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In the Cetacea the principal locomotor organ is the tail, flattened dorso-ventrally into a triangular fluke, and moved up and down in a sort of ‘crawl’ action. The hind-limbs are missing and the fore-limbs are well developed into flippers. Not only are the digits joined by thick webbing but the number of phalangeal bones is greatly increased so that the flipper becomes extremely flexible in its use as a propulsive organ and also in causing change in direction. The Sirenia are rather lethargic and movement is obtained by the action of the flattened tail and by the broad, short fore flippers. The latter are peculiar in having a great power of rotation so that their direction of action can vary over a wide angle. This is of considerable advantage when used as a paddle, the animal being able to turn almost in its own length, or when erect in the water, in little more than its own breadth.
A feature associated with streamlining is the reduction of the pinna or external ear flap. In the Pinnipedia all variations are found; among the fur-seals and sea-lions it is still fairly well developed but narrow (furled) and elongate, lying back alongside the head. For this reason they are often called the ‘eared’ seals. In the true seals it is much reduced and does not extend beyond the dried hair. When the hair is wet it can just be seen, if the light is right, as a circular rim round the earhole (Pl. 1 (#ulink_b7079451-76c4-519f-8ef5-576dc8ab0436)). In the walrus it is equally inconspicuous. In both Cetaceans and Sirenia it is completely absent and in the former the earhole is plugged. (Only recently has the extraordinary hearing mechanism of whales and porpoises been demonstrated by Drs Fraser and Purves.)
FIG. 2. Limb bones of seal and fur-seal: left, fore-limb skeletons; right, hind-limb skeletons. Note particularly the relatively small fore-limb of the seal (Phocidae) and the almost equal size of the ‘big’ and ‘little’ toes in the hind-limbs. In the Otariidae the ‘thumb’ and ‘big’ toe are much larger than the other digits, indicating the driving use made of both limbs. Notice too the very short thigh (femur) and upper arm (humerus) bones in both seal and fur-seal. For comparisons the hind-limbs of both are drawn to the same length and the fore-limbs to the same scale. c. x
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The normal resting closed position of the nostrils has already been mentioned as common to all three groups. It remains to point out that the pinnipedes retain a ‘rhinarium’ external to the nostrils. This is the equivalent of the ‘wet nose’ of the dog and must constitute an important sense organ for the reception of chemical stimuli (scent). That it has to operate in water is no drawback because the molecules of the ‘scent’ must be dissolved before they can stimulate a receptor nerve ending, for which reason the rhinarium of land mammals is always kept moist with secreted mucus. In the pinnipedes it is possibly the sense organ which locates prey, such as shoals of fish at a distance.
The teeth of pinnipedes are greatly modified from the normal mammalian pattern. The differentiation into incisors, canines and molars is still recognisable, but they do not differ so much from each other as in other (land) mammals, consisting basically of single pegs of varying lengths. The incisors are small and degenerate as shown by the variation in their number. (It is not unusual to find two on one side and three on the other.) The canines are massive cones, used for offensive purposes in the males of some species but basically the prey-catching tooth as in land carnivores. The molars are no longer grinders or mashers but consist of a single major cusp or spike with one or more smaller cusps on each side in line with the length of the jaw. In this way there is formed a long line of pointed cusps of varying heights admirably adapted to the retention of struggling prey. The only exceptions are the walrus and the bearded seal. The walrus feeds on large bivalve molluscs, like clams and mussels, which are crushed between stub-like molars. The bearded seal is not predominantly a fish feeder, shrimps, crabs, holothurians, clams, whelks, snails and octopus forming the bulk of its food and the molars are usually much worn and not sharply pointed. In some species of seal the young do have milk teeth for a short time. Usually there is only one set of functional teeth, the milk dentition being resorbed while the foetus is still in utero. Cetacea either have no teeth and feed by a filter mechanism (whale-bone whales) or have a single row of simple cusps (the toothed whales, porpoises and dolphins), all alike, which are far more numerous than in any other mammal. This is a high specialisation for fish-eating, much greater than the pinnipede condition. The Sirenia have flattened grinders of degenerate form since the seaweeds on which they feed hardly require munching.
The skulls of most pinnipedes show traces of slow and incomplete ossification. This is particularly true of the region on a level with the eyes so that the front part can be easily detached from the hinder brainbox in even old animals. The fur-seals and seals differ considerably in the general appearance of their skulls thus lending support to the view that they are derived from different sections of the land carnivores (Fig. 3 (#ulink_78499ad0-1f06-5aae-9620-ad39aa7013a2)). The walrus is again an exception since there is massive ossification to provide support for the huge tusks. Cetacea have evolved quite differently since many of the cranial bones contain spaces filled with air or occasionally with oil. The Sirenia have massive skulls although the bone itself is not dense.
We now come to the respiratory modifications and it is impossible to separate these from peculiarities of the blood system since the oxygen required by the tissues is transported by the haemoglobin in the red cells of the blood. The modifications of the nostrils have already been mentioned, but there are others equally significant. Many pinnipedes have cartilaginous rings in the trachea which are incomplete on the upper side but some, and both of our British species are among them, have complete rings which thus prevent any collapse of the trachea when the seal is under pressure in diving. These rings are continued into the bronchi and bronchioles and cartilage continues to be found in the connective tissue of the lungs lying between the respiratory lobules. In addition there are, in the bronchi, valves of muscle and connective tissue which are able to form air-locks in the lungs and so prevent the residual air in the larger (and non-respiratory) tubes being forced under pressure into the respiratory alveoli. This appears to be a device to prevent nitrogen, which forms four-fifths of the air, being absorbed under pressure into the blood stream. If it were so absorbed, on return to the surface it would come out of solution in the blood under the reduced pressure to form gas bubbles in the smaller blood vessels and so cause ‘bends’ which can easily prove fatal, as it does when it occurs in man when diving.
FIG. 3. Skulls of seals and sea-lion. All the skulls are of adult males. For comparisons the grey seal skull is drawn to the same length as that of the Californian sea-lion and the common seal skull to the same scale as that of the grey seal. Note the general similarities, particularly of the dentition, but also the differences which are most marked in the region behind the articulation of the lower jaw. c. x
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The lungs themselves are not abnormally large and all pinnipedes exhale before or on diving so that there is literally little or no oxygen in the lungs to provide for tissue respiration during the activities of swimming and catching prey below the surface. The thorax, which also contains the heart and great vessels besides the lungs, is more elongate than normal in mammals and the diaphragm, which separates its cavity from that of the abdomen, is set much more obliquely, its upper attachment to the body wall being set farther back than normal and the sternal support of the lower margin is shorter than usual (Fig. 4 (#ulink_88773492-2ac3-54d4-b3c1-d534ba61ac44)). This means that the cavity can be more completely compressed and a greater proportion of the air in the lungs exhaled than in normal land carnivores and other mammals. The small residium is driven into the nonrespiratory trachea and bronchi. When the seal returns to the surface breathing recommences and a series of deep inhalations and expirations takes place. From my own observations on a southern elephant seal the number of such breaths is roughly proportional to the length of time that the nostrils have been closed. Even when on land and hauled-out seals will continue to remain with closed nostrils for considerable periods separated by series of breathings.
FIG. 4. Side view of the pinnipede body, to show the principal organs. The right side of the body is diagram-matically opened by removing the skin, blubber and outer muscle layers. The right fore-limb has also been removed as far as the ‘elbow’. The genitalia are omitted. The oesophagus is indicated as passing above the heart and between the right and left lungs. (#ulink_1ed46e98-964c-5d20-a978-44a5ac02d5b0)
By way of contrast Cetaceans dive with full lungs and all the modifications are towards the prevention of collapse and the transmission of the external pressure to the air contained in the lungs; another ‘anti-bends’ device.
In the pinnipedes we are still left with the puzzle of how they obtain and maintain sufficient oxygen for their activities below the surface, and we must turn to the blood system for further information.
