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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, McDonald BI, Tift MS, Williams CL.  2017.  Heart rate regulation in diving sea lions: the vagus nerve rules. Journal of Experimental Biology. 220:1372-1381.   10.1242/jeb.146779   AbstractWebsite

Recent publications have emphasized the potential generation of morbid cardiac arrhythmias secondary to autonomic conflict in diving marine mammals. Such conflict, as typified by cardiovascular responses to cold water immersion in humans, has been proposed to result from exercise-related activation of cardiac sympathetic fibers to increase heart rate, combined with depth-related changes in parasympathetic tone to decrease heart rate. After reviewing the marine mammal literature and evaluating heart rate profiles of diving California sea lions (Zalophus californianus), we present an alternative interpretation of heart rate regulation that de-emphasizes the concept of autonomic conflict and the risk of morbid arrhythmias in marine mammals. We hypothesize that: (1) both the sympathetic cardiac accelerator fibers and the peripheral sympathetic vasomotor fibers are activated during dives even without exercise, and their activities are elevated at the lowest heart rates in a dive when vasoconstriction is maximal, (2) in diving animals, parasympathetic cardiac tone via the vagus nerve dominates over sympathetic cardiac tone during all phases of the dive, thus producing the bradycardia, (3) adjustment in vagal activity, which may be affected by many inputs, including exercise, is the primary regulator of heart rate and heart rate fluctuations during diving, and (4) heart beat fluctuations (benign arrhythmias) are common in marine mammals. Consistent with the literature and with these hypotheses, we believe that the generation of morbid arrhythmias because of exercise or stress during dives is unlikely in marine mammals.

Ponganis, PJ, Gentry RL, Ponganis EP, Ponganis K.  1989.  Analysis of swimming velocity in deep and shallow dives of two northern fur seals, Callorhinus ursinus. Proceedings of the Eighth Biennial Conference on the Biology of Marine Mammals. , Pacific Grove, Calif. Abstract
Ponganis, PJ.  2007.  Bio-logging of physiological parameters in higher marine vertebrates. Deep-Sea Research Part Ii-Topical Studies in Oceanography. 54:183-192.   10.1016/j.dsr2.2006.11.009   AbstractWebsite

Bio-logging of physiological parameters in higher marine vertebrates had its origins in the field of bio-telemetry in the 1960s and 1970s. The development of microprocessor technology allowed its first application to bio-logging investigations of Weddell seal diving physiology in the early 1980s. Since that time, with the use of increased memory capacity, new sensor technology, and novel data processing techniques, investigators have examined heart rate, temperature, swim speed, stroke frequency, stomach function (gastric pH and motility), heat flux, muscle oxygenation, respiratory rate, diving air volume, and oxygen partial pressure (PO(2)) during diving. Swim speed, heart rate, and body temperature have been the most commonly studied parameters. Bio-logging investigation of pressure effects has only been conducted with the use of blood samplers and nitrogen analyses on animals diving at isolated dive holes. The advantages/disadvantages and limitations of recording techniques, probe placement, calibration techniques, and study conditions are reviewed. (c) 2007 Elsevier Ltd. All rights reserved.

Ponganis, PJ, Kooyman GL.  2000.  Diving physiology of birds: a history of studies on polar species. Comparative Biochemistry and Physiology a-Molecular and Integrative Physiology. 126:143-151.   10.1016/s1095-6433(00)00208-7   AbstractWebsite

Our knowledge of avian diving physiology has been based primarily on research with polar species. Since Scholander's 1940 monograph, research has expanded from examination of the 'diving reflex' to studies of free-diving birds, and has included laboratory investigations of oxygen stores, muscle adaptations, pressure effects, and cardiovascular/metabolic responses to swimming exercise. Behavioral and energetic studies at sea have shown that common diving durations of many avian species exceed the calculated aerobic diving limits (ADL). Current physiological research is focused on factors, such as heart rate and temperature, which potentially affect the diving metabolic rate and duration of aerobic diving. (C) 2000 Elsevier Science Inc. All rights reserved.

