DEVELOPMENT OF A BIMODAL HEART RATE PATTERN IN UNDISTURBED FETAL HARBOR SEALS

Fetal and maternal heart rates were studied in unrestrained, pregnant harbor seals during the last third of gestation. Heart rates were recorded while the mothers were resting on land or performing trained simulated dives of up to 2.25 min. Data from resting mothers showed the development of a bimodal or two-speed fetal heart rate pattern during late gestation. The mean faster and slower fetal heart rates at term were 125 ± 3.7 and 79 ± 3.1 (mean + SEM) respectively. The amount of fetal bradycardia observed increased steadily towards term, and fetal heart rate changes were not correlated with changes in maternal heart rate or maternal respiration. The bimodal fetal heart rate was also seen during the simulated dives, and no decrease in either the faster or slower heart rate was found. Heart rates from resting, unrestrained harbor seal pups were also studied. The pups displayed a bimodal heart rate similar to the fetuses' with the slower rate occurring during breath-holds. The bradycardia in the pups was equivalent to the slower fetal heart rate. These findings suggest that the regulatory mechanism that determines the apneic bradycardia in young harbor seals during non-stressful conditions develops in the last quarter of gestation.     

Diving Related Changes in the Blood Oxygen Stores of Rehabilitating Harbor Seal Pups (Phoca vitulina)

Harbor seal (Phoca vitulina) pups begin diving within hours of birth, stimulating the development of the blood oxygen (O₂) stores necessary to sustain underwater aerobic metabolism. Since harbor seals experience a brief nursing period, the early-life development of these blood O₂ stores is necessary for successful post-weaning foraging. If mothers and pups become prematurely separated, the pup may be transported to a wildlife rehabilitation center for care. Previous studies suggest that the shallow pools and lack of diving in rehabilitation facilities may lead to under-developed blood O₂ stores, but diving behavior during rehabilitation has not been investigated. This study aimed to simultaneously study the diving behaviors and blood O₂ store development of rehabilitating harbor seal pups. Standard hematology measurements (Hct, Hb, RBC, MCV, MCH, MCHC) were taken to investigate O₂ storage capacity and pups were equipped with time-depth recorders to investigate natural diving behavior while in rehabilitation. Linear mixed models of the data indicate that all measured blood parameters changed with age; however, when compared to literature values for wild harbor seal pups, rehabilitating pups have smaller red blood cells (RBCs) that can store less hemoglobin (Hb) and subsequently, less O₂, potentially limiting their diving capabilities. Wild pups completed longer dives at younger ages (maximum reported <25 days of age: 9 min) in previous studies than the captive pups in this study (maximum <25 days of age: 2.86 min). However, captivity may only affect the rate of development, as long duration dives were observed (maximum during rehabilitation: 13.6 min at 89 days of age). Further, this study suggests that there may be a positive relationship between RBC size and the frequency of long duration dives. Thus, rehabilitating harbor seal pups should be encouraged to make frequent, long duration dives to prepare themselves for post-release foraging.     

Variations in heart rate and rhythm of harbor seal pups during rehabilitation

Heart rate and rhythm is regulated by the autonomic nervous system, which matures during the first months of life. Little is known about heart rate and rhythm development and potential arrhythmias in seal pups during rehabilitation in seal centers. Using an iPhone ECG device, 1 min ECGs were obtained from harbor seal pups admitted to a seal rehabilitation facility. ECGs were taken from 55 seals after admission, 53 seals after 14 d, and 52 seals prior to release. From 24 seal pups additional ECGs were taken daily for the first week of rehabilitation. At admission sinus rhythm with a median heart rate of 148 complexes per minute was detected, prior to release sinus bradycardia or sinus arrhythmia with a median heart rate of 104 complexes minute was present. P wave morphology was highly variable and single supra‐ and ventricular premature complexes were recorded in individual animals. The first 14 d were characterized by highly variable heart rates and rhythms, including episodes of sinus tachycardia and 2nd degree atrioventricular blocks. The reduction in heart rates and development of a regular heart rhythm during rehabilitation suggest adaptation to the unfamiliar environment, resolution of disease, and/or maturation of the autonomic nervous system.     

