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Summary 1 Three hypotheses have been advanced to account for age-related improvement in performance: the selection hypothesis predicts improved due to the loss of lower quality phenotypes, the constraint hypothesis predicts individuals improve function, and the restraint hypothesis predicts younger individuals forego or reduce effort because of mortality risks. A decline in age-related performance (i.e. senescence) is predicted by mutation accumulation, antagonistic pleiotropy and disposable soma (wear and tear) hypotheses. 2 Using five measures of performance − birth rate, maternal and pup birth mass, pup weaning mass, weaning success and lactation length − we tested these hypotheses concerning age-related change in reproduction in 279 female grey seals (Halichoerus grypus), ages 4–42 years, over a 23-year period between 1983 and 2005 on Sable Island, Nova Scotia. These females produced 2071 pups. 3 Although body mass of primiparous females increased with age (4–7 years) birth mass of their pups did not, but pup weaning mass did. Second- and third-parity females of the same age as primiparous females gave birth to and weaned heavier pups. However, parity and age were dropped from models when maternal body mass was included. 4 The proportion of females giving birth varied significantly with maternal age, increasing in young females and then declining late in life. Weaning success rate also increased rapidly to about 8 years and subsequently declined in females > 32 years. 5 Generalized additive models indicated nonlinear changes in 3 day body mass (i.e. ∼ birth mass) and weaning mass of pups as a function of maternal age, after accounting statistically for the effects of maternal body mass. Mixed-effects, repeated-measures models fitted to longitudinal data further supported the conclusion that pup birth mass and weaning mass vary nonlinearly with maternal age and indicated nonlinear changes in lactation duration. 6 We found some support for the constraint hypothesis, but our findings were not consistent with the selection hypothesis or the restraint hypothesis as the basis for improvement in reproductive performance. 7 Senescence was evident in multiple female and offspring traits, indicating the degeneration in function of several physiological systems as predicted by the disposable soma hypothesis.

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.

The Concorde produces audible sonic booms as it passes 15 km north of Sable Island, Nova Scotia, where gray and harbor seals occur year round. The purpose of this research was to assess how sonic booms affect these seals. The intensity of the booms was measured and three types of data (beach counts, frequency of behavior, and heart rate) were collected before and after booms during the breeding seasons of the two species. In addition to the data taken during breeding, beach counts were made before and after booms during the gray seal moult. The greatest range in overpressure within a single boom was 2.70 psf during gray seal breeding and 2.07 psf during harbor seal breeding. No significant differences were found in the behavior or beach counts of gray seals following sonic booms, regardless of the season. Beach counts and most behaviors of harbor seals also did not differ significantly following booms, however, harbor seals became more vigilant. The heart rates of four gray seal mothers and three pups showed no clear change as a result of booms, but six male harbor seals showed a nonsignificant tendency toward elevated heart rates during the 15-s interval of the boom. These results suggest sonic booms produced by the Concorde, in level flight at altitude and producing on average a sonic boom of 0.9 psf, do not substantially affect the breeding behavior of gray or harbor seals.

Behavioural estimates of male mating success in polygynous grey seals, Halichoerus grypus, may be misleading as females are known to be promiscuous. At Sable Island, Nova Scotia, we collected behavioural observations and skin samples for paternity analysis from 56 females and their attending males. Twenty-four of these females were found in the following year and their offspring were sampled. Using seven hypervariable microsatellite loci, we excluded the consort male as the father in 43% of the cases. The probability of exclusion of these seven loci was 98.2%. Contrary to expectations, inland females had higher rates of extraconsort fertilizations (ECFs) (70%) than beach females (23%). Younger females (9 years) had slightly more ECFs than older females, but this was not significant. The duration of male consortship did not differ between females with ECFs and females fertilized by their consort male. Two explanations may account for the inland females having more ECFs: a higher ratio of females to tenured males inland may provide a greater opportunity for nonconsort males to obtain copulations; and inland females travel greater distances to depart for the ocean and may attract more males. These results are more consistent with the hypothesis that ECFs are a by-product for females of male strategies to maximize reproductive success than with hypotheses concerned with either material or genetic benefits gained by females. Copyright 1999 The Association for the Study of Animal Behaviour.

