Energetics of moulting in phocid seals

Abstract

The moult in phocid seals is a distinct period when behavioural and physiological changes occur. During this key stage in the annual life cycle animals elevate skin temperature to facilitate proliferation of hair follicle cells as they shed and renew their entire pelage. Due to the physiological constraints of raising skin temperature while in the water animals must haul out on land with increasing duration as the moult proceeds. The overall aim of this thesis was to provide insight into the physiology of moulting in phocid seals and to determine the physiological consequences associated with changes in haulout behaviour caused by anthropogenic disturbance. In harbour seals, metabolic rate was higher during the moult compared to when the moult had finished, particularly during the first 40 minutes after hauling out. Subcutaneous temperature increased at a faster rate and reached a higher asymptote when seals were moulting. High skin temperatures were also recorded in moulting southern elephant seals resulting in increased heat flux to the surrounding environment. Heat loss values equated to animals having a metabolic rate of up to 2.3 x Kleiber. Disturbance trials of harbour seals showed that individuals were highly site faithful to haulout locations despite repeated disturbance. The impact of disturbance is therefore not to cause animals to transition to another site but to increase the frequency with which animals enter the water and the duration of time spent at sea. Similar levels of disturbance may have thermoregulatory consequences when seals are in a moulting state. These results demonstrate physiological changes during the moult that incur an increased metabolic demand. Anthropogenic disturbance that causes seals to enter the water at a higher frequency than normal when moulting may incur a cumulative energetic cost. Mitigation to protect seals at haulout sites during the moult are supported by these findings.