MARINE MAMMAL SCIENCE, 33(3): 934–945 (July 2017)
©2017 Society for Marine Mammalogy
Complex prey handling of octopus by bottlenose dolphins
KATE R. SPROGIS,
Murdoch University Cetacean Research Unit, School of Veterinary and
Life Sciences, Murdoch University, Perth, Western Australia 6150, Australia; HOLLY C.
Murdoch University Cetacean Research Unit, School of Veterinary and Life
Sciences, Murdoch University, Perth, Western Australia 6150, Australia and Marine Science
Program, Department of Parks and Wildlife, Perth, Western Australia 6151, Australia;
DAVID HOCKING,School of Biological Sciences, Monash University, Melbourne, Victoria
3800, Australia; LARS BEJDER,Murdoch University Cetacean Research Unit, School of
Veterinary and Life Sciences, Murdoch University, Perth, Western Australia 6150, Australia.
Marine predators use prey handling behaviors that are best suited to the proper-
ties (e.g., size, shape, and texture) of the prey species being targeted (Hocking
et al. 2016, 2017). Predators that target large prey species that cannot be swal-
lowed whole are required to process prey extensively before consumption (either
breaking it into smaller pieces or softening it). For example, crocodiles and alliga-
tors perform a spinning “death roll” to dismember large prey items (Fish et al.
2007). Leopard seals (Hydrurga leptonyx) thrash sea birds and seal pups to break
them into edible pieces (Edwards et al. 2010). Australian fur seals (Arctocephalus
pusillus doriferus) shake and toss large ﬁsh and cephalopods before consumption
(Hocking et al. 2016). Similarly, for toothed whales, if prey items are too large to
swallow whole they also need to spend time processing prey. For example, killer
whales (Orcinus orca) shake sea lions and beluga whales (Delphinapterus leucas)
(Lopez and Lopez 1985, Frost et al. 1992), and toss dusky dolphins (Lagenor-
hynchus obscurus) and stingrays into the air (Constantine et al. 1998, Visser 1999).
Bottlenose dolphins (Tursiops spp.) shake and toss ﬁsh to break them into smaller
pieces and to soften them for ease of consumption (W€ursig and W€ursig 1979,
Shane 1990). Bottlenose dolphins also use complex prey handling to break giant
cuttleﬁsh (Sepia apama) into manageable pieces, using a sequence of steps to
remove the head, ink, and cuttlebone before the ﬂesh of the mantle is consumed
Corresponding author (e-mail: email@example.com).
(Finn et al. 2009, Smith and Sprogis 2016). Prey handling behaviors vary among
species and locations and are inﬂuenced by the availability of prey species.
Within a population, foraging for speciﬁc prey may be linked with ecological vari-
ables, age- and/or sex, and/or be socially learned from conspeciﬁcs (Weiss 2006, Sar-
geant et al. 2007, Torres and Read 2009, Patterson et al. 2016). For example, in
Shark Bay, Western Australia, “sponging” is a solitary foraging specialization where
predominantly adult female bottlenose dolphins (T. aduncus)useamarinespongeon
their rostrum as a protective tool to probe the seaﬂoor to feed on burrowing ﬁsh (Pat-
terson and Mann 2011). Sponging is linked to speciﬁc environments, being mainly
employed in deep-water channels (>10 m) where conical marine sponges occur (Sar-
geant et al. 2007, Tyne et al. 2012). This foraging tactic is also vertically transmitted
from mother to female offspring (Kr€utzen et al. 2005), and requires an extensive
period of exposure to promote calf learning (Mann et al. 2008). Similarly to foraging
tactics, prey handling behaviors may also be linked to ecological variables, be
age/sex-speciﬁc, or socially learned from conspeciﬁcs.
In this study, we describe the complex prey handling behavior of benthic octopus
by T. aduncus in southwestern Australia. We investigate whether this behavior is (1)
associated with speciﬁc ecological variables, (2) is age- or sex-speciﬁc, and (3) is a
socially learned behavior.