Although harbour seals may not recognize their relatives, relatives could be chosen preferentially for fostering (i.e. kin selection) if harbour seals display natal philopatry coupled with breeding site fidelity, and thus kin are clustered within the colony. We used behavioural and genetic data to investigate population structure within the Sable Island breeding colony and to test whether harbour seals tend to foster related pups. Adult females on Sable Island showed a high level of breeding-colony site fidelity but low levels of within-colony site fidelity both within and between years. Similarly, although lactating females showed a clumped distribution, group composition was highly variable, suggesting that this study colony was not composed of groups of related animals. DNA fingerprint data supported the hypothesis that female distribution within the colony was not correlated with genetic relatedness. Furthermore, the mean DNA band sharing among foster dyads did not differ significantly from that for unrelated animals. These results indicate that among harbour seals, related pups are not usually chosen preferentially for fostering and hence, kin selection is not likely to be influencing the occurrence of this behaviour. Copyright 1999 The Association for the Study of Animal Behaviour.

Substantial advances have been made in the past two decades toward a theory of mating systems (Orians, 1969; Selander, 1972; Trivers, 1972; Jarman, 1974; Emlen and Oring, 1977; Bradbury and Vehrencamp, 1977; Kleiman, 1977; Wittenberger, 1979; Thornhill and Alcock, 1983; Rubenstein and Wrangham, 1986). These recent efforts have focused on the interplay between sexual selection and environmental factors that determine temporal and spatial dispersion of males and females (e.g. resource distribution, predation pressure). Increased information on behavioural reproductive strategies has led to examination of theory both within and between taxa to assess the breadth of its applicability (see Bradbury and Vehrencamp, 1977; Ostfeld, 1985; Rubenstein and Wrangham, 1986 for reviews of different taxa). A comparison between antelope and emballonurid bats has shown that the form of mating systems in both groups is set within the bounds of female dispersion, which is strongly related to food distribution (Bradbury and Vehrencamp, 1977). On the other hand, factors such as habitat type and body size are good predictors of social dispersion and mating strategies in antelopes but not bats.

Researchers were on Sable Island, Canada (440°N, 600°W), for the 1997 grey seal (Halichoerus grypus) breeding season to study the affects of sonic booms on seal behavior. The physical parameters of 36 sonic booms associated with the Concorde’s trans‐Atlantic flights were recorded. The average minimum overpressure was −0.568 PSF and mean maximum overpressure was 0.935 PSF. Data were collected on frequency of aggression, movements, and distances moved in 10‐min periods before and after booms to detect changes in general agitation of pups and adults. The number of mother‐pup pairs nursing and number of nursing bouts interrupted during the minute of sonic booms were compared to those in randomly chosen minutes to measure immediate startle responses of seals. There was no difference in the behavior of adults nor pups between 10‐min periods before and after booms, nor did their behavior differ in the minute of booms when compared to randomly chosen control minutes. Female heart rates did not vary before, during and after booms but pup heart rates were variable. A similar study on Sable Island harbour seals (Phoca vitulina) is being conducted for comparison.

Adult males of the grey seal, Halichoerus grypus (Fab.) (Phocidae), display the large snout conspicuously in threats. The male's snout has probably evolved through sexual selection as a visual display organ, as in some other extant phocids: the hooded seal, Cystophora cristata (Nilsson) and the two species of elephant seals, Mirounga (Gray). This may also be true of the extinct desmatophocid Allodesmus Kellogg. Cephalic display organs in the form of long tusks have also evolved twice in the Odobenidae (walruses). Comparable display structures do not occur in the Otariidae (fur seals and sea lions). However, the massive neck of adult male otariids is important in undirected static-optical threat displays, especially at long range, and in some kinds of short-range threats. Also, adult otariids show sexual dimorphism in facial appearance, which varies interspecifically.Pinniped species in which large mature males have prominent, constant-growing cephalic display structures show fluid spacing among rutting males, and much agonistic communication at the water surface and on land or ice. This correlation may reflect selective pressures on males to affirm social status repeatedly, through displays which communicate their age (hence strength and experience), and their resource-accruing abilities.

