42
South African participation in cruise MD-08 of MS Marion Dufresne, March-April 1976, S. Afr. J. Antarct. Res., 6, 28-29, 1976.
Fuller, N.R. A preliminary report on the littoral ecology of Marion and Prince Edward Islands, S. Afi·. J. Sci., 63, 248-252, 1967.
Gaillard, J.M. Mollusca. ln Marion and Prince Edward Islands, edited by E.M. van Zinderen Bakker Sr., J.M. Winterbottom
& R. A. Dyer, 291-299. Cape Town, A.A. Balkema, 1971.
Grindley, J.R. Tigriopus angu/a1us Lang. In Marion and Prince Edward Islands, edited by E.M. van Zinderen Bakker Sr., J.M.
Winterbottom & R.A. Dyer, 373-378. Cape Town, A.A. Balkema, 1971.
Grindley, J.R. Proposed marine biological research at Marion ls/and (Unpublished report), 1974.
Grindley, J.R. & Lane, S.B. Zooplankton around Marion and Prince Edward Islands. CNFRA, 44, 111-120, 1979.
Kensley, B. Five species of Jaeropsis from the Southern Indian Ocean (Crustacea, Isopoda: Asselota), Ann. S. Afr.
Mus., 67, 367-380, 1975. ·
Linklater, E. The Voyage of the Challenger. London, John Murray, 1972.
Marsh, J.H. No Pathway Here. Cape Town, Timmins, 1948.
Millard, N.A.H. Hydrozoa. In Marion and Prince Edward Islands, edited by E.M. van Zinderen Bakker Sr., J.M. Winterbottom
& R.A. Dyer, 396-408. Cape Town, A.A. Balke:na, 1971.
Mitchell-Innes, B.A. Primary production studies in the south-west Indian Ocean, 196.1-1963. Invest/. Rep. Oceanogr. Res. Inst., 14, 1-20, 1967.
Moseley, H.N. Notes by a Naturalist. London, Murray, 1892.
Net, E.A. The microplankfon of the south-west Indian Ocean.
S. Afr. T. Antarkt. Nav., Deel 8. 1978
Invest!. Rep. Div. Sea Fish. S. Afr., 62, 1-40, 1968.
Pawson, D.L. Holothuroidea. In Marion and Prince Edward Islands, edited by E.M. van Zinderen Bakker Sr., J.M. Winter- bottom & R.A. Dyer, 288-290. Cape Town, A.A. Balkema, 1971.
Rowe, F.W.E. & Clarke, A.M. Notes on some echinoderms from Marion Island. Bull. Brit. Mus. Nat. Hist. (D: Zoology) 28, 187-190, 1975.
Sawyer, R.T. A new species of 'tentacled' marine fish leech parasitic on Notothenia from the sub-Antarctic Marion and Crozet islands.
Hydrobio/ogia, 40, 345-354, 1972.
SCAR. Biological Investigations of Marine Antarctic Systems and Stocks (BIOMASS). Volume 1: Research Proposals. Washing- ton, D.C., SCAR/SCOR/1977.
Seguy, E. Diptera. In Marion and Prince Edward Islands, edited by E.M. van Zinderen Bakker Sr., J.M. Winterbottom & R.A.
Dyer, 344-348. Cape Town, A.A. Balkema, 1971.
Smith, W.A. & Sayers, R.L. Entomostraca. In Marion and Prince Edward Islands, edited by E.M. van Zinderen Bakker Sr., J.M.
Winterbottom & R.A. Dyer, 361-372. Cape Town, A.A. Balkema, 1971.
Thomson, C.W. The Voyage of the Challenger, London, Macmillan, 1877.
Van Pletzen, R. & Kok, D.J. Oribatei. In Marion and Prince Edward Islands, edited by E.M. van Zinderen Bakker Sr., J.M. Winter- bottom & R.A. Dyer, 314-326. Cape Town, A.A. Balkema, 1971.
