From ice to ocean: changes in the thermal function of harp seal pelt with ontogeny

Many animals exhibit ontogenetic changes associated with adaptations for survival. Harp seals (Pagophilus groenlandicus) live in the Arctic and rely on thick insulation to maintain thermal homeostasis. Adult harp seals primarily use blubber for insulation, but newborn harp seals rely on a lanugo pelt while nursing, as their blubber layer develops and their first-year pelage grows. This study compared ontogenetic changes in the thermal properties of harp seal pelts in water and in air. Thermal conductivity, pelt thickness, and thermal resistance were measured in water for pelts of harp seal neonates (1 day old), thin whitecoats (4 day old), fat whitecoats (9 day old), ragged jackets (2 week old), beaters (3 week old), and adults and compared to previously published measurements made on the same pelts in air. Pelt conductivity was significantly higher in water than air for pre-molt and molting pups (P ≤ 0.031). Unlike adult pelage, which flattened underwater, lanugo hairs lifted underwater, a phenomenon that has not been reported previously. Thermal resistance of the pelt was significantly reduced in water compared to air for neonates and thin whitecoats (P ≤ 0.0001). A mathematical model of conductive heat transfer for an ellipsoid body showed volume-specific heat loss in water decreased and then stabilized as harp seals aged (P = 0.0321) and was significantly higher for neonates, thin whitecoats, and ragged jackets in water than in air (P ≤ 0.0089). Overall, pelt function is reduced in water for harp seal pups with lanugo, and this renders neonates and thin whitecoats particularly vulnerable to heat loss if submerged.

Variation in adrenal and thyroid hormones with life-history stage in juvenile northern elephant seals (Mirounga angustirostris)

The classical approach to quantifying the impact of stressors on wildlife is through characterization of hormones associated with the generalized stress response. However, interpretation of hormone data can be difficult due to the range of natural variation within a species and potential confounds of individual and life-history variables. Blood adrenal and thyroid hormones were measured in 144 chemically immobilized yearling northern elephant seals (Mirounga angustirostris) to characterize variation between sexes and across semiannual haul-outs. There was no relationship between hormone concentrations and time needed for collecting blood nor evidence of diel patterns, suggesting that collection of samples for baseline values can be accomplished without bias due to handling artifacts or time of day. Serum cortisol concentrations did not vary with gender or across haul-out fasts but increased dramatically during molting. Cortisol was correlated with aldosterone across all measured life-history stages. Thyroid hormone levels were lower in females and decreased with fasting in both sexes during the fall haul-out. Cortisol concentrations were inversely associated with total triiodothyronine (T3) and positively associated with reverse T3 concentrations across all measured life-history stages suggesting an important impact of cortisol on deiodinase enzymes and thyroid function. Epinephrine concentrations increased across fasts and norepinephrine concentrations were higher in males than in females. Significant variation in stress hormone concentrations with gender and life-history stage emphasizes the importance of contextual variables when interpreting serum hormone concentrations.

Five decades on: Use of historical weaning size data reveals that a decrease in maternal foraging success underpins the long-term decline in population of southern elephant seals (Mirounga leonina)

The population of Southern elephant seals (Mirounga leonina) at Macquarie Island has declined since the 1960s, and is thought to be due to changing oceanic conditions leading to reductions in the foraging success of Macquarie Island breeding females. To test this hypothesis, we used a 55-year-old data set on weaning size of southern elephant seals to quantify a decrease in weaning size from a period of population stability in 1950s to its present state of on-going decline. Being capital breeders, the size of elephant seal pups at weaning is a direct consequence of maternal foraging success in the preceding year. During the 1940-1950s, the mean of female pups at weaning was similar between the Heard and Macquarie Island populations, while the snout-tail-length length of male weaners from Heard Island were longer than their conspecifics at Macquarie Island. Additionally, the snout-tail-length of pups at weaning decreased by 3cm between the 1950s and 1990s in the Macquarie Island population, concurrent with the observed population decline. Given the importance of weaning size in determining first-year survival and recruitment rates, the decline in the size at weaning suggests that the decline in the Macquarie Island population has, to some extent, been driven by reduced maternal foraging success, consequent declines in the size of pups at weaning, leading to reduced first-year survival rates and recruitment of breeding females into the population 3 to 4 years later.

Shipping noise in a dynamic sea: a case study of grey seals in the Celtic Sea

Shipping noise is a threat to marine wildlife. Grey seals are benthic foragers, and thus experience acoustic noise throughout the water column, which makes them a good model species for a case study of the potential impacts of shipping noise. We used ship track data from the Celtic Sea, seal track data and a coupled ocean-acoustic modelling system to assess the noise exposure of grey seals along their tracks. It was found that the animals experience step changes in sound levels up to ~20dB at a frequency of 125Hz, and ~10dB on average over 10-1000Hz when they dive through the thermocline, particularly during summer. Our results showed large seasonal differences in the noise level experienced by the seals. These results reveal the actual noise exposure by the animals and could help in marine spatial planning.

Effects of environmental variables on surface temperature of breeding adult female northern elephant seals, Mirounga angustirostris, and pups

Pinnipeds spend extended periods of time on shore during breeding, and some temperate species retreat to the water if exposed to high ambient temperatures. However, female northern elephant seals (Mirounga angustirostris) with pups generally avoid the water, presumably to minimize risks to pups or male harassment. Little is known about how ambient temperature affects thermoregulation of well insulated females while on shore. We used a thermographic camera to measure surface temperature (T_s) of 100 adult female elephant seals and their pups during the breeding season at Point Reyes National Seashore, yielding 782 thermograms. Environmental variables were measured by an onsite weather station. Environmental variables, especially solar radiation and ambient temperature, were the main determinants of mean and maximum T_s of both females and pups. An average of 16% of the visible surface of both females and pups was used as thermal windows to facilitate heat loss and, for pups, this area increased with solar radiation. Thermal window area of females increased with mean T_s until approximately 26°C and then declined. The T_s of both age classes were warmer than ambient temperature and had a large thermal gradient with the environment (female mean 11.2±0.2°C; pup mean 14.2±0.2°C). This large gradient suggests that circulatory adjustments to bypass blubber layers were sufficient to allow seals to dissipate heat under most environmental conditions. We observed the previously undescribed behavior of females and pups in the water and determined that solar radiation affected this behavior. This may have been possible due to the calm waters at the study site, which reduced the risk of neonates drowning. These results may predict important breeding habitat features for elephant seals as solar radiation and ambient temperatures change in response to changing climate.

