Urinary glucocorticoids in harbour seal (Phoca vitulina) pups during rehabilitation

The glucocorticoid (GC) hormone cortisol is often measured in seals to indicate their stress levels, although other endogenous GCs are usually overlooked. We investigated concentrations of four endogenous GCs in the urine of "orphan" harbour seal pups in rehabilitation. We hypothesised that the GC levels would be elevated if pups were socially isolated, without water access, and with low body mass. Ninety-six samples were collected from 32 pups at four different rehabilitation centres and were analysed by Ultra Performance Liquid Chromatography and Tandem Mass Spectrometry. Median urinary creatinine (Cr) concentrations of endogenous prednisolone (31.6 ng/mg/Cr) and prednisone (31.1 ng/mg/Cr) occurred in similar magnitude to cortisol (37.0 ng/mg/Cr), while median cortisone concentrations were higher (390 ng/mg/Cr). Prednisolone and prednisone concentrations were more strongly inversely related to pup growth rate and pup mass than cortisol and cortisone. Concentrations of all four GCs decreased with mass gain for pups with water access but did not decrease for pups without water; linear mixed models indicated the interaction between these trends was significant for cortisol and cortisone, but not for prednisolone or prednisone. These results indicate the potential value of measuring all four of these endogenous GC hormones in phocid seal pups.

Estimating reproductive costs in marine mammal bioenergetic models: a review of current knowledge and data availability

Reproductive costs represent a significant proportion of a mammalian female's energy budget. Estimates of reproductive costs are needed for understanding how alterations to energy budgets, such as those from environmental variation or human activities, impact maternal body condition, vital rates and population dynamics. Such questions are increasingly important for marine mammals, as many populations are faced with rapidly changing and increasingly disturbed environments. Here we review the different energetic costs that marine mammals incur during gestation and lactation and how those costs are typically estimated in bioenergetic models. We compiled data availability on key model parameters for each species across all six marine mammal taxonomic groups (mysticetes, odontocetes, pinnipeds, sirenians, mustelids and ursids). Pinnipeds were the best-represented group regarding data availability, including estimates of milk intake, milk composition, lactation duration, birth mass, body composition at birth and growth. There were still considerable data gaps, particularly for polar species, and good data were only available across all parameters in 45% of pinniped species. Cetaceans and sirenians were comparatively data-poor, with some species having little or no data for any parameters, particularly beaked whales. Even for species with moderate data coverage, many parameter estimates were tentative or based on indirect approaches, necessitating reevaluation of these estimates. We discuss mechanisms and factors that affect maternal energy investment or prey requirements during reproduction, such as prey supplementation by offspring, metabolic compensation, environmental conditions and maternal characteristics. Filling the existing data gaps highlighted in this review, particularly for parameters that are influential on bioenergetic model outputs, will help refine reproductive costs estimated from bioenergetic models and better address how and when energy imbalances are likely to affect marine mammal populations.

Age as a primary driver of the gut microbial composition and function in wild harbor seals

Dietary changes are the major variation cause in the composition of the gut microbiota. The short lactation phase in phocids provides an exceptional opportunity to explore the microbiota's response to a quick transition from a milk-based to a solid diet. We investigated the effects of age and sex on the gut microbiota of harbor seals in Mexico using rectal and fecal samples from pups and adults. 16S gene sequencing revealed age explains most of the observed variations in microbial composition. Individuals with frequent contact (pups-female adults) have major microbial similarities than those with little or no contact (pups-male adults). Overall, adults and females (regardless of sex and age, respectively) have a greater microbial richness; as seals grow, the core microbiome shrinks, and microbial diversity increases. We found pathways related to milk and chitin digestion in pups' microbiomes, indicating pups were transitioning to a solid diet. An enrichment of routes related to dramatic weight loss and body mass indicated higher metabolic stress in pups in late breeding season, when they are weaned and start intermittent fasting. Our findings highlight the host-microbiome interaction in harbor seals during late breeding season in response to food shifts and metabolic stress.

Allo-suckling occurrence and its effect on lactation and nursing duration in harbour seals (Phoca vitulina) in Orkney, Scotland

Fostering and allo-suckling are widespread among pinnipeds, and several hypotheses have been formulated to explain their occurrence. Here, we describe the occurrence of allo-suckling in harbour seals from photo-identification data of females and pups in Orkney (Scotland) during the pupping seasons between 2016 and 2019. We used a generalised linear model framework to investigate the effect of allo-suckling on the duration of lactation (females) and of nursing period (pups). A generalised additive model framework was used to explore how the probability of allo-suckling varied throughout the pupping season, and with changes in mother-pup separation time. Allo-suckling was observed in 31 females, at higher rates (18–37% of lactating females and 18–47% of the pups every year) than those observed in other phocid populations, with 13 females allo-suckling in multiple years. The duration of the pups’ nursing period was not affected by allo-suckling occurrence. However, females in mother-pup pairs where both mother and pup allo-suckled had longer lactation duration than when only the pup allo-suckled, or than in pairs where no allo-suckling was observed. The probability of allo-suckling increased during the pupping season and with increased mother-pup separation time. However, the proximate causes and the consequences on future reproductive output and pup survival remain unknown.