Postnatal development of muscle biochemistry in nursing harbor seal (Phoca vitulina) pups: limitations to diving behavior?

Adult marine mammal muscles rely upon a suite of adaptations for sustained aerobic metabolism in the absence of freely available oxygen (O₂). Although the importance of these adaptations for supporting aerobic diving patterns of adults is well understood, little is known about postnatal muscle development in young marine mammals. However, the typical pattern of vertebrate muscle development, and reduced tissue O₂ stores and diving ability of young marine mammals suggest that the physiological properties of harbor seal (Phoca vitulina) pup muscle will differ from those of adults. We examined myoglobin (Mb) concentration, and the activities of citrate synthase (CS), β-hydroxyacyl coA dehydrogenase (HOAD), and lactate dehydrogenase (LDH) in muscle biopsies from harbor seal pups throughout the nursing period, and compared these biochemical parameters to those of adults. Pups had reduced O₂ carrying capacity ([Mb] 28–41% lower than adults) and reduced metabolically scaled catabolic enzyme activities (LDH/RMR 20–58% and CS/RMR 29–89% lower than adults), indicating that harbor seal pup muscles are biochemically immature at birth and weaning. This suggests that pup muscles do not have the ability to support either the aerobic or anaerobic performance of adult seals. This immaturity may contribute to the lower diving capacity and behavior in younger pups. In addition, the trends in myoglobin concentration and enzyme activity seen in this study appear to be developmental and/or exercise-driven responses that together work to produce the hypoxic endurance phenotype seen in adults, rather than allometric effects due to body size.     

DEVELOPMENT OF DIVING BY HARBOR SEAL PUPS IN TWO REGIONS OF ALASKA: USE OF THE WATER COLUMN

Satellite-linked dive recorders were attached to 53 harbor seal pups in Prince William Sound (PWS) and at Tugidak Island, Alaska, during 1997–1999. We used generalized additive models and bootstrap techniques to describe pup diving behavior during their first year of life. Pups increased their ability to dive during the first 3–6 mo, as indicated by increases in proportion of time in the water (time wet) and maximum dive depth achieved by a pup each day (max-depth) values. Time wet and/or max-depth later decreased, suggesting a seasonal component to diving behavior. Monthly time wet varied from an overall minimum of 0.68 at tagging in July to a maximum of 0.89 in November. Pups spent half of their time wet swimming in water <25 m deep, the shallowest 30% of the available water column. They spent only 5% of their time swimming in the deepest 30% of the available water column, at depths >60–70 m. This strongly suggests they were not feeding on or near bottom during their first year. Average max-depths and deepest actual dives were similar for PWS and Tugidak pups. PWS pups dove deeper sooner and spent less time wet than Tugidak pups during the first few months after tagging, probably as a result of regional bathymetric differences. Diving behavior and body condition suggest that food availability was not likely a major factor in the population decline in PWS during the period of this study.     

Diving heart rate development in postnatal harbour seals, Phoca vitulina

Harbour seals, Phoca vitulina, dive from birth, providing a means of mapping the development of the diving response, and so our objective was to investigate the postpartum development of diving bradycardia. The study was conducted May-July 2000 and 2001 in the St. Lawrence River Estuary (48 degrees 41'N, 68 degrees 01'W). Both depth and heart rate (HR) were remotely recorded during 86,931 dives (ages 2-42 d, n = 15) and only depth for an additional 20,300 dives (combined data covered newborn to 60 d, n = 20). The mean dive depth and mean dive durations were conservative during nursing (2.1 +/- 0.1 m and 0.57 +/- 0.01 min, range = 0-30.9 m and 0-5.9 min, respectively). The HR of neonatal pups during submersion was bimodal, but as days passed, the milder of the two diving HRs disappeared from their diving HR record. By 15 d of age, most of the dive time was spent at the lower diving bradycardia rate. Additionally, this study shows that pups are born with the ability to maintain the lower, more fully developed dive bradycardia during focused diving but do not do so during shorter routine dives.     

