Diving behavior and swimming style of nursing bearded seal pups

Seals are born on land or ice and must acquire the diving and swimming skills required to forage and avoid predators during their early lives. While diving behavior, including swim speed and swimming style (e.g. prolonged gliding and stroke-and-glide swimming), of adult seals is well documented, knowledge regarding the diving behavior of pups is still limited to records of dive depth and duration measured by simple time-depth recorders. In the present study, we attached multi-sensor data loggers to 6 bearded seal Erignathus barbatus pups weighing between 33 kg (newborn) and 104 kg (close to weaning). The mean swim speed and the mean distance covered by a stroke cycle was lowest (0.5 m s(-1) and 0.3 m, respectively) in the smallest pup and highest (0.9 m s(-1) and 0.6 m) in the largest pup. The largest pup showed substantial periods (17% of transit time) of prolonged gliding, as adult seals commonly do. However, the 3 medium-sized pups glided only during <5% of the transit time, and the 2 smallest pups did not glide. Stroke-and-glide swimming was not observed in any pups. The stroke cycle frequency of the smallest pup was highly variable, while that of the largest pup was relatively stable. These results suggest that the swimming performance of the pups developed during the short nursing period.