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Food caching by a marine apex predator, the leopard seal (Hydrurga leptonyx)

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The foraging behaviors of apex predators can fundamentally alter ecosystems through cascading predator–prey interactions. Food caching is a widely studied, taxonomically diverse behavior that can modify competitive relationships and affect population viability. We address predictions that food caching would not be observed in the marine environment by summarizing recent caching reports from two marine mammal and one marine reptile species. We also provide multiple caching observations from disparate locations for a fourth marine predator, the leopard seal (Hydrurga leptonyx (de Blainville, 1820)). Drawing from consistent patterns in the terrestrial literature, we suggest the unusual diversity of caching strategies observed in leopard seals is due to high variability in their polar marine habitat. We hypothesize that caching is present across the spectrum of leopard seal social dominance; however, prevalence is likely to increase in smaller, less-dominant animals that hoard to gain competitive advantage. Given the importance of this behavior, we draw attention to the high probability of observing food caching behavior in other marine species.
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Food caching by a marine apex predator, the leopard seal
(Hydrurga leptonyx)
Douglas J. Krause and Tracey L. Rogers
Abstract: The foraging behaviors of apex predators can fundamentally alter ecosystems through cascading predator–prey
interactions. Food caching is a widely studied, taxonomically diverse behavior that can modify competitive relationships and
affect population viability. We address predictions that food caching would not be observed in the marine environment by
summarizing recent caching reports from two marine mammal and one marine reptile species. We also provide multiple
caching observations from disparate locations for a fourth marine predator, the leopard seal (Hydrurga leptonyx (de Blainville,
1820)). Drawing from consistent patterns in the terrestrial literature, we suggest the unusual diversity of caching strategies
observed in leopard seals is due to high variability in their polar marine habitat. We hypothesize that caching is present across
the spectrum of leopard seal social dominance; however, prevalence is likely to increase in smaller, less-dominant animals that
hoard to gain competitive advantage. Given the importance of this behavior, we draw attention to the high probability of
observing food caching behavior in other marine species.
Key words: food hoarding, food storage, intraspecific competition, foraging behavior, pilferage, carnivore, leopard seal, Hydrurga
leptonyx.
Résumé : Les comportements d’approvisionnement de prédateurs de niveau trophique supérieur peuvent modifier fondamen-
talement les écosystèmes par l’entremise de cascades d’interactions prédateurs–proies. La mise en cache de nourriture est un
comportement abondamment étudié et adopté par des taxons variés qui peut modifier les relations concurrentielles et avoir une
incidence sur la viabilité de populations. Nous nous penchons sur des prédications selon lesquelles la mise en cache de
nourriture ne serait pas observée dans le milieu marin en résumant des signalements récents de cas de mise en cache pour deux
espèces de mammifères marins et une espèce de reptiles marins. Nous présentons également différentes observations de cas de
mise en cache dans des lieux disparates pour un quatrième prédateur marin, le léopard de mer (Hydrurga leptonyx (de Blainville,
1820)). À la lumière de motifs cohérents dans la documentation sur les espèces terrestres, nous proposons que la diversité
inhabituelle de stratégies de mise en cache observée chez les léopards de mer est due à la grande variabilité de leur habitat marin
polaire. Nous postulons que la mise en cache est présente à tous les niveaux de dominance sociale chez les léopards de mer; il est
toutefois probable que sa prévalence soit plus grande chez les animaux plus petits et moins dominants qui se constituent des
réserves pour se donner un avantage concurrentiel. Étant donné l’importance de ce comportement, nous soulignons la forte
probabilité d’observer des comportements de mise en cache de nourriture chez d’autres espèces marines. [Traduit par la Rédaction]
Mots-clés : accumulation de nourriture, stockage de nourriture, concurrence intraspécifique, comportement d’approvisionnement,
vol, carnivore, léopard de mer, Hydrurga leptonyx.
Introduction
Rapid shifts in the abundance or foraging behavior of apex
predators can fundamentally alter ecosystems through cascad-
ing predator–prey interactions (Paine 1966;Dayton et al. 1995;
Ballance et al. 2006;Estes et al. 2011). The behavioral mechanisms
of large marine predators, in particular, are important to under-
stand because ecosystem-level changes may be induced by rela-
tively few individuals (Estes et al. 1998;Williams et al. 2004). Food
caching, for example, is a widely studied, taxonomically diverse
behavior that can modify competitive relationships and affect
population viability (Vander Wall 1990).
For carnivores, food caching describes a satiated predator that
continues to kill prey and either stores or defends it for later
consumption (Vander Wall 1990). Food caching, also called hoard-
ing or storage, is a behavioral hedge against resource competition
(Andersson and Krebs 1978) and is associated with variable food
availability (Smith and Reichman 1984). Caching manifests differ-
ently depending upon the species, resource, and environment,
but successful strategies are driven by a need to prevent pilfering
or to tolerate pilfering by recovering other caches reciprocally
(Vander Wall and Jenkins 2003). Although many birds and small
mammals engage in reciprocal pilfering, large carnivorous mam-
mals typically take a larder hoarding approach with one or a
few large prey items that they (i) hide (e.g., wolverines, Gulo gulo
(Linnaeus, 1758); spotted hyenas, Crocuta crocuta (Erxleben, 1777);
red foxes, Vulpes vulpes (Linnaeus, 1758); leopards, Panthera pardus
(Linnaeus, 1758)) (Haglund 1966;Kruuk 1972;Macdonald 1976;
Eltringham 1979), (2) defend (e.g., lions, Panthera leo (Linnaeus,
Received 21 July 2018. Accepted 17 October 2018.