Significance statement

Allo-suckling, where females nurse others’ young, is widespread in pinnipeds, particularly among true seals. Given the high costs of lactation in pinnipeds, allo-suckling is a puzzling behaviour. Using photo-identification and field observations, we examined the occurrence of allo-suckling in harbour seals at a colony in Orkney, Scotland. We found that allo-suckling is common among seals at the study site, and at rates higher than reported elsewhere. Our results show that allo-suckling does not appear to affect the duration of the pups’ nursing period but does increase the lactation duration of females who suckle other pups and whose own pups also allo-suckle. This study highlights an area which requires further investigation as the energetic costs and benefits of allo-suckling remain poorly understood.

Postnatal development of diving physiology: implications of anthropogenic disturbance for immature marine mammals

Marine mammals endure extended breath-holds while performing active behaviors, which has fascinated scientists for over a century. It is now known that these animals have large onboard oxygen stores and utilize oxygen-conserving mechanisms to prolong aerobically supported dives to great depths, while typically avoiding (or tolerating) hypoxia, hypercarbia, acidosis and decompression sickness (DCS). Over the last few decades, research has revealed that diving physiology is underdeveloped at birth. Here, I review the postnatal development of the body's oxygen stores, cardiorespiratory system and other attributes of diving physiology for pinnipeds and cetaceans to assess how physiological immaturity makes young marine mammals vulnerable to disturbance. Generally, the duration required for body oxygen stores to mature varies across species in accordance with the maternal dependency period, which can be over 2 years long in some species. However, some Arctic and deep-diving species achieve mature oxygen stores comparatively early in life (prior to weaning). Accelerated development in these species supports survival during prolonged hypoxic periods when calves accompany their mothers under sea ice and to the bathypelagic zone, respectively. Studies on oxygen utilization patterns and heart rates while diving are limited, but the data indicate that immature marine mammals have a limited capacity to regulate heart rate (and hence oxygen utilization) during breath-hold. Underdeveloped diving physiology, in combination with small body size, limits diving and swimming performance. This makes immature marine mammals particularly vulnerable to mortality during periods of food limitation, habitat alterations associated with global climate change, fishery interactions and other anthropogenic disturbances, such as exposure to sonar.

Risk exposure trade-offs in the ontogeny of sexual segregation in Antarctic fur seal pups

Sexual segregation has important ecological implications, but its initial development in early life stages is poorly understood. We investigated the roles of size dimorphism, social behavior, and predation risk on the ontogeny of sexual segregation in Antarctic fur seal, Arctocephalus gazella, pups at South Georgia. Beaches and water provide opportunities for pup social interaction and learning (through play and swimming) but increased risk of injury and death (from other seals, predatory birds, and harsh weather), whereas tussock grass provides shelter from these risks but less developmental opportunities. One hundred pups were sexed and weighed, 50 on the beach and 50 in tussock grass, in January, February, and March annually from 1989 to 2018. Additionally, 19 male and 16 female pups were GPS-tracked during lactation from December 2012. Analysis of pup counts and habitat use of GPS-tracked pups suggested that females had a slightly higher association with tussock grass habitats and males with beach habitats. GPS-tracked pups traveled progressively further at sea as they developed, and males traveled further than females toward the end of lactation. These sex differences may reflect contrasting drivers of pup behavior: males being more risk prone to gain social skills and lean muscle mass and females being more risk averse to improve chances of survival, ultimately driven by their different reproductive roles. We conclude that sex differences in habitat use can develop in a highly polygynous species prior to the onset of major sexual size dimorphism, which hints that these sex differences will increasingly diverge in later life.

Space use of Pacific harbor seals (Phoca vitulina richardii) from two haulout locations along the Oregon coast

BACKGROUND

There are approximately 10,000-12,000 Pacific harbor seals (Phoca vitulina richardii) inhabiting the Oregon coast, and unlike other species of pinnipeds in this region, are reliably present year-round. Despite this, and drastic rebounds in population since the enactment of the Marine Mammal Protection Act, limited data is available for the present period regarding their space use at sea, and within estuarine, riverine, or bay areas within the state.

OBJECTIVE

To examine site-based differences in space use for 24 adult Pacific harbor seals captured and outfitted with satellite transmitters at two predominant haulout sites on the Oregon Coast, USA.

DESIGN

We captured 24 adult harbor seals from two haulout sites on the Central Oregon coast between September 2014-16 and fitted them with external Wildlife Computers SPOT5 satellite transmitters to track movement. Using state-space modeled locations derived from satellite telemetry data, we evaluated spatial behavior of these animals using a correlated random walk model via R package crawl. Kernel density estimation was subsequently used to calculate home range and core area for each animal. Percent use of open ocean habitat versus use of estuaries, rivers and bays was quantified, as was an initial examination of presence within five newly-established marine reserves in Oregon. Examination of haulout site-related differences in spatial behavior were examined for seals captured in Netarts and Alsea Bays, Oregon and haul out behavior related to time of day, season, and tidal level was also investigated.

RESULTS

The average individual home range for seals was 364.47 ± 382.87 km2 with seals captured in Alsea bay demonstrating a significantly higher home range area than those captured in Netarts Bay. Alsea bay seals also tended to range farther from shore than Netarts Bay animals. The average calculated core area for seals encompassed on average 29.41 ± 29.23 km2 per animal, however the home range of one animal was so small, core area could not be calculated. Use of marine reserves was limited for animals in this study, representing less than 2% of locations with a majority occurring in Cape Perpetua Marine Reserve and North Marine Protected Area. Seals were more likely to haul out during low tides and periods of low light (dusk, night and dawn), and hauling out behavior increased in winter months.

