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14. Moulting haul-out at Aber Foel Fawr, Ramsey Island (#litres_trial_promo)
Closer view of the moulting haul-out at Aber Foel Fawr (K. M. Backhouse) (#litres_trial_promo)
15. Two types of moulting grey seal pups, Ramsey Island (#litres_trial_promo)
16. Newly-landed grey seal bull, shell-sand beach, Shillay (#litres_trial_promo)
Grey seal cow giving birth, Farne Islands (W. N. Bonner) (#litres_trial_promo)
17. Newly-born grey seal pup, Ramsey Island (#litres_trial_promo)
Grey seal pup with erupting teeth, Ramsey Island (#litres_trial_promo)
18. Grey seal cow identifying her pup by smell, Ramsey Island (#litres_trial_promo)
Grey seal cow attacking pup not her own, Shillay (#litres_trial_promo)
19. Grey seal pup suckling, Farne Islands (#litres_trial_promo)
14-day-old grey seal pup, Ghaoidmeal, Inner Hebrides (#litres_trial_promo)
20. Grey seal pup in typical early moult, Scroby Sands, Norfolk (J. Woolston) (#litres_trial_promo)
Grey seal bull moulter, Ramsey Island (#litres_trial_promo)
21. Two grey seal bulls contesting territory, North Rona (#litres_trial_promo)
Grey seals in copulation, Farne Islands (J. C. Coulson) (#litres_trial_promo)
22. Branded grey seal cow, Farne Islands (J. C. Coulson) (#litres_trial_promo)
Grey seals hauled-out on West Hoyle Bank, Cheshire (J. C Gittins) (#litres_trial_promo)
23. Common seal cow and pup, the Wash (W. N. Bonner) (#litres_trial_promo)
Two common seals (heads), the Wash (W. N. Bonner) (#litres_trial_promo)
24. Common seals hauled-out on sandbank, the Wash (W. Vaughan) (#litres_trial_promo)
Common seal bull ‘salmon-leaping’, Mousa, Shetland (#litres_trial_promo)
FIGURES (#ulink_67d5bedc-f5dd-5ac2-98e9-ecef19448708)
1. External features of seal and sea-lion (#ulink_5eddff4e-b332-5f45-b048-e5a158a547b8)
2. Limb-bones of seal and fur-seal (#ulink_9d5b1dd9-9054-5a58-9321-c8490975ac70)
3. Skulls of seals (grey and common) and of sea-lion (#ulink_78499ad0-1f06-5aae-9620-ad39aa7013a2)
4. Side view of pinnipede body (#ulink_88773492-2ac3-54d4-b3c1-d534ba61ac44)
5. Bradycardia in seal, porpoise and manatee (#ulink_0608d78a-c940-5bb9-8027-aa681c9e2953)
6. Kidneys and posterior vena cava in seals (#ulink_51785113-9149-5b5f-a670-3e44cca514a6)
7. World distribution of the grey seal (#ulink_e4f4a5c1-b71e-53ea-b33b-a94603b00bde)
8. The origin of the three populations of grey seals (#ulink_109864a9-7451-5232-9663-9955bca7a3aa)
9. Distribution of grey seals in British waters – recorded sightings (#ulink_8113edc1-2885-5ecd-8a32-cf4c6197e586)
10. Distribution of grey seals in British waters – breeding areas (#ulink_013a188a-1fc0-56fd-b4f3-137c299fba14)
11. External differences between grey and common seals and between bull and cow grey seals (#ulink_18dd6e49-bea7-5a3a-b718-1c14a5def608)
12. Jaws and teeth in grey and common seals (#ulink_4910a6c1-6dd0-5ba3-a295-b28759bfb95d)
13. Growth and maturation of the os penis (#litres_trial_promo)
14. The os penis index (#litres_trial_promo)
15. Distribution by age of cow and bull grey seals (#litres_trial_promo)
16. The male genitalia of the grey seal (#litres_trial_promo)
17. Growth and maturation of the testis in the grey seal (#litres_trial_promo)
18. Variations during the year in adult testicular weights in the grey seal (#litres_trial_promo)
19. The female genitalia of the grey seal (adult) (#litres_trial_promo)
20. The female genitalia of the grey seal at birth (#litres_trial_promo)
21. Foetal growth rate in the grey seal (#litres_trial_promo)
22. Counts of grey seals on West Hoyle Bank and on the Farne Islands (#litres_trial_promo)
