ArticlePDF Available

Abstract

Scavenging is an important component to the overall ecology of consumers in virtually all ecosystems on Earth. Given the energetic benefits of foraging on these resource subsidies, opportunistic predators will adjust their behaviors accordingly to maximize access. One of the many consequences of large-scale scavenging opportunities is species interactions that are rarely observed in nature. Here we describe the first published record of predatory sharks (tiger sharks, Galeocerdo cuvier) and saltwater crocodiles (Crocodylus porosus) foraging together in space and time, as documented on a large whale carcass off Western Australia. We report on and discuss the behaviors of the sharks and crocodiles in the hope of shedding new light on the interactions between apex predators that are rarely seen together, but may overlap under specific contexts.
1 23
Journal of Ethology
ISSN 0289-0771
J Ethol
DOI 10.1007/s10164-018-0543-2
Apex predatory sharks and crocodiles
simultaneously scavenge a whale carcass
Austin J.Gallagher, Yannis
P.Papastamatiou & Adam Barnett
1 23
Your article is protected by copyright and
all rights are held exclusively by Japan
Ethological Society and Springer Japan KK,
part of Springer Nature. This e-offprint is
for personal use only and shall not be self-
archived in electronic repositories. If you wish
to self-archive your article, please use the
accepted manuscript version for posting on
your own website. You may further deposit
the accepted manuscript version in any
repository, provided it is only made publicly
available 12 months after official publication
or later and provided acknowledgement is
given to the original source of publication
and a link is inserted to the published article
on Springer's website. The link must be
accompanied by the following text: "The final
publication is available at link.springer.com”.
Vol.:(0123456789)
1 3
Journal of Ethology
https://doi.org/10.1007/s10164-018-0543-2
SHORT COMMUNICATION
Apex predatory sharks andcrocodiles simultaneously scavenge
awhale carcass
AustinJ.Gallagher1,2 · YannisP.Papastamatiou3· AdamBarnett4
Received: 16 January 2018 / Accepted: 4 March 2018
© Japan Ethological Society and Springer Japan KK, part of Springer Nature 2018
Abstract
Scavenging is an important component to the overall ecology of consumers in virtually all ecosystems on Earth. Given the
energetic benefits of foraging on these resource subsidies, opportunistic predators will adjust their behaviors accordingly
to maximize access. One of the many consequences of large-scale scavenging opportunities is species interactions that are
rarely observed in nature. Here we describe the first published record of predatory sharks (tiger sharks, Galeocerdo cuvier)
and saltwater crocodiles (Crocodylus porosus) foraging together in space and time, as documented on a large whale carcass
off Western Australia. We report on and discuss the behaviors of the sharks and crocodiles in the hope of shedding new light
on the interactions between apex predators that are rarely seen together, but may overlap under specific contexts.
Keywords Behavior· Carcass· Saltwater crocodile· Predator· Tiger shark· Whale
Introduction
Food pulses create resource subsidies that organisms can
exploit over discrete spatial and temporal scales. Scaveng-
ing, the opportunistic feeding on dead organic material by
heterotrophic species, is a fundamental but poorly under-
stood ecological process. Studies have suggested that scav-
enging can exert important top-down ecological effects that
influence food web dynamics, while imparting that it is
likely more common than previously thought (DeVault etal.
2003; Wilson and Wolkovich 2011). Carrion attracts a wide
variety of consumers; however, the ecology of scavenging
among top predators is becoming an area of focus (Wilson
and Wolkovich 2011), particularly in fragmented habitats
affected by human activities (Gomo etal. 2017). Moreover,
the advent of portable, high quality video recording devices
has made the observation of predators scavenging in the wild
more common, thereby fostering new questions and perspec-
tives on their foraging and social interactions (Moleón and
Sánchez-Zapata 2015). The benefits of opportunistically uti-
lizing random food pulses are arguably greatest for preda-
tory animals who otherwise must burn significant energy
to encounter and subjugate agile prey (Krofel etal. 2012).
Knowledge of scavenging by predators may help us better
understand their trophic dynamics and the drivers that gov-
ern their physiological and metabolic processes (Bouveroux
etal. 2014; Hammerschlag etal. 2016). Scavenging studies
also provide a unique window into the social behaviors of
species which otherwise remain cryptic or poorly under-
stood, thus overcoming the challenges of observing both
feeding events (which are stochastic) and the rarity of find-
ing multiple predators within close proximity (Fallows etal.
2013).
Sharks and crocodilians overlap in some coastal envi-
ronments where they act as reciprocal intra-guild predators
(Nifong and Lowers 2017). The majority of these docu-
mented interactions are between adults of one species and
juveniles of another. Even less is known about competitive
interactions between adult crocodilians and larger shark spe-
cies. Here we present the first published record of predatory
Electronic supplementary material The online version of this
article (https ://doi.org/10.1007/s1016 4-018-0543-2) contains
supplementary material, which is available to authorized users.
* Austin J. Gallagher
austin@beneaththewaves.org
1 Beneath theWaves, Herndon, VA, USA
2 Rosenstiel School ofMarine andAtmospheric Science,
University ofMiami, Miami, FL33149, USA
3 Department ofBiological Sciences, Florida International
University, NorthMiami, FL, USA
4 College ofScience andEngineering, James Cook University,
Townsville, QLD, Australia
Author's personal copy
Journal of Ethology
1 3
sharks and crocodiles foraging together in space and time, as
documented on a large whale carcass off Western Australia.
Methods andresults
On September 24, 2017, an approximately15-m male hump-
back whale (Megaptera novaeangliae) was found dead and
floating upside down just north of Montgomery Reef, Kim-
berley, Western Australia (−15.99S, 124.239722E), about
1km from shore at 0815h by a dive charter company. Based
on the odor and rotted appearance of the whale carcass, the
charter staff estimated the whale had been dead for over
1week (there were also hundreds of bite marks from sharks
on the ventral side of the whale). Upon closer inspection,
four tiger sharks (Galeocerdo cuvier) and one saltwater croc-
odile (Crocodylus porosus) were seen feeding on the carcass.