The study region encompassed a 540 km
area in the temperate waters off Bunbury
(33°320S, 115°630E), Western Australia. Water depth ranged from <1 m in estuarine
waters and up to 24 m in open coastal waters. Data were collected year-round from
March 2007 to August 2013, and ﬁeld methods were the same as for Sprogis et al.
(2016b). Boat-based, photographic-identiﬁcation surveys of dolphins were conducted
along systematic line transects. Once dolphins were sighted, a dolphin group encoun-
ter began and photographs were taken of dolphin dorsal ﬁns for identiﬁcation pur-
poses (W€ursig and W€ursig 1977). The Global Positioning System (GPS) location,
depth, water temperature, turbidity (secchi depth), and dolphin group size were
recorded. During the ﬁrst ﬁve minutes, the predominant group behavioral state (the
behavioral state that >50% of the group was engaged in) was recorded (i.e., foraging,
feeding, resting, socializing, travelling). During encounters, photographs of dolphins
handling octopus at the surface were taken and details were recorded (time, number
of tosses, and dolphin identiﬁcation). Data were available on individual dolphins (in-
cluding sex and age class) from a long-term research program focused on the Bunbury
dolphin population (Smith et al. 2013, 2016; Sprogis et al. 2016a,b).
To explore if there was a relationship between octopus handling events and habitat
type, a benthic habitat map was created following Sprogis (2015). High-resolution
satellite imagery was validated via 185 validation points following the drop-down
camera methods described in Tyne et al. (2010). Each validation point was rated post
hoc for the percentage of habitat cover following Kohler and Gill (2006). To discrimi-
nate between benthic habitat types, a k-means unsupervised classiﬁcation was con-
ducted and habitats were clustered into eight classes; reef, sand, seagrass, deep waters,
algae/reef, algae/sand, mud/sand, and mud/silt.
We explored whether octopus handling might be a socially transmitted behavior
by quantifying association histories of individual dolphins observed engaging in these
events over a 7 yr period. To test for preferred/avoided associations, association
indices between individuals were calculated to estimate the proportion of time they
were sighted together (Whitehead 2008). Pairs of individuals were assumed to be
associated if they were sighted in the same group. A group wasdeﬁnedasoneormore
dolphins within 100 m of other individuals and behaving similarly (Irvine et al.
1981, Wells et al. 1987). The simple ratio index (SRI, Ginsberg and Young 1992)
was used as we expected each individual to have an equal chance of being identiﬁed.
Association index values range from zero (never sighted together) to one (always
sighted together), and were calculated between (1) dolphins that were observed han-
dling octopus and (2) dolphins observed handling octopus with dolphins that were
not observed with octopus.
We tested for preferred/avoided associations using permutation analyses, where
the data were randomized multiple times (two-sided signiﬁcance level =0.05,
Bejder et al. 1998, Whitehead et al. 2005). Analyses were run using SOCPROG
2.7 (Whitehead 2009) and only included dolphins that were sighted ≥5occasions.
The sampling period was set to ﬁve days, which was based on the mean number
of days needed to complete all transects in the main study area to optimize equal
probability of encountering individual dolphins (Sprogis et al. 2016a). To test
whether the observed data differed signiﬁcantly from random, we determined the
number of permutations required to obtain an accurate P-value by increasing the
number of permutations (maximum 20,000) until the P-value stabilized (Bejder
et al. 1998), with 1,000–5,000 trials per permutation. To examine the strength of
associations between individual dolphins we compared the SRI values against the
randomly generated values. For long-term associations (between sampling periods)
the null hypothesis was rejected if the standard deviation (SD) and coefﬁcient of
variation (CV) of the observed SRI value was signiﬁcantly higher (P<0.05) than
the SD and CV of the randomly permuted data (Whitehead et al. 2005, White-
Our study resulted in 587 surveys completed with homogenous sampling effort
across seasons (Table S1), with 177 surveys conducted within bay and estuarine
waters and 410 surveys in open coastal waters (Table S2). A total of 1,567 dolphin
groups were sighted and photographed (Table S1). We observed 45 octopus handling
events, with 33 of these observed while on survey effort. Handling events occurred
during separate group encounters, apart from one group encounter where three differ-
ent individuals in the same group were observed handling octopus.
