Journal of Threatened Taxa |
www.threatenedtaxa.org | 26 September 2020 | 12(13): 16742–16751
ISSN 0974-7907 (Online) | ISSN 0974-7893
(Print)
doi: https://doi.org/10.11609/jott.5006.12.13.16742-16751
#5006 | Received 14 April 2019 | Final
received 06 September 2020 | Finally accepted 13 September 2020
Killer Whale Orcinus
orca (Linnaeus, 1758) (Mammalia: Cetartiodactyla:
Delphinidae) predation on Sperm Whales Physeter macrocephalus Linnaeus,
1758 (Mammalia: Cetartiodactyla: Physeteridae)
in the Gulf of Mannar, Sri Lanka
Ranil P. Nanayakkara
1, Andrew Sutton 2,
Philip Hoare 3 & Thomas A. Jefferson 4
¹ Biodiversity Education And
Research (BEAR), 92/2, Ananda Rajakaruna Mawatha,
Colombo 10, Sri Lanka.
¹ Department of Zoology,
University of Kelaniya, Kelaniya, Sri Lanka.
¹ IUCN/SSC Sirenia
Specialist Group
2 291, Portobello Road, London,
W10 5TD, UK.
3 Department of Humanities,
University of Southampton, UK.
4 Clymene Enterprises, Lakeside, CA
92040, USA.
1 ranil_n@hotmail.com
(corresponding author), 2 drew@eco2.com, 3 philipwhale1@icloud.com,
4 sclymene@aol.com
Editor: E. Vivekanandan,
Central Marine Fisheries Research Institute, Chennai, India. Date
of publication: 26 September 2020 (online & print)
Citation: Nanayakkara,R.P., A. Sutton, P. Hoare & T.A.
Jefferson (2020). Killer Whale Orcinus
orca (Linnaeus, 1758) (Mammalia: Cetartiodactyla:
Delphinidae) predation on Sperm Whales Physeter macrocephalus Linnaeus,
1758 (Mammalia: Cetartiodactyla: Physeteridae)
in the Gulf of Mannar, Sri Lanka. Journal of Threatened Taxa 12(11): 16742–16751. https://doi.org/10.11609/jott.5006.12.13.16742-16751
Copyright: © Nanayakkara
et al. 2020. Creative Commons Attribution
4.0 International License. JoTT allows unrestricted use, reproduction, and
distribution of this article in any medium by providing adequate credit to the
author(s) and the source of publication.
Funding: Biodiversity Education
And Research (BEAR).
Competing interests: The authors
declare no competing interests.
Author details: Ranil P. Nanayakkara is a conservation biologist, who
has been working with terrestrial and marine mammals for over 20 years. He is
the founder of Biodiversity Education And Research (BEAR). He is a member of
the IUCN/SSC Sirenia Specilaist
Group. His main interest are investigating the ecology and biogeography of
terrestrial and marine mammals. Andrew Sutton, filmmaker, photographer
naturalist founder of ECO2 marine and Eco2 marine research, southern Tanzania.
Creator of HYPERLINK
“http://www.grindahvalur.org/english.html”Grindhvalur
film highlighting the plight of pilot whales in The Faroe islands. Philip Hoare’s books include Leviathan
or, The Whale and RISINGTIDEFALLINGSTAR.
He is associate professor of English at the University of Southampton,
and co-curator http://ofwww.ancientmarinerbigread.com/ and
www.mobydickbigread.com. Dr. Thomas A. Jefferson has been
studying marine mammals since 1983, when he was an undergraduate at the
University of California, Santa Cruz. His Master’s degree is from Moss Landing
Marine Laboratories, and his PhD is from Texas A&M University. He is Director of Clymene Enterprises and an
independent researcher as the Southwest Fisheries Science Center, NOAA Fisheries,
where his main interests are the development of marine mammal identification
aids, and investigating the systematics and population ecology of the more
poorly-known species of dolphins and porpoises. Most of his work has been
related to conservation and management of marine mammals threatened by human
activities.
Author contribution: RN–conceptualisation,
research design, data collection, data analysis, drafting manuscript,
interpretation; TJ–critical review, edit, research design; AS–data collection
& review draft; PH–data collection & review draft.
Acknowledgements: We would like to thank Mr. H.D. Rathnayake (Director), Mr. Dharmathilake,
Dr. Lakshman Pieris, Mr. Manjula Morathenne
and and the staff of the Department of Wildlife
Conservation for all their help both in and out off the field. We thank the Sri Lankan Navy personnel and
the coastal villagers for their support and help at all times. We are grateful to Mr. B.A.Y.B. Jayawardana for preparing the map. Lastly, we are indebted to the anonymous
reviewers and subject editor for their rigorous reviews and edits.
