In this paper we describe a detailed model of the thermal balance of a seal in air. We tested the model against the limited experimental information available on thermoregulation for harbour seals (Phoca vitulina) in air. Since a mother must meet both her own and her pups' energetic costs, we suggest that there may be an energetic advantage for harbour seals in Scotland if lactation is timed to coincide with the most favourable conditions for hauling out. To test this hypothesis, we used the harbour seals in the Moray Firth as our case study. The model does predict an energetic cost resulting from thermoregulation during haul-out for a mother and her pup in the Moray Firth. Taking the mother and pup as a unit, we estimate the minimum cost during lactation. This combined cost, which must be met by the female seal, is similar to the minimum metabolic rate during haul-out for the summer predicted from the model. In winter the predicted minimum metabolic rate exceeds the lactation cost, and an additional cost of thermoregulation results. The model predicts the most energetically favourable time for lactation to be June and July, and this is coincident with the timing of pupping in this seal population. We suggest that for harbour seals in Scotland, the timing of pupping may be influenced by the thermoregulation costs of haul-out. This provides indirect evidence that thermoregulation influences haul-out behaviour in this small phocid species.
Occurrence and development of folding related to normal faulting within a mechanically heterogeneous sedimentary sequence: a case study from Inner Moray Firth, UK