Van Zinderen Bakker Sr., E.M. Introduction. In Marion and Prince Edward Islands, edited by E.M. van Zinderen Bakker Sr., J.M.
Winterbottom & R.A. Dyer, l-15. Cap::: Town, A.A. Balkema, 1971.
The distribution and Mirounga leonina
abundance (Linn.) on
of southern elephant seals the Prince Edward islands
P.R. Condy Mammal Research Institute, University of Pretoria, Pretoria 0002.
On Marion (46°54'S, 31°45'£) and Prince Edward (46°38'S, 37°57'£) Islands, southern elephant seals (M. leonina) occur- red mainly on the leeward east and north coasts between 1973 and 1917. During the spring breeding h2ul-Dut, alults and pups remained on beaches scattered along these coasts. During the sumrmr and autum -x m:1ult haul-out, adult an:i subadults arrived on the beachis and then m:1ved inland into noulting areas, while mnlting yearlings rennined on the beaches.
MJu/ting areas a/o occurred m:rinly 0.1 tht le!!ward coasts, th,mgh their distrib:ttio.1 di/f?red slightly to that of the breeding beaches. The distrib:1tiJ11 of e/?p 'iant se::tfs during the breeding and m:111/ting phases of the sumn?r h:iul-out season therefore differed bDth vertically and horizontally. Pup cou'lts totalled 1115 and 386 on Marion and Prince Ed.v:ird Islands respec- tively, indicating a 69,5 per cent decline in population size on Marion Island betwee., 1951 and 1976. Competition with man for fish in winter feeding grounds, pred:ition by killer whales
at the islands and competition for local food resources with fur .seals, are considered to have led to the population decline.
Introduction
The southern elephant se1ls (Mirounga leoninc1) which occur at.Marion Island (46°54'S, 37°45'E) were first investigated by Rand (1955, 1962) in the austral summer of 1951/J,2. La Grange (1962) also obtained some data on numbers and annual h,rnl-out cycle. No data on so~1thern elephant seals on Prin,;e Ed.vard Island (46°38'S, 37°57'E) have been publi,he:i, alt\ng'1 Grindley (in lit!.) re::orded the abundance and di~trib-.ition. of m )Ultirlg and mciulted elephant seals on the i,land in April 1973. In 1973 a study on the southern elep:nnt se1L, w is initi1t!i u:1:ier the au,pice, of the Mamm1l Re,e1rc'1 Imtitute. Tne d1t1 pre,e:-tted here wue obtained between Augu,t 1973 and De:e:n')er 1977, and formed part
y .
,,
!h
Jr
>Y .a td .Is :n ce ,n rn
111
!d
1rt
of a larger study on this species on Marion and Prince Edward islands.
Methods
Censuses of elephant se1ls were taken by direct counting, as all sites occupied by the:n were accessiole on foot. Population estim1te3 were b1sed on bull, pup and under-yearling counts, and cow num'J:::rs were e,tim1t-!d fro.11 the number of births that occurred. When counted, individuals older than under- yearlings (weaning to 12 months old) were assigned to broad age classes, which were based on the descriptions of body size and appearance give;-i by Laws (1953). The classes were: bulls (> 6 yens old), cow3 (> 5 ye1rs old), subadults, and ye3rlings (12-24 m:rnths old). Prior to we,rning, w!iic:1 occurred at 22-23 d1ys of ag::: (Condy, in press a), pups remained on the be1c:1e3 w:1ere they were born and were easily counted. After we1ning they wer.:: classed as under-yearlings, and for 6-10 d1y3 p:,,t-werning they re:n1ined on the be1ches or in the surf zo:1e (Condi, in pre» a), and were also easily counted.