Abstract: To date in Sri Lankan waters,
there has been limited research on Killer Whales. These animals have been recorded almost all
around the island, except in the northernmost waters and in Palk Bay. The highest observed concentrations are from
the northeastern, south/southwestern and northwestern coastal waters of Sri Lanka. These have come from both opportunistic
observations and dedicated scientific surveys.
Seasonal trends in sightings in some locations suggest fairly consistent
occupancy. Transient Killer Whales have
been documented attacking/killing Sperm Whales from many geographic locations
around the world. To date, there is only
one published account of Killer Whales feeding in Sri Lankan waters. Our paper presents, for the first time, field
observations of Killer Whales preying upon superpods
of Sperm Whales in the waters off the Kalpitiya
Peninsula (eastern half of the Gulf of Mannar), northwestern Sri Lanka.
The incidents took place on two separate occasions during the months of
March and April, 2017.
Keywords: Dolphin, feeding, Kalpitiya Penninsula, marine
mammal, observations.
Introduction
The Killer Whale Orcinus
orca is an Odonocete belonging to the family Delphinidae (Oceanic dolphins) and is the largest member of
the family. Killer Whales are found in
all oceans (Forney & Wade 2006).
They range from polar ice edges to the tropics and from the shoreline to
the open oceans. Their abundance is
highest in temperate and polar waters (Forney & Wade 2006). Killer Whales are the dominant oceanic
predator, with a varied diet, including cephalopods, bony fish, sharks,
seabirds, marine turtles, and a variety of marine mammals (Jefferson et al.
1991; Dahlheim & Heyning
1999; Ford & Ellis 1999; Ford 2017).
Prey specialization of Killer Whale communities
depends on the ‘type’ they belong to; currently there are three recognized
types in the North Pacific: (i) resident, (ii)
transient, and (iii) offshore Killer Whales (Ford 2017). Out of the three types, the transients are
specialised marine mammal hunters with the occasional bird or cephalopod taken,
whereas the other two types appear to feed almost exclusively on fish and
invertebrates (Ford 2017), to date only the transient type has been recorded in
Sri Lankan waters. Killer Whale
predation on marine mammals has been documented from localities around the
world (Jefferson et al. 1991). Long-term
research in the northeastern Pacific has given us
most of our understanding of mammal hunting by Killer Whales. Pinniped and dolphin predation by Killer
Whales is reasonably well documented (see Dahlheim
& White 2010, for example), but scientific reports of them hunting the
great whales are less common (Jefferson et al. 1991; Reeves et al. 2006;
Gemmell et al. 2015).
In Sri Lankan waters, there has been limited research
on Killer Whales. These animals have
been recorded almost all around the island, except in the northernmost waters
and in Palk Bay (Illangakoon 2011; Martenstyn 2013).
The highest observed concentrations are from the northeastern,
south/southwestern, and northwestern coastal waters
of Sri Lanka. These have come from both
opportunistic observations and dedicated scientific surveys. Seasonal trends in sightings in some
locations suggest fairly consistent occupancy (Ranil
P. Nanayakkara 2010, 2011, 2015, 2016, 2017,
2018). Most sighting data so far,
however, have been collected during whale-watching trips, Sri Lanka Coast Guard
records and from fisher folk; none of these can be considered scientifically
rigorous.
Transient Killer Whales have been documented
attacking/killing Sperm Whales from many geographic locations around the world
(Pitman et al. 2001). To date, there is
only one published account of Killer Whales feeding in Sri Lankan waters. Gemmell et al. (2015) observed Killer Whales
off southwestern Sri Lanka (Mirissa) preying on a mesoplodont beaked whale and Sperm Whales. The latter incident coincided with the egress
of the migration (leaving) of Sperm Whales from the Gulf of Mannar. In the same paper, there is a report of a
Blue Whale Balaenoptera musculus that
bore scars from an attack by Killer Whales.
Our paper presents, for the first time, field observations of Killer
Whales preying upon superpods of Sperm Whales in the
waters off the Kalpitiya Peninsula (eastern half of
the Gulf of Mannar), northwestern
Sri Lanka. The incidents took place on
two separate occasions during the months of March and April 2017.
Methods
Study Site
The Gulf of Mannar is an
inlet of the Indian Ocean that lies between southeastern
India and western/ northwestern Sri Lanka (Image
1). Observations were made from a 19ft
fibreglass boat fitted with a 40BHP outboard motor, dedicated to cetacean
research during the months of March and April 2017; this period coincides with
large mating aggregations of Sperm Whales in the eastern half of the Gulf of Mannar. The vessel
departed Kandakuliya fishing harbour (6:45h),
northwest, Sri Lanka, and headed offshore, approximately 15nm in a westerly
direction in a zig-zag manner. The
survey was dedicated to the study of large aggregations of Sperm Whales in the
eastern Gulf of Mannar.