D.J. Krause. Antarctic Ecosystem Research Division, NOAA Fisheries–Southwest Fisheries Science Center, 8901 La Jolla Shores Drive, La Jolla, CA 92037, USA.
T.L. Rogers. Evolution and Ecology Research Centre, School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney,
NSW 2052, Australia.
Corresponding author: Douglas J. Krause (email: douglas.krause@noaa.gov).
This work is free of all copyright and may be freely built upon, enhanced, and reused for any lawful purpose without restriction under copyright or database law.
This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction
in any medium, provided the original author(s) and source are credited.
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1758)) (Schaller 1972), or (3) both (e.g., mountain lions, Puma
concolor (Linnaeus, 1771); brown bears, Ursus arctos Linnaeus, 1758;
Weddell seals, Leptonychotes weddellii (Lesson, 1826)) (Hornocker
1970;Elgmork 1982;Kim et al. 2005).
Although a taxonomically broad spectrum of terrestrial birds
and mammals store food (Roberts 1979;Sherry 1985), it has only
recently been reported for marine animals. In fact, Smith and
Reichman (1984) erroneously suggested that marine carnivores
likely do not cache food due to low environmental variability in
marine habitats. Marine environments do not lack environmental
variability; however, predator–prey size dynamics frequently
differ. Compared with terrestrial carnivorous mammals, fully
aquatic (e.g., whales and dolphins) and semiaquatic (e.g., seals and
sea lions) mammals typically select small prey relative to their
body size (Tucker and Rogers 2014a,2014b;Tucker et al. 2016).
Small prey are swallowed whole obviating the need to process
food into smaller meals and, accordingly, the need to protect an
uneaten carcass from pilfering. Unsurprisingly, reported marine
food caching species feed upon large prey, typical of the predator–
prey body mass relationships of terrestrial mammals. In the
northeastern Pacific, transient killer whales (Orcinus orca (Linnaeus,
1758)) were reported to kill and then return on subsequent days to
feed on the submerged carcasses of gray whales (Eschrichtius robustus
(Lilljeborg, 1861)) (Barrett-Lennard et al. 2011). And although Wed-
dell seals target a variety of prey sizes, they have been observed in
the Ross Sea caching and defending large (1 m) Antarctic tooth-
fish (Dissostichus mawsoni Norman, 1937) in breathing holes (Kim
et al. 2005;Ponganis and Stockard 2007). Similarly, saltwater croc-
odiles (Crocodylus porosus Schneider, 1801) more frequently cache
their largest prey items including agile wallaby (Macropus agilis
(Gould, 1841)) and water buffalo (Bubalus bubalis (Linnaeus, 1758))
(Doody 2009).
Leopard seals (Hydrurga leptonyx (de Blainville, 1820)) are numer-
ous, apex mammalian predators within Antarctic and sub-Antarctic
coastal ecosystems (Laws 1984;Rogers 2017). Their large size and
gape, maneuverability, wide distribution, and carnivorous-and-
plankton-sieving dentition (Hamilton 1939;Kooyman 1981;Rogers
2017) enable them to exploit a range of prey from Antarctic krill
(Euphausia superba Dana, 1852) to seabirds, otariids, and phocids
(Siniff and Stone 1985;Hall-Aspland and Rogers 2004). Their affin-
ity for consuming other seals is unrivaled among pinnipeds
and they have a demonstrated ability to effect Antarctic fur seal
(Arctocephalus gazella (Peters, 1875)) abundance (Boveng et al. 1998;
Goebel and Reiss 2014).
The leopard seal, like the killer whale, is one of the few marine
mammals that consumes large prey relative to its body size
(Tucker and Rogers 2014a,2014b;Tucker et al. 2016). As such, they
are an ideal candidate to display food caching behavior. A recent
study at Cape Shirreff in the Antarctic Peninsula identified scav-
enging behavior that suggested food caching (Krause et al. 2015).
Here we provide multiple, geographically diverse observations
(Table 1) confirming that leopard seals engage in all three carniv-
oran caching behaviors: hiding, defense, and a combination of
both. Given that any single terrestrial species typically employs
only one caching strategy (Sherry 1985), the intraspecific variety of
leopard seal food caching behaviors is notable.
Materials, methods, and results
With exceptions (e.g., Rogers and Bryden 1995,Vera et al. 2005),
there have been few studies dedicated to observing leopard seal
foraging behavior. The majority of leopard seal caching observa-
tions reported here were obtained opportunistically during day-
light hours. These observations were made visually from above
the waterline and frequently by biologists focused on other taxa.
Animal-borne cameras deployed by Krause et al. (2015) provided
the first continuous, underwater surveillance of foraging leopard
seals. Based on those recordings of cache recoveries, these histor-
ical reports from other Antarctic programs were offered.
According to multiple (n= 11), independent observations
(Table 1), leopard seals employ food caching strategies across dis-
parate Antarctic locations. These include seals using either one or
a combination of food hiding (n= 6 observations; e.g., hiding kills
in ice leads or kelp beds and returning later to consume), direct
defense (n= 1 observation; e.g., hauling out with the carcass;
Fig. 1), or a dual guarding and storage (n= 4 observations; e.g.,
hiding carcasses in ice leads but remaining close and patrolling;
Fig. 2) strategies.