Total pup and und!r-yeirlin5 co:.nt; were conducted on Mario:1 Island oa 14-18 Nove:n':,::r 1973 and 16-19 November 1976, with p1rti1l cJ:nt; 0:1 15-17 NJve:11'Jer 1974 and 14-17 Novem'Jer 1975. Til:::;e co:.mts occurred during the period Novem':,er 16 ±3 diy.,, when all births had occurred and the combin::d pJp and under-ye1rling totll w.15 at a nnximum (Condy, 19n). Cemuses c:,;i.duct::d every 3-5 days at six study be1ches on M.1rion Island (Ship's Cove, Rockhopper Bay, Boulder and Tryp:,t be1c'.1es, Mac1roni Bay and Arch- way Bay: Fig. 1), indicated that no under-yearlings had moved to other beac:1es, or left the island by the time the last births occurred. Therefore the com':lined pup and under- yearling totals for the wh::>le island were not adjusted for over- or undercaunting. On Prince Edward Island pups and under yearling, on the e1st coast (Fig. 2) were counted on 30 November 1977.
During the regular censuses at the six study beaches, new pup carcasses were counted and marked with white spray paint, or stockpiled in an undisturbed corner of the beach.
An estimate of pre-weaning mortality at each beach and in the study area as a whole, expressed as a percentage of the number of births, was calculated after all pups had been weaned.
Results
Distribution during the breeding season
During the breeding seasoa (August to Dxember) adult elephant seals congreg1ted in harems on the beaches. They gathered on beaches which had flat, even profiles, and sur- faces consisting of smooth rounded rocks and boulders
( < 0,5 m in diameter), or even smaller stones and pebbles.
Two sandy beaches occ:.ir on Marion Island (Ship's Cove and Goodhope Bay), and both were used as breeding beaches.
Most beaches with a suitably smooth surface occurred on the leeward east and north coasts of Marion and Prince Edward islands, with the result that most breeding occurred along these coasts (Figs. I and 2), while t11e windward north and south co1sts which had numerous beaches, but usually with extremely rugg~d and irregular surfaces, were occupied by fur se1ls, Arctocep.'1a/11s tropicalis and A. gaze/la (Condy 1978).
Approxi.111tely 60 per cent of beaches occupied by breed- ng elephant seals on Marion Island occurred on drainage
Plate la. -a typical drainage line beach (Try pot beach) on ,Marion Island. Plate I b. · a typical cliff-base beach (Macaroni Bay) on Marion d sland.
Plate 2a. -two harems on the lariac cliff-base beach at Sh~p's Cove, Marion Island. Plate 2b. -a major moulting area (Kaal- koppie) on Marion Island.
Ia
lb
2a
2b
44
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Kilometres
Fig. 1. Major and minor breeding beaches (closed stars); large star> 60 births annually, small star< 60 births annually and; moulting areas (open stars); large star> 60 individuals, small star< 60 individuals on Marion Island. Site reference numbers correspond to those given in Table 2.
Fig. 2. Major and minor breeding beaches (closed stars); large star > 60 births annually, small star< 60 births annually) and moulting areas (open stars); large star> 60 individuals, small star< 60 individuals on Prince Edward Island. Site ref- erence numbers correspond to those given in Table 3 (suspected breeding beaches and moulting areas are not arrowed) .
_,,
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S. Afr. J. Antarct. Res., Vol. 8., 1978
lines (Plate la), with most of the remainder occurring at the base of coastal cliffs (Plate lb). The drainage line beaches were generally small ( < 100 m long), while those at the base of coastal cliffs were much longer ( ± 1 km long). Drainage-line beaches were usually occupied by one harem only (Plate I a), and although most cliff-base beaches were also occupied by a single harem occurring on the smoothest and flattest part of the beach, some (Ship's Cove and Macaroni Bay) were occupied by two harems (Plate 2a).
Only the leeward eastern part of the Prince Edward Jsland coastline was inspected during the breeding season. The coast west of the central dividing Western Escarpment (Fig. 2) was inspected from the sea, from the air (Van Aarde, pers. comm.) and in part on foot (Grindley, in litt.), in the months of March to May after the breeding season. These observations indi- cated beaches where breeding might occur on that part of the coast (Fig. 2). The largest harem occurred on Boggel beach ,Fig. 2), the only known sandy beach on the island.
