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MARINE SCIENCE, 16(2):494-500 (April 2000) 0 2000 by the Society for Marine Mammalogy

INFANTICIDE AND CANNIBALISM IN THE SEA , PHOCARCTOS HOOKERZ

The New Zealand , Phocarctos hookeri, (also known as Hooker's sea lion), is one of the rarest and in August 1997 was declared Threat- ened under the provisions of Section 2 of the New Zealand Marine Protection Act 1978. The species is highly localized in its distribution. Breed- ing occurs predominantly on New Zealand's subantarctic islands between 48"s and 53"S, with over 95% of pups born at four rookeries in the group. The two most important breeding locations are Dundas Island (50"35'S, 166"19'E) and Sandy Bay, Enderby Island (50"30'S, 166"17'E), which have, respectively, 70% and 20% of the total pup production. Based on pup production for the 1995/1996 breeding season, the population of P. hookeri was estimated to be between 11,100 and 14,200 (95% CI) (Gales and Fletcher 1999). The causes of mortality for this species are poorly understood, although it is recognized that both human activities and infectious agents may have a significant impact. Among the former, a documented cause of non-natural mortality has been the annual average bycatch of 80 sea by the trawl fishery for arrow squid () over the period 1988-1997 (De- partment of Conservation 1999a). Among the causes of natural mortality are infectious agents such as the bacterial pathogen that caused mass mortality during the 1997/1998 breeding season in the Auckland Islands (Department of Conservation 19996). In many species the most easily identified causes of mortality occur among pups while they are still present at natal sites, and P. hookeri is likely no different. Among otariids, causes of pup mortality fall into those that are passive (starvation, disease) and those resulting from direct physical trauma (trampling, biting, displaced sexual behavior, interspecific predation). Infan- ticide has been found to be significant in several pinniped species (Campagna et al. 1988, Higgins and Tedman 1990, Harcourt 1992, Le Boeuf and Cam- pagna 1994, Cassini 1998). The only causes of P. hookerz pup mortality that have been observed include trampling by adult males, starvation due to moth- er-pup separation, and starvation after pups became trapped in rabbit (Oryc- tolagus cannicalas) burrows (Marlow 1975).Cawthorn (1986)recovered 82 dead pups from a wallow at Sandy Bay, representing approximately 20% pup mor- tality at that site. However, with eradication of rabbits at this site and the subsequent collapse of the unused burrow systems this has become less of a problem. This paper reports on several incidents of infanticide and cannibalism in I? hookerz. While cannibalism has been recorded in two phocids, the gray seal, Halzchoerus grypus, (Bkdard et al. 1993) and the southern , Mir- 494 NOTES 495 ounga leonina,' this is the first reported instance in an otariid (Le Boeuf and Campagna 1994). Opportunistic behavioral observations were made of male P. hookeri at Dundas Island in January and February 1999. No formal obser- vation protocol to monitor this behavior was followed, as the primary aim of the research visits was to capture adult females to determine population age- structure from extracted teeth. Visits coincided with the later part of the breeding season when all sexual activity had ceased, and very few large adult males were ashore at this time. Dates and times of the incidents occurring during the visit to Dundas Island between 7 and 9 February were not recorded, but it is known that three pups were cannibalized during this period. Males were seen abducting pups and carrying them out to sea on two occasions, and on a further nine occasions males were seen eating pups at sea. These incidents are described below. In all instances the male seen feeding on the pup was surrounded by a raft of giant petrels (Macronectes giganteus and M. halli), Indeed, in several of the cases our attention was drawn to the cannibalistic activity by the presence of giant petrels. As no identification characteristics other than size, and age class (adulthbadult) where possible, were recorded, it is unclear from the observations how many different males were involved. However, given the sighting of adult and subadult males in these events, a minimum of two males must have been exhibiting these be- haviors.