Ponganis, PJ, Kooyman GL, Castellini MA.  1993.  Determinants of the aerobic dive limit of Weddell seals: analysis of diving metabolic rates, postdive end tidal PO2's, and blood and muscle oxygen stores. Physiological Zoology. 66:732-749. AbstractWebsite

The mean aerobic dive limit (ADL) for Weddell seals was calculated from data collected on diving metabolic rates (VO2) and blood and muscle O2 stores. Mean diving VO2 of adult seals during predominantly exploratory dive patterns was 4.5 mL O2 kg-1 min-1; mean VO2 of a subadult seal engaged in foraging dive bouts was 8.5 mL O2 kg-1 min-1. The adult value was 30% greater than that used in past ADL calculations. Mean plasma volume was 7% body mass (BM); blood volume calculated with the highest hematocrit (Hct) observed (66) was 21% BM. Hemoglobin concentration at such an Hct was 26% by weight. End tidal PO2 (pre- and postdive) justified the use of 95% and 20% arterial O2 saturations in the blood O2 store calculation. Total blood O2 stores were 50% greater than those used in past ADL calculations. Mean myoglobin concentration (5.4% by weight) and more recent anatomical estimates of muscle mass yielded a 35% increase in muscle O2 stores. The mean estimated ADL for a 450-kg seal calculated with these new data was 19.1 min, 2.3 min greater than in past calculations and only 1 min less than the 20-min inflection point of the curve of dive duration versus postdive lactic acid appearance. For the subadult engaged in foraging dives, the mean estimated ADL was about 9 min, again quite similar to past ADL calculations.

Ponganis, PJ.  2011.  Diving Mammals. Comprehensive Physiology. 1: John Wiley & Sons, Inc.   10.1002/cphy.c091003   AbstractWebsite

The ability of diving mammals to forage at depth on a breath hold of air is dependent on gas exchange, both in the lung and in peripheral tissues. Anatomical and physiological adaptations in the respiratory system, cardiovascular system, blood and peripheral tissues contribute to the remarkable breath-hold capacities of these animals. The end results of these adaptations include efficient ventilation, enhanced oxygen storage, regulated transport and delivery of respiratory gases, extreme hypoxemic/ischemic tolerance, and pressure tolerance. © 2011 American Physiological Society. Compr Physiol 1:447-465, 2011.

Ponganis, PJ, van Dam RP, Knower T, Levenson DH, Ponganis KV.  2004.  Deep dives and aortic temperatures of emperor penguins: new directions for bio-logging at the isolated dive hole. Memoirs of National Institute of Polar Research Special Issue. 58:155-161. AbstractWebsite
Ponganis, PJ, Kooyman GL.  1999.  Heart rate and electrocardiogram characteristics of a young California gray whale (Eschrichtius robustus). Marine Mammal Science. 15:1198-1207.   10.1111/j.1748-7692.1999.tb00885.x   AbstractWebsite

Electrocardiogram (ECG) analyses of Holter monitor recordings from a young California gray whale were performed to determine ECG waveform characteristics, evaluate the heart rate pattern for sinus arrhythmia, obtain resting heart rates at known body masses as the whale increased in size, and compare those heart rates with predicted heart rates from allometric equations. The PR and QRS intervals (475 +/- 35 msec, 208 +/- 24 msec, respectively, n = 20) support the concept (Meijler et al. 1992) that atrioventricular transmission and ventricular excitation times do not increase linearly in very large mammals. A sinus arrhythmia pattern at rest (apneic heart rates of 15-25 beats per min [bpm] and eupneic heart rates of 34-40 bpm) is consistent with a relative eupneic tachycardia and apneic bradycardia during diving activity of whales. The heart rate-body mass measurements (35-24 bpm at body masses of 3,531-8,200 kg) in this study (1) extend the range of allometric heart rate and body mass data in mammals a full order of magnitude, to almost 10,000 kg, (2) support the use of allometric equations (based primarily on mammals <1,000 kg in body mass) in estimating resting heart rates in whales, and (3) demonstrate that previously reported heart rates in large whales are not representative of resting heart rate, probably secondary to circumstances during measurement.

Ponganis, PJ, Kooyman GL, Zornow MH.  1991.  Cardiac output in swimming California sea lions, Zalophus californianus. Physiological Zoology. 64:1296-1306. AbstractWebsite

Cardiac output was determined by the thermodilution technique in three California sea lions while resting and while swimming. Metabolic rates increased seven-to ninefold above resting rates during maximal exercise. While the sea lions were at rest, stroke volume was also determined by simultaneously counting heart rate during cardiac output determinations. At rest, cardiac output (2.5-3.0 mL kg-1s-1) and stroke volume (2 mL kg-1) were similar to those of harbor seals and terrestrial mammals of similar mass. During exercise, mean cardiac output increased linearly with work load and surface/submerged intervals were short and frequent. The exercise capacity of swimming sea lions appears similar to that of harbor seals, but the exercise response resembles that of terrestrial mammals more than that of harbor seals.