An aerial drone (DJI Phantom 4) was launched at 0847h to
capture photographs and videos of the event.
A total of 5min and 48s of 4K footage from the carcass
were obtained. Two tiger sharks, estimated to be ~300cm
total length (adults), were recorded feeding on the carcass
throughout the footage. Only one shark was ever observed
feeding at any given time. Tiger sharks showed a preference
for the pectoral fins of the carcass (Fig.1a), and after a feed-
ing event would sink beneath the surface and slowly swim
away from the carcass. Sharks would then approach from
depth to the surface for subsequent feeding passes, which
included large half-moon bites that pulled flesh from the
whale. Throughout the footage, all tiger sharks appeared to
be in a state of post-feeding torpor, as seen in other sharks
when gorging themselves on whale carcasses (Fallows etal.
2013), suggesting they had been foraging for some time. The
saltwater crocodile estimated to be 400cm in length (adult)
was observed from the beginning and throughout the foot-
age (Fig.1b). The crocodile fed at various locations on the
carcass, including the rostrum and fluke, with a preference
for the pectoral fins (Bornatowski etal. 2012). Unlike the
half-moon bite marks left by the tiger sharks, the crocodile
appeared to pull and tear smaller pieces of flesh from the
carcass with a ripping motion (ESM1). There were no major
apparent bite marks left like those seen from tiger sharks.
Crocodile feeding behaviors were characterized into two cat-
egories: (1) horizontal bites where the crocodile floated on
the surface of the water, which were common on pectoral
fins and the fluke (Fig.2a); and (2) vertical body position-
ing which included tearing and ripping, with use of the tail
to generate pull and maintain body position, which focused
on the fleshy rorquals of the whale (Fig.2b). Behavior (2)
on the rorquals occurred once, and during this event a tiger
shark made brief contact with the crocodile, appearing to
splash the water with its tail, likely in an effort to deter the
crocodile from the region (ESM1, 0:28s). After this inter-
action, the shark quickly abandoned the region, after which
the crocodile buried its head into the cavity of the whale,
presumably in an effort to find more desirable pieces of
flesh (ESM1). Afterwards, the crocodile used its front legs
to climb on to the pectoral fin where it remained for ~1min
to either rest or avoid detection by tiger sharks (Fig.2c).
At 1251h the drone stopped recording and the main ship
departed north towards the Prince Regent River. On the
return trip 7days later, the carcass had washed ashore and up
to 12 saltwater crocodiles were seen foraging on and remain-
ing around the carcass (although no footage was obtained).
Discussion
Scavenging by sharks is relatively common, and likely an
important component of their feeding ecology (Barnett
etal. 2012; Fallows etal. 2013; Hammerschlag etal. 2016).
A number of whale carcass scavenging events by sharks,
mainly white (Carcharodon carcharias) and tiger sharks,
have been documented (e.g., Long and Jones 1996; Dudley
etal. 2000; Dicken 2008; Clua etal. 2013; Fallows etal.
2013). Apart from highlighting the importance of whale
Fig. 1 a Tiger shark (white filled arrow) scavenging on pectoral fin
of humpback whale (top-center of image), note the half-moon bite
marks indicative of shark scavenging throughout. b A solitary saltwa-
ter crocodile (white open arrow) scavenging on the front of the whale
carcass (top-left of image)
Author's personal copy
Journal of Ethology
1 3
carcasses to shark diets, these opportunistic studies also
revealed information on shark behavior. Dudley etal. (2000)
observed both tiger and white sharks feeding concurrently on
a whale carcass, with no competition or aggression observed
between the two shark species or between tiger shark indi-
viduals; conversely, white sharks showed some intra-specific
antagonistic behavior. Clua etal. (2013) identified at least
46 individual tiger sharks feeding on a blue whale (Balae-
noptera musculus) carcass over 8days. A size-based domi-
nance hierarchy was observed, but with an increased toler-
ance toward smaller animals over time. Fallows etal. (2013)
documented over 40 individual white sharks feeding on a
whale carcass off South Africa, with no evidence of aggres-
sion despite a clear size-based pecking order.
Tiger sharks are known generalist predators (Lowe etal.
1996; Dicken etal. 2017). They are also highly opportun-
istic and will respond quickly to and subsequently forage
on novel prey items including fresh carcasses (Gallagher
etal. 2011). Although saltwater crocodiles will eat dead
animals (Taylor 1979), information on scavenging behav-
ior by this species is lacking in the literature, and noth-
ing is known about the prevalence of saltwater crocodile
scavenging on whale carcasses. Indeed, limited quantita-
tive data are available for the diets of large crocodiles in
Australia, but consumption of prey such as cattle, kan-
garoos, dogs, buffalo, goats, horses, reptiles and fish has
been observed (Taylor 1979; Whiting and Whiting 2011).
Body size is believed to be a good predictor of diet of salt-
water crocodiles, with larger individuals (> 188cm total
length) targeting larger prey, and potentially consuming
prey from three distinct food webs, linking terrestrial,
freshwater and saltwater ecosystems (Whiting and Whit-
ing 2011; Hanson etal. 2015). Saltwater crocodiles from
Northern Australia primarily feed on small marine fishes
and benthic estuarine prey, although larger individuals are
known to prey on terrestrial mammals and birds (Taylor
1979). Habitat use of saltwater crocodiles and tiger sharks
is likely to show minimal overlap (e.g., coastal areas when
crocodiles move out of river systems), largely separating
these two apex predators. The saltwater crocodile’s most
pronounced dietary overlap with sharks could be sea tur-
tles, as nesting turtles are important seasonal prey for both
predatory species (Heithaus etal. 2008; Whiting and Whit-
ing 2011; Hammerschlag etal. 2016). Given that saltwater
crocodiles typically occur in riverine and coastal wetlands,
the likelihood of feeding on whale carcasses is influenced
by the carcass being close enough to shore (i.e., ~1km or
less) and in areas with higher saltwater crocodile densities,
Fig. 2 Saltwater crocodile (white open arrow) exhibiting a horizontal biting behavior on the tail fluke of a humpback whale carcass, b vertical
tearing on the whale’s rorquals, and c resting on the pectoral fin in between foraging bouts
Author's personal copy
Journal of Ethology
1 3
as seen in our observations. This is further supported by
our observation of up to 12 crocodiles scavenging on the
whale carcass once it had washed ashore.
