Physiological effects on dive patterns and foraging strategies in yearling Weddell seals (Leptonychotes weddellii)

Fifteen yearling Weddell seals (Leptomychotes weddellii) were captured, measured, weighed, bled, equipped with time-depth recorders, and released to determine if diving behavior was related to physical condition. Upon recovery of the time-depth recorders, dives were classified into four types based on shape, using cluster analysis. Based on maximum depth, two groups were further subdivided, for a total of seven types. The mean and maximal dive depth, duration, and frequency were determined for each yearling for all dive types combined and for each type separately. Stepwise regression and ANOVA techniques were used to test the relationship between diving behavior and physiological and morphometric measurements. In general, half of the variation in the pooled diving behavior could be explained by body-size differences. Larger yearlings made longer and shallower dives than smaller yearlings. Dive patterns suggested that large yearlings foraged primarily on small shallow-water prey items, while small yearlings concentrated on energy-dense deep-water prey. However, the interpretation of diving behavior, foraging locations, and diet that resulted from separating individuals and dive types was very different from that based on average diving behavior. This argues against ignoring variation among individuals and using only average diving behavior when describing marine mammal dive patterns.