23. Counts of grey seals on West Hoyle Bank, 1951–56 and 1966–70 (#litres_trial_promo)
24. Early stages in territory formation on Shillay (#litres_trial_promo)
25. Daily pupping rates for Ramsey Island, North Rona, Staple Island and Brownsman (#litres_trial_promo)
26. Daily pupping rates in neighbouring rookeries (#litres_trial_promo)
27. Breeding sites on Ramsey Island (#litres_trial_promo)
28. Breeding sites on Eilean nan Ron and Ghaoidmeal (#litres_trial_promo)
29. Breeding sites on Shillay (#litres_trial_promo)
30. Breeding sites on North Rona (#litres_trial_promo)
31. The Outer Farne Islands (#litres_trial_promo)
32. Breeding sites on the Farne Islands (#litres_trial_promo)
33. Different types of social arrangements in different groups of grey seals (#litres_trial_promo)
34. The grey seal pup in the first four weeks (#litres_trial_promo)
35. Bull territories on Shillay (#litres_trial_promo)
36. Types of marker used on grey seal pups (#litres_trial_promo)
37. Recoveries of young marked grey seals (#litres_trial_promo)
38. Growth rates in grey seal pups (#litres_trial_promo)
39. World distribution of common seals (#litres_trial_promo)
40. Distribution of common seals in British waters – recorded sightings (#litres_trial_promo)
41. Distribution of common seals in British waters – breeding areas (#litres_trial_promo)
42. Rare species of pinnipede in British waters – ringed seal, harp seal and bearded seal (#litres_trial_promo)
43. World distribution of ringed seals (#litres_trial_promo)
44. World distribution of harp seals (#litres_trial_promo)
45. World distribution of bearded seals (#litres_trial_promo)
46. Rare species of pinnipede in British waters – hooded seal and walrus (#litres_trial_promo)
47. World distribution of hooded seals (#litres_trial_promo)
48. World distribution of the walrus (#litres_trial_promo)
49. Numbers of pups born on the Farne Islands, 1956–70 (#litres_trial_promo)
50. Maximum counts and numbers of pups born on the Farne Islands, 1956–68 (#litres_trial_promo)
51. The Farne Islands (#litres_trial_promo)
52. Average monthly counts on the Farne Islands, 1956–68 (#litres_trial_promo)
53. World distribution of Phocidae (#litres_trial_promo)
54. World distribution of Otariidae and Odobænidae (#litres_trial_promo)
EDITORS’ PREFACE (#ulink_43849034-2509-56f9-919c-ca56cbea774c)
SEALS are fascinating animals. Everyone knows what they look like, but most people, even some experienced naturalists, have only seen them alive in zoos, where the seals, and their relatives the sea lions, are such firm favourites with the crowds. It is not really difficult to see quite large numbers of both grey and common seals by visiting the correct coastal areas of Britain, but few casual visitors find themselves in the right place at the right time. The exception is the Farne Islands, where for many years great numbers of tourists have been able to see equally large numbers of grey seals, and to see the animals from boats without having to make the effort of walking long distances over sandy beaches and mud flats, or of scrambling energetically down steep and often treacherous cliffs.
Although seals are so well known, and are the subject of many fables and nursery tales, our knowledge of their life history and ecology was, until recently, very imperfect. We had little accurate knowledge of the size of their populations, and of whether they were increasing – as fishermen who believed they endangered their livelihood said – or whether they were in imminent danger of extinction – as some conservationists firmly insisted. Legislation on their protection, and efforts towards their control, were based on guesswork.