Ponganis, PJ, Stockard TK, Meir JU, Williams CL, Ponganis KV, Howard R.  2009.  O-2 store management in diving emperor penguins. Journal of Experimental Biology. 212:217-224.   10.1242/jeb.026096   AbstractWebsite

In order to further define O-2 store utilization during dives and understand the physiological basis of the aerobic dive limit (ADL, dive duration associated with the onset of post-dive blood lactate accumulation), emperor penguins (Aptenodytes forsteri) were equipped with either a blood partial pressure of oxygen (P-O2) recorder or a blood sampler while they were diving at an isolated dive hole in the sea ice of McMurdo Sound, Antarctica. Arterial P-O2 profiles (57 dives) revealed that (a) pre-dive P-O2 was greater than that at rest, (b) P-O2 transiently increased during descent and (c) post-dive P-O2 reached that at rest in 1.92 +/- 1.89 min (N=53). Venous P-O2 profiles (130 dives) revealed that (a) pre-dive venous P-O2 was greater than that at rest prior to 61% of dives, (b) in 90% of dives venous P-O2 transiently increased with a mean maximum P-O2 of 53 +/- 18 mmHg and a mean increase in P-O2 of 11 +/- 12 mmHg, (c) in 78% of dives, this peak venous P-O2 occurred within the first 3 min, and (d) post-dive venous P-O2 reached that at rest within 2.23 +/- 2.64 min (N=84). Arterial and venous P-O2 values in blood samples collected 1-3 min into dives were greater than or near to the respective values at rest. Blood lactate concentration was less than 2 mmol l(-1) as far as 10.5 min into dives, well beyond the known ADL of 5.6 min. Mean arterial and venous P-N2 of samples collected at 20-37 m depth were 2.5 times those at the surface, both being 2.1 +/- 0.7 atmospheres absolute (ATA; N=3 each), and were not significantly different. These findings are consistent with the maintenance of gas exchange during dives (elevated arterial and venous P-O2 and P-N2 during dives), muscle ischemia during dives (elevated venous P-O2, lack of lactate washout into blood during dives), and arterio-venous shunting of blood both during the surface period (venous P-O2 greater than that at rest) and during dives (arterialized venous P-O2 values during descent, equivalent arterial and venous P-N2 values during dives). These three physiological processes contribute to the transfer of the large respiratory O-2 store to the blood during the dive, isolation of muscle metabolism from the circulation during the dive, a decreased rate of blood O-2 depletion during dives, and optimized loading of O-2 stores both before and after dives. The lack of blood O-2 depletion and blood lactate elevation during dives beyond the ADL suggests that active locomotory muscle is the site of tissue lactate accumulation that results in post-dive blood lactate elevation in dives beyond the ADL.

Ponganis, PJ, Kreutzer U, Sailasuta N, Knower T, Hurd R, Jue T.  2002.  Detection of myoglobin desaturation in Mirounga angustirostris during apnea. American Journal of Physiology-Regulatory Integrative and Comparative Physiology. 282:R267-R272. AbstractWebsite

H-1 NMR solution-state study of elephant seal (Mirounga angustirostris) myoglobin (Mb) and hemoglobin (Hb) establishes the temperature-dependent chemical shifts of the proximal histidyl NdeltaH signal, which reflects the respective intracellular and vascular PO2 in vivo. Both proteins exist predominantly in one major isoform and do not exhibit any conformational heterogeneity. The Mb and Hb signals are detectable in M. angustirostris tissue in vivo. During eupnea M. angustirostris muscle maintains a well-saturated MbO(2). However, during apnea, the deoxymyoglobin proximal histidyl NdeltaH signal becomes visible, reflecting a declining tissue PO2. The study establishes a firm methodological basis for using NMR to investigate the metabolic responses during sleep apnea of the elephant seal and to secure insights into oxygen regulation in diving mammals.

