MEASURING THE BODY-COMPOSITION OF ANTARCTIC FUR SEALS (ARCTOCEPHALUS-GAZELLA) - VALIDATION OF HYDROGEN ISOTOPE-DILUTION

We examined the accuracy of hydrogen isotope dilution (tritium and deu terium) as a means of determining total body water (TBW), and hence bo dy composition, by comparison with whole-carcass chemical analysis in five adult female and four pup Antarctic fur seals. On average, tritiu m isotope (HTO) dilution overestimated TBW by 1.92% +/- 1.00% (n = 9). Deuterium isotope (D2O) dilution also overestimated TBW (1.71% +/- 1. 74%, n = 5), bur this trend was not significant. The following equatio ns were developed for predicting TBW from hydrogen isotope dilution es timates: TBW (kg) = 0.11 + 0.97 . HTO space (kg) (r(2) = 0.999, n = 9, P < 0.0001) and TBW (kg) = 2.10 + 0.89 . D2O space (kg) (r(2) = 0.980 , n = 5, P < 0.001). Whole-carcass chemical analysis showed adult fema les were composed of 14.5% +/- 1.0% total body lipid (TBL), whereas pu ps were composed of only 9.4% +/- 1.0% lipid. Adult females had lower TBW contents (60.1% +/- 0.7%) than pups (67.6% +/- 1.2%;) and conseque ntly, higher energy contents (adults, 10.59 +/- 0.30 MJ . kg(-1); pups , 8.24 +/- 0.41 MJ . kg(-1)). Pups had higher ratios of TBW to lean bo dy mass (LBM) (0.747 +/- 0.009) than adults (0.707 +/- 0.004), which i ndicates they had not yet reached chemical maturity. The following bes t-fit predictive equations based on TBW and body mass (BM) were develo ped for TBL, total body protein (TBP) total body ash (TBA), and total body gross energy (TBGE): TBL (kg) = 0.875 . BM (kg) - 1.187 . TBW (kg ) - 0.633 (adults); TBL (%) = 66.562 - 0.845 . TBW (%) (pups); TBP (kg ) = 0.058 . BM (kg) + 0.209 . TBW (kg) + 0.996 (adults); TBP (kg) = 0. 267 . BM (kg) - 0.130 . TBW (kg) + 0.087 (pups); TBA (kg) = 0.071 . TB W (kg) - 0.088 (adults and pups); TBGE (MJ . kg(-1)) = 34.1 - 0.391 . TBW (%) (adults); TBGE (MJ . kg(-1)) = 31.7 - 0.347 . TBW (%) (pups). With the use of these predictive equations, hydrogen isotope dilution is an accurate means of determining body composition in live Antarctic fur seals. Differences in these relationships between adults and pups , and in comparison to those in phocids, emphasize the need for the us e of equations derived from appropriate data sets when predicting body composition in pinnipeds.