SIGNIFICANCE

These findings demonstrate the first major documentation of space use of harbor seals in the state for nearly three decades, and lends itself to future comparison and formation of mechanistically-based hypotheses for behavior of a common marine mammal in the highly productive northern California Current System.

Large-scale molecular diet analysis in a generalist marine mammal reveals male preference for prey of conservation concern

Sex-specific diet information is important in the determination of predator impacts on prey populations. Unfortunately, the diet of males and females can be difficult to describe, particularly when they are marine predators. We combined two molecular techniques to describe haul-out use and prey preferences of male and female harbor seals (Phoca vitulina) from Comox and Cowichan Bay (Canada) during 2012-2013. DNA metabarcoding quantified the diet proportions comprised of prey species in harbor seal scat, and qPCR determined the sex of the individual that deposited each scat. Using 287 female and 260 male samples, we compared the monthly sex ratio with GLMs and analyzed prey consumption relative to sex, season, site, and year with PERMANOVA. The sex ratio between monthly samples differed widely in both years (range = 12%-79% males) and showed different patterns at each haul-out site. Male and female diet differed across both years and sites: Females consumed a high proportion of demersal fish species while males consumed more salmonid species. Diet composition was related to both sex and season (PERMANOVA: R 2 = 27%, p < 0.001; R 2 = 24%, p < 0.001, respectively) and their interaction (PERMANOVA: R 2 = 11%, p < 0.001). Diet differences between males and females were consistent across site and year, suggesting fundamental foraging differences, including that males may have a larger impact on salmonids than females. Our novel combination of techniques allowed for both prey taxonomic and spatiotemporal resolution unprecedented in marine predators.

A comparison of blood nitric oxide metabolites and hemoglobin functional properties among diving mammals

The ability of marine mammals to hunt prey at depth is known to rely on enhanced oxygen stores and on selective distribution of blood flow, but the molecular mechanisms regulating blood flow and oxygen transport remain unresolved. To investigate the molecular mechanisms that may be important in regulating blood flow, we measured concentration of nitrite and S-nitrosothiols (SNO), two metabolites of the vasodilator nitric oxide (NO), in the blood of 5 species of marine mammals differing in their dive duration: bottlenose dolphin, South American sea lion, harbor seal, walrus and beluga whale. We also examined oxygen affinity, sensitivity to 2,3-diphosphoglycerate (DPG) and nitrite reductase activity of the hemoglobin (Hb) to search for possible adaptive variations in these functional properties. We found levels of plasma and red blood cells nitrite similar to those reported for terrestrial mammals, but unusually high concentrations of red blood cell SNO in bottlenose dolphin, walrus and beluga whale, suggesting enhanced SNO-dependent signaling in these species. Purified Hbs showed similar functional properties in terms of oxygen affinity and sensitivity to DPG, indicating that reported large variations in blood oxygen affinity among diving mammals likely derive from phenotypic variations in red blood cell DPG levels. The nitrite reductase activities of the Hbs were overall slightly higher than that of human Hb, with the Hb of beluga whale, capable of longest dives, having the highest activity. Taken together, these results underscore adaptive variations in circulatory NO metabolism in diving mammals but not in the oxygenation properties of the Hb.

Navigating uncertain waters: a critical review of inferring foraging behaviour from location and dive data in pinnipeds

In the last thirty years, the emergence and progression of biologging technology has led to great advances in marine predator ecology. Large databases of location and dive observations from biologging devices have been compiled for an increasing number of diving predator species (such as pinnipeds, sea turtles, seabirds and cetaceans), enabling complex questions about animal activity budgets and habitat use to be addressed. Central to answering these questions is our ability to correctly identify and quantify the frequency of essential behaviours, such as foraging. Despite technological advances that have increased the quality and resolution of location and dive data, accurately interpreting behaviour from such data remains a challenge, and analytical methods are only beginning to unlock the full potential of existing datasets. This review evaluates both traditional and emerging methods and presents a starting platform of options for future studies of marine predator foraging ecology, particularly from location and two-dimensional (time-depth) dive data. We outline the different devices and data types available, discuss the limitations and advantages of commonly-used analytical techniques, and highlight key areas for future research. We focus our review on pinnipeds - one of the most studied taxa of marine predators - but offer insights that will be applicable to other air-breathing marine predator tracking studies. We highlight that traditionally-used methods for inferring foraging from location and dive data, such as first-passage time and dive shape analysis, have important caveats and limitations depending on the nature of the data and the research question. We suggest that more holistic statistical techniques, such as state-space models, which can synthesise multiple track, dive and environmental metrics whilst simultaneously accounting for measurement error, offer more robust alternatives. Finally, we identify a need for more research to elucidate the role of physical oceanography, device effects, study animal selection, and developmental stages in predator behaviour and data interpretation.

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.

