Marine Biology (1998) 131: 559±566 Ó Springer-Verlag 1998

N. T. W. Klages á M. N. Bester Fish prey of fur seals Arctocephalus spp. at subantarctic Marion Island

Received: 16 July 1997 / Accepted: 2 March 1998

Abstract The analysis of scats collected between 1989 Marion Island, while breeders of the smaller A. gazella and 1995 from the two fur seal species resident on population are found on the southern coast. Their adult subantarctic Marion Island, Arctocephalus gazella and population sizes were approximately 39 000 and 1000 A. tropicalis, showed that they fed predominantly on ®sh seals, respectively, in 1994/95 (Hofmeyr et al. 1997). of the family Myctophidae (lantern®shes). Scat compo- In 1989 a sampling programme of fur seal scats sition (prey species, abundance) was very similar for the (faeces) was initiated in order to address our lack of two species. The seven species of myctophids that knowledge of the diets of both species of fur seals resi- formed numerically 90 and 86% of the scat composition dent on Marion Island. Speci®c aims of this investiga- for A. gazella and A. tropicalis, respectively, all showed tion were to determine to what extent their ®sh diets seasonal ¯uctuations in their contribution to seal diets. di€er and whether temporal changes in the prey species Electrona carlsbergi, E. subaspera, Metelectrona ven- composition are evident. It was also of interest to what tralis and Gymnoscopelus fraseri increased in winter in degree fur seal ®sh diets overlap with those of king both species of fur seals, whereas Gymnoscopelus piabilis, penguins (Aptenodytes patagonicus) on Marion Island, Protomyctophum choriodon and P. tenisoni showed the as they were perceived as potential competitors for food. opposite trend. Seal diets overlapped substantially with those of the king penguins (Aptenodytes patagonicus) resident on Marion Island, but no evidence for com- Materials and methods petitive exclusion could be found between these two major warmblooded consumers of marine resources at Scats of Arctocephalus tropicalis were collected at the Cape Davis the Prince Edward Islands. breeding colony site from August 1989 to November 1994. Scat sampling from A. gazella was done at the Watertunnel Stream breeding colony site from November 1989 to April 1995. An attempt was made to clear the study sites from old scats prior to collection, Introduction thereafter only the freshest material was taken. Neither age group nor sex of the seals frequenting the beaches was determined at the Two species of otariids, the subantarctic fur seal Arc- time of sampling as the haulout pattern of both species of fur seals at Marion Island is well known (Condy 1978; Kerley 1983). A break- tocephalus tropicalis and the Antarctic fur seal A. gazella down of the numbers collected by month and by year for each breed on Marion Island (46°54¢S; 37°45¢E), southern species is given in Table 1. At collection in the ®eld, scats were kept Indian Ocean. Each species favours its own breeding sites separate, i.e. the material was not pooled. On return to base they on the island, although some hybridization occurs in were provisionally washed with water in a sieve with 0.5 mm mesh size to remove most of the non-diagnostic soft material and then mixed colonies (Kerley 1984). Breeding sites of A. tropi- stored dry until analysis. In the laboratory, the hard prey remains calis are mainly con®ned to the exposed west side of contained in the faeces (mostly otoliths, several squid beaks) were cleaned further using an ultrasound shaker, then dried and sorted. The otoliths were identi®ed by comparison with reference specimens held in the collections of the Port Elizabeth Museum, and with il- Communicated by O. Kinne, Oldendorf/Luhe lustrations in the pertinent literature (Nolf 1985; Williams and McEldowney 1990; Smale et al. 1995). Otolith diameters of pristine N.T.W. Klages (&) Port Elizabeth Museum, P.O. Box 13147, specimens were measured under a dissecting microscope ®tted with a graticule, while eroded otoliths were only identi®ed and counted. Humewood 6013, Republic of South Africa Prey lengths and masses were estimated from regressions published M.N. Bester in Adams and Klages (1987), Hecht (1987), Williams and McEl- Department of Zoology and Entomology, downey (1990), Cherel et al. (1997) and Olsson and North (1997). University of Pretoria, Pretoria 0002, Insucient data precluded estimating length and mass of some ®sh Republic of South Africa species of minor numerical importance. 560

Table 1 Arctocephalus gazella (A.g.), A. tropicalis (A.t.). Numbers of scats sampled from both fur seal species resident on Marion Island each month and year from 1989 to 1995

Month 1989 1990 1991 1992 1993 1994 1995 Totals

A.g.. A.t A.g. A.t. A.g. A.t. A.g. A.t. A.g. A.t. A.g. A.t. A.g. A.t. A.g. A.t.