Professor Hewer would be the first to insist, as he does in several places in this book, that our knowledge is still imperfect and that much more research on these animals is still needed. But nevertheless our knowledge is now reasonably firmly based, and we are therefore glad to be able to publish this up to date and authoritative book at this time. We believe that, for the first time, it gives in one place the overall picture of these animals that many have been waiting for. It also enables the reader to understand the complex problems of seal conservation. Seals must be preserved, and this may sometimes include killing seals where (as in the Farne Islands) their numbers are too great for the habitat to support.
Professor Hewer modestly plays down his own contribution to our vastly increased knowledge of seals. He has himself, for over twenty years, been closely involved in all the major research in Britain. He has combined the careful laboratory investigations of the trained scientist with detailed studies of the animals, alive, in their natural habitats. As one fully employed as a university teacher (where his many students will testify to his conscientiousness) he has not always had the time or the opportunity to do, himself, all the experimental or observational work he would clearly have enjoyed, but all other workers in this field have gained so much from his freely given help and advice that his contribution to the whole subject has been unique. All other workers on British seals will readily acknowledge Professor Hewer as their spokesman.
Scientific knowledge of a subject is one thing, and this is the basis of this book, but its value is immensely enhanced by the fact that Professor Hewer really ‘knows’ seals. He has watched and lived alongside his subjects, and has come to know them as only one who is a skilled observer and a field naturalist can. These genuine observations on the living animals give this book a quality rarely found in works which also satisfy the most rigid canons of scientific accuracy.
AUTHOR’S PREFACE (#ulink_a6016f23-0697-572b-a77f-69cda465cb38)
THIS book has taken an unconscionable time being born. The usual excuses can be given but basically the subject has been a particularly active field of research over the past ten years, not only for myself but for the number of workers who have been drawn into it and whose contributions have been constantly filling in gaps in our knowledge. It has always been tempting to put off the day so that something interesting and useful might be included. The present moment is apt, not because there is a lull in research work, but because several events have combined to give research an added impetus and considerable advances can be anticipated in the near future. A stock-taking is therefore appropriate and this I have attempted to do.
Public opinion during this time has been aroused and the whole question of our seal populations has become over-heated largely in inverse ratio to the information available. While such debate is not conducive in itself to the elucidation of facts, it does create a political atmosphere in which funds become available for research. While my own work in the laboratory has been covered by the usual university finance, the collection of material and the field observations could only have been possible with the aid of official support, in this case through the Nature Conservancy. As the problems grew in number and scope, the appointment of special workers in seal biology became possible and I have not suffered the undue frustration of seeing interesting aspects neglected because they were beyond the capabilities of myself.
When I became involved in this work (1951) Mr J. L. Davies had already given some account of grey seal breeding on Ramsey Island and this had been followed up by Dr L. Harrison Matthews and others in 1950. Apart from Fraser Darling (now Sir Frank Darling) these were the only zoologists to interest themselves actively in research on British seals this century. Yet there were a number who had experience in Antarctica such as Dr Matthews himself and much is owed to their interest and encouragement over the last twenty years. It is very fitting that the head of the newly formed Seals Research Unit at Lowestoft, Nigel Bonner, served his apprenticeship in the antarctic.
For two things, and two things only, I take some credit; the first, a matter of priority, was that I decided that no further advance could be made in the understanding of the biology of the seals without having a completely reliable method of determining the age of a specimen. When in 1960 it was first possible to obtain specimens of breeding cows and bulls (in the otherwise ‘protected season’) the rapid formulation of a provisional life-table, which appeared as a breakthrough in understanding the life of the grey seal, was really due to the finding of a reliable method of age-determination some 5 years earlier.
The second, a matter of method, was that I believed that advances could best be made by keeping laboratory findings and field observations in close contact, each feeding back information or suggestion to the other for further research. For this reason I have spent much time in the field at all times of the year as well as using laboratory techniques to unravel the yearly sexual cycles.