Ponganis, PJ, Kooyman GL, Baranov EA, Thorson PH, Stewart BS.  1997.  The aerobic submersion limit of Baikal seals, Phoca sibirica. Canadian Journal of Zoology-Revue Canadienne De Zoologie. 75:1323-1327.   10.1139/z97-756   AbstractWebsite

An aerobic dive limit (ADL), the diving duration beyond which postdive lactate concentration increases above the resting level, has been estimated theoretically for many species. Such calculations have been based on an oxygen store/diving metabolic rate (MR) equation. Until now, an ADL has been determined empirically from measurements of blood lactate concentration only in the Weddell seal, Leptonychotes weddellii. We measured post-submergence plasma lactate concentrations during spontaneous voluntary submersions of three captive adult Baikal seals (Phoca sibirica). Two-phase regression analysis revealed a transition in the lactate concentration - submersion duration relationship after the animal had been diving for 15 min. Data collected in prior studies on oxygen stores and submersion metabolic rates of Baikal seals yielded a calculated aerobic limit of 16 min. As in Weddell seals, the empirically determined aerobic limit was very similar to the theoretical limit. Furthermore, most diving durations recorded during recent studies of free-ranging Baikal seals are under this limit. These data support the concept of an ADL and its estimation by means of an oxygen store/diving MR calculation.

Ponganis, PJ, McDonald BI, Tift MS, Gonzalez SC, DaValle B, Gliniecki RA, Stehman CC, Hauff N, Ruddick B, Howard R.  2017.  Effects of inhalational anesthesia on blood gases and pH in California sea lions. Marine Mammal Science. 33:726-737.   10.1111/mms.12388   AbstractWebsite

Despite the widespread use of inhalational anesthesia with spontaneous ventilation in many studies of otariid pinnipeds, the effects and risks of anesthetic-induced respiratory depression on blood gas and pH regulation are unknown in these animals. During such anesthesia in California sea lions (Zalophus californianus), blood gas and pH analyses of opportunistic blood samples revealed routine hypercarbia (highest P-CO2 = 128 mm Hg [17.1 kPa]), but adequate arterial oxygenation (P-O2 > 100 mm Hg [13.3 kPa] on 100% inspiratory oxygen). Respiratory acidosis (lowest pH = 7.05) was limited by the increased buffering capacity of sea lion blood. Amarkedly widened alveolar-to-arterial P-O2 difference was indicative of atelectasis and ventilation-perfusion mismatch in the lung secondary to hypoventilation during anesthesia. Despite the generally safe track record of this anesthetic regimen in the past, these findings demonstrate the value of high inspiratory O-2 concentrations and the necessity of constant vigilance and caution. In order to avoid hypoxemia, we emphasize the importance of late extubation or at least maintenance of mask ventilation on O-2 until anesthetic-induced respiratory depression is resolved. In this regard, whether for planned or emergency application, we also describe a simple, easily employed intubation technique with the Casper zalophoscope for sea lions.

Ponganis, PJ, Kooyman GL.  1990.  Diving physiology of penguins. Acta XX Congressus Internationalis Ornithologici, Christchurch, New Zealand, 2-9 December 1990. ( Butler PJ, Jones DR, Eds.).:6., Wellington, N.Z.: New Zealand Ornithological Congress Trust Board Abstract
Ponganis, PJ, Stockard TK.  2007.  The Antarctic toothfish: how common a prey for Weddell seals? Antarctic Science. 19:441-442.   10.1017/s0954102007000715   AbstractWebsite

The Antarctic toothfish (Dissostichus mawsoni Norman) has been considered an occasional large prey item of the Weddell seal (Leptonychotes weddellii Lesson) (Kooyman 1967, Calhaem & Christoffel 1969, Testa et al. 1985, Castellini et al. 1992, Davis et al. 1999, Fuiman et al. 2002). The seal's most common prey is the Antarctic silverfish (Pleuragramma antarcticum Boulenger) as well as benthic and sub-ice fish, cephalopods, and crustaceans (Dearborn 1965, Green & Burton 1987, Plotz 1987, Plotz et al. 1991, Castellini et al. 1992, Burns et al. 1998).

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.

Ponganis, PJ, Kooyman GL, Castellini MA, Ponganis EP, Ponganis KV.  1993.  Muscle temperature and swim velocity profiles during diving in a Weddell seal, Leptonychotes weddellii. Journal of Experimental Biology. 183:341-346. AbstractWebsite

Locomotory muscle temperature and swim velocity profiles of an adult Weddell seal were recorded over a 21 h period. The highest temperatures occurred during a prolonged surface period (mean 37.3-degrees-C, S.D. 0.16-degrees-C). Muscle temperature averaged 36.8 and 36.6-degrees-C (S.D. 0.25-degrees-C, 0.19-degrees-C) during two dive bouts and showed no consistent fluctuations between dive and interdive surface intervals. Swim velocities were also constant, near 1.3 m s-1. These data indicate that past records of low aortic temperatures (35-degrees-C) during and after prolonged dives are not indicative of whole-body temperature changes, and that muscle temperature, even during dives as long as 45 min, remains near 37-degrees-C.

