Effect of a low-fat diet on body composition and blubber fatty acids of captive juvenile harp seals (Phoca groenlandica)

We investigated the effects of a change from a high-fat diet to a low-fat d iet of differing fatty acid (FA) composition on the body composition and bl ubber FA of five captive juvenile harp seals. Seals that had been maintaine d for 1 yr on a diet of Atlantic herring (greater than or equal to 9% fat) were switched to a diet of Atlantic pollock (1.7% fat) for 30 d. On days 0, 14, and 30, mass and body composition (using isotope dilution) were measur ed, and blubber biopsies (5 cm x 6 mm) were taken for FA analysis. Fat acco unted for 38%-49% of body mass at the start of the experiment. When switche d to the pollock diet, and despite food intakes averaging 6.5 kg/d (32.3 MJ /d), body fat: declined by an average of 6.4 kg or by 32% over the 30-d exp eriment. In contrast, body protein increased in direct relation to protein intake (r(2) = 0.836, P = 0.030). Despite substantial loss of body fat, blu bber FA signature changed significantly to reflect the changes in dietary i ntake of FA, and the deposition of FA was quantifiably predictable. Our res ults suggest that young growing phocids are unable to maintain body fat sto res on low-fat diets even when protein intakes are high. This may have sign ificant implications for juvenile pinniped survival in the wild. In additio n, turnover and deposition of dietary FA in blubber takes place in nonfatte ning seals.