First it must be clear that if there is little or no air in the lungs there is no profit in circulating the blood from the lungs for there is no oxygen to pass on to the active tissues. It is therefore not altogether surprising to find that seals exhibit a phenomenon known as ‘bradycardia’. This is a reduction in the heart beat both in the number per minute and in the strength of the beat. In fact it is reduced to little more than an occasional flutter by which some blood is circulated along the carotid artery to the brain. This has been shown to arise almost immediately the seal has dived, and in this it differs from the bradycardia of Cetaceans in which the rate and strength of the heart beat is gradually reduced to a low level. This difference must be associated with the difference of lung contents, the gradual bradycardia of Cetaceans keeping pace with the gradual exhaustion of the oxygen in the lungs (Fig. 5 (#ulink_0608d78a-c940-5bb9-8027-aa681c9e2953)).
To prevent the ‘used’ blood from the tissues of the body being circulated even to a very minor degree in the pinnipedes, they have evolved a powerful sphincter muscle which closes the huge venous blood vessel leading to the heart and which draws blood from the hinder part of the body, the viscera and liver. This large blood vessel (posterior vena cava) is disproportionately large (usually double and enlarged) and so can act as a reservoir for the non-circulating blood. In addition there is a large vein lying below and up the sides of the spinal cord (extradural vein) which is enormously enlarged in pinnipedes. From it only a little blood can find its way back to the heart in the front region. Elsewhere this vein is connected by special large veins both directly to the posterior vena cava (at the hinder end where it is double) and indirectly round the kidneys in huge blood sinuses (Fig. 6 (#ulink_51785113-9149-5b5f-a670-3e44cca514a6)). All these peculiarities increase the storage capacity of the venous system when bradycardia is in action. Some idea of the size of the veins will be conveyed by saying that in the grey seal the posterior vena cava in its posterior part is ‘nearly as thick as your wrist’ and King (1964) refers to their size in the walrus ‘by the often quoted reference that they can be “pulled on like a pair of trousers”’.
FIG. 5. Bradycardia in seal, porpoise and manatee. These are representatives of the three groups of truly marine mammals, the manatee, a surface feeder on seaweeds, being the least modified for diving. The seal immediately responds to diving by reducing heart activity, having expelled all the air from the lungs, while the porpoise, retaining air in the lungs, reduces the heart-beat rate only slowly. (Redrawn from Irving, Scholander and Grinell, 1941) (#ulink_36fa4554-5256-5840-bc80-3dce24ef50f4)
But all these modifications tend to show that the blood is not the continuing source of oxygen during active diving. This is confirmed by two other facts; firstly the red blood cell count (the number of red blood cells per unit volume) is nothing out of the way, about 5–6 million (cf. human 4–5 million), and secondly that the amount of haemoglobin in a unit volume is not very high either, about 1.2 compared to the standard in man of 1.0. If this is all true, then how do seals manage to respire in their tissues during diving?
Part of the answer lies in another pigment known as myoglobin because it is present in muscle. Here we find an enormous difference from the normal and we hardly need figures to show it. Myoglobin is also coloured though not so deeply as haemoglobin and it gives the normal pink colour to muscle meat. In the Pinnipedia the muscle is almost black in colour, certainly very deep red. Those who remember the whale meat which was available after the second world war will recognise that Cetaceans too have a very high myoglobin content. To both of these groups then part of the answer is the ability to store oxygen attached to the myoglobin on the site where it is required for the respiration of the active muscle cells.
There is also evidence that these animals can run into oxygen debt, particularly in respect of metabolising the waste products, which are normally toxic if allowed to accumulate without treatment. This adaptation is not so extraordinary as it sounds, for it is known that, in humans, when slow starvation is prolonged and the organism begins to live on its muscle protein (autolysis of the muscle) a level of waste nitrogen products can build up to many times the normally lethal concentration. In these diving mammals this ability has become normal rather than a pathological occurrence. On return to the surface the repeated inhalations and exhalations rapidly restore the oxygen balance.
FIG. 6. Kidneys and posterior vena cava, showing the extra storage space in the blood sinuses. This is a view from above, the vertebral column and nerve cord being omitted. Part of the extradural vein is also omitted so as to allow the junction of the right and left branches of the posterior vena cava to be seen, with its continuation into the huge hepatic (liver) sinus. Arrows indicate the direction of the blood flow. (Redrawn and somewhat modified from Harrison and Tomlinson, 1956) X
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So atypic of mammals is the environment of the pinnipedes that speculation as to the value of their principal sense organs must come to mind. Not a great deal has been found out but Harrison, working on captive common seals, has contributed some useful basic information. He finds that the eyes are well adapted for night vision or for murky water but this is associated with short-sightedness. The Weddell seal, however, avoids this myopia by having a slit pupil. Their effectiveness must therefore be strictly limited particularly in those species which live and feed through the polar winter. Auditory and touch stimuli are well received, the latter being particularly relevant to the well-developed vibrissae on the muzzle which have very large nerves running from them to the brain. Water being an incompressible medium is excellent for the transmission of sound waves, so that sensitivity to auditory stimuli is to be expected. My own impression is that grey seals are more sensitive to sounds in the higher frequency range than those in the lower. Phoca and Zalopus both have good hearing in the upper range. It is possible that they can hear sounds which, to man, are ultrasonic but this has not been proved. Recent work has shown that many marine organisms make use of these higher frequencies and sensitivity to them may well be an advantage to carnivores in search of food. Harrison also found that the common seals have an excellent sense of orientation. This is obviously of great benefit to an animal making use of a three dimensional medium such as the sea. Anyone who has done any flying will know that man, although he has the necessary sense organs, has to learn how to use and interpret the stimuli received.
In discussing the characteristics of the Pinnipedia and comparing them with those of other marine mammalia it has been necessary to draw a distinction between the true, haired or earless seals on the one hand and the fur-seals and sea-lions or eared seals on the other. This is a very profound demarcation if we add the walrus to the second group. So clearly marked are these two groups that it is now thought that they had separate origins among the land carnivora, the true seals being derived from otter-like ancestors and the fur-seals and their relatives from bear-like forms. This can be expressed as shown at the top of See here (#ulink_d2fe9d6c-3cab-55e1-ba5b-4a53f387dc33).
The Otariidae are the least modified for marine existence. They retain a prominent external ear flap, there is an obvious neck region between the head and trunk, so that the body form is not perfectly streamlined or bobbin shaped, and their hind-limbs can be turned forward and used on land as feet. The pelvic region is also very obvious when they are on land. On the other hand the claws are much reduced either in numbers or size, and the flippers of both hind- and fore-limbs large and very well developed.
Their distribution is remarkable in that they are completely missing from the north Atlantic while present in all other oceans. Moreover, of the 12 species, 9 occur in the southern waters of the Atlantic, Indian and Pacific Oceans (including the circumpolar antarctic seas), 1 in sub-tropical Pacific waters and 2 in northern waters of the Pacific. Although this suggests that the family is southern in origin, palaeozoogeographical evidence (McLaren 1960) points to a north Pacific origin and that they evolved from a littoral canoid of bear-like appearance along the north-western coasts of North America, some time before the upper middle Miocene when their first fossils appear. Weight is given to this by the presence of the other ursine derivative, the walrus, in the circumpolar seas of the arctic. There are two sub-families: the Otariinae or sea-lions (with 5 species) and the Arctocephalinae or fur-seals (with 7 species). (See Appendix A (#litres_trial_promo), See here (#litres_trial_promo).)
The Odobaenidae contain two species,* (#litres_trial_promo) one Pacific and one Atlantic, both in arctic waters. It is probably better to consider them as sub-species of the one species: Odobenus rosmarus. Like the Otariidae they still retain hind flippers which can be used as feet, but they have become greatly modified in other respects. They are specialised feeders on shell fish; the tusks are used for digging the bivalves out of sand or mud and then the flattened molars crush them† (#litres_trial_promo). In the males the tusks are particularly well developed and used for fighting as well. Unlike the members of both the other families the walrus is almost hairless although the vibrissae on the muzzle are well developed as tactile organs. Although they have been hunted for many years and almost exterminated, they are now protected and some study is being made of their habits. The Atlantic form breeds on some of the Canadian islands and occasionally an immature individual is reported on the British coast.