Jan 6 17 9 5 5 5 9 4 29 31 Feb 5 8 10 3 6 11 5 5 26 27 Mar 30 11 6 3 5 5 15 56 19 Apr 7 10 5 5 6 5 5 5 28 20 May 2 3 1 5 4 15 5 12 23 Jun 3 3 4 5 2 10 3 12 18 Jul 3 1 6 6 8 3 10 17 Aug 7 2 3 1 4 5 3 6 19 Sep 8 3 1 5 6 11 Oct 5 3 3 1 2 3 11 Nov 1 4 3 5 2 9 2 5 21 Dec 16 20 8 3 3 5 4 31 28 Sums 17 44 63 70 33 24 27 45 37 53 23 9 24 0 224 245

The scat material was augmented with a small collection of prey 5 g as the frequency distributions of the prey masses remains ¯ushed from the stomachs of ®ve subadult males and one show (Fig. 2). The heavier prey items with masses of 20 adult female Arctocephalus tropicalis at Marion Island. The seals had been restrained during methodological trials of stomach lavage to 30 g were mostly G. piabilis. Overall, the median ®sh techniques in April 1990 (Ferreira and Bester 1998). lengths estimated from the scats were 75 and 83 mm SL for A. tropicalis and A. gazella, respectively. The overall median ®sh masses were 5.8 and 7.3 g, respec- Results tively, for the two predators. Thus, the ratio between predator and prey was approximately 0.05 in length and Otoliths of the mesopelagic ®sh family Myctophidae 0.0001 in weight, as the cows of both species of Arc- (lantern®sh) were by far the most numerous hard-prey tocephalus can weigh up to 50 kg and attain a total body components identi®ed in the scats of both species of fur length of 1.4 m (Je€erson et al. 1993). For males the seals, with up to six di€erent species making up an in- ratios would be even smaller. dividual scat. Fish from other families were rare, con- Scat collection was too irregular over the years (Ta- tributing <1% by numbers to the diet of Arctocephalus ble 1) to permit a full-scale investigation of inter-annual gazella or A. tropicalis (Table 2). Squid beaks appeared and seasonal changes in their composition, but di€er- in small numbers only. They were invariably of such a ences became evident when the data were divided into small size or so damaged that positive species identi®- summer and winter collection periods. These trends were cation was impossible. Remains of other prey classes, essentially identical for both species of fur seals. Winter e.g. crustaceans, were not found. Prey species lists and was de®ned as those 6 months of the year when the mean numerical compositions of the scats from both fur seals sea surface temperature at Marion Island drops below (Table 2) showed much similarity, although statistically 5 °C (1 May to 31 October; Schulze 1971). Summer there was a highly signi®cant di€erence (v2 1524, comprised the remaining half year. All seven species that df 32, p < 0:0001). A. gazella had a slightly moreˆ di- formed 90 and 86% of the scat composition by numbers verseˆ diet (28 versus 25 taxa), but the two predators still for Arctocephalus gazella and A. tropicalis, respectively, shared 21 out of 32 taxa (65.6%) identi®ed in the scats. showed seasonal ¯uctuations in their contribution to Using equations given in Pianka (1975), the percent- seal diets (Table 4). Electrona carlsbergi, E. subaspera, numerical diet data of both fur seals indicate a dietary Metelectrona ventralis and Gymnoscopelus fraseri in- overlap of 0.86 (where 1.0 indicates complete overlap creased in winter in both species of fur seals, whereas and 0.0 indicates none). G. piabilis, Protomyctophum choriodon and P. tenisoni The length and weight characteristics of ®sh con- showed the opposite trend. A sensitivity analysis showed sumed by Arctocephalus gazella and A. tropicalis were that these trends were also discernible, although not as also very similar (Table 3) although not identical pronounced, when winter was assumed to start a month (v2 1703, df 1352, p < 0:0001). The frequency dis- later (1 June instead of 1 May) or when the start of tributionˆ of theˆ sizes (Fig. 1) peaked at about 50 mm winter was moved a month forward (1 April instead of standard length (SL), and this peak was entirely due to 1 May). Protomyctophum tenisoni. A second elevation of both The stomachs of all six animals of Arctocephalus curves at 80 to 90 mm SL originated from a species mix tropicalis subjected to lavage were nearly empty. Re- chie¯y belonging to the genera Electrona and Gym- sults of the identi®cation of the few hard parts that noscopelus. Gymnoscopelus piabilis were responsible for were recovered from the stomachs are shown in the third mode at 140 mm SL. Most prey weighed about Table 5. 561

