Although breath holding during diving has been studied extensively in seals, the recent observation that these mammals also exhibit long-duration apnea while apparently sleeping has not been systematically examined. This project examined sleep apnea in northern elephant seal pups (Mirounga angustirostris). The animals exhibited a sequential sleep pattern of wakefulness-slow-wave sleep (SWS)-rapid eye movement (REM) sleep that resembled the normal pattern of mammalian sleep. The typical respiratory pattern during sleep in 4-mo-old pups consisted of short periods of continuous breathing separated by periods of apnea of up to 12 min. Several cycles of apnea and eupnea could occur during a single sleep episode. Breathing during a sleep cycle occurred only in SWS, never during REM sleep. The eupneic heart rate was characterized by significant sinus arrhythmia, and the apneic heart rate was similar to the minimum value during normal sinus arrhythmia. Patterns of change in breathing and heart rate associated with wakefulness and sleep were similar in seals sleeping underwater and on land. When sleeping underwater, the seals raised their heads to the surface to breathe without awakening. The changes in heart rate associated with normal sinus arrhythmia, sleep apnea, and diving apnea appear to be similar, suggesting regulation by a common homeostatic control mechanism.

The development of heart rate and respiratory patterns related to sleep-associated apnea were studied in northern elephant seal (Mirounga angustirostris) pups and adult males. Heart rate patterns became more refined in conjunction with an age-related increase in apnea duration in pups. That is, older pups showed significant sinus arrhythmia, while breathing and apneic heart rate were both stable and similar in magnitude to the sinus arrhythmia minimum. By contrast, younger pups showed poor or nonexistent sinus arrhythmia and shorter apnea durations with a variable and/or high heart rate during apnea. Apnea duration was positively correlated with the development of sinus arrhythmia and negatively correlated with both eupneic and apneic heart rate. Adult males showed extremely well-developed patterns of sinus arrhythmia and, in all cases, the minimum heart rate during the sinus arrhythmia was lower than the average heart rate recorded during apnea. These results suggest that seal pups are not born with the cardiac control associated with voluntary long duration apnea, but that apnea tolerance increases with refined cardiorespiratory control.

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Hematocrit data are relatively easily obtained from blood samples of pinnipeds but differences in methodology and variable physiological conditions of the subjects can significantly alter their values. This two‐fold problem makes comparative data and modeling efforts difficult. To quantify the difficulty of obtaining accurate and representative hematocrit values in pinnipeds, hematocrit was measured by both microcentrifugation and Coulter counter methods in a range of pinnipeds under a variety of physiological and handling conditions. The data show that the Coulter counter hematocrit values were 4%‐15% higher than those measured by microcentrifugation. In addition, blood samples from restrained animals showed consistently elevated hematocrit values relative to resting subjects. A significant difference was also found between hematocrit values from pups and adults. Finally, hematocrit was shown to decline over the course of isofluorane anesthesia. Taken together, these results suggest that laboratory methodology, developmental state, and animal handling techniques can significantly alter hematocrit values in pinnipeds. Thus, modeling efforts that require representative hematocrit values, such as calculations of total blood oxygen stores, can be markedly impacted by variations in hematocrit measurement techniques and sampling regimes.

BackgroundUnderstanding mercury (Hg) distribution in blood and the importance of hair as an excretory pathway is critical for evaluating risk from long term dietary Hg exposure. The major objective of this study was to characterize changes in total Hg concentrations in specific blood compartments and hair over time due to long term piscivory.MethodsEight sled dogs (Canis lupus familiaris) were fed either a fish and kibble diet (n = 4), or a fish-free control diet (n = 4) for 12 weeks. Concentrations of Hg were monitored throughout the exposure period, and for 10 weeks post exposure, until Hg concentrations in all blood compartments of one of the exposed dogs dropped below detection limit. Additionally, foreleg hair was sampled during acclimation and weeks 0 and 12.ResultsHg was detected primarily in whole blood and packed cells, although it was sporadically detected at low concentrations in plasma and serum in two of the fish fed dogs. Dogs ingested an estimated average of 13.4 ± 0.58 μg Hg per kg body weight per day. Hg was detectable in whole blood and packed cells within a week of exposure. Detected concentrations continued to rise until plateauing at approximately 3-6 weeks of exposure at a mean of 9.2 ± 1.97 ng/g (ppb) in whole blood. Hg concentration decreased post exposure following 1st order elimination. The mean half-life (t1/2) in whole blood for Hg was 7 weeks. Mean Hg in hair for the fish-fed dogs at week 12 was 540 ± 111 ppb and was significantly greater (about 7-fold) than the Hg hair concentration for the control dogs. The hair to blood ratio for Hg in fish-fed dogs was 59.0 ± 7.6:1.ConclusionsThis study found the sled dog model to be an effective method for investigating and characterizing blood Hg distribution (whole blood, serum, plasma, packed cells) and toxicokinetics associated with a piscivorous diet, especially for Hg-exposed fur bearing mammals (such as polar bears). Although hair excretion and hair to blood Hg ratios were not similar to human concentrations and ratios, the sled dog toxicokinetics of Hg in blood, was more similar to that of humans than traditional laboratory animals (such as the rat).

Mercury is a global contaminant of concern for the fetus and the neonate of piscivores. Methylmercury, produced within marine ecosystems, is of particular concern as a readily absorbed neurotoxicant transported across the blood brain barrier and transplacentally. In the North Pacific Ocean, Steller sea lions are broadly distributed apex predators and, as such, integrate complex food webs and the associated exposure and possible adverse effects of toxic and infectious agents. Hair, including lanugo, was examined using regional and age groupings to assess mercury concentrations in young Alaskan Steller sea lions. The highest concentrations of mercury occurred in the youngest animals, likely via in utero exposure. Based on the adverse developmental outcomes of methylmercury toxicity this specific cohort is of concern. Regionally, higher concentrations of mercury were observed in the endangered western population of Steller sea lions and mirrored patterns observed in human biomonitoring studies of Alaskan coastal communities. These data have broader implications with respect to human and ecosystem health as Steller sea lions rely on similar prey species and foraging areas as those targeted by commercial fisheries and subsistence users and are therefore valuable sentinels of marine ecosystem health.

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