The Phocidae have an inconspicuous external ear, concealed by dry hair but usually visible when wet. The neck is short and thick, smoothing the body outline into that of the head. The fore limbs are small and used for grooming, with well developed claws. Their use in swimming is small, usually only for changing direction or ‘treading water’. On land they are not much employed in locomotion, although in the sub-family Phocinae the digital flexure enables them to clamber over rocks and broken ice. The hind flippers are the principal locomotor organs in water but trail on land. The movement of seals on land appears clumsy, but they can move faster for short distances than would be supposed. They occur in all the oceans of the world including the Mediterranean and Baltic Seas and several inland lakes which have had connection with the sea in glacial or post-glacial times. Until recently three sub-families have been recognised: Phocinae (with 8 species), Monachinae (with 7 species) and the Cystophorinae (with 3 species). Miss King (1966) however, has shown that the characters uniting the species of Cystophorinae are only superficial and differ in fundamentals, while many other characters show that the hooded seal is really a member of the Phocinae while the two elephant seals are closer to the Monachinae. Each of the two Sub-families are divided into two Tribes thus:
All the Phocinae are northern in both Atlantic and Pacific waters and their presently or recently connected seas and lakes. The Monachini or monk seals are tropical or sub-tropical while the Lobodontini are antarctic or sub-antarctic and circumpolar. The recent reallotting of the Cystophorinae species solves their equivocal position for the hooded seal as northern Atlantic and Pacific like the other Phocinae, while the elephant seals are brought more into line geographically with the southern distribution of the Lobodontini.
Despite the present wide distribution of the Phocidae the fossil evidence suggests their origin is Palaearctic from lutrine (otter-like) ancestors somewhere between early Oligocene and lower middle Miocene times.
Thus we can now say that the two seals which breed in British waters belong to the Phocinae, the two species, Phoca vitulina and Halichoerus grypus falling into the tribe Phocini.
Until recently much more had been discovered by British workers about the antarctic species of Lobodontini (and about the southern elephant seal) than about our own British species. How little was known until recently will become apparent when we consider each species separately, but something must be said about the reason for this neglect of our pinnipedes. Basically our ignorance has been due to the physical difficulties of obtaining information. Here we are dealing with animals which are amphibious. While they are on land we can watch them from the land but the slightest shift of the wind to send our scent towards them and they are away to sea where we cannot follow them. Extending this example to the period when they leave their breeding grounds on land, the problem becomes even greater. Antarctic forms, both mammals and birds, do not have a built-in fear of man and even the experiences of man’s culling them over the last century and a half have not induced such a timidity as we find in the northern Atlantic species. Consequently there has been no easy way in which naturalists and zoologists could become interested in seals or, even if interested, pursue the study of them without a great deal of trouble, preparation and expense. It has, of course, been easier to kill them than to study them alive, but even then the difficulties involved have been sufficient to enable both species to survive under as great a pressure of persecution as man has found it possible and economical to mount. Had they been solely terrestrial they would have disappeared long ago. Had they been marine and social they may well have been as reduced in numbers as their fellow mammals the Cetacea. Only in modern times with greatly increased resources of powered boats, helicopters and of camping facilities in remote and uninhabited islands and coasts has it been possible to pursue a planned scheme of research on the grey seal. Investigation on the same scale for the common seal is yet to come, in fact it may not be necessary as its habits do not appear to be quite so complex, but it may be almost equally difficult to prove it.
Undoubtedly the species of pinnipede about which most is known is the northern fur-seal (Callorhinus ursinus). Its value as a fur-bearing animal made it essential that the main breeding colonies should be saved and during this century the United States Fish and Wildlife Service has carried out a series of investigations of the greatest importance. As a result of the knowledge gained it is now possible to ‘manage’ the population so as to obtain a maximum return of seal skins, consistent with the maintenance of the population at the necessary level of numbers and condition, at the same time preventing too great an excess which would adversely affect the important fishing interests of the north Pacific. While giving every credit to the ingenuity and skill of the research workers, it must be admitted that several factors have greatly assisted them. The first and obvious one is the economic value of the fur-seal which not only sanctioned the expenditure of money in research, but also provided considerable man-power (non-scientific) for major operations of tagging tens of thousands of the seal pups. The second factor involved is the behaviour of the immature groups which assemble on sites near to the breeding rookeries, segregated into the sexes. The adult bulls and cows too are markedly different in size and pelage and so can easily be distinguished at a distance without the aid of binoculars. Even in the non-breeding season help was available in an extensive pelagic sealing industry over the north Pacific. Nothing comparable is available in the north Atlantic. For all the information available from ships in the North Sea, it might have no seals in it at all, yet we know now that young grey seals cross it regularly and that at certain times of the year the majority of grey seal cows are not in coastal waters. Consequently the pattern set out in detail for the northern fur-seal is of the greatest importance for purposes of comparison wherever possible.
British workers have been responsible for a great deal of work on antarctic pinnipedes such as the Weddell, crabeater and southern elephant seals (Phocidae), the southern sea-lion and southern fur-seal (Otariidae) in the course of the ‘Discovery’ investigations of the inter-war period and of the Falkland Islands Dependencies Survey after the second world war. These researches were undertaken in an attempt to save the natural resources of the southern whale and pinnipede populations. The latter had already been brought to a point of near extinction and the former could easily follow. As a matter of history the pinnipedes have been saved, while the whales have been brought near their end. We were probably right to put our energies into this exercise when we did for not only did it have a happy result for the seals, but we have acquired a national expertise in seals and sealing which is only equalled by that of the United States Fish and Wildlife Service who were responsible not only for the work in the Pribilov Islands, but also for research on the northern elephant seal and other pinnipedes off the Californian coast.
More recently the Canadian Arctic Biological Unit has been formed and is doing good work on seals and walrus off the western north Atlantic seaboard. In the Soviet Union attention has also been turned to this natural resource and work has been done on several species in the north western Pacific Ocean.
In the next chapter we shall see how in the last thirty years or so there has been a considerable growth in the interest shown by both professional and amateur zoologists in Britain in our own species. There has also been expressed a great deal of public concern over the status of our seals but much of this has been ill-informed. The problems are complex and over simplification can lead, as it has done in the past, to harmful action when only good is meant. Intentions are not enough; knowledge is essential.
CHAPTER 2 (#ulink_4a3f8745-fd61-52a0-a3f6-35bffdcb6a8c)
THE GREY SEAL – INTRODUCTORY (#ulink_4a3f8745-fd61-52a0-a3f6-35bffdcb6a8c)
THE relationships of the grey seal, Halichoerus grypus (Fab.) have been discussed in the previous chapter. It clearly emerges that this species occupies a unique position being the only species of the genus.
The world distribution of the grey seal is peculiar and unlike that of any other seal species. There appear to be three distinct populations (Fig. 7 (#ulink_e4f4a5c1-b71e-53ea-b33b-a94603b00bde)). To prove that there is never any interchange of individuals is practically impossible, but all the available evidence suggests that no real exchange takes place. The three populations are centred on the Baltic Sea, on the eastern north Atlantic and in the western north Atlantic. Davies (1957), in a very interesting paper which dealt with the possible geographical and historical reasons for this separation, suggested that these three populations should be called the Baltic, eastern Atlantic and western Atlantic respectively. There are also very good biological reasons for the separation. The eastern Atlantic grey seals, most of which are present in British waters, breed in the autumn;* (#litres_trial_promo) the other two populations breed in late winter to early spring. Similarly the eastern Atlantic seals breed on land, either on beaches or on the landward slopes; the others tend to breed on ice and only if it is an exceptional year and there is little ice do the western Atlantic ones breed on the adjacent shore. Consequent upon these differences the social structure of the breeding seals is different. The eastern Atlantic seals tend to form large rookeries in which the cows outnumber the bulls by 5 to 10 times; in the ice-breeding forms a much closer approximation to equality is found in the western Atlantic region and such information as is available for the Baltic seems to suggest that the same applies there – isolated cows with their pups with attendant bulls over a wide area of ice floe.