This book is about seals and not about the people who study seals. I have therefore not introduced a lot of extraneous matter about the difficulties of field work other than as explanations as to why certain information is not available. Those of us, professional and amateur alike, who have observed seals in the ‘field’ have done so because we like the work no matter that occasionally conditions are somewhat inclement. Such do not last for long and modern types of transport and facilities really make things much easier than heretofore. When Dr Gorvett and I went to Shillay in 1954–55 no suitable portable radio equipment was available. In 1959 for the first North Rona expedition we had a receiver-transmitter capable of covering 100 miles. True it needed two people to carry the two parts and the massive batteries, while a 12 ft. aerial had to be erected (and dismantled each time in case it blew away). By 1962 the several parties working in Orkney each had two-way radio to each other (and the coastguard) in apparatus easily portable by one person. Parallel advances were made in sound apparatus for recording vocalisations. But perhaps the greatest benefit has been in the use of plastic containers and insulating material for the collection of material for later laboratory examination. By the mid-1960’s I was able to obtain specimens of tissues and blood in Shetland, keep them at the low temperature necessary and send them to Oxford, where they arrived in perfect condition, for electron-microscopy and biochemical analyses. The advent of the high-speed inflatable dinghy has also contributed much towards landing parties obtaining material just as the helicopter and small plane have aided observation and censusing. One marvels at the work of early investigators such as Prof. W. Turner of Edinburgh who contributed much to our knowledge of seal and whale anatomy by the dissection of bodies many days old cast up on the beaches of Scotland. Nowadays it is possible to live among the seals in comfort and safety thanks to the advances in camping equipment, desiccated and tinned foods and weatherproof clothing. Although as Dr Backhouse has said there comes a time when we exclaim, ‘What we suffer in the cause of science!’, it is soon over and success is an ample reward.
It remains for me to thank the very large number of people without whose co-operation both the research and this book would have been impossible. First come the field-workers: J. L. Davies who started the ‘seal movement’ after the second war; the members of the Northumberland, Durham and Newcastle-upon-Tyne Natural History Society ably inspired and led by Mrs Grace Hickling assisted by Dr J. Goulson of Durham University, A. W. Jones, I. M. Telfer and others; Prof. J. D. Craggs, N. F. Ellison and others who have recorded on the West Hoyle Bank for 15 years; U. M. and L. S. V. Venables whose work on common seals has been outstanding; Dr J. Morton Boyd who has maintained the grey seal work in the Nature Conservancy (Scotland) over the past 15 years, assisted by numerous other workers on the annual visits to North Rona. Among these must also be counted those who collected material: Dr J. D. Lockie who sent me the first from carcases in the Berwick-on-Tweed area, E. A. Smith who contributed so much from Orkney, Jack Landscail of Orkney and William Laurenson of Shetland whose marksmanship and skill in reclaiming bodies made collection as humane and as least wasteful as possible. My thanks go especially to those who have accompanied me on trips to uninhabited islands and have had to put up with my eccentricities: Dr Gorvett and the late J. W. Siddorn, both of Imperial College, Drs J. D. Boyd and J. D. Lockie and the late James MacGeogh, all of Nature Conservancy (Scotland) and most of all Dr K. M. Backhouse, who has been with me so often and to so many places and whose cheerfulness and resourcefulness have meant so much to me. I must also thank those who have encouraged me from time to time in the work: Dr L. Harrison Matthews F.R.S., Prof. E. C. Amoroso F.R.S., Prof. R. J. Harrison F.R.S., Dr R. M. Laws and other members of the Joint Committee.
Lastly I come to those who have read the manuscript and whose comments have been of great value to me: W. N. Bonner for the grey seal and W. Vaughan for the common seal. Nevertheless I must emphasise that all errors and omissions together with expressions of opinion are my sole responsibility. I do not mind sticking my neck out if it stimulates someone to find out the true facts.