To each its own: Thermoregulatory strategy varies among neonatal polar phocids

Cold environmental conditions and small body size promote heat loss and may create thermoregulatory challenges for marine mammals born in polar regions. However, among polar-born phocid seal species there are variations in physical attributes and environmental conditions at birth, allowing for an interesting contrast in thermoregulatory strategy. We compared thermoregulatory strategies through morphometrics, sculp attributes (conductivity and resistance), nonshivering thermogenesis (NST via uncoupling protein 1; UCP1), and muscle thermogenesis (via enzyme activity) in neonatal harp (Pagophilus groenlandicus), hooded (Cystophora cristata), and Weddell seals (Leptonychotes weddellii). Harp seals are the smallest at birth (9.8±0.7 kg), rely on lanugo (82.49±3.70% of thermal resistance), and are capable of NST through expression of UCP1 in brown adipose tissue (BAT). In contrast, hooded seal neonates (26.8±1.3 kg) have 2.06±0.23 cm of blubber, accounting for 38.19±6.07% of their thermal resistance. They are not capable of NST, as UCP1 is not expressed. The large Weddell seal neonates (31.5±4.9 kg) rely on lanugo (89.85±1.25% of thermal resistance) like harp seals, but no evidence of BAT was found. Muscle enzyme activity was highest in Weddell seal neonates, suggesting that they rely primarily on muscle thermogenesis. Similar total thermal resistance, combined with marked differences in thermogenic capacity of NST and ST among species, strongly supports that thermoregulatory strategy in neonatal phocids is more closely tied to pups' surface area to volume ratio (SA:V) and potential for early water immersion rather than mass and ambient environmental conditions.

Metabolic responses to adrenocorticotropic hormone (ACTH) vary with life-history stage in adult male northern elephant seals

Strong individual and life-history variation in serum glucocorticoids has been documented in many wildlife species. Less is known about variation in hypothalamic-pituitary-adrenal (HPA) axis responsiveness and its impact on metabolism. We challenged 18 free-ranging adult male northern elephant seals (NES) with an intramuscular injection of slow-release adrenocorticotropic hormone (ACTH) over 3 sample periods: early in the breeding season, after 70+ days of the breeding fast, and during peak molt. Subjects were blood sampled every 30 min for 2h post-injection. Breeding animals were recaptured and sampled at 48 h. In response to the ACTH injection, cortisol increased 4-6-fold in all groups, and remained elevated at 48 h in early breeding subjects. ACTH was a strong secretagogue for aldosterone, causing a 3-8-fold increase in concentration. Cortisol and aldosterone responses did not vary between groups but were correlated within individuals. The ACTH challenge produced elevations in plasma glucose during late breeding and molting, suppressed testosterone and thyroid hormone at 48 h in early breeding, and increased plasma non-esterified fatty acids and ketoacids during molting. These data suggest that sensitivity of the HPA axis is maintained but the metabolic impacts of cortisol and feedback inhibition of the axis vary with life history stage. Strong impacts on testosterone and thyroid hormone suggest the importance of maintaining low cortisol levels during the breeding fast. These data suggest that metabolic adaptations to extended fasting in NES include alterations in tissue responses to hormones that mitigate deleterious impacts of acute or moderately sustained stress responses.

The role of canine distemper virus and persistent organic pollutants in mortality patterns of Caspian seals (Pusa caspica)

Persistent organic pollutants are a concern for species occupying high trophic levels since they can cause immunosuppression and impair reproduction. Mass mortalities due to canine distemper virus (CDV) occurred in Caspian seals (Pusa caspica), in spring of 1997, 2000 and 2001, but the potential role of organochlorine exposure in these epizootics remains undetermined. Here we integrate Caspian seal mortality data spanning 1971–2008, with data on age, body condition, pathology and blubber organochlorine concentration for carcases stranded between 1997 and 2002. We test the hypothesis that summed PCB and DDT concentrations contributed to CDV associated mortality during epizootics. We show that age is the primary factor explaining variation in blubber organochlorine concentrations, and that organochlorine burden, age, sex, and body condition do not account for CDV infection status (positive/negative) of animals dying in epizootics. Most animals (57%, n = 67) had PCB concentrations below proposed thresholds for toxic effects in marine mammals (17 µg/g lipid weight), and only 3 of 67 animals had predicted TEQ values exceeding levels seen to be associated with immune suppression in harbour seals (200 pg/g lipid weight). Mean organonchlorine levels were higher in CDV-negative animals indicating that organochlorines did not contribute significantly to CDV mortality in epizootics. Mortality monitoring in Azerbaijan 1971–2008 revealed bi-annual stranding peaks in late spring, following the annual moult and during autumn migrations northwards. Mortality peaks comparable to epizootic years were also recorded in the 1970s–1980s, consistent with previous undocumented CDV outbreaks. Gompertz growth curves show that Caspian seals achieve an asymptotic standard body length of 126–129 cm (n = 111). Males may continue to grow slowly throughout life. Mortality during epizootics may exceed the potential biological removal level (PBR) for the population, but the low frequency of epizootics suggest they are of secondary importance compared to anthropogenic sources of mortality such as fishing by-catch.

Spatially explicit estimates of prey consumption reveal a new krill predator in the Southern Ocean

Development in foraging behaviour and dietary intake of many vertebrates are age-structured. Differences in feeding ecology may correlate with ontogenetic shifts in dispersal patterns, and therefore affect foraging habitat and resource utilization. Such life-history traits have important implications in interpreting tropho-dynamic linkages. Stable isotope ratios in the whiskers of sub-yearling southern elephant seals (Mirounga leonina; n = 12) were used, in conjunction with satellite telemetry and environmental data, to examine their foraging habitat and diet during their first foraging migration. The trophic position of seals from Macquarie Island (54°30′S, 158°57′E) was estimated using stable carbon (δ¹³C) and nitrogen (δ¹⁵N) ratios along the length of the whisker, which provided a temporal record of prey intake. Satellite-relayed data loggers provided details on seal movement patterns, which were related to isotopic concentrations along the whisker. Animals fed in waters south of the Polar Front (>60°S) or within Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) Statistical Subareas 88.1 and 88.2, as indicated by both their depleted δ¹³C (<−20‰) values, and tracking data. They predominantly exploited varying proportions of mesopelagic fish and squid, and crustaceans, such as euphausiids, which have not been reported as a prey item for this species. Comparison of isotopic data between sub-yearlings, and 1, 2 and 3 yr olds indicated that sub-yearlings, limited by their size, dive capabilities and prey capture skills to feeding higher in the water column, fed at a lower trophic level than older seals. This is consistent with the consumption of euphausiids and most probably, Antarctic krill (Euphausia superba), which constitute an abundant, easily accessible source of prey in water masses used by this age class of seals. Isotopic assessment and concurrent tracking of seals are successfully used here to identify ontogenetic shifts in broad-scale foraging habitat use and diet preferences in a highly migratory predator.

Shifts in thermoregulatory strategy during ontogeny in harp seals (Pagophilus groenlandicus)

Heat balance can be difficult for young and/or small animals in polar regions because environmental conditions in combination with small body size or physiological immaturity can increase heat loss. We investigated how thermoregulatory patterns change with ontogeny in 5 age classes of harp seal (Pagophilus groenlandicus) from birth to post-molt to further understand the timing of thermoregulatory development in relation to their potential vulnerability to ongoing fluctuations in the extent and stability of Arctic pack ice. We measured changes in the amount, conductivity, and resistance of the seal pups׳ insulative layers (blubber and fur), the potential for endogenous heat-generation by shivering (muscle enzyme activity), and nonshivering thermogenesis (NST; brown adipose tissue (BAT) uncoupling protein 1 (UCP1) expression and mitochondrial density). There was no significant difference in blubber conductivity among age classes, though the amount of blubber insulation significantly increased from birth to weaning. Pelage conductivity was low (0.12±0.01Wm(-1)°C(-1)) except in 9-day old pups (0.40±0.08Wm(-1)°C(-1)); the significantly higher conductivity may signal the beginning of the molt, and this age group may be the most vulnerable to early water entry. Citrate synthase activity significantly increased (49.68±3.26 to 75.08±3.52μmolmin(-1)gwetweight(-1)) in the muscle; however it is unlikely that increasing a single enzyme greatly impacts heat generation. BAT of younger pups contained UCP1, though expression and mitochondrial density quickly declined, and the ability of pups to produce heat via NST was lost by weaning. While total thermal resistance did not differ, neonatal and early nursing animals gained the majority of their thermal resistance from lanugo (82.5±0.03%); however, lanugo is not insulative when wet, and NST may be important to maintain euthermia and dry the coat if early immersion in water occurs. By late nursing, blubber seems sufficient as insulation (75.87±0.01% of resistance after 4 weeks), but high conductivity of fur may be responsible for retention of UCP1 expression. Weaned animals rely on blubber insulation, and no longer need NST, as wetted fur is no longer a threat to euthermia.