Table 2 Arctocephalus gazella, A. tropicalis. Frequency of occurrence (FO) and numerical abundance (NOS) of prey identi®ed in scats collected from both species of fur seals resident on Marion Island

Prey A. gazella (N = 224) A. tropicalis (N = 245)

FO NOS %FO %NOS FO NOS %FO %NOS

Bathylagidae Bathylagus sp. 2 2 0.89 0.03 12 15 4.90 0.21 Gonostomatidae Photichthys argenteus 1 2 0.41 0.03 Myctophidae Electrona antarctica 1 7 0.41 0.10 Electrona carlsbergi 30 156 13.39 2.31 50 724 20.41 10.24 Electrona sp. 35 113 15.63 1.67 50 460 20.41 6.51 Electrona subaspera 60 280 26.79 4.15 55 279 22.45 3.95 Gymnoscopelus bolini 13 31 5.80 0.46 24 74 9.80 1.05 Gymnoscopelus fraseri 42 406 18.75 6.01 69 792 28.16 11.21 Gymnoscopelus microlampas 2 2 0.89 0.03 1 2 0.41 0.03 Gymnoscopelus nicholsi 26 150 11.61 2.22 39 289 15.92 4.09 Gymnoscopelus piabilis 125 1309 55.80 19.39 112 668 45.71 9.45 Gymnoscopelus sp. 105 1418 46.88 21.01 156 1863 63.67 26.36 Kre€tichthys anderssoni 1 1 0.45 0.01 4 5 1.63 0.07 Lampichthys procerus 1 4 0.45 0.06 Metelectrona ventralis 23 256 10.27 3.79 47 425 19.18 6.01 Protomyctophum bolini 8 14 3.57 0.21 5 10 2.04 0.14 Protomyctophum choriodon 41 223 18.30 3.30 46 188 18.78 2.66 Protomyctophum sp. 18 65 8.04 0.96 26 104 10.61 1.47 Protomyctophum tenisoni 60 2172 26.79 32.18 71 1091 28.98 15.44 Myctophidae unident. 12 28 5.36 0.41 12 19 4.90 0.27 Paralepididae Magnisudis prionosa 3 5 1.34 0.07 2 2 0.82 0.03 Muraenolepididae Muraenolepis sp. 1 1 0.45 0.01 Congiopodidae Zanclorhynchus spinifer 1 1 0.45 0.01 Nototheniidae Dissostichus eleginoides 1 2 0.45 0.03 Gobionotothen marionensis 2 9 0.89 0.13 Notothenia squamifrons 3 31 1.34 0.46 Paranotothenia magellanica 1 1 0.45 0.01 1 1 0.41 0.01 Nototheniidae unident. 3 7 1.34 0.10 Channichtyidae Champsocephalus gunnari 1 1 0.41 0.01 Gempylidae Paradiplospinus gracilis 2 2 0.82 0.03 Unidenti®ed ®sh 21 40 9.38 0.59 16 28 6.53 0.40 Unidenti®ed squid 13 23 5.80 0.34 14 16 5.71 0.23 Total 6750 100.00 7067 100.00

restraint and the drugs needed to subdue the animal, Discussion often with questionable results (Ferreira and Bester 1998). However, scat analysis in fur seals has a number There are three main sources of material suitable for of inherent biases. Otoliths are subjected to a variable studies of seal diets: (a) complete stomachs from culled degree of abrasion while they pass through the gut, seals; (b) partial stomach contents obtained from live which leads to an underestimate of the ®sh sizes con- seals using stomach-¯ushing techniques; or (c) collec- sumed by the seals (Jobling and Breiby 1986) if the di- tions of scats and natural regurgitations (Croxall 1993). ameters of eroded, and not pristine, otoliths are The ®rst source of material is likely to provide the most measured during analysis. This problem can only be detailed, and the least biased, information. However, overcome if the analyst has a substantial degree of fa- this is often a very wasteful approach as only a small miliarity with the otoliths in question. Otoliths of ®sh proportion of randomly shot seals contain food (Condy known to occur around the Prince Edward Islands (Gon 1981; Bester and Laycock 1985). Of the two non-lethal and Klages 1988), especially those of myctophids, are methods (b and c), the collection of scats provides ample generally much smaller than squid beaks. The largest material with minimal e€ort, whereas stomach-¯ushing hard-part recovered in the present study was an otolith is labour-intensive and costly because of the physical from Dissostichus eleginoides with the longest axis 562