In addition to the sharks and crocodiles in this study
appearing not to feed from the same location on the whale
simultaneously, we also did not observe any repeated inter-
specific agonistic interactions or indications of dominance
hierarchies from our limited sample (except for the one
instance when the tiger shark splashed with its tail). Croco-
diles have been observed killing smaller sharks (e.g., bull
sharks, Carcharhinus leucas) in narrow estuaries and riv-
ers where they may have the advantage, and there is even
some evidence for juvenile sharks being chemically aware of
crocodiles (Rasmussen and Schmidt, details within Nifong
and Lowers 2017). Alternatively, there is some evidence of
an adult crocodile having been killed by sharks (Nifong and
Lowers 2017). Our observations suggest adult tiger sharks
and saltwater crocodiles can scavenge the same food source
simultaneously with few or no agonistic interactions. How
often these situations arise is unknown, as is the response of
crocodiles when the number of sharks on the carcass start
to increase (therecould be more sharks at discretecoastal
siteswith signigicant tidal flow, since oils and sensory cues
from the carcass travel widely).
Through the opportunistic capture of drone footage, we
present one of the first ethograms of large, apex predatory
sharks and crocodiles simultaneously foraging together on
a shared resource. Scavenging events attract a diversity of
species, some of which may not be commonly encountered
together. Upon closer examination, our footage suggests
that sharks can detect and perceive the presence of a large
crocodile, but whether crocodiles are perceived as a risk or
threat to sharks remains unknown. We recognize that our
report is only one small record of these species co-existing;
however, it may provide a window into future studies inter-
ested in evaluating the trophic linkages and social interac-
tions between aquatic apex predators. Recent studies sug-
gest increased interest in scavenging research (Moleón and
Sánchez-Zapata 2015), and the growing body of empirical
work suggests that this process is crucial for understand-
ing the biology, evolution, and the behavioral ecology of
top predators (e.g., DeVault etal. 2003; Wilson and Wolko-
vich 2011). Furthermore, as ecosystems change and mobile,
aquatic predators are pushed into new areas, these types of
interactions could increase in certain coastal areas. As such,
we believe the reporting of these types of events is valuable
and ecologically important, especially for threatened species
of top predators.
Acknowledgements Thank you to Jeremy Tucker for obtaining and
sharing the drone footage, as well as the staff of Great Escape Charters
for assisting with the event. The authors declare that they have no con-
flict of interest. This article does not contain any studies with animals
performed by any of the authors.
References
Barnett A, Braccini JM, Awruch CA, Ebert DA (2012) An overview
on the role of Hexanchiformes in marine ecosystems: biology,
ecology and conservation status of a primitive order of modern
sharks. J Fish Biol 80:966–990
Bornatowski H, Wedekin LL, Heithaus MR, Marcondes MCC,
Rossi-Santos MR (2012) Shark scavenging and predation on
cetaceans at Abrolhos Bank, eastern Brazil. J Mar Biol Assoc
UK 92:1767–1772
Bouveroux T, Kiszka JJ, Heithaus MR, Jauniaux T, Pezeril S (2014)
Direct evidence for gray seal (Halichoerus grypus) predation
and scavenging on harbor porpoises (Phocoena phocoena). Mar
Mammal Sci 30:1542–1548
Clua E, Chauvet C, Read T, Werry JM, Lee SY (2013) Behavioural
patterns of a tiger shark (Galeocerdo cuvier) feeding aggrega-
tion at a blue whale carcass in Prony Bay, New Caledonia. Mar
Fresh Behav Physiol 46:1–20
DeVault TL, Rhodes OE, Shivik JA (2003) Scavenging by verte-
brates: behavioral, ecological, and evolutionary perspectives on
an important energy transfer pathway in terrestrial ecosystems.
Oikos 102:225–234
Dicken ML (2008) First observations of young of the year and juve-
nile great white sharks (Carcharodon carcharias) scavenging
from a whale carcass. Mar Freshw Res 59:596–602
Dicken ML, Hussey NE, Christiansen HM, Smale MJ, Nkabi N,
Cliff G, Wintner SP (2017) Diet and trophic ecology of the tiger
shark (Galeocerdo cuvier) from South African waters. PLoS
ONE 12:e0177897
Dudley FJS, Anderson-Reade DM, Thompson SG, McMullen BP
(2000) Concurrent scavenging off a whale carcass by great
white sharks, Carcharodon carcharias, and tiger sharks Gale-
ocerdo cuvier. Fish Bull 98:646–649
Fallows C, Gallagher AJ, Hammerschlag N (2013) White sharks
(Carcharodon carcharias) scavenging on whales and its poten-
tial role in further shaping the ecology of an apex predator.