Metabolic response to a glucagon challenge varies with adiposity and life-history stage in fasting northern elephant seals

Metabolic adaptations for extended fasting in wildlife prioritize beta-oxidation of lipids and reduced glucose utilization to support energy metabolism. The pancreatic hormone glucagon plays key roles in regulating glycemia and lipid metabolism during fasting in model species but its function in wildlife species adapted for extended fasting is not well understood. Northern elephant seals (NES) undergo natural fasts of 1-3months while under constraints of high nutrient demands including lactation and development. We performed a glucagon challenge on lactating, molting and developing NES, early and late in their natural fasts, to examine the impact of this important regulatory hormone on metabolism. Glucagon caused increases in plasma glucose, insulin, fatty acids, ketones and urea, but the magnitude of these effects varied widely with adiposity and life-history stage. The strong impact of adiposity on glucose and insulin responses suggest a potential role for adipose derived factors in regulating hepatic metabolism and pancreatic sensitivity. Elevations in plasma glucose in response to glucagon were strongly associated with increases in protein catabolism, suggesting negative impacts of elevated glucagon on protein sparing. Glucagon promoted rapid ketone accumulation suggesting that low ketoacid levels in NES reflect low rates of production. These results demonstrate strong metabolic impacts of glucagon and support the idea that glucagon levels are downregulated in the context of metabolic adaptation to extended fasting. These results suggest that the regulation of carbohydrate and lipid metabolism in NES changes with adiposity, fasting duration and under various constraints of nutrient demands.

Assessment of legacy and emerging persistent organic pollutants in Weddell seal tissue (Leptonychotes weddellii) near McMurdo Sound, Antarctica

Muscle samples were collected from pup, juvenile and adult Weddell seals (Leptonychotes weddellii) near McMurdo Sound, Antarctica during the austral summer of 2006. Blubber samples were collected from juvenile and adult seals. Samples were analyzed for emerging and legacy persistent organic pollutants (POPs) including current and historic-use organochlorine pesticides, polychlorinated biphenyls (PCBs), and polybrominated diphenyl ethers (PBDEs). Of the 41 target analytes, 28 contaminants were recovered from the Weddell seal blubber, in this order of prevalence: p,p'-DDE, p,p'-DDT, trans-nonachlor, mirex, cis-nonachlor, PCB 153, PCB 138, dieldrin, heptachlor epoxide, nonachlor III, PCB 187, oxychlordane, cis-chlordane, PCB 118, PBDE 47, PCB 156, PCB 149, PCB 180, PCB 101, PCB 170, PCB 105, o,p'-DDT, PCB 99, trans-chlordane, PCB 157, PCB 167, PCB 189, and PCB 114. Fewer POPs were found in the muscle samples, but were similar in the order of prevalence to that of the blubber: p,p'-DDE, o,p'-DDT, trans-nonachlor, nonachlor III, oxychlordane, p,p'-DDT, dieldrin, mirex, cis-nonachlor, PCB 138, and PCB 105. Besides differences in toxicant concentrations reported between the muscle and blubber, we found differences in POP levels according to age class and suggest that differences in blubber storage and/or mobilization of lipids result in age class differences in POPs. To our knowledge, such ontogenetic associations are novel. Importantly, data from this study suggest that p,p'-DDT is becoming less prevalent temporally, resulting in an increased proportion of its metabolite p,p'-DDE in the tissues of this top predator. In addition, this study is among the first to identify a PBDE congener in Weddell seals near the McMurdo Station. This may provide evidence of increased PBDE transport and encroachment in Antarctic wildlife.

Could seals prevent cod recovery in the Baltic Sea?

Fish populations are increasingly affected by multiple human and natural impacts including exploitation, eutrophication, habitat alteration and climate change. As a result many collapsed populations may have to recover in ecosystems whose structure and functioning differ from those in which they were formerly productive and supported sustainable fisheries. Here we investigate how a cod (Gadus morhua) population in the Baltic Sea whose biomass was reduced due to a combination of high exploitation and deteriorating environmental conditions might recover and develop in the 21st century in an ecosystem that likely will change due to both the already started recovery of a cod predator, the grey seal Halichoerus grypus, and projected climate impacts. Simulation modelling, assuming increased seal predation, fishing levels consistent with management plan targets and stable salinity, shows that the cod population could reach high levels well above the long-term average. Scenarios with similar seal and fishing levels but with 15% lower salinity suggest that the Baltic will still be able to support a cod population which can sustain a fishery, but biomass and yields will be lower. At present knowledge of cod and seal interactions, seal predation was found to have much lower impact on cod recovery, compared to the effects of exploitation and salinity. These results suggest that dual management objectives (recovery of both seal and cod populations) are realistic but success in achieving these goals will also depend on how climate change affects cod recruitment.

Effects of mass and body composition on fasting fuel utilisation in grey seal pups (Halichoerus grypus Fabricius): an experimental study using supplementary feeding

This study used supplementary feeding to test the hypothesis that fuel partitioning during the postweaning fast in grey seal pups is affected by size and composition of energy reserves at weaning, and by extra provisioning. Mass and body composition changes were measured during suckling and fasting to investigate the effect of natural differences in energy reserves at weaning on subsequent allocation of fat and protein to energy use. We fed seven pups for 5 days after weaning, to investigate the effect of increased fuel availability, and particularly protein, on fuel utilisation. After correcting for protein used during the moult, the proportional contribution of fat was 86-99% of total energy use. Pups with greater energy reserves, i.e. those that were heavier and fatter at weaning, had higher rates of fat and energy use. There was no significant relationship between adiposity at weaning and proportional contribution of fat to energy use, perhaps due to a limited sample size or range of body masses and adiposity. Supplemented individuals used energy, specifically fat, much faster and utilised proportionally less of their endogenous protein by departure than non-supplemented individuals. Fat metabolism contributed a similar percentage to daily energy use in both groups. These findings show that pups spare protein, even when energy use is dramatically increased. Pups that receive greater maternal provisioning and lay down more protein may have increased survival chances at sea. This study highlights the importance of protein reserves in first year survival of grey seal pups.