Table 3 Arctocephalus gazella, A. tropicalis. Summary of standard length and mass of ®sh consumed by both species of fur seals resident on Marion Island

Prey A. gazella A. tropicalis

Standard length (mm) Mass (g) Standard length (mm) Mass (g)

(N) Mean SD Range Mean SD Range (N) Mean SD Range Mean SD Range

Champsocephalus gunnari (1) 141 17 Dissostichus eleginoides (1) 454 1350 Electrona antarctica (7) 72 3.0 69±77 5 0.7 4.3±6.2 Electrona carlsbergi (56) 71 13.3 34±97 7 3.1 0.8±14.6 (114) 65 8.7 38±88 5 1.8 1.1±11.1 Electrona subaspera (98) 80 13.4 39±106 10 5.4 1.0±23.0 (70) 78 13.4 50±124 9 5.7 2.2±38.4 Gobionotothen marionensis (4) 116 25.9 97±153 15 13.6 6.8±35.5 Gymnoscopelus bolini (12) 117 14.1 97±142 20 7.5 10.6±34.3 (40) 106 27.1 65±145 17 11.4 3.0±37.0 Gymnoscopelus fraseri (189) 88 20.8 58±139 9 7.4 2.1±32.5 (275) 78 14.6 35±134 6 4.1 0.5±28.6 Gymnoscopelus microlampas (2) 90 9 (2) 86 3.4 84±89 9 0.3 8.5±9.0 Gymnoscopelus nicholsi (46) 84 22.2 57±144 8 7.1 1.9±35.6 (62) 85 28.3 48±157 10 10.2 1.1±46.7 Gymnoscopelus piabilis (447) 123 18.0 47±155 23 8.9 1.1±44.8 (283) 116 21.7 58±160 20 9.7 2.2±49.8 Kre€tichthys anderssoni (1) 56 2 (1) 44 1 Lampichthys procerus (4) 69 6.4 60±74 3 0.6 2.2±3.4 Magnisudis prionosa Metelectrona ventralis (78) 71 12.6 38±102 7 3.1 1.1±16.6 (188) 71 14.4 32±122 7 3.8 0.7±27.5 Muraenolepis sp. Notothenia squamifrons (12) 114 49.6 36±224 42 58.6 1.0±208.0 Paradiplospinus gracilis (2) 215 21.9 199±230 9 3.2 6.5±11.0 Paranotothenia magellanica (1) 140 60 (1) 179 126 Protomyctophum bolini (11) 57 19.4 28±97 3 2.8 0.5±10.0 (9) 40 5.4 29±50 1 0.3 0.3±1.7 Protomyctophum choriodon (82) 86 20.7 40±137 7 6.4 0.6±41.0 (73) 95 13.7 54±131 8 5.7 1.1±32.5 Protomyctophum tenisoni (322) 46 5.1 19±69 2 0.5 0.2±5.0 (225) 46 6.0 26±79 2 0.7 0.2±7.6 563

Table 5 Arctocephalus tropicalis. Hard prey remains ¯ushed from the stomachs of six individuals at Marion Island

Prey No. Frequency of Estimated of items occurrence mass (g)

Squid beaks Martialia hyadesi, 3 2 269.0, 407.0, Ommastrephidae 490.0 Teuthowenia pellucida, 1 1 11.8 Cranchiidae Brachioteuthis sp., 1 1 4.3 Brachioteuthidae Fish otoliths Electrona carlsbergi, 2 2 4.5, 4.1 Myctophidae

