|Fur vs. Blubber|
For my Ph.D. thesis, I studied differences between fur and blubber as insulation in mammals, with a focus on the otariids (fur seals and sea lions). The otariids represent the only mammalian family to include both types of insulation: fur seals have dense, waterproof fur and a moderate blubber layer, while sea lions rely solely on their blubber for thermoregulation in water. I examined the thermal properties of the fur and blubber of various otariid species, and compared the physiological and behavioral responses of the California sea lion and northern fur seal to different temperatures.
Thermal properties of fur and blubber
Thermal conductivity of sculps
Lipid and water content of blubber
Effects of hydrostatic pressure
Masako Abney, a 2006-2007 senior thesis student, examined the effects of hydrostatic pressure on the air layer in pinniped fur. As an animal dives in the ocean, it experiences great pressure changes associated with being underwater. Masako found that true seals and sea lions are not able to keep air in their fur under pressure, while fur seals do maintain an air layer at depth. However, the air layer is compressed greatly under pressure, and this will reduce the effectiveness of the fur as insulation.
Thermal neutral zone of California sea lions and northern fur seals
California sea lions
Northern fur seals pups wean at four months of age, and embark on a pelagic phase for up to nine months. During these extended trips to sea, northern fur seals need to rest, and often perform a behavior called jughandling, in which the animals float with one foreflipper held between both hind flippers above the water’s surface. The purpose of this behavior is unknown, but popular hypotheses indicate opposing thermoregulatory consequences: either the animals remove the flippers from the water to avoid heat loss to cold water, or they position the flippers in the air to increase convective heat loss when warm. I measured jughandling metabolic rate, and found that this unique behavior is energetically costly to northern fur seal pups, but it may help to mitigate thermal costs below the lower critical temperature.
Otariids are highly communal pinnipeds that often congregate in large numbers on coastal rookeries. Although this behavior serves a social role, it also has the potential to change the microhabitat, and thus the local thermal conditions experienced by the animals. We would expect pinnipeds to be overinsulated on land, but they have been observed to huddle extensively on shore. I quantified huddling behavior in California sea lions, and found that there is a significant thermal benefit to huddling behavior in these animals.