Pup Abductions 21 January 1999-An adult male was observed carrying a pup from the rocky beach at the western end of Dundas Island. The male entered the surf and swam at least 50 m offshore before being lost from view. The mother of the pup followed the bull and the pup into the surf, but it is unclear whether or not she was successful in attempts to recover her pup, or whether the male proceeded to eat the pup (see next section). 1 February 1999-A cow and pup came ashore during low tide at the rocky platform on the northeastern side of Dundas Island followed by a subadult male. As the male left the water he grabbed the pup by the neck and turned back towards the sea. As he did so the cow bit him on the neck and he dropped the pup. The male in turn bit the cow, causing her to move away. The male then picked the pup up by the neck for a second time and carried it into the surf and out to sea. The cow did not follow but remained on the rock platform calling the pup for a period of 20 minutes. The male was observed to swim with the pup to approximately 100 m offshore. About two minutes afterwards a male, probably the same one, was seen in the same area violently thrashing a pup from side to side before consuming the flesh off the carcass. This thrashing and eating behavior was repeated on several occasions before observations were discontinued.

' Personal communication from Claudio Campagna, Centro Nacional Patagonico, 9 120 Puerto Madryn, Argentina, August 1999. 496 SCIENCE, VOL. 16, NO. 2, 2000

Cannibalism

21 Junuary 1999-Within 30 min of the abduction described above, a male was seen in the same area eating a pup. The behavior pattern followed that described above where the adult male shook the pup from side to side in a similar fashion to that described for P. hookeri feeding on ( tropicalis and A. gazella) pups at Macquarie Island (Robinson et a/. 1999) and then bit off flesh and consumed it. Around 15 min later a large male was seen eating a pup on the eastern side of the island. Due to the short time interval and the distance between the two locations, at opposite ends of Dundas Island, it was assumed that this was a different male from the one described above. 24 Junuary 1999-A pup was observed being eaten by a large male in the water. 26 January 1999-A large male was seen eating a pup on the eastern side of the island. 1 February 1999-A subadult male was seen eating a pup in the same area as that described in the pup abduction above but three hours later. This was unlikely to have been the same pup given the amount of flesh remaining on the carcass seen at 1100. 3 February 1999-A subadult male was seen eating a pup in the water. 7-9 February 1999-Three pups were observed being eaten by subadult males in the water around Dundas Island during this period. Observations of males abducting pups have been reported on several occa- sions among otariids, both inter- and intraspecifically (Marlow 1975, Vaz Fer- reira 1975, Campagna et al. 1988, Le Boeuf and Campagna 1994, Cassini 1998). Cassini (1998) reported southern sea lions, Oturiu fivescens, abducting , A. australis, pups in Uruguay and suggested that deaths resulting from the abductions were not the result of predatory behavior but rather the misplaced sexual behavior of subadult males using pups as female surrogates. A similar explanation was offered for intraspecific abduc- tions in a study of 0. ffavescens, at Punte Norte, Argentina (Campagna et al. l988), where 163 pups were abducted over four breeding seasons. In many cases the pups were guarded in the manner females would be by adult males, suggesting misplaced sexual behavior. Nineteen (11.7%) of the pups abducted were carried out to sea as seen in the current study, and nine (5.6%) of those abducted died due to physical injuries inflicted by the males. None of the animals taken to sea was observed being eaten. It was not possible in the current study to identify the breeding status of the males involved. However, given the timing of the abductions at the end of the breeding season, and the lack of large breeding males seen at Dundas Island, it would seem likely that those involved were sexually, but not socially, mature individuals. Despite the apparent status of males seen abducting pups at Dundas Island being similar to that observed in 0. jlavescens, the function of the abductions seems to differ, with l? hooker2 males possibly abducting pups as part of a predatory behavior. NOTES 497

