Classification and behavior of free-ranging Weddell seal dives based on three-dimensional movements and video-recorded observations
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The goal of this study was to classify free-ranging (FR) dives of Weddell seals (Leptonychotes weddellii) and to compare them to isolated hole (IH) dives. Classification and comparisons were based on 58 descriptors for three-dimensional dive paths computed from data obtained by attaching video and data recorders to the backs of 12 adult Weddell seals that were free-ranging in eastern McMurdo Sound, Antarctica. We then inferred behavioral functions for the dive classes based on video-recorded observations. Three of the four dive types previously identified from seals diving at an IH occurred in FR seals. Although there were differences associated with location, Types 1, 2 and 3 dives clustered in a similar pattern in the discriminant analysis for FR and IH dives. Most prey (79%) captures occurred during Type 1 dives, and the primary (99%) prey was Antarctic silverfish (Pleuragramma antarcticum). Type 1 dives were the deepest (mean maximum depth 324-378. m), longest in duration (15.0-27.0. min), covered the greatest total distance (1470-2197. m), and had the steepest dive angles (descents: -30; ascents: +27). Types 2 and 3 dives formed a continuum from short duration (3.6-7.5. min), shallow (mean maximum depth 30-66. m) dives that were close to the ice hole (farpoint distance 75-130. m) and often involved aggressive interactions with other seals for breathing opportunities (Type 2) to progressively longer (7.9-17.2. min), deeper (mean maximum depth 81-143. m) dives that covered greater total distances (878-1194. m) and were associated with transiting between holes, exploring and occasionally foraging (Type 3). Very long distance Type 4 exploratory dives that were identified in the IH study were completely absent in FR seals. 2012 Elsevier Ltd.
