PA,Plms AND PnOCENDINGS OF THE HOYAL SOCnJTY OF TASMANIA, VOLUi\IE 102
DEVELOPMENT AND GROWTH OF THE SOUTHERN ELEPHANT SEAL (MIROUNGA LEONINA) (LINN. ) A review of the literature with some further observations
By
M. M. BRYDEN Antarctic Division. Department oj External Affairs, Melbourne, Victoria* Communicated by Dr W. Bryden
(With three plates and one text figure)
ABSTRACT that the Tasmanian Government in 1919 discon A study of development and growth of the tinued issuing licences for the l{illing of elephant Southern Elephant Seal was carried out at Mac seals at the island. The success of this move was quarie Island (54'S, 159°E) while the author was soon evident, for, when the" Discovery" called at a member of the Australian National Antarctic Macquarie Island in 1930, it was found that large Research Expeditions, 1964-1966. numbers of elephant seals were again breeding there (Mawson, 1932). HISTORY The study of the Southern Elephant Seal is difficult due to its ina.ccessibility, and more Until recently very little was known of the natural importantly to the 'fact that less than half of its history and physiology of the Southern Elephant life is spent ashore, where observation is possible. Seal, although its economic significance has been Virtually nothing is known about the life of the realised and the species has been exploited com animal at sea, and any form of controlled experi mercially since early in the nineteenth century. mentation is difficult due to its amphibious habits. The inaccessibility of the habitat of the animal has been largely responsible, although relatively Two major ecological studies have been made on little work has been done on the dosely related the species, one by Laws (l953a, 1956a, 1956b) on Northern Elephant Seal (Mirounga angustirostris the Falkland Islands Dependencies populations, the (Gil]), which is much more accessible. The mass other at Macquarie Island (Carrick and Ingham, slaughter of elephant seals, both northern and 1962a, band c; Carrick Csordas and Ingham, 1962; southern species, for their valuable oil in the Carrick, Csordas, Ingham and Keith, 1962). These nineteenth century and the early part of the major works have expanded and oorrelated earlier present century, is well known, and it is thought observations performed by a number of other that the total world population of Northern workers (Murphy, 1914; Ring, 1923; Matthews. Elephant Seals may have been as low as 20 during 1929; Sorenson, 1950; Aretas, 1951; Paulian, 1953, the nineteenth century (Bar'tholomew and Hubbs, 1957; Angot, 1954; Gibbney, W53, 1957) and pro 1960). Apathy, and a general ignorance of the vided the first quantitative data on various aspects biology of these species, almost caused their com of the biology of the Southern Elephant Seal. plete extinction. It was not until results of a These studies have rendered the Southern Elephant large scale study by Dr R. M. Laws at the Falkland Seal a well-known animal insofar as its distribu Islands Dependencies in the late 1940's became tion and annual cycle on land, its breeding ecology available that slaughter of elephant seals at South and physiology, and its numbers are concerned. Georgia was put on a sound scientific footing, in The detailed study of moulting and the integument order to prevent any repetition of the mass of this species made by Ling (l965a, b) has added slaughter and decimatton of the species which had to our knowledge of the animal. occurred during the previous century. Some work on the postnatal growth of Mirounga Soon after the discovery of Maoquarie Island in leonina has been reported, but it is limited to 1810, sealers began exploiting the elephant seal observations on growth of body length and weight and in 1826 and 1827 over 1,000 tons of oil were of seals during early postnatal life, and body length procured (Carrick, 1956). The island was quickly changes in later life (Laws, 195,3a; Carrick, Csordas depleted of its stock, breeding cows, young animals, and Ingham, 1962). These studies have revealed an surplus bachelor bulls and breeding bulls being interesting and unusual growth pattern in this taken. Intermittent killing continued in the same species. Sivertson (941) reported a study of reckless way. and it was after a great deal of growth and changes in gross body composition publicity concerning the danger of indiscriminate (blubber and carcass) during early postnatal Iife killing of seals, initiated by Sir Douglas Mawson in the harp seal (Phoca groenlandica) , and Scheffer following his journey to Antarctica in 1911-1913, and Wilke (1953) studied relative growth (changes
* Present address: Anatomy Department, N.Y. State Veterinary College, Cornell University. Ithaca New York 14850, U.S.A.