Size and distribution of oxygen stores in harp and hooded seals from birth to maturity

Pinnipeds rely primarily on oxygen stores in blood and muscles to support aerobic diving; therefore rapid development of body oxygen stores (TBO(2)) is crucial for pups to transition from nursing to independent foraging. Here, we investigate TBO(2) development in 45 harp (Pagophilus groenlandicus) and 46 hooded (Cystophora cristata) seals ranging in age from neonates to adult females. We found that hooded seal adults have the largest TBO(2) stores yet reported (89.5 ml kg(-1)), while harp seal adults have values more similar to other phocids (71.6 ml kg(-1)). In adults, large TBO(2) stores resulted from large blood volume (harp169, hood 194 ml kg(-1)) and high muscle Mb content (harp 86.0, hood 94.8 mg g(-1)). In contrast, pups of both species had significantly lower mass-specific TBO(2 )stores than adults, and stores declined rather than increased during the nursing period. This decline was due to a reduction in mass-specific blood volume and the absence of an increase in the low Mb levels (harp 21.0, hood 31.5 mg g(-1)). Comparisons with other phocid species suggests that the pattern of blood and muscle development in the pre- and post-natal periods varies with terrestrial period, and that muscle maturation rates may influence the length of the postweaning fast. However, final maturation of TBO(2) stores does not take place until after foraging begins.

Incorporating movement into models of grey seal population dynamics

1. One of the most difficult problems in developing spatially explicit models of population dynamics is the validation and parameterization of the movement process. We show how movement models derived from capture-recapture analysis can be improved by incorporating them into a spatially explicit metapopulation model that is fitted to a time series of abundance data. 2. We applied multisite capture-recapture analysis techniques to photo-identification data collected from female grey seals at the four main breeding colonies in the North Sea between 1999 and 2001. The best-fitting movement models were then incorporated into state-space metapopulation models that explicitly accounted for demographic and observational stochasticity. 3. These metapopulation models were fitted to a 20-year time series of pup production data for each colony using a Bayesian approach. The best-fitting model, based on the Akaike Information Criterion (AIC), had only a single movement parameter, whose confidence interval was 82% less than that obtained from the capture-recapture study, but there was some support for a model that included an effect of distance between colonies. 4. The state-space modelling provided improved estimates of other demographic parameters. 5. The incorporation of movement, and the way in which it was modelled, affected both local and regional dynamics. These differences were most evident as colonies approached their carrying capacities, suggesting that our ability to discriminate between models should improve as the length of the grey seal time series increases.

Juvenile Southern Elephant Seals Exhibit Seasonal Differences in Energetic Requirements and Use of Lipids and Protein Stores

Growing juvenile animals undergo many morphological, physiological, and behavioural changes that influence their energetic requirements, patterns of energy use, and ultimately, their survival and reproductive success. We examined changes in mass loss and body composition of juvenile southern elephant seals (1- and 2-yr-olds) during their two annual haul-outs. At the start and end of the midyear and molt haul-outs, we caught, weighed, and measured 41 and 14 seals, respectively. We measured blubber depth using ultrasound to estimate body composition (lean and adipose tissue mass). Using energy densities of the adipose and lean tissue, we calculated total, lean, and adipose mass changes and energy expenditure. While molting, juvenile seals used more energy than during the midyear, which is related to the increased use of lean tissue for hair and skin regeneration. The amount of energy used increases with mass as individuals mature. We found sexual differences in energy use where females retained greater fat reserves than males by utilizing more lean tissue. These differences are most likely related to haul-out function and behavior, growth, and earlier development of females toward sexual maturity.

Serum immunoglobulin G concentration in Southern elephant seal, Mirounga leonina (Linnaeus, 1758), from Elephant island (Antarctica): Sexual and adrenal steroid hormones effects

Serum immunoglobulin G (IgG; indirect enzyme-linked immunosorbent assay), as well as sexual and adrenal steroid hormones' concentrations (radioimmunoassay) were determined in 63 (male and female) Southern elephant seals (Mirounga leonine) at different developmental stages (weaned pups, juveniles and adults). In females, IgG values (mean+/-S.D.) were higher (P<0.05) in adults (15.9+/-6.5mg ml(-1)) than in juveniles (7.9+/-4.0mg ml(-1)), but similar to weaned pups (12.0+/-5.0mg ml(-1)). Estrogen concentration was higher (P<0.05) in adults than in the weaned pups. In females, a significant (P<0.05) correlation (R=0.4) between serum IgG level and progesterone concentration was observed. In males, testosterone concentration was higher (P<0.05) in adults than in the juveniles and weaned pups. Aldosterone and cortisol concentrations were higher (P<0.05) in weaned pups (1056.0+/-643.1pmol 1(-1) and 272.7+/-110.0 nmol 1(-1), respectively) than in the juveniles (638.6+/-579.7pmol1(-1) and 152.9+/-97.3nmol 1(-1), respectively) and adults (386.5+/-209.1pmol (-1) and 145.7+/-67.3nmol 1(-1), respectively). These findings indicate that weaned pups are subjected to a higher natural stressful condition in the field. Despite this, humoral immunity, measured through IgG concentration, is not impaired in weaned pups.

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.

Inferring extinction from a sighting record

The extinctions of plant and animal species are almost never observed directly, but must be inferred from sighting records. This paper reviews some methods for statistical inference about the extinction of a single species based on a record of its sightings.

Ocean climate and seal condition

Background

The condition of many marine mammals varies with fluctuations in productivity and food supply in the ocean basin where they forage. Prey is impacted by physical environmental variables such as cyclic warming trends. The weaning weight of northern elephant seal pups, Mirounga angustirostris, being closely linked to maternal condition, indirectly reflects prey availability and foraging success of pregnant females in deep waters of the northeastern Pacific. The aim of this study was to examine the effect of ocean climate on foraging success in this deep-diving marine mammal over the course of three decades, using cohort weaning weight as the principal metric of successful resource accrual.

Results

The mean annual weaning weight of pups declined from 1975 to the late 1990s, a period characterized by a large-scale, basin-wide warm decadal regime that included multiple strong or long-duration El Niños; and increased with a return to a cool decadal regime from about 1999 to 2004. Increased foraging effort and decreased mass gain of adult females, indicative of reduced foraging success and nutritional stress, were associated with high ocean temperatures.

Conclusion

Despite ranging widely and foraging deeply in cold waters beyond coastal thermoclines in the northeastern Pacific, elephant seals are impacted significantly by ocean thermal dynamics. Ocean warming redistributes prey decreasing foraging success of females, which in turn leads to lower weaning mass of pups. Annual fluctuations in weaning mass, in turn, reflect the foraging success of females during the year prior to giving birth and signals changes in ocean temperature cycles.

