Stroke rates and diving air volumes of emperor penguins: implications for dive performance

Abstract

SUMMARYEmperor penguins (Aptenodytes forsteri), both at sea and at an experimental dive hole, often have minimal surface periods even after performance of dives far beyond their measured 5.6min aerobic dive limit (ADL: dive duration associated with the onset of post-dive blood lactate accumulation). Accelerometer-based data loggers were attached to emperor penguins diving in these two different situations to further evaluate the capacity of these birds to perform such dives without any apparent prolonged recovery periods. Minimum surface intervals for dives as long as 10min were less than 1min at both sites. Stroke rates for dives at sea were significantly greater than those for dives at the isolated dive hole. Calculated diving air volumes at sea were variable, increased with maximum depth of dive to a depth of 250m, and decreased for deeper dives. It is hypothesized that lower air volumes for the deepest dives are the result of exhalation of air underwater. Mean maximal air volumes for deep dives at sea were approximately 83% greater than those during shallow (<50m) dives. We conclude that (a) dives beyond the 5.6min ADL do not always require prolongation of surface intervals in emperor penguins, (b) stroke rate at sea is greater than at the isolated dive hole and, therefore, a reduction in muscle stroke rate does not extend the duration of aerobic metabolism during dives at sea, and (c) a larger diving air volume facilitates performance of deep dives by increasing the total body O 2 store to 68ml O 2 kg -1 . Although increased O 2 storage and cardiovascular adjustments presumably optimize aerobic metabolism during dives, enhanced anaerobic capacity and hypoxemic tolerance are also essential for longer dives. This was exemplified by a 27.6min dive, after which the bird required 6min before it stood up from a prone position, another 20min before it began to walk, and 8.4h before it dived again.

Flipper stroke rate and venous oxygen levels in free-ranging California sea lions

“…Interestingly, elephant seals also began prolonged glides during deep dives at approximately 60 m depth (Davis et al, 2001). The gliding pattern seen on the ascent phase of sea lions has also been documented in other marine mammals and diving birds, and was suggested to be influenced by respiratory air volume (Sato et al, 2011;Watanuki et al, 2006;Williams et al, 2000). Ascent glides in sea lions are likely secondary to increased buoyancy near the surface owing to lung re-expansion during ascent.…”

“…The resulting dynamic acceleration was then analyzed using power spectral density analysis to identify the dominant frequency of a stroke for each individual animal (approximately 0.8-1.2 strokes s −1 ). A peak detection algorithm, similar to those in other studies (Jeanniard-du-Dot et al, 2016;Sato et al, 2011), was used to identify flipper strokes. A single flipper stroke was identified when there was a prominent acceleration peak (≥0.4-0.5 m s −2 ) in the x-axis ('forward surge') or z-axis ('heave surge') ( Fig.…”

Regional variability in diving physiology and behavior in a widely distributed air-breathing marine predator, the South American sea lionOtaria byronia

“…Instead, some of the deepest diving air breathers (e.g. beaked whales, elephant seals and emperor penguins) are medium-sized vertebrates (Hindell et al, 1992;Sato et al, 2011;Schorr et al, 2014). Furthermore, it has been proposed that despite its positive effect on body oxygen stores, large body size might actually be disadvantageous for otariids given their high absolute metabolic rate (i.e.…”

Point of no return in diving emperor penguins: is the timing of the decision to return limited by the number of strokes?

“…These are the same data as used in our previous papers (Sato et al, 2011;Shiomi et al, 2008 (Shiomi et al, 2008). VHF transmitters (Model MM130, ATS, Isanti, MN, USA) were also deployed on all the birds at sea to locate them when they returned to the dense colony.…”

“…Emperor penguins (Aptenodytes forsteri Gray 1844) are consummate avian divers, which have been reported to dive deeper than 550m (Wienecke et al, 2007) and for longer than 27min (Sato et al, 2011). In deep dives, the time lag between the decision to return the surface and the end of a dive is inevitably long and, therefore, examination of dive duration alone may not be sufficient to understand their diving strategies.…”