Field anaesthesia of leatherback sea turtles (Dermochelys coriacea).

Ten nesting leatherback sea turtles on Trinidad were anaesthetised for electroretinogram (ERG) measurements, using ketamine and medetomidine, reversed with atipamezole. They weighed 242 to 324 kg and were given initial doses of 3 to 8 mg/kg ketamine and 30 to 80 microg/kg medetomidine administered into an external jugular vein; six of the turtles received supplementary doses of 2.6 to 3.9 mg/kg ketamine combined with 0 to 39 microg/kg medetomidine. The lower doses were used initially to ensure against overdosage and reduce the chances of residual effects after the turtles returned to the water, but successful ergs called for step-wise dose increases to the required level of anaesthesia. Respiratory rate, heart rate, electrocardiogram, cloacal temperature, and venous blood gases were monitored, and blood was collected for plasma biochemistry. At the end of the erg procedure, atipamezole was administered at 150 to 420 microg/kg (five times the dose of medetomidine), half intramuscularly and half intravascularly. The turtles were monitored and prevented from re-entering the water until their behaviour was normal. No apparent mortalities or serious anaesthetic complications occurred. The observed within-season return nesting rate of the anaesthetised turtles was comparable with that of unanaesthetised turtles.

Genetic evidence for the ancestral loss of short-wavelength-sensitive cone pigments in mysticete and odontocete cetaceans.

All mammals ancestrally possessed two types of cone pigments, an arrangement that persists in nearly all contemporary species. However, the absence of one of these cone types, the short-wavelength-sensitive (SWS) cone, has recently been established in several delphinoid cetacean species, indicating that the loss of this pigment type may be widespread among cetaceans. To evaluate the functional condition of SWS cones in cetaceans, partial SWS cone-opsin gene sequences were obtained from nuclear DNA for 16 species representing 12 out of the 14 extant mysticete (baleen) and odontocete (toothed) families. For all these species one or more mutations were identified that indicate that their SWS cone-opsin genes are pseudogenes and thus do not code for functional visual pigment proteins. Parsimonious interpretation of the distribution of some of these mis-sense mutations indicates that the conversion of cetacean SWS coneopsin genes to pseudogenes probably occurred before the divergences of the mysticete and odontocete suborders. Thus, in the absence of dramatic homoplasy, all modern cetaceans lack functional SWS cone visual pigments and, by extension, the visual capacities that such pigments typically support.

Blood oxygen depletion during rest-associated apneas of northern elephant seals (Mirounga angustirostris).

Blood gases (P(O)2, P(CO)2, 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 degree 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(O)2 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(O)2 values were indistinguishable from arterial values after the first minute of apnea; the lowest venous P(O)2 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(O)2 values during late apnea that were less than human thresholds for shallow-water blackout. Despite such low P(O)2s, there was no evidence of significant anaerobic metabolism, as changes in blood pH were minimal and attributable to increased P(CO)2. 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.

Cardiac output and muscle blood flow during rest-associated apneas of elephant seals.

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.

Intravascular pressure profiles in elephant seals: hypotheses on the caval sphincter, extradural vein and venous return to the heart.

In order to evaluate hemodynamics in the complex vascular system of phocid seals, intravascular pressure profiles were measured during periods of rest-associated apnea in young elephant seals (Mirounga angustirostris). There were no significant differences between apneic and eupneic mean arterial pressures. During apnea, venous pressure profiles (pulmonary artery, thoracic portion of the vena cava (thoracic vena cava), extradural vein, and hepatic sinus) demonstrated only minor, transient fluctuations. During eupnea, all venous pressure profiles were dominated by respiratory fluctuations. During inspiration, pressures in the thoracic vena cava and extradural vein decreased -9 to -21 mm Hg, and -9 to -17 mm Hg, respectively. In contrast, hepatic sinus pressure increased 2-6 mm Hg during inspiration. Nearly constant hepatic sinus and intrathoracic vascular pressure profiles during the breath-hold period are consistent with incomplete constriction of the caval sphincter during these rest-associated apneas. During eupnea, negative inspiratory intravascular pressures in the chest ("the respiratory pump") should augment venous return via both the venae cavae and the extradural vein. It is hypothesized that, in addition to the venae cavae, the prominent para-caval venous system of phocid seals (i.e., the extradural vein) is necessary to allow adequate venous return for maintenance of high cardiac outputs and blood pressure during eupnea.

Sub-ice foraging behavior of emperor penguins.

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 1 h 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.

Why pinnipeds don't echolocate.

