Deep foraging dives in relation to the energy depletion of Weddell seal (Leptonychotes weddellii) mothers during lactation

Abstract.

We examined the behavioral adaptations of Weddell seals (Leptonychotes weddellii) that may help them to compensate for decreasing energy stores during lactation. Field studies were conducted from late October to early December in 1999 and 2000 at breeding colonies in Antarctica. Data loggers were attached to adult females with pups aged 12–49 days old to record depth and temperature. Additionally, digital still cameras were also mounted on the mothers to monitor their behaviors and environment. The loggers were deployed on free-ranging seals (1999, n=11; 2000, n=30) for 16–62 h. Diving behavior varied markedly among individuals. Some seals did not dive below 50 m, while others spent more than 30% of their time repeatedly diving to depths greater than 50 m. The recorded images showed that seals sometimes stretched their necks to capture fish and other prey-like objects that were encountered near depths of 300 m. The percentage of the total time spent per day diving below 50 m was significantly correlated with date, pup age, and fatness (=girth/length) of the mother. Since thinner females spent a greater percentage of time in deep dives, we concluded that nursing Weddell seals adjust their diving behavior accordingly and dive deeper to feed on fish in order to replenish their own energy stores, which decrease during lactation.