Interspecific consumption of pinniped prey has been reported in at least three of the five extant sea lion species. Steller sea lions (Eumetopias jabatus) have been reported feeding on northern fur seals (Callorbinus ursinzls; Gentry and Johnson 198l), ringed seals (Pbocu bispida, Riedman 1990), and harbor seals (I? vitulina, Pitcher and Fay 1982). Southern sea lions consume A. aus- trulis pups in Peru (Harcourt 1991, 1992, 1993), and New Zealand sea lions are reported to feed on New Zealand fur seal (A. forsteri) pups (Mattlin 1978, Bradshaw et al. 1998) and both Antarctic (A. gazella) and subantarctic (A. tropicalis) fur seals (Robinson et al, 1999). Infanticide, the killing of conspecific young, is commonly reported among mammals, occurring in at least 100 species from 5 orders and 18 families (Hausfater and Hrdy 1984, Parmigiani and vom Saal 1994). Hrdy (1979) proposed five hypotheses to explain the occurrence of infanticide: (1) exploi- tation, young are killed and eaten as food; (2) resource competition, adults kill unrelated young to increase access to resources (e.g., food, breeding space) for themselves or their offspring; (3) sexual selection, males kill unrelated offspring to provide reproductive access to the female; (4) parental manipu- lation, a parent (commonly the mother) eliminates all or part of a litter to reduce litter size or eliminate defective young; and (5) social pathology, a maladaptive behavior in response to some extrinsic or intrinsic stimulus. The most applicable of Hrdy’s hypotheses in the case of the observed behaviors are (1) exploitation and (5) social pathology. Whether adaptive or maladaptive to the individuals performing the can- nibalism, such behavior has a negative effect on this threatened species. In view of the opportunistic nature of the observations it is not possible to provide accurate quantitative estimates of the impacts of cannibalism on the population at Dundas Island, but some crude preliminary estimates are possible. If we assume a minimum of two males are involved in this activity, and that this type of activity occurred for at least the period from the first (21 January 1999) to the last (9 February 1999) observation at a frequency of one incident per day per bull, then the total number of pups consumed would be 38, or approximately 2% of the pup production figure for Dundas Island. Limited data on cannibalism are available for other species. On Amet Island, Nova Scotia, Canada, a gray seal bull was seen to eat one, and assumed to eat another two, recently weaned pups (Bidard et al. 1993), while a bull was seen killing and eating an undetermined number of weaned pups at Peninsula Valdes, Argentina.’ While comparative data on impacts of cannibalism are lacking, figures are available for interspecific pre- dation. It is worthwhile noting that a single male I? bookeri may have been responsible for the mortality up to 43% of the 1996-1997 cohort of fur seal (A. gazella and A. tropicalis) pups at Macquarie Island (Robinson et al. 1999) and that seals (Hydrurga leptonyx) are thought to be limiting popula- tion growth of A. gazella populations in the South Shetland Islands (Boveng et al. 1998). Both these studies highlight the vulnerability of small populations to these kinds of predation pressures. While not dismissing the “social pathology” explanation for the behaviors 498 MARINE MAMMAL SCIENCE, VOL. 16, NO. 2, 2000 observed, as advanced by authors of other studies (Campagna et al. 1988, Le Boeuf and Campagna 1994, Cassini 1998,’), it is possible that the males are exploiting a resource and this behavior is reinforced by selective pressures. Recent studies of foraging female €? hookeri have suggested that these animals are operating at or near their physiological limits (Gales and Mattlin 1997, Costa et al. 1998a, 6). If the conclusions from these studies on females are applicable to the males, it may provide some basis for the observed cannibal- istic behavior. €? hookeri pups are an easy target for males and provide an energy-rich food source, at little cost either in terms of “foraging” or in repelling the mother’s attempts to protect her young. Daily energy requirements for a 300-kg male are around 3.3 X basal metabolic rate (from data on A. gazella [Boyd and Duck 1991]), where BMR equals 0.293 W MJ/d (Lavigne et al. 1986). This formula produces a metabolic requirement of 69.7 MJ/day. The energy content of a pup (mean weight 15 kg at this stage of the season, with ap- proximately 75% body water) would be about 75 MJ, (see Harcourt 1993) and would, therefore, provide energy in excess of the daily requirements of the male. Similar energy benefits have been reported for 0. JEauescens males preying on A. australis pups in Peru (Harcourt 1993). These data report the first observations of cannibalism in an otariid. It is unclear why this type of behavior has not been seen at the more intensively studied Sandy Bay rookery. At any rate, the prevalence of the behavior at Dundas Island requires further investigation. Given recent findings on the effects of predation on small fur seal populations (Boveng et al. 1998, Robinson et al. 1999) and the crude estimate of the magnitude of cannibalism at Dundas Island, this is a potentially significant cause of mortality of New Zealand sea lion pups. Systematic observations at both Sandy Bay and Dundas Island would allow determination of the number of males involved in this behavior and its frequency of occurrence.

