Experimental evidence of seawater drinking in juvenile hooded (Cystophora cristata) and harp seals (Phoca groenlandica)

This study was undertaken to measure whether young harp seals (Phoca groenl andica) and hooded seals (Cystophora cristata) drink seawater and, if so, t o investigate how the excess salt load is handled. Blood and urine samples were collected from hooded seal pups (n = 3) and harp seal pups (n = 3) aft er 2 weeks of freshwater exposure, at intervals during 3 weeks of seawater exposure and, finally, after 2 weeks of re-exposure to fresh water. Total w ater turnover, as measured by injection of tritiated water, was 2200 ml.day (-1) and 3300 ml.day(-1) in hooded seals and harp seals, respectively. The extent of mariposia was taken as the difference between total water turnove r and influx of water through food (free and metabolic water) and respirato ry water exchange. Seawater drinking amounted to 14% and 27% of total water turnover (rH(2)O) for the hooded seals and harp seals, respectively. Furth er evidence of mariposia was obtained from an increase in the excretion rat e of the urine osmolytes Na+, Cl- and Mg2+, during the period of seawater e xposure. It is concluded that water influx due to seawater drinking can not be excluded as a source of error when estimating food consumption of free- ranging harp seals and hooded seals, by use of labeled water techniques.