PLoS ONE 8:e60797
Gallagher AJ, Jackson T, Hammerschlag N (2011) Occurrence of
tiger shark (Galeocerdo cuvier) scavenging on avian prey and
its possible connection to large-scale bird die-offs in the Florida
Keys. Florida Sci 74:264–269
Gomo G, Mattisson J, Hagen BR, Moa PF, Willebrand T (2017)
Scavenging on a pulsed resource: quality matters for corvids
but density for mammals. BMC Ecol 17:22
Hammerschlag N, Bell I, Fitzpatrick R, Gallagher AJ, Hawkes
LA, Meekan MG, Stevens JD, Thums M, Witt MJ, Barnett A
(2016) Behavioral evidence suggests facultative scavenging by a
marine apex predator during a food pulse. Behav Ecol Sociobiol
70:1777–1788
Hanson JO, Salisbury SW, Campbell HA, Dwyer RG, Jardine TD,
Franklin CE (2015) Feeding across the food web: the interaction
between diet, movement and body size in estuarine crocodiles
(Crocodylus porosus). Aust Ecol 40:275–286
Heithaus MR, Wirsing AJ, Thomson JA, Burkholder DA (2008) A
review of lethal and non-lethal effects of predators on adult
marine turtles. J Exp Mar Biol Ecol 356:43–51
Krofel M, Kos I, Jerina K (2012) The noble cats and the big bad
scavengers: effects of dominant scavengers on solitary preda-
tors. Behav Ecol Sociobiol 66:1297–1304
Long DJ, Jones RE (1996) White shark predation and scavenging on
cetaceans in the eastern North Pacific Ocean. In: Klimley AP,
Jones E (eds) Great white sharks: the biology of Carcharodon
carcharias. Academic Press, New York, pp 293–307
Author's personal copy
Journal of Ethology
1 3
Lowe CG, Wetherbee BM, Crow GA, Tester AL (1996) Ontogenetic
dietary shifts and feeding behavior of the tiger shark, Galeocerdo
cuvier, in Hawaiian waters. Environ Biol Fish 47:203–211
Moleón M, Sánchez-Zapata JA (2015) The living dead: time to
integrate scavenging into ecological teaching. Bioscience
65:1003–1010
Nifong JC, Lowers RH (2017) Reciprocal intraguild predation
between Alligator mississippiensis (American alligator) and
Elasmobranchii in the Southeastern United States. Southeast Nat
16:383–396
Taylor JA (1979) The foods and feeding habits of subadult Croco-
dylus porosus (Schneider) in northern Australia. Wildlife Res
6:347–359
Whiting SD, Whiting AU (2011) Predation by the saltwater crocodile
(Crocodylus porosus) on sea turtle adults, eggs, and hatchlings.
Chelonian Conserv Biol 10:198–205
Wilson EE, Wolkovich EM (2011) Scavening: how carnivores and car-
rion structure communities. Trend Ecol Evo 26:129–135
Author's personal copy
... Aquatic birds (n = 53) continued to be (Jones 2003;Martin et al. 2012). More recent articles concerning crocodilians have been ecological or behavioural studies of crocodilian species incorporating drone flights Gallagher et al. 2018;. The earliest article concerning sea turtles was published in 2015 , which has been accompanied by one to two additional articles each year from 2016 to 2020. ...
... Animal detection and population surveys through drone flights appear in the scientific literature as early as 2005 and 2010, respectively, progressively increasing in the volume of We found 12 research articles related to using drones to observe natural animal behaviour, mostly from 2018 onwards. All but one of these research articles concerned aquatic taxa ) such as elasmobranchs (Lea et al. 2018;Frixione et al. 2020;, crocodilians (Gallagher et al. 2018), turtles , and cetaceans . ...
Full-text available
Article
Drones or unoccupied aerial vehicles are rapidly being used for a spectrum of applications, including replacing traditional occupied aircraft as a means of approaching wildlife from the air. Though less intrusive to wildlife than occupied aircraft, drones can still cause varying levels of disturbance. Policies and protocols to guide lowest-impact drone flights are most likely to succeed if considerations are derived from knowledge from scientific literature. This study examines trends in the scientific literature on using drones to approach wildlife between 2000 and 2020, specifically in relation to the type of publications, scientific journals works are published in, the purposes of drone flights reported, taxa studied, and locations of studies. From 223 publications, we observed a large increase in relevant scientific literature, the majority of which were peer-reviewed articles published across 87 scientific journals. The largest proportions of peer-reviewed research articles related to aquatic mammals or aquatic birds, and the use or trial of drone flights for conducting population surveys, animal detection or investigations of animal responses to drone flights. The largest proportion of articles were studies conducted in North America and Australia. Since animal responses to drone flights vary between taxa, populations, and geographic locations, we encourage further growth in the volume of relevant scientific literature needed to inform policies and protocols for specific taxa and/or locations, particularly where knowledge gaps exist.
... A broad range of marine megafauna has been studied using drones, including sea turtles [3][4][5][6][7], cetaceans [8][9][10][11] and elasmobranchs (sharks and rays) [12,13], and multiple species have also been surveyed simultaneously [14][15][16][17][18][19][20][21][22]. Despite their popularity in elasmobranch research, a recent review highlighted the underutilization of drone technology in batoid (ray) research compared to sharks [13]. ...
Full-text available
Article
Drones have become increasingly popular tools to study marine megafauna but are under- utilized in batoid research. We used drones to collect video data of manta ray (Mobula cf. birostris) swimming and assessed behavior-specific kinematics in Kinovea, a semi-automated point-tracking software. We describe a ‘resting’ behavior of mantas making use of strong currents in man-made inlets in addition to known ‘traveling’ and ‘feeding’ behaviors. No significant differences were found between the swimming speed of traveling and feeding behaviors, although feeding mantas had a significantly higher wingbeat frequency than traveling mantas. Resting mantas swam at a signifi- cantly slower speed and wingbeat frequency, suggesting that they were continuously swimming with the minimum effort required to maintain position and buoyancy. Swimming speed and wingbeat frequency of traveling and feeding behaviors overlapped, which could point to other factors such as prey availability and a transitional behavior, influencing how manta rays swim. These base- line swimming kinematic data have valuable applications to other emerging technologies in manta ray research.