Estradiol and Testosterone Concentrations Increase with Fasting in Weaned Pups of the Northern Elephant Seal (Mirounga angustirostris)

Although neonatal development is generally associated with increased levels of circulating testosterone (T) and estradiol (E2), food deprivation may inhibit steroidogenesis. Therefore, these potentially conflicting stimuli were examined in fasting weaned northern elephant seal (Mirounga angustirostris) pups by measuring serum concentrations of T, E2, progesterone (P4), and luteinizing hormone (LH) by either radioimmunoassay (P4, LH) or enzymeimmunoassay (T, E2). Blood samples were obtained from 20 male and 20 female pups at both early (<1 wk postweaning) and late (6-8 wk postweaning) periods during their natural postweaning fast. T in males (early: 2.9 +/- 0.4 ng/mL; late: 16 +/- 2 ng/mL; P < 0.0001) and E2 in females (early: 42 +/- 6 pg/mL; late: 67 +/- 5 pg/mL; P < 0.01) increased between the two measurement periods, while P4 (early: 2.5 +/- 0.3 ng/mL; late: 2.1 +/- 0.3 ng/mL; P > 0.05) did not. LH increased (early: 46 +/- 4 pg/mL; late: 65 +/- 6 pg/mL; P < 0.05) in males but not in females (early: 69 +/- 9 pg/mL; late: 65 +/- 6 pg/mL; P > 0.05). Increases in LH and T suggest that LH may stimulate T secretion. Alternatively, relatively low concentrations of LH in both males and females may reflect negative feedback inhibition imposed by elevated T and E2 concentrations. Despite the inherent postweaning fast, concentrations of T and E2 increased, suggesting that they may be critical for the continued development of pups. Therefore, compensatory mechanisms may exist that alleviate the fasting-induced inhibition of gonadal steroidogenesis during neonatal development in elephant seal pups.

The immunocompetence handicap hypothesis in two sexually dimorphic pinniped species--is there a sex difference in immunity during early development?

The 'immunocompetence handicap hypothesis' predicts that highly sexually dimorphic and polygynous species will exhibit sex differences in immunity. We tested this hypothesis in southern elephant and grey seals during their early development by measuring the following parameters: leucocyte counts, serum IgG levels, erythrocyte sedimentation rate and haematocrit. We failed to find any differences due to sex as assessed by the parameters investigated. Animals were sampled longitudinally during their development and there were significant age effects from birth to weaning in both species. Total and differential leucocyte counts and erythrocyte sedimentation rates increased just prior to weaning then decreased. Haematocrits declined whilst total circulating immunoglobulin G concentrations increased. Body temperatures remained constant throughout the postnatal period. Differences between the species were seen in total leucocyte counts and in polymorphonuclear cells and eosinophils. Southern elephant seals had higher concentrations than grey seals and total leucocyte counts in the former were among the highest reported for mammals.

Hormonal changes associated with the transition between nursing and natural fasting in northern elephant seals (Mirounga angustirostris)

To better interpret previously described hormonal changes observed during the natural postweaning fast (2-3 months) endured by pups of the northern elephant seal (Mirounga angustirostris), we compared plasma cortisol, thyroid hormones, and leptin in pups (n=5) measured during nursing and fasting periods. Blood samples were taken at four times; early (9 days postpartum) and late (18-22 days postpartum) nursing, and early (second week postweaning) and late (eighth week postweaning) fasting. Plasma cortisol increased 39% between early and late nursing and almost 4-fold by late fasting. After the early nursing period, cortisol and body mass were negatively correlated (y=28.3-0.19 x; R=0.569; p=0.027). Total thyroxine (tT(4)), free T(4) (fT(4)), total triiodothyronine (tT3) and reverse T(3) (rT(3)) were greatest at early nursing and reduced by late nursing and remained so throughout the fast, with the exception of tT(4), which increased between late nursing (17.7+/-2.1 ng mL(-1)) and late fasting (30.1+/-2.8 ng mL(-1)) periods. Leptin remained unaltered among the four sampling periods and was not correlated with body mass. Pups appear to exhibit a shift in the relationship between cortisol and body mass suggesting a potential role for cortisol in the regulation of body fat. The higher concentrations of tT(3) and tT(4) during early nursing may reflect enhanced growth and development during this period, however the increase late in fasting is likely physiologically insignificant and an artifact of reduced metabolic clearance of these hormones. Transition of the pups from nursing to fasting states is characterized by a striking lack of change in cortisol, thyroid hormones, and leptin suggesting that any metabolic alterations associated with this transition may occur independent of these hormones.

The trouble with sealworms (Pseudoterranova decipiens species complex, Nematoda): a review

Sealworms or codworms, larvae of ascaridoid nematodes belonging to the Pseudoterranova decipiens species complex, infect the flesh of numerous species of marine and euryhaline fish, and have proven a chronic and costly cosmetic problem for seafood processors. Moreover, the parasite may cause abdominal discomfort in humans when consumed in raw, undercooked or lightly marinated fish. In this review, the phylogeny, life cycle and distributions of sealworms are discussed along with biotic and abiotic factors which may influence distributions of these parasites in their intermediate and final hosts. Also considered here are efforts to control the problem through commercial fishing practices, fish processing technology, and the reduction of infection parameters in marine fish populations by biological means. Ironically, concern over sealworm problem has subsided in some fisheries in recent years, not as a result of falling infection parameters in fish stocks or innovations in processing technology, but as a consequence of declines in abundance and size of groundfish.

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.

Postweaning duration and body composition changes in Southern elephant seal (Mirounga leonina) pups at King George Island

Weaning mass in southern elephant seals is highly variable, the heaviest pups being three times as heavy as the lightest ones. After weaning, pups undergo an extensive postweaning period in which they draw on their reserves. To quantify the energy expenditure during the postweaning period, changes in mass, body composition, and postweaning duration were measured in southern elephant seals at King George Island, South Shetland Islands, Antarctica. Overall, mean pup weaning mass was 154 +/- 26 kg (n=117) and did not differ between sexes. Mean minimum postweaning duration was 42.5 +/- 7.5 d. Heavier animals at weaning had lower mass-specific mass loss rates than lighter ones, and a faster depletion of body reserves was associated with a shorter postweaning period. The proportion of body mass represented by fat at weaning was 37% +/- 4% (n=47) and did not differ between sexes. Of these pups, 36 were recaptured after a mean period of 36 d after weaning. On average, total mass loss measured in these animals (39 kg) was composed of 39% water, 47% fat, and 12% protein. The composition of mass loss was not significantly different between sexes and was not related to weaning mass or total body energy reserves. However, fatter animals at weaning lost more fat per kilogram lost than thinner ones. Late in the fast, males and females appeared to be in a similar body condition. Nevertheless, the overall proportion of body mass represented by fat at this time was lower than that presented by the same animals at weaning. We estimated that during the postweaning period pups lost, on average, 30% of their mass at weaning. This comprised approximately 35% of the energy and 32% of the fat in the pup's body.

Mercury, cadmium, lead and selenium in ringed seals (Phoca hispida) from the Baltic Sea and from Svalbard

The concentrations of mercury (Hg), cadmium (Cd), lead (Pb) and selenium (Se) were determined in liver, kidney and muscle samples from 20 Baltic ringed seals (Phoca hispida botnica) (3-32 years), and from 17 ringed seals (Phoca hispida) (0-20 years) from Svalbard, in the Arctic. The concentrations of Hg and Se were considerably higher in the Baltic ringed seals, but the Cd concentrations lower than in the Svalbard ringed seals. There was no big geographical difference with respect to Pb concentrations. Se and Hg concentrations showed a significant positive correlation in both regions. By comparison with earlier studies on Baltic seals, the metal concentrations have remained at the same level since the 1980s. Of the metals we studied, only the level of Hg in Baltic ringed seals can be considered high (mean 53 mg/kg, range 6.5-124 mg/kg wet wt. for liver), but probably not high enough to cause metal intoxication. No pathological changes associated with metal intoxication were observed in the seals.

