Perinatal activities in the Grey seal (Halichoerus grypus)

Births and postnatal behaviour were observed at a breeding assembly of Grey seals on North Rona. Birth is extremely rapid and the cow immediately turns to smell the pup. Smelling continues at intervals, particularly during the first 10 min after birth and allows the cow to establish the identity of her pup. She also smells the placenta and defends it against attack by gulls. Disturbance by gulls, neighbouring seals and human intrusion may lead to the cow failing to establish a bond with the pup and consequently abandoning it.     

Reproductive behaviour of the Grey seal (Halichoerus grypus) on Sable Island, Nova Scotia

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.     

Territorial behaviour in the Western Atlantic Grey seal (Halichoerus grypus)

Virtually all published accounts of territorial behaviour in the Grey seal apply to breeding males only. Long-range field studies reveal, however, that lactating cows also maintain territories for a period of several weeks. During the summer months, adults and sub-adults have specific resting places to which they return each day at low water and which they defend against other individuals of their own species.     

Maternal Oxytocin Is Linked to Close Mother-Infant Proximity in Grey Seals (Halichoerus grypus)

Maternal behaviour is a crucial component of reproduction in all mammals; however the quality of care that mothers give to infants can vary greatly. It is vital to document variation in maternal behaviour caused by the physiological processes controlling its expression. This underlying physiology should be conserved throughout reproductive events and should be replicated across all individuals of a species; therefore, any correlates to maternal care quality may be present across many individuals or contexts. Oxytocin modulates the initiation and expression of maternal behaviour in mammals; therefore we tested whether maternal plasma oxytocin concentrations correlated to key maternal behaviours in wild grey seals (Halichoerus grypus). Plasma oxytocin concentrations in non-breeding individuals (4.3 ±0.5 pg/ml) were significantly lower than those in mothers with dependent pups in both early (8.2 ±0.8 pg/ml) and late (6.9 ±0.7 pg/ml) lactation. Maternal plasma oxytocin concentrations were not correlated to the amount of nursing prior to sampling, or a mother’s nursing intensity throughout the dependant period. Mothers with high plasma oxytocin concentrations stayed closer to their pups, reducing the likelihood of mother-pup separation during lactation which is credited with causing starvation, the largest cause of pup mortality in grey seals. This is the first study to link endogenous oxytocin concentrations in wild mammalian mothers with any type of maternal behaviour. Oxytocin’s structure and function is widely conserved across mammalian mothers, including humans. Defining the impact the oxytocin system has on maternal behaviour highlights relationships that may occur across many individuals or species, and such behaviours heavily influence infant development and an individual’s lifetime reproductive success.     

Seasonal movements and diurnal activity rhythms of the Grey seal (Halichoerus grypus)

The seasonal movements and diurnal activity rhythms of the Grey seals occurring along the Atlantic Coast of Nova Scotia and in the southern part of the Gulf of St Lawrence have been studied over a period of three and a half years. The seasonal movements of the adults can be divided into five periods or phases: (1) prepupping, (2) pupping and mating, (3) postmating, (4) spring concentration and (5) summer dispersal. The diurnal activity rhythm is attuned to the tides; the effects of the hours of daylight appear to be minimal. During the breeding season the cows go to sea as the tide is falling and return when it is rising. Adults of both sexes have a similar rhythm at other times of the year, except in mid-summer when the pattern is reversed.     

Bite Injuries of Grey Seals (Halichoerus grypus) on Harbour Porpoises (Phocoena phocoena)

Bite-like skin lesions on harbour porpoises (Phocoena phocoena) have been suspected to be caused by grey seals (Halichoerus grypus), and a few field observations have been reported. Bite-like skin lesions observed on stranded animals were characterized by two main components: large flaps of loose or missing skin and blubber with frayed edges and puncture lesions. Definitive demonstration of predation by a grey seal was not reported so far in those stranded animals. In this study, five stranded porpoises with bite-like skin lesions were swabbed for genetic investigations. In addition, the head of a recently dead grey seal was used to mimic bite-like skin injuries on a porpoise carcass. Subsequently, the artificial skin injuries were swabbed, along with the gum of the seal used for inflicting them (positive controls). Total DNA was extracted from the swabs and was used to retrieve a fragment of mitochondrial DNA by PCR. Primers were designed to amplify a specific stretch of mitochondrial DNA known to differ between grey seals and porpoises. The amplicon targeted was successfully amplified from the positive control and from two of the stranded porpoises, and grey seal-specific mitochondrial DNA was retrieved from all those samples. We conclude that (1) it is possible to detect grey seal DNA from dead porpoises even after several days in seawater and (2) bite-like skin lesions found on dead porpoises definitively result from grey seals attacks. The attacks are most likely linked with predation although, in a number of cases, scavenging and aggressive behaviour cannot be excluded.     

Pregnancy and ovulation rates in Grey seals (Halichoerus grypus) on the British coast

This study determined the pregnancy and ovulation rates in two stocks of Grey seals from Britain and described changes in pregnancy and ovulation rate with age. Seals sampled from the Hebrides during August 1978 and from the Fame Islands between March 1979 and October 1981 were used. Adult female pregnancy rate in the stock from the Fame Islands was estimated to be 94–29%, compared with 82–95% for seals from the Hebrides. These values were not significantly different. Pregnancy rate estimated by direct observation of a conceptus was comparable with an estimate from the presence or absence of corpora albicantia in the ovaries. By the age of four years and over (4 +), i.e. at maturity, 50% of females became pregnant. Pregnancy rate remained constant from age 5 + onwards. Pregnancy rate amongst females which became sexually mature at a younger than average age was lower than in older age classes.     

