Tuatara: Volume 12, Issue 1, March 1964
Key to the Seals (Pinnipedia) of New Zealand
Key to the Seals (Pinnipedia) of New Zealand
The seals are carnivores highly adapted to an aquatic environment, mainly marine. They simulate the smaller cetaceans very closely in shape and in the storage of fat, blubber, under the skin, thereby insulating the body against low temperatures; very little fat is stored in the mesenteries or in the body cavity, as land mammals normally do. But, unlike cetaceans, seals have retained their external coating of hair and the osteological identity of all four limbs, down to, at least, the rudiments of claws; they have also retained the flexibility of the limbs and, to a varying degree, that of the spinal column. In addition seals have retained their differentiated teeth, but the molars (postcanines) have deviated from the true carnassial form; they are more adapted to the seizure of slippery food. The prey consists largely of cephalopods, crustaceans, fish and marine birds. (The Crabeater Seal feeds largely on ‘Krill’ (Euphausia) and the Leopard Seal has been reported to eat other seals and carrion).
With the stream-lining of the body for rapid progression through water, all likely ‘obstructing’ organs have been modified or dispensed with. The limbs have been transformed into flippers or paddles: the fore limbs, no longer required to carry the weight of the body (except when on land), as with terrestrial mammals, into propelling or balancing organs and when not in use, they are tucked out of the way, alongside the body when the animal is travelling through water at speed. The hind limbs, in keeping with terrestrial animals, have retained their locomotory function, but are turned backwards and brought parallel with vertebral column, the ‘feet’ serving as efficient propellers. Even the tail is reduced to almost vestigial proportions. Although some seals proceed clumsily on all fours when on land, others have been ‘condemned’ to be ‘belly-walkers’, progressing like gigantic caterpillars, with undulating abdominal movements, aided by the fore flippers, but in water they are equally, if not more efficient swimmers than their more favoured brethren. Speed in water, where food is obtainable and enemies are to be avoided, page 41 is more necessary than speed on land where enemies are normally few. Their movements in water are most graceful and they often indulge in ‘water-sports’.
The external ears or pinnae, so marked a feature on the head of most terrestrial mammals, would, if retained in seals, not only offer some resistance to the water, but would be wholly unsuited to under water hearing and against pressure, when sounding. Accordingly, some species have modified these appendages very considerably, till they are almost rudimentary, while others, the pelagic forms, have dispensed with the pinnae entirely. Although the pinnae have been reduced or discarded, the hearing of seals is fairly acute. (Perhaps, a parallel to this form of reduction of the pinnae is found in the camels, among land mammals, which are subject to high winds accompanied with blown sand). Science has seized on this character and divided the Pinnipedia into two groups: the Eared-seals, such as Arctocephalus and the Earless-seals, such as Hydrurga. Likewise the presence or absence of underfur (wool) has been used as a means of classification — fur-seals and hair-seals.
In addition to the external modifications observed above, numerous other external and internal changes have occurred in the course of the evolution of seals from terrestrial to aquatic animals. The accompanying plate (Pl.1) shows clearly the modifications which have taken place in the formation of the teeth and scapulae. The great differences in the teeth probably betray a variation in the diet of the various species. However, it is significant that in the two genera, Arctocephalus and Neophoca the spine of the scapula is more posterior and the acromion more ventrally situated (more in Arctocephalus than in Neophoca) than in the remaining four seals illustrated, in which the spine is more centrally placed and the acromion less developed and more distant from the glenoid cavity. The change in position appears to be associated with the mode of progression: a greater use of the fore limbs in Arctocephalus and Neophoca on land, and, perhaps, in water, than the ‘belly-walking’ genera. Regardless of the distance the seals have travelled along the road of their evolution, unlike the cetaceans, they still have to return to the land (or ice) to rest, moult and to give birth to their young.
Polygamy is rather the rule than the exception. The males are normally larger than the females, but with the Crabeater Seal, the Leopard Seal and Weddell's Seal, the females appear to be the larger of the two sexes (Scheffer, 1958: 8). With the advent of the breeding season the males normally select the breeding sites and on the arrival of the females establish large or small harems, according to species. The territory and the harem is zealously guarded against all intruders as long as the season lasts, after which, the breeding animals disperse to form mixed or ‘bachelor’ colonies, or to roam as lone animals.page 42
Breeding takes place during the late spring and summer of the Southern Hemisphere. Normally, a single pup is produced annually, but twins have been known to occur, occasionally. At birth the pup is approximately one-third the length of the parent. The pup is weaned after several weeks during which time it has grown rapidly and is enormously fat. In some species there is evidence of a pre-natal moult. Moulting of the adults usually takes place during the autumn and winter. During the moult solitary animals may be found resting among the rocks or on beaches. In some species the moult proceeds gradually, little change being noticed in the appearance of the animal, while in others the moult is pronounced, the coat being shed in patches — the Sea Elephant is a good example of the second form.