Odontocete cetaceans have evolved a highly advanced system of active biosonar. It has been hypothesized that other groups of marine animals, such as the pinnipeds, possess analogous sound production, reception, and processing mechanisms that allow for underwater orientation using active echolocation. Despite sporadic investigation over the past 30 years, the accumulated evidence in favor of the pinniped echolocation hypothesis is unconvincing. We argue that an advanced echolocation system is unlikely to have evolved in pinnipeds primarily because of constraints imposed by the obligate amphibious functioning of the pinniped auditory system. As a result of these constraints, pinnipeds have not developed highly acute, aquatic, high frequency sound production or reception systems required for underwater echolocation. Instead, it appears that pinnipeds have evolved enhanced visual, tactile, and passive listening skills. The evolutionary refinement of alternative sensory systems allows pinnipeds to effectively forage, navigate, and avoid predators under water despite the lack of active biosonar capabilities.

Temperature regulation in emperor penguins foraging under sea ice.

Inferior vena caval (IVC) and anterior abdominal (AA) temperatures were recorded in seven emperor penguins (Aptenodytes forsteri) foraging under sea ice in order to evaluate the hypothesis that hypothermia-induced metabolic suppression might extend aerobic diving time. Diving durations ranged from 1 to 12.5 min, with 39% of dives greater than the measured aerobic dive limit of 5.6 min. Anterior abdominal temperature decreased progressively throughout dives, and partially returned to pre-dive values during surface intervals. The lowest AA temperature was 19 degrees C. However, mean AA temperatures during dives did not correlate with diving durations. In six of seven penguins, only minor fluctuations in IVC temperatures occurred during diving. These changes were often elevations in temperature. In the one exception, although IVC temperatures decreased, the reductions were less than those in the anterior abdomen and did not correlate with diving durations. Because of these findings, we consider it unlikely that regional hypothermia in emperor penguins leads to a significant reduction in oxygen consumption of the major organs within the abdominal core. Rather, temperature profiles during dives are consistent with a model of regional heterothermy with conservation of core temperature, peripheral vasoconstriction, and cooling of an outer body shell.

Stroke frequencies of emperor penguins diving under sea ice.

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+/-0.31 Hz, 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.

Regional heterothermy and conservation of core temperature in emperor penguins diving under sea ice.

Temperatures were recorded at several body sites in emperor penguins (Aptenodytes forsteri) diving at an isolated dive hole in order to document temperature profiles during diving and to evaluate the role of hypothermia in this well-studied model of penguin diving physiology. Grand mean temperatures (+/-S.E.) in central body sites during dives were: stomach: 37.1+/-0.2 degrees C (n=101 dives in five birds), pectoral muscle: 37.8+/-0.1 degrees C (n=71 dives in three birds) and axillary/brachial veins: 37.9+/-0.1 degrees C (n=97 dives in three birds). Mean diving temperature and duration correlated negatively at only one site in one bird (femoral vein, r=-0.59, P<0.05; range <1 degrees C). In contrast, grand mean temperatures in the wing vein, foot vein and lumbar subcutaneous tissue during dives were 7.6+/-0.7 degrees C (n=157 dives in three birds), 20.2+/-1.2 degrees C (n=69 in three birds) and 35.2+/-0.2 degrees C (n=261 in six birds), respectively. Mean limb temperature during dives negatively correlated with diving duration in all six birds (r=-0.29 to -0.60, P<0.05). In two of six birds, mean diving subcutaneous temperature negatively correlated with diving duration (r=-0.49 and -0.78, P<0.05). Sub-feather temperatures decreased from 31 to 35 degrees C during rest periods to a grand mean of 15.0+/-0.7 degrees C during 68 dives of three birds; mean diving temperature and duration correlated negatively in one bird (r=-0.42, P<0.05). In general, pectoral, deep venous and even stomach temperatures during diving reflected previously measured vena caval temperatures of 37-39 degrees C more closely than the anterior abdominal temperatures (19-30 degrees C) recently recorded in diving emperors. Although prey ingestion can result in cooling in the stomach, these findings and the lack of negative correlations between internal temperatures and diving duration do not support a role for hypothermia-induced metabolic suppression of the abdominal organs as a mechanism of extension of aerobic dive time in emperor penguins diving at the isolated dive hole. Such high temperatures within the body and the observed decreases in limb, anterior abdomen, subcutaneous and sub-feather temperatures are consistent with preservation of core temperature and cooling of an outer body shell secondary to peripheral vasoconstriction, decreased insulation of the feather layer, and conductive/convective heat loss to the water environment during the diving of these emperor penguins.