DISPERSAL and BYCATCH MORTALITY IN GRAY, HALICHOERUS GRYPUS, AND HARBOR, PHOCA VITULINA, SEALS TAGGED AT THE NORWEGIAN COAST

Between 1975 and 1998, 3,571 gray and 630 harbor seal pups were tagged along the Norwegian coast, and 259 (7%) gray and 80 (13%) harbor seal tags were returned. Incidental mortality, mainly in bottom-set nets, accounted for the majority of deaths (79% in gray and 48% in harbor seals, respectively). Seals were most vulnerable to incidental mortality in fishing gear during the first three months after birth, but high incidental mortality prevailed during the first 8–10 mo. Gray seals dispersed more widely (mean distance: 120 km) than harbor seals (mean distance: 69 km). Both species dispersed most widely during the two first months after tagging. The maximum distance moved was 739 km for gray and 463 km for harbor seals. Strong fidelity for their place of birth was observed in adult gray seals during breeding season. No significant difference in incidental mortality was detected between the areas of tagging. However, for 37 harbor seals tagged in a 724 km nature reserve no returns were reported.     

Making it through the first year: Ontogeny of movement and diving behavior in harbor seals from Svalbard,Norway

Phocid seal pups must learn successful survival strategies, largely independently, following their abrupt weaning at a relatively young age. To explore the ontogeny of aquatic skills, space use and first‐year habitat choices made by harbor seals, pups (n = 30) were instrumented with satellite relay data loggers (SRDLs) in Svalbard, Norway in 2009 and 2010. Initially, the pups had small home ranges and showed rapid changes in their activity budgets and diving capabilities, displaying steep linear increases in diving depth and duration and in the amount of time spent diving. Most pups underwent an abrupt shift in movement patterns at ca. 50 d of age, which likely marked the end of the postweaning fast. Around this same time, the steep progression in diving performance slowed, though longer, deeper dives gradually became the norm. However, bottom time, ascent and descent rates, and postdive recovery times remained stable after the postweaning fast, suggesting that most aquatic skill acquisition was completed during the first months of life. Few clear effects of environmental variables such as upwelling phenomenon, which are known to influence the diving behavior of adults from the same population, were detected in the diving patterns of pups.     

Effects of age and body mass on development of diving capabilities of gray seal pups: costs and benefits of the postweaning fast

Development of adequate diving capabilities is crucial for survival of seal pups and may depend on age and body size. We tracked the diving behavior of 20 gray seal pups during their first 3 mo at sea using satellite relay data loggers. We employed quantile analysis to track upper limits of dive duration and percentage time spent diving, and lower limits of surface intervals. When pups first left the breeding colony, extreme (ninety-fifth percentile) dive duration and percentage time spent diving were positively correlated with age, but not mass, at departure. Extreme dive durations and percentage time spent diving peaked at [Formula: see text] d of age at values comparable with those of adults, but were not sustained. Greater peaks in extreme percentage time spent diving occurred in pups that had higher initial values, were older at their peak, and were heavier at departure. Pups that were smaller and less capable divers when they left the colony improved extreme dive durations and percentage time spent diving more rapidly, once they were at sea. Minimum survival time correlated positively with departure mass. Pups that were heavier at weaning thus benefitted from being both larger and older at departure, but smaller pups faced a trade-off. While age at departure had a positive effect on early dive performance, departure mass impacted on peak percentage time spent diving and longer-term survival. We speculate that once small pups have attained a minimum degree of physiological development to support diving, they would benefit by leaving the colony when younger but larger to maximize limited fuel reserves, rather than undergoing further maturation on land away from potential food resources, because poor divers may be able to "catch up" once at sea.     

Caloric restriction may reverse age-related autonomic decline in humans

Caloric restriction (CR) retards aging in laboratory rodents. No information is available on the effects of long-term CR on physiologic markers of aging and longevity in humans. Heart rate variability (HRV) is a marker for cardiac autonomic functioning. The progressive decline in HRV with aging and the association of higher HRV with better health outcomes are well established. Heart rate variability assessment is a reliable tool by which the effects of CR on autonomic function can be assessed. Time- and frequency-domain analyses compared 24-h HRV in 22 CR individuals aged 35-82 years and 20 age-matched controls eating Western diets (WD). The CR group was significantly leaner than the WD group. Heart rate was significantly lower, and virtually, all HRV values were significantly higher in the CR group than in the WD group (P < 0.002). Heart rate variability in the CR individuals was comparable with published norms for healthy individuals 20 years younger. In addition, when differences in heart rate (HR) and HRV between CR and WD were compared with previously published changes in HRV induced in healthy adults given atenolol, percent differences in each measure were generally similar in direction and magnitude and suggested declines in sympathetic and increases in parasympathetic modulation of HR and increased circadian variability associated with CR. These findings provide evidence that CR has direct systemic effects that counter the expected age-associated changes in autonomic function so that HRV indexes in CR individuals are similar to those of individuals 20 years younger eating WDs.     

