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CHAPTER 2 THE GREY SEAL – INTRODUCTORY
ОглавлениеTHE 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). 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;* 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). 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.
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.
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.* 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 and 10).
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). 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.
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). 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).
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). 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.*
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). 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), but Gaskeir has about 700–800 pups annually (Pl. 6). Shillay (Pl. 3), 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). 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) 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).* 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). 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.)
The best time to start describing the annual cycle is during the summer months of June, July and August. This is a very active feeding period for both bulls and cows. The bulls have to put on sufficient blubber to sustain them during their period of starvation, while they are maintaining territory. The cows also have to put on blubber to provide the fat for the rich milk suckled by the pups, but in addition, must eat sufficient to permit the foetus within to grow. (During the summer the foetus may increase by more than a pound a week.) Towards the end of August there is a tendency for both bulls and cows to move towards their breeding areas. This has been shown by J. Morton Boyd by the ingenious analysis of observations made at a number of points along the coastline of north-west Scotland. In the south-western group this drift is probably a little earlier, but newly arrived cows have been seen by me in early September on Ramsey Island. It is difficult to be precise in an animal whose breeding period extends over at least 2 months. The most that can be done is to note when such a tendency is at its peak and therefore most conspicuous. Other individual seals will still be at sea feeding, others still may already have arrived at the breeding rookeries and have pupped.
Bulls and cows must now be studied separately because the purpose of their assembling in the rookeries is quite different and consequently their behaviour and timing is different. Put very briefly and perhaps in an over simplified way, bulls assemble for mating, cows for pupping and only secondarily for mating.
Bulls seem to predominate at the beginning of the breeding season on or near the rookeries. Here they appear to sort themselves into a dominance order, those having previously bred clearly taking precedence over the younger ones. Gradually they take up station on a territory which they defend against all comers (Pl. 7). Although they immediately approach an invading cow, their agonistic behaviour dies down as soon as they recognise her sex. Invasion by new and younger bulls (Pl. 6) continues for a considerable time and for at least a fortnight or so defence is the dominant activity of each bull holding territory.
Meanwhile cows begin to arrive at the rookeries (Pl. 7) and shortly give birth to their pups. Suckling commences within the hour and is repeated several times a day for at least a fortnight, sometimes for nearly three weeks. During this period the cows resent any approaches by the bull, who is repelled by hooting and rapid waving of the fore flippers (‘flippering’). Eventually, some time in the third week after giving birth, the cow accepts the bull in mating. Mating is often repeated several times at intervals. The cows desert their pups and leave the rookeries. Whether they go immediately to sea or remain in nearby waters is not yet certain, although I am inclined to believe the former is more likely.
The deserted pups moult their first or ‘puppy’ coat of white hair and appear in their ‘moulter’ coat which is similar to the adult pelage. In a healthy pup this process takes about a week; the fourth week of their life. When moulted the pups may, as in the south-west, immediately leave their natal beach, or as in the north and north-west remain on land and in fact move farther inland. Hunger will however eventually drive them to sea within a week or two.
The bulls remain on station for five to six weeks before becoming exhausted. They then move away from the rookeries to sea and recommence feeding to restore the blubber they have used during their enforced fast.
While this is the time-table of individual cows and bulls, it must be remembered that the time-table of the rookery is more extended. Thus a fortnight after the first pups have been born matings will begin, but this will probably be before the peak of the pupping. Consequently while the peaks of the various processes, pupping, mating, moulting, desertion by cows and leaving by bulls will be separated by periods corresponding to the normal time-table of individuals, this central period will be preceded by two or three weeks when arrivals of bulls and cows and some pupping are the only phenomena and will be followed by several weeks in which mating and desertions will predominate. The overall period will be about months.
Now follows a period about which not so much is known. The nearby haul-out sites are used but not to a great extent. Probably the answer is that both bulls and cows are feeding as much as possible to replace their lost blubber, to fit themselves for the rigours of the winter. One of the most remarkable facts of this period, which covers about months, is that among the cows found on the haul-outs, non-pregnant ones predominate. A high proportion of these non-pregnant cows are comparatively young and virgin or nulliparous. The differential behaviour of pregnant and non-pregnant cows is very remarkable, the more so because very little development of the embryo takes place for the first hundred days after conception (about months). (See Chapter 4.) Towards the end of this period most of the cows go into the annual moult.
I have not mentioned the actual dates through this breeding and post-breeding period because there are differences between the geographical groups and generalisation is therefore difficult. What makes precision even more difficult is that the full story is not known in detail for all of the groups. However, some attempt may be made to give an overall picture if we omit the Farne Islands group. In the south-western group the peak of pupping is probably in the first week in October, and by mid-November all the beaches are completely deserted. In the Hebrides and North Rona the dates are about 10–14 days later, although the much larger size of the rookeries results in more early and late puppings so that the season appears to be longer and a few adults may still be found in the breeding grounds in early December. In Orkney and Shetland a further 7–10 days should be allowed, so that mid-December would be a reasonable date to compare with mid-November in the south-west. January to March may be counted as the months of the cow moult, although few Orcadian cows will have begun in January and few, if any, Pembrokeshire ones will remain unmoulted in March.
