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First published online August 8, 2008
Journal of Experimental Biology 211, 2566-2575 (2008)
Published by The Company of Biologists 2008
doi: 10.1242/jeb.020065
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The role of infrequent and extraordinary deep dives in leatherback turtles (Dermochelys coriacea)

Jonathan D. R. Houghton1,2,*, Thomas K. Doyle3, John Davenport4, Rory P. Wilson2 and Graeme C. Hays2

1 School of Biological Sciences, Queen's University Belfast, Medical Biology Centre, 97 Lisburn Road, Belfast, BT9 7BL, UK
2 Institute of Environmental Sustainability, School of the Environment and Society, Swansea University, Singleton Park, Swansea, SA2 8PP, UK
3 Coastal Marine Resources Centre, University College Cork, Lewis Glucksman Marine Facility, Haulbowline, Cork, Ireland
4 Department of Zoology, Ecology and Plant Sciences, University College Cork, Distillery Fields, North Mall, Cork, Ireland


Figure 1
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  		Fig. 1. Movements of 12 leatherback turtles tracked between 2002 and 2006. Composite figure based on previously published work (Hays et al., 2004aGo; Hays et al., 2006Go; McMahon and Hays, 2006Go; Doyle et al., 2008Go). All tracks originate in Grenada with the exception of the two turtles tracked from the west coast of Ireland, shown in black (2005) and dark blue (2006).

 

Figure 2
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  		Fig. 2. Frequency histogram of all dives completed by the 13 turtles combined, where maximum depth data were available (N=26,146 dives).

 

Figure 3
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  		Fig. 3. (A) Mean (±1 s.d.) vertical rate of descent to the first point of inflection (D1) for all turtles combined, classified into 100 m depth bins (N=22,085 dives); (B) mean (±1 s.d.) vertical rate of descent to the deepest point of inflection (Dmax) for all turtles classified into 100 m depth bins (N=21,196 dives). For both parts of the figure all data are from dives displaying five points of inflection. (C) Dive depth versus dive duration for dives where data were available (N=21,196 dives). Dotted line shows maximum inferred aerobic dive limit (ADL) for leatherbacks (Bradshaw et al., 2007Go).

 

Figure 4
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  		Fig. 4. Satellite relay data logger (SRDL) dive profiles showing deep-diving behaviour. (A) Turtle 5 (platform terminal transmitter, PTT no. 4935) 23 July 2003, 25.54°N, 58.85°W, 946 m; (B) turtle 4 (PTT no. 4934) 13 August 2003, 24.41°N, 60.81°W, 1010 m; (C) turtle 13 (PTT no. 66360) 30 November 2006, 18.58°N, 25.79°W, 1250 m (the deepest dive ever recorded for the species). Arrowed numbers represent duration in hours for pre-dive, dive and post-dive surfacing events.

 

Figure 5
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  		Fig. 5. (A) Each profile represents temperature data gathered from an individual turtle during a single dive. Data are given in raw format to demonstrate how profiles varied with latitude (marked in the key to the side of the figure). (B) Rate of temperature change ({Delta}T, °C) at 50 m depth intervals based upon power relationships derived from the temperature profiles given in A.

 

Figure 6
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  		Fig. 6: Frequency distribution of all dives >300 m (N=95) revealing a peak in occurrence just after midday.

 

Figure 7
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  		Fig. 7. (A) Spatial pattern of deep dives (>300 m) throughout the North Atlantic. Data from individual depth profiles are shown as open circles (N=97 dives). On occasion a maximum depth >300 m would be recorded in the summary data without an actual profile being recorded. To account for these events, all summary periods with maximum depths >300 m are shown as open triangles (N=147 periods). (B) The occurrence of deep dives as a proportion of the total number of dives recorded at different latitudes (combined into 4° bins). Data are given as mid-points for 4° latitude bins. The decreased occurrence of deep dives between 4.00 and 7.99°N should be interpreted with caution as data were only available for these latitudes from three of the 13 turtles.

 

Figure 8
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  		Fig. 8. The maximum depth recorded in 6h summary periods for the entire tracking period are given for six turtles tracked from Grenada in 2002 and 2003 (PTT number given on individual figures). Depths <300 m are shaded on each figure to help identify deep dives according to our classification. Distance from home (i.e. Grenada) is also given on the secondary y-axis and denoted by a solid line. Time is classified into different stages of migration, which can be observed from changes in the distance from home data: II, internesting interval; TP, transit period; RP, residence period; PRP, post-residence period.

 

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© The Company of Biologists Ltd 2008