Development of body oxygen stores in harbor seals: effects of age, mass, and body composition

Harbor seal pups are highly precocial and can swim and dive at birth. Such behavioral maturity suggests that they may be born with mature body oxygen stores or that stores develop quickly during the nursing period. To test this hypothesis, we compared the blood and muscle oxygen stores of harbor seal pups, yearlings, and adults. We found that pups had smaller oxygen stores than adults (neonates 57%, weaned pups 75%, and yearlings 90% those of adults), largely because neonatal myoglobin concentrations were low (1.6+/-0.2 g% vs. 3.8+/-0.3 g% for adults) and changed little during the nursing period. In contrast, blood oxygen stores were relatively mature, with nursing pups having hematocrit (55%+/-0.2%), hemoglobin (21.7+/-0.4 g%), and blood volume (12.3+/-0.5 mL/kg) only slightly lower than the corresponding values for adults (57%+/-0.2%, 23.8+/-0.3 g %, and 15.0+/-0.5 mL/kg). Because neonatal pups had relatively high metabolic rates (11.0 mL O2/kg min), their calculated aerobic dive limit was less than 50% that of adults. These results suggest that harbor seals' early aquatic activity is primarily supported by rapid development of blood, with immature muscle oxygen stores and elevated use rates limiting aerobic diving ability.     

Terrestrial apnoeas and the development of cardiac control in Australian fur seal (<Emphasis Type="Italic">Arctocephalus pusillus doriferus</Emphasis>) pups

The development of cardiac control in association with terrestrial respiration patterns was examined throughout the period of maternal dependence in Australian fur seal pups. Resting eupnoic heart rate and respiration rate were significantly correlated (r ² = 0.49) and both decreased with age (P < 0.05 in both cases). From an early age (1 month), pups displayed terrestrial apnoeas (18.1 ± 0.5 s) accompanied by substantial bradycardia (127 beats min⁻¹, a 13% decrease from eupnoic HR). Terrestrial apnoea duration increased significantly with age reaching a mean of 41 s just prior to weaning, slightly lower than the mean dive duration (52 s) previously recorded for pups of the same age. Correspondingly, mean apnoic heart rate decreased with age to 74 beats min⁻¹ just prior to weaning, representing a 25% decrease on eupnoic heart rate. Importantly, concomitant with the decrease in mean apnoic heart rate with age, an increase in the control of bradycardia was evident with the variability in instantaneous apnoic heart decreasing such that older pups were able to maintain a low steady heart rate for the duration of the apnoea. The changes seen in these parameters are similar to those reported during postnatal development in elephant seals (Mirounga spp.) and harbour seals (Phoca vitulina), and are considered indicative of the development of cardiac control. These findings suggest a common strategy for the development of bradycardia control in both otariid and phocid seals.     

Endocrine Changes in Harbor Seal (Phoca vitulina) Pups Undergoing Rehabilitation

Rehabilitating pinniped pups are often admitted to care centers as neonates and generally lack maternal investment and are in poor body condition. Upon admittance to a rehabilitation facility, pups are typically fed a milk replacement formula via gavage, which is switched to frozen fish upon weaning. While rehabilitation has been successful in terms of recovery and release, preweaning growth rates in captivity are consistently lower than in the wild. Indicators of stress (cortisol and total thyroxine; TT4), and standard morphometrics, of harbor seal pups in rehabilitation (n = 20) were determined for both preweaned and weaned pups. Hormone concentrations and standard morphometrics from pups in care were compared with free‐ranging harbor seal pups (n = 59). Pups in rehabilitation gained mass on both milk and fish diets. Preweaned pups had greater mean serum cortisol and similar TT4 concentrations than weaned pups. Free‐ranging harbor seal pups were heavier and longer than preweaned and weaned pups in rehabilitation. The free‐ranging pups had the lowest cortisol and highest TT4 concentrations of any of the pups. These results suggest that weaned pups that have undergone rehabilitation are not physiologically equivalent to free‐ranging weaned pups. Additional research is needed regarding physiological changes in endocrine values during early development under captive care conditions. This information should be useful to marine mammal rehabilitation centers in their development of care protocols and release criteria for rehabilitating harbor seal pups. Zoo Biol. 32:134–141, 2013. © 2012 Wiley Periodicals, Inc.     