Dolphins were observed handling octopus using two different methods (Fig. 1,
Movie S1, Fig. S1). The ﬁrst method (shake) involved dolphins arching and rotating
their body out of the water, while holding the octopus in the jaws and forcefully hit-
ting it onto the surface of the water (Fig. 1d, Movie S1). The second method (toss)
involved the dolphins also raising their head and/or body out of the water and ﬂick-
ing the octopus out of the water, but instead of keeping their jaws closed, they
opened their mouths so that the octopus was released and tossed into the air, often
travelling over several meters (Fig. 1, Movie S1). The dolphin would subsequently
retrieve the octopus and continue to shake and toss it at the surface (commonly 10–
15 times). In some cases, a “shake” became a “toss” if the prey item tore and frag-
mented during the shake, and hence was then thrown across the water rather than
being hit onto the water’s surface.
The observed octopus handling events lasted from <1 min to >6min.Insome
instances, octopus handling had already commenced when dolphins were sighted, so
these are considered minimum durations for dolphins to process octopus. No observa-
tions were made underwater; therefore, it was not possible to determine whether any
processing occurred below the surface. Generally, the head and the mantle of the
octopus was removed prior to our observations, making it difﬁcult to identify octopus
to the species level. We were not able to retrieve any octopus parts during sightings
for species veriﬁcation.
936 MARINE MAMMAL SCIENCE, VOL. 33, NO. 3, 2017
Octopus handling events occurred throughout all seasons (Poisson generalized lin-
ear model, P=0.05), with the majority of sightings in winter and spring (Fig. 2).
Events took place in water temperatures ranging from 14.4°C to 23.3°C(x=18.4°C
0.47 SE, Fig. 2). Sightings were in water depths between 0.8 m and 14.7 m
(x=9.09 m 0.66 SE) and in waters with a turbidity ranging from 0.8 to 10 m
(x=3.30 m 0.38 SE). Events took place predominantly over sand, algae/sand, and
mud/silt habitats (33.3%, 21.2%, 21.2%, respectively; Fig. 3).
Of the 33 octopus handling events observed while on survey, six dolphins were
unable to be identiﬁed and 26 were known from our photo-identiﬁcation catalogue
(with one individual observed handling octopus on two occasions). Of these known
Figure 1. A sequence of an octopus handling event by an adult male bottlenose dolphin off
Bunbury, Western Australia. This event lasted for approximately 5 min, with 12 octopus
shakes and/or tosses observed. Each row (a–f) represents consecutive actions, displaying exam-
ples of the different types of handling methods: shaking (d) and tossing (a, b, c, e, f).
dolphins, 20 were adults, 4 were juveniles, and 2 were calves. Sex was determined for
14 females and 4 males, while 8 animals were of unknown sex. The mean group size
of all encountered dolphin groups was 5.98 (0.14 SD, range 1–45 dolphins,
Table S1). For foraging and feeding groups, mean group size was 4.38 (4.41 SD) and
4.82 (7.09 SD), respectively (Table S3). For octopus handling events, the mean group
size was 9.55 (9.55 SD, range =1–36 dolphins). Octopus handling was observed in
conjunction with all group behavioral activities, with traveling and feeding groups
the most likely groups to observe a dolphin handling octopus (30.3% and 27.3% of
the events, respectively).
Of the 26 dolphins identiﬁed handling octopus, 25 were sighted on ﬁve or more
occasions and were used in the permutation analyses. Over the long-term (between
sampling periods), there was indication of long-term preferred associations between
dolphins that handled octopus, as both the observed SD and CV of the SRI were
signiﬁcantly higher than the randomized SD (observed =0.052, randomized =
0.048, P=<0.0001) and CV (observed =1.605, randomized =1.500, P=0.0001),
with 8 pairs among 25 dolphins (dyadic P>0.97).