Satellite tracking of grey seals (Halichoerus grypus)

Three types of Argos satellite transmitter were attached to grey seals ( Halichoerus grypus ) at Donna Nook (South Humberside, UK) between 1985 and 1989 in order to investigate their movements. With the first two transmitters (A and B) the entire package was attached to the seal's back. Seal A was tracked for 29 days but although it was located on sandbanks up to 150 km south-east of Donna Nook, no locations were obtained at sea. Transmitters B and C used a submergence sensor to regulate transmissions. Seal B was tracked for 51 days and remained within 40 km of Donna Nook. A few locations were obtained at sea but all within 10 km of Donna Nook. Transmitter C incorporated a head-mounted aerial in order to increase the number of location fixes when the seal was at sea. This seal was tracked for 111 days, producing an average of 9·1 location fixes per day while at sea. It used two sites 265 km apart and undertook three transits between them. On the second visit to the northern site it made several trips up to 55 km out to sea. The majority of the remainder of the time was spent within 10 km of the haulout sites. Estimates of swimming speed were consistent with values required for minimum cost of transport.     

Suckling behaviour in the Grey seal (Halichoerus grypus) and the Northern elephant seal (Mirounga angustirostris)

The suckling behaviour of Grey seals and Northern elephant seals was investigated. Evidence suggested that in both species it is usual for females and young to select consistently the same suckling partner though certain conditions bring about changes in this behaviour. Instances of inconsistency in both species are described and the conditions that bring this about are discussed.     

Control Control Control: A Reassessment and Comparison of GenBank and Chromatogram mtDNA Sequence Variation in Baltic Grey Seals (Halichoerus grypus)

Genetic data can provide a powerful tool for those interested in the biology, management and conservation of wildlife, but also lead to erroneous conclusions if appropriate controls are not taken at all steps of the analytical process. This particularly applies to data deposited in public repositories such as GenBank, whose utility relies heavily on the assumption of high data quality. Here we report on an in-depth reassessment and comparison of GenBank and chromatogram mtDNA sequence data generated in a previous study of Baltic grey seals. By re-editing the original chromatogram data we found that approximately 40% of the grey seal mtDNA haplotype sequences posted in GenBank contained errors. The re-analysis of the edited chromatogram data yielded overall similar results and conclusions as the original study. However, a significantly different outcome was observed when using the uncorrected dataset based on the GenBank haplotypes. We therefore suggest disregarding the existing GenBank data and instead using the correct haplotypes reported here. Our study serves as an illustrative example reiterating the importance of quality control through every step of a research project, from data generation to interpretation and submission to an online repository. Errors conducted in any step may lead to biased results and conclusions, and could impact management decisions.     

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.     

Experimental Toxoplasma gondii infection in grey seals (Halichoerus grypus)

Laboratory-reared animals were used to assess the susceptibility of seals (Halichoerus grypus) to Toxoplasma gondii infection. Four seals were each orally inoculated with 100 or 10,000 oocysts of T. gondii (VEG strain), and another 4 seals served as negative controls. Occasionally, mild behavioral changes were observed in all inoculated seals but not in control animals. A modified agglutination test revealed the presence of antibodies to T. gondii in sera collected from inoculated seals and mice inoculated as controls. No evidence of the parasite was found on an extensive histological examination of seal tissues, and immunohistochemical staining of tissue sections from inoculated seals revealed a single tissue cyst in only 1 seal. Control mice inoculated with 10 oocysts from the same inoculum given to seals became serologically and histologically positive for T. gondii. Cats that were fed brain or muscle tissue collected from inoculated seals passed T. gondii oocysts in feces. This study demonstrates that T. gondii oocysts can establish viable infection in seals and supports the hypothesis that toxoplasmosis in marine mammals can be acquired from oocysts in surface water runoff and sewer discharge.     

Retinal epithelial fine structure in the grey seal (Halichoerus grypus)

The morphology of the retinal epithelium and the closely associated choriocapillaris and Bruch's membrane (complexus basalis) has been investigated in the eye of the grey seal (Halichoerus grypus) by electron microscopy. The retinal epithelium is composed of a single layer of cuboidal cells joined laterally by apically-located junctional complexes. Basally (sclerally) these cells display numerous infoldings while apically (vitreally) abundant processes enclose rod outer segments. Internally the large vesicular nucleus is centrally located. Smooth endoplasmic reticulum, mitochondria and lysosome-like bodies are abundant. Rough endoplasmic reticulum and polysomes while present are not plentiful. Phagosomes of outer-segment discs are only occasionally noted in the light-adapted state. As the entire fundus is overlain with a choroidally located tapetum cellulosum, only at the extreme periphery is an occasional melanosome present in these epithelial cells. The choriocapillaris endothelium is highly fenestrated and the profiles of these capillaries are deeply indented into the epithelial layer. Bruch's membrane (complexus basalis) is reduced to a trilaminate structure rather than the typical pentalaminate membrane seen in most mammalian species and when associated with capillary profiles is further reduced to a single thick basal lamina.     

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.