... One potential of drones that has not been widely explored is the ability to investigate animal behaviours, although a few examples have highlighted their potential. For instance, drones have been used to gain novel insights about the foraging behaviour of many marine species (i.e., gray whales, Eschrichtius robustus (Lilljeborg, 1861), Torres et al. 2018;tiger sharks, Galeocerdo cuvier (Péron and Lesueur in Lesueur, 1822); saltwater crocodiles, Crocodylus porosus Schneider, 1801, Gallagher, Papastamatiou, and Barnett 2018;and white sharks, Carcharodon carcharias (Linnaeus, 1758), Tucker et al. 2021); the courting and mating behaviour of green sea turtles (Chelonia mydas (Linnaeus, 1758), Bevan et al. 2016) and loggerhead sea turtles (Caretta caretta (Linnaeus, 1758), Schofield et al. 2017); the parasitic micro-predation behaviour of kelp gulls (Larus dominicanus Lichtenstein, 1823) on southern right whales (Eubalaena australis (Desmoulins, 1822), Azizeh et al. 2021); and the nursing behaviour of southern right whales with associated bioenergetic costs (Nielsen et al. 2019). In a similar fashion, our research team used DJI Phantom 3 and 4 Pro (multirotor) drones to film polar bears foraging on seabird eggsan increasing phenomenon at our study site (Iverson et al. 2014)and subsequently estimate the energetic consequence of this behaviour (Jagielski et al. 2021a) and examine the foraging performance of bears (Jagielski et al. 2021b). ...
Article
Climate-induced sea-ice loss represents the greatest threat to polar bears (Ursus maritimus), and utilizing drones to characterize behavioural responses to sea-ice loss is valuable to forecasting polar bear persistence. In this manuscript, we review previously published literature and draw on our own experience of using multirotor aerial drones to study polar bear behaviour in the Canadian Arctic. Specifically, we suggest that drones can minimize human-bear conflicts by allowing users to observe bears from a safe vantage point; produce high-quality behavioural data that can be reviewed as many times as needed and shared with multiple stakeholders; and foster knowledge generation through co-production with northern communities. We posit that in some instances drones may be considered as an alternative tool for studying polar bear foraging behaviour, interspecific interactions, human-bear interactions, human safety and conflict mitigation, and den-site location at individual-level, small spatial scales. Finally, we discuss flying techniques to ensure ethical operation around polar bears, regulatory requirements to consider, and recommend that future research focus on understanding polar bears’ behavioural and physiological responses to drones and the efficacy of drones as a deterrent tool for safety purposes.
... Estuarine crocodiles are also regarded as the most agonistic and least social crocodylian (Lang 1987), with interactions between conspecifics potentially leading to severe injuries (i.e., loss of limbs, tail, and lacerations) and death (Webb and Manolis 1989). However, telemetry studies tracking multiple co-habiting individuals have revealed substantial spatial overlap between males in both lacustrine and riverine systems (Kay 2004;Brien et al. 2008;Campbell et al. 2013), and the formation of aggregations around feeding opportunities (Gallagher et al. 2018). Tracking studies have also revealed that individual crocodiles within the same population are not homogenous in the way they use space, with some individuals adopting a more nomadic strategy while others are more siteattached (Campbell et al. 2013;Dwyer et al. 2015;Hanson et al. 2015;Baker et al. 2019). ...
Article
Examining the social behaviors of solitary species can be challenging due to the rarity in which interactions occur and the large and often inaccessible areas which these animals inhabit. As shared space-use is a prerequisite for the expression of social behaviors, we can gain insights into the social environments of solitary species by examining the degree of spatial overlap between individuals. Over a 10-year period, we examined how spatial overlap amongst 105 estuarine crocodiles Crocodylus porosus was influenced by season, sex, and movement tactic. We discovered that crocodiles displayed highly consistent spatial overlaps with conspecifics between months and across years. Furthermore, male crocodiles that exhibited a greater degree of site fidelity displayed more stable social environments, while females and males that were less site-attached had more dynamic social environments with spatial overlaps between conspecifics peaking during the mating season. Our results demonstrate how long-term tracking of multiple individuals within the same population can be used to quantify the spatial structure and social environment of cryptic and solitary species.
... Indeed, even gaping wounds and missing limbs sustained in battles with predators, prey, or conspecifics do not seem to seriously incapacitate crocodilians [274]. Furthermore, being opportunistic feeders, many crocodilians scavenge dead and rotting flesh or other germ-infested foods, aggressively steal it from other predators, or let their food deliberately decompose in order to be better able to tear apart and digest the softened flesh without falling ill [275]. ...
Full-text available
Article
Introduction New drug discovery and development programs have historically relied on the identification of novel lead compounds from plant origin. This is understandable when considering that plants have been the main, if not the only sources of therapeutics for managing human diseases for millennia [1]. Only in 1806, a pharmacologically active ingredient (morphine) from a plant (the opium poppy Papaver somniferum (Papaveraceae)) was for the first time isolated from a plant [2]. Currently, morphine is used for, among others, the palliation of severe chronic pain in, for instance, terminal cancer patients [2], and serves as a precursor for a large number of opioid medications such as the antitussive codeine and the antidiarreal agent loperamide [2]. The identification of morphine from P. somniferum was soon followed by many others such as, among others, the central nervous system stimulant caffeine from the beans of the coffee plant Coffea arabica (Rubiaceae) in 1819 [3], the antimalarial quinine from the bark of the cinchona tree Cinchona officinalis (Rubiaceae) in 1820 [4], and the analgesic salicin from the bark of the white willow Salix alba (Salicaceae) in 1828 [5]. Since then, many more breakthrough drugs have been developed from plants, including the antineoplastic agents vincristine and paclitaxel from the periwinkle plant Catharanthus roseus (Apocynaceae) [6] and the Pacific yew Taxus brevifolia (Taxaceae) [7], respectively; the phytoestrogen diosgenin from yam species in the genus Dioscorea (Dioscoreaceae) that serves as precursor for, among others, oral contraceptives and cortisone [8]; and the oral antihyperglycemic biguanide metformin from the French lilac Galega officinalis (Fabaceae) [9]. Other important sources of novel drugs were microorganisms. The fungus Penicillium rubens (Trichocomaceae) and the actinomycete bacterial species Saccharopolyspora erythraea (Pseudonocardiaceae) gave the antibacterial agents penicillin [10] and erythromycin Abstract New drug discovery and development efforts have traditionally relied on ethnopharmacological information and have focused on plants with medicinal properties. In the search for structurally novel and mechanistically unique lead compounds, these progams are increasingly turning to the bioactive molecules provided by the animal biodiversity. This not only involves bioactive constituents from marine and terrestrial invertebrates such as insects and arthropods, but also those from amphibians and other 'higher' vertebrates such as reptiles. The venoms of lizards and snakes are complex mixtures of dozens of pharmacalogically active compounds. So far, these substances have brought us important drugs such as the angiotensin-converting enzyme inhibitors captopril and its derivates for treating hypertension and some types of congestive heart failure, and the glucagon-like peptide-1 receptor agonist exenatide for treating type 2 diabetes mellitus. These drugs have been developed from the venom of the Brazilian pit viper Bothrops jararaca (Viperidae) and that of the Gila monster Heloderma suspectum (Helodermatidae), respectively. Subsequently, dozens of potentially therapeutically applicable compounds from lizards' and snakes' venom have been identified, several of which are now under clinical evaluation. Additionally, components of the immune system from these animals, along with those from turtles and crocodilians, have been found to elicit encouraging activity against various diseases. Like the venoms of lizards and snakes, the immune system of the animals has been refined during millions of years of evolution in order to increase their evolutionary success. This paper addresses some of the bioactive compounds from reptiles, and elaborates on the therapeutic potential of some of them as anticoagulants and antiplatelet drugs, as well as wound healing-promoting, antileishmanial, antiviral, immunomodulating, antimicrobial, and anticancer compounds.
