Acquisition of gliding skills by Weddell seal (Leptonychotes weddellii) pups during lactation

Pinnipeds give birth to their pups ashore or on ice and forage in water. Therefore, neonates initially lack the adaptations to sustain prolonged underwater diving activity. Although the physiological development for breath-holding during diving has been investigated in seal pups, little is known about the concurrent development of behavioral adaptations during lactation. In this study, multisensor data loggers were used to record diving behavior and swimming gaits of pre-weaned Weddell seal (Leptonychotes weddellii) pups. Experiments were conducted in 16 pups at the Syowa Station, Antarctica, from November to December 1999 and 2004. Swimming speeds, dive depths and flipper stroking rates were recorded for each individual for about 24 h. We found that the glide index during ascending was increased with body length, whereas the dominant stroke cycle frequency were not affected by body length, dive depth and descent or ascent phase. All pups had significantly higher stroke rates in descent than in ascent, but there was no difference between swimming speed. As we found a positive relationship between the body length and age, we considered body length as an index of growth. Therefore, we conclude that pups gradually acquire the ability to glide with utilizing positive buoyancy during ascending toward the end of lactation.