Peripheral components of feedthrough loops were psychophysiologically measured from the brain, both forelimbs, the tongue and the eyes during simple and choice reaction time tasks using linguistic and non-linguistic stimuli. Closing a microswitch with the little finger was the overt response. Covert electromyographic (EMG) responses were computer identified in the following average temporal order: generally, the earliest covert reactions were in the tongue, brain, eyes, and passive arm-hand region. Next were complex EMG events in the active limb. These covert reactions may function in feedthrough loops to generate and transmit codes during internal information processing. The passive arm-hand responses occurred significantly earlier than the onset of the covert EMG burst for closing the microswitch; perhaps there is an inhibitory response "commanding" the passive arm not to respond, before the other (active) limb can overtly respond. Mean response patterns to linguistic and non-linguistic stimuli were almost identical. Reaction time to the onset of the EMG burst for switch closing was from 40 to 95 milliseconds earlier than the usual overt reaction time measure (that to switch closing), suggesting that reaction time studies might be improved by using the onset of EMG increase as the more sensitive and precise measure.

We obtained milk from 22 hooded seals on pack ice off the southeast coast of Labrador. Milk composition was not affected by degree of mammary evacuation or method of milk collection (drug immobilization vs. postmortem collection). Lactation stage exerted relatively little influence on milk composition over the course of the 4-day lactation period, but colostrum was higher in crude protein content. At mid to late lactation (2 – 4 days postpartum), hooded seal milk contains the highest dry matter (70%), fat (61%), and gross energy (5.9 kcal/g) contents that have been reported for any mammalian milk. This high fat content may be essential to achievement of the extremely rapid rate of fat deposition (about 4 kg/d) by suckling pups. The relatively low protein content (4.9%) at mid to late lactation is consistent with the small proportion of postnatal weight gain that is lean body mass. The proportion of milk energy contributed by protein is the lowest known for any mammal.

Breeding activity budgets of male gray seals were estimated to determine how they are fine tuned to changing demands and to determine whether or not the limited body reserves produced by fasting act to minimize energetically demanding activities. Behaviors were divided into nonsocial and social activities with each category including both active and inactive behaviors. The overall frequency of social behavior did not change throughout a male's tenure but aggressive behavior decreased while sexual behavior increased. Even though resting accounted for the greatest proportion of activity, males that were most active had the greatest copulatory success, suggesting that fasting does not place severe limitations on their activity levels.

Observed changes in maternal investment due to an environmentally induced decrease in food supply (the 1983 El Nino-Southern Oscillation) are compared witha priori predictions for the California sea lion (Zalophus californianus). Changes in behavior, growth and mortality of off-spring were also examined. Data collected in the first two months postpartum for the years before (PRE), during (EN), and the two years after (POST1 and POST2) the 1983 El Nino indicate that females initiated postpartum feeding trips earlier during the food shortage, and spent more time away on individual feeding trips in both the El Nino year and the year after. Perinatal sex ratios (♀:♂) in the years PRE, EN, POST1 and POST2 were 1:1, 1.4:1, 1.1:1 and 1:1.4, respectively. Fewer copulations were observed during the El Nino year, but this difference was not statistically significant. Pups spent less time suckling in the food shortage year and the year following, but attempted to sneak suckle more. Pups were less active and played on land less in the El Nino and following year. Finally, maternal investment as measured by milk intake of offspring was decreased, pups grew more slowly, and suffered increased mortality during the food shortage year. Despite expected sex differences in maternal investment and pup behavior in response to food shortage, there were no sex-biased differences in response in either females or pups. As expected, the food shortage did not affect adult males since they migrate north during the non-breeding season where the environmental perturbation was less severe.