CHAPTER 1 (#ulink_11c2820d-a590-54dc-aca0-95f0d07dbe5c)
THE PINNIPEDIA, THEIR MODE OF LIFE AND RELATIONS WITH OTHER MAMMALS (#ulink_11c2820d-a590-54dc-aca0-95f0d07dbe5c)
THERE are only two truly British species of seal, although a number of others may occasionally be seen in our water, usually in the north. Before these are considered in detail it is necessary to see how they fit into the group (Order) to which they belong, the Pinnipedia. These comprise the hair or true seals, (Phocidae), the fur-seals and sea-lions (Otariidae) and walruses (Odobaenidae). Collectively they may be found in all the oceans of the world although they are certainly most numerous, both in species and in individuals, in the cooler waters of the arctic and antarctic regions. A systematic list of all species of Pinnipedia with their common names and rough distributions will be found in Appendix A. However they are not the only group of marine mammals and a glimpse at the other forms which have reverted to an aquatic existence is an aid in recognising the special features which are the basic adaptations to life in the sea for warm-blooded air-breathing vertebrates such as the mammals.
Two other groups have forsaken their ancestral methods of living on land and taken to a wholly marine existence. These are the Cetacea, or whales, porpoises and dolphins, and the Sirenia, or sea-cows. All three groups are of great antiquity (in terms of mammals) and it is not altogether easy to be certain of their ancestral connections in any detail, since fossil forms are scarce and fragmentary. On the whole it may be stated that the Sirenia have connections with forms which are also related to the elephants (Proboscidea) while both Cetacea and Pinnipedia are related to carnivoran stock. It is not surprising therefore to find that the Sirenia are vegetarians, feeding on seaweed, the Cetacea and Pinnipedia carnivorous, feeding on fish, squids and crustacea and other marine animals. The Cetacea broke away at a very early date long before the present carnivora became a defined Order of mammals. The Pinnipedia on the other hand have more recent connections and are directly related to the Carnivora. Indeed until recently they were always included as a Sub-order, and some systematists still so regard them.
The members of these three orders have features in common which have been evolved independently as essential adaptations to marine life. The most conspicuous of these is the streamlining of the animal by the production of a thick layer of blubber under the skin which not only smoothes out angularities but also provides an insulating layer against the low temperature of the water. In addition the limbs are reduced in all, the long bones of the fore-limbs are shortened and in the Cetacea and Sirenia the hind-limbs are lost altogether, while in the Pinnipedia these hind-limbs are much modified. The body too is elongated and roughly spindle-shaped in its proportions. These modifications deal with two problems connected with water, namely its low temperature and its greater density. There remains a third which is in some ways more serious, namely, that these animals being mammals are firmly committed to air breathing, possessing lungs, so that access to the air is essential and a means of preventing the entry of water into the trachea and lungs equally so. All therefore have nostrils which are normally closed and are opened only by voluntary muscles when the head is above the surface of the water. The provision of oxygen to maintain activities when the animal is submerged is made in different ways in the different groups. For example Cetaceans dive with full lungs, pinnipedes with empty ones, but the details of respiration are complex and will be dealt with later. Propulsion through the dense medium of water has also led to another convergent feature, the fusing of the digits by webbing, either thin or thick, thus forming a flipper or fin out of the normal mammalian hand or foot. There is also a tendency for the hair to be reduced in length although this is not universal in the groups. In Cetacea and Sirenia the body is almost naked, but the vibrissae or moustachial hairs are retained either as normal tactile organs as in the Sirenia or much reduced in the Cetacea. In neither of these groups does the hair contribute to insulation. Nor does it do so in the hair-seals and other pinnipedes where the hair is short and easily wetted so that the water comes into direct contact with the skin. Only in the fur-seals is the hair dense so that on immersion a layer of air is trapped among the hairs of the undercoat and direct water to skin contact is prevented. Here the hair is accessory to the blubber as an insulating structure.
We are now beginning to deal with features in which there are considerable and obvious divergences between the groups and these can best be described by noting them in the pinnipedes and then briefly contrasting them with what appears in the other two orders. Unlike the Cetacea and Sirenia which are entirely aquatic throughout life, the Pinnipedia have not lost all contact with the land. Some spend more time in the water than others, but all come to land (or ice) for breeding and for basking between feeding bouts and therefore have retained an ability to move on land. This is achieved by two different methods, one found in the true seals and the other in the fur-seals, sea-lions and walruses (Fig. 1 (#ulink_5eddff4e-b332-5f45-b048-e5a158a547b8)). In these latter the hind-limbs are still capable of being directed forwards and acting as a foot, albeit on an extremely short leg which is buried in blubber down to the ankle. Thus with the associated flexure of the trunk in the lumbar region they can move rapidly over a land surface. The true seals, however, have hind-limbs which are directed backwards and can only trail on land. Movement is therefore much more laboured in a terrestrial habitat. A comparison between the limbs of a furseal or sea-lion and those of a true seal shows clearly the very considerable differences not only in structure and posture, but also in use.