Rapid maturation of the muscle biochemistry that supports diving in pacific walruses (Odobenus rosmarus divergens)

Physiological constraints dictate animals' abilities to exploit habitats. For marine mammals, it is important to quantify physiological limits that influence diving and their ability to alter foraging behaviors. We characterized age-specific dive limits of walruses by measuring anaerobic (acid buffering capacity) and aerobic (myoglobin content) capacities of the muscles that power hind (longissimus dorsi) and fore (supraspinatus) flipper propulsion. Mean buffering capacities were similar across muscles and age classes (a fetus, 5 neonatal calves, a 3-month old, and 20 adults), ranging from 41.31 – 54.14 slykes and 42.00 – 46.93 slykes in the longissimus and supraspinatus, respectively. Mean myoglobin in the fetus and neonatal calves fell within a narrow range (longissimus: 0.92 – 1.68 g 100 g wet muscle mass−1; supraspinatus: 0.88 – 1.64 g wet muscle mass−1). By 3 months postpartum, myoglobin in the longissimus increased by 79%, but levels in the supraspinatus remained unaltered. From 3-months postpartum to adulthood, myoglobin increased by an additional 26% in the longissimus and increased by 126% in the supraspinatus; myoglobin remained greater in the longissimus compared to the supraspinatus. Walruses are unique among marine mammals because they are born with mature muscle acid buffering capacity and attain mature myoglobin content early in life. Despite rapid physiological development, small body size limits the diving capacity of immature walruses and extreme sexual dimorphism reduces the diving capacity of adult females compared to adult males. Thus, free-ranging immature walruses likely exhibit the shortest foraging dives while adult males are capable of the longest foraging dives.

Fine-scale variability in harbor seal foraging behavior

Understanding the variability of foraging behavior within a population of predators is important for determining their role in the ecosystem and how they may respond to future ecosystem changes. However, such variability has seldom been studied in harbor seals on a fine spatial scale (<30 km). We used a combination of standard and Bayesian generalized linear mixed models to explore how environmental variables influenced the dive behavior of harbor seals. Time-depth recorders were deployed on harbor seals from two haul-out sites in the Salish Sea in 2007 (n = 18) and 2008 (n = 11). Three behavioral bout types were classified from six dive types within each bout; however, one of these bout types was related to haul-out activity and was excluded from analyses. Deep foraging bouts (Type I) were the predominant type used throughout the study; however, variation in the use of bout types was observed relative to haul-out site, season, sex, and light (day/night). The proportional use of Type I and Type II (shallow foraging/traveling) bouts differed dramatically between haul-out sites, seasons, sexes, and whether it was day or night; individual variability between seals also contributed to the observed differences. We hypothesize that this variation in dive behavior was related to habitat or prey specialization by seals from different haul-out sites, or individual variability between seals in the study area. The results highlight the potential influence of habitat and specialization on the foraging behavior of harbor seals, and may help explain the variability in diet that is observed between different haul-out site groups in this population.

Stomach temperature records reveal nursing behaviour and transition to solid food consumption in an unweaned mammal, the harbour seal pup (Phoca vitulina)

Knowledge of milk transfer from mother to offspring and early solid food ingestions in mammals allows for a greater understanding of the factors affecting transition to nutritional independence and pre-weaning growth and survival. Yet studies monitoring suckling behaviour have often relied on visual observations, which might not accurately represent milk intake. We assessed the use of stomach temperature telemetry to monitor suckling and foraging behaviour in free-ranging harbour seal (Phoca vitulina) pups during lactation. Stomach temperature declines were analysed using principal component and cluster analyses, as well as trials using simulated stomachs resulting in a precise classification of stomach temperature drops into milk, seawater and solid food ingestions. Seawater and solid food ingestions represented on average 15.3±1.6% [0–40.0%] and 0.7±0.2% [0–13.0%], respectively, of individual ingestions. Overall, 63.7% of milk ingestions occurred while the pups were in the water, of which 13.9% were preceded by seawater ingestion. The average time between subsequent ingestions was significantly less for seawater than for milk ingestions. These results suggest that seawater ingestion might represent collateral ingestion during aquatic suckling attempts. Alternatively, as solid food ingestions (n = 19) were observed among 7 pups, seawater ingestion could result from missed prey capture attempts. This study shows that some harbour seals start ingesting prey while still being nursed, indicating that weaning occurs more gradually than previously thought in this species. Stomach temperature telemetry represents a promising method to study suckling behaviour in wild mammals and transition to nutritional independence in various endotherm species.

The mammalian diving response: an enigmatic reflex to preserve life?

The mammalian diving response is a remarkable behavior that overrides basic homeostatic reflexes. It is most studied in large aquatic mammals but is seen in all vertebrates. Pelagic mammals have developed several physiological adaptations to conserve intrinsic oxygen stores, but the apnea, bradycardia, and vasoconstriction is shared with those terrestrial and is neurally mediated. The adaptations of aquatic mammals are reviewed here as well as the neural control of cardiorespiratory physiology during diving in rodents.

The world's northernmost harbour seal population-how many are there?

This study presents the first abundance estimate for the world's northernmost harbour seal (Phoca vitulina) population, which resides in Svalbard, Norway, based on three digital stereoscopic photographic surveys conducted in 2009 and 2010. The counts from these high resolution 3D images were combined with a novel method for estimating correction factors for animals that were in the water at the time of the surveys, in which extensive behavioural data from radio-tagged harbour seals were used together with age distribution data to estimate the proportion of seals of various age and sex classes hauled out at the times of the surveys. To detect possible seasonal shifts in age distribution between surveys, lengths of hauled out seals were measured from the stereoscopic images. No body-length differences were detected between the surveys; but, this may be due to a high degree of sexual dimorphism exhibited in this population. Applying the modelled correction factors, a total of 1888 (95% CI: 1660-3023), 1742 (1381-3549) and 1812 (1656-4418) harbour seals were estimated for the surveys flown on 01 August 2009, 01 August 2010 and 19 August 2010, respectively. The similarity between the three survey estimates (despite significant differences in the number of animals actually counted on the photos from each survey effort) suggests that the variation in numbers of hauled out seals is reasonably accurately adjusted for by the haul-out probability model. The low population size, the limited spatial distribution of the population and its reduced genetic diversity make this population vulnerable to chance events, such as disease epidemics.

