Female Grey Seals Research Articles

Dispersion and site fidelity of breeding female grey seals (Halichoerus grypus) on North Rona, Scotland

Female grey seals (Halichoerus grypus) formed breeding aggregations on the island of North Rona, Scotland. Aggregations of females were associated particularly with gullies leading from the sea, leaving large areas of available space unoccupied. Changes in the degree of aggregation of females during the breeding season were similar in 1987, 1988 and 1989. Pronounced aggregations occurred in the early and late parts of each breeding season.Of 67 breeding females marked in 1985, 62 (93%)) returned to N. Rona to breed in at least one season up to 1989, but 18 (27%) were present in all five years. Females came ashore up to 14 days before giving birth and 82% were observed first in the vicinity of their subsequent pupping site. Between 1985 and 1989, marked females which returned were faithful to their previous pupping sites, even when the previous pup had died. There was no evidence of a gradual change in the location of individual pupping sites over time. This pupping site fidelity may generate aggregations whose location, timing and composition is predictable.

Nasal heat and water exchange is not an effector mechanism for water balance regulation in grey seals.

Phocid seals may effectively restrict respiratory heat and water loss by nasal heat and water exchange (NHE), and respiratory heat loss is, in fact, subject to thermoregulatory control. We have investigated whether phocid seals also control NHE and respiratory water loss to regulate water balance. Three resting juvenile female grey seals (Halichoerus grypus) were subjected to: (i) 5 days of food and water deprivation, (ii) intravenous infusion of 1000 ml of a hypersomotic (930 mM) solution of the diuretic mannitol, and (iii) oral injection of 1500 ml distilled water. During these experiments in air of 0 degree C, expired air temperature (T(ex)) and respiratory frequency (f) were recorded, and urine and blood samples collected. The results were compared with results from control experiments. Five days of food and water deprivation caused an average 10.5% and 20.8% increase in plasma (PO) and urine (UO) osmolality, respectively. Mannitol infusion induced excessive diuresis and caused an average 2.45% reduction of the estimated body water pool. Water loading caused an average 4.5% and 60% reduction in PO and UO, respectively, while urine production increased by 365%, on average. However, in no case did either T(ex) or f change significantly from mean control levels of 22.4 (range: 20.7-25.2) degrees C and 7.3 (range: 6.6-8.4) breaths min-1, respectively. Thus, water balance disturbances that initiate renal compensatory mechanisms fail to affect NHE in grey seals. This suggests that control of NHE is not an effector mechanism for regulation of water balance in grey seals.

Growth and feeding habits of grey seals (Halichoerus grypus) in the northwestern Gulf of St. Lawrence, Canada

Growth and feeding habits were determined for 82 grey seals (Halichoerus grypus) collected in the northwestern Gulf of St. Lawrence, Canada, between 3 July and 6 December 1983. Male grey seals reached an asymptotic standard length of 242 cm, whereas females attained a length of 201 cm. Most (96%) females 175 cm or longer and 5 years of age or older were pregnant. A larger proportion of grey seal stomachs contained food items in July than in the other months sampled, regardless of sex or maturity status. The diet consisted primarily of cod (Gadus morhua), herring (Clupea harengus harengus), and capelin (Mallotus villosus), which together contributed 72% of the wet mass and 76% of the gross energy of all the prey consumed. Invertebrates contributed negligible mass or gross energy to the diet. Grey seals primarily consumed fish ≤30 cm in length and ate only one or two different fish species during any one feeding bout. Based on our stomach content analyses, the food consumed daily by adult male and female grey seals provided an average gross energy of 3628 and 2925 kcal (1 kcal = 4.18 kJ), respectively, which is consistent with daily energy requirements estimated using bioenergetic models. However, the large percentage of empty stomachs (50%), together with differential digestion of fish species, suggests that grey seals may not feed every day.

Radionuclides in grey seals

Milk from live female grey seals ( Halichoerus grypus) and tissues from dead individuals were analysed for caesium isotopes and for plutonium and americium. The samples were collected at two sites, one in the North Sea and one in the north-east Atlantic. Levels of Cs 137 in milk were low (mean value 2.9 Bq I −1) and were only slightly higher in tissues (range 6.4–27.5 Bq kg −1). Plutonium and americium levels were at or below detection limits in most samples. There were no differences between the results from the two locations. Radionuclide levels were similar to those in fish species commonly consumed by grey seals.