Associations were tested between the 25 dolphins handling octopus and the
remaining 280 dolphins in the population that met the threshold of ﬁve or more
occasions. For long-term associations, both the observed SD and CV of the SRI were
signiﬁcantly higher than the randomized SD (observed =0.049, randomized =
0.042, P=0.0001) and CV (observed =2.404, randomized =2.110, P=<0.0001),
indicating the occurrence of preferred (189 pairs, dyadic P>0.975) and avoided asso-
ciations (50 pairs, dyadic P<0.025).
The behavior of octopus handling (shaking and tossing) is previously undescribed.
We suggest that T. aduncus shake octopus forcefully onto the water’s surface and toss
octopus several meters into the air multiple times to (1) remove the octopus head and
mantle, (2) tenderize and ensure the arms are inactive, and (3) break the octopus into
smaller pieces for easier consumption. We documented that octopus handling behav-
ior (1) was a seasonal occurrence, peaking during winter and spring in water
Figure 2. The cumulative number of octopus handling events (gray bars, n=33) and the
mean sea surface temperature (black dots) during each austral season between Autumn 2007
and Spring 2013. Continuity between dots is not implied.
938 MARINE MAMMAL SCIENCE, VOL. 33, NO. 3, 2017
temperatures around 18°C, (2) was most prevalent among adult females, and (3) was
conducted by dolphins that showed a close association with other dolphins that han-
Figure 3. Locations of octopus handling events (black circles, n=33) by Indo-Paciﬁc bot-
tlenose dolphins off Bunbury, Western Australia, over benthic habitat consisting of sand,
algae/sand, and mud/silt, and seagrass.
Octopus can be difﬁcult for dolphins to handle (see dos Santos and Lacerda 1987,
Orbach and Kirchner 2014), and in our study area dolphins were required to arch
their head and/or body out of the water in order to shake or toss octopus clear of the
water. As a result, this handling method involves a large body movement that is
likely energetically expensive. Although more energetically demanding, this complex
prey handling behavior allows dolphins to process large prey type that may be risky
to consume without processing (dos Santos and Lacerda 1987).
It is apparent that octopus handling is a risky behavior, as within our study area a
known adult male stranded and a necropsy conﬁrmed the cause of death was from
suffocation from a large 2.1 kg octopus.
The dolphin had attempted to swallow the
octopus, however, the octopus was found almost intact, with the head and the mantle
of the octopus in the dolphin’s stomach and the 1.3 m long arms separated from the
head and extending out of its mouth.
Similarly, another T. aduncus died from sus-
pected asphyxiation due to an octopus lodged in its mouth and pharynx approxi-
mately 140 km north of our study area (Shoalwater Bay Islands Marine Park).
these two cases, the dolphins may not have processed the octopus sufﬁciently by shak-
ing and tossing it to ensure the arm’s reﬂex withdrawal responses were inactive. Octo-
pus arms have a defensive response, as their receptors can detect stimuli that cause
damage to their tissues (Hague et al. 2013). These receptors allow octopus arms to
continue reacting even after the arms have been detached from the head, allowing the
arms to coordinate a reﬂex withdrawal response (Hague et al. 2013). Dolphins must
therefore process the octopus sufﬁciently to reduce the arms reﬂex withdrawal
response and limit their suckers adhering to them, which otherwise would make
them difﬁcult to swallow.
The species of octopus that the dolphin suffocated on in Bunbury was identiﬁed as
the benthic-dwelling Maori octopus (Macroctopus maorum).
