Southern elephant seals (Mirounga leonina) are prodigious divers. They spend 90 % of their time while at sea diving to average depths of 300–600 m (Slip et al., 1994) and are able to reach depths in excess of 1500 m (McConnell and Fedak, 1996). The mean dive duration of southern elephant seals is 25...
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| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.618.1423 http://jeb.biologists.org/content/204/4/649.full.pdf |
| Summary: | Southern elephant seals (Mirounga leonina) are prodigious divers. They spend 90 % of their time while at sea diving to average depths of 300–600 m (Slip et al., 1994) and are able to reach depths in excess of 1500 m (McConnell and Fedak, 1996). The mean dive duration of southern elephant seals is 25.2 min for females and 24.1 min for males (Boyd and Croxall, 1996); however, the longest recorded dive lasted 2 h (Hindell et al., 1992). Both physiological and ecological constraints influence dive duration. Seals exploiting food sources at depth are forced to return to the surface to breathe and are entirely dependent upon internal oxygen reserves whilst submerged. From calculations based on mass-specific oxygen stores of 79 ml O2 kg- 1 body mass (Kooyman, 1989) and estimates of diving metabolic rate, the theoretical aerobic dive limit (ADL) of southern elephant seals is 27.5–30.2 min in females and 42.0–51.4 min in males (Hindell et al., 1992). This is the estimated dive duration after which a net increase in lactate production is expected to occur as a result of the exhaustion of oxygen stores and a shift to anaerobic respiration in some tissues (Kooyman et al., 1983). The key word here is ‘estimated’. There is very little information on how metabolic rate varies in seals diving at sea. Most dives performed by southern elephant seals are within their predicted ADL and show considerable variability in both depth and duration. This behavioural variability in dive duration may reflect the availability and distribution of prey and immediate foraging success (McConnell et al., 1992; Jonker and Bester, 1994). Elephant seals frequently perform dives approaching and even in excess of their estimated ADL. Because these dives are rarely followed by extended surface intervals or short aerobic processing dives to eliminate lactate, elephant seals appear to rely on aerobic pathways of metabolism while submerged (Hindell et al., 1992; Fedak and Thompson, 1993). The disparity between theoretical predictions and empirical ... |
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