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Sato, K, Shiomi K, Watanabe Y, Watanuki Y, Takahashi A, Ponganis PJ.  2010.  Scaling of swim speed and stroke frequency in geometrically similar penguins: they swim optimally to minimize cost of transport. Proceedings of the Royal Society B-Biological Sciences. 277:707-714.   10.1098/rspb.2009.1515   AbstractWebsite

It has been predicted that geometrically similar animals would swim at the same speed with stroke frequency scaling with mass(-1/3). In the present study, morphological and behavioural data obtained from free-ranging penguins (seven species) were compared. Morphological measurements support the geometrical similarity. However, cruising speeds of 1.8-2.3 m s(-1) were significantly related to mass(0.08) and stroke frequencies were proportional to mass(-0.29). These scaling relationships do not agree with the previous predictions for geometrically similar animals. We propose a theoretical model, considering metabolic cost, work against mechanical forces (drag and buoyancy), pitch angle and dive depth. This new model predicts that: (i) the optimal swim speed, which minimizes the energy cost of transport, is proportional to (basal metabolic rate/drag)(1/3) independent of buoyancy, pitch angle and dive depth; (ii) the optimal speed is related to mass(0.05); and (iii) stroke frequency is proportional to mass(-0.28). The observed scaling relationships of penguins support these predictions, which suggest that breath-hold divers swam optimally to minimize the cost of transport, including mechanical and metabolic energy during dive.

Sato, K, Watanuki Y, Takahashi A, Miller PJO, Tanaka H, Kawabe R, Ponganis PJ, Handrich Y, Akamatsu T, Watanabe Y, Mitani Y, Costa DP, Bost CA, Aoki K, Amano M, Trathan P, Shapiro A, Naito Y.  2007.  Stroke frequency, but not swimming speed, is related to body size in free-ranging seabirds, pinnipeds and cetaceans. Proceedings of the Royal Society B-Biological Sciences. 274:471-477.   10.1098/rspb.2006.0005   AbstractWebsite

It is obvious, at least qualitatively, that small animals move their locomotory apparatus faster than large animals: small insects move their wings invisibly fast, while large birds flap their wings slowly. However, quantitative observations have been difficult to obtain from free-ranging swimming animals. We surveyed the swimming behaviour of animals ranging from 0.5 kg seabirds to 30 000 kg sperm whales using animal-borne accelerometers. Dominant stroke cycle frequencies of swimming specialist seabirds and marine mammals were proportional to mass(-0.29) (R-2=0.99, n=17 groups), while propulsive swimming speeds of 1-2 m s(-1) were independent of body size. This scaling relationship, obtained from breath-hold divers expected to swim optimally to conserve oxygen, does not agree with recent theoretical predictions for optimal swimming. Seabirds that use their wings for both swimming and flying stroked at a lower frequency than other swimming specialists of the same size, suggesting a morphological trade-off with wing size and stroke frequency representing a compromise. In contrast, foot-propelled diving birds such as shags had similar stroke frequencies as other swimming specialists. These results suggest that muscle characteristics may constrain swimming during cruising travel, with convergence among diving specialists in the proportions and contraction rates of propulsive muscles.

Sato, K, Shiomi K, Marshall G, Kooyman GL, Ponganis PJ.  2011.  Stroke rates and diving air volumes of emperor penguins: implications for dive performance. Journal of Experimental Biology. 214:2854-2863.   10.1242/jeb.055723   AbstractWebsite

Emperor 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.

Sato, K, Ponganis PJ, Habara Y, Naito Y.  2005.  Emperor penguins adjust swim speed according to the above-water height of ice holes through which they exit. Journal of Experimental Biology. 208:2549-2554.   10.1242/jeb.01665   AbstractWebsite

