Thermoregulatory control of expired air temperature in diving harp seals

Expired air temperature (Tex), metabolic rate (MR), and skin (Ts) and body (Tb; rectal) temperatures were recorded in four or five young (1-2 yr) harp seals (Phoca groenlandica) in air [mean air temperature (Ta) = -30, -10, or 10 degrees C] and in water [mean water temperature (Tw) = 2.3 or 24.8 degrees C, with Ta = -30, -10, 0, or 10 degrees C]. Apparent lower critical temperature was below -10 degrees C in air. Above this Ta, mean MR was 5.85 W.kg-0.75 (2.23 W.kg-1), while mean MR was 12.56 W.kg-0.75 (4.69 W.kg-1) at Ta -30 degrees C. When seals were immersed in water of 2.3 degrees C, mean MR was 6.13 W.kg-0.75 (2.31 W.kg-1), regardless of Ta. At Ta -30, -10, and 10 degrees C, mean Tex in air were 9.5, 13.0, and 25.0 degrees C, respectively. The corresponding values for seals in water (Tw = 2.3 degrees C) were 8.0, 9.5, and 15.5 degrees C, respectively. The low Tex recorded at Ta -30 and -10 degrees C in air and at all Ta in water (Tw = 2.3 degrees C) suggests that heat was conserved by nasal heat exchange. At Ta 10 degrees C, mean Tex of seals in air was approximately 10 degrees C higher than mean Tex of seals in water (Tw = 2.3 degrees C). Furthermore, seals subjected to a Tw of 24.8 degrees C at Ta 0 degrees C had a mean Tex 10 degrees C higher than when subjected to Tw 2.3 degrees C at the same Ta. These observations suggest that Tex in seals is under thermoregulatory control. In a series of forced dives of up to 5-min duration Tex was found to be the same before and after the dive regardless of dive duration and Ta.