonal and ontogenetic variation in subcutaneous adipose of the bowhead whale (Balaena mysticetus). The Anatomical Record doi:10.1002/ar.23125.
- Ball, H.C., et al. 2016. Beyond thermoregulation: metabolic function of cetacean blubber in migrating bowhead and beluga whales. Journal of Comparative Physiology B doi:10.1007/s00360-016-1029-6.
In August 2005, Douglas Henry of Gambell Alaska, found a section of bowhead blubber about 12 feet underground. He excavated the mangtak as he recognized that it was in a very old ice cellar and quite unique. The blubber was given to biologist Craig George, who was in Gambell working with Merlin Koonooka sampling bowhead skulls as part of a bowhead whale “stock structure” DNA study. The purpose was to determine if whales harvested at St. Lawrence Island might be genetically different from those taken in other villages. Sections of the old blubber were sent out to laboratories for analysis of age, contaminants, and fats. Information from this specimen should give scientists baseline information to compare to modern whales.
The estimated age of the sample was about 1,050 years old (± 70 yr). These results need further checking since marine environments affect carbon dating. Regardless, it is safe to say that this mangtak is extremely old. In fact, this sample likely represents some of the oldest blubber ever collected and analyzed. People of Gambell were excited because this confirms what they have always said – “we have hunted bowheads for thousands of years.” We thank the Gambell residents for offering this specimen for science. (Note: Craig did taste the mangtak and would not recommend it for dinner).
Update on Analysis of Ancient Blubber:
These results suggest:
- The ancient whale is closely related to bowhead whales in the Bering-Chukchi-Beaufort Sea stock found today.
- The ancient whale appeared to feed on the same diet as bowhead whales do today.
- Levels of mercury measured in the skin of the ancient whale are similar to levels found in bowhead whales today.
- George, J.C., et al. 2008. An analysis of ancient bowhead whale mangtak from Gambell Alaska: What can it tell us? Presented to the 60th International Whaling Commission.SC/60/E2.