Emperor penguins leap from the water onto the sea ice. Their ability to reach above-water height depends critically on initial vertical speed of their leaping, assuming that the kinetic energy is converted to gravitational potential energy. We deliberately changed the above-water heights of ice hole exits, in order to examine whether penguins adjusted swim speed in accordance with the above-water height of the ice. Penguins were maintained in a corral on the fast ice in Antarctica, and voluntarily dived through two artificial ice holes. Data loggers were deployed on the penguins to monitor under water behavior. Nine instrumented penguins performed 386 leaps from the holes during experiments. The maximum swim speeds within 1 s before the exits through the holes correlated significantly with the above-water height of the holes. Penguins adopted higher speed to exit through the higher holes than through the lower holes. Speeds of some failed exits were lower than the theoretical minimum values to reach a given height. Penguins failed to exit onto the sea ice in a total of 37 of the trials. There was no preference to use lower holes after they failed to exit through the higher holes. Rather, swim speed was increased for subsequent attempts after failed leaps. These data demonstrated that penguins apparently recognized the above-water height of holes and adopted speeds greater than the minimal vertical speeds to reach the exit height. It is likely, especially in the case of higher holes (>40 cm), that they chose minimum speeds to exit through the holes to avoid excess energy for swimming before leaping. However, some exceptionally high speeds were recorded when they directly exited onto the ice from lower depths. In those cases, birds could increase swim speed without strokes for the final seconds before exit and they only increased the steepness of their body angles as they surfaced, which indicates that the speed required for leaps by emperor penguins were aided by buoyancy, and that penguins can sometimes exit through the ice holes without any stroking effort before leaping.

Shiomi, K, Sato K, Ponganis PJ.  2012.  Point of no return in diving emperor penguins: is the timing of the decision to return limited by the number of strokes? Journal of Experimental Biology. 215:135-140.   10.1242/jeb.064568   AbstractWebsite

At some point in a dive, breath-hold divers must decide to return to the surface to breathe. The issue of when to end a dive has been discussed intensively in terms of foraging ecology and behavioral physiology, using dive duration as a temporal parameter. Inevitably, however, a time lag exists between the decision of animals to start returning to the surface and the end of the dive, especially in deep dives. In the present study, we examined the decision time in emperor penguins under two different conditions: during foraging trips at sea and during dives at an artificial isolated dive hole. It was found that there was an upper limit for the decision-to-return time irrespective of dive depth in birds diving at sea. However, in a large proportion of dives at the isolated dive hole, the decision-to-return time exceeded the upper limit at sea. This difference between the decision times in dives at sea versus the isolated dive hole was accounted for by a difference in stroke rate. The stroke rates were much lower in dives at the isolated hole and were inversely correlated with the upper limit of decision times in individual birds. Unlike the decision time to start returning, the cumulative number of strokes at the decision time fell within a similar range in the two experiments. This finding suggests that the number of strokes, but not elapsed time, constrained the decision of emperor penguins to return to the surface. While the decision to return and to end a dive may be determined by a variety of ecological, behavioral and physiological factors, the upper limit to that decision time may be related to cumulative muscle workload.

Shiomi, K, Narazaki T, Sato K, Shimatani K, Arai N, Ponganis PJ, Miyazaki N.  2010.  Data-processing artefacts in three-dimensional dive path reconstruction from geomagnetic and acceleration data. Aquatic Biology. 8:299-304.   10.3354/ab00239   AbstractWebsite

Tri-axis magnetism and acceleration data loggers have recently been used to obtain time-series headings and, consequently, the 3-dimensional dive paths of aquatic animals. However, problems may arise in the resulting calculation process with multiple parameters. In this study, the dive paths of loggerhead turtles and emperor penguins were reconstructed. For both species, apparently unrealistic movements were found. Time-series heading data of turtles showed small regular fluctuations synchronous with stroking. In the dive paths of penguins, infrequent abrupt changes in heading were observed during stroke cycles. These were unlikely to represent true behaviours according to observations of underwater behaviour and tri-axis magnetism and acceleration data. Based on the relationship between sampling frequency and frequency of body posture change, we suggest that (1) the changes in the animals' posture concurrent with strokes and (2) the mismatched treatment (i.e. filtering and non-filtering) of the acceleration and magnetism data caused the artefacts. These inferences are supported by the results of simulations. For data sets obtained at a given sampling frequency, the error pattern in calculated dive paths is likely to differ depending on the frequency and amplitude of body posture changes and in swim speed. In order to avoid misinterpretation, it is necessary to understand the assumptions and inherent problems of the calculation methods as well as the behavioural characteristics of the study animals.

Shiomi, K, Sato K, Mitamura H, Arai N, Naito Y, Ponganis PJ.  2008.  Effect of ocean current on the dead-reckoning estimation of 3-D dive paths of emperor penguins. Aquatic Biology. 3:265-270.   10.3354/ab00087   AbstractWebsite

The dead-reckoning technique is a useful method for obtaining 3-D movement data of aquatic animals. However, such positional data include an accumulative error. Understanding the source of the error is important for proper data interpretation. In order to determine whether ocean currents affect dive paths calculated by dead-reckoning, as has previously been hypothesized, we examined the directions of the estimated positions relative to the known real points (error direction) and the relationship between the error direction and the current direction. 3-D dive paths of emperor penguins Aptenodytes forsteri diving at isolated dive holes in eastern McMurdo Sound were reconstructed by dead-reckoning, and the net error and error direction were calculated. The net error correlated positively with the dive duration. The error directions were not distributed uniformly, and the mean error direction tended to be north of the starting point of dives. Because there was a southward-flowing current in eastern McMurdo Sound, the ocean current was likely to affect the calculated dive paths. Therefore, the method of error correction generally used, in which the net error divided by the dive duration is applied to each estimated position, is realistically appropriate, provided that the current does not change significantly during a dive.