For each encounter, we attempted to photograph all the
Killer Whales present using DSLR cameras with telephoto zoom lenses following
established protocols for photo-identification studies of cetaceans (Ford 2017;
Barrett-Lennard 2011). Individual
animals were identified by a combination of features including notches of the
dorsal fin and fin shape, as well as differences in the eye patch and saddle
patch pigmentation and shape.
Furthermore, for each encounter we used a GoPro Hero 6 underwater camera
to record the underwater activities <https://vimeo.com/227727434>. Additionally, we used a SQ26-08 (Cetacean
Research Technology) hydrophone to record the codas, clicks of the Sperm Whales
and Killer Whales.
Observation 1: 18 March 2017
The research team followed and observed a pod of
100–200 Sperm Whales distributed in a radius of about 1–3 km. The sea was calm (Beaufort 1) and the team
could see to the horizon with blows of Sperm Whales scattered around the
research vessel. At around 09.45h, a
group of Sperm Whales broke away from the larger aggregation and started
travelling in a north-easterly direction at great speed (almost porpoising); the breakaway group consisted of the largest
members of the superpod (males), numbering
approximately 15–20 individuals. We
followed the breakaway group for approximately 1nautical mile. The other whales were far behind and widely
spread out. Meanwhile, the breakaway
group slowed down and joined up with a smaller group of Sperm Whales,
consisting of approximately 10 individuals, which was a maternal pod that consisted
of females, sub-adults, and calves. They
reoriented in one great mass, packed as close together as possible (the depth
of the water was 1,068m). We then
noticed a commotion on the water surface just ahead of us; when the vessel
approached, we saw the Sperm Whales huddled in a tight group on the surface,
with the largest individuals occupying the outer margins of the group; they
were arranged laterally, aligned together.
They all appeared agitated. Body
orientation changed haphazardly, respiration became frequent, there was rolling
and tail slapping and the large males kept opening and shutting their jaws
below the surface of the water.
Suddenly, a falcate dorsal fin surfaced approximately
5m from the research vessel. Several
more falcate dorsal fins soon appeared followed by the unmistakable large
triangular dorsal fin of an adult male Killer Whale. It was clear now that the breakaway group had
responded to Sperm Whales who were in danger and had sent out sonar signals. They may have been delegated to deal with the
situation perhaps even to act as a decoy to allow the Sperm Whales they’d left
behind to get away.
The Killer Whales then surfaced again and charged
directly into the Sperm Whale pod, with a female Killer Whale leading the
attack, while the large male remained 10m away from the focus of attack. The Sperm Whales reacted by thrashing their
tails and clustering close together on the surface, with the large mature males
guarding the maternal pod by forming a defensive flotilla facing the attacking
predators. The Killer Whales attack pod,
which comprised approximately 12 individuals including one large male and two
calves, was led by a female (Female 1) with a notch on its dorsal fin (Image
2). Female 1 repeatedly charged at the
Sperm Whales along with five other Killer Whales (Image 3), whilst the
remaining Killer Whales started circling the prey, not letting them get away
(Image 4). The Killer Whales circled
around the Sperm Whales, diving in among them, apparently trying to separate the
smaller juveniles and the calves. The
water at the centre of the Sperm Whales turned white as they started tail
slapping. Two Killer Whales then
suddenly cut into the midst of the Sperm Whales and moved aggressively between
individual Sperm Whales in an apparent attempt to break the pod apart (Image 5
& 6). At times, the attacking Killer
Whales seemed to withdraw from the attack and busily jostle along the outer
edges before resuming the assault. All
the while the large male Killer Whale kept its distance, patrolling the
perimeter. The Killer Whales displayed a
lot of surface behaviour while attacking the Sperm Whales, e.g., tail slapping,
breaching, whilst the members that were not involved in the attack, were seen
rolling as well.
The attack lasted from 10.03h to 11.37h. In the turmoil, two Sperm Whales got
separated from the pod and were immediately pursued by about six Killer Whales,
which swam about 2m from their quarry.
The two separated Sperm Whales managed to re-join the maternal pod when three
large male Sperm Whales rushed to their rescue and came between them and the
attackers. It was evident that the Sperm
Whales were agitated; their faeces stained the water orange (Image 7). As the Killer Whales continued their attack,
the Sperm Whales changed orientation, bringing their heads into the middle,
tails outwards, creating a ‘marguerite’ formation (Nishiwaki
1962). This did not seem to slow the
intensity of the attack, however, so the Sperm Whales reoriented their heads
outward, while maintaining the circle formation, now apparently using our
nearby boat as another line of defence.