Vitamin E and fatty acids in the grey seal (Halichoerus grypus)

Vitamin E levels in serum, liver and blubber (subcutaneous adipose tissue) were determined for 66 male and female grey seals of varying age in the pupping colony on Sable Island in the Northwest Atlantic by high-performance liquid chromatography (HPLC). Fatty acid concentrations were determined for all blubber specimens. Adult males and pups had significantly higher levels of vitamin E and cholesterol in serum than females and juveniles. A close relationship between vitamin E and cholesterol in serum could be observed. Suckling pups had significantly higher levels of vitamin E in liver (191 mg·kg−1) than juveniles and adults (21–41 mg·kg−1). Levels of vitamin E in blubber showed an age-dependent increase, with the highest levels being found in adult males; overall, these levels were much lower than in man. Vitamin E levels in blubber and liver of lactating females were only half that of adult males. This might be due to an intensive transfer of vitamin E from mother to pup during lactation, a process which may also explain the much higher levels of vitamin E in serum and liver of nursing pups. The low levels of vitamin E in blubber of seals might be a result of its high percentage of unsaturated fatty acids (79%). Highest percentage was represented by 18:1, 16:1, 22:6 and 16:0. Pups had lower values of monounsaturated, and a higher percentage of saturated fatty acids compared to mothers.

Maternal behaviour and early behavioural ontogeny of grey seals (Halichoerus grypus) on the Isle of May, UK

Female grey seals allocated more resources to individual sons than to individual daughters. Mothers of male pups spent significantly larger proportions of their time defending and feeding their young than did mothers of female pups. The amount of time females spent ashore and the proportion of time spent in various behavioural states was influenced by the habitat of the birth site and the age of the pup.Grey seal neonates spent the majority of their time prone and immobile, perhaps to allow maximum energy retention (maximum mass gain) and to facilitate mothers relocating their pups. The proportion of time pups spent in the various behavioural states was influenced by the whelping habitat. Pups became increasingly active with age. Males were significantly more aggressive than females and, at one site they performed nosing behaviour with their mothers significantly more often than did female neonates.

Grey seal, Halichoerus grypus, energetics: females invest more in male offspring

Grey seal females transfer large amounts of energy to their pups during the brief lactation period. The costs of lactation have been measured using weight changes of mother and pup pairs. Large females come ashore to give birth earlier in the season and lose weight more rapidly than smaller females. The sex ratio of Grey seal pups born is skewed towards males in the early part of the breeding season. Male pups are larger at birth and gain weight more rapidly than female pups, and their mothers show a correspondingly faster rate of weight loss than mothers of female pups. The energy costs of gestation and lactation to a Grey seal mother are 31 GJ for male pups and2–8 GJ for female pups. Males are therefore 10% more costly in energy terms to raise to weaning. Because, on average, large females arrive at breeding sites before smaller animals, biased results on weight changes would be obtained from methods which do not use repeated weighings. We suggest that the high efficiencies of lactation estimated for Harp seals compared with other phocid seals could be accounted for by such a bias.

Growth of grey seal (Halichoerus grypus) neonates: differential maternal investment in the sexes

Male grey seals are larger at birth, grow faster during the nursing period, and are weaned at a heavier mass than females. Estimated mean energy expenditure by females from conception to the time of weaning (maternal investment), including the heat increment of gestation, cost of foetal tissue, and energy contained in milk acquired during the nursing period, was greater for male than for female offspring. This pattern of energy investment by female grey seals in their young is consistent with Maynard Smith's model of sexual investment (J. Maynard Smith. Behav. Ecol. Sociobiol. 7: 247–251. 1980).

Histology of reproduction in harp and grey seals during pregnancy, postparturition, and estrus

Reproductive tracts were collected on the eastern coast of Canada from adult female grey seals (Halichoerus grypus) during gestation and postparturition, and from adult female harp seals (Phoca groenlandica) during delayed implantation and postparturition. Reproductive tracts were fixed in 10% buffered formalin for light microscopy. The placental site and adjacent tissue were preserved in 2% glutaraldehyde – 1% paraformaldehyde for scanning electron microscopy. During the delay of blastocyst implantation, the endometria of the gravid and nongravid uterine horns were similar in microscopic appearance. During gestation, maternal septa were often surrounded by maternal epithelium deep into the placental labyrinth except distally, where the maternal cells were replaced by syncytium. Marginal hematomas increased in size and complexity throughout placentation. Following parturition, uterine regression occurred earlier in harp seals (10 days postpartum) than in grey seals (21–25 days postpartum). Postpartum changes were most pronounced in the placental site where the blood vessels underwent extensive reorganization. In some specimens, the extensively vascularized placental site of the previous pregnancy was still apparent 12 months later. Epithelial replacement in the uterus was complete in grey seals 21–25 days postpartum and sooner in harp seals. Cervical and vaginal stratification occurred in both phocids following parturition and increased towards estrus. A recently ovulated grey seal was obtained between 21 and 25 days postpartum. The vaginal stratification and the presence of sperm in their uterine horns indicated that grey seals began estrus about 12–17 days postpartum. In harp seals, estrus appeared to occur towards the end of the lactational period, about 10–12 days postpartum.