We describe an unusual mating system, observed in a land-breeding colony of Grey seal, Halichoerus grypus, in the western Atlantic. Males and females begin to visit the breeding beach about a week before the season begins, but none stay ashore for long until the first pup is born. The cows are gregarious, probably return to the same part of the beach to give birth from one year to the next, and tend to remain in the general vicinity of the birth site during their two and a half week sojourn ashore. Within these limits, however, they are quite mobile, and the size, location and composition of the temporary aggregations which they form vary from one day to the next. The cows become thinner and more sedentary as oestrus approaches, but otherwise they give no overt signs of receptivity. The males do not defend territories, nor do they form dominance hierarchies. Instead, they compete for tenure, the right to remain within the shifting population of females. Tenured bulls directly test the receptivity of nearby cows from time to time, and they continually manoeuvre in ways which maximize their chances of being next to cows which are either in oestrus or likely to become so in the near future. Bulls which fail to establish themselves amongst females try to intercept cows as they are leaving for the sea at the end of their season, but their reproductive success, estimated in several ways, is significantly lower than that of bulls with tenure. The system would be adaptive for seals which breed on the pack ice, but it is unique amongst land-breeding pinnipeds. If, as some circumstantial evidence suggests, Grey seals were originally pack-ice breeders, the persistence of such a system in a land-breeding colony raises some interesting questions about the plasticity of mating behaviour.

Resting metabolic rate and body temperature of California sea lion pups (Zalophus californianus: Otariidae) were measured for 39 animals (12,000 g, mean body mass) captured from breeding areas on San Nicolas Island, California. These 3-5-wk-old pups had a mean specific resting metabolic rate of 0.780 ± .010 ml O₂ g⁻¹ h⁻¹, which is 2.380 times the value predicted by Kleiber for adult mammals with similar body mass; mean body temperature was 37.8 ± .08 C. This level of metabolism is similar to those reported for young seals (Phocidae). The heat-transfer coefficient (h) was 24.6 times that predicted from body mass, and it appeared that some individuals were on the verge of hypothermia at ambient air temperatures below 19 C. Although high metabolic rates are typically associated with high growth rates in terrestrial mammals, high heat loss associated with relatively poor insulation in sea lion pups may require allocation of relatively large amounts of energy to thermoregulation (=maintenance), thus limiting t...

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 weighed 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 had 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.

We studied the components of mass transfer from mother to pup during the lactation period and weight loss by fasting pups postweaning in the hooded seal, Cystophora cristata. Measurements were taken from 33 mother–pup pairs and 69 weaned pups. Mean body weight of mothers declined from an average of 179 kg at the beginning of lactation to 150 kg for mothers nursing fat pups near the end of lactation. Over 80% of this weight loss was from the sculp (i.e., skin and blubber). Pup weight doubled during the 4 days of lactation, with about 70% of this weight gain in the form of blubber. Fasting pups lost 29% or 13 kg of their body weight between weaning and mid to late April when feeding begins. Sculp and core weight accounted for 51% and 49%, respectively, of total weight loss during this fasting period. Hooded seal mothers invest a smaller portion of their stored fat (33%) in their pup than do grey seals (85%) and northern elephant seals (58%). Our hooded seal data are consistent with the hypothesis that the abbreviation of lactation allows a reduction in overhead costs and more efficient transfer of nutrients from mother to pup.

Aggression of female grey seals Halichoerus grypus toward conspecifics was studied during the pupping and mating season on Sable Island, N.S. The responses of 65 individually identified females with pups toward known males and females were recorded throughout each female's stage of lactation. Female aggression varied both quantitatively and qualitatively as a function of the sex of an approaching animal. Males were threatened more often than females even though females outnumbered males. The likelihood of females threatening other females was affected by the location of the threatening female's pup, but aggression towards males was not affected by the pup's position. Females responded aggressively less often in the second half of lactation, when both weaning of the pup and oestrus occur, than in the first half. They were also more likely to threaten transient males than tenured males. However, a male approaching or mounting a female, whatever his status, was more likely to be challenged by another male if the female threatened him than if she did not. These challenges generally interrupted a male's approach or mount and hence a potential copulation. The results are consistent with the hypothesis that female aggression during the lactation period helps to protect the pup and increases the likelihood that a female mates with a dominant male. This latter function may be viewed as a form of mate choice.