This octopus is robust
and muscular, and is the largest octopus found in Australasia weighing >10 kg with
an arm span of over 3 m (Norman 1999, Norman and Reid 2000). It occurs over soft
sediment and reefs where it occupies rocky lairs (Anderson 1999, Norman and Reid
2000). Other octopus species found within the study area are the common Perth octo-
pus (Octopus (cf.) tetricus) and the velvet octopus (Grimpella thaumastocheir).
mon Perth octopus is medium sized (mean 4 kg; Joll 1976) and inhabits rocky reefs,
seagrass meadows and sandy substrates (Hart et al. 2016). The velvet octopus is a
smaller species that has an arm span <60 cm (Norman and Reid 2000) and has been
caught in traps in Bunbury inner waters (McCluskey et al. 2016). Due to the larger
size of octopus observed during feeding events, dolphins off Bunbury are most likely
handling the Maori and common Perth octopus.
Octopus handling events occurred more often during winter and spring when the
water temperature reached approximately 18°C (Fig. 2). Although the ecology of the
Maori octopus is poorly understood in Western Australia, in New Zealand the mat-
ing period for this octopus is in spring with the optimal water temperature for eggs
to hatch at 18°C (Anderson 1999). Similarly, the optimal water temperature for the
eggs of the common Perth octopus to hatch is under 22°C(Hartet al. 2016). How-
ever, the common Perth octopus has no distinct mating period and they are able to
Unpublished data, Nahiid Stephens, veterinary pathologist, Murdoch University Cetacean Research
Unit, School of Veterinary and Life Sciences, Murdoch University, Perth, Western Australia, Australia.
Personal communication from Douglas Coughran, Department of Parks and Wildlife, Perth,
Australia. 2 September 2015.
Personal communication from Stephen Leporati, SCS Global Services, 19 October 2015.
940 MARINE MAMMAL SCIENCE, VOL. 33, NO. 3, 2017
spawn throughout the year (Hart et al. 2016). Octopus are semelparous, once
males mate and females brood their eggs they become senescent until their death
(Anderson et al. 2002). Senescence occurs for approximately one month, during
which octopus have uncoordinated movements, suboptimal camouﬂage abilities
and a deteriorating physical condition. Senescence may put octopus in a compro-
mised state, increasing their risk of predation (Anderson et al. 2002). As such, it
is likely that the opportunity for dolphins to capture octopus is increased in win-
ter and spring.
Octopus handling events occurred, on average, in 9 m depth and in turbid (x=
3.30 m) waters, predominantly over sand, algae/sand, and mud/silt habitat types. As
benthic habitat type in Bunbury is highly heterogeneous it was difﬁcult to determine
exactly which habitat octopus were captured from. Furthermore, the octopus species
found off Bunbury occur over a range of habitats, therefore the capture of octopus
appears to be opportunistic over various habitats.
The majority of dolphins handling octopus were adults (20 of the 26 identiﬁed
dolphins), suggesting that there may be differences in physical abilities and/or learn-
ing experiences between adults and juveniles/calves. Similarly, in the case of foraging
tactics, bottlenose dolphins generally show differences between ages, which may
reﬂect energy requirements throughout life history stages and/or reﬂect a required
learning period (Patterson et al. 2016). In addition, of the adults observed handling
octopus (n=20), 60% were female and 20% were male (20% unknown sex). Thus,
adult females were the most prevalent age-sex class to handle octopus, however, more
data are needed to conﬁrm that this sex-speciﬁc ﬁnding is not an artefact of females
having smaller home ranges (Sprogis et al. 2016b), and therefore being observed more
frequently throughout the year than males (Sprogis et al. 2016a).
Group size for octopus handling events was nearly twice the average group size for
feeding and foraging groups. Bottlenose dolphins are known to be a highly social
species (Connor et al. 2000), and in our study area adult females display low-level
associations among a large number of females and these associations re-form season-
ally (Smith et al. 2016). Adult males exhibit strong bonds with other adult males
(Sprogis et al. 2016a). Given their social nature, we explored whether there were pre-
ferred associations between dolphins observed handling octopus. There was evidence
of long-term preferred associations between dolphins handling octopus, however,
similar long-term preferred associations were also evident between dolphins with
octopus and dolphins never sighted predating on octopus. These initial ﬁndings are
not surprising given the strong social bonds that exist in this dolphin population.
Further information on the number of different dolphins that handle octopus is
needed to determine if octopus handling is indeed a socially learned behavior.