ACKNOWLEDGMENTS

We thank Wally Hockly and Gus McAllister for assistance in the field and the New Zealand Squid Fishery Management Company Ltd. for funding the participation of FMDG in this work. The work was conducted under permit from the New Zealand Department of Conservation (DOC) and was funded by DOC and by the Conservation Services Levy from the New Zealand fishing industry. The constructive comments of two referees, Dr. Claudio Campagna and Dr. Leslie Higgins, are gratefully acknowl- edged.

LITERATURECITED

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BOYD,I. L., AND C. D. DUCK.1991. Mass changes and metabolism in territorial male Antarctic fur seals (Arctocephalus gazella). Physiological Zoology 64:375-392. BRADSIIAW,C. J. A,, C. LALASAND S. D. MCCONKEY.1998. New Zealand sea lion predation on New Zealand fur seals. New Zealand Journal of Marine and Fresh- water Research 32:lOl-104. CAMPAGNA,C., B. J. LE BOEUFAND H. L. CAPPOZZO.1988. Pup abduction and infan- ticide in southern sea lions. Behaviour 107:44-60. CASSINI,M. H. 1998. inter-specific infanticide in South American otariids. Behaviour 13 5:1005-1 012. CAWTHORN,M. W. 1986. Hooker’s sea lion Survey of Enderby Island, Auckland Is- lands, April 1983. In A. Penniket, A. Garrick and E. Breese, eds. Preliminary reports of expeditions to the Auckland Islands Nature Reserve 1973-1984. Avail- able from Department of Lands and Survey, Wellington, New Zealand. COSTA,D. P., N. J. GALESAND D. E. CROCKER.1998a. Blood volume and diving ability of the New Zealand Sea Lion, Phocarctos hookeri. Physiological Zoology 7 1:208- 213. COSTA,D.P., N. J. GALESAND D. E. CROCKER.19986. Foraging energetics and physi- ological adaptation to diving in the New Zealand sea lion, Phocarctos hookeri. New Zealand Natural Sciences 23 (Supplement):4 1. DEPARTMENTOF CONSERVATION. 1999a. Draft New Zealand Sea Lion population man- agement plan. (Unpublished). 6lpp. Available from Department of Conservation, P. 0. Box 10-420, Wellington, New Zealand. DEPARTMENTOF CONSERVATION. 19996. Unusual mortality of the New Zealand sea lion, Phocarctos hookeri, at the Auckland Islands, January-February 1998. Report of a workshop held 8-9 June 1998, Wellington, and a contingency plan for future events. (Unpublished). 84 pp. Available from Department of Conservation, P. 0. Box 10-420, Wellington, New Zealand. GALES,N.J., AND D. J. FLETCHER.1999. Abundance, distribution and status of the New Zealand sea lion, Phocarctos hookeri. Wildlife Research 26:35-52. GALES,N. J., AND R. H. MATTLIN.1997. Summer diving behaviour of lactating New Zealand sea lions Phocarctos hookeri. Canadian Journal of Zoology 75:1695-1706. GENTRY,R. L., AND J. H. JOHNSON. 1981. Predation by sea lions on neonates. Mammalia 45 :423-430. HARCOURT,R. 1991. Survivorship costs of play in the South American fur seal. Behaviour 42:509-511. HARCOIJRT,R. 1992. Factors affecting early mortality in the South American fur seal (Arctocephalus australis) in Peru: Density related effects and predation. Journal of Zoology, London 226:259-270. HARCOURT,R. 1993. Individual variation in predation on fur seals by southern sea lions (Otaria byronia) in Peru. Canadian Journal of Zoology 71:1908-1911. HAUSFATER,G., AND S. B. HRDY.1984. Infanticide: Comparative and evolutionary perspectives. Aldine Press, New York, NY. HIGGINS,L. V., AND R. A. TEDMAN.1990. Effect of attacks by male Australian sea lions, cinerea, on mortality of pups. Journal of Mammalogy 71:617-619. HRDY,S.B. 1979. Infanticide among mammals: A review, classification, and exami- nation of the implications for the reproductive strategies of females. Ethology and Sociobiology 1 : 13-40. LAVIGNE,D. M., S. INNES,G. A. J. WORTHY,K. M. KOVACS,0. J. SCHMITZAND J. P. HICKIE.1986. Metabolic rates of seals and whales. Canadian Journal of Zoology 6412 79-2 84. LE BOEUF,B. J., AND C. CAMPAGNA.1994. Protection and abuse of young in pinnipeds. Pages 257-276 in S. Parmigiani and F. S. vom Saal, eds. Infanticide and parental care. Harwood Academic Publications, London. MARLOW,B. J. 1975. The comparative behaviour of the Australian sea lions, Neophoca cinerea and Phocarctos hookeri. Mammalia 39: 159-230. 5 00 MARINE MAMMAL SCIENCE, VOL. 16, NO. 2, 2000

