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.