Discussion
Leopard seal food caching behavior has been reported regularly
in recent decades across a wide geographical area. The relatively
low number of observations likely relates to the opportunistic
surveillance and the limitations of land-based observations of ma-
rine predators that are often submerged. However, non-dedicated
observers saw caching consistently, and underwater recordings
revealed a high rate (3 of 7 animals studied; Krause et al. 2015)of
occurrence. This suggests that the behavior is prevalent despite
being difficult to observe using traditional methods.
In general, caching strategies are adapted in light of food type,
available microhabitats, competition type (intra- versus inter-
specific), and intensity (Smith and Reichman 1984;Vander Wall
1990). Therefore, it is plausible that the unusual plasticity ob-
served in leopard seal caching behavior is a result of adaption
to an elevated variety of prey, habitat, and competition. In fact,
leopard seal diets are considered to be catholic (Laws 1984;
Hall-Aspland and Rogers 2004), although there may be prey spe-
cialization by individuals (Krause et al. 2015). Their circum-
Antarctic distribution is vast and variable, ranging from within
the pack ice (Rogers et al. 2005;Meade et al. 2015) up through the
sub-Antarctic Islands (Southwell et al. 2012;Rogers 2017).
Leopard seals are territorial to varying degrees and typically
process and consume their kills at the water’s surface (Kooyman
1965;Rogers and Bryden 1995). As such, competition for prey
items is both inter- and intra-specific. For example, leopard seals
thrash, vocalize at, and chase predatory birds, including Brown
Skuas (Stercorarius antarcticus (Lesson, 1831)), Giant Petrels
(Macronectes giganteus (Gmelin, 1789)), and Wilson’s Storm Petrels
(Oceanites oceanicus (Kuhl, 1820)) to reduce scavenging of their food.
Intraspecific competition has also been observed, particularly in
high density areas (Rogers and Bryden 1995;Hiruki et al. 1999;
Vera et al. 2005;Krause et al. 2015). Densities of this typically
solitary predator range from 0.003 seals/km
2
near the pack-ice
edge (Rogers and Bryden 1997;Southwell et al. 2008) to over
68.6 seals/km
2
near fur seal and penguin colonies at Cape Shirreff
in the Antarctic Peninsula (Krause et al. 2015). These concentra-
tions are two orders of magnitude higher than previous regional
surveys (Forcada et al. 2012). Niche partitioning is a hallmark of
carnivoran competition (Hairston et al. 1960;Palomares and Caro
1999) and evidence of prey, spatial, and temporal niche partition-
ing was observed at Cape Shirreff (Krause et al. 2016).
When prey is limited, there is adaptive advantage to caching.
The resultant competitive asymmetry allows hoarding animals to
gather a larger share of the resource because they are not re-
strained by food consumption rate (Vander Wall 1990). Addition-
ally, species that demonstrate preferred foraging times (e.g., the
leopard seal; Krause et al. 2016) may decouple prey acquisition and
consumption to maximize access during peak periods (Sherry
1985). This strategy may also reduce kleptoparasitism, or direct
prey theft, especially for short-term hoarders (Balme et al. 2017).
Therefore, temporal decoupling is a likely driver of caching be-
havior in high density leopard seal foraging grounds where klepto-
parasitism has been consistently observed (Hiruki et al. 1999;Vera
574 Can. J. Zool. Vol. 97, 2019
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Table 1. Observations of food caching behaviors by leopard seals (Hydrurga leptonyx).
Sex, age class
Prey
species Location, year
Relative leopard
seal density
Caching
strategy Behavior Sources
Female, adult EMPE Cape Washington, 2011 Low Both Patrolled within 10 m of a previously killed, partially
stripped an EMPE in an ice lead. That seal made
aggressive movements and vocalizations when
researchers approached the EMPE carcass; it
eventually consumed the carcass (photo in Krause
et al. 2015)
Krause et al. 2015; P.J. Ponganis
and G.J. Marshall, personal
communication, 2014
Unknown, adult SES DeLaca Island, 2016 Low Both Submerged and stored a dead SES pup carcass under
an iceberg; defended and later consumed it
B. Cook, S. Farry, and C.
McAtee, personal
communication, 2018
Unknown, adult SES Elephant Rocks, 2017 Low Both Killed a SES pup and stored most of the carcass while
it consumed a small portion (ca. 10%) at the surface
(Fig. 2)
B. Cook, S. Farry, and C.
McAtee, personal
communication, 2018
Female, adult SES Bird Island, South
Georgia, 2008
Medium Both Fed on a SES pup carcass in a series of 1–2 h bouts
over the course of 3 days in the same location,
proximate to shallow kelp beds where the prey
may have been stored
J. Forcada, personal
communication, 2018
Male, juvenile GEPE Bird Island, South
Georgia, 2016
Medium Defense Carried dead GEPE in its mouth as it hauled out onto
a rocky beach. It defended the prey from Snowy
Sheathbills (Chionis albus (J.F. Gmelin, 1789)) (Fig. 1)
S. Tarrant, personal
communication, 2016
Female, adult WS Prydz Bay, 2001 Medium Hiding Stored a WS pup in an ice lead and fed on it over the
course of 2 days
This manuscript
Female, adult SES Heard Island, 1990s Medium Hiding Regularly observed killing and eating SES pups.
