ENERGY-METABOLISM AND THERMOREGULATION IN JUVENILE HARBOR SEALS (PHOCA-VITULINA) IN AIR

We measured metabolic rates (mL O-2 h(-1), converted to rkcal d(-1)), deep body temperatures (T-b's; degrees C), and skin temperatures (T-s' s; degrees C), and calculated whole-animal thermal conductances (C; mL O-2 g(-1) h(-1) degrees C-1), of five juvenile harbor seals (Phoca vi tulina concolor) at ambient air temperatures (T-a's) between -10 degre es and 32.5 degrees C. The mean thermal neutral zone (TNZ) of our sear s extended from a lower critical temperature (T-lc) of-2.3 degrees +/- 0.03 degrees C to an upper critical temperature (T-uc) of 25.1 degree s +/- 0.07 degrees C. Hyperthermia was observed at T-a = 32.5 degrees C. Mean standard metabolic rate was 1,399 +/- 92 kcal d(-1), approxima tely 1.6 times the value expected for adult animals of similar body ma ss. Mean T-b increased from 38.2 degrees +/- 0.3 degrees C at T-a = 27 .5 degrees C and reached 40.2 degrees +/- 1.4 degrees C at T-a = 32.5 degrees C. Skin temperatures decreased with decreasing T-a but remaine d well above T-a. Mean C decreased from T-a = 32.5 degrees C until it reached a minimum value of 0.012 mL O-2 g(-1) h(-1) degrees C at T-a = 27.5 degrees C; it then increased with further decreases in T-a below 0 degrees C. Our results, together with the observation that the sout hern limit of harbor seal distribution in both the Atlantic and Pacifi c Oceans closely coincides with the warmest-month isotherm of 25 degre es C for air temperature, strongly suggest that warm ambient air tempe ratures may limit the distribution of this species.