Selective blubber fatty acid mobilization in lactating gray seals (Halichoerus grypus)

During negative energy balance periods, fatty acids (FAs) are mobilized to cover the metabolic demands of the body. FAs from adipose tissue are selectively mobilized according to their carbon length (CL) and number of double bonds (DBs); however, studies in vivo have focused only on fasting and nonlactating animals. During lactation, UK gray seals fast for 18 d, mobilizing a large amount of lipid from blubber to sustain their own metabolic demands and the nutritional requirements of pups. We investigated FA mobilization in individual gray seal mothers from two UK colonies sampled in 2005 and 2006. Linear mixed-effects models were used to examine to what extent the mobilization observed from FAs in blubber can be explained as a function of FAs' CL and number of DBs. FAs were mobilized according to their structure, such that for a given CL, mobilization increased with the number of DBs, and for a given number of DBs, mobilization decreased as CL increased. This pattern of selective mobilization was very similar between colonies, although the relative amounts of component FAs in blubber at early lactation were different between them. FAs, which are considered crucial to pup development, were mobilized more than predicted by the model. This suggests that selective mobilization of FAs is not related solely to the physicochemical characteristics of the FAs but also to the needs of a growing pup.