Distribution during the moulting season
Yearlings hauled-out to moult in November and December on Marion Island. Most were found on the same beaches occupied earlier in the season by breeding adults (Condy, 1979).
From December to March all older seals hauled-out on to the drainage line beaches (Condy, 1979) but then moved inland to moulting areas on the coastal plains. In these areas (Plate 2b) they congregated in tightly bunched groups of up to 20 individuals, in natural depressions or in de- pressions created by their erosive impact on the soft peaty ground. Thus, during the moulting season the distribution of elephant seals differed both vertically and horizontally from that occurring during the breeding season, and this shift in distribution of the seals was associated with a distinct change in their influence on the local environment.
Distribution during the winter season
From May to August some yearlings and occasional adults and subadults hauled-out on beaches round Marion Island.
Overwintering animals, regardless of age and sex, generally remained on the beaches and did not move inland.
Influence of the seals on the local environment
During the breeding season placentae and carcasses (mainly those of pups) provided food for giant petrels (Macronectes spp.), skuas (Stercorarius skua), gulls (Larus dominicanus), and sheathbills ( Chionis minor). Faeces and urine were washed into the sea, and may have contributed to local inshore food chains. During the moulting season a distinct change in their impact on the local environment occurred. Most metabolic wastes were deposited in the moulting areas, where the effect of manuring and trampling had a significant local influence on soil chemistry (Smith, 1976) and the vegetation and topo- graphy (Huntley, 1971 ). Killer whales ( Orcinus orca) were seen to prey on elepha11t seals during the summer months, and the presence of the seals appeared to be of importance in attracting these predators to the islands (Condy, Van Aarde
& Bester, 1978).
Harem sizes on Marion Island
All adult male elephant seals, hauled-out during the breed- ing season, were considered to be breeding bulls, and were classified as being either beachmasters, assistant beachmasters, challengers or bachelors according to the definitions given
45
Table 1
The size and occurrence of southern elephant seal harems, along part of the Marion Island coastline, during the period when cow numbers were at a maximum (October 17 ±5 days, 1974; Condy
1979).
Beach (number of harems Number of *Number of in brackets) cows in breeding bulls
the harems
b ab bs C
Ship's Cove (2) 65 1 2 0
7 0 0 0
Rockhopper Bay (1) 10 l 0 0 0
Boulder beach (1) 18 1 0 0 1
Trypot beach (I) 70 1 2 0
Macaroni Bay (2) 70 1 3 0
10 0 l l
Archway Bay (1) 152 2 5 0
Hansen Point (1) 13 0 0 I
Kildalkey Bay (2) 130 2 10 0
40 0 4 0
King Penguin Bay (2) 18 0 1 0
27 I 0 1 0
Sea Elephant Bay (I) 38 1 1 0
Blue Petrel Bay (I) 18 1 0 0 0
Sealer's Beach (2) 80 1 1 4 0
5 l 0 0 0
Total (17) 771 17 9 34 3
*b = beachmasters, ab= assistant beach masters, bs = bachelors, c=challengers
by Carrick, Csordas and Ingham (1962b). Harem sizes and the occurrence of these categories of bulls were determined (Table I) during the period October 17 ±5 days, 1974, when number of cows hauled-out was at a maximum (Condy, 1979).
The mean ( ±S.D.) harem structure (beachmasters: assistant beach masters :cows) from these data was l :0,53 :±:0, 72:
45,35:±:43,77 (11=17). Since the numbers of challengers and bachelors varied almost hourly because they were not strongly attached to harems, mean numbers for these two categories were not meaningful. In general, harems consist- ing of more than 50-60 cows included an assistant beach- master, and those containing more than 130 cows included two assistant beachmasters (Table 1).
Estimated size of the breeding population
Results of the censuses on Marion and Prince Edward islands are given in Tables 2 and 3. Bulls and cows were counted during the pup and under-yearling counts except on Prince Edward Island, but since the peak in numbers of cows and bulls occurred on I 7 October ± 5 days and 24 October
±3 days respectively (Condy, 1979), their numbers were declining when the pups were counted (Table 2).