For the Farne Islands group all these dates must be delayed by about a further month. There the first pups are in late October and the peak about 3–4 weeks later in November, pupping continuing actively well into December.
Our knowledge of the growth of the foetus is derived solely from northern material from Orkney. The mean date of the recommencement of the growth of the embryo is the middle of February. Thereafter the foetus grows apace in about 80% of the cows, the others are non-pregnant. So far as can be made out they continue to fish in the adjacent seas periodically coming ashore in fishing haul-outs for short periods at low tide. In the summer months the haul-outs must be both few and short because the numbers seen are very few indeed compared to those at other times of the year.
We have left the bulls at sea after the breeding season and it is not until mid-February that we have any evidence that large numbers come ashore. Their annual moult appears to be timed about two months after that of the cows. It was first observed in April in Pembrokeshire, but by then many were completely moulted and few remained unmoulted early in May. Dr Backhouse and myself, having found the comparatively large moulting haul-outs of bulls in Pembrokeshire, were able to direct attention to this in other groups, such as the Farne Islands, where the same phenomenon was then seen by other observers. These moulting haul-outs of the bulls are very remarkable and often number thousands at a time in the large northern groups. The bulls, like the cows, largely disappear in the summer months from all the inshore sites and we can only conclude that they too are feeding at sea to prepare themselves for the breeding season.
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 cwt. are usual during the yearly cycle.
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 puberty still have such a straight profile that their identification by this character alone is by no means sure.
The teeth of the grey seal are very distinctive and unlike those of any other phocid. The formula is normally and the dentition which erupts during puppyhood is the adult or definitive one. The milk dentition, in which the molars are not represented, is formed and resorbed in the foetal stages. The molars and premolars possess one large cusp and two others so small that often they appear to be missing (Fig. 12a) (cf. common seal with three well developed cusps). Wear of the teeth is no criterion of age. Normally the teeth of the upper jaw fit between and behind those of the lower jaw but occasionally the jaws are relatively misplaced (prognathous) and the teeth meet over part or all of their basal area. In an extreme case the teeth of both jaws then become worn down to flattened stumps. One such has been recorded at only 11 years of age. Very few instances of diseased teeth have been found, although deformed and diseased conditions of the jaws are a little more frequent. It must be assumed that in such vital structures any major deficiency rapidly leads to semi-starvation, loss of condition and death.
In the bulls the canines are much larger than in the cows. Not only are they heavier, but the root is more bulbous. It is quite possible to sex an isolated lower jaw of any animal over the age of 5 years by the shape of the canine tooth. In the bulls the upper incisors are also broader and this results in a greater width between the canines. Externally these features unite in producing a broader muzzle and a greater gap between the nostrils in the male. The breadth of the male muzzle is further accentuated by the massive pads on which the vibrissae are mounted (Fig. 12).
The position and arrangement of the nostrils are also diagnostic features distinguishing grey from common seals. In the latter the two nostrils almost meet at their most anterior and ventral point and diverge above this at a distinct angle. In the grey seal the nostrils are almost parallel and their anterior ventral points are separated by a large pad of skin (Fig. 11).
The grey seal is highly vocal, particularly the cow. All aggression by cows, if only jostling for position in a haul-out, is accompanied by high-pitched hooting which has a peculiar quavering quality, partly of pitch and partly of volume. This hooting often carried out by several cows at once produces a weird sound which has been called ‘singing’ but it is far from singing at its best! The bulls are capable of a snarling hiss which also has a guttural quality. However, often in mild aggression they do no more than open their mouths and emit an exhalation which is almost soundless. The high pitched voice of the pup is described later (See here).
There are many parts of Britain where the species of seal present can be almost certainly determined by the habitat. Thus, as Fraser Darling has said, the common seal on the west coast of Scotland is a sea-loch seal, the grey a seal of the outer islands and the strong Atlantic seas. And again on the Essex coast the mud and sand flats are typical haul-out sites for common seals, while the rock-bound coasts of west Wales provide typical grounds for the grey. Nevertheless it is not possible to generalise completely. Certainly the grey seal uses habitats which would rarely be used by common seals, isolated skerries and islands swept by Atlantic gales and surrounded by tidal rips which throw the sea into tumultuous heaps. The common seal will use estuarine waters and the mud and sand banks associated with them where the grey would never go. Yet between these extremes there are many habitats which both use. Many of the haul-outs in Orkney and Shetland are mixed, although of course the breeding grounds never are.
