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First published online August 31, 2007
Journal of Experimental Biology 210, 3285-3294 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.007542
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How fast does a seal swim? Variations in swimming behaviour under differing foraging conditions

Susan L. Gallon1,*, Carol E. Sparling1, Jean-Yves Georges2, Michael A. Fedak1, Martin Biuw1 and Dave Thompson1

1 NERC Sea Mammal Research Unit, University of St Andrews, Fife KY16 8LB, UK
2 Centre National de la Recherche Scientifique, Institut Pluridisciplinaire Hubert Curien, Centre d'Ecologie Physiologique et Ethologie, 23 rue Becquerel, 67087 Strasbourg, France


Figure 1
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  		Fig. 1. Plan of the experimental pool (40 mx6 mx2.5 m). Animals could only surface to breathe at the respirometry chamber (RC). The feeding patch (FP) could be placed at 40, 80 or 120 m away from the surface. This set-up allowed us to measure dive duration, `descent' speed (1), bottom time, `ascent' speed (2), oxygen consumption and quantity of prey eaten, for every dive.

 

Figure 2
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  		Fig. 2. Time–depth recorder (TDR) data for seal K on the 8th of April 2002 showing changes in velocity over a dive. This was a dive to 40 m with a density of 3.2 fish min–1 at the patch.

 

Figure 3
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  		Fig. 3. Swim speeds (in m s–1) obtained from TDR and from visual observations. Each point represents the mean swim speed for the `descent' or `ascent' of a particular dive.

 

Figure 4
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  		Fig. 4. Index of transit swim speeds in relation to body mass (kg). There is a different symbol for the pups, the adult L and the adult Q.

 

Figure 5
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  		Fig. 5. Transit swim speeds index in relation to distance (40, 80 and 120 m) for the adult female Q. Data for early and late experiments at 80 m are indicated on the graph.

 

Figure 6
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  		Fig. 6. Index of transit swim speeds in relation to prey encounter rate (PER; fish min–1) for each animal (N,R,K,L). Each point represents the index of transit swim speed during a particular dive. The solid lines give linear least-squares fit.

 

Figure 7
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  		Fig. 7. Index of transit swim speeds in relation to distance (m) for each animal (N,R,K,L). Each point represents the index of transit swim speed during a particular dive.

 

Figure 8
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  		Fig. 8. Boxplot of the differences in mean swim speeds (in m s–1) between the `descent' and the `ascent' of dives to 40 m and to 80 m for each seal. *Mean swim speed significantly higher on the `descent' (paired t-tests, P<0.05). The bottom and top of each box marks the 25th and 75th percentile, respectively. The black and grey lines within the box represent the median and mean, respectively. Whiskers above and below the box indicate the 90th and 10th percentiles.

 

Figure 9
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  		Fig. 9. Boxplot of the differences in the number of peaks between the `ascent' and the `descent' for dives to 40 m and to 80 m for each seal. *Number of strokes significantly higher on the `ascent'; {dagger}number of strokes significantly higher on the `descent'; NS, not significant (paired t-tests, P<0.05). The bottom and top of each box marks the 25th and 75th percentile respectively. The black and grey lines within the box represent the median and mean respectively. Whiskers above and below the box indicate the 90th and 10th percentiles.

 

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© The Company of Biologists Ltd 2007