25 R.S.-4 26 DEVELOPMENT AND GROWTH OF SOUTHERN ELEPHANT SEAL
in body length, body weight, flipper measurements dead animal, or by more recent in vivo techniques and skull dimensions with growth) in the Northern which have been reviewed by Brozek (1963), Fur Seal, Callorhinus ursinus. However, no Panaretto (963), and Kirton (1963, 1964), into its detailed systematic study of development and component parts. growth in the Pinnipedia has been attempted. In some animals, including many aqua,tic speCies, certain linear measurements are more useful than REVIEW OF DEVELOPMENT AND GROWTH body weight to define growth operationally in terms of time relations. The body J.ength i.s a useful nifferential growth of the constituent parts of an means of estimating growth in terms of chrono animal's body has been recognised for centuries as logical time in seals (Scheffer and Wilke, 1953), being necessary in order to give rise to the animal's since body length gives a better indication of body inherent shape. It was known to Xephenon size than does body weight-weight depends on (400 B.C.) and reported by Markham (1617). that both size and" condition ". However any linear one could predict the ultimate size of a horse from measurement can measure growth in only one the measurement of its shin hone. "1"01' in all dimenSion, whereas it is obvious that growth is quadrupeds the shanks increase but little in size as three-dimensional, as defined above. time goes on, whereas the rest of the body grows The regular changes which take place in the to them, so as to be in the right proportion" body composition and conformation of animals (Marchf1nt, 1925). Systematic quantitative stUdies during development and growth from birth to on postnatal development in animals were com maturity were studied by Huxley 09:32), who menced by Lawes and Gilbert (1859, 1861). showed that the allometry equation, y = bx" (where Several authors have proposed definitions of y = size of organ, x = size of rest of body, k = growth and development, each of which has certain growth coefficient of organ) gave a useful quanti advantages and disadvantages. The definitions tative description of many of these changes. A furnished by Brody (1945) appear adequate for the valuable characteristic of this allometry equation is study of development and growth in the elephant that it can be transformed into: seal. He defined (1) development as the directive co-ordination of the diverse processes into an Log y = log b + k log x adult-into an "organised heterogeneity" (Need to give, generally a straight line. This transforma ham, 1933); (2) growth as biologic synthesis, tion accentuates the three-dimenSional and multi production of new biochemieal units. It; is the plicative nature of the growth process. aspect of development concerned with increase in The theory associated with Huxley's formula and living substance or protoplasm, and includes one or its logarithmic transformation implied that the all of three processes: (i) cell multiplication, Oi) form of an animal depends solely on its absolute cell enlargement, and (iii) incorporation of material size and not on the length of time taken to reach taken from the environment. that size. The concept of physiological age (Brody, The inclusion of non-protoplasmic substances 1937, 1945) also implies this basic relationship, such as fat, blood plasma, cartilage, &c., is an although m a less direct way. Huxley showed increase by incorporation of material from the that this relationship applied over a wide range environment. Such increase is not regarded as of speCIes and environmental conditions, but " true growth" by this definttion, yet operationally, pointed om. that it may be influenced by some from the standpoint of quantitative measurement external cond.itions such as extremes of nutrition of growth of the organism as a whole we must and temperature. Severe undernutritton associated consider these non-protoplasmic inclusions as parts with loss of body weight has been shown by of the growth process. It is difficult in practice Widdowson, Dickerson and McCance (1960), and to separate "true growth" and accretion, or Wilson and Osbourne (1960), to affect this relation increase in amount of non·,living structural matter, ship. Mendes and Waterlow (958) demonstrated since the parameter used most in the study of that even when animals were held at an almost growth is body weight. Eisley, McDonald and constant weight by undernutrition, some growth Fowler (964) have pointed out some of the took place in tissues such as bones and collagen, inaCCUracies of using total body weight increase which have good structural