On Marion Island a minimum of 115 bulls participated in breeding, and the mean number of live pups and under- yearlings counted was 1 049 (Table 2). Pre-weaning mortality at the six intensively studied beaches was 5,99 per cent (Table 4). Assuming this value to be representative of the entire population, then an estimated 1 115 births occurred.
Ignoring twinning, which was observed only twice, account- ing for 0, I 8 per cent of the total pup crop, the cow population also numbered at least I J 15. No culling was done on Marion Island and, therefore, no population-specific pregnancy rate data were obtained. However, Laws (1960) estimated an 82 per cent pregnancy rate for the population on South Georgia,
46 S. Afr. T. Antarkt. Nav .. Deel 8. 1978
at a time when that population was increasing as well as compared to the estimate of 1 l15 from the present study, being commercially exploited. Assuming that 82 per cent indicating a decline of 69,5 per cent between November 1951 represents a maximum pregnancy rate for the Marion Jsland and November 1976.
population, and that 1 J 15 cows (82 per cent) hauled-out to
give birth each year of the study, then some 244 ( 18 per cent)
D iscussion
additional cows did not haul-out to give birth each year,
Carrick, Csordas, Ingham & Keith (1962a) believed that on giving an estimated total of I 359 cows in the population.
Macquarie Jsland ease of access to a beach, especially for The size of the southern elephant seal breeding population pregnant cows hauling-out to give birth, determined the between 1973 and 1976 on Marion lsland is therefore esti- local distribution of the seals and the location of harems. On mated to be 1 474 adults ( 115 bulls, I 359 cows), with an Marion Island some apparently accessible beaches were not annual pup crop of I 115. The size of the breeding population
on Prince Edward Jsland is not known, and the east coast Table 3 pup crop of 386 (Table 3) is likely to be an underestimate of
Number of southern elephant seal pups and under-yearlings the total number, since the size of the pup crop on the west
coast, if any, is not known, and the count was conducted late counted (30 Nov. 1977) on the east coast of Prince Edward Island.
in November by which stage under-yearlings were already Beach Actual count leaving the beaches (Condy, 1979). Rand (1962) counted the *I McNish Bay 10 breeding population on Marion Island during the summer of 2 Penguin beach 87
1951/52. During the latter half of November 1951 (actual 3 Cave Bay 85
dates not known, Rand in litt.), he counted a maximum of 4 Boggel beach (sandy) 128 309 bulls, I 276 cows, and 3 662 pups, and estimated that the 5 Cave Bay to Albatross Valley 49 breeding population consisted of 300-400 bulls and 4 000 6 Albatross Valley beach 27
cows. The number of pups counted included carcasses (Rand, Total 386
in litt.), and therefore his estimate of pup numbers can be *Site references to Figure 2.
Table 2
Maximum number of live southern elephant seals counted during the breeding season on Marion Island (A=adult, P=pups and under-yearlings).
