Cutaneous heat flux models do not reliably predict metabolic rates of marine mammals

Heat flux models have been used to predict metabolic rates of marine mammal s, generally by estimating conductive heat transfer through their blubber l ayer. Recently, Kvadsheim et al. (1997) found that such models tend to over estimate metabolic rates, and that such errors probably result from the asy mmetrical distribution of blubber. This problem may be avoided if reliable estimates of heat flux through the skin of the animals are obtained by usin g models that combine calculations of conductive heat flux through the skin and fur, and convective heat flux from the surface of the animal to the en vironment. We evaluated this approach based on simultaneous measurements of metabolic rates and of input parameters necessary for heat flux calculatio ns, as obtained from four harp seals (Phoca groenlandica) resting in cold w ater. Heat flux estimates were made using two free convection models (doubl e-flat-plate and cylindrical geometry) and one forced convection model (sin gle-flat-plate geometry). We found that heat flux estimates generally under estimated metabolic rates, on average by 26-58%, and that small variations in input parameters caused large variations in these estimates. We conclude that cutaneous heat flux models are too inaccurate and sensitive to small errors in input parameters to provide reliable estimates of metabolic rates of marine mammals. (C) 2000 Academic Press.