Thermal windows on the trunk of hauled-out seals: hot spots for thermoregulatory evaporation?

Abstract

SUMMARY Seals have adapted to the high heat transfer coefficient in the aquatic environment by effective thermal insulation of the body core. While swimming and diving, excess metabolic heat is supposed to be dissipated mainly over the sparsely insulated body appendages, whereas the location of main heat sinks in hauled-out seals remains unclear. Here, we demonstrate thermal windows on the trunk of harbour seals, harp seals and a grey seal examined under various ambient temperatures using infrared thermography. Thermograms were analysed for location, size and development of thermal windows. Thermal windows were observed in all experimental sessions, shared some common characteristics in all seals and tended to reappear in similar body sites of individual seals. Nevertheless, the observed variations in order and location of appearance,number, size and shape of thermal windows would imply no special anatomical site for this avenue of heat loss. Based on our findings, we suggest that, in hauled-out seals, heat may be transported by blood flow to a small area of the wet body surface where the elevation of temperature facilitates evaporation of water trapped within the seals' pelages due to increased saturation vapour pressure. The comparatively large latent heat necessary for evaporation creates a temporary hot spot for heat dissipation.

The effects of water temperature on the energetic costs of juvenile and adult California sea lions (Zalophus californianus): the importance of skeletal muscle thermogenesis for thermal balance

“…Such a response may be due to modifications in the level of perfusion and concomitant thermal conductance of the insulating blubber layer. Such vascular modifications have been observed for phocid seals, which use a dynamic insulating blubber layer as means for heat conservation or dissipation, even along the well-insulated trunk region (Mauck et al, 2003). It is possible that the variability in metabolism below the T LC observed in the present study for California sea lions reflects variability in the level of perfusion across the blubber layer, a hypothesis that warrants further investigation.…”

Environment and activity affect skin temperature in breeding adult male elephant seals (Mirounga angustirostris)

“…Thermography in phocid seals is likely to be facilitated by their short fur, which reduces the potential for errors associated with fur length and camera viewing angle (McCafferty, 2007). Thermography has been used in captive phocid seals to observe transient areas of increased skin temperature (Mauck et al, 2003). These 'thermal windows' have been described as "body surfaces functioning as a temporary heat dissipater during heat stress" (Mauck et al, 2003) and might be important for mitigating thermal stresses resulting from environmental influences and reproductive behaviors.…”

“…Thermography has been used in captive phocid seals to observe transient areas of increased skin temperature (Mauck et al, 2003). These 'thermal windows' have been described as "body surfaces functioning as a temporary heat dissipater during heat stress" (Mauck et al, 2003) and might be important for mitigating thermal stresses resulting from environmental influences and reproductive behaviors. The definition of thermal window by Mauck and colleagues (Mauck et al, 2003) is more limited than the historical use of the term for an area through which heat can pass easily, even without the requirement of thermal stress (Molyneaux and Bryden, 1978).…”

“…These 'thermal windows' have been described as "body surfaces functioning as a temporary heat dissipater during heat stress" (Mauck et al, 2003) and might be important for mitigating thermal stresses resulting from environmental influences and reproductive behaviors. The definition of thermal window by Mauck and colleagues (Mauck et al, 2003) is more limited than the historical use of the term for an area through which heat can pass easily, even without the requirement of thermal stress (Molyneaux and Bryden, 1978). Nevertheless, it is a useful definition for understanding how animals transiently respond to conditions of heat stress to regulate body heat.…”

Body temperature depression and peripheral heat loss accompany the metabolic and ventilatory responses to hypoxia in low and high altitude birds

“…T b depression is believed to result from a decrease in T b setpoint that is regulated by thermoregulatory control regions in the hypothalamus and/or spinal cord (Crawshaw et al, 1985;Simon et al, 1986;Wood and Gonzales, 1996;Bicego et al, 2007), presumably by altering the balance between metabolic heat generation and heat loss. Peripheral heat loss is regulated by controlling blood flow to specific regions of the body surface, which alters surface temperature and thus the temperature differential driving heat dissipation (Klir and Heath, 1994;Mauck et al, 2003). These 'thermal windows' are typically poorly insulated, and include the ears, feet and nose of mammals (Klir and Heath, 1992), or the bill and feet of birds (Kilgore and Schmidt-Nielsen, 1975;Baudinette et al, 1976;Hagan and Heath, 1980).…”