J973 1974 1975 1976 **Mean
Beach
Ai5 A ¥
pAo
AO .,. p A(SA ¥
p AoA ¥
pA o A ¥
p- - - - -
* J Transvaal Cove (Boulder
Beach) 3 16 II 2 18 15 2 II IO 2 12 13 2 14 12
2 Trypot Beach 6 72 72 4 62 67 I 67 60 5 52 59 4 63 65
3 Macaroni Bay (South Beach) 5 90 78 7 78 87 3 63 68 7 5 l 55 6 71 72
4 Archway Bay 3 120 93 9 155 147 5 J 16 J 12 J3 109 112 8 125 116
5 1-lansen Point 2 13 13 3 13 2 6 11 2 7 12
6 Bullard Beach 2 24 18 I 17 39 2 20 28
7 Bullard Beach south 3 20 21 3 13 20 3 16 20
8 Killerwhale Cove 2 8 14 2 J 1 13 2 9 13
9 Waterfall beach 1 3 6 3 6
JO Landfall beach l 10 30 3 J3 34 2 11 32
1 l Sealer's Cave 4 20 24 3 15 23 3 17 23
12 Kildalkey Bay 14 50 151 5 34 101 12 65 163 lO 50 138
J 3 Cape Hooker (Hooker Cove) 3 5 0 1 4 I 2 4
14 Crawford Bay JO 20 28 l3 9 20 13 37 43 12 22 30
J 5 Goodhope Bay 7 17 60 3 67 10 48 65 7 22 64
16 Kaalkoppie 14 21 47 12 7 52 JO 33 38 12 20 46
17 Mixed Pickle Cove l 0 1 1 0 1
18 Cape Davis (Sealer's Beach) 2 8 13 12 4· 7 JO I 9 9
19 Storm Petrel Bay 1 8 8 I 12 13 10 JO
20 Goney beach 9 70 63 6 5 58 6 45 60 7 40 60
21 Log beach 9 JO 0 6 0 6 4 5 7
22 King Penguin Bay 7 36 46 6 8 37 8 13 35 6 53 65 7 28 46
23 Sea Elephant Bay 2 29 4l 3 ll 58 4 30 39 2 18 35
24 Blue Petrel Bay I JO 8 3 18 24 4 JO 30 2 29 29 3 17 23
25 Sealer's beach 3 50 84 3 44 96 2 17 53 3 44 60 3 39 73
26 Sealer's beach south 3 20 25 3 18 34 2 20 13 3 19 24
27 Ship's Cove 7 119 104 6 72 76 5 55 59 6 48 52 6 74 73
'28 Rockhopper Bay (mouth of
Yan den Boogaard River) 7 14 15 7 6 JO 3 JO 5 3 10 7
- -- - - ~
Total 111 863 1028 85 530 843 41 412 615 J 19 787 10:B 115 741 .1049
~Sile references to figure 1. **Mean calculated to nearest whole number.
S. Afr. J. Antarct. Res., Vol. 8., 1978
occupied during the breeding season. These had uneven profiles with rough, irregular surfaces and the elephant seals appeared unable or unwilling to negotiate them. It appeared therefore that the surface nature of a beach was the critical factor influencing its occupation by elephant seals, and ulti- mately their local distribution on Marion lsland, and not accessiblity as was the case on Macquarie Island. The absence of breeding seals on some of the more rugged and less access- ible beaches, especially on the east and north coasts, may, however, be due to the reduced size of the population.
On islands with large expanses of suitable beach habitat, such as Macquarie Island (Carrick & Jngham, 1960), South Georgia (Laws, 1956) and Kerguelen (Angot, 1954; Van Aarde, pers. comm.), large concentrations of elephant seals occurred. On Marion Island the population was dispersed along the east and north coasts, occurring in relatively small numbers (Table 2) at each suitable beach or moulting site, with no major concentration in one particular area. Local density, during both breecing and moulting seasons, prob- ably remained considerably lower than at these other islands which support much larger breeding populations.
Carrick et al. ( 1962b) noted that on Macquarie Island harems of fewer than 50 cows contained a single breeding bull, and those larger than this cont2ined one or more assistant beach- masters. A similar situation occurred on Marion Island (Table I). Harems on Marion Island were smaller than those on Macquarie Island (Carrick et al. 1962b) and Kerguelen (mean harem structure I :2,5±4,03:102,3 I 135,4; n=375, Van Aarde, pers. comm.), owing to the much smaller popula- tion size and lower density. However, it seems that regardless of population density a breeding bull was capable of main- taining exclusive control of up to about 50-60 cows, but thereafter was unable to prevent the intrusion of at least one other bull, which became an assistant beachmaster. At most breeding sites only single harems occurred, and therefore it seems likely that intraspecific competition between bulls occurred at a relatively low intensity on both Marion and Prince Edward islands. Under the present conditions of reduced population size, this would seem to be beneficial to the two populations, particularly since trampling as a result of fighting between bulls was an important cause or pup mortality on Marion Island, as well as on Kerguelen (Van Aarde, pers. comm.).