Fig. 1 Arctocephalus gazella, A. tropicalis. Frequency distributions of ®sh prey sizes of both species of fur seals resident on Marion Island seals, including otariids, accumulate squid beaks in their stomachs (Dellinger and Trillmich 1988; Gales and Cheale, 1992; present study, Table 5). The central tenet of scat analysis, that the solid prey remains pass into the faeces in the same proportions as they were consumed, may therefore not hold for squid beaks, especially if they are large beaks (>10 mm overall diameter). Conse- quently, scat analysis may be an unsuitable method to fully determine the contribution of cephalopods to the diet of both fur seals resident on Marion Island, and the pertinent values for frequency of occurrence and nu- merical abundance given in Table 2 should be interpre- ted with caution. Antarctic fur seals have repopulated Marion Island relatively recently in the wake of the expansion of the world population after the severe depression that fol- Fig. 2 Arctocephalus gazella, A. tropicalis. Frequency distributions of lowed the days of sealing. A substantial increase is evi- ®sh prey masses of both species of fur seals resident on Marion Island dent in comparison to when population monitoring started: the Arctocephalus gazella population numbered Table 4 Arctocephalus gazella (A.g.), A. tropicalis (A.t.). Numbers in excess of 335 individuals in 1988/89 (Wilkinson and of otoliths per scat in the summer half year (1 November to 30 Bester 1990) and had trebled by 1994/95 (Hofmeyr et al. April) and in the winter half year (1 May to 31 October) at Marion Island 1997). A. gazella show a summer (breeding) and an au- tumn (moulting) peak in numbers ashore, and are Prey Summer Winter largely absent from the island from May to September (Kerley 1983). Relatively few individuals (largely smaller A.g. A.t. A.g. A.t. adult and subadult males, juveniles and a few adult fe- Electrona carlsbergi 0.37 0.29 2.02 6.88 males) were the source of the scat material during the Electrona subaspera 0.82 0.75 3.04 1.71 winter months of our study. We do not know on what Gymnoscopelus fraseri 1.51 2.40 3.16 4.46 the pelagic rest of the seal population feeds in winter. Gymnoscopelus piabilis 6.35 3.38 4.38 1.77 Protomyctophum choriodon 1.21 0.84 0.27 0.67 Subantarctic fur seals also show peaks in their numbers Protomyctophum tenisoni 12.37 5.50 0.16 2.91 ashore in December (breeding) and in March/April Metelectrona ventralis 0.91 1.38 2.16 2.26 (moulting) (Kerley 1983), but due to the larger popula- tion size and the long period of dependance of the pups on their mothers, there are always substantial numbers measuring 8.7 mm (but most otoliths were half that of adult females hauled out from which to collect. The size). This leads us to believe that small objects of this age and sex distribution of the population therefore kind pass almost unimpeded through the pyloric shifts towards adult females and immatures of both sphincter and that therefore scat analysis is likely to sexes in winter. provide a relatively unbiased insight into the ®sh portion While there is spatial and some temporal segregation of the diet of fur seals. when they are ashore (Kerley 1983), the present study There is no evidence of selective oral ejection of hard- demonstrated a substantial overlap in the diet of both parts in either Arctocephalus tropicalis or A. gazella on members of the genus Arctocephalus at Marion Island. a routine basis (Green et al. 1989), but many species of Both prey on the same species in very similar propor- 564 tions and both follow the same temporal pattern of re- prehensive data on subantarctic fur seals to date. Their source use. Evidently the Antarctic fur seal now occupies study