The fore-limbs of a fur-seal are long and on land are capable of reflexion between the wrist and palmar surface. The forearm and wrist form a vertical prop as it were, while the hand, supported by the meta-carpal and digital bones, lies flat on the ground (Fig. 2a (#ulink_9d5b1dd9-9054-5a58-9321-c8490975ac70)). The web between the digits is thin, in fact the whole of the distal part is much thinner and longer than in the true seals. This is associated with the much greater use which the fur-seals make of their fore-limbs in swimming. The claws are quite rudimentary and in some almost missing altogether. In the true seals the fore-arm is buried in blubber, and only the wrist and palmar surface with short digits protrude as short flaps (Fig. 1 (#ulink_5eddff4e-b332-5f45-b048-e5a158a547b8)). The webbing cannot be distinguished as such for the digits are united by thick tissue so that the separate digital lines are not visible externally. The claws are strong and used for grooming the surface of the body. In the water these limbs are used principally for changing direction or for slow paddling, never for rapid movement, when they are held tightly pressed against the flanks. The digits still retain, as Backhouse has shown, an ability to flex with considerable power so that the animal can haul itself up over boulders and rocks and to some extent compensates for the loss of power of the hind-limbs. At any rate this is true for the northern true seals. In the antarctic species this ability if present is not used, so far as observations made by a number of observers appear to confirm (O’Gorman).
FIG. 1. External features of seal and sea-lion. Note the differences in the external ear, the longer fore-limb of the sea-lion and the way the hind-limbs of the sea-lion can turn forward compared with the trailing position in the seal. The sea-lion can raise the forepart of the body into an almost erect position.. The claws of the sea-lion are small and set back from the edge of the flippers. (#ulink_9cbbd9da-732a-5b29-8e17-d381420bb5f8) (See also Plate 1)
The hind-limbs of a fur-seal are also long but can be directed forwards for movement on land. They are also used on land during basking as fans. When fur-seals are hauled-out for breeding the bulls have to remain on their territories for a long time and they soon dry out. Their layer of blubber and the thick undercoat of fur, which keeps them warm in water, is now a disadvantage when the sun comes out. They then use the hind flippers as huge fans, turning the body on one side so that both flippers can fan the anterior part of the body and head which has less fur on it (Pl. 1 (#ulink_b7079451-76c4-519f-8ef5-576dc8ab0436)). The claws here are usually absent altogether or quite rudimentary on the first and fifth digit but well developed in the middle three which can thus be used for grooming. In the true seals the hind-limbs are permanently directed backwards and form powerful sculling organs (Fig. 2 (#ulink_9d5b1dd9-9054-5a58-9321-c8490975ac70)). The palmar surfaces of the feet are turned inwards to face each other. The digits are united by thin and extensive webbing and the digits themselves are strong, the outer ones (the first and fifth) being much longer and thicker than the others. By alternate sweeps from side to side in a sculling movement these flippers are able to drive the seal through the water at great speed which has been estimated at as much as 12 to 15 m.p.h. Claws are retained on all the digits but their function is obscure. On land these hind flippers trail behind and take no part in locomotion which is achieved by a ‘humping’ motion. The body is flexed and the pelvic region advanced to give a forward push to the anterior part of the body, the stomach and the chest taking the main load as the animal moves forward. The fore-limbs are not used in this motion unless obstacles have to be surmounted when they assist in dragging the body upward, helped by the thrust of the pelvis. Thus in the Pinnipedia there are two distinct means of progression both on land and in water.