Davies points out that all three populations must have been united during the last Inter-glacial period, occupying the seas from northern Labrador to Greenland, Iceland, Norway and the White Sea, on the average about 15° north of the present range (Fig. 8 (#ulink_109864a9-7451-5232-9663-9955bca7a3aa)). As the species is a land-breeder as opposed to an ice-breeder the succeeding Glacial period would have forced the grey seals to separate into two populations, one occupying the seas from Newfoundland to Florida and the other the seas from the ‘British Isles’ (which were not separated from the continent at that time) to the Moroccan coast. With the first retreat of the ice and glacial conditions covering the ‘British Isles’ and northern Europe, the North Sea and Baltic Sea came into existence again broadly joined in the region now known as southern Sweden and Denmark. The grey seals of the eastern Atlantic had meanwhile moved northward again occupying the seas from the Bay of Biscay round the ‘British Isles’ and into the Baltic. However after this changes in the land and sea levels caused a land connection to appear between Sweden and north Germany (Pomerania) thus cutting off a lake comprising the area of the present Baltic, including the Gulf of Bothnia and most of present-day Finland. This is known as the Ancylus Lake and in it were isolated grey seals which formed the origin of the present Baltic population. Much more recently the North Sea and the Baltic have again been joined but only by very narrow channels at the southern end of the Kattegat. As we shall see later there is evidence that only the very northern end of the Kattegat is entered very occasionally by young grey seals. The main eastern Atlantic population of grey seals no longer use the southern shores of the North Sea which are sand and mud only, quite unlike the preferred rocky situations in Britain and Norway.
FIG. 7. World distribution of the grey seal. There are three distinct populations in: 1. the Western Atlantic, 2. the Eastern Atlantic and 3. the Baltic. (#ulink_f5ebcae7-c714-505e-a88a-b87a87acde66)
Until recently there has been a paucity of museum material. While this has been largely overcome for the eastern Atlantic form and some is being collected in Canada of the western Atlantic seals, practically nothing is yet available from the Baltic. In any case no one has yet brought what material there is together for comparison. When this is done it is quite likely that sufficient difference will be found to warrant the recognition of 3 sub-species. The geographical isolation, which is normally required for such a recognition, appears to be complete and biologically reinforced. The Baltic grey seals occur in the Baltic itself and in the Gulf of Finland, but do not penetrate westward into the Bornholm area or the Kattegat. The eastern Atlantic seals occur from the west coast of Brittany, all round the British Isles and on the Norwegian coast, but few records exist of their appearance as adults on the Dutch coast or Frisian shores. Grey seals are certainly present in the Faeroes and Iceland region and it is thought that these are eastern Atlantic from their autumnal breeding season, but it is a far cry from Iceland to the western Atlantic breeding grounds off Nova Scotia.
FIG. 8. The origin of the three populations of grey seals. Gross-hatched areas = glacial ice; diagonal lines = permanent sea (polar) ice; dotted line = approximate limit of seasonal drift ice; dotted areas = distribution of grey seals. A. shows the grey seals in one population close to the Arctic Circle in the Last Inter-glacial Period. B. shows the grey seals split into two populations, east and west Atlantic, by the maximum glaciation of the Last Glacial Period. C. shows the northward movement of the eastern Atlantic grey Seals following the retreating ice. The Baltic Sea is open to the North Sea across Denmark and southern Sweden, allowing entry of the grey seal. D. shows further northward movement of both ice and both populations of grey seals. England is still united to the continent but a bridge of land from Denmark to southern Sweden has locked off the Baltic population of grey seals. Since the period of the Ancylus Lake, Denmark has become separated from Sweden and England from the continent. (Redrawn from Davies 1957) (#ulink_3105cb1a-5808-572e-abaf-132b032a34c5)
In Canada the Arctic Unit has for a number of years been investigating both common and grey seals. While some of their results parallel our observations for the eastern Atlantic, others tend to emphasise the differences. Dr Mansfield and his collaborators have of course an interest in several other species of arctic seals but for our two species contact is maintained with British workers.
For the Baltic grey seal the story is not so satisfactory. Mr Oliver Hook has for a number of years been into the Baltic to track down the pups and to relate the ice movements with the probable centres of breeding. So far, however, except for willing co-operation in his work, the Swedes have not undertaken much research on their own. Political difficulties are probably the cause since further investigation of breeding areas and so on would almost certainly involve Finnish and Soviet coastal waters. There seems, however, some urgency for work in the Baltic since the indications are that the population is decreasing considerably. In an enclosed sea this could lead to near extermination, unless international co-operation is established and this is difficult in the absence of facts.
The species has a number of characteristics not normally taken into account by systematists which emphasise its uniqueness. All the other members of the Phocinae are either much more aquatic in their normal behaviour, or are confined to colder waters and associated with ice, or both. In British waters Halichoerus grypus is a truly temperate seal and always breeds on land. Both physical and behavioural (or ecological) characteristics tend to show that Halichoerus grypus diverged from the main Phocine stock early on. Its habit of breeding on land with the establishment of a social system may thus have evolved quite separately and does not indicate connecting links with other Pinnipede species in the Otariidae.
For many years the grey seal of Britain was thought to be the bearded seal, Erignathus barbatus, and it was not until 1825 that it was firmly established that it was Halichoerus grypus. This may appear to the layman as either merely a matter of words or else plainly stupid. But there is some excuse for this confusion. Normally when a species is named and described its name and description are tied to a specimen which is located in a museum, and any more specimens which might belong to that species can be compared with it. Unfortunately this is not the case with most species of seal and there has been an enormous amount of confusion, because everything depended on a verbal description. Consequently although it could confidently be asserted that Halichoerus grypus existed (it could easily be seen in the Baltic) and that Erignathus barbatus was clearly different and occurred, widespread, in the north Atlantic, it was not known to which the grey seal of Britain belonged. The earlier descriptions of it were too vague, although several of the early workers thought they corresponded more nearly with those of the bearded seal. The really astounding thing was that there was such a paucity of material for comparison. Hundreds of grey seals were killed each year for blubber or hide, yet until very recently the British Museum (Natural History) had only one adult skull, and many international museums had none. No complete skeleton existed in any museum except the National Museum of Wales in Cardiff where that of a cow was mounted.* (#litres_trial_promo) If the hard parts were not preserved then certainly the soft parts were not. No account of the general disposition of the viscera can be found in the literature and the information about most of the anatomy of soft parts contained in this book has been specially obtained by first-hand dissection.
An equal ignorance was displayed about the general behaviour and life-history of the animal. The principal account is given by Millais (1905) who collected together what previous writers had said and added a great many observations of his own. But all of this was anecdotal and largely based on occasional visits to rookeries lasting a few hours or at most a day or two. The basic difficulty was one of accessibility for, as we shall see, even the breeding sites are isolated and situated in some of the stormiest waters round the British Isles. When the seals are no longer on these rookeries they may be hauled-out on any of dozens of islets or skerries spread over many square miles of sea and can only be found by meticulous searching. We know now that these sites can alter with the seasons and may, to a lesser degree, alter from day to day depending on wind and tide or even, one feels, on the idiosyncrasies of the seals themselves. It is no wonder, therefore, that earlier workers found difficulties in establishing even the basic facts of the yearly cycles and life-histories of this seal, without the aid of modern means of transport.