MATTLIN,R.H. 1978. Pup mortality of the New Zealand fur seal (Arctocephulus forsteri Lesson). New Zealand Journal of Ecology 1:138-144. PARMIGIANI,S., AND F. S. VOM SAAL.1994. Infanticide and parental care. Harwood Academic Publications, London. PITCHER,K. W., AND F. H. FAY. 1982. Feeding by Steller sea lions on harbor seals. Murrelet, summe~70-71. RIEDMAN,M. L. 1990. The pinnipeds: Seals, sea lions and . University of California Press, Berkeley, CA. ROBINSON,S., L. WYNENAND S. D. GOLDSWORTHY.1999. Predation by a Hooker’s sea lion (Phocurctos hookerz) on a small population of fur seals (Arctocephulus spp.) at Macquarie Island. Marine Mammal Science 15:888-893. VAZ-FERREIRA,R. 1975. Behaviour of the southern sea lion, Otaria &vescens (Shaw) in the Uruguayan islands. Rapports et Procks-verbaux des Reunions, Conseil Inter- national pour I’Explorationde la Mer 169:219-227 I. S. WILKINSONand S. J. CHILDERHOUSE,Department of Conservation, Science and Research Unit, F? 0. Box 10420, Wellington, New Zealan& e-mail iwillunson@ doc.govt.nz; P. J. DUIGNAN,Institute of Veterinary, Animal, and Biomedical Sciences, Massey University, Private Bag 11-222, Palmerston North, New Zea- land; F. M. D. GULLAND,The Marine Mammal Center, Marin Headlands, Sausalito, California 94965, U.S.A. Received 15 June 1999. Accepted 20 Au- gust 1999.

MARINE MAMMAL SCIENCE, 16(2):500-504 (April 2000) 0 2000 by the Society for Marine Mammalogy

MARKING OF SOUTHERN ELEPHANT SEALS WITH PASSIVE INTEGRATED TRANSPONDERS

In the study of life histories, a longitudinal protocol has many advantages over a cross-sectional one: avoidance of sampling bias, estimates of survival and reproduction from lifetime individual records, full coverage of selection episodes, and the opportunity to relate life history strategies to phenotypic traits (Clutton-Brock 1988). A longitudinal protocol requires unequivocal rec- ognition of individuals, to allow identification and tracking across years. In some species, natural marks permit reliable identification of individuals (Bate- son 1977), but recognition is usually accomplished by artificial marking, in particular when a large number of individuals is involved. An important com- ponent of mark-recapture studies is reliability of marks, and mark-loss rate may affect estimation of survival and reproduction (Arnason and Mills 1981). The most common long-term marking techniques for pinnipeds are plastic tags and branding (Erickson et al. 1993). While tags may last for many years, they are affected by a variable rate of tag loss, and their readability may be reduced by wear (Testa and Rothery 1992). Branding is not affected by the risk of mark loss (although readability of marks may degrade over time), but