stability. McCance, as a measure of growth. They showed that ·fat is Ford and Brown (961) showed that dental develop a unique tissue with functions very different from ment, although delayed by undernutrition, was those of the other major ;tissues, and fat deposition more closely linked to the animal's chronological is not closely related to the growth O'f the fat-free age than that of other tissues. Nerve cells in the body mass. Nalbandov (963) produced evidence central nervous system which have already made which indicated t,hat reduced growth rate and most of their growth do not regress in size, but eventual growth stasis in the growing animal could the cells in the skeletal muscles do (Widdowson, be attributed to a steady reduction in the amount Dickerson and McCance, 1960). of available growth hormone per unit of fat-free body weight, but fat deposition was not related to Extremes of temperature have been shown to the growth of the fat-free body mass from this affect the relationship, as Huxley predicted. Barnett (1959) observed that mice reared at -- 3°C point of view. reduced thoir heat loss by developing shorter tails The use of body weight increase as a measure and longer hair. The relationship of tail length of growth can never be done away with completely, to body weight in rats was altered in a hot in spite of the shortcomings, since a vast amount environment (Harrison, Morton and Weiner, 1959). of work is involved to divide the animal body, However, for animals growing on a normal plane either by anatomical or biochemical means in the of nutrition, Huxley's equation is a most us-eful M. M. BRYDEN 27 empirical formula for the study of gl'owth growth which is known to occur soon after birth gradients (Medawar, 1945; Richards and Kavanagh, (Laws, 195381; Carrick, Csordas and Ingham, 1962) 1945; Needham, 1950). may be illuminating due to the exaggeration of all the physiological processes involved with growth at Huxley examined growth gradients in a wide this time. variety of species through application of the allo metric equation. His results and those of other In planning the pre,sent study, knowledge of workers were reviewed by Palsson (955), who the seasonal movements of the Southern Elephant described a centripetal pattern of postnatal gl'Owth. Seal at Macquarie Island furnished by Carrick, At bil'th the head, limbs and forequarters are Csordas, Ingham and Keith (962) was invaluable. relatively well-developed, the skeleton relatively Immediately after birth ,the elephant seal under better developed than the musculature. Develop goes a 23-day suckling period on land, during which mental changes in the skeleton were 'attributed to a time growth is extremely rapid (see Plate 1), primary wave of growth beginning at the head and fonowed by a five- to seven-week postweaning fast passing down to the nose and lower jaw, and while the animal becomes adapted for a lif·e at caudally towards the lumbar region; and to a sea. After the attainment of nutritional indepen Eecondary wave from the lower parts of the trunk dence, individuals spend most of their lives !lit sea and limbs ending in the lumbar region. The but from time to time they haul out on land wher~ lumbar region was descri:bed as the last part of they undergo a complete fast lasting up to two the body to attain maximum growth rate and was months, and suffer dramatic body weight losses in therefore the latest maturing part of the body. some instances. Following pubel'ty, a very marked Growth in length of the long bones takes place discrepancy in size develops between males and earlier than growth in thickness. A similar centri females (Plate 2). petal pattern of growth was descri:bed for the musculature, but some of the details of this have (b) Materials and Methods been challenged by Butterfield and Berg (966), A description of the anatomical methods used in who showed that although ,there was evidence of and the results obtained from, this work have been centripetal growth in the limbs of cattle, develop submitted for publication elsewhere (Bryden ment did not terminate in the lumbar region. 