Characterization of ethoxyresorufin O-de-ethylase in grey seal Halichoerus grypus

Ethoxyresorufin O-de-ethylase (EROD), a typical mixed function oxidase enzyme, was studied in liver and kidney of adult and pup grey seals, Halichoerus grypus. EROD activity was present in most liver samples but was only barely detectable in a few of the kidney samples. Liver EROD activity was greatest at pH 7.5-8.0; activity increased with temperature from 20 degrees C to a plateau starting at about 33 degrees C and extending to 37 degrees C, and fell off sharply above 37 degrees C. Km values ranged from 3 X 10(-7) to 3 X 10(-6)M; Vmax ranged from 5 X 10(-12) to 1 X 10(-10) moles product formed X min-1 X mg protein-1. Liver EROD activity was not detectable in pups less than 1 day old, and activity increased with age in pups up to 5-12 days old. Adults had greater EROD activity than did pups.     

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.     

Mass changes of grey seal Halichoerus grypus pups on Sable Island: differential maternal investment reconsidered

Theory predicts that where variance in reproductive success differs between sexes, as in many sexually dimorphic species, mothers should invest more in male than in female offspring. In pinnipeds, parental investment is the sole responsibility of the mother. Both size at birth and subsequent mass gain during lactation are measures of that investment. We studied mass gain of grey seal pups, a sexually dimorphic species, during lactation and mass loss during the first 13 days of the postweaning fast using longitudinal data obtained on Sable Island, Canada. A mixed-effects repeated measures model was used to account for the serial correlation in these longitudinal data. We found no significant difference in the birth mass of male (16.6 ± 0.45 kg) and female (15.6 ±0.74 kg) pups. Rate of mass gain by males (3.0 ± 0.13 kg/d) and females (2.7 ± 0.12 kg/d) also did not differ significantly during the lactation period. Grey seal pups on Sable Island tended to be larger at birth and gain mass more rapidly (70%–100%) during lactation than those in the United Kingdom. Mass loss of weaned pups was curvilinear over time. Over the first 10 days of the fast, pups lost 22% of their weaning mass. In both males and females, large pups lost mass more slowly than small ones during the postweaning fast. Based on our results and a review of previous studies, we found little evidence of differential maternal investment in male and female grey seal pups.     

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

Summary 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.     

Movements and diurnal behaviour patterns in a Baltic grey seal (Halichoerus grypus)

A sub-adult grey seal was caught and tagged with a satellite relay data logger at Tihällan (61°2800N, 17°2540E), Sweden, on 21 August 1992. We tracked it for 115 days during which time we recorded 841 locations, data on 3556 dives and 80 haulout periods. It travelled 730 km in the first 12 days to the southern Archipelago Sea. It stayed most of the remaining time within 25 km of a haulout site, with a major exception of an 8-day trip of 520 km. Dive shape and swimming activity were used to distinguish dive types. Square-shaped foraging dives were more common over the midday period. Haulout periods were more common during the night.     

Fine structure of the tapetum cellulosum of the grey seal (Halichoerus grypus)

The morphology of the tapetum lucidum of the grey seal (Halichoerus grypus) has been studied by light and electron microscopy. The reflective layer in this species is a tapetum cellulosum situated in the choroid and covering the entire effective fundus. Posteriorly the tapetum is composed of 30-35 layers of flattened polygonal cells. This number gradually declines to 15-20 layers in the extreme periphery. Near the retinal epithelial layer the tapetal cells are larger and more regular (brick-like) in arrangement whereas further from the retina the tapetal cells become more irregular in outline and more widely separated by collagen fibrils and connective tissue cells. In this outer region the tapetal cells are gradually replaced by melanocytes of the choroid. Within the tapetal cells a few mitochondria and profiles of smooth endoplasmic reticulum are scattered peripherally while the majority of the cell organelles are clustered near the centrally located vesicular nucleus. The dominant feature of the tapetal cells is, however, an accumulation of numerous electron-dense rodlets of presumed zinc cysteine. These rodlets are the reflective material of the tapetum and are arranged with their long axes perpendicular to the incoming light. The orientation of these rodlets is usually uniform within each tapetal cell but varies between adjacent cells. The diameter (0.10 micron) and spacing (0.15 micron) of these rodlets is consistent with the principles of constructive interference. Blood vessels penetrate the tapetum at right angles to supply the choriocapillaris which is indented into the amelanotic retinal epithelium to give a flat reflective surface to the tapetum.     

Molecular methods for differentiating grey seal (Halichoerus grypus) and harbour seal (Phoca vitulina) scat

Pinniped dietary information is crucial for understanding marine ecosystems; however, in the North Atlantic, grey and harbour seals haulout concomitantly and their faeces are visually indistinguishable. Therefore, we developed molecular methods to differentiate the species' scat. PCR primers were created that amplify a portion of mitochondrial 16S ribosomal DNA in grey and harbour seals. The samples were amplified and the resulting products were digested using the restriction enzyme Tsp509I, producing diagnostic banding patterns. These tools provide a mechanism by which separate dietary analysis can be achieved for grey and harbour seals at mixed haulouts in New England.     