... The potential of UAVs to determine shark abundance has been shown for blacktip reef sharks (Carcharhinus melanopterus) in French Polynesia (Kiszka et al., 2016), fine-scale movements of small coastal species have been tracked in Australia (Raoult et al., 2018) and the shoaling tendencies of C. melanopterus (Rieucau et al., 2018) and swimming kinematics of blacktip sharks (Carcharhinus limbatus) (Porter et al., 2020) have also been investigated. UAVs have also captured the attempted predation of C. limbatus by great hammerhead sharks (Sphyrna mokarran) (Doan & Kajiura, 2020), the predation of a humpback whale (Megaptera novaeangliae) by white sharks (Carcharodon carcharias) (Dines & Gennari, 2020), the effects of the presence of whale carcass on shark swimming behaviour (Tucker et al., 2021) and multiple species simultaneously feeding (Gallagher et al., 2018;Lea et al., 2019). In addition, the use of UAVs in the surveillance and detection of potentially dangerous sharks has been explored (Butcher et al., 2020;Colefax et al., 2020a;Colefax et al., 2020b) including identifying optimum light wavelengths to increase detection probability . ...
Article
Cabo Pulmo National Park was established in 1995 and has since seen a large increase in fish biomass. An unoccupied aerial vehicle (UAV) was used to survey shallow coastal habitat in which lemon sharks (Negaprion brevirostris), bull sharks (Carcharhinus leucas) and Pacific nurse sharks (Ginglymostoma unami) were recorded. Sharks were more common in the afternoon, potentially utilising warmer shallow areas to behaviourally thermoregulate. This study highlights UAV surveying to be a viable tool for species identification, a limitation of previous terrestrial surveys conducted in the area. This article is protected by copyright. All rights reserved.
... Despite the numerous studies dealing with stomach contents of extant tiger sharks (e.g. Bass et al. 1975;Stevens and Mc Loughlin 1991;Randall 1992;Lowe et al. 1996;Simpfendorfer et al. 2001;Dicken et al. 2017) and their feeding behaviour (Clua et al. 2013;Gallagher et al. 2018;Lea et al. 2019), reports on the feeding habits of the extinct tiger sharks are scarce and limited to indirect evidence (Applegate 1965;Cicimurri and Knight 2009). In rare cases, however, fossil stomach contents of some other sharks (e.g. ...
Article
Based on a shark-bitten partial skeleton of an immature sirenian (Metaxytherium cf. medium) from the middle Miocene of the Styrian Basin (Austria), we report on the oldest predator–prey interaction between tiger sharks and dugongs. The bite mark-bearing ribs and vertebrae are associated with seven teeth of Galeocerdo aduncus, which are otherwise rare in the fossil record of the Styrian Basin. The unique tooth morphology of the genus Galeocerdo is reflected by an unambiguous pattern of bite marks, which is repeatedly detected on one rib fragment. Similar bite marks were reproduced experimentally by using clay instead of bone. The obtained pattern is consistent with the observed bite marks on the sirenian rib fragment, which demonstrates that tiger sharks fed upon the Metaxytherium carcass. Furthermore, we also report on the first record of the angel shark Squatina sp. within the Styrian Basin.
Full-text available
Article
Drones are becoming more accessible and efficient. This article presents a review of recent scientific literature focusing on their use to study wildlife. The 250 publications consulted were grouped into one of 4 categories: wildlife surveys, the behavioural response of wildlife to drones, the study of wildlife behaviour and wildlife protection. The review highlighted the great potential of drones for helping in the survey of animals, especially birds and mammals, and it also revealed the developments underway to allow their use for studying aquatic fauna, amphibians, reptiles and insects. The main impacts of drones on animals are presented and, based on the available information, preliminary recommendations are made to limit their disturbance to wildlife. Drones have multiple advantages and the rapid development of this technology suggests that several of the current limits to their use will soon be overcome. Finally, elements of the Canadian regulations on the use of drones are presented. In conclusion, in the medium-term, drones have the potential to play a significant role in the protection and management of biodiversity.
Full-text available
Article
Drones are a modern alternative to manned aircraft for aerial surveys, however approaching wildlife with drones may still cause disturbance. Understanding the factors influencing animal responses to drone flights is fundamental for informing guidance on lowest-impact flight practices. We reviewed scientific literature on drone flights conducted to approach wildlife and collated and quantified references to factors that should be considered in the development of guidelines and policies. The most referenced controllable factors were approach distance, noise emissions and airspeed. Other frequently referenced controllable factors included drone type, take-off distance, flight pattern, pilot experience and competence, whether consecutive flights were conducted and flight duration. The most referenced environmental factors were animal taxa, biological state of animals and ambient noise, followed by whether conspecifics are present, weather variables, habitat variables, whether animals have received previous exposure to anthropogenic settings, animals’ behaviour prior to drone flights and whether predators are present. Policies and protocols that address these factors have an increased probability of minimising disturbance of drone flights. The variability in animal responses across different taxa, different ways drone flights are performed and the different circumstances they are deployed in highlights the need for taxa-specific protocols that also account for geographical and biological variations.