Apparently, most feeding is done at night which suggests that the eyes are accommodated to darkness or feeble light. The animals are able to survive long periods of fasting; this is particularly true of the bulls during the breeding season, for, they do not feed for several weeks, not till the season is over. The greatest enemies of seals (apart from Man) are Killer Whales (Orcinus orca), Sharks and other species of seals (Leopard Seal).
The commonest seal in New Zealand waters is Forster's Fur Seal (Arctocephalus forsteri (Lesson)). The Sea Lion (Neophoca hookeri Gray) is next in order of freqency but it is more southern in its distribution, frequenting the Sub-Antarctic Islands and southern and south western parts of the South Island. The Sea Elephant (Mirounga leonina (Linn.)), particularly young animals, frequently haul ashore during the moulting season — to wit, the celebrated, ‘Blossom’ which spent several weeks in Wellington Harbour, till it completed its moult, in spite of the efforts of the Marine Department and the S.P.C.A. to dissuade it from remaining in the area. ‘Blossom’ was a young bull. Perhaps, the next in order of frequency is the Leopard Seal (Hydrurga leptonyx (Blainville)) which makes its appearance as an occasional visitor. On rare occasions the Crabeater Seal (Lobodon carcinophaga (Hombron and Jacquinot)) has been recorded. Lastly, on very rare occasions, Weddell's Seal (Leptonychotes weddelli (Lesson)) has forsaken its Antarctic ice to appear in New Zealand waters.
Left: Forster's Fur Seal (Arctocephalus forsteri), adult male. (Photo by courtesy F. C. Kinsky. Copyright). Right: Southern Sea Elephant (Mirounga leonina), adult male. Note inflated nostrils and battle scars on body. (Photo by courtesy J. H. Sorensen. Copyright).
The investigations of several scientific observers have produced no evidence that the seals subsist entirely on fish, leave alone commercial fish. On the contrary, these researches prove that the seals are largely molluscan feeders, subsisting mainly on cephalopods (octopus and squid) which diet is supplemented by a modicum of small fish and crustacea. The evidence for this statement is based on the examination of the stomach and intestinal contents. Again, there are large numbers of seals which (during the breeding season, for example) do not feed at all for several weeks! Normally, Nature provides a seasonal respite from predators in the case of most animals, else all animal life would soon disappear!
The ‘depletion’ of marketable commercial fishes at the regular fishing grounds, falsely attributed to the presence of seals in the vicinity, appears to be largely due to one of two factors, or both: a) the seasonal movement of the fish themselves to and from spawning and feeding grounds; b) the wholesale capture of fish by most modern methods and equipment all the year round with little or no respite for breeding or recuperation of stocks. Nature is bountiful but not inexhaustable—She is not proof against the ingenuity of scientific devices! Lack of knowledge and exploitation to the extreme ring the death knell of commercialisation—the present position of the whaling industry to wit!
However, there is the possibility that seals may damage fishing nets, occasionally, when accidentally trapped, in their efforts to escape, but this aspect has little or no bearing on commercial fishing. The fur seal itself, a national asset, has been a victim of ruthless commercial exploitation in the past. Protection, in time, has given it a chance to survive and make a come back, and judicious conservation of stocks will, it is hoped, enable it to survive and remain a national asset.
Incidentally, it is worthy of note, by way of warning, that all seals are strictly protected by law and molesting or the killing of seals may result in a very heavy fine—up to £500.
The author's thanks are due to Mr. J. H. Sorenson of the Marine Department and to Mr. F. C. Kinsky of the Dominion Museum for the use of the photographs of the various animals.page 45
Classification of New Zealand Seals (Order Pinnipedia)
Family: Otariidae (Gill, 1866)
Subfamily: Otarinae (v. Boetticher, 1934)
Genus: Neophoca (Gray, 1844)
Neophoca hookeri (Gray). The New Zealand Sea Lion.
Distribution: New Zealand region, breeding between 51 and 53 degrees south: Enderby Island, Auckland Islands, straggling northwards to Campbell Island, Stewart Island and the southern shores of the South Island.
Subfamily: Arctocephalinae (v. Boetticher, 1934)
Genus: Arctocephalus (E. G. St.-Hilaire and F. Cuvier, 1826)
Arctocephalus forsteri (Lesson). Forster's Fur Seal.
Distribution: Widely spread in both New Zealand and south Australian waters and Subantarctic Islands as far south as 55 degrees south. Breeding in some of the Subantarctic Islands and since its spread and increase there is good reason to suspect it is breeding in some other suitable localities of its present range. At one time the Fur Seal was close on extinction due to the activities of sealers, but since its protection it has increased rapidly and is spreading to new localities.
Family: Phocidae (Brooks, 1828)
Subfamily: Monachinae (Trouessart, 1897)
Tribe: Lobodontini (Scheffer, 1958)
Genus: Lobodon (Gray, 1844)
Lobodon carcinophagus (Hombron and Jacquinot, 1842) Crabeater Seal.