Patterns of parental relatedness and pup survival in the grey seal (Halichoerus grypus)

Levels of parental relatedness can affect offspring survival and susceptibility to disease. We investigated parental relatedness of live and dead Halichoerus grypus pups between and within island populations and between possible causes of mortality. Nine microsatellites were used to calculate internal relatedness (IR) and standardized mean d2. We find that pups with higher than average levels of IR have significantly lower survival and that this varied between island populations and that certain loci contributed to the effect more than others. Although, there were no significant differences between causes of mortality, peritonitis, infection and stillborn had the highest levels of IR. These results provide evidence that parental relatedness is an important determinant of pre-weaning pup survival in the grey seal and that this may vary with cause of mortality given a larger sample size.     

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.     

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.     

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.     

Trichinella nativa in grey seal Halichoerus grypus: spill-over from a highly endemic terrestrial ecosystem

Trichinella spp. infections of marine mammals pose a human health risk in Arctic regions where game meat is an important part of the diet. In the last decade, the grey seal population of the sub-arctic Baltic Sea has reached a level at which hunting is possible and seal meat is now available for food. We conducted a survey on the occurrence of Trichinella spp. in grey seals Halichoerus grypus (n = 171) and ringed seals Phoca hispida botnica (n = 56) of the Baltic Sea in the coastal waters of Finland, a highly Trichinella sp. endemic area. Muscle samples were examined by a mechanically assisted digestion method during 2006-2010. One grey seal was positive for Trichinella nativa , while all samples from ringed seals were negative. Even though just 1 grey seal was infected, the finding here emphasizes the importance of proper meat inspection of seals intended for human consumption, especially in areas with high infection pressure.     

Body condition at weaning affects the duration of the postweaning fast in gray seal pups (Halichoerus grypus)

Gray seals (Halichoerus grypus) undergo a terrestrial postweaning fast (PWF) that depletes energy reserves acquired during the suckling interval. Plasticity in PWF duration may ensure that pups of variable body condition depart for sea with adequate energy reserves. To test this hypothesis, we examined body condition of 30 gray seal pups at weaning and monitored their PWF duration. On average, fat accounted for 47.3% +/- 0.7% of their 53.2 +/- 1.3-kg weaning mass. Although fasting duration averaged 21 +/- 1.1 d (n = p28), there was considerable variation in fasting duration (9 to > 31 d) and the resulting age when pups departed to sea (26 to > 49 d). Percent fat at weaning(38.6%-54.6%) was positively correlated with fasting duration(n = 28, r = 0.376, P = 0.0489). In contrast, total body gross energy (735.3-1,447.4 MJ) and body mass (39.0-66.0 kg) were not correlated with fasting duration. Thus, body composition,not overall body reserves, predicted fasting duration, but the effect was weak, indicating that other factors also account for the observed variation in fasting duration. We speculate that pups with greater percent fat more effectively utilized lipid and conserved protein while meeting metabolic costs throughout the PWF. As a result, fatter pups extended the PWF duration,which may be critical for development of diving physiology and may have facilitated their survivorship to age 1.     

Organochlorine residue concentrations and burdens in grey seal (Halichoerus grypus) blubber during the first year of life

Between 1988 and 1991 grey seal ( Halichoerus grypus ) pups at various developmental stages were sampled at Sable Is., NS, and blubber samples were analysed for lipid content and organochlorine (OC) residue concentrations. Blubber lipid content increased significantly between birth and 12 d, and then stayed relatively constant. Blubber OC residue concentrations were fairly constant during the first 12–16 d of life. From weaning (approx. 16 d) until four months, the pups are learning to feed but are relying on blubber fat reserves; thus, during this period blubber weight declined to minimum levels, and OC residue concentrations in blubber lipid increased significantly. Blubber lipid OC concentrations then declined slightly as the pups gained weight, until at the end of one year they were about twice those immediately post-weaning. Blubber lipid residue burdens calculated from these data showed that at weaning, about 98% of the seal's residues were accumulated from maternal milk. After weaning, there were no significant changes in the burdens of any residue until the end of the first year of the pup's life, and the organochlorine concentration changes reflected a fairly constant organochlorine burden around which lipid contents varied. These data suggest that the capacity of the seal to degrade the residue inherited from its mother is very limited. Furthermore, the absence of any significant accumulation of organochlorines during the second six months of the seal's life suggests that the juvenile seal must feed at a low trophic level which is not highly contaminated with organochlorines.     

Effects of environment on grey seal (Halichoerus grypus) pup mortality. Studies on the Isle of May

Breeding sites, including beach environment and topography, play a significant role in the causes of death of grey seal ( Halichoerus grypus ) pups, in particular the incidence of starvation, peritonitis/navel ill, other infectious diseases and injuries as a result of adult-pup interactions. The bacteria involved are opportunistic invaders. A wide and differing sex ratio in dead pups was found on different beaches and this has not been satisfactorily explained.     

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.     

Movements and diving of grey seal females (Halichoerus grypus) in the Gulf of St. Lawrence, Canada

Five female grey seals were tracked with satellite-linked time-depth recorders during September to April 1993-1994. Seals remained in the northern Gulf of St. Lawrence (Gulf) for 1-2.5 months after capture. Four females dove primarily to depths <10 m and 20-70 m, while all dives of the fifth female, a blind animal, were <10 m. During October/November, all animals moved into the southern Gulf or onto the Scotian Shelf. This migration lasted 6-10 days, during which time animals covered 350-800 km. During that migration, all females, including the blind animal, dove up to 100 m, but the majority of dives were to depths of 40-70 m. Two seals stayed in the southern Gulf through the winter while the others left the Gulf in January. When in the southern Gulf and on the Scotian Shelf, dive depths and bathymetry information indicated that dives were to the bottom.