Effect of a low-Fat diet on body composition and blubber fatty acids of captive juvenile harp seals (Phoca groenlandica)

We investigated the effects of a change from a high-fat diet to a low-fat diet of differing fatty acid (FA) composition on the body composition and blubber FA of five captive juvenile harp seals. Seals that had been maintained for 1 yr on a diet of Atlantic herring (>/=9% fat) were switched to a diet of Atlantic pollock (1. 7% fat) for 30 d. On days 0, 14, and 30, mass and body composition (using isotope dilution) were measured, and blubber biopsies (5 cmx6 mm) were taken for FA analysis. Fat accounted for 38%-49% of body mass at the start of the experiment. When switched to the pollock diet, and despite food intakes averaging 6.5 kg/d (32.3 MJ/d), body fat declined by an average of 6.4 kg or by 32% over the 30-d experiment. In contrast, body protein increased in direct relation to protein intake (r2=0.836, P=0.030). Despite substantial loss of body fat, blubber FA signature changed significantly to reflect the changes in dietary intake of FA, and the deposition of FA was quantifiably predictable. Our results suggest that young growing phocids are unable to maintain body fat stores on low-fat diets even when protein intakes are high. This may have significant implications for juvenile pinniped survival in the wild. In addition, turnover and deposition of dietary FA in blubber takes place in nonfattening seals.

Fat transfer and energetics during lactation in the hooded seal: the roles of tissue lipoprotein lipase in milk fat secretion and pup blubber deposition

Hooded seals (Cystophora cristata) lactate for 3.6 days during which females simultaneously fast and transfer large amounts of energy to their pups through fat-rich milk. Pups grow rapidly, principally due to blubber deposition. Lipoprotein lipase (LPL), the primary enzyme responsible for tissue uptake of triglyceride fatty acids, may strongly influence both maternal milk fat secretion and pup blubber deposition. We measured the energetic costs of lactation (using hydrogen isotope dilution, 3H2O), milk composition, prolactin, and LPL activity (post-heparin plasma LPL [PH LPL], blubber, mammary gland and milk; U) in six females. PH LPL and blubber LPL were measured in their pups. Females depleted 216.3 MJ.day-1 of body energy and fat accounted for 59% of maternal mass loss and 90% of postpartum body energy loss, but maternal body composition changed little. Maternal blubber LPL was negligible (0.0-0.2 U), while mammary LPL was elevated (1.8-2.5 U) and was paralleled by changes in prolactin. Estimated total mammary LPL activity was high (up to 20,000 U.animal-1) effectively favoring the mammary gland for lipid uptake. Levels of total blubber LPL in pups increased seven-fold over lactation. Pups with higher PH LPL at birth had greater relative growth rates (P = 0.025). Pups with greater blubber stores and total blubber LPL activity had elevated rates of fat deposition (P = 0.035).

Effects of hypoxia and hypercapnia on aerobic metabolic processes in northern elephant seals

An hypoxia-induced metabolic down-regulation has been implicated as an important protective mechanism against tissue deoxygenation in mammals. Whether the same response to hypoxia occurs in northern elephant seals was studied. The effects of hypercapnia were also examined to determine whether the reduced ventilatory response of seals to CO2 is associated with an analogous protective metabolic down-regulation. Thirty three seals (7-300-days-old) were studied using open-flow respirometry with simultaneous monitoring of apnea frequencies and heart rates. Hypoxia (11% O2) and hypercapnia (7% CO2) caused increases in metabolism of up to 38% with corresponding decreases in the percent time spent apneic (%AP) and increases in heart rate. The metabolic, breathing and heart rate responses to altered inspired gases were independent of age. Metabolism was strongly negatively correlated with %AP suggesting that elevated metabolism during hypoxia and hypercapnia exposure is attributable to decreases in %AP. In young elephant seals metabolic down-regulation is not an automatic protective response to experimentally-imposed hypoxia or hypercapnia.

Development of cardiorespiratory patterns associated with terrestrial apneas in free-ranging southern elephant seals

Elephant seals resting on land show an irregular breathing pattern that combines periods of eupnea and apnea. In this article we describe ontogenetic changes in the breathing pattern and in the associated cardiac response in resting pups and weanlings of the southern elephant seal, Mirounga leonina. Apnea duration and the percentage of time spent in apnea were positively correlated with age: mean apnea length was greater in weanlings than in pups, with weanlings holding their breath for up to 8.7 min. Apnea length was not correlated with the duration of preceding or subsequent eupneas. The heart rate of pups and weanlings on land followed the pattern of bradycardia during apnea and tachycardia during eupnea. Young weanlings had a significantly smaller decrease in heart rate during apnea than older weanlings (28% vs. 36%). The instantaneous heart rate response to breathing changed from a variable to a regular pattern. These results suggest that the control processes that modulate the physiological cardiorespiratory changes necessary for diving start to develop on land during the first 11 wk of life.

Ontogeny of humoral immunity in northern elephant seal (Mirounga angustirostris) neonates

Northern elephant seal (NES) serum concentrations of total immunoglobulin (Ig) G, an IgG sub-class, and an IgM-like protein were determined by capture immunoassay using three monoclonal antibodies with specificities for Ig of members of the Phocidae pinniped family. These assays were calibrated for use with NES sera using affinity column purified Ig. Concentrations of these Ig populations were estimated in adult female sera sampled at two time points during the lactation period, as well as sera from their pups collected during the first 5 weeks after birth. In pups, concentrations of the IgM-like protein was found to increase rapidly post-partum. In some individuals, values reached mean concentrations within 10-14 days. In addition, rapid increases in pup total IgG and IgG sub-class concentrations were also observed. Collectively, these findings suggest that the majority of post-partum increases in serum Ig can be accounted for by de-novo synthesis.

Blood chemistry and hematology of gray seal (Halichoerus grypus) pups from birth to postweaning

Serum and plasma samples were collected from 92 gray seal (Halichoerus grypus) pups, all less than 5 wk old, and from 21 yearlings during the breeding season at the Isle of May, Firth of Forth, Scotland, for hematologic and clinical chemistry analysis. In the pups, total WBC, total protein, and glucose values increased until weaning and declined during the postweaning fast. Liver enzymes, particularly alkaline phosphatase, were high at birth and decreased steadily with age, most rapidly during the postweaning fast. In the yearlings, total WBC, erythrocyte sedimentation rates, and rectal temperatures were significantly higher than in the pups and glucose levels were significantly lower. Therefore, consideration should be given to the growth phase of gray seal pups (lactation or postweaning fast) or stage of development when hematology and clinical chemistries are used for diagnostic purposes.