Ponganis, PJ, Meir JU, Williams CL.  2011.  In pursuit of Irving and Scholander: a review of oxygen store management in seals and penguins. Journal of Experimental Biology. 214:3325-3339.   10.1242/jeb.031252   AbstractWebsite

Since the introduction of the aerobic dive limit (ADL) 30 years ago, the concept that most dives of marine mammals and sea birds are aerobic in nature has dominated the interpretation of their diving behavior and foraging ecology. Although there have been many measurements of body oxygen stores, there have been few investigations of the actual depletion of those stores during dives. Yet, it is the pattern, rate and magnitude of depletion of O(2) stores that underlie the ADL. Therefore, in order to assess strategies of O(2) store management, we review (a) the magnitude of O(2) stores, (b) past studies of O(2) store depletion and (c) our recent investigations of O(2) store utilization during sleep apnea and dives of elephant seals (Mirounga angustirostris) and during dives of emperor penguins (Aptenodytes forsteri). We conclude with the implications of these findings for (a) the physiological responses underlying O(2) store utilization, (b) the physiological basis of the ADL and (c) the value of extreme hypoxemic tolerance and the significance of the avoidance of re-perfusion injury in these animals.

Ponganis, PJ, Stockard TK, Levenson DH, Berg L, Baranov EA.  2006.  Cardiac output and muscle blood flow during rest-associated apneas of elephant seals. Comparative Biochemistry and Physiology a-Molecular & Integrative Physiology. 144:105-111.   10.1016/j.cbpa.2006.02.009   AbstractWebsite

In order to evaluate hemodynamics and blood flow during rest-associated apnea in young elephant seals (Mirounga angustirostris), cardiac outputs (CO, thermodilution), heart rates (HR), and muscle blood flow (MBF, laser Doppler flowmetry) were measured.. Mean apneic COs and HRs of three seals were 46% and 39% less than eupneic values, respectively (2.1 +/- 0.3 vs. 4.0 +/- 0.1 mL kg(-1) s(-1), and 54 6 vs. 89 14 beats min(-1)). The mean apneic stroke volume (SV) was not significantly different from the eupneic value (2.3 +/- 0.2 vs. 2.7 +/- 0.5 mL kg(-1)). Mean apneic MBF of three seals was 51% of the eupneic value. The decline in MBF during apnea was gradual, and variable in both rate and magnitude. In contrast to values previously documented in seals during forced submersions (FS), CO and SV during rest-associated apneas were maintained at levels characteristic of previously published values in similarly-sized terrestrial mammals at rest. Apneic COs of such magnitude and incomplete muscle ischemia during the apnea suggest that (1) most organs are not ischemic during rest-associated apneas, (2) the blood O-2 depletion rate is greater during rest-associated apneas than during FS, and (3) the blood O-2 store is not completely isolated from muscle during rest-associated apneas. (c) 2006 Elsevier Inc. All rights reserved.

Ponganis, PJ, Kooyman GL, Van Dam R, Lemaho Y.  1999.  Physiological responses of king penguins during simulated diving to 136 m depth. Journal of Experimental Biology. 202:2819-2822. AbstractWebsite

To evaluate blood N-2 uptake and the role of the respiratory volume (air sacs/lungs) as a N-2 and O-2 reservoir in deep-diving penguins, diving respiratory volume (V-DR), heart rate (f(H)), venous P-N2, blood volume (V-b) and hemoglobin (Hb) concentration were measured in king penguins (Aptenodytes patagonicus) during forced submersions and compressions equivalent to depths up to 136 m, V-DR was 69+/-18 ml kg(-1) (mean +/- S.D.) in 62 submersions ranging from 4.4 atmospheres absolute (ATA; 1 ATA=101 kPa) (34 m) to 14.6 ATA (136 m), Submersion f(H) averaged 30+/-7 beats min(-1) (N=18), approximately 20% of pre- and post-submersion values. Venous P-N2 values during and after submersions as deep as 11.2 ATA (102 m) were all less than 2.8 atmospheres N-2 (283 kPa) above ambient pressure, a previously measured threshold for symptomatic bubble formation. Mean V-b was 83+/-8 ml kg(-1) (N=6); [Hb] was 17.6+/-0.7 g dl(-1) (N=7), On a mass-specific basis, mean V-DR, and therefore total available N-2, is 41% of that in shallow-diving penguin species. Total body O-2 stores, calculated from measured V-DR, V-b, [Hb], muscle mass and myoglobin concentration, are 45 ml kg(-1), with 23 % in the respiratory system. This small respiratory fraction in comparison with that in shallow-diving penguins suggests a lesser reliance on the respiratory oxygen store for extended breath-holding and also a reduced uptake of nitrogen at depth.

