We can now turn to some of the distinguishing characteristics of this species, both in structure and habits.
It is always extremely difficult, if not impossible, to estimate the length or size of seals in the field since there is rarely, if ever, any standard for comparison. Measurements therefore, while of use on a carcase, cannot really be used by an observer in the field. Any deductions based on claims to be able to ‘age’ seals in the field must therefore be regarded as highly dubious and probably very misleading. The pup is born at a length of about 33 ins. and 32–33 lbs. Bull pups appear to be very slightly heavier, but the difference is not truly significant having regard to the numbers which have been weighed. In any case it could only amount to a few ounces. It is very difficult indeed to speak about moulters since by that time all the differences in nutrition have taken effect and weights can vary between 100 lbs. or more and little more than the birth weight, if the moulter has been starved and is likely soon to die. The growth in length is quite small so that few moulters reach 40 inches until well after they have left their natal beaches however great their weight. Some of these very heavy moulters (over 100 lbs.) are so bloated with blubber that they can hardly turn their heads and movements are quite lethargic. There is some evidence that pups which do not reach the weight of 90 lbs. before being deserted by their mothers and moulting, have little or no chance of surviving their first year of life. Certainly all those below 60 lbs. appear to die before the first six months is out and all the recorded weights of grey seals in their first year of life are about 90 lbs. or less. Further, yearlings which have been weighed on the Farne Islands appear to fall more or less within the limits shown by the largest moulters. In other words there is little, if any, increase in weight in the first year of life.
These conclusions appear to be confirmed by the known weights of older bulls and cows. 3–4 year old bulls only weigh 170–190 lbs. while the same age group of cows weigh 130–150 lbs.; 5–6 year old cows may reach 170–180 lbs. but records for bulls are very few, although they suggest that by that age they may attain 2 cwt. There are practically no weights of fully mature bulls or cows to justify generalisations. All that can be said is that probably the older well-established breeding cows are over 2 cwt. and the older territorial bulls probably top 3 cwt. or even reach 4 cwt. In any case the bulls vary much more than the cows and in both sexes changes in weight amounting to
Much more data is available about lengths. Although little, if any, weight is acquired during the first year, the moulters grow considerably in length, an average of 55–60 ins. being normal at the end of the first year for both sexes. Thereafter some differences can be considered significant between the two sexes. The rate of growth is fairly steady until puberty at 5–6 years when cows will average about 6 ft. and bulls 6 ft. 6 ins. During the following 3 or 4 years the rate of growth of cows declines so that at 10 years of age they have attained their near maximum of 80–84 ins. (7 ft.). Some growth appears to continue throughout life but it is very small in the cows.
The years following puberty in the bulls account for the great difference between the older bulls and cows, for their rate of growth falls off much more slowly and is continued at the higher rate for a longer period. By 10 years of age the average is 90 ins. and 96 ins. is reached about 2 years later. Thus in round figures mature cows are about 7 ft. long and territorial bulls average about 8 ft. but may vary about 6 ins. more or less.
Turning now to the pelage we find very useful characters to distinguish bulls and cows in the field. These features are, in fact, visible in the pigmentation of the skin of the foetus at a comparatively early age, namely at 110–120 days of active gestation. Growth of the white pup hair coat however obscures this pigmentation by the 150th day of foetal growth. This puppy coat is uniformly unpigmented except occasionally in the region of the muzzle and top of the head. The hair is very long and creamy white on the newly born pup. The occurrence of the greyish areas around muzzle and crown has been interpreted as part of the moult which has taken place before birth and only resumed later at about 3 weeks of age. The excuse for this belief lies in the peculiar hormonal situation existing in the pup at birth, but examination of the hair from these areas shows that the pigment is confined to the tops of the hair and that the hairs themselves are quite unlike those of the later moulter coat. No explanation of these greyish areas is yet available, and their occurrence is very odd. Some groups, notably Pembrokeshire, show a much higher incidence than others, such as the Farnes. Further, these areas are the first to show any hair in the foetus and the time of their eruption makes it clear that the tops must have been formed in the follicles before the appearance of any general pigmentation in the skin.
The pup may begin to moult as early as the 10th day, but this is most unusual and it is generally the 18th day before the first signs appear on the fore and hind flippers and on the head. If the pup belongs to a group such as the Pembrokeshire where entering the sea is a common occurrence, much of the moulting hair is washed off and, as the puppy coat becomes thinner, the pattern of the moulter coat shows through. Even here, however, many of the pups do not enter the sea during the moult and in the northern groups, of course, this is the usual pattern of behaviour. Under these conditions the puppy coat is rubbed off in patches and often the moulter can be found lying on a carpet of its old hair.
This moulter coat is to all intents and purposes the same as all the subsequent coats, heavily pigmented on the back and sides at least and marked by even darker spots and blotches. It is in the abundance and distribution of the darker spots that the difference between bulls and cows can be seen. In cows the lighter pattern consists of a medium grey back shading to a lighter belly, the darker spots are comparatively few and only rarely run together. In the bulls the darker pattern is so extensive that the lighter one is seen only as small triangular patches between the dark spots and blotches which have run together over most of the body.
There is, however, considerable variation in both sexes. In the cows the pale underside may be any colour from pale cream to tawny yellow and the upperside may vary from grey or blue-grey to brown. Some cows may have very considerable blotching, but never to the extent shown in the bulls. In bulls the chief variation is in the overall tone of the darker pattern which may be dark brown to black in colour. A number of older bulls too show a markedly lighter head and sometimes the blotches unite so much as to give the impression of uniform black or dark brown.
These remarks of course apply to the new coat which is grown each year. As the time of moult approaches the whole pelage becomes duller, browner and more uniform in appearance due to the splitting of the hairs so that it is only in the wet pelt that the patterns can be distinguished. It should always be borne in mind when observing grey seals on shore that the appearance of the pelage alters considerably as it dries and that the change is more marked as the moulting season approaches.
The disparate growth of the bulls and cows is well seen in the skull and reflected in their profiles. The skull of the grey seal has a long flat vault which clearly distinguishes it from that of the common seal where the shorter, rounder vault gives rise to the dome-like head. The nasal bones too are differently placed so that the grey seal has, in the bull, a ‘roman’ nose profile and in the cow a straight or ‘grecian’ profile, while the common seal in both sexes shows a slight depression or ‘retroussé’ nose (Fig. 11). The young grey seal however has a skull very similar in appearance to that of the common seal and to that it owes its puppyish look. Within the first year the specific elongation and flattening of the skull takes place and there is little difficulty in distinguishing the two species in the field.
As grey seals grow older these characteristics are accentuated. At 5–6 years of age the sutures between the frontals, parietals, squamosals and occipitals fuse but the anterior sutures between frontals, nasals and premaxillae remain free throughout life and some increase in both length and breadth of the skull continues. In some of the oldest of the cows the profile may begin to take on a ‘roman’ bend, just as the young bulls approaching