The large male Sperm Whales appeared to be trying to shield the females
and young from the attacking Killer Whales, opening and closing their mouths to
show their teeth. By now, blood was
visible in the water. We observed the
predators led by the same adult female (Female 1) take bites out of the male
defenders, mostly from their bellies and tail stock, beneath the surface. Several Sperm Whales bore scars, from bite
marks of the Killer Whales.
After approximately 90 minutes of sustained attack,
the Killer Whales gradually started to peel off and we observed them at a
distance; they were very active, tail slapping, breaching and, at times, spy
hopping. We followed the Killer
Whales. Abruptly, the Killer Whales came
directly at our research vessel and started to circle it. Closer and closer they came, surrounding us
the same way they had surrounded the Sperm Whales. Then one butted our boat; we clearly felt the
impact. As we recorded the incident on
our GoPro camera, five Killer Whales charged directly at our vessel and dove
suddenly just a couple of metres below our boat, passing <1m away from the
hull. This behaviour was similar to the
technique used by Killer Whales in the Antarctic to dislodge seals from ice
floes (Pitman et al. 2001). After this,
the Killer Whales broke off and moved away from us all the while displaying a
lot of surface activity.
Observation 2: 3 April 2017
At 10.00h, a group of about 20 Killer Whales was
observed, comprising all the members of the pod observed on 18 March 2017, as
well as eight new members. This pod was
made up of adult females, two large adult males, sub-adult males/females and
two calves and they were sighted approximately 10nm from shore. The pod was travelling in a northerly
direction with consistent surfacing intervals.
At around 10.20h, the pod suddenly changed direction and started heading
north-east with increasing speed. Our
first sighting of Sperm Whales occurred at 10.45h, about 2nm from the 18 March
location. It is customary for the superpods of Sperm Whales in the Gulf of Mannar to break up into smaller pods of 20–30 individuals
around the end of March (RN unpublished).
The Sperm Whales we encountered on 3 April comprised such a smaller grouping
and consisted of females, young, and five large males.
The Killer Whales started to attack the Sperm Whales
as soon as they encountered them at 10.52h (the depth of the water was
1,021m). Led by the same lead female
(Female 1) (Image 3) we observed during the March 18 encounter, the Killer
Whales commenced by nudging and ramming the adult females, in an attempt to get
at the calves, while swimming abreast of them.
The Sperm Whales responded by swimming rapidly away, with their bodies
almost leaving the water, with the predators in close pursuit. Except for the two male Killer Whales that
stayed about 20m away, all the other Killer Whales repeatedly charged the Sperm
Whale pod from left and right. The Sperm
Whales were swimming abreast with the calves in the middle. At 11.09h we observed at least five
additional Killer Whales appearing to join the attack. The Sperm Whales stopped swimming, and seemed
agitated, with considerable surface activity and splashing. They were defecating as was evident from the
orange-stained water. The large Sperm
Whale males, turned on the Killer Whales, and began to chase them away, the
Killer Whale pod started to swim away at great speed. The whole incident lasted two hours.
Curiously, the attack seemed to be confined to
harassment because we never observed the Killer Whales lunging to bite chunks
from their quarry as we had on 18 March.
No signs of physical injury were noted in the Sperm Whales after the
attack, nor was blood evident. Perhaps
the Killer Whales may have been trying to determine whether there were any
particularly vulnerable individual Sperm Whales to take advantage of or perhaps
the encounter may have constituted practice or play for the juvenile Killer
Whales, which were present in the pod.
Discussion
Sperm Whales are found in Sri Lankan waters year-round
in small pods that mostly number 2–15 individuals (Illangakoon
2002). Between January and April,
however, they start to occur in larger pods to ultimately form superpods numbering 100–450 individuals (https://uk.whales.org/2015/04/01/an-armada-of-whales-wdc-in-sri-lanka/
& https://www.theguardian.com/environment/gallery/2017/mar/29/sex-death-sperm-whales-orcas-indian-ocean-in-pictures). At that time of the year large males are seen
in Sri Lankan waters; these males, denizens of temperate and polar waters,
migrate to tropical waters to mate. Superpods congregate in the eastern half of Gulf of Mannar, northwestern Sri
Lanka. Our observations confirm Gemmell
et al. (2015)’s finding that Killer Whales are predators of Sperm Whales in Sri
Lankan waters. For the first time, we
show that Killer Whales enter Sri Lankan waters and prey on large aggregations
of Sperm Whales.
It was clear that the adult Killer Whales we saw
during both incidents were experienced hunters of Sperm Whales. The attacks were well-coordinated and
efficient. The copious defecation by the
Sperm Whales may well have been occasioned by hyperarousal (Jansen et al. 1995)
because we observed that particular response during both incidents. It was interesting to see