The first serious attempt to come to grips with the problems posed by this species was made by F. Fraser Darling in the late 1930’s. He decided to live with the grey seals and nearly all subsequent workers have done the same. This involves some difficulties and dangers, for all the islands involved are uninhabited and some are without fresh water. Consequently all supplies and a form of habitation must be taken ashore to cover not only the intended stay but for a much longer period, since return to the mainland is entirely dependent on weather and an enforced stay of up to a week tacked on to a planned three weeks is not unusual. Darling began his studies in small rookeries where each individual could be recognised and the progress of its behaviour related from day to day. Only in this way could the correct succession or pattern of behaviour become firmly established. To plunge into a large rookery with hundreds or even thousands of individuals, more arriving and others departing, makes it impossible for the observer to understand what is happening unless prior experience has shown him the correct sequence of activities. Darling’s observations in the Treshnish and Summer Isles therefore prepared him for North Rona, and his accounts of the breeding season are remarkably accurate.
In a book published in 1936 (A Beast Book for the Pocket) some 27 statements are made concerning the biology of the grey seal. Of these 22 are wrong; not slightly wrong but completely and utterly so. Darling’s work altered all that for the autumnal period and for much of the summer.
After the second world war our knowledge increased rapidly. Mr J. L. Davies began in 1947 by investigating the breeding season in the comparatively small group found off the Pembrokeshire coast, notably on Ramsey Island. In two subsequent years, 1950–51 a small group from London led by Dr L. Harrison Matthews F.R.S. continued the work there and enlarged it to cover the nutrition of the pup and some basic aspects of reproduction. Quite independently in 1951 a group from the Northumberland, Durham and Newcastle-upon-Tyne Natural History Society led by Mrs Grace Hickling began to weigh and tag pups in the hope of tracing the movements of the moulters when once they had left the Farne Islands. Their success was immediate and the idea caught on. I had been with the group on Ramsey Island in 1951 and in the next two years tagged as many pups as I could. In the last of these years I was joined by Dr K. M. Backhouse who had taken part in the Farne Island work and who has continued to work with me both in the field and the laboratory ever since.
In 1954 and 1955 I went to Shillay in the Outer Hebrides to follow up a report of a disproportionate number of bull seals seen there by Dr J. Morton Boyd (who afterwards became Director of the Scottish Nature Conservancy). This led to interesting observations in pre-breeding behaviour, a field which is still largely open for the investigator. In 1956–57 Dr Backhouse joined me in observations in the Inner Hebrides, on islets off Oronsay, again to cover the pre-breeding period and the establishment of a breeding community on the rookery.
All these observations were connected with the breeding season, as, in fact, had been all the pre-war observations. In 1954 Dr Backhouse and myself decided to begin investigations during the winter and spring using the Ramsey Island group as our base as being within reasonable touch of London, travelling down over Friday night and back on Sunday night. This was dictated by our teaching duties during term time, but could be altered and ameliorated during the Christmas or Easter vacations. Our success was very limited since only two weekends a month were suitable on account of tides, and winter gales, either before or during the weekend, prevented us or the seals from reaching the island on many occasions.
Three very significant results emerged however; first that there was a delay in the development of the embryo (January 1956) and secondly that there was a small but quite significant number of births of spring pups (April 1956) and thirdly that this was associated in the Pembrokeshire group with large haul-outs of moulting bulls in the spring (April 1957).
Meanwhile quite unknown to us Prof. J. D. Craggs, an electronics engineer in the University of Liverpool, and N. F. Ellison, both active members of the Liverpool Natural History Society, turned their attention from the birds of Hilbre Island, off the Wirral peninsula, to the seals which gathered at low-water on the West Hoyle Bank a mile or so farther out to sea. These had previously not been very numerous and had always been thought to be common seals. They turned out to be grey seals and a series of observations made almost every fortnight throughout the year over five years (1952–57) showed not only that the numbers were increasing, but that they fluctuated regularly during the year. They were observing the obverse of those investigating the breeding grounds and thereby made a most valuable contribution.
To estimate the numbers of grey seals on and around the breeding grounds has always been an objective of observers and one of the difficulties has been the tendency of the seals to use small islands and skerries within a considerable radius from the breeding centre itself. Thus it was physically impossible to make a simultaneous count over the whole area, and this was imperative if the count was to have any significance. The use of an aeroplane had been tried during the breeding season in 1947 when J. L. Davies knew the numbers of seals from a ‘ground count’ in Pembrokeshire. It showed that little reliance could be placed on such observations unless the ground was fairly clear or only pups were being counted. Adults and moulters are too cryptically coloured to be easily recognisable. The only group which showed a promise of success was that of the Farne Islands where the haul-out points are necessarily limited to the outermost of the Outer Farnes and are not in fact far from the breeding islands of the Outer Farnes. From 1958 onwards monthly ground counts were made there by Mrs Hickling and Dr J. Coulson and so gave a picture the converse of Craggs and Ellison’s.
In 1958 breeding of grey seals was discovered on Scroby Sands off Great Yarmouth and appeared to point to an increase and spread of the Farne Island group. In this year, too, North Rona became a National Nature Reserve so that in 1959 an expedition comprising Dr J. Morton Boyd and Dr J. Lockie of Nature Conservancy (Scotland), Mr J. MacGeogh, the honorary warden of North Rona and Sula Sgeir and myself (the only Sassenach!) landed there on October 1st to stay for at least three weeks and make periodic censuses of the pups and other observations. Similar expeditions have gone almost every year since with varying personnel to keep a check on the numbers. Dr Boyd also organised over several years observations from scattered points over the west coast of Scotland to see whether data could be collected indicating movements of seals to or from the breeding centres. Some interesting facts have emerged from this too and from aerial photographs of some islands to which access is extremely difficult and rarely possible.
But all this was field work and without a background of knowledge based on the examination of material in the laboratory many of the deductions which one would like to have made could only be very tentative. One of the outstanding problems related to the time-scale of the grey seal’s life. Several views had been put forward in the past without any firm basis. This is very dangerous because such ideas are often repeated as though they were well established facts. Here was such an instance. Davies accepted the view that a 12-year life span was normal for the female grey seal and had based his calculations of the total south-western group population on this. There neither was then, nor is now, any way of determining the age of a seal in the field. At that time there was not any way of doing so even if the carcase of the animal was available for examination. ‘How long do they live?’ or ‘How old is it?’ are two of the commonest questions asked about animals and they are almost the most difficult to answer. To find a method was, therefore, of first priority.
Researches on the Pribilov fur-seal and several other mammals had shown during the post-war years that the deposition of some of the hard parts of the teeth was periodic and could be interpreted in terms of years, just as one can determine the age of some fish from their scales. By the late 1950’s I had satisfied myself that the layers of cement on the outside of the root of the teeth could, after some practice, be so used in the grey seal with reasonable accuracy. All that was now wanted was more material.
During these years complaints from the salmon fishers, both rod and net, had been growing. Also from the white fish industry came reports that the occurrence of cod-worm was very much on the increase and the grey seal was blamed as the vector of this parasite while the Farne Island group were thought to be the centre of the culprits. Consequently the grey seal became of economic importance. The carcases of seals killed at the salmon nets along the east coast of Scotland were then made available and a great deal of material began to come in. It was not very well preserved of course and it was highly selective consisting only of those seals whose bodies could be recovered; if they were too heavy to handle they were not brought ashore. However, it was a start. Added to this an investigator, Mr E. A. Smith, was appointed in 1959 jointly by the Development Commission (on the Fisheries side) and by Nature Conservancy; he soon found that there was a group of grey seals (as well as common seals) in Orkney. Tagging soon showed that they were as guilty as the Farne Islands ones for depredations on the salmon of the Scottish east coast. Moreover the group was a very large one and could supply material in sufficient quantity for research without fear of seriously depleting the stocks. Of the other two known large groups, Farne Islands and North Rona, one was a sanctuary under the National Trust and the other a National Nature Reserve. Orkney and later Shetland then supplied most of the really valuable material. Further, when some degree of cull was decided upon during the breeding season, the statutory protection afforded the grey seal since the early 1930’s was lifted and for the first time we were able to obtain a sample of a breeding population in October 1960. Using the already discovered method of age determination an entirely new light was thrown on the age structure of the population, on the sexual life of both bulls and cows and many of the field observations previously made began to fall into place and to make sense.