Distribution: Circumpolar in the Southern Ocean. Occasionally seen as far north as Wanganui along the coast of the North Island, in New Zealand waters.
Genus: Hydrurga (Gistel, 1848)
Hydrurga leptonyx (Blainville, 1820). Leopard Seal or Sea Leopard.
Distribution: Very widely distributed in the Southern Hemisphere. Occasionally, it appears along the New Zealand coasts. It has been recorded as far north as Lord Howo Island.
Genus: Leptonychotes (Gill, 1872)
Leptonyx weddelli (Lesson, 1826). Weddell's Seal.
Distribution: Circumpolar, Antarctic Continent and adjacent islands. There have been four records of this species in New Zealand waters, one was recorded from Titahi Bay and another in Wellington Harbour.page 47
Plate 1: Teeth and Scapulae of Seals
Fig. 1-4: Arctocephalus forsteri; 1. Scapula; 2. Canine; 3. External; 4. lingual aspects of postcanine. C. Acromion process; S. Spine of Scapula. Fig. 5-8: Neophoca hookeri; 5. Scapula; 6. external, and 7. lingual aspects of postcanine; 8. Canine. Fig. 9-11: Mirounga leonina; 9. Scapula; 10. Postcanine; 11. Canine. Fig. 12-15: Hydrurga leptonyx; 12. Scapula; 13. Canine; 14. External, and 15. linqual aspects of postcanine. Fig. 16-19: Lobodon carcinophaga; 16. Scapula; 17. Canine; 18. External; and 19. lingual aspects of postcanine. Fig. 20-23: Leptonychotes weddelli; 20. Scapula; 21. Canine; 22. External, and 23. lingual aspects of postcanine. (All scapulae are reduced to the same scale as Fig. 9).
Subfamily: Cystophorinae (Gill, 1866)
Genus: Mirounga (Gray, 1827)
Mirounga leonina (Linn., 1758). The Southern Sea Elephant.
Distribution: Circumpolar and Subantarctic waters. Breeding on many of the Subantarctic Islands. A still-born pup was found at Castle Point, east coast of the North Island, on September 18, 1961 (Dom. Mus. 1455). Young animals frequently visit the New Zealand coasts during the moulting season, late summer and autumn. Mr. J. H. Sorenson (1950) made a special study of these interesting animals and his paper is of special interest to any one seeking information on the life of them at Campbell Island.
Key to the Species
|1||(4) External ears present: palms and soles devoid of hair beneath: progression on land on all four limbs.|
|2||(3) Underfur present, copious; snout acutely pointed; total length of adult male 2m.; length of skull (CBL) reaching 25.1cm.; female ca. 1.6m., skull 21cm.||A. forsteri|
|3||(2) Underfur absent (sparse in very young pups), hair only; snout obtuse; total length of adult male 2.7-2.9m., skull reaching 34cm.; female, 1.79m., skull 25.8cm.||N. hookeri|
|4||(1) External ears absent; palms devoid of hair, soles hairy beneath; progression on land abdominal, hind flippers trailed.|
|5||(8) Colour uniform throughout.|
|6||(7) Nostrils inflatable in males; colour brownish or greyish; total length of adult male 6-6.5m., skull 51.5-56.1cm.; female 3.3-3.5m., skull 33.3cm.||M. leonina|
|7||(6) Nostrils not inflatable, colour creamy white or creamy, slightly darker along the spine; total length of male 2.57m., skull 25.6-30.6cm.; female 2.62m., skull 28.6cm.||L. carcinophagus|
|8||(5) Colour not uniform, irregularly blotched or mottled.|
|9||(10) Head ophioid, gape long, postcanine teeth tricuspid; total length of male 3.2m., skull 41.6cm.; female 3.81m., skull 43.1cm.||H. leptonyx|
|10||(9) Head more rounded, gape shorter; postcanines lobed; total length of adult male 2.79m., skull 29cm.; female 2.93m., skull 28.7cm.||L. weddelli|
Clark, J. W., 1873. On the eared seals of the Auckland Islands. Proc. Zool. Soc. Lond. 1873: 750-760.
Hamilton, J. E., 1934. The Southern Sea-Lion, Otaria byronia (De Blainville) Discovery' Dept. 8: 269-319. pls. 1-13, tables 1-6.
Scheffer, V. B., 1958. Seals, Sea Lions and Walruses. Stanford Univ. Press, California. pp. 179, 32 pls. and 14 figures.
Sivertsen, E., 1954. A survey of the eared seals (Family Otariidae) with remarks on the Antarctic seals collected by M/K ‘Norvegia’ in 1928-1929. Det. Norske Videns. Akad. Oslo. No. 36, text p. 5-76, pls. 10, figs. 46.
Sorensen. J. H., 1950. Elephant Seals of Campbell Island. Cape Exped. Bull. 6: 5-31, figs. 1-14 (Photos, map and table).
Turbott, E. G., 1949. Observations on the occurrence of Weddel Seal in New Zealand. Rec. Auck. Inst. 3: 377-379, 1 pl.