Isotope dilution was used to measure milk intake of 43 California sea lion pups on San Nicolas Island, California, from 1982 to 1984. Deuterium concentration was monitored in serial blood samples collected at about 5-day intervals for 3 wk after isotope administration. Estimated milk intakes differed significantly between male (723 ± 31.0 g ․ day⁻¹) and female (609 ± 24.0 g ․ day⁻¹) pups but did not increase from the first to second month postpartum. On a metabolic size basis (weight0.83), gross energy intakes did not differ between male and female pups but did differ between years, apparently as a consequence of the 1983 El Nino. The mean energy intakes (kcal ․ day⁻¹) of sea lion pups in the first (61 · W0.83) and second (308 · W0.83) months were high relative to terrestrial species. Regression of energy intake on growth rate predicted that maintenance energy requirements (kcal ․ day⁻¹) were also high (168 and 252 · W0.83 in the first and second months). The fact that California sea lion pups devote a la...

Based on scant empirical data, the mating system of the hooded seal (Cystophora cristata) has been variously characterized as monogamous or polygynous. To evaluate the hypothesis that female hooded seals are clustered to a degree that would facilitate polygyny, we collected data on the spatial dispersion of female and male seals on the ice floes off the Labrador coast. While flying from a ship at the edge of the seal herd to a study site within the herd, we recorded each sighting of female seals as a "solitary female" or a "cluster of females" (using an approximate 10 body length radius to differentiate these conditions). The numbers of males near females were also recorded. Nearest-neighbor distances were obtained during on-ice transects. The frequency of nearest-female-neighbor distance classes peaked at 6–10 seal body lengths (one body length = 1.9–2.6 m) and then declined to distances of greater than 25 body lengths. About 40% of 357 females with pups (or 22% of 279 sightings of seals) were in clusters consisting of two or more mother–pup pairs; the maximal cluster size observed was five. The majority of females or clusters of females had a single male in attendance (54% of 245 sightings). Females in the central part of the herd were both clustered and attended by males more often than were females at the periphery. Observations of a few marked males suggested that some took up positions near additional females when their original female companions departed. These results are consistent with the hypothesis that the spatial pattern of hooded seals should facilitate polygyny.

A brief lactation period with rapid neonatal weight gain may be adaptive for seals breeding on unstable pack ice. We studied the duration of lactation and growth of known-age pups of the hooded seal, Cystophora cristata, on the pack ice off Labrador. Mean body weight of pups increased from 22.0 kg at birth (n = 21) to a maximum of 42.6 kg on day 4 (n = 11) and then declined. On the basis of maternal absence, weight change, gastric contents, and clarity of blood serum, we conclude that pups are weaned 4 days after birth (range, 3–5 days). This is the shortest lactation period known for any mammal. Tagged pups captured on sequential days gained on average 7.1 kg per 24 h from the day after birth to weaning. Maternal effort supported a relative rate of weight gain (145 g∙kg maternal weight−0.75∙day−1) that is 2.5–6 times that of other phocids. By combining a large birth weight with rapid neonatal weight gain, hooded seals achieve a weaning weight comparable to other phocids in one-third to one-tenth the amount of time after birth.

Lactation represents a major proportion of maternal reproductive effort. In ungulates the energetic costs of lactation comprise 75–80% of the total energetic costs of reproduction (Oftedal, 1985). Although pinnipeds feed at sea, they return to land or ice to give birth and to nurse their young (Fig. 1) (Bonner, 1984). Thus, the bulk of a female’s reproductive expenditure is in an environment in which she cannot feed. The temporal separation of feeding and lactation is achieved by a wide range of behavioral, physiological, and anatomic adaptations.