Many more minor problems have been worked on since, particularly by Mr Smith in the field and by Dr Backhouse and myself in the laboratory. None of us however has failed to take part in the other type of work involved, since cross-fertilisation of ideas between field and laboratory is essential for orderly progress to be made. There remained of course a number of outstanding puzzles which will be mentioned in the pages which follow.
Within the last few years however, there have been developments which promise a continuation of systematic and sophisticated research, not only on the grey seal, but also on the common. The establishment of the ‘Seals Research Unit’ at Lowestoft under the National Environment Research Council with Mr Nigel Bonner in charge assisted by a small team of very active and resourceful zoologists has already shown what can be done using more modern equipment and the importance of prolonged co-ordination in work which must of necessity be scattered over a wide geographical area. Some of these results will be referred to later on.
It is now necessary to define certain words which will be used to describe collections of grey seals when found on land. In the past the term ‘colony’ has been used in so many different senses that it has become almost meaningless and I shall not employ it. Before appropriate alternative words could be found it was necessary to know something about the seals and how the world population was organised. Already it has been shown that there are three major units and I propose to refer to these as ‘forms’. This term does not have the precise meaning taxonomically that ‘sub-species’ would carry but it does suggest that we are dealing with sub-units of the world population which are distinct on biological grounds as well as geographical. So little is known as yet of the break-down of the Baltic and western Atlantic forms that it is only possible to supply terms to describe the composition of the eastern Atlantic. Here first we must distinguish between the centre of breeding and places where, in the non-breeding season, the seals may haul out. The breeding centre will consist of ‘rookeries’ where pups are born and mating takes place. In addition there are collections of seals associated with the rookeries to which reference will be made later. The important biological fact of the rookery in relation to seal populations is that it is the origin of the population. If therefore the females may use one of several adjacent rookeries, the products of these rookeries must be considered as a single population arising from a ‘group’ of breeding centres. Here I propose the use of the word ‘group’ to describe a subdivision of the eastern Atlantic population which appears to behave as an entity and to possess some definable characteristics, either geographical or biological or both, which separate them from other ‘groups’.
In some instances we still do not know enough to be certain whether we are dealing with one or two groups. For example, a number of grey seals breed on the north Cornish coast, there is an occasional birth on the Isle of Lundy and many more breed on the islands and coast of Pembrokeshire and Cardiganshire. Are we justified in thinking of these as a single working unit or ‘group’, or are there two? To add to the difficulty, just across the St George’s Channel, grey seals breed on the Irish islands of the Saltees and farther north on Lambay Island off Dublin. Should these be separated or included? What sort of evidence is there? We know that there are no breeding sites in the northern part of the Irish Sea but in the area of the Mersey Bight many can be seen in the non-breeding period of the year as well as on Bardsey Island off the Caernarvonshire coast and around Holyhead Island. Their numbers wane during the period when the Pembrokeshire seals are breeding but some, instead of going south, might well go west or south-west and breed on the Irish coast. Many a young seal in its first grey coat, only a month or so old, marked in Pembrokeshire, has turned up on the coast of Ireland even as far west as Galway Bay. Do they come back to the Welsh coast when they are mature, or do they join the Irish breeding seals? So far we have no definite answer and I prefer to think of a south-western group which would include all those I have already mentioned on the west and south coasts of Ireland, the Irish Sea, west Wales and Cornwall, the Isles of Scilly and Ushant off the Brittany coast.
Other ‘groups’ for which there is some evidence are: Southern Hebridean, comprising breeding areas on the Treshnish Isles (off Mull), in the islands around Oronsay such as Eilean nan Ron and Ghaoidmeal and the occasional birth recorded on Rathsay Island off Antrim, Northern Ireland; Outer Hebridean, covering Gaskeir, Shillay, Coppay, Haskeir, Causamell, St Kilda and North Rona, including Sula Sgeir; Orkney and Shetland; North Sea comprising the Farne Islands, Isle of May and Scroby Sands (Figs. 9 (#ulink_8113edc1-2885-5ecd-8a32-cf4c6197e586) and 10 (#ulink_013a188a-1fc0-56fd-b4f3-137c299fba14)).
The islands detailed here are noted for the presence in the breeding season of rookeries but there are other kinds of collections of grey seals particularly in the non-breeding season to which descriptive names have been given. Where the character of the collection is unknown it may simply be called a ‘haul-out’. This may be qualified by the addition of an adjective as in a ‘fishing haul-out’. Such a haul-out is temporary in the sense that although it may be regularly used the number of the individuals may vary from day to day and no one seal will necessarily remain there for very long. A fishing haul-out is one where there are collected a sample of the grey seal population using that area for fishing, as a temporary resting or basking site. The West Hoyle Bank off the Wirral peninsula is a good example (Pl. 22 (#ulink_a7cd1553-6771-5434-8d7b-c1e66b88d79c)). The seals there may vary from a very few (less than a dozen) to upwards of 200 depending on weather and tide. When not hauled-out they are probably feeding in the northern part of the Irish Sea. In some groups the absence of widely distributed haul-out sites often results in the same islands or groups of islands being used both as rookeries and for fishing haul-outs. It is rare however for exactly the same site to be used for the two purposes.
FIG. 9. Distribution of the grey seal in British waters. Coasts where sightings have been recorded are shown in thick black line. (#ulink_c0b9697f-b960-5db2-a8d0-2e12e11c1d8d)
Another type of haul-out is the ‘moulting haul-out’. These occur only in the later part of winter or early spring and consist predominantly of one sex or the other (Pl. 14 (#ulink_4df158f0-7ade-5ba8-a3a1-ebd8d8618553)). Such sites may be also used at other times as fishing haul-outs, but during the moult the numbers are often very great amounting to several thousand in the larger groups such as Orkney and Shetland. The number of these sites appears to be quite small, one or two alternative sites for use in different weather conditions sufficing.
As the breeding season approaches there are pre-breeding ‘assemblages’, not on the actual ‘rookeries’ or breeding sites, but usually adjacent. The number of seals there diminishes as the breeding season gets under way, but are replaced often on different skerries or islands by ‘reservoirs’ of grey seals. More will be said about the characteristics of these haul-outs later.
It cannot be too strongly emphasised that all of these haul-outs, including even the breeding rookeries, are biased samples of the population of the group. Never are all the members of a group collected together even within the land area covered by a number of breeding rookeries and reservoirs. Consequently there is no easy way to estimate the total number of grey seals in a group even if it were possible to carry out a simultaneous census on all land sites. The question ‘How many grey seals are there?’ is often asked by the layman. It is one of the most difficult to be answered by the scientist.
Some description of the geography involved is now desirable. Fraser Darling drew attention to the very variable conditions in which the grey seal breeds and considered that the land rookeries of North Rona represented the ancestral habit. Davies, who was a geographer as well as a zoologist, believed that the various breeding behaviours were forced on to the grey seal by the geographical features. Certainly it must be admitted that since the last glacial period the grey seal will have spread northward and that the most southern localities now used would have been the first to be occupied in these islands, if in fact they were ever entirely deserted. On the whole the evidence supports Davies. Certainly to understand the differences in behaviour the geography must be taken into account (Fig. 10 (#ulink_013a188a-1fc0-56fd-b4f3-137c299fba14)).