was based on scats and identi®ed the myctophids the same dietary niche, although the recolonization Electrona spp. and Gymnoscopelus spp. as the most im- process at Marion Island gained momentum much later portant components. than it did for its more numerous congener (Bester 1984; A fairly clear picture is now emerging from these diet Hofmeyr et al. 1997). studies. At localities where the shelf is narrow (Macqu- The diet of the Antarctic fur seal has been investi- arie, Marion) myctophids form the staple of seals, where gated at a number of major breeding localities. Full diet it is wide (Heard, Kerguelen) demersal and benthic ®sh samples and scats inspected at South Georgia deter- (Champsocephalus gunnari, nototheniids, skates) gain mined krill Euphausia superba and channichthyids as the importance in seal diets. Lastly, where Euphausia superba main prey (North et al. 1983; Doidge and Croxall 1985; is abundant at times (South Georgia, South Orkneys) fur Reid 1995; Reid and Arnould 1996). Krill, accompanied seals consume a large quantity of this prey along with its by the myctophids Electrona antarctica and Gym- ®sh predators (C. gunnari, Lepidonotothen larseni). noscopelus nicholsi, was also the main food at the South Green et al. (1990) noted an increasing proportion of Orkney Islands (Daneri and Coria 1992, 1993). At the Gymnoscopelus spp. in the diet of fur seals as the summer South Shetland Islands, myctophids and nototheniids progressed, with a concomitant decrease in the propor- represented together almost 90% of the ®sh eaten tion of Electrona spp. The same trends were evident in (Daneri 1996). Scat analyses completed at Macquarie the present study, and they have also been documented Island (Green et al. 1990), at Heard Island (Green et al. by Adams and Klages (1987) in king penguin diet. It 1989, 1991) and Ià les Kerguelen (Cherel et al. 1997) found seems likely that the seasonal patterns in the abundance a wide spectrum of myctophids together with the re¯ect peculiar features of the life histories of these channichthyid Champsocephalus gunnari. Much less de- myctophids. However, no progress can be made is this tail is known about the food of the subantarctic fur seal. regard until the biology of these myctophids is better Accumulated squid beaks collected at Gough Island understood. from culled Arctocephalus tropicalis comprised the The overwhelming dominance of open-ocean mid- ommastrephid cephalopod Todarodes sp. as well as water myctophids and the rarity of demersal or benthic representatives of Histioteuthidae, Onychoteuthidae, prey (e.g. nototheniids) in the scats shows that fur seals Cranchiidae and Octopoteuthidae (Bester and Laycock exert only a minor predatory impact on the nearshore 1985). The ®sh component in the stomachs was not ®sh resources present around the Prince Edward Islands identi®ed. The only information for Marion Island is by and that they feed o€shore. The seven main species Condy (1981), who reported from 56 inspected stomachs identi®ed in the diet of both species of fur seals in this that 21 were empty, 20 contained squid beaks, 9 con- study (Table 4) generally have a notal or subantarctic tained seaweeds, 7 contained ®sh remains and 22 con- distribution and they undertake daily vertical migration tained small stones. None of the prey items in Condy's in the water column (Hulley 1981; Bekker 1985; Efre- material were identi®ed in detail. The investigation of menko 1987; Oven et al. 1990; Konstantinova et al. the diets of three di€erent fur seals species at Macquarie 1994). Since their prey rises nearer to the surface at night Island by Green et al. (1990) contains the most com- time, fur seals are likely to gain an energetic advantage