Observers believed that after initially feeding, the
leopard seal hid the SES carcasses under rocks
underwater. She returned to feed on the carcasses
over the course of days
This manuscript
Female, adult CHPE Cape Shirreff, Livingston
Island 2015
High Hiding Carried a recently killed, unprocessed CHPE into the
intertidal zone, hid it under a large rock, and
hauled out above the cache. The low tide exposed
the cache while the animal slept. The seal departed
during the next high tide and the cached CHPE was
gone by the following low tide
This manuscript
Female, adult AFS, UNPE Cape Shirreff, Livingston
Island 2013–2014
High Hiding Of the seven leopard seals carried animal-borne video
cameras, three were observed to eat previously
hidden, submerged carcasses (1 UNPE, 2 AFS) from
coastal, shallow water benthos (18–32 m)
Krause et al. 2015
Note: Prey species are Emperor Penguin (Aptenodytes forsteri; EMPE), southern elephant seal (Mirounga leonina; SES), Gentoo Penguin (Pygoscelis papua; GEPE), Weddell seal (Leptonychotes weddellii; WS), Chinstrap Penguin
(Pygoscelis antarcticus; CHPE), Antarctic fur seal (Arctocephalus gazella; AFS), and unidentified penguin (UNPE). Relative leopard seal density is a subjective category based on a locations relative position within the range
of reported leopard seal densities across the Antarctic and sub-Antarctic. Caching strategy is either defense, hiding, or both hiding and defense.
Krause and Rogers 575
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et al. 2005;Krause et al. 2015; J. Forcada, personal communication,
2018).
Conclusions
Given the consistent observation of food caching by leopard
seals, it is likely a widely adapted behavior. This catalog of obser-
vations is demure and variable; however, some patterns emerge.
In areas of low to moderate intraspecific competition, leopard
seals show a preference for larder hoarding in or under coastal ice
or in kelp beds; where neither are available, caches are submerged
in shallow water and secured with rocks (Table 1). At high densi-
ties, they tend to hide prey. Given that social dominance within a
species or guild can play an integral role in determining caching
strategy (Brodin et al. 2001), we hypothesize that the choice to
hide or defend a cache will be driven by an individual’s domi-
nance. As intraspecific competition increases and larder hoarding
becomes untenable, the prevalence of hiding prey underwater
and away from prey acquisition sites is likely to increase (Vander
Wall 1990). Finally, we expect caching to be more prevalent in
smaller, less dominant animals that hoard to gain competitive
advantage and reduce the incidence of kleptoparasitism (Balme
et al. 2017). Overall, it is likely that variability in the leopard seal’s
polar marine habitat and conspecific density necessitates a
greater diversity of caching strategies compared with terrestrial
bioregions.
Despite earlier predictions that food caching would not be ob-
served in the marine environment (Smith and Reichman 1984),
the last decade provides convincing evidence for caching in one
marine reptile and three marine mammal species all of which
exhibit atypical predator–prey body size strategies (Tucker and
Rogers 2014a,2014b;Tucker et al. 2016). Considering the impor-
tance of these foraging behaviors, we draw attention to the high
probability of observing food caching in other marine species. As
more attention is focused and as bio-logging tools improve (Cooke
et al. 2004;Rutz and Hays 2009), observations are likely to in-
crease. We anticipate other marine mammals employ food cach-
ing, particularly those that target large, preservable prey (e.g.,
Fig. 1. A male leopard seal (Hydrurga leptonyx; nicknamed “Melvin”) that hauled out on a beach at Bird Island, South Georgia, with a recently
killed, uneaten Gentoo Penguin (Pygoscelis papua) and defended it from scavenging birds. Photo credit: S. Tarrant and British Antarctic Survey.
Color version online.
Fig. 2. An adult leopard seal (Hydrurga leptonyx) near Elephant Rocks, Antarctica, consuming a small portion (10%) of a recently killed southern
elephant seal (Mirounga leonina) pup. The rest of the carcass was cached nearby. Photo credit: B. Cook and Polar Oceans Research Group. Color
version online.
576 Can. J. Zool. Vol. 97, 2019
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gray seals, Halichoerus grypus (Fabricius, 1791); polar bears, Ursus
maritimus Phipps, 1774; other killer whale ecotypes). Additional
observations and manipulated experiments are needed to test
these hypotheses and illustrate behavioral mechanisms such as
cache location cues or the potential presence of reciprocal pilfer-
ing.
Acknowledgements
This note was greatly improved by suggestions and comments
from P.K. Dayton, R.L. Pitman, J. Forcada, and two anonymous
reviewers. We are grateful to K.W. Pietrzak, M.L. Mudge, J.R.
Wright, A.N. Cook, M.L. Zimmerman, M. Goh, T.W. Joyce, N. Pussini,
D.O. Vejar, J.T. Hinke, K.J. Abernathy, G.J. Marshall, A.J. Kroeger, N. de
Gracia, M.R. Klostermann, W.H. Archibald, W.M. Taylor, S.M.
Woodman, J. Senzer, and the National Oceanic and Atmospheric
Administration Antarctic Marine Living Resources (NOAA AMLR)
Pinniped Program leader M.E. Goebel for their assistance in the
field. The financial, infrastructure, and logistical support of the
US–AMLR Program made this work possible. B. Cook, S. Farry, and
C. McAtee made observations while supported by C-013 Palmer
Long-Term Ecological Research (LTER) program, apex predator
component, lead by W.R. Fraser. Leopard seal interactions and
observations at Cape Shirreff were conducted in accordance with
Marine Mammal Protection Act Permit No. 16472 granted by the
Office of Protected Resources, National Marine Fisheries Service,
the Antarctic Conservation Act Permit No. 2012-005, and the
NOAA National Marine and Fisheries Service – Southwest Fisher-
ies Science Center (NOAA NMFS–SWFSC) Institutional Animal
Care and Use Committee Permit No. SWPI2011-02.
