Seasonal changes in the energy budgets of captive harbour seals (Phoca vitulina concolor)

Rosen, David A. S. (1995) Seasonal changes in the energy budgets of captive harbour seals (Phoca vitulina concolor). Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Seasonal changes in several components of the energy budgets of captive harbour seals (Phoca vitulina concolor) were studied to further understand previously documented cycles of energy conservation and utilization. Body mass in adult seals varied by 16-30% (15-32 kg) throughout the year, resulting in net production energy of ±200 MJ/week. Circannual variation in gross energy intake (GE) resulted in a range of 30-300 MJ/week. Combined, concurrent changes in GE and body mass resulted in a range in available energy (EA) of 50-350 MJ/week. Resting metabolic rate (RMR) displayed significant seasonal variation (45-129 MJ/week), and accounted for 10-90% of EA throughout the year. Changes in RMR may serve as either an adaptation or a response to varying levels of energy turnover. Mass-specific metabolism exhibited a stronger statistical relationship to EA than did RMR. Locomotor activity was significantly related to EA for all the male seals, but not for the female. The strength of the statistical relationship in the mature males derived largely from the high levels of activity and EA during the breeding season. However, increases in locomotor activity could not account for all of the observed EA. Rectal temperatures, which displayed a circannual variation of 2.0-2.8°C, were related to EA for only three of the seals and were more closely related to water temperature. The observed variation in core temperature was speculated to result from changes in deep body set-points. The substantial changes that were documented to occur throughout the year in many aspects of the seals’ energy budgets highlight the need for long-term investigations of energetics, metabolic physiology and feeding ecology.

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