Food consumption estimates of southern elephant seal females during their post-breeding aquatic phase at South Shetland Islands

Labelled water methodology was used to quantify energy expenditure during lactation and energy gain during the post-breeding aquatic phase in Southern elephant seal females at Stranger Point, King George Island (25 de Mayo). During lactation females spent a mean of 6021±1365 Mj, which resulted in a loss of 35% of the initial mass, comprising 63% of initial body fat and 20% of initial body protein. During the 58±5.4 d post-breeding foraging period, females gained 135±39 Kg, which allowed them to recover an average of 55% of the mass, including 46% of the fat, 71% of the protein and 47% of the energy lost during lactation. Neither the mass nor the energy lost during lactation were related to those gained while at sea. However, protein loss expressed in absolute terms or as a proportion of that present at the beginning of lactation explained about 50% of the variation in the protein gained during the post-breeding phase. This might indicate the presence of a mechanism favouring an increase in lean tissue during post-breeding.
Daily energy requirements for an average sized female during the post-breeding aquatic phase were estimated at 96 Mj. Estimation of prey consumption varies according to assumptions about diet composition. On a basis of 450 females, the total biomass of fish and squid consumed by the breeding group, assuming a diet composed of 75% cephalopods and 25% fish, was estimated at 521 t and 174 t respectively for the period examined.