AUTONOMIC CONTROL OF HEART RATE AFTER EXERCISE IN TRAINED WRESTLERS

The objective of this study was to establish differences in vagal reactivation, through heart rate recovery and heart rate variability post exercise, in Brazilian jiu-jitsu wrestlers (BJJW). A total of 18 male athletes were evaluated, ten highly trained (HT) and eight moderately trained (MT), who performed a maximum incremental test. At the end of the exercise, the R-R intervals were recorded during the first minute of recovery. We calculated heart rate recovery (HRR_60s), and performed linear and non-linear (standard deviation of instantaneous beat-to-beat R-R interval variability – SD1) analysis of heart rate variability (HRV), using the tachogram of the first minute of recovery divided into four segments of 15 s each (0-15 s, 15-30 s, 30-45 s, 45-60 s). Between HT and MT individuals, there were statistically significant differences in HRR_60s (p <0.05) and in the non linear analysis of HRV from SD1_30-45s (p <0.05) and SD1_45-60s (p <0.05). The results of this research suggest that heart rate kinetics during the first minute after exercise are related to training level and can be used as an index for autonomic cardiovascular control in BJJW.     

Hematology and serum chemistry comparisons between free-ranging and rehabilitated harbor seal (Phoca vitulina richardsi) pups

The objectives of this study were to compare the hematology and serum chemistry values between free-ranging and stranded harbor seal (Phoca vitulina richardsi) pups and to ascertain how blood values of stranded pups changed during the rehabilitation process. Coincident with these comparisons, reference values were obtained for free-ranging pups. Stranded harbor seal pups (n = 28) recovered from areas between Pebble Beach and Moss Landing, California (USA) were admitted to The Marine Mammal Center, Sausalito, from March to May 1995, 1996, and 1998. Blood samples were collected from harbor seal pups before and after rehabilitation. As a control group, wild harbor seal pups were captured at Pebble Beach and Elkhorn Slough (n = 42) during the 1995, 1996, and 1998 pupping seasons. Mean eosinophil and calcium values of wild pups were significantly greater than those of newly admitted pups, whereas mean bands, aspartate aminotransferase, alanine aminotransferase, total bilirubin, and chloride values were significantly lower (P < or = 0.05). Mean neutrophil, band, lymphocyte, eosinophil, basophil, calcium, phosphorus, blood urea nitrogen, potassium, total protein, and globulin values of rehabilitated pups increased significantly after 2-3 mo in captivity, whereas, mean red blood cell, hemoglobin, hematocrit, cholesterol, and total bilirubin values decreased significantly (P < or = 0.05).     

Postrelease movement of rehabilitated harbor seal (Phoca vitulina richardii) pups compared with cohort‐matched wild seal pups

Harbor seal (Phoca vitulina richardii) populations in the inland waters of Washington and British Columbia are at or near carrying capacity. Stranded pups often are collected and admitted to rehabilitation centers, and then released when they reach a weight of 22 kg and meet a variety of preestablished health and release conditions. While rehabilitation is common practice, it is unclear if rehabilitated seal pups behave like wild weaned pups. Using satellite transmitters, we compared movement patterns of 10 rehabilitated pups with 10 wild weaned pups. When released, rehabilitated seals were longer and heavier than wild pups, while wild pups had a larger mean axillary girth. No clinically different blood parameters were detected. On average, rehabilitated harbor seal pups traveled nearly twice as far cumulatively, almost three times as far daily, and dispersed over three times as far from the release site compared to wild weaned seals. Additionally, wild harbor seals transmitted nearly twice as long as did rehabilitated seals. These patterns suggest that learned behavior during the brief 3–4 wk nursing period likely enables wild harbor seal pups to move less daily and remain closer to their weaning site than rehabilitated pups.     