Spragg, RG, Ponganis PJ, Marsh JJ, Rau GA, Bernhard W.  2004.  Surfactant from diving aquatic mammals. Journal of Applied Physiology. 96:1626-1632.   10.1152/japplphysiol.00898.2003   AbstractWebsite

Diving mammals that descend to depths of 50 - 70 m or greater fully collapse the gas exchanging portions of their lungs and then reexpand these areas with ascent. To investigate whether these animals may have evolved a uniquely developed surfactant system to facilitate repetitive alveolar collapse and expansion, we have analyzed surfactant in bronchoalveolar lavage fluid (BAL) obtained from nine pinnipeds and from pigs and humans. In contrast to BAL from terrestrial mammals, BAL from pinnipeds has a higher concentration of phospholipid and relatively more fluidic phosphatidylcholine molecular species, perhaps to facilitate rapid spreading during alveolar reexpansion. Normalized concentrations of hydrophobic surfactant proteins B and C were not significantly different among pinnipeds and terrestrial mammals by immunologic assay, but separation of proteins by gel electrophoresis indicated a greater content of surfactant protein B in elephant seal surfactant than in human surfactant. Remarkably, surfactant from the deepest diving pinnipeds produced moderately elevated in vitro minimum surface tension measurements, a finding not explained by the presence of protein or neutral lipid inhibitors. Further study of the composition and function of pinniped surfactants may contribute to the design of optimized therapeutic surfactants.

Stockard, TK, Levenson DH, Berg L, Fransioli JR, Baranov EA, Ponganis PJ.  2007.  Blood oxygen depletion during rest-associated apneas of northern elephant seals (Mirounga angustirostris). Journal of Experimental Biology. 210:2607-2617.   10.1242/jeb.008078   AbstractWebsite

Blood gases (P-O2, P-CO2, pH), oxygen content, hematocrit and hemoglobin concentration were measured during rest-associated apneas of nine juvenile northern elephant seals. In conjunction with blood volume determinations, these data were used to determine total blood oxygen stores, the rate and magnitude of blood O-2 depletion, the contribution of the blood O-2 store to apneic metabolic rate, and the egree of hypoxemia that occurs during these breath-holds. Mean body mass was 66 +/- 9.7 kg (+/- s.d.); blood volume was 196 +/- 20 ml kg(-1); and hemoglobin concentration was 23.5 +/- 1.5 g dl(-1). Rest apneas ranged in duration from 3.1 to 10.9 min. Arterial P-O2 declined exponentially during apnea, ranging between a maximum of 108 mmHg and a minimum of 18 mmHg after a 9.1 min breath-hold. Venous P-O2 values were indistinguishable from arterial values after the first minute of apnea; the lowest venous P-O2 recorded was 15 mmHg after a 7.8 min apnea. O-2 contents were also similar between the arterial and venous systems, declining linearly at rates of 2.3 and 2.0 ml O-2 dl(-1) min (-1), respectively, from mean initial values of 27.2 and 26.0 ml O-2 dl(-1). These blood O-2 depletion rates are approximately twice the reported values during forced submersion and are consistent with maintenance of previously measured high cardiac outputs during rest-associated breath-holds. During a typical 7-min apnea, seals consumed, on average, 56% of the initial blood O-2 store of 52 ml O-2 kg(-1); this contributed 4.2 ml O-2 kg(-1) min(-1) to total body metabolic rate during the breath-hold. Extreme hypoxemic tolerance in these seals was demonstrated by arterial P-O2 values during late apnea that were less than human thresholds for shallow-water blackout. Despite such low P-O2s, there was no evidence of significant anaerobic metabolism, as changes in blood pH were minimal and attributable to increased P-CO2. These findings and the previously reported lack of lactate accumulation during these breath- holds are consistent with the maintenance of aerobic metabolism even at low oxygen tensions during rest- associated apneas. Such hypoxemic tolerance is necessary in order to allow dissociation of O-2 from hemoglobin and provide effective utilization of the blood O-2 store.