Development of myoglobin concentration and acid buffering capacity in harp (Pagophilus groenlandicus) and hooded (Cystophora cristata) seals from birth to maturity

Pinnipeds rely on muscle oxygen stores to help support aerobic diving, therefore muscle maturation may influence the behavioral ecology of young pinnipeds. To investigate the pattern of muscle development, myoglobin concentration ([Mb]) and acid buffering ability (beta) was measured in ten muscles from 23 harp and 40 hooded seals of various ages. Adult [Mb] ranged from 28-97 to 35-104 mg g tissue(-1) in harp and hooded seals, respectively, with values increasing from the cervical, non-swimming muscles to the main swimming muscles of the lumbar region. Neonatal and weaned pup muscles exhibited lower (approximately 30% adult values) and less variable [Mb] across the body than adults. In contrast, adult beta showed little regional variation (60-90 slykes), while high pup values (approximately 75% adult values) indicate significant in utero development. These findings suggest that intra-uterine conditions are sufficiently hypoxic to stimulate prenatal beta development, but that [Mb] development requires additional postnatal signal such as exercise, and/or growth factors. However, because of limited development in both beta and [Mb] during the nursing period, pups are weaned with muscles with lower aerobic and anaerobic capacities than those of adults.

Quantitative analysis of the 2002 phocine distemper epidemic in the Netherlands

Phocine distemper virus (PDV) caused thousands of deaths among harbor seals (Phoca vitulina) from the North Sea in 1988 and 2002. To examine the effects of different factors on the pathology of phocine distemper, we performed necropsies and laboratory analyses on 369 harbor seals that stranded along the Dutch coast during the 2002 PDV epidemic. Diagnostic tests for morbillivirus infection indicated a differential temporal presence of morbillivirus in lung and brain. Seals of 3 years or older were significantly more often IgG positive than younger seals. The most frequent lesions in PDV cases were bronchopneumonia, broncho-interstitial pneumonia, and interstitial emphysema. Extra-thoracic emphysema was rare in <1-year-olds compared with older seals, even though severe pneumonia was more common. PDV cases generally had empty stomachs and less blubber than by-caught seals from before the epidemic. In PDV cases involving older animals, lung, kidney, and adrenal weights were significantly increased. Bordetella bronchiseptica was isolated from lungs in two thirds of the PDV cases examined. Our results indicate that brain should be included among the tissues tested for PDV by RT-PCR; that either phocine distemper has a longer duration in older seals or that there are age-related differences in immunity and organ development; that dehydration could play a role in the course and outcome of phocine distemper; and that bacterial coinfections in lungs are more frequent in PDV cases than gross lesions suggest. These results illustrate how quantitative analysis of pathology data from such epidemics can improve understanding of the causative disease.

Tracking of biogenic hydrodynamic trails in harbour seals (Phoca vitulina)

For seals hunting in dark and murky waters one source of sensory information for locating prey consists of fish-generated water movements, which they can detect using their highly sensitive mystacial vibrissae. As water movements in the wake of fishes can persist for several minutes, hydrodynamic trails of considerable length are generated. It has been demonstrated that seals can use their vibrissae to detect and track hydrodynamic trails generated artificially by miniature submarines. In the present study, we trained a harbour seal to swim predefined courses, thus generating biogenic hydrodynamic trails. The structure of these trails was measured using Particle Image Velocimetry. A second seal was trained to search for and track the trail after the trail-generating seal had left the water. Our trail-following seal was able to detect and accurately track the hydrodynamic trail, showing search patterns either mostly congruent with the trail or crossing the trail repeatedly in an undulatory way. The undulatory trail-following search pattern might allow a seal to relocate a lost trail or successfully track a fleeing, zigzagging prey fish.

A longitudinal and cross-sectional analysis of total body oxygen store development in nursing harbor seals (Phoca vitulina)

This study compared the efficacy of longitudinal and cross-sectional sampling regimes for detecting developmental changes in total body oxygen (TBO(2)) stores that accompany behavioral development in free-ranging harbor seal pups. TBO(2) stores were estimated for pup (n = 146) and adult female (n = 20) harbor seals. Age related changes were compared between pups captured repeatedly during the lactation period (longitudinal dataset) and a second group of pups handled only once (cross-sectional dataset). At each handling, hematocrit, hemoglobin, red blood cell count, total plasma volume, blood volume, muscle myoglobin concentration, and blood and muscle oxygen stores were determined. Comparisons across age categories revealed newborn blood oxygen stores were initially elevated, declined to low values by early lactation, and increased through post-weaning. Muscle oxygen stores remained low and constant throughout lactation and only increased significantly post-weaning. Overall TBO(2)stores increased 17% during lactation, and weaned pups had TBO(2)stores that were 55% as large as those of adults. Thus, significant increases in TBO(2) stores must occur after weaning, as pups begin to forage independently. Results from the two sampling schemes did not differ, indicating that the logistically simpler cross-sectional design can be used to monitor physiological development in harbor seals.