Table 6 Aptenodytes patagonicus. Revised ®sh prey species list and diet composition (percent by number) of the king penguin at Marion Island (Adams and Klages 1987)

Prey Proportion (%) of diet Comment

Unidenti®ed Myctophidae 34.75 Kre€tichthys anderssoni/Protomyctophum tenisoni, 31.76 Treated as a species complex Myctophidae Electrona carlsbergi, Myctophidae 13.16 Arctozenus risso, Paralepididae 1.45 Previously identi®ed as Myctophid A Protomyctophum choriodon, Myctophidae 0.98 Previously identi®ed as P. normani Gymnoscopelus bolini, Myctophidae 0.23 Magnisudis prionosa, Paralepididae 0.17 Previously identi®ed as Paralepis coregonoides Protomyctophum bolini, Myctophidae 0.12 Protomyctophum sp., Myctophidae 0.12 Unidenti®ed ®sh 0.06 Notothenia squamifrons, Nototheniidae 0.02 Paranotothenia magellanica, Nototheniidae 0.02 Previously identi®ed as Notothenia magellanica Squid 17.06 Crustaceans 0.11 Total 100.00 565 by hunting at night rather than in conditions of bright Boyd IL, Arnould JPY, Barton T, Croxall JP (1994) Foraging sunlight. Such nocturnal diving behaviour of fur seals behaviour of Antarctic fur seals during periods of contrasting prey abundance. J Anim Ecol 63: 703±713 has been demonstrated (Boyd and Croxall 1992; Boyd Boyd IL, Croxall JP (1992) Diving behaviour of lactating Antarctic et al. 1994). fur seals. Can J Zool 70: 919±928 Fur seal ®sh diets show many striking similarities Cherel Y, Guinet C, Tremblay Y (1997) Fish prey of Antarctic with that of king penguins at Marion Island (popu- fur seals Arctocephalus gazella at ^Ile de Croy, Kerguelen. Polar Biol 17: 87±90 lation: 215 230 breeding pairs, Watkins 1987), sug- Condy PR (1978) Distribution, abundance, and annual cycle of fur gesting that these two warmblooded predators could seals (Arctocephalus spp.) on the Prince Edward Islands. S Afr J be major competitors for food. Myctophids made up Wildlife Res 8: 159±168 82.6% of the diet by numbers of the king penguin Condy PR (1981) Annual food consumption, and seasonal ¯uc- (Adams and Klages 1987), whereas they formed 98.2 tuations in biomass of seals at Marion Island. Mammalia 45: 21±30 and 99.1%, respectively, in Arctocephalus gazella and Croxall JP (1993) Diet. In: Laws RM (ed) Antarctic seals: research in A. tropicalis scats in this study (Table 2). A re- methods and techniques. Cambridge, Cambridge University examination by the ®rst author (N.K.) of the otoliths Press, pp 268±290 studied by Adams and Klages (1987) showed that Daneri GA (1996) Fish diet of the Antarctic fur seal, Arctocephalus gazella, in summer, at Stranger Point, King George Island, there was also a considerable overlap in the species of South Shetland Islands. Polar Biol 16: 353±355 Myctophidae consumed by the three predators Daneri GA, Coria NR (1992) The diet of Antarctic fur seals Arc- (Table 6). On the other hand, the comparison reveals tocephalus gazella during the summer±autumn period at that king penguins proportionally eat more Pro- Mossman Peninsula, Laurie Island and South Orkneys. Polar Biol 11: 565±566 tomyctophum spp. (which are small ®sh) and less Daneri GA, Coria NR (1993) Fish prey of Antarctic fur seals, Gymnoscopelus spp. (which are large ®sh) than fur Arctocephalus gazella, during the summer±autumn period at seals. Cephalopods (mostly Onychoteuthidae) consti- Laurie Island, South Orkney Islands. Polar Biol 13: 287±289 tuted 17.1% by numbers in the diet of king penguins, Dellinger T, Trillmich F (1988) Estimating diet composition from and they were present only in traces in fur seal scats. scat analysis in otariid seals (Otariidae): is it reliable? Can J Zool 66: 1865±1870 Moreover, king penguins possess superior diving ca- Doidge DS, Croxall JP (1985) Diet and energy budget of the pabilities compared to fur seals, which allow them to Antarctic fur seal, Arctocephalus gazella, at South Georgia. In: follow the vertical movements of their prey with Siefried WR, Condy PR, Laws RM (eds) Antarctic nutrient shallow dives at night and deep dives at daytime cycles and food webs. Springer, Berlin, pp 543±550 Efremenko VN (1987) Distribution of eggs and larvae of Myc- (Kooyman et al. 1992). It is suggested that these three tophidae in the southern Atlantic. J Ichthyol (USSR) 26: 141± factors together sum up to the ecological segregation 147 of king penguins and fur seals at sea. It is probably Ferreira SM, Bester MN (1998) Chemical immobilization, physical also a signi®cant observation in this context that king restraint and stomach lavaging of fur seals (Arctocephalus spp.) at Marion Island. Onderstepoort J vet Res (in press) penguin colonies did not decrease at Marion Island as Gales NJ, Cheale AJ (1992) Estimating diet composition of the seal numbers rose during this century (Watkins 1987; Australian sea-lion (Neophoca cinerea) from scat analysis: an N. Adams, personal communication). unreliable technique. Wildl Res 19: 447±456 Green K, Burton HR, Williams R (1989) The diet of Antarctic fur Acknowledgements Seal research at Marion Island is conducted as seals Arctocephalus gazella (Peters) during the breeding season part of the South African National Antarctic Programme with the at Heard Island. Antarctic Sci 1: 317±324 ®nancial and logistic support of the South African Department of Green K, Williams R, Burton HR (1991) The diet of Antarctic fur Environmental A€airs and Tourism. We wish to thank Y. Cherel seals during the late autumn and early winter around Heard for sharing with us his insight in myctophid otolith identi®cation, Island. Antarctic Sci 3: 359±361 and we wish to thank S. Ferreira, A. la Cock, H. Pansegrouw, Green K, Williams R, Handasyde KA, Burton HR, Shaughnessy, F. Roux, J. Fourie, J. de Lange, G. Hofmeyr, J. Klopper and PD (1990) Interspeci®c and intraspeci®c di€erences in the diet F. 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