196781). In brief, seals of both sexes from 'birth U; Differential growth also occurs in the major rna turity were dissected anatomically into skin, tissues and organs which attain their maximum fat and connective tissue, and individual muscles, rate of growth in a definite order with age: 'bl"oadly, bones and organs. A total of 96 animals was nervous tissue, bone, muscle and fat. Allometric dissected. growth of individual organs appears to be primarily functional: brain, eyes, kidneys and heart, Seals could only be studied during their periods for example,' being early maturing organs. Those on land, and the numbers of animals of the organs of most physiological significance to the different age groups ashore at Macquarie Island animal are relatively well developed at bir,th, as during the year are illustrated in Figure 1. Growth distinct from those organs which have little was studi.ed in most detail during the early post functional importance until some time after birth. na tal period, from bil'th of the pup to the time of its departure to the s'oo, which meant that a very Most mammals on which detailed systematic large portion of ,the work was concentrated in ,the growth and development studies have been made breeding season, from mid-'September to mid have been domestic species. Growth and develop November, 1965; a;dult females were studied during ment have been studied in several wild mammalian their annual moult period in January and species, but most of these studies have only involved February; immature seals of both sexes were studied body weight changes where possible, and more often, from April to August when they .appeared at the external changes in form in terms of linear island for winter "rest .periods"; and breeding measurements, and have not considered the re},ative bulls ashore for the breeding season were studied gl"owth of the body tissues and organs. A problem during the latter half of August and the firsrt half met with in studying growth in many wild species of S'eptember, up to the beginning of the breeding is the absence of any reiiable method of ageing. season. Foetal growth was not considered in any detail EXPERIMENTAL in this study owing ·to the lack of material. (a) Introduction Pregnant females spend the entire gestation A systematic study of development and growth of following implantation of the blastocyst at sea Mirounga leonina was attempted, on the assump and only the occasional straggler returns to land tion that such a study might reveal interesting during winter. An a'ttempt was made to keep six comparisons with growth and developmental pregnant females in captivity during the winter patterns in other mammals. The mammals on months in a large enclosure in which a swimming which detailed studies of this nature have been tank was provided (Plate 3), but the many hours made exhibit external forms and ·ecological spent on attempts at feeding the animals were patterns markedly different from those of the seal. unfruitful. Suggestions for encoura.gement of It was felt that the unusual pattern of postnatal fee~ding this and closely related species (Bullier, growth in the elephant seal could possibly provide 1954; Pournelle, 1962 and personal communication) details of some facets of th~ growth. process not were observed, but with no success. Subsequent revealed by studies of growth m domestlc mammals, discussions with Dr C. R. Schroeder, Director of and clarify some of the hitherto misun~erstoo.d the San Diego Zoo, California, U.S.A., have aspects of mammalian growth.. In partlcular 1t revealed that for all practical purposes, it is was considered that the perlOd of accelerated impossible to train adult elephant seals to eat in 28 DEVELOPMEN1' AND GIlOWTH OF SOUTHERN ELEPHANT SEAL
MOULT MOUL, MOULT WINTER HAUL. - OUT BREEDING SEASON MOULT 10000 r IMMATURE:> BREEDING BREEDING IMMATURES IMMATURE!; I COWS BULLS
,/ 5000
,, ,, , f, I' 20=1 ~""\' : '-... , , ,, ' \ ,, I \ ,, : \ , I l000~ ,, ,I '. ~ .. _I
1957 100 1959
~_~...--L i_ DEC. JAN, FEB, MAR. FIG. l.---·Total number of elevhant seals in the lsthmus Study area, Macqual'ie Island. each week during 1957 and 1959 (from Carrick, Csordas and ingham, ]9(2).
captivity. All of the elephant seals (Mirounga shown to change little with increasing weight, and angustirostris) which have been kept successfully whose ultimate size was not an important factor at the San Diego Zoo have been introduced at an in the growth process. The form of the elephant immature stage, and the most successful have been seal must alter with increasing weight beca,use, recently-weaned pups. although most of its life is spent at sea, it is still subjected to the effects of gravity during its haul Measurements of six elephant seal foetuses out times. This study has revealed that the control collected at Macquarie Island in 1956 by Mr K. of ultimate size in the elephant seal is of great Keith were kindly made available by Dr R. Carrick, importance, particularly in the male (which is Mawson Institute for Antarctic Research, Adelaide, very much larger than the female), due to the and measurements of these plus the one foetus periodic influence of gravity during times when collected in 1965, were