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... But rather than being restricted to only large prey, their unique dual-functioning dentition is well suited to both sieving smaller prey from the water and processing larger prey (Hamilton, 1939;Kooyman, 1981;Hocking et al., 2013;Robbins et al., 2019). As such, they take a wide selection of prey, ranging from Antarctic krill (Euphausia superba), cephlapods and fishes, to seabirds and other pinnipeds (Siniff and Stone, 1985;Hall-Aspland and Rogers, 2004;Krause and Rogers, 2019). In addition, the composition of their diet is known to vary with both season (Laws, 1984;Krause et al., 2020) and location (Laws, 1984). ...
... However, the author Erb (1993) described the account as "irrational and untypical behavior" for leopard seals. Evidence of leopard seals caching prey, has however been repeatedly documented (n = 11 observations) (Krause et al., 2015;Krause and Rogers, 2019). One of these observations, on Bird Island, South Georgia, involved a leopard seal carrying a dead Gentoo Penguin (Pygoscelis papua) in its mouth as it hauled onto a rocky beach (Krause and Rogers, 2019). ...
... Evidence of leopard seals caching prey, has however been repeatedly documented (n = 11 observations) (Krause et al., 2015;Krause and Rogers, 2019). One of these observations, on Bird Island, South Georgia, involved a leopard seal carrying a dead Gentoo Penguin (Pygoscelis papua) in its mouth as it hauled onto a rocky beach (Krause and Rogers, 2019). Such prey caching behavior makes it plausible that the leopard seals observed in this study may have captured their prey at sea and then brought it onshore. ...
Article
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Leopard seals (Hydrurga leptonyx) are top-order predators that prey on a wide variety of species including crustaceans, cephalopods, fishes, birds, and pinnipeds. While multiple diet studies have been conducted worldwide, there are no previous accounts of leopard seals predating on chondrichthyans. As part of a wider study on the diet of leopard seals in New Zealand (NZ) waters, researchers and citizen scientists recorded 39 observations of predation and collected 127 scats (166 total records) between 1942 and 2019. Predation on chondrichthyans was detected in 23.1% (n = 9) of observations of predation and 7.1% (n = 9) of scats (the latter via morphological examination and DNA sequencing). From both observations of predations and scats, three chondrichthyan species or genus were identified; elephantfish (Callorhinchus milii), ghost sharks (Hydrolagus spp.) and spiny dogfish (Squalus acanthias). While this is the first published record of leopard seals feeding on chondrichthyans, the relatively high frequency of occurrence within our NZ records, and that certain individuals appeared to target this type of prey, indicates that these species could constitute a substantial, or important, part of the diet for some leopard seals in this region. As chondrichthyans form an important part of the NZ marine ecosystems, our recognition of an additional top-order predator of these species contributes to understanding the overall health of, and future impacts of predators on, the wider NZ marine ecosystem.
... Leopard seals have the broadest diet of the Antarctic packice seals, with krill, penguins, fish and other seals reported as the most frequent food items (Lowry et al. 1977;Øritsland 1977;Rogers and Bryden 1995;Krause and Rogers 2019;Krause et al. 2020). For leopard seals, we included the same five prey items for both FA and SI models. ...
... Conversely, FAs predicted a higher contribution of A. gazella, followed by P. antarcticum. The model using FA data potentially over represents the contribution of fur seals, since leopard seals prey on the fur seals between December and mid-February, when pups are 1-2 months old (Hiruki et al. 1999;Krause and Rogers 2019;Krause et al. 2020). Since the outer blubber reflects a long-term diet, the overall contribution of this prey species is expected to be smaller. ...
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The quantitative use of stable isotopes (SIs) for trophic studies has seen a rapid growth whereas fatty acid (FA) studies remain mostly qualitative. We apply the Bayesian tool MixSIAR to both SI and FA data to estimate the diet of three sympatric predators: the crabeater (Lobodon carcinophaga), Weddell (Leptonychotes weddellii) and leopard seal (Hydrurga leptonyx). We used SI data of their vibrissae and FA data of their outer blubber to produce comparable diet estimates for the same individuals. Both SI and FA models predicted the same main diet components, although the predicted proportions differed. For the crabeater seal, both methods identified krill, Euphausia superba, as the main, and almost exclusive, food item, although the FA model estimated a slightly lower proportion, potentially due to the low lipid content of krill compared to the fish species used in the model. For the Weddell seal the FA model identified the fish Pleuragramma antarcticum as the most important prey, whereas the SI model was not able to distinguish among prey species, identifying a ‘fish-squid’ group as the main diet component. For the leopard seal, both models identified krill as the main contributor; however, the predicted proportions for the secondary sources differed. Although vibrissae and outer blubber may not represent the same timeframe, the use of MixSIAR with FA data provides diet estimates comparable to those obtained with SI data, thus, both approaches were complimentary. The use of both biotracers offers a feasible option to study diets of wild animals in a quantitative manner.