Vocal development in captive harbor seal pups, Phoca vitulina richardii: age, sex, and individual differences

The goal of this research was to determine when harbor seal pup vocalizations become sufficiently distinctive to allow individual recognition. A total of 4593 calls were analyzed from 15 captive pups. Nineteen were harsh, broadband, staccato calls used in an aggressive context. The rest were tonal "mother attraction calls," having an inverted "v"- or "u"-shaped spectrogram with harmonics and a fundamental frequency around 200-600 Hz. Calls were individually distinctive even in pups less than 2 weeks old, suggesting that mothers may be able to recognize pup vocalizations at this early age. Classification rates from discriminant function analysis were generally comparable to those of other phocids and less than in otariids, supporting the theory that recognition is more highly developed in otariids. Significant differences were found between male and female pup calls, and there were significant interactions between pup sex and age. The results of this study should be interpreted with caution until the findings are verified in wild harbor seal pups.

Erythropoietin concentration in developing harbor seals (Phoca vitulina)

Tissue hypoxia elicits the production of erythropoietin (Epo), a hormone that stimulates red blood cell production. In young diving mammals, oxygen is stored primarily in the blood, and blood oxygen stores increase significantly during the first weeks of life. In an effort to establish the role of Epo during this period of blood development, this study measured Epo concentration in plasma of 134 harbor seal (Phoca vitulina) pups and adults. Concurrent measurements of hematocrit (Hct), hemoglobin concentration [Hb], and red blood cell (RBC) counts allowed the evaluation of the effect of Epo on blood oxygen store capacity. Erythropoietin and most blood parameters varied with age. At birth, neonatal [Hb], Hct, and RBC were elevated, possibly due to the rapid expansion of plasma volume associated with growth rates of 0.5 kg/day. In contrast, Epo concentration increased from 6.64 +/- 0.83 mU/ml in newborns to 9.53 +/- 0.86 mU/ml in early nursing pups. Erythropoietin concentration remained elevated above newborn and adult concentration (5.71 +/- 0.79 mU/ml) through weaning, suggesting that Epo was responding to tissue hypoxia brought on by early anemia. Since similar changes in erythropoietin have been documented in terrestrial mammals, it appears that Epo plays a similar role in the blood development of harbor seals.

Individual variation in milk composition over lactation in harbour seals (Phoca vitulina) and the potential consequences of intermittent attendance

We studied milk composition over the course of lactation in 21 harbour seal (Phoca vitulina L., 1758) females on Sable Island, Nova Scotia. Milk fat content increased significantly from 40.8% ± 1.01% at parturition to 50.2% ± 1.39% at day 7 and then remained relatively constant throughout the remainder of lactation. Changes in dry matter mirrored changes in fat content. Protein content averaged about 9% over mid to late lactation. There was considerable between-individual variation in the composition of milk and how it changed over lactation, particularly in milk fat content (CV 9.1%–11.4%). In three females that were separated from their pups for 4–6 days, milk fat content declined by 20%–23% and milk protein content increased by 6%–11%. These changes in milk composition indicate that changes in mammary gland function occur rapidly following the onset of milk stasis in harbour seals. The rapid response of the mammary glands to separation suggests that, in direct contrast to the glands of otariids, the glands of harbour seals rely on regular evacuation to maintain normal function. These results suggest that there may be a significant physiological constraint on the duration that harbour seal females, and presumably other phocid seals, can forage without negatively affecting energy transfer to their pups.

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.

The ontogeny of diving behaviour in New Zealand fur seal pups (Arctocephalus forsteri)

This study investigated the development of diving in 21 New Zealand fur seal pups, Arctocephalus forsteri (Lesson, 1828), prior to weaning at Cape Gantheaume, Kangaroo Island. Diving behaviour was examined using time–depth recorders, which were deployed during two time periods, 5 months prior to weaning (n = 6) and 2 months prior to weaning (n = 15). Scats were also examined to assess whether fur seal pups foraged prior to weaning. The maximum dive depth attained was 44 m, while the maximum dive duration was 3.3 min. Immediately prior to weaning, fur seal pups spent a greater proportion of their time diving at night, and concomitantly several measures of diving performance also increased. In general, pups dived successively deeper (6–44 m between June and September), and the average number of dives per day, dive frequency, and vertical distance travelled increased. Prey remains were present in approximately 30% of scats and indicated that some pups were foraging as early as June (5–6 months of age, approximately 4–5 months prior to weaning). Of the scats that contained prey remains, fish (South American pilchard, Sardinops sagax (Jenyns, 1842); Australian anchovy, Engraulis australis (White, 1790); and redbait, Emmelichthys nitidus Richardson, 1845) accounted for 43% of the prey items found, crustaceans accounted for 36%, and cephalopods (Gould's squid, Nototodarus gouldi (McCoy, 1888)) accounted for 20%.

Development of the blood and muscle oxygen stores in gray seals (Halichoerus grypus): implications for juvenile diving capacity and the necessity of a terrestrial postweaning fast

To successfully transition from nursing to foraging, phocid seal pups must develop adequate diving physiology within the limited time between birth and their first independent foraging trip to sea. We studied the postpartum development of oxygen stores in gray seals (Halichoerus grypus, n=40) to better understand the ontogeny of diving capacity in phocids. Hemoglobin (Hb), hematocrit (Hct), blood volume (BV), and myoglobin (Mb) levels in newborn (3 d postpartum [DPP]) and newly weaned (17+/-0.4 DPP) pups were among the lowest measured across age classes. During the pups' terrestrial postweaning fast (PWF), Hb, Hct, mass-specific BV, and Mb increased by 28%, 21%, 13%, and 29%, respectively, resulting in a 35% increase in total body mass-specific oxygen stores and a 23% increase in calculated aerobic dive limit (CADL). Although Hb and Hct levels at the end of the PWF were nearly identical to those of yearlings, total body mass-specific oxygen stores and CADL of weaned pups departing for sea were only 66%-67% and 32%-62%, respectively, of those for yearlings and adult females. The PWF represents an integral component of the physiological development of diving capacity in phocids; however, newly independent phocids still appear to have limited diving capabilities at the onset of foraging.