included in this study as animals are ashore (Bryden, 1967b). Thus it they were the only foetal measurements available differs from a totally aquatic mammalian group to the author. such as the whales, whose development does not need to allow for the effects of gravity. (c) Results and Discussion The change in form of the elephant seal during Development and growth of the elephant seal were growth is quite marked, and was illustrated by a considered along two main channels of ,thought, quotation of Charles Eyre, cited by Sorenson (950) : first the aspects of development (which, by the " Over a big hill which separated us from the next definition given earlier, includes growth) associated bay some of the party had seen, the previous day, with the ecology of the species, and secondly the a huge sea-elephant . . , The first thing which changes in form which are similar to those in caught our eye when we reached the bay was a other animals, small seal of the sort I had never seen before. Its eyes were about the size of a five-shilling piece and The ecology of the species, so very different from something awful to look at". The latter was later that of other mammalian species on which detailed identified as a young ,elephant seal. The early studies of development have been made, has development of the eyes of the elephant seal is resulted in alterations to many of the postnatal very obvious, as this observation illustrates, and in developmental processes within the body and has this and certain respects differential growth in this exaggerated some of the physiological mechanisms species is similar to other mammals studied. How associated with development. Brody (1945) stated ever in other respects the pattern of differential " aquatic animals are not forced to change much in growth has been shown to be different from form with increasing weight because their weight is domestic mammals. For example, postnatal counterpoised by the displaced water". This development of the subcutaneous fat in the elephant statement was based on earlier observations of seal occurs much earlier than does the fat in Hecht (see Jackson, 1928) in fish, whose form was terrestrial mammals; considerable relative post- M. M. BRYDEN 29 natal growth of the blood occurs in the seal, and hauling-out places around the Southern Ocean, so relative growth within the muscular and skeletal the chances of a marked animal returning to a systems in elephant seals, showing patterns part of the small area of coastline of Macquarie different from those in domestic mammals, occurs. Island are high. Thirdly, animals can be a.ged Details of these observUltions have been submitted with a considerable degree of accuracy as a re,~ult for publication elsewhere (Bryden, 1967a). of the findings of Laws (1953b) and Carrick and Ingham
CARRICK. R. and INGHAM, S. E. (1962a) .-Studies on tht! MCCANC~, H. A., FORD, E. H. H. and BHOW" , W. A. Il. (1861). SuuLhE'l'n Elephant Seal, Mirou,nf]a leonina (L.) .-L Severe undt."l'nutrition in growing and adult animah:;. Introduction to the sedeR. C.S.I.R.O. Wildl. [(e3. -,: Development of the skull, jaw8 and teeLh in pigs. Hrit. ~9-101. .1, Nl1tr. 15: 218-224. .----.----.. -- .------(1962b) .-Studies on the J\IARCHA"K'1', E. C. (1925) .---Xephcnon: scripta, minora, English Southern ElephanL Seal, Mirounga leonina (L.) ,-_.[1. tl'am;lation: Loeb Classical Libl'aryo (London: Heineman;. Canine tooth strueture in relation to function and age MAItKHA". G. (1617) .--Cavalariee; Book 1, Chap. 14. Cited by determination. C.S.l.R.O. Wildl. Res. 7: 102-118. l\lcCance, R. A. (1962)-Footl, growth and time. Lancet, -~------.. ------.--~---- (1962e).·-·Studies on the ii, G2]-6~G. Southern Elephant Seal Miroun.Qu leonina (L.) ,---V. MATTHEWS, L. If. (l82!J).-The natural history of the elephant Population dynamics and utilisation. C.S.I.R.O. W·ildl. seal, with notes on other seals found at South Georgia. Hes. 7: 198-206. • Disc01JCry' !lap. 1: 233-256 . . ------.---., CSOH))AS, S. E. and INGHAM, S. K (1962) .' MAWSON, D. (1932) .--The B.A.N.Z. An!aretic Heseal'ch Expedi Studies on the Southern Elephant Seal, Mirouugu leonina tion, 1929-19:11. Gcograph. J, 80, No.2. (L.).-IV. Breeding and development. C.S.I.R.O. W-ildl. lWEDAWAH, P. B. (1945) .-Size, shape and age. In Essa,ys on Res. 7: 161-197. Grou;th and F'orm. Ed. Ie GrUB Clark, W. E. and .Medawa]·, - .- --.---~----~------_., LKGHAM, S E. and KEITH, K. P. B. (Oxford: Clarendon Press). (1962) .-Studies on the Southern Elephant Seal, Mirou,Ylfja NLEXDES. C. B. and \VATERLOW, J. C. (1958).---The effed of a leonina (L.).---III. ThE' annual cycle in relation to age low protein diet. and of l'efeeciing, on the eomposition of and sex. C.S.I.R.O, Wildl. Res. 7, 119-160. liver and muscle in the weanling rat. Brit. J. Nulr. 12: ClJTHBEH'l'SON, A. and' POMRROY, .R. W. (1962) .--Quantitative 14-88.