Article
The disposal of whale carcasses in beach burials has raised perceptions of shark attraction to the adjacent water. Understanding the concerns and perceptions of the community is key to creating sound management practices and educational resources. We surveyed community perception of the disposal of whale carcasses and the factors influencing public opinion. Overall, the community underestimated carcass disposal costs, and considered nonviable methods (oceanic tow and carcass recycling) as their preferred options. Responses were divided into two groups: (1) those previously aware of this management issue, and (2) those unaware. The ‘aware’ group had polarised opinions with strong opinions about the safety of beach burial and its influence on shark attraction. The source of information for respondents drove perceptions with personal opinion being the highest, followed by media, perceived natural processes, and research in the aware group. Expert opinion, and common management practice were the lowest ranked information sources suggesting a lack of access to reliable information, or a disconnect between experts and the external community. Surprisingly, 27.8% of respondents would not change their opinion based on research, emphasising the complexity of the issue and of the relationship between managers and the public. This information will assist managers in the creation of comprehensive management practices, educational resources, communication of facts, and reduction of misconceptions around the disposal of whale carcasses.
Full-text available
Article
The food habits and predatory interactions of Alligator mississippiensis (Ameri-can Alligator) have been thoroughly studied within populations inhabiting inland freshwater ecosystems; however, it is increasingly evident that coastal populations habitually forage in estuarine and nearshore marine ecosystems inhabited by other top predators. While few studies have been performed, data reported thus far from marine-foraging populations indicate individuals chiefly consume small-bodied prey such as crustaceans, fish, and wading birds. Nonetheless, capture and consumption of large-bodied marine prey such as multiple species of sea turtles and a single species of Elasmobranchii (sharks and rays) have been documented. Here, we examine evidence regarding reciprocal intraguild predation between American Alligators and elasmobranchs. We provide the first evidence of American Alligator depredation of 4 Elasmobranchii species and review putative evidence for Elas-mobranchii depredation of American Alligators. We discuss the ecological significance of these interactions, draw comparisons to similar interactions experienced by other crocodil-ians, and recommend further avenues for research on the subject.
Full-text available
Article
Background Human food subsidies can provide predictable food sources in large quantities for wildlife species worldwide. In the boreal forest of Fennoscandia, gut piles from moose (Alces alces) harvest provide a potentially important food source for a range of opportunistically scavenging predators. Increased populations of predators can negatively affect threatened or important game species. As a response to this, restrictions on field dressing of moose are under consideration in parts of Norway. However, there is a lack of research to how this resource is utilized. In this study, we used camera-trap data from 50 gut piles during 1043 monitoring days. We estimated depletion of gut piles separately for parts with high and low energy content, and used these results to scale up gut pile density in the study area. We identified scavenger species and analyzed the influences of gut pile quality and density on scavenging behavior of mammals and corvids (family Corvidae). Results Main scavengers were corvids and red fox (Vulpes vulpes). Parts with high energy content were rapidly consumed, mainly by corvids that were present at all gut piles shortly after the remains were left at the kill site. Corvid presence declined with days since harvest, reflecting reduction in gut pile quality over time independent of gut pile density. Mammals arrived 7–8 days later at the gut piles than corvids, and their presence depended only on gut pile density with a peak at intermediate densities. The decline at high gut pile densities suggest a saturation effect, which could explain accumulation of gut pile parts with low energy content. Conclusions This study shows that remains from moose harvest can potentially be an important food resource for scavengers, as it was utilized to a high degree by many species. This study gives novel insight into how energy content and density of resources affect scavenging patterns among functional groups of scavengers.
Full-text available
Article
Knowledge of the diet and trophic ecology of apex predators is key for the implementation of effective ecosystem as well as species-based management initiatives. Using a combination of stomach content data and stable isotope analysis (δ¹⁵N and δ¹³C) the current study provides information on size-based and sex-specific variations in diet, trophic position (TP) and foraging habitat of tiger sharks (Galeocerdo cuvier) caught in the KwaZulu-Natal Sharks Board bather protection program. This study presents the longest time-series and most detailed analysis of stomach content data for G. cuvier worldwide. Prey identified from 628 non-empty stomachs revealed a size-based shift in diet. Reptiles, birds, mysticetes, and large shark species increased in dietary importance with G. cuvier size, concomitant with a decrease in smaller prey such as batoids and teleosts. Seasonal and decadal shifts in diet driven primarily by changes in the importance of elasmobranchs and mammal (cetacean) prey were recorded for medium sized (150–220 cm) G. cuvier. Both stomach content and stable isotope analysis indicated that G. cuvier is a generalist feeder at the population level. Size-based δ¹³C profiles indicated a movement to offshore foraging habitats by larger G. cuvier. Calculated TP varied by method ranging from 4.0 to 5.0 (TPSCA for stomach contents) and from 3.6 to 4.5 (TPscaled and TPadditive for δ¹⁵N). Large (> 220 cm) G. cuvier did not feed at discrete trophic levels, but rather throughout the food web. These data provide key information on the ecological role of G. cuvier to improve the accuracy of regional food web modelling. This will enable a better understanding of the ecological impacts related to changes in the abundance of this predator.
