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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.

Van Dam, RP, Ponganis PJ, Ponganis KV, Levenson DH, Marshall G.  2002.  Stroke frequencies of emperor penguins diving under sea ice. Journal of Experimental Biology. 205:3769-3774. AbstractWebsite

During diving, intermittent swim stroke patterns, ranging from burst/coast locomotion to prolonged gliding, represent potential energy conservation mechanisms that could extend the duration of aerobic metabolism and, hence, increase the aerobic dive limit (ADL, dive duration associated with onset of lactate accumulation). A 5.6 min ADL for emperor penguins had been previously determined with lactate measurements after dives of <50 m depth. In order to assess locomotory patterns during such dives, longitudinal acceleration was measured with an attached accelerometer in 44 dives of seven adult birds diving from an isolated dive hole in the sea ice of McMurdo Sound, Antarctica. Detection of wing strokes in processed accelerometer data was verified in selected birds with analysis of simultaneous Crittercam underwater video footage. Mean dive duration of birds equipped with the accelerometer and a time-depth recorder (TDR) was 5.7+/-2.2 min; 48% of these dives were greater than the measured 5.6 min ADL (ADL(M)). Highest stroke frequencies (0.92+/-0.31Hz, N=981) occurred during the initial descent to 12 m depth. Swimming effort was reduced to a mean stroke frequency <0.70 Hz during other phases of the dive (while traveling below 12 m depth, during foraging ascents/descents to and from the sub-ice surface, and during final ascents to exit). The longest stroke interval (8.6 s) occurred during a feeding excursion to the undersurface of the ice. In dives >ADL(M), mean stroke frequency during travel segments was significantly less than that in dives 10 s) periods of prolonged gliding during these shallow (<60 m) foraging dives. However, a stroke/glide pattern was evident with more than 50% of strokes associated with a stroke interval >1.6 s, and with lower stroke frequency associated with increased dive duration.

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.

Ponganis, PJ, Costello ML, Starke LN, MathieuCostello O, Kooyman GL.  1997.  Structural and biochemical characteristics of locomotory muscles of emperor penguins, Aptenodytes forsteri. Respiration Physiology. 109:73-80.   10.1016/s0034-5687(97)84031-5   AbstractWebsite

Structural and biochemical characteristics of the primary muscles used for swimming (pectoralis, PEC and supracoracoideus, SC) were compared to those of leg muscles in emperor penguins (Aptenodytes forsteri). The mass of PEG-SC was four times that of the leg musculature, and mitochondrial volume density in PEC and SC (4%) was two-thirds that in sartorius (S) and gastrocnemius. The differences in muscle mass and mitochondrial density yielded a 2.2-fold greater total mitochondrial content in PEG-SC than leg muscles, which appears to account for the 1.8-fold greater whole-body highest oxygen consumption previously recorded in emperor penguins during swimming compared to walking. Calculation of maximal mitochondrial O-2 consumption in PEG-SC and leg muscle yielded values of 5.8-6.9 mi O-2 ml(-1) min(-1), which are similar to those in locomotory muscles of most mammals and birds. A distinct feature of emperor penguin muscle was its myoglobin content, with concentrations in PEG-SC (6.4 g 100 g(-1)) among the highest measured in any species. This resulted in a PEG-SC O-2 store greater than that of the entire blood. In addition, ratios of myoglobin content to mitochondrial volume density and to citrate synthase activity were 4.4 and 2.5 times greater in PEG than in S, indicative of the significant role of myoglobin in the adaptation of muscle to cardiovascular adjustments during diving. (C) 1997 Elsevier Science B.V.

Ponganis, PJ, Van Dam RP, Marshall G, Knower T, Levenson DH.  2000.  Sub-ice foraging behavior of emperor penguins. Journal of Experimental Biology. 203:3275-3278. AbstractWebsite

Emperor penguins (Aptenodytes forsteri) were equipped with a remote underwater video camera, the Crittercam, to evaluate sub-ice foraging behavior while the birds dived from an isolated dive hole. Three birds dived and foraged successfully for Ih periods after being trained to wear and to dive with a harness for camera attachment. Video and depth profile recordings revealed that emperor penguins travel at shallow depths (<50 m), ascend to the undersurface of the ice to feed on fish, and descend back to depth to return to the exit hole. Although the mean durations of dives of individual birds with the Crittercam were 21-35 % shorter than the diving durations of these same birds without the camera, the dive profiles in both situations were similar, thus demonstrating a similar foraging strategy in birds diving without the camera. Despite shorter diving durations with the camera, the penguins were still successful at prey capture in 80 % of 91 dives greater than 1 min in duration. Prey included the sub-ice fish Pagothenia borchgrevinki. Hunting ascents (from depth to within 5 m of the surface) occurred in 85 % of dives, ranged from zero to three per dive, and were associated with successful prey capture in 77 % of 128 ascents, Occasionally, several fish were captured during a single ascent, These observations and this application of video technology create a model for further physiological and behavioral studies of foraging, and also emphasize the potential importance of shallow dives as sources of food intake for emperor penguins during foraging trips to sea.

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.

Ponganis, PJ, Ponganis EP, Ponganis KV, Kooyman GL, Gentry RL, Trillmich F.  1990.  Swimming velocities in otariids. Canadian Journal of Zoology-Revue Canadienne De Zoologie. 68:2105-2112.   10.1139/z90-293   AbstractWebsite

Velocities during surface swimming and diving were measured with microprocessor recorders in four otariid species: northern fur seals (Callorhinusursinus), Galapagos sea lions (Zalophuscalifornianuswollebaeki), Galapagos fur seals (Arctocephalusgalapagoensis), and Hooker's sea lions (Phocarctoshookeri). Mean surface swimming velocities ranged from 0.6 to 1.9 m/s. Transit distances to feeding sites (1.2–90 km) were calculated using these velocities. Dive velocities, recorded every 15 s, ranged from 0.9 to 1.9 m/s. These velocities were consistent with calculated minimal cost of transport velocities in the smaller species. Using time partitioning, the metabolic cost of a northern fur seal foraging trip is estimated on the basis of recorded velocities and their calculated energy costs. This value is within 6% of that previously made with doubly labeled water techniques.