Meeting Abstract
26.6 Friday, Jan. 4 How Weddell seals stay in shape: Using morphometric and isotopic dilution techniques to assess seasonal changes in body condition SHERO, M.R.*; PEARSON, L.E.; GOETZ, K.T.; ROBINSON, P.W.; HÜCKSTÄDT, L.A.; COSTA, D.P.; BURNS, J.M.; Univ. of Alaska Anchorage; Univ. of Alaska Anchorage; Univ. of California Santa Cruz; Univ. of California Santa Cruz; Univ. of California Santa Cruz; Univ. of California Santa Cruz; Univ. of Alaska Anchorage mrshero@alaska.edu
Adult Weddell seals (Leptonychotes weddellii) haul-out on the ice in Oct/Nov for their pupping and breeding period and remain relatively inactive for ~4 months until their molt in Jan/Feb. Because phocid seals rely on stored lipid reserves for fuel across periods of reduced foraging, seasonal changes in body composition are indicative of past foraging success and energy allocated towards reproduction. In this study, body composition was assessed via morphometric (truncated cones) and isotopic dilution (3H2O) techniques for pre-breeding (Oct/Nov; 34F:5M) and post-molt (Jan/Feb; 51F:11M) seals. Nine females were handled in both seasons. Blubber mass estimated by morphometric models was significantly correlated with lipid mass estimated by isotopic dilution(P<0.001). However, morphometric models overestimated body mass by 20.6±0.6%, indicating that this method cannot be used as an unbiased estimate of Weddell seal mass or condition, as in other pinniped species. Therefore, seasonal comparisons were based on lipid content estimated via tritiated water. While there was no seasonal difference in lipid stores (as %body mass) in the cross-sectional study(P=0.691), individual animals that were handled in both seasons were larger (kg) in October (lipid mass increased 33%, lean mass 22%). These findings suggest that animals lose both lipid and lean mass during the summer reproduction and molt periods, but regain it during the winter months. In addition, larger and fatter Weddell seals made significantly longer dives during the 8 weeks following tagging in Jan/Feb (P<0.001), likely affecting the Weddell seal’s ability to regain mass after the breeding period.