Oxygen uptake and heart rate in young Green turtles (Chelonia mydas)

Oxygen uptake. heart rate and breathing frequencies were monitored in yearling Green turtles. Routine fed animals used about 100μ O₂ g live turtle^-1 h^-1 at 25C; this value was not significantly affected by size or short term food deprivation. Starved turtle showed a doubling of oxygen uptake after a satiation meal and heightened uptake persisted for five days. Between 15 and 30C oxygen consumption increased with rising temperature; below 15C there was falling temperature. Vigorous activity increased oxygen uptake to two or three times thr routine fed levels.
Turtles swimming gently at 25C exhibited a heart rate of around 46–48 beats min^-1; this rose to 64–68 beats min^-1 during vigorous and continuous activity. Contrary to expectations profound bradycardia was not seen during diving; even during 10 min dives a rate of 25–28 beats min^-1 was sustained. Significantly lower heart rates were only seen in turtles which were apparently asleep.     

REBUILDING SEAL STOCKS IN THE KATTEGAT-SKAGERRAK

The harbor seal ( Phoca vitulina ) population in the Kattegat-Skagerrak area has been dwindling for several centuries due to excessive hunting pressure. Corrected hunting statistics during 1890–1976 are used to estimate changes in population size over the past century. After protection was introduced in the 1960s and 1970s the harbor seal population in the area increased at an exponential rate of 0.12 and exceeded 5,000 animals in 1986. The present rate of population growth is used for modelling the influence of fertility and age-specific mortality. It is found that the observed high rate of increase is only realistic if female fertility rate is very high, the range of juvenile mortality rate is 0.33–0.52 and adult mortality is less than 0.15. Commonly cited higher mortality rates are not realistic in the Kattegat-Skagerrak area.     

Interannual differences in postrelease movements of rehabilitated harbor seal pups (Phoca vitulina richardii) in the Salish Sea

Despite the large number of harbor seals (Phoca vitulina richardii) rehabilitated worldwide, few studies have been conducted on postrelease movement and behavior of rehabilitated harbor seal pups. We compared interannual differences in movements and survival of 24 rehabilitated seal pups released in the Salish Sea in 2010 (n = 10), 2012 (n = 5), 2013 (n = 5), and 2014 (n = 4). We also compared the postrelease movement of these seals to the movement of 10 wild seal pups tracked in the same ecosystem in 2010. Transmission duration, total cumulative distance, and average daily distance varied annually. Maximum linear distance traveled from the release site was similar for the rehabilitated seal groups. Compared to wild seals (n = 10), and consistent with prior studies, rehabilitated pups (n = 24) traveled significantly farther daily and cumulatively than wild weaned pups. Unlike in a prior study in this ecosystem, we found no significant difference between transmission duration in wild and rehabilitated pups.     

CLIMATE CHANGE AND RINGED SEAL (PHOCA HISPIDA) RECRUITMENT IN WESTERN HUDSON BAY

Climate warming is predicted to reduce the extent of ice cover in the Arctic and, within the Hudson Bay region, the annual ice may be significantly decreased or entirely lost in the foreseeable future. The ringed seal ( Phoca hispida ), a key species that depends on sea ice, will likely be among the first marine mammals to show the negative effects of climatic warming. We used 639 ringed seals killed by Inuit hunters from western Hudson Bay (1991–1992, 1999–2001) to assess trends in recruitment relative to snow depth, snowfall, rainfall, temperature in April and May, North Atlantic Oscillation (NAO) from the previous winter, and timing of spring break-up. Snowfall and ringed seal recruitment varied from lower than average in the 1970s, to higher in 1980s and lower in 1990s. Prior to 1990, seal recruitment appeared to be related to timing of spring ice break-up which was correlated with the NAO. However, recent 1990–2001 environmental data indicate less snowfall, lower snow depth, and warmer temperatures in April and May when pups are born and nursed. Decreased snow depth, particularly below 32 cm, corresponded with a significant decrease in ringed seal recruitment as indicated by pups born and surviving to adults that were later harvested. Earlier spring break-up of sea ice together with snow trends suggest continued low pup survival in western Hudson Bay.