Off Bunbury, stomach content analyses of stranded dolphins (n=13) identiﬁed
squid beaks (n=6 of 10 that had prey parts), however octopus beaks were not
As the head of the octopuses were already removed during several of our
observations the heads may not have always been consumed, thus the beaks would
not be found in stomach contents. Therefore, the importance of octopus in the diet of
the Bunbury dolphin population remains unknown. However, octopuses, like other
cephalopods, are a source of high protein content and are common in the diet of
toothed whales (Clarke 1996, Santos et al. 2001a). From stomach content analysis,
Unpublished data, Shannon McCluskey, Ph.D. candidate, Murdoch University Cetacean Research
Unit, School of Veterinary and Life Sciences, Murdoch University, Perth, Western Australia, Australia.
benthic octopus are found in the diet of Tursiops spp.off the Spencer Gulf, Australia
(Gibbs et al. 2011), Brazil (dos Santos and Haimovici 2001), Hong Kong (Barros
et al. 2000), South Africa (Cockcroft and Ross 1990), Scotland (Santos et al. 2001b),
Ireland (Hernandez-Milian et al. 2015), and the Mediterranean Sea (Miokovic et al.
1999, Blanco et al. 2001, Pedaet al. 2015). Evolution of novel methods for process-
ing cephalopods could therefore have an important inﬂuence on the success of ceta-
cean species targeting these prey types.
This research complements the limited studies demonstrating that bottlenose dol-
phins carry out complex handling of prey. Octopus handling is a highly risky behav-
ior for bottlenose dolphins, especially if processing is not executed correctly. For an
animal to engage in such a risky behavior, the nutritional value of the prey must be
substantial. Hence, while octopus handling appears to be relatively rare in the popu-
lation, this prey and handling behavior might still be of great importance for dol-
phins, especially during periods when alternate prey may be limited.
Thank you to S. Leporati and F. Brice~no for discussions on octopus and assistance in species
identiﬁcation. We thank our research assistants and S. McCluskey, M. Cannon, D. Chabanne,
V. Buchanan, and K. Nicholson, who participated with ﬁeldwork and data processing. Thanks
to S. Allen, J. Symons, D. Harvey, and F. Harvey for off-survey effort octopus handling
records. We thank the partners of the South West Marine Research Program for ﬁnancial sup-
port: Bemax Cable Sands, BHP Billiton Worsley Alumina Ltd, Bunbury Dolphin Discovery
Centre, Bunbury Port Authority, City of Bunbury, Cristal Mining, the Western Australian
Department of Parks and Wildlife, Iluka, Millard Marine, Naturaliste Charters, Newmont
Boddington Gold, South West Development Commission, and WA Plantation Resources. All
research was approved and permitted through the Department of Parks and Wildlife
(SF005811, SF007986, SF008624) and Murdoch University’s Animal Ethics Committee
(W2009/06, W2342/10). KS conceived the study. KS and HR carried out the ﬁeld research
and analyses. LB conceived and obtained funding for the long-term research program. DH
assisted with video and photo analysis. KS wrote the paper with input from DH, LB, and HR.
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Received: 14 November 2016
Accepted: 8 February 2017
The following supporting information is available for this article online at http://
Table S1. Survey effort pooled by austral season from March 2007 to August 2013,
including the number of on-effort sightings and average end group size (standard
Table S2. Summary of annual survey effort by transect location from March 2007
to August 2013.
Table S3. Mean dolphin group size (standard deviation) for each of the behavioral
Figure S1. Octopus tossing and shaking; row (a) an adult male dolphin tossing octo-
pus and leaping out of the water with the octopus still in its mouth, and row (b) an
adult female dolphin with a large shark bite on her left side (bottom left image) arch-
ing her body to shake octopus.
Movie S1. An octopus handling event by an adult male Indo-Paciﬁc bottlenose dol-
phin off Bunbury, Western Australia, showing the different types of handling meth-
ods (shake and toss) used to process the octopus for easier consumption.