AN EXPERIMENTAL VALIDATION OF HEAT-LOSS MODELS FOR MARINE MAMMALS

Various heat loss models have been used to predict metabolic rates or lower critical temperatures of marine mammals. We have evaluated the a ccuracy of four models by making detailed measurements of all input pa rameters, while simultaneously recording the metabolic rate in two res ting harp seals (Phoca groenlandica) in ice water. We subtracted respi ratory heat loss from metabolic rate and compared the resulting value with estimated heat loss rates. The models overestimated heat loss rat e by between 28% and 76% on average. Measurements of body and body cor e surface areas of four other harp seals showed that the large overest imation resulting from the use of the flat plate model, is due to the large difference between body and body core surface area. The bad perf ormance of the three other models, which all describe the seals as cyl indrical in shape, appears to be due to the fact that the blubber enve lope and the body core of seals are not two perfect and concentrically positioned cylinders. Model experiments with a cylindrical heat eleme nt placed eccentrically inside an insulating polyethylene pipe showed that the established use of these models overestimates the true heat l oss rate, unless data input are based on direct morphometrical measure ments on the core. When making a correction for this for the best perf orming cylinder model, the overestimation of heat loss rate ranged bet ween 3% and 18%. (C) 1997 Academic Press Limited