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.

Regional differences in diving behavior of harbor seals in the Gulf of Alaska

Adult and subadult harbor seals (Phoca vitulina richardii (Gray, 1864); n = 108) from Southeast Alaska (SE), Kodiak Island (KO), and Prince William Sound (PWS) were instrumented with satellite data recorders to examine dive parameters for harbor seals in the Gulf of Alaska at regional and annual scales. Most dives (40%–80%) were <20 m in depth and <4 min in duration; however, dives from 50 to 150 m depth were not uncommon and dives to 508 m were recorded. PWS seals spent less time in the water during the prebreeding and breeding seasons than SE and KO seals. SE seals used a greater diversity of depths than KO and PWS seals. Only seals in PWS and SE (i) dived deeper and longer and spent more time diving in winter than during spring and summer and (ii) dived deepest during the day only in winter. Seals in all regions and seasons dived most frequently and spent the most time diving at night. Subadult seals spent more time diving, dived more often, displayed a stronger diurnal pattern with deepest dives during the day in the winter, and dived deeper than adults.

Autumn diet of harbour seals (Phoca vitulina) at Prins Karls Forland, Svalbard, assessed via scat and fatty-acid analyses

This study used hard-part analyses from scats (n = 117) and stomachs (n = 3) to investigate the diet of high Arctic harbour seals (Phoca vitulina L., 1758) living on Prins Karls Forland, Svalbard, in early autumn. Additionally, it compared the results of fatty-acid analyses of the seals' blubber versus that of potential prey with the findings of the more traditional diet assessment method. Svalbard harbour seals appear to be opportunistic, polyphagous feeders similar to the situation in other parts of their range. Members of the cod-family, and secondarily the sculpin-family, dominated the diet of harbour seals on Svalbard. Small fish comprised most of the diet of the harbour seals; invertebrates appeared to be insignificant. Atlantic cod (Gadus morhua L., 1758) was the most important species in the diet in terms of biomass, whereas polar cod (Boreogadus saida (Lepechin, 1774)) was the most frequently consumed prey. Our comparison between hard-part diet analyses and fatty acids is far from definitive, but it indicates a general influence of the diet on the fatty-acid composition of the inner blubber layer. However, it also suggests systematic selective processes in the incorporation of fatty acids into the blubber. Observed differences between the fatty-acid composition of the different blubber layers and possible differences between sex and age classes warrant further investigation.

Correlation of depth and heart rate in harbour seal pups

Harbour seal (Phoca vitulina L., 1758) pups are aquatically active from birth and have been shown to develop increased cardiac control throughout the nursing period. In an attempt to quantify and compare these developmental changes, data previously collected on pups in the St. Lawrence River estuary, Quebec, Canada, were analyzed. Time–depth recorders and heart-rate recorders were employed on eight pups to obtain depth and heart-rate measurements simultaneously. Analyses involved partitioning the data into intervals of surface–dive–surface. These intervals were then allocated into nine consecutive segments: presurface, predive surface, descent, prebottom, bottom, postbottom, ascent, postdive surface, and postsurface. Mean heart rate for each segment was then correlated with the mean depth per segment and overall dive duration. With increasing dive depth, a decrease in heart-rate variability with age was observed. There was no apparent relationship between mean heart rate during the dive and overall dive duration. The proportion of time spent in the lower heart-rate mode was observed to increase with age during most phases of a dive. Relative changes in mean heart rate between consecutive dive segments indicated an initial decrease in mean heart rate prior to submersion and an increasing trend before surfacing. These findings indicate that harbour seal pups develop increased cardiac control prior to weaning and that anticipatory cardiac responses to diving and surfacing (bradycardia and tachycardia, respectively) may be evident.

Surfactant from diving aquatic mammals

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.

Weaning mass affects changes in body composition and food intake in harbour seal pups during the first month of independence

In phocid seals, the transition to nutritional independence is abrupt, with females abandoning their offspring after weaning and returning to sea. We hypothesized that body size at weaning may play an important role in the nature of this transition. We studied the changes in body composition and water flux of newly weaning harbour seals over the first 4-6 wk postweaning. Thirty-three pups were dosed with deuterium oxide to estimate total body water (TBW) and a subset of 24 was dosed twice to estimate changes in body composition and water flux. All pups lost body mass over the study period, but TBW increased during the period of mass loss, indicating continued lean tissue growth. Combined data from this and our early study indicated that heavy (>median mass) pups were relatively fatter (41.0% vs. 37.1%) and had significantly greater total body energy at weaning than did light (< or = median mass) pups. Percentage TBW declined linearly over time in light pups but was constant in heavy pups for the first 19 d postweaning and then declined linearly. Both the temporal pattern and composition of mass loss differed between light and heavy pups. Estimated food intake increased in the second 2 wk of study compared to the first 2 wk, in both light and heavy pups, reflecting increased foraging success but at levels still insufficient to meet daily expenditures of most individuals.