... While Ross seals feed for most of the year north of the pack ice (i.e. in the open ocean) on squid and fish, but also on krill, in low proportions (Rau et al. 1992;Skinner and Klages 1994;Thomas and Rogers 2009;Brault et al. 2019), most leopard seals remain within the Antarctic pack ice (Rogers et al. 2005;Meade et al. 2015). Leopard seals use a wide range of prey, including penguins and other seabirds (Rogers and Bryden 1995;Lowry et al. 1988), Antarctic krill, Euphausia superba, fish, squid and juveniles of other seal species (i.e. the Weddell, crabeater, southern elephant, Mirounga leonina, and fur seals, Arctocephalus gazella) (Hall-Aspland and Rogers 2004;Krause and Rogers 2019). Leopard seals may even switch their diet in response to seasonal and local changes in prey abundance and distribution (Hall-Aspland and Rogers 2004;Guerrero et al. 2016;Botta et al. 2018). ...
... The acoustic presence of leopard seals from the sea ice edge to the open ocean, close to the polar fronts, is likely due to the their broad (i.e. catholic) diet, allowing them to prey on a wide variety of small to large prey species (i.e. from Antarctic krill, fish, to larger vertebrates; Rogers and Bryden 1995;Hall-Aspland and Rogers 2004;Forcada et al. 2012;Krause and Rogers 2019). The close association of high numbers of leopard seal calls and the sub-Antarctic Circumpolar Current could indicate that these polar front waters provide suitable foraging habitats for this species (Staniland et al. 2018). ...
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Full-text available
Two of the Antarctic pack ice seals, Ross, Ommatophoca rossii , and leopard, Hydrurga leptonyx, seals, are extremely difficult to study via traditional visual survey techniques, yet are ideal for an acoustic survey as they are highly vociferous and produce an array of underwater sounds during the austral summer. To determine their acoustic occurrence in the Antarctic pack ice, we use their calls, detected within 680 acoustic recordings made between 1999 and 2009 as part of two multinational programmes. Siren calls of Ross seals were detected mainly in January, and 9.88 calls per minute from low siren calls was the highest call rate for this species. High numbers of Ross seal calls were detected close to the ice edge in areas between 0° and 20° E and 60° and 130° E, suggesting these are important summer habitats. Leopard seal calls were detected mainly in December and January, and December had the highest percentage of calls. Call rate of 11.93 calls per minute from low double trills was the highest call rate for leopard seals. Leopard seal calls were detected throughout the Southern Ocean with more calls detected throughout the pack ice. There was little spatio-temporal overlap in call occurrence of Ross and leopard seals, but both species were more vocally active during the day. Longitude and latitude were the most important predictors of Ross seal occurrence, and month of the year highly predicted leopard seal occurrence. This is the first study to examine the circumpolar acoustic occurrence of Ross and leopard seals in the Southern Ocean pack ice.
... While Ross seals feed for most of the year north of the pack ice (i.e. in the open ocean) on squid and fish, but also on krill, in low proportions (Rau et al. 1992;Skinner and Klages 1994;Thomas and Rogers 2009;Brault et al. 2019), most leopard seals remain within the Antarctic pack ice (Rogers et al. 2005;Meade et al. 2015). Leopard seals use a wide range of prey, including penguins and other seabirds (Rogers and Bryden 1995;Lowry et al. 1988), Antarctic krill, Euphausia superba, fish, squid and juveniles of other seal species (i.e. the Weddell, crabeater, southern elephant, Mirounga leonina, and fur seals, Arctocephalus gazella) (Hall-Aspland and Rogers 2004;Krause and Rogers 2019). Leopard seals may even switch their diet in response to seasonal and local changes in prey abundance and distribution (Hall-Aspland and Rogers 2004;Guerrero et al. 2016;Botta et al. 2018). ...
... The acoustic presence of leopard seals from the sea ice edge to the open ocean, close to the polar fronts, is likely due to the their broad (i.e. catholic) diet, allowing them to prey on a wide variety of small to large prey species (i.e. from Antarctic krill, fish, to larger vertebrates; Rogers and Bryden 1995;Hall-Aspland and Rogers 2004;Forcada et al. 2012;Krause and Rogers 2019). The close association of high numbers of leopard seal calls and the sub-Antarctic Circumpolar Current could indicate that these polar front waters provide suitable foraging habitats for this species (Staniland et al. 2018). ...
Article
Full-text available
Two of the Antarctic pack ice seals, Ross, Ommatophoca rossii, and leopard, Hydrurga leptonyx, seals, are extremely difficult to study via traditional visual survey techniques, yet are ideal for an acoustic survey as they are highly vociferous and produce an array of underwater sounds during the austral summer. To determine their acoustic occurrence in the Antarctic pack ice, we use their calls, detected within 680 acoustic recordings made between 1999 and 2009 as part of two multinational programmes. Siren calls of Ross seals were detected mainly in January, and 9.88 calls per minute from low siren calls was the highest call rate for this species. High numbers of Ross seal calls were detected close to the ice edge in areas between 0° and 20° E and 60° and 130° E, suggesting these are important summer habitats. Leopard seal calls were detected mainly in December and January, and December had the highest percentage of calls. Call rate of 11.93 calls per minute from low double trills was the highest call rate for leopard seals. Leopard seal calls were detected throughout the Southern Ocean with more calls detected throughout the pack ice. There was little spatio-temporal overlap in call occurrence of Ross and leopard seals, but both species were more vocally active during the day. Longitude and latitude were the most important predictors of Ross seal occurrence, and month of the year highly predicted leopard seal occurrence. This is the first study to examine the circumpolar acoustic occurrence of Ross and leopard seals in the Southern Ocean pack ice.