Energetics during nursing and early postweaning fasting in hooded seal (Cystophora cristata) pups from the Gulf of St Lawrence, Canada

In this study we measured growth and milk intake and calculated energy intake and its allocation into metabolism and stored tissue for hooded seal (Cystophora cristata) pups. In addition, we measured mass loss, change in body composition and metabolic rate during the first days of the postweaning fast. The mean body mass of the hooded seal pups (n = 5) at the start of the experiments, when they were new-born, was 24.3 +/- 1.3 kg (SD). They gained an average of 5.9 +/- 1.1. kg.day-1 of which 19% was water, 76% fat and 5% protein. This corresponds to an average daily energy deposition of 179.8 +/- 16.0 MJ. The pups were weaned at an average body mass of 42.5 +/- 1.0 kg 3.1 days after the experiment was initiated. During the first days of the postweaning fast the pups lost an average of 1.3 +/- 0.5 kg of body mass daily, of which 56% was water, 16% fat and 28% protein. During the nursing period the average daily water influx for the pups was 124.6 +/- 25.8 ml.kg-1. The average CO2 .production during this period was 1.10 +/- 0.20 ml.g-1.h-1, which corresponds to a field metabolic rate of 714 +/- 130 kJ. kg-1. day-1, or 5.8 +/- 1.1 times the predicted basal metabolic rate according to Kleiber (1975). During the postweaning fast the average daily water influx was reduced to 16.1 +/- 6.6 ml.kg-1. The average CO2 production in this period was 0.58 +/- 0.17 ml.g-1.h-1 which corresponds to a field metabolic rate of 375 +/- 108 kJ.kg-1.day-1 or 3.2 +/- 0.9 times the predicted basal metabolic rate. Average values for milk composition were 33.5% water, 58.6% fat and 6.2% protein. The pups drank an average of 10.4 +/- 1.8 kg of milk daily, which represents an energy intake of 248.9 +/- 39.1 MJ.day-1. The pups were able to store 73.2 +/- 7.7% of this energy as body tissue.

Metabolic and hormonal changes during the molt of captive gray seals (Halichoerus grypus)

Body mass, resting metabolic rates (RMRs), and serum thyroid hormones concentrations of six captive gray seals (Halichoerus grypus) were measured at regular intervals before, during, and after the annual molt. Changes in body mass suggested that the animals had increased energy expenditures during the last stage of the molt. These were associated with significantly elevated RMRs during the molt, the increase being more pronounced in juveniles ( < or = 53%) than in adults ( < or = 17%). The increase in RMR probably reflects the cost of generating a new pelt or to sustain a high skin temperature. Serum total and free thyroxine concentrations were elevated for all animals during the molt, but only juveniles had elevated serum triiodothyronine concentration. The increase in thyroid hormones occurred only during the last stage of the molt, suggesting that the role of thyroid hormones during the molt may be to sustain rapid hair growth in the last stage of molt or to maintain elevated heat production, rather than to initiate hair growth.

Milk intake, growth and energy consumption in pups of ice-breeding grey seals (Halichoerus grypus) from the Gulf of St. Lawrence, Canada

In this study we document growth, milk intake and energy consumption in nursing pups of ice-breeding grey seals (Halichoerus grypus). Change in body composition of the pups, change in milk composition as lactation progresses, and mass transfer efficiency between nursing mothers and pups are also measured. Mass transfer efficiency between mother-pup pairs (n = 8) was 42.5 +/- 8.4%. Pups were gaining a daily average of 2.0 +/- 0.7 kg (n = 12), of which 75% was fat, 3% protein and 22% water. The total water influx was measured to be 43.23 +/- 8.07 ml.kg-1.day-1. Average CO2 production was 0.85 +/- 0.20 ml.g-1.h-1, which corresponds to a field metabolic rate of 0.55 +/- 0.13 MJ.kg-1.day-1, or 4.5 +/- 0.9 times the predicted basal metabolic rate based on body size (Kleiber 1975). Water and fat content in the milk changed dramatically as lactation progressed. At day 2 of nursing, fat and water content were 39.5 +/- 1.9% and 47.3 +/- 1.5%, respectively, while the corresponding figures for day 15 were 59.6 +/- 3.6% fat and 28.4 +/- 2.6% water. Protein content of the milk remained relatively stable during the lactation period with a value of 11.0 +/- 0.8% at day 2 and 10.4 +/- 0.3% at day 15. Pups drank an average of 3.5 +/- 0.9 kg of milk daily, corresponding to a milk intake of 1.75 kg per kg body mass gained. The average daily energy intake of pups was 82.58 +/- 19.80 MJ, while the energy built up daily in the tissue averaged 61.72 +/- 22.22 MJ.(ABSTRACT TRUNCATED AT 250 WORDS)

Identification, characterisation, and measurement of immunoglobulin concentrations in grey (Haliocherus grypus) and common (Phoca vitulina) seals

Concentrations of macroglobulin, total gammaglobulin, and a gammaglobulin subclass were measured in grey and common seals. In pups, immunoglobulin M (IgM) was found to rise rapidly, concentrations reaching adult values by approximately 14 days postpartum. Total IgG concentrations increased more slowly, only approaching 50% of juvenile and adult male values by 30 days after birth. Concentrations of the IgG subclass did not change significantly postpartum. Total IgG concentrations measured in adult female grey seals sampled during lactation were found to be lower than in males and juveniles. This apparent immunosuppression may be associated with pregnancy.

Skeletal development in newborn and weanling northern elephant seals

The neonatal period in the northern elephant seal (Mirounga angustirostris) differs markedly from that of most mammals. An intense 1-mo nursing period is followed by 2-3 mo during which seal pups consume neither food nor water. Because skeletal development in other species is rapid during this period, we determined the capability of elephant seals to continue skeletal growth under fasting conditions. We analyzed indirect markers of bone turnover [serum osteocalcin and alkaline phosphatase activity and urinary calcium and hydroxyproline (Hyp) excretion] in samples obtained sequentially from live pups throughout the fast. Serum osteocalcin was low at the beginning of the fast, peaked between 17 and 42 days, and then decreased to initial levels after 10 wk. Alkaline phosphatase activity increased linearly through 9 wk of fasting. Urinary calcium was relatively constant through 9 wk but decreased after 10 wk, whereas free and total Hyp decreased linearly. Clearance of 3H-labeled Hyp showed that virtually all (> 99%) free Hyp was oxidized and that only bound Hyp, for which there is no degradative mechanism, was excreted. Kinetics of 45Ca clearance, a direct measurement of mineral turnover, was virtually identical to that for young humans. Histomorphometry of ulnae obtained from pups which died of natural causes (usually trauma inflicted by adult males) indicated active surfaces (osteoid plus eroded) between 30 and 60% of total surface of highly porous bone containing < 60% bone area/tissue area. Thus all indicators of skeletal activity confirmed that young elephant seals continue skeletal development, notwithstanding the prolonged period during which they take in no food or water.

Pseudopregnancy in harp seals (Phoca groenlandica)

Concentrations of circulating progesterone were monitored in a captive breeding group of harp seals. Five females were monitored for 2 years, over which time they either became pregnant (four instances) or displayed an overt pseudopregnancy (five instances). Only one female exhibited consecutive pseudopregnancies. In all pseudopregnancies, serum progesterone values were high and remained high until July, which is close to the time when implantation normally occurs. After this time progesterone concentrations remained high, gradually declining to baseline values over the following four months. In the three females that were pregnant one year and pseudopregnant in the other year, the average progesterone concentration during pseudopregnancy was lower than that exhibited during pregnancy (P < 0.05). All females (except one) increased their mass, girth and condition index over the normal gestation period whether they were pregnant or pseudopregnant. The potential consequences of such a high rate of pseudopregnancy on the use of ovarian scars for estimating reproductive rates and population size are discussed.