SOUTH-WESTERN GROUP
This is the most widely dispersed group and although a considerable amount is known about the Welsh section, little information is available about either the Cornish or Irish sections apart from the barest outlines of the breeding localities. Throughout this group there is a tendency for the breeding sites to be small and contained in sea caves; they can hardly be dignified by the term rookeries as rarely more than a dozen cows pup in any one of the caves. Towards the middle of the breeding season pupping spreads to the beaches. These are either rocky or stony and backed by steep cliffs. Generally they are narrow so that at high water the sea may be lapping the base of the cliffs (Pl. 2 (#ulink_52aa1939-562e-575e-aaed-95525a12a9f8)). If this is not true at neap tides, it certainly is at springs. Several authors have referred to this group as the ‘cave breeding seals’. Throughout the area will be found ‘seal caves’, the name may be used locally or may be ‘official’ and appear on Ordnance Survey maps. In many of the caves there are beaches only towards the back of the caves so that investigation can only be made from the sea. This feature has added to the difficulties of investigation for few, if any, of the local boatmen are willing to risk their craft close in among the rocks and currents of such exposed coasts. The steep cliffs also present problems if only of time in making a descent and return. However, they do provide vantage points for observation and counts of white coated pups can be made from the cliff-tops above the narrow beaches. At the sea caves observation can only be made of the cows bobbing about in the water. Observations over open beaches indicate that for every six pups on the beach about five cows can be seen as a maximum at any one time with their heads above water. One or more are usually off on a swim. This ratio can be applied to the caves to arrive at an approximate count of pups. Neither method allows one to make an accurate assessment of the age of the pup or its sex. This can only be done by ground investigation at close quarters. It is not surprising, therefore, that there is less accurate numerical information about the grey seals of this area than of any of the other groups. Another feature which adds to the difficulties of obtaining even the basic information is the length of the coastline involved. The island sites off the Welsh and Irish coasts are comparatively easy. As long ago as 1910 when the Clare Island survey was undertaken off Galway a reasonably complete account was given by Barrett-Hamilton of the breeding sites there. Similarly Lord Revelstoke (1907) describes the cave sites on Lambay Island, while more recently Davies gave an excellent record of the breeding season on Ramsey Island off Pembrokeshire. But the small widely distributed coastal beaches of Cornwall, the Welsh mainland and south-west Ireland have only been cursorily surveyed within the last few years.* (#litres_trial_promo)
FIG. 10. Distribution of the grey seal in British waters. The areas where breeding rookeries are known to occur are shown by black circles. On the Irish coast the exact localities are not known but possible sites are indicated by black spots. The size of the circle is not indicative of the numbers of seals involved in breeding. (#ulink_d8b6a3ff-9ad6-514f-85c9-edb2813578fc)
The narrow entrances to the caves and the shallow beaches both militate against the building of a social structure on shore during the breeding season. In this group the organisation takes its form in the sea and consequently the behaviour of both bulls and cows is very different from that found in the more northern groups. Over many weeks of observation maintained during the hours of daylight, I have only seen bulls ashore on four occasions and on two of these they were at the water’s edge. Only in the most secluded coves can more than a few cows be seen at any one time, and then most will be seen to be suckling their pups and will have newly come ashore.
Little is known in the area occupied by this group of the use made of skerries and islands for non-breeding purposes. Haul-outs, presumably fishing ones, are usual on Lundy, the exact site being dictated by the weather. Skokholm and other Pembrokeshire islands and skerries have records of non-breeding haul-outs. Ramsey Island which provides one of the principal centres of breeding sites also has a moulting haul-out site in the late winter and spring. This beach, Aber Foel Fawr, which is inaccessible except by boat, but can be fully observed from a neighbouring cliff, is also used as a ‘reservoir’ during the breeding season as Davies has pointed out. Lockley has published a photograph of a beach with a similar moulting haul-out, but does not mention where it is. Since upwards of 200 seals, mostly of one sex, have been seen on each of these two beaches, it is possible that these are the only moulting sites for the Cornish-Pembroke-Wexford section of the group.
From what has been said about the difficulties of obtaining an accurate count of the pups and also from the absence of precise information about parts of the area occupied by this group, it will be readily appreciated that an estimate of the total number of grey seals in the group is very difficult to make. Estimates of the Welsh section made by Davies and, independently, by myself suggest that there were about 1,000 of all ages and both sexes connected with the breeding grounds of west Wales and the southern Irish Sea. This may now be exceeded. For Cornwall, the Scilly Isles and the west of Ireland the estimates cannot be much more than inspired guesses and would possibly add a total of 1,000+, making 2,000+ in all.
Despite the vagueness of this total it can be confidently said that the numbers are on the increase. Reference has already been made to the fishing haul-out on the West Hoyle Bank, off the Wirral peninsula, where Craggs and Ellison made counts of the grey seals. Quite apart from the seasonal variations, which were reported annually, their figures showed a steady increase year by year. Since the publication of their paper (1960) the number continued to increase but has levelled off in the last five years. This could, of course, mean that the Mersey Bight has become a more popular fishing ground, but independent observations, without however the numerical precision of Craggs and Ellison’s data, show an increase on Bardsey Island and on the west Wales breeding sites.
SOUTHERN HEBRIDEAN GROUP
This group is centred around the southern Inner Hebrides, more correctly known as The Ebudes. The group is a small one but of considerable geographical interest. The breeding rookeries are on the Treshnish Isles (west of Mull) and the islands of Ghaoidmeal and Eilean nan Ron, off Oronsay. Occasional pups are born on beaches on Colonsay. The skerries adjoining Ghaoidmeal called Eilean an Eoin, Sgeir Leathan and Cearn Riobha may also have a few pups born on them but also provide the sites of the ‘reservoirs’, while the pre-breeding assembly occurs on the skerries which lie between Oronsay and Eilean nan Ron. Nothing is yet known about the haul-outs during the non-breeding period.
The geographical peculiarity of these islands is that all are surrounded by erosion platforms which are exposed at low water. These platforms are very extensive and riven by channels so that, although the tides are very small (8–12 feet), within a very short time the area of exposed ‘land’ is vastly increased but cut across by deep water channels which thus connect the true beaches with the open sea. Only in the Treshnish Isles are the platforms narrow.
As will be seen later, this geography has a profound effect on the social organisation and behaviour of the bulls and cows (Pl. 2 (#ulink_52aa1939-562e-575e-aaed-95525a12a9f8)). The pups are born on the small beaches and, although none have insuperable barriers separating them from the grass-covered tops of the islands, they do not move inland until they have become moulters. The cows make frequent visits to the open sea along the channels and the bulls hold territory along these channels and on the platform to intercept the cows and mate with them. The group is not large numerically, but has certainly increased under the total protection afforded by the late Lord Strathcona and Mount Royal. It is probably limited by the number of available breeding sites. The total population based on these islands is probably about 2,000.
OUTER HEBRIDEAN GROUP
This may well have been more extensive in the past although one of the largest collection of rookeries, on North Rona, must be of comparatively recent date since there is no record of grey seals using that island during the time of human habitation up to the mid-19th century. Breeding on Canna and a few other islands has taken place until the last century but now all rookeries occur on islands in the open Atlantic. Chief of these is North Rona (Pl. 4 (#ulink_5d614bb0-5ffb-56d1-9b2a-49892929035f)), but Gaskeir has about 700–800 pups annually (Pl. 6 (#ulink_d48cae9d-2ce7-57df-bd3e-dcf2a1cb6a70)). Shillay (Pl. 3 (#ulink_8ed24986-595f-5585-b3ce-6843b040a06c)), Coppay, Haskeir, Causamell and St Kilda have small breeding sites and there is some evidence that while the numbers on Haskeir were larger in the past, Coppay and St Kilda are new sites and increasingly used.
All these islands are largely rock-bound, several with precipitous sides which in many places can be dignified by the term cliff. All however have some point (a geo) or points of access to the vegetation-covered top of the island. This is necessary because, situated where they are, they are subjected to continual Atlantic swell. Thus on none are there any beaches in the normal meaning of the word except on the east or leeward side if the geology permits it. Shillay and St Kilda have such easterly bays and, as Shillay is uninhabited, full use is made of it both as a site for pre-breeding assembly and for a rookery (Pl. 3 (#ulink_8ed24986-595f-5585-b3ce-6843b040a06c)). On all these islands, the main rookeries are developed well above sea-level where the swell cannot reach, and we find a completely terrestrial set-up as opposed to the almost marine one of Pembrokeshire.