anatomical studiep, of the composition of the pig at 50 j MURPHY. H. C. (1!H4) .----Notes OIl the sea elephant, Mirou1igu 68 and 92 kg carccu.:;s welght."-·-l. Experimental rnat.€yial Leonina (Linne). Bull. Ant. MU8. lVat ..Rist. 33: (j3~7H. and methods. ,1. Agri, Sci. 59, 207-214. NALBANDOV, Ao V. (lBG3) .-Symposium on growth: endocrine ELSLEY, P. W. H., McDONALD, L and FOWLER, V. R (1964) ." causef5 of growth and growth stasis. J. A nirn. Be'£. 22: The effed of plane of nutl'ition on the earcasses of pigs 558··560. and Iambs when variationR in fat content are excluded. NEEDHAM, A. l~. (1950) .---·The form transformation of the Anim. Prod. 6: 141-154. abdomen of the feluale pea. cl'ab, Pinnothercs pisum. GIBBNEY, L. I'i'. (1953) .-Delayed implantation in the elephant Proc. Roy. Soc, B, 137: 115-136. seal. N atnre, Lond. 172: 590. PAl,SSOX, H. (1055) .~-C()nformation and body eonlposition. In (1957). ---The seasonal l'eproduetive cycle of Progress in the Physiology of Far-m Ani,mals. (London: the fenlale elephant seal-Mirounga, leonina (h)-at Buttcrwol'ths) . Heard Island. A.N.A.R.k'. Rep, (B) 1: 1-26. PANAHETTO. B. Ao (1963) .--The estimation of body composition HUXLEY, J. S. (l932).-Problcms of Relative G,.owth. 1st ~d, in living animals. In Selected Papers of A'Ust. C.S.l.R.O. (London: 1vlethuen). Sump. on Carcasc Co'mposition and Appn.dsal of .Meat J-ACKSON. C. M. (1928) .--Some aspects of forTn and growth. Animals. (Melboul'lle: C.S.LRO.). Tn Hobins. W. J., Brody. S.} Jackson, C. IVL, Hogan, A. C. PAGLIAN, P. (058) .-Pinnipedes, cetaces, oisea"Ux des Iles and Green, C. W.---Growth. (New Haven: Yale Press). Kel'gueJen et Amsterdam. j)'lC1n [nst. Sci. Madagascar 8: KIHTON, A. H. (1963) .-·Some relations between the potassium 111-234. and sodium. eontents of animals and their composition. ------.------(1957) .--Note sur les phoques des Iles Amsterdam Sect. 3, PI'. 1-18. In Selected Papers of Au.st C.S.I.R.O. et Saint .. Paul. Ma.mmalia 21: 210-215. Symp. on, Carcase Composition amd Appraisal of Meat POliRNELLE, G. H. (1962) .---The Northern F;]ephant Seal, Animals, (Melbourne: C,S.LRO.). Mirm('nga nng1Astirostri.". Gill, in the· San Diego Zoo. --~------(19G4).----Assessment of body eOITlposition in the lntcr'fwt. Zoo Handbook 4: 32-33. lIve anirnal. Proc. N.Z. Soc. Anim. Prod. 24: 77-89. RICHARDS, O. W. and KAVANAGH, A. ,J, (1945).-The analysis LAWES, J. B. and GILBERT, J. II. (1859).-Experimental enquiry of growing form. In Es.'wys on Growth and Form. Ed. into the composition of some of the animals fed and leGl'os Clark, W. E. and Medawar, P. B, (Oxford: slaughtered as human food. Philos. Trnns. 2: 494-680. Clarendon Pyess). ------..---.------.. ---.-.- (1861) .--On the composition HING, T. P. A. (1923) .-The elephant seals of Kerguelen Land. of oxen. sheep and pigs and of their increase whilst Proc. Zool. Soc. Lond., 431-483. fattening . .T.R. Agric. Soc. 21: 433-488. SCH~FFER, V. B. and WILKE, F. (1953) .-Helative growth in the LAWS, R M. (1953a) .--The elephant seal (Mirou,nga, leonina., Northern Fur Seal. Growth 17: 129-145. Linn.). I. Growth and age. P.I.D.S. Scienti!. Rep, of the Southern Elephant Seal, Miro'U,nga lconina, (Linn.) 0 (1960). --Severe undernutrition in growing and <:Idult Ph. D. Thesis, Am,tralian National University. animals. 4. The impaet of severe undernutrition 011 the ------(1965b) .-·Hair growth and moulting in the chemical composition of the soft tissues of the pig. Brit. Southel'n Elephant Seal, Mirounga leonina {Linn.). In J, Nntr. 14: 457-471. Biology oj thc Skin nnd l-fair Growth. Ed. Lyne, A. G. WILSON, P. N. and OSBOlJRNE, D. F. (1960) .-Compensatory and ShOl't, B. F. (New York: American lmscviel' Pub!. growth after undenmll'ition in mmnmals and birds. Biol, Co.) . Rev. 35, 324-363. ~ :-c "" '"1l ". '"";:::! ~ :> ~ " ;; a " '"o § rc: ~ rl tI; '" ,.""~ c" en ~ ...; ;. en :.:,. z 1- < .=, N Pl,ATg l.--The relative !:Size (If co"\vs and pups change:::; rapidly during growth of the pup, as can be :seen herE". Snrne pups are very mueh smaller than their mothers, whereas others appear to be almost as lar,!:!'e as their mothen;, 'tl > w~ > Z " 'tlg; i;J "'"z "w o ..,OJ :,; ;0'" o ~ w o co &1 >-l -< ~ >-l w> z~ F < c:~ 0: ,..,'" o '" PLATE 2.-Relative size of a mature male and a mature female elephant seal at Macquarie Island. The male is approximately eight times as heavy as the female. PAPE:}tS )'\NP PROCEEDTNGS OF THE HOYAL SOC·IET'l Or' TAS;'vtANIA. VOLUM.r-: 102