... For instance, Krause et al. (2022) showed that a small number of leopard seals at Cape Shirreff in the South Shetland Islands has caused the local colony of Antarctic fur seal to collapse. Moreover, leopard seal diet can vary according to life history traits (e.g., sex, age, and mass; Krause et al., 2020;Sperou et al., 2023) and seasonality (Hall-Aspland et al., 2005;Krause et al., 2020) and they also exhibit a high degree of individual behavioral plasticity, employing strategies such as ambush tactics, kleptoparasitism, scavenging, and group prey processing (Krause et al., 2015;Krause and Rogers, 2019;Robbins et al., 2019). Together, their varied diet and behavioral plasticity likely enhances leopard seals' resilience to changes in prey availability and abundance. ...
Article
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Leopard seals have traditionally been considered Antarctic predators with a Southern Ocean distribution. Historically, sightings north of the Antarctic Polar Front were considered extralimital. However, recent studies suggest a significant presence of leopard seals in subantarctic regions. Here, we assess the spatial occurrence, residency status, and temporal trends of leopard seals in Chile using historical records, stranding reports, standardized monitoring data, photo-identification (photo ID) catalogs, and sightings from four research expeditions. We also characterize glaciers where sightings are concentrated, identifying glaciological and geomorphic attributes that prolong iceberg residency time, which is linked to high leopard seal concentrations. Based on these attributes, we evaluated other potential suitable glacial habitats in Patagonia. We obtained 438 sighting records of leopard seals from 1927 to 2023. Over the last 15 years, we documented a 4-18% annual increase in stranding events reported to national authorities. Most sightings (75%) were concentrated in two hotspots: National Park San Rafael Lagoon, located in Northern Patagonia, and Parry Fjord in Tierra del Fuego. Using photo ID catalogs, we identified 19 resident leopard seals, including 16 multi-year residents observed between 2010-2023 (10 in San Rafael, 6 in Tierra del Fuego) and 3 potential residents (observed multiple months in the same year in Tierra del Fuego). San Rafael monitoring data showed no inter-annual trend, but seasonal trends were observed. We also provide evidence of breeding in Chile, with records of at least 14 pups born and at least two females giving birth in multiple years. Our habitat characterization suggests that calving flux, fjord sinuosity, and fjord width variation are crucial for prolonging iceberg residency in hotspot areas. Based on these attributes, we identified 13 additional fjords in Patagonia as “very likely” suitable for leopard seals. Our study confirms that Patagonia is part of the species’ breeding distribution, shifting the paradigm that leopard seals are merely visitors north of the Antarctic Polar Front. Given the limited number of suitable glaciers in Chile and the potential impacts of climate change, our assessment highlights glacial retreat as a major threat for the ecosystem of this pagophilic marine apex predator in South America.
... Between 2013 and 2017, AFS pups contributed an estimated 21.3-37.6% of female leopard seal summer diets at Cape Shirreff (Krause et al. 2020). High leopard seal density and the associated intra-specific competition over access to SSAFS pups (Krause et al. 2016), including kleptoparasitism and food caching behaviour (Krause & Rogers 2019), produced extremely high rates of pup mortality at Cape Shirreff. Between 2002 and 2020 the percentage of all pups born being killed by leopard seals rose from 7.1% to 73.8% and has averaged 69.3% (range: 50.3-80.9%) ...
Article
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Antarctic fur seals ( Arctocephalus gazella ) are an iconic marine mammal, an important component of Antarctic ecosystems, and a key indicator species for regional fisheries management. Recent studies have demonstrated Arctocephalus gazella is composed of at least four distinct subpopulations, including one breeding on the South Shetland Islands. These South Shetland Antarctic fur seals (SSAFS) are the highest latitude population of otariids in the world. As such, this subpopulation faces a unique array of environmental and ecological challenges, harbours a disproportionately large reservoir of genetic diversity for the species, and has experienced catastrophic population decline in the last 15 years (2008–2023). We review the array of current and potential threats to the successful recovery of SSAFS. If decision makers wish to promote resilience and support a robust population of this species with future recovery potential, actions are needed to address threats ranging from uncertain to critical, including debris entanglement, climate change, incidental mortality, and resource competition with the krill fishery. In particular, the risks associated with overlap in the spatial and temporal distribution of the young of the year and the krill fishery should be addressed carefully. There is an urgent need for updated population estimates for all Antarctic fur seal subpopulations, analysis on the population viability of the SSAFS, and further characterising summer and winter foraging behaviours to better inform potential conservation actions.
... Long-term studies at Cape Shirreff have documented that large adult female leopard seals haul-out more frequently and in higher concentrations near Antarctic fur seal and penguin breeding colonies than anywhere else in the region (Krause et al., 2015;Krause et al., 2016;Kienle et al., 2022). Further, large female leopard seals exclude males and less dominate females from these nutrient rich resources (Krause et al., 2015;Krause and Rogers, 2019). These large female leopard seals are so successful at predating on pups that they are driving the decline of (Ferreira et al., 2005) 8 ; (Verrier et al., 2012) 9 ; (Guinet et al., 2004) 10 ; (Tryland et al., 2006) 11 ;(Rainer Engelhardt, 1982) 12 ; (Engelhardt and Ferguson, 1980) 13 ; (Nordøy et al., 1993) 14 ; (Tryland et al., 2009) 15 ; (Tryland et al., 2021) 16 ; (Champagne et al., 2005) 17 ; (Ensminger et al., 2014) 18 ; (Crocker et al., 2012) 19 ; (Lidgard et al., 2008) 20 ; (Bennett et al., 2012) 21 ; (Nordøy et al., 1990) 22 ; (Gardiner and Hall, 1997) 23 ; (Gulland et al., 1999) Antarctic fur seals at Cape Shirreff (Hiruki et al., 1999;Krause et al., 2015;Krause et al, 2020). ...