Movement of seals inland during the moulting season appears to be a feature common to most breeding grounds.
The bowl-shaped depressions with darkened faecal-smeared surfaces, within which moulting seals lie, appear to be well suited for increasing the temperature of the depression micro-environment. Smith (1976) noted that the temperature of mud in a study wallow in January increased on one occasion to 24,7 °C, well above the mean monthly ambient temperature (6,7 °C) for January (Schulze, 1971). Ling (1968) noted that reduction in hair covering on marine mammals seemed to accompany increased adaptation to the aquatic environment, until the original role of hair in thermoregula- tion was lost. Since southern elephant seals rely largely on a : thick blubber layer for insulation (Ling, 1972), moulting itself
may not result in increased susceptibility to cold stress. How- ever, as the seals are hauled-out for 25-31 days (Condy, 1979), they may experience an increasing need for environmental assistance with thermoregulation, as their insulating blubber layers are depleted while the period of fasting progresses.
King (1964) suggested that the mud in wallows helped to
- a
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reduce irritation of the skin during the moult, while Murray
& Nicholls ( 1965) stated that the blood-sucking louse, Lepidoplrthirus macrorhini, did not reproduce on seals that moulted in muddy wallows, and consequently fewer lice occurred on these animals. lt would seem therefore that dur- ing the moult both physical and physiological factors lead to the selection of inland areas rather than beaches.
The decline in the elephant seal population on Marion Island is surprising, particularly since it is currently believed that the availablity of squid, one of the main components, along with fish, in the diet of southern elephant seals has improved following the decline in large whale stocks (Laws, 1977), and no seal culling or commercial exploitation has occurred there since about I 930 (Rand, 1962). Condy (in press b) has indicated that competition for food (mainly fish and squid) between elephant seals and fur seals (Arcto- cephalus tropicalis and A. gaze/la) inhabiting Marion lsland is unlikely to be of major significance at present, except in the case of newly independent under-yearling elephant seals, which may compete for food resources with the fur seals in the local oceanic zone. Ki.Iler whales prey on elephant seals at Marion Island, especially on the younger seals (Condy, et al. 1978), and this may also have contributed to their decline. However, the magnitude of the decline would suggest that other factors, particularly the availability of fish, are implicated. As far as is known, there is little commercial fishing near the Prince Edward islands, but since the elephant seals may utilize winter feeding grounds far from these islands, it is possible that considerable competition with man for fish may be occurring, although it is not known where.
Acknowledgements
I would like to thank the Department of Transport for the logistical and financial aid which made this study possible, and SASCAR for co-ordinating these aspects. A special word of thanks is due to my field assistants, G.D. Anderson, A.O.
Scott and A. Harris, and to Dr M.N. Bester, R.J. van Aarde and B. H. Erasmus for collecting additional data on Marion Island. I would also like to thank Professors J.D.
Skinner and J.A.J. NeLfor useful discussions and assistance throughout this study.
References
Angot, M. Observations sur les mammiferes de l'archipel de Kerguelen, avec une etude detaillee de !'elephant de mer Mlr- 01111ga leo11i11a (L.) Mammalia, 18, 1-111, 1954.
Carrick, R. & Ingham, S.E. Ecological studies of the southern elephant seal, Mirounga leoni11a (L.) at Macquarie Island and Heard Island. Mammalia, 24, 325-343, 1960.
Carrick, R., Csordas, S.E., Ingham, S.E., & Keith, K. Studies on the southern elephant seal, Mirou11ga leo11i11a (L.). Ill. The annual cycle in relation to age and sex. CS/RO Wildlife Research, 1,
ll 9-160, 1962a.
S. Afr. T. Antarkt. Nav., Deel 8. 1978
Carrick, R., Csordas, S.E. & Ingham, S.E. Studies on the southern elephant seal, Miro1111ga leonina (L,), IV. Breeding and develop- ment. CS/RO Wildlife Research, 1, 161-197, 1962b.
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