Development and regression of the corpus luteum in grey seal (Halichoerus grypus) ovaries and its use in determining fertility rates

Adult female grey seals were sampled at the Fame Islands at monthly intervals from November 1980 to October 1981. The distribution, size, and number of ovarian corpora were recorded in each case and blood samples were obtained for progesterone analysis. The concentration of plasma progesterone was about 6 ng/mL for most of gestation, including embryonic diapause, and rose to about 10 ng/mL during the final month. Progesterone declined sharply to less than 1 ng/mL at parturition. The size of the corpus luteum was constant throughout embryonic diapause, but after implantation it grew continuously until parturition. Following parturition, it regressed rapidly at first, forming a corpus albicans, and then more slowly, regression being arrested during the period of foetal growth of the following reproductive cycle. Most corpora albicantia had disappeared 1 year after their formation. Corpora albicantia may be useful indicators of reproductive history in grey seals, providing that allowance is made for the reproductive condition of females at the time of sampling and for several other possible errors which could arise. Retrospective calculation of reproductive statistics by more than 1 year using corpora albicantia is not valid for grey seals.

The relationship between body condition and the timing of implantation in pregnant Grey seals (Halichoerus grypus)

Adult female Grey seals were sampled from the Farne Islands, Northumbria at monthly intervals during 1980 and 1981. The mean date of implantation was 7 April and most females implanted between 11 March and 5 May. Sculp, core and total body weights declined most at the time of lactation in November and were lowest during February. These weights increased most rapidly during March and April; at the same time as implantation occurred. The pectoral blubber depth followed a similar pattern. Females in which the spring increase in body condition occurred earliest also had the earliest implantation. The study demonstrates a correlation between body condition and the time of implantation.

The energetics of lactation: accurate measurements from a large wild mammal, the Grey seal (Halichoerus grypus)

Female Grey seals transfer large amounts of energy rapidly and efficiently to their pups. Using information from serial weighings and from carcase analysis the energy costs of repro duction and the efficiency of lactation for female Grey seals have been calculated. Females use over 125·6 MJ/day for maintenance and milk production. Pups consume 71·2 MJ/day in milk and can convert 58·6 MJ/day into growth and stored fat. The gross efficiency of the transfer from mother to pup is about 57%. Over 80% of the females' energy reserves are used to feed their pups. This massive transfer of resources in a short time period is thought to be an adaptation of an offshore aquatic feeder which has to return to land to give birth.

Functions of female aggression during the pupping and mating season of grey seals, Halichoerus grypus (Fabricius)

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.

Observations on the grey seal ( Halichoerus grypus) at North Rona in 1960 : Boyd J.M. and R.M. Laws 1962. Proc. Zool. Soc. Lond., 139, Pt. 2: 249–260

The measurement of sociality has been primarily concerned either with the quantification of pairwise associations between individuals or using network approaches to describe multiple relationships between individuals in a group. However, these approaches may not be appropriate or necessary for all studies, for instance, where group dynamics are more biologically relevant than individual associations or interactions. Such a case occurs when the changes to a number of different social groups are to be compared over varying temporal and spatial scales. Methods for assessing comparative group dynamics have been conspicuously lacking from the biologist's toolbox. Here, we investigated the suitability of indexes derived from quantification of diversity as methods for direct quantification of changes in social group composition. First, we specified the requirements of a suitable index for social stability, then we reviewed indexes available for such a task, examining their suitability, through tests of their mathematical properties, in this new context. Finally, we used the specific model of the breeding female grey seal, Halichoerus grypus, on North Rona, Scotland to conclude that the Jaccard index is the most suitable tool for quantifying social stability in this system. We advocated that this approach can offer advantages in any study where social stability rather than any specific interaction is the principal focus.