Reservoir sites are known for North Rona on Loba Sgeir, the northern skerries of Fianuis such as Lisgear Mὸire and Lice Mhor and on Gealldruig Mhor to the south-east of the island. Reports of seals on Sula Sgeir and on Sule Skerry point to these being used as fishing haul-outs, but moulting haul-outs have not yet been seen because no one has been there at the right time of year. Elsewhere nothing is known of the reservoir and non-breeding haul-outs, although the Flannen Isles are likely to be so used to the west of Lewis.
This group is a large one comprising probably about 15,000+ seals of all ages. There is little evidence as to whether the numbers are increasing or not. The population based on North Rona appears to be fairly stable, although there seems to be room for the expansion of the existing rookeries. However, the recent establishment of breeding rookeries on St Kilda and Coppay may indicate a small increase.
ORKNEY AND SHETLAND GROUP
Until about ten years ago virtually nothing was known about the seal population in this area. Darling writing in 1947 said that ‘this seal occurs in Orkney and Shetland in relatively small numbers’. We know now that this is very far from the truth and that a population of 8,000 or more are based on these two groups of islands. They have, since 1960, been subjected to a great deal of research. All the main and most of the minor rookeries are known and several moulting sites and other types of haul-out places have been identified. The task has not been made easier because common seals are also present in the area so that records and reports are often not clear as to which species is referred to.
The types of rookeries are rather variable. Perhaps this is because, being an archipelago, the Atlantic swell, already somewhat broken by the north coast of Scotland particularly in Orkney, is not an overwhelming factor. In South Ronaldsay, for example, wide and deep beaches are used as rookeries much as the narrower ones of Pembrokeshire are. The bulls however are stationed on the beaches and not offshore. Elsewhere, such as on the Greenholms, the rookeries, beginning on the rocky foreshore (Pl. 5 (#ulink_b93a4b2f-e18d-530c-8dae-3fdb6c886df1)) stretch inland on the grassland in a very Hebridean manner. Perhaps here more than anywhere else one is driven to concede that the grey seal is extremely adaptable and much of an opportunist.
About half the annual pup production was accounted for in the Muckle and Little Greenholms (1,100–1,500).* (#litres_trial_promo) Several other islands in this central area of the archipelago, such as Wart Holm, Rusk Holm, Holm of Fara, Fara, Holms of Spurness, Little Linga and Gairsay provide another total of about 1,000. North Ronaldsay probably has only about 100 pups a year, but south of Mainland on South Ronaldsay, Swona and Little Skerry (in the Pentlands) another 250–300 are born. The research work and a local intensification of sealing has recently reduced the population a little and disturbance in one breeding season has been reflected by a change of site or a redistribution of numbers in the next.
Many other skerries, such as Auskerry, Taing Skerry, Wyre Skerry, Eynhallow, Boray Holm, Holm of Birsay, Damsay, the Barrel of Butter and others are used as haul-out sites during the non-breeding period, some of the breeding islands such as Rusk Holm, Holms of Spurness and Little Greenholm are also used in the early months of the year. It is, however, very noticeable that non-breeding haul-outs are never seen on the major breeding rookeries. This differentiation of site use is particularly well shown on Rusk Holm where the two southern skerries are used as reservoir haul-outs during the breeding season, the rookery is on the eastern pebble beach and north-eastern rocks, while the moulting haul-outs are either on the north-western rocks or on the south or south-eastern rocks according to wind and tide.
The numbers in Shetland are much fewer. This must be attributed as much to the rock-bound nature of the coast-line as to the scarcity of small uninhabited islands. In the southern part Lady Holm, Horse Holm and the geos or narrow beaches under Fitful Head provide small rookeries. Only in the north does the lie of the islands provide any lee so that small rookeries are found around Yell and Fetlar. The beaches under Ronas Hill are important breeding sites. In total there are probably only 200–300 pups each year.
In the non-breeding season the major haul-outs in the south and west are on Horse Holm, Lady Holm, around Fitful Head and on the Ve Skerries, west of Papa Stour. Small though these last are they sometimes hold up to 2,000 seals not all of which can be considered as Shetland grey seals in the sense that in the breeding season they will be found on the Shetland rookeries. Fair Isle, halfway between Orkney and Shetland, also has haul-outs and as a number of young seals marked in Orkney have been found in Shetland there is little doubt that the adults move freely between the two groups of islands. The picture here too is somewhat complicated by the presence of common seals and there is no doubt that much more is to be learnt about their distribution here, particularly in the northern islands.
In Orkney and Shetland there has persisted a tradition of sealing which has never been so strong in the Hebrides, possibly by reason of the Norse connections. The grey seal population here, therefore, appears to be fairly stable, fluctuating largely as a result of variations in sealing effort dependent, in turn, on the market price of seal-skins.
NORTH SEA GROUP
There is little difficulty in deciding that the centre of this group is the Farne Islands (Pl. 5 (#ulink_b93a4b2f-e18d-530c-8dae-3fdb6c886df1)). The North Sea is peculiarly free of islands and it may as well be stated straight away that only on the Island of May in the Firth of Forth and on Scroby Sands off Great Yarmouth are there any breeding rookeries other than on the Outer Farnes. Elsewhere there is evidence of their fishing inshore along the east as far south as the Wash, and the coast of Holland, and as far north as the Moray Firth. Fishing haul-outs have been recorded from the Abertay Sands to the Wash, but there is always a haul-out on the outermost islands of the Outer Farnes. At certain times of the year, notably the spring, they consist of very large numbers indeed. The population has been rising steadily in recent years. Annual counts of pup production have been made with considerable accuracy over the past fifteen years or so and an annual increase of about 7% has been calculated. Undoubtedly at the turn of the century the population was at a very low ebb. The islands at present involved as rookeries are the North and South Walmses, Staple and Brownsman, but in the more distant past others were used as rookery sites such as the Wide Opens and other islands of the Inner Farnes. At times of the year, other than the breeding, haul-outs are found on the Longstone and Longstone End, the Harcars and on other skerries of the Outer Farnes. All of these islands are low with at least one or two shelving rock beaches so that access is easy and sheltered within the archipelago. The interiors of the islands are used as well as the ‘beaches’ for rookery sites, but usually only after the more shoreward zones have become congested.
At the time of writing the number of pups produced annually had reached 2,011 (1971) making the Farne Islands group the third largest known in the British Isles with an estimated total population of almost 6,500–7,000.
Before going into the details of the life history of the grey seal, it is necessary to give a brief description of the yearly cycle of both adult males and females. Until recently it was really quite unknown. Even worse, statements appeared in the literature which cannot have been founded on observation because they were so wildly wrong. Until the early 1950’s this species had only been studied during the breeding season. It is not difficult to find the reasons for this. During the late autumn and winter months the weather makes visits to the islands a very chancy affair and few people feel inclined to camp on these isolated spots during this time of year. Yet these are the only ways in which information can be gathered. During the summer months the weather is generally good but on the other hand very few seals will be seen. For the spring however, there is no excuse and it is a very important season indeed. Dr K. M. Backhouse and myself started visiting the Ramsey Island sites in 1952 and soon every month except December and July had been covered. Later all months in Orkney had been covered by Mr E. A. Smith and in the Farnes by Dr J. C. Coulson and Mrs Hickling. The work of Craggs and Ellison throughout the year on West Hoyle Bank has already been referred to. (Oddly enough it was undertaken quite independently of the other work in Pembrokeshire, Orkney and Farnes on which there was considerable interchange of knowledge and information. An example of this interchange will be given below when dealing with the annual moult.)