Growth in pinnipeds

This review presents summary figures of, and fits growth curves to, data on body lengths (as standard length, SL, whenever possible) of pinnipeds at ages estimated to O.I y. (1) Generalized von Bertalanffy (vB) growth curves are fitted to most data: Lx = L infinity (I - ea(x-x0)b, Lx is length at age x, x0 is the origin of the curve (here chosen a priori as time of initiation of embryonic growth), L infinity is asymptotic length, a (which is negative) determines rate of approach to the asymptote, and b influences the 'shape' of the approach. (2) No single monotonic growth equation suffices for growth in length, which is linear before birth and remains so during early life. The vB equation is only suitable to describe mean lengths of newborns, and animals one or more years old. (3) Also, for males of polygynous species, two functions are needed to account for accelerated growth at puberty. Generally a Gompertz equation is adequate for adult males of these species. (4) The fitted growth equations permit statistical comparisons of sizes and growth rates, as well as of individual variability (as growth-curve residuals), among populations and species. (5) For the following species (including different populations when available), the reliability of data is assessed and parameters of growth curves are presented (with sexes separated where significantly different): walrus, California and Steller sea lions, Antarctic, subantarctic and northern fur seals, Hawaiian monk seal, crabeater, Weddell and Leopard seals, southern and northern elephant seals, bearded, hooded, ringed, Baikal, Caspian, spotted, harbour, harp, ribbon and grey seals. (6) Some novel findings pertain to individual species as follows. Although the Pacific walrus is generally stated to be the larger subspecies, females from Hudson Bay and males from Foxe Basin, in the eastern Canadian Arctic, may be as long as those from the Bering Sea. Although female Weddell seals have been assumed to grow larger than males, there is no significant difference in growth curves fitted to the most complete data. Uniquely among populations examined, the relative variability (absolute growth curve residuals/predicted lengths) of male southern elephant seals is amplified with age. Among ringed seals from Svalbard, the eastern, western and high Canadian Arctic, and the Bering, Chukchi, Okhotsk, Barents and Baltic Seas, asymptotic sizes are larger among those that breed on land-fast ice rather than floes, and size may be more variable in more extreme Arctic environments. The Baikal seal is confirmed as the smallest species of pinniped.(ABSTRACT TRUNCATED AT 400 WORDS)

[Adrenal histostructure in the postnatal ontogeny of the Greenland seal, Pagophilus groenlandica Erxleben, 1777 (Phocidae)]

Histological structure of adrenal gland is studied in four age groups of the harp seal: in adults, in two juvenile groups (6 and 1-1.5 months), and in newborns (1-1.5 days). Development of the adrenal gland in this species is analogous to that of terrestrial mammals, but also has some peculiarities of its own. Differentiation of the definitive cortex occur in the prenatal development. In the newborns it is, though weakly developed, clearly differentiated into arched, fascicle and reticular zones. The foetal cortex is discovered in newborns, which further develops in juveniles and is present (without any signs of involution and degeneration) in adults. Adrenal gland persistence was previously known in horses only, but in that case the foetal cortex was partly degenerated in adults. Chromaffin cells undergo differentiation in embryonic development, as newborns already possess two types of such cells. The final differentiation ends in juvenile of 1.5 months old.

Insulation and thermal balance of fasting harp and grey seal pups

1. Harp and grey seal pups were examined during the post-weaning period to quantify their thermoregulatory abilities and thermal limits. 2. Deep body temperatures of harp seals (37.8 +/- 0.8 degrees C) were not significantly different from those of grey seals (38.9 +/- 0.4 degrees C). 3. As blubber depth declined during the fast, temperature gradients extended increasingly deeper into the muscle layer potentially decreasing heat loss. 4. Blubber conductivity (approximately 0.18 W/m/degrees C) did not vary regionally within an animal, or between animals or species. 5. Calculated lethal cold limits in air were between -85.4 degrees C and -116.1 degrees C, suggesting that fasting, weaned pups can easily cope with temperatures they would normally experience.

Rearing and rehabilitation of common seal pups (Phoca vitulina)

Veterinary surgeons may be presented with seal pups that require rearing and rehabilitation. This paper describes the feeding, weight gains and clinical care of 22 harbour or common seal pups (Phoca vitulina) that were reared and rehabilitated at the RSPCA Seal Assessment Unit in Norfolk during 1989. Eighteen of the seals survived and were released but four died. On arrival the pups' mean (+/- sd) bodyweight was 9.2 +/- 2.1 kg; those which survived stayed an average of 14.2 +/- 2.3 weeks before they were released at an average weight of 35.5 +/- 3.5 kg.

Circulatory water concentration in suckling and fasting northern elephant seal pups

This study examined circulatory water concentrations in the neonatal northern elephant seal (Mirounga angustirostris) in order to determine how suckling and fasting would alter the percentage of water in the whole blood, plasma, and red blood cells (RBC). Plasma water concentration dropped by about 3% during suckling and recovered about 1% during the fast (92.38 +/- 0.48% less than 1 week old, 90.15 +/- 0.36% weaning, 91.02 +/- 0.68% end of fast). RBC water values during this time were more variable than plasma values: RBC water increased about 1% during the first 2 weeks of suckling (from 67.80 +/- 0.28% to 68.68 +/- 0.51%) but dropped to slightly below original neonatal values by weaning (67.15 +/- 0.63%). The first several weeks of fasting were marked by wide variability in RBC water, but by the end of the fast RBC water was comparable to that at weaning. These results indicate: 1) Northern elephant seal pups do not exhibit circulatory dehydration during 10 weeks of fasting; 2) Measurements of plasma or RBC metabolites (such as plasma glucose or RBC hemoglobin) may show variations or trends due not to metabolic regulation but rather to changes in circulatory water concentration.

Effects of suckling and the postsuckling fast on weights of the body and internal organs of harp and hooded seal pups

The weights of harp seal pups quadruple during 13 days of suckling while hooded seal pups double in weight in a lactation period of just 4 days. Pups of both species then fast for a month or longer. As a first measure of tissue responses to this 'feast and famine' pattern, we weighted the body, sculp (blubber and attached skin), core (carcass including viscera) and major internal organs of seal pups at birth, at the end of suckling, and at the end of the fast. When expressed as a percentage of body weight, the weights of the internal organs of newborn harp and hooded seals were within the range reported for newborn land mammals. During suckling, harp and hooded seals gained 2.3 and 6.5 kg/day body weight, respectively, but a large part (64-73%) of this gain was blubber and skin rather than core. Even though pups were ingesting great quantities of fat, their digestive organs (stomach, small and large intestines, pancreas) were neither particularly large at birth nor did these organs gain in weight or length unusually rapidly. Most organs increased in weight in proportion to the increase in core weight, but the liver and spleen increased proportionately more than the core, and the stomach, heart and kidneys increased proportionately less. At the end of suckling, sculp accounted for more than half of the body weight in both species. The subsequent 4-week fast resulted in weight loss from both the sculp and core, and the liver and spleen decreased in weight by about 70%. The net effect of sequential suckling and fasting was particularly striking in the hooded seal pup, which has a lighter core, heart, liver and spleen at 1 month postpartum than at birth. These data illustrate a remarkable cycle of nutrient deposition and depletion which is undoubtedly central to the survival of young seals in the harsh pack-ice environment.