Figure 1.
The iterative process of the broken stick algorithm is presented from panel A to H. The broken stick method iteratively selects the data points (in blue) of maximum difference between the original dive profile (black line) and the dive profile reconstructed by linear interpolation (red lines) between the points selected during the previous iterations (in red). A Weddell seal dive was used as an example for this graph.
Figure 2.
Optimization of the broken stick algorithm.
Any number of broken stick points can be chosen depending on the resolution required to describe a dive. A: Mean distance according to the number of broken stick points (from 6 to 33) which are used to describe the dive represented below (B). The mean distance is the average of the differences between each data point of the original profile and the corresponding point of the reconstructed profile obtained by linear interpolation between the broken stick points (from 6 to 33). The inflexion point of the mean distance curve (A, red data point) is determined by calculating the maximal distance between the asymptote curve obtained by fitting a Gompertz model to the mean distance (A, black line) and the linear approximation (A, dashed black line) between its start and end points. B: Original dive profile (B, black line) summarized by the optimal number of broken stick points (B, black data points) as estimated by mean distance represented above (A). The blue lines represent transit segmentsBS and the red lines represent hunting segmentsBS. The green dashed line represents the depth below which bottom time is calculated with the classical dive analysis method. A Weddell seal dive was used as an example for this graph.
Figure 3.
Distribution of the mean distance.
Distribution of the mean distance (m) according to the optimal number of broken stick points calculated for each dive for the southern elephant seals (A) and the Weddell seal dataset (B). See figure 2 for calculation of the optimal number of broken stick points.
Figure 4.
Density plots representing the distribution of the vertical sinuosity calculated for each broken stick segment from the elephant seal dives (A) and the Weddell seal dives (B). The 0.9 sinuosity threshold represented by the vertical red line was used to discriminate “transit” modeBS versus “hunting” modeBS.
Table 1.
General information on tag transmission and diving behaviour.
Table 2.
Comparison of dives with or without prey capture attempts as inferred from acceleration data in southern elephant seals.
Figure 5.
Behavioural differences in prey capture attempts in SES.
Distribution of the number of prey capture attempts calculated for each segmentsBS according to transit modeBS and hunting modeBS, respectively for the elephant seal foraging dives.
Table 3.
Comparison of within dive behavioural modesBS in southern elephant seals and Weddell seal.
Figure 6.
Complexity of the dives for the southern elephant seals.
For each panel, the top graph represents the mean distance according to the number of broken stick points in order to select the optimal number of broken stick points to best describe each dive. See figure 2.A for a full description. The lower graph of each panel represents the original dive profile (black line) summarized by the optimal number of broken stick points (black data points). The blue lines represent transit segmentsBS, the red lines represent hunting segmentsBS and the green dots indicate prey capture attempts (estimated from acceleration data). The green dashed line represents the depth below which bottom time is calculated with the classical dive analysis method. Figures are represented from A to I, from the simplest to the most complex dives, with zero (A, grey frame) to four (H and I, blue frame) hunting phasesBS.
Figure 7.
Complexity of the dives for the Weddell seal.
For each panel, the top graph represents the mean distance according to the number of broken stick points in order to select the optimal number of broken stick points to best describe each dive. See figure 2.A for a full description. The lower graph of each panel represents the original dive profile (black line) summarized by the optimal number of broken stick points (black data points). The blue lines represent transit segmentsBS and the red lines represent hunting segmentsBS. The green dashed line represents the depth below which bottom time is calculated with the classical dive analysis method. Figures are represented from A to I, from the simplest to the most complex dives, with zero (A, grey frame) to four (H and I, blue frame) hunting phasesBS.
Figure 8.
Proportion of dives containing from zero to seven hunting phasesBS (%) for the southern elephant seals (A) and the Weddell seal (B).
Figure 9.
Behavioural modeBS differences.
Distribution of each behavioural phaseBS duration (sec.) expressed in percentage of the corresponding dive total duration (sec.) for transit modeBS and hunting modeBS, respectively (A: southern elephant seals, C: Weddell seal). Distribution of each behavioural phaseBS depth (m) expressed in percentage of the corresponding dive maximal depth (m) for each of the two modesBS (B: southern elephant seals, D: Weddell seal). The horizontal bold line of the box shows the median. The bottom and top of the box show the 25th and 75th percentiles.
Figure 10.
Behavioural differences in ascent/descent rates.
Distribution of the ascent/descent rates (m.sec−1) calculated for each segmentsBS according to transit modeBS and hunting modeBS, respectively for the southern elephant seals (A) and the Weddell seal (B). The horizontal bold line of the box shows the median. The bottom and top of the box show the 25th and 75th percentiles.
Table 4.
Comparison of the broken stick and the classical dive analysis.