Full-text available
Article
The ability of predators to switch between hunting and scavenging (facultative scavenging) carries both short-term survival and long-term fitness advantages. However, the mechanistic basis for facultative scavenging remains poorly understood. The co-occurrence of tiger sharks (Galeocerdo cuvier) and green turtles (Chelonia mydas) at Raine Island (Australia), provides an opportunity to examine a top marine predator’s feeding mode in response to seasonal pulses in nesting turtles that offer both hunting and scavenging opportunities. Using satellite telemetry, we evaluated home range overlap between sharks and turtles and quantified their surfacing behavior around Raine Island during the turtle nesting season. We found core home range overlap to be highest during the nesting season. Both sharks and turtles spent significantly more time at the surface in areas of greatest range overlap closest to shore, where turtle density was highest. Both sharks and turtles showed decreased surfacing with increasing distance from Raine Island. Combined with published data on turtle demography at Raine Island, we propose the following: (1) sharks patrol the surface to increase scavenging opportunities on turtle carcasses and intercept weakened individuals after nesting; (2) healthy turtles may not perceive sharks as a major threat and/or other biological factors override anti-predatory responses; and (3) sharks during the nesting season may primarily scavenge on dead turtles individuals rather than actively hunt. Our study results and approach may be applicable to other situations in which direct observations of predator-prey interactions are limited. Significance Statement Every animal encounters dead or dying resources, yet the role of facultative scavenging has been difficult to study, and thus largely overlooked in marine behavioral ecological research. Movement analyses of tiger shark and green turtle movement and surfacing behavior at Raine Island (Australia) suggest that facultative scavenging may be a prevalent, yet underappreciated, feeding strategy in tiger sharks. Our integration of behavioral ecology theory with multi-species electronic tagging provided a valuable approach for investigating predator-prey interactions in situations where direct observations are limited or not possible.
Full-text available
Article
In recent years, exciting scientific evidence has emerged highlighting the ecological importance of dead animals (i.e., carrion) and their consumption (i.e., scavenging), to the point that we could consider this the golden age of scavenging research. We now have a considerable body of theoretical and empirical work that indicates that scavenging is fundamental to properly understanding not only food web, community, and population ecology but also evolution, biodiversity conservation, and human well-being. However, universities fail to integrate scavenging into ecological teaching, as can be judged from the lack of importance of this process in ecology textbooks. We consider this a paramount gap in ecological education, and we advocate that students should be aware of the important role that carrion and scavengers play in ecosystems. Integrating scavenging principles and applications into ecology textbooks will broaden the ecological foundation of the next generation of ecologists.
Full-text available
Article
The estuarine crocodile (Crocodylus porosus) is an apex predator across freshwater, estuarine and coastal environments. The impact of a changing C. porosus population upon the ecosystem is unknown, but due to large ontogenetic changes in body mass (>1000-fold) their impact may be wide reaching and substantial. Here we investigated the relationship between diet, movement and body size in a population of C. porosus inhabiting a tidal river in northern Australia. Subcutaneous acoustic transmitters and fixed underwater receivers were used to determine the activity space and movement patterns of 42 individuals (202–451 cm in total length). There was no size-related spatial partitioning among different sized crocodiles. Large individuals (snout–vent length (SVL): 160 cm < SVL < 188.5 cm) did, however, exhibit a much larger activity space than other size classes. Diet and individual specialization was assessed using the composition of stable carbon (δ13C) and nitrogen (δ15N) isotopes in tissues with different turnover rates. There was a quadratic relationship between body size and δ15N, suggesting that medium-sized individuals (110 cm < SVL < 160 cm) incorporated a greater proportion of high trophic prey into their diets than small (SVL < 110 cm) or large individuals (SVL > 160 cm). Tissue δ13C composition on the other hand was positively correlated with body size, indicating that different size classes were trophically linked to primary producers in different habitats. Individual-level analyses showed that small crocodiles were generalist feeders while medium and large size classes specialized on particular prey items within the food webs they fed. The findings further our understanding of ontogenetic variation in C. porosus diet, and suggest that change in C. porosus population size or demographics may be influential at various levels across the local food web.
Article
This paper describes predation tactics used by the saltwater crocodile (Crocodylus porosus) on flatback (Natator depressus) and olive ridley (Lepidochelys olivacea) sea turtles on nesting beaches in northern Australia. For adult turtles, crocodiles used both a sit-and-wait tactic in which they attacked a turtle at the water's edge after it completed nesting and an active hunting strategy in which crocodiles followed turtle tracks into the dunes to attack turtles at nest sites. Saltwater crocodiles also hunted sea turtle hatchlings in the dunes and excavated a sea turtle nest and consumed the eggs. The protection of saltwater crocodiles in Australia starting in the early 1970s has led to increased population sizes and a greater proportion of larger individuals. This likely has resulted in increased predation rates on sea turtles over several decades, which should be considered as an important mortality component for some tropical nesting aggregations.
Article
Tiger Sharks, Galeocerdo cuvier, are large top-level predators usually solitary as adults. Observation of their scavenging activity on the carcass of a dead whale offered a rare opportunity for better understanding the pattern of intra-specific behaviour within the aggregations of these large predators. In January 2002, the stranding, subsequent death and consumption of a 17.4m total length (TL) blue whale, Balaenoptera musculus, was observed and filmed in Prony Bay, southern New Caledonia. After three weeks of confinement in the bay, the cetacean was killed by adult bullsharks Carcharhinus leucas. The first adult Tiger Shark was subsequently observed around the carcass after 36h. The fat slicks from the carcass attracted further Tiger Sharks which arrived after an additional 24h. The use of photo-identification on video footage collected during four observation sessions over an eight-day period identified 46 individual Tiger Sharks (primarily adult females between 3.3 and 4m TL) participating in the feeding aggregation. Only four animals were identified in two seperate observation sessions (over two consecutive days), suggesting a short-term residency pattern of several hours (<36h) around the carcass. As the arrival time of Tiger Sharks to the carcass differed, most arrivals of a new participant were followed by a frenzied period of intense intra-specific interaction. Different biting and agonistic behaviours were demonstrated by the Tiger Sharks on the carcass, including three new behaviours previously undescribed for this species. Size and level of aggressiveness appeared to be the determining factors of dominance amongst Tiger Sharks. These observations and analysis demonstrate that systematic study of feeding aggregations supported by photo-identification could contribute to knowledge of large shark ecology when coupled with capture-recapture, genetic fingerprinting and tagging techniques.