Article
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Evaluating physiological responses in the context of a species’ life history, demographics, and ecology is essential to understanding the health of individuals and populations. Here, we measured the main mammalian glucocorticoid, cortisol, in an elusive Antarctic apex predator, the leopard seal (Hydrurga leptonyx). We also examined intraspecific variation in cortisol based on life history (sex), morphometrics (body mass, body condition), and ecological traits (δ ¹⁵N, δ ¹³C). To do this, blood samples, life history traits, and morphometric data were collected from 19 individual leopard seals off the Western Antarctic Peninsula. We found that adult leopard seals have remarkably high cortisol concentrations (100.35 ± 16.72 μg/dL), showing the highest circulating cortisol concentration ever reported for a pinniped: 147 μg/dL in an adult male. Leopard seal cortisol concentrations varied with sex, body mass, and diet. Large adult females had significantly lower cortisol (94.49 ± 10.12 μg/dL) than adult males (120.85 ± 6.20 μg/dL). Similarly, leopard seals with higher isotope values (i.e., adult females, δ¹⁵N: 11.35 ± 0.69‰) had lower cortisol concentrations than seals with lower isotope values (i.e., adult males, δ¹⁵N: 10.14 ± 1.65‰). Furthermore, we compared cortisol concentrations across 26 closely related Arctoid taxa (i.e., mustelids, bears, and pinnipeds) with comparable data. Leopard seals had the highest mean cortisol concentrations that were 1.25 to 50 times higher than other Arctoids. More broadly, Antarctic ice seals (Lobodontini: leopard seal, Ross seal, Weddell seal, crabeater seal) had higher cortisol concentrations compared to other pinnipeds and Arctoid species. Therefore, high cortisol is a characteristic of all lobodontines and may be a specialized adaptation within this Antarctic-dwelling clade. Together, our results highlight exceptionally high cortisol concentrations in leopard seals (and across lobodontines) and reveal high variability in cortisol concentrations among individuals from a single location. This information provides the context for understanding how leopard seal physiology changes with life history, ecology, and morphology and sets the foundation for assessing their physiology in the context of a rapidly changing Antarctic environment.
... One explanation for why leopard seals do not take long, deep dives is simply that they do not need to do so. Leopard seals are often observed at the surface of the water when hunting large endothermic prey; if/when leopard seal prey occur in shallow waters, there is no reason for leopard seals to dive to their maximum capacity (Penney and Lowry, 1967;Hiruki et al., 1999;Costa, 2007;Krause et al., 2015;Krause et al., 2016;Krause and Rogers, 2019). ...
Article
Full-text available
Animals that display plasticity in behavioral, ecological, and morphological traits are better poised to cope with environmental disturbances. Here, we examined individual plasticity and intraspecific variation in the morphometrics, movement patterns, and dive behavior of an enigmatic apex predator, the leopard seal (Hydrurga leptonyx). Satellite/GPS tags and time-depth recorders were deployed on 22 leopard seals off the Western Antarctic Peninsula. Adult female leopard seals were significantly larger (454±59 kg) and longer (302±11 cm) than adult males (302±22 kg, 276±11 cm). As females were 50% larger than their male counterparts, leopard seals are therefore one of the most extreme examples of female-biased sexual size dimorphism in marine mammals. Female leopard seals also spent more time hauled-out on land and ice than males. In the austral spring/summer, three adult female leopard seals hauled-out on ice for 10+ days, which likely represent the first satellite tracks of parturition and lactation for the species. While we found sex-based differences in morphometrics and haul-out durations, other variables, including maximum distance traveled and dive parameters, did not vary by sex. Regardless of sex, some leopard seals remained in near-shore habitats, traveling less than 50 kilometers, while other leopard seals traveled up to 1,700 kilometers away from the tagging location. Overall, leopard seals were short (3.0±0.7 min) and shallow (29±8 m) divers. However, within this general pattern, some individual leopard seals primarily used short, shallow dives, while others switched between short, shallow dives and long, deep dives. We also recorded the single deepest and longest dive made by any leopard seal—1, 256 meters for 25 minutes. Together, our results showcased high plasticity among leopard seals tagged in a single location. These flexible behaviors and traits may offer leopard seals, an ice-associated apex predator, resilience to the rapidly changing Southern Ocean.
... Between 2013 and 2017 AFS pups alone contributed an estimated 21.3-37.6% of female leopard seal summer diets (Krause et al., 2020). High leopard seal density, focused feeding on AFS pups, and the associated intraspecific competition (Krause et al., 2016), including kleptoparasitism (i.e., prey stealing) and food caching behavior (Krause and Rogers, 2019), have significantly elevated rates of pup mortality at Cape Shirreff. ...
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... For example, larger females regularly kleptoparasitize fur seal pups from their smaller conspecifics [21]. Additionally, leopard seals maximize fur seal and penguin harvesting by caching carcasses, potentially adjusting their caching strategy based on their body size [85]. Likely due to such size-based trophic interactions, larger animals have higher δ 15 N values at a predictable rate (Fig. 4) that reflect their increased consumption of prey with higher δ 15 N values (fur seals or fish). ...
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