Ponganis, PJ, Gentry RL, Ponganis EP, Ponganis KV.  1992.  Analysis of swim velocities during deep and shallow dives of two northern fur seals, Callorhinus ursinus. Marine Mammal Science. 8:69-75.   10.1111/j.1748-7692.1992.tb00126.x   AbstractWebsite

Swim velocities at 15-sec intervals and maximum depth per dive were recorded by microprocessor units on two "mixed diver" adult female northern fur seals during summer foraging trips. These records allowed comparison of swim velocities of deep (> 75 m) and shallow (< 75 m) dives. Deep dives averaged 120 m depth and 3 min duration; shallow dives averaged 30 m and 1.2 min. Mean swim velocities on deep dives were 1.8 and 1.5 m/ sec for the two animals; mean swim velocities on shallow dives were 1.5 and 1.2 m/sec. The number of minutes per hour spent diving during the deep and shallow dive patterns were 11 and 27 min, respectively. Swim velocity, and hence, relative metabolic rate, did not account for the differences in dive durations between deep and shallow dives. The long surface durations associated with deep dives, and estimates of metabolic rates for the observed swim velocities, suggest that deep dives involve significant anaerobic metabolism.

Ponganis, PJ, Meir JU, Williams CL.  2010.  Oxygen store depletion and the aerobic dive limit in emperor penguins. Aquatic Biology. 8:237-245.   10.3354/ab00216   AbstractWebsite

The aerobic dive limit (ADL), dive duration associated with the onset of post-dive blood lactate elevation, has been widely used in the interpretation of diving physiology and diving behavior. However, its physiological basis is incompletely understood, and in most studies, ADLs are simply calculated with an O(2) store/O(2) consumption formula. To better understand the ADL, research has been conducted on emperor penguins diving at an isolated dive hole. This work has revealed that O(2) stores are greater than previously estimated, and that the rate of depletion of those O(2) stores appears to be regulated primarily through a diving bradycardia and the efficiency of swimming. Blood and respiratory O(2) stores are not depleted at the 5.6 min ADL determined by post-dive blood lactate measurements. It is hypothesized that muscle, isolated from the circulation during a dive, is the primary source of lactate accumulation. To predict this 5.6 min ADL for these shallow dives at the isolated dive hole with the classic O(2) store/O(2) consumption formula, an O(2) consumption rate of 2x the predicted metabolic rate of a penguin at rest is required. In contrast, if the formula is used to calculate an ADL that is defined as the time for all consumable O(2) stores to be depleted, then a 23.1 min dive, in which final venous partial pressure of oxygen (P(O2)) was 6 mm Hg (0.8 kPa), represents such a maximum limit and demonstrates that an O(2) consumption rate of about 0.5x the predicted rate of an emperor penguin at rest is required in the formula.

Ponganis, PJ, Kooyman GL, h. Ridgway S.  2003.  Comparative Diving Physiology. Bennett and Elliott's physiology and medicine of diving. ( Brubakk AO, Neuman TS, Bennett PB, Elliott DH, Eds.).:16., Edinburgh; New York: Saunders Abstract
Ponganis, PJ, Kooyman GL, Starke LN, Kooyman CA, Kooyman TG.  1997.  Post-dive blood lactate concentrations in emperor penguins, Aptenodytes forsteri. Journal of Experimental Biology. 200:1623-1626. AbstractWebsite

In order to determine an aerobic diving limit (ADL) in emperor penguins (Aptenodytes forsteri), post-dive blood lactate concentrations were measured in penguins foraging at an isolated sea ice hole. Resting lactate concentrations were 1.2-2.7 mmol l(-1). Serial samples revealed that lactate level usually peaked within 5 min after dives and that 7-12 min was required for lactate concentrations to decrease from 5-8 mmol l(-1) to less than 2.5 mmol l(-1). Post-dive lactate level was not elevated above 3 mmol l(-1) for dives shorter than 5 min. Two-phase regression analysis revealed a transition at 5.6 min in the post-dive lactate level versus diving duration relationship. All dives longer than 7 min were associated with lactate concentrations greater than 5 mmol l(-1). We conclude that the ADL in emperor penguins ranges between 5 and 7 min. These are the first determinations of post-dive lactate concentrations in any free-diving bird and are currently the only physiological assessment of an ADL in an avian species.