Pup development and timing of pupping in harbour seals (Phoca vitulina) in the St. Lawrence River estuary, Canada

Surveys to estimate the daily growth rate of harbour seal (Phoca vitulina) pups from birth to weaning and to determine the distribution of births were carried out from early May to late August 1998, 1999, and 2000 at two haulout areas in the St. Lawrence River estuary, Canada. Pups gained mass at a rate of 0.544 kg/day (standard error (SE) = 0.141, range 0.118–0.875 kg/day, N = 110). Births began between 12 and 17 May. The median dates of birth were 28 May (95% confidence interval (CI), 27–30 May) in 1998, 25 May (95% CI, 24–28 May) in 1999, and 26 May (95% CI, 24–27 May) in 2000. Births followed a normal distribution in 2000, but late pupping led to an extended tail in both 1998 and 1999. Pupping occurred at the same time in the St. Lawrence River estuary as at Sable Island, a colony located 600 km to the south, but occurred earlier than predicted by the relationship of Temte et al. (1991). The estimated median dates of weaning were 1 July (95% CI, 20 June to 12 July) in 1998, 30 June (95% CI, 19 June to 11 July) in 1999, and 26 June (95% CI, 20 June to 2 July) in 2000. Pooling years resulted in an average lactation duration of 34 days (SE = 1.8).

Pharmacological blockade of the dive response: effects on heart rate and diving behaviour in the harbour seal (Phoca vitulina)

While diving, harbour seals (Phoca vitulina) manage their oxygen stores through cardiovascular adjustments, including bradycardia, a concurrent reduction in cardiac output, and peripheral vasoconstriction. At the surface,post-dive tachycardia facilitates rapid reloading of oxygen stores. Although harbour seals can tolerate &gt;20 min of submergence, the majority of their natural dives are only 2-6 min and are usually followed by surface intervals that are &lt;1 min, so they spend approximately 80% of their time submerged. Given that harbour seals meet their ecological needs through repetitive short aerobic dives, we were interested in the functional role, if any, of the dive response during these short dives. During voluntary diving in an 11 m deep tank, the cardiovascular responses to submergence of five harbour seals were manipulated using specific pharmacological antagonists, and the effects on diving behaviour were observed. Effects of pharmacological blockade on heart rate were also examined to assess the autonomic control of heart rate during voluntary diving. Heart rate was recorded using subcutaneous electrodes and data loggers, while diving behaviour was monitored using a video camera. The muscarinic blocker methoctramine blocked diving bradycardia, theα-adrenergic blocker prazosin blocked diving vasoconstriction, and theβ-adrenergic blocker metoprolol blocked post-dive tachycardia. Heart-rate analysis indicated that diving bradycardia is primarily modulated by the vagus, while post-dive tachycardia results from parasympathetic withdrawal as well as increased sympathetic stimulation of the heart. None of the pharmacological blockers had any effect on average dive or surface interval duration. Seals maintained a high percentage of time spent diving in all treatments. Thus, harbour seals do not appear to need the dive response during short dives in order to maintain an efficient dive strategy.

Dive shapes reveal temporal changes in the foraging behaviour of different age and sex classes of harbour seals (Phoca vitulina)

Classifying dives into two-dimensional shapes based on time and depth is an attempt to extract additional information about the behaviour of aquatic air-breathing predators. In some species, there is considerable circumstantial evidence that different dive shapes represent different behaviours. However, few studies have provided direct evidence of the relationship between dive shape and function. We classified over 283 000 dives of adults (31 males and 45 females) and suckling (13) and recently weaned (15) harbour seal (Phoca vitulina) pups into seven shapes using supervised discriminant function analysis. Changes in the percentage of U-shaped dives over time within adults and weaned pups were associated with changes in food intake derived from water-flux studies on subsets of the same individuals. The changes in the percentage of U-shaped dives were accompanied by roughly reciprocal changes in V-shaped dives, whereas there was little change in other dive shapes, indicating that V-shaped dives are not generally exhibited during foraging. Video of adult males (from an animal-borne video system) also showed that there was a strong but not exclusive association between foraging and U-shaped dives. Our results indicate that changes in the percentage of U-shaped dives may serve as a reasonable index of changes in foraging behaviour. However, behaviours of suckling pups and adult males during the breeding season cannot be easily inferred from dive shape alone.

Diving development in nursing harbour seal pups

This study investigated physiological and behavioural aspects of diving development in pups of the harbour seal Phoca vitulina. Behavioural data (4280 h, 6027 dives) from time/depth recorders (N=13) deployed on pups aged 0–19 days are presented concomitantly with physiological measurements (N=8, sampled both early and late in the nursing period) of blood oxygen stores and body composition. Pups grew from 12.6±1.8 kg (mean age 2 days, total body fat 16±4 %) to 22.2±2.5 kg (mean age 16 days, total body fat 35±5 %; means ± s.d.) over the duration of the experiment. Pups less than 5 days of age had an elevated haematocrit and reduced plasma volume compared with older pups. Although plasma volume and blood volume increased, mass-specific blood oxygen stores (total haemoglobin) fell during the study period. Simultaneously, the following behavioural indicators of diving ability increased: the proportion of time spent in the water, dive depth, dive duration, bottom time and maximum daily swimming velocity. In addition, the proportion of dives that were identified by cluster analyses as being U-shaped increased significantly with age. On the basis of the measured blood oxygen stores, less than 1 % of the recorded dives exceeded the calculated aerobic dive limit. Thus, development in blood oxygen stores or rates of oxygen consumption did not seem to restrain the rate of neonatal dive development in harbour seals. It appears that behavioural modifications (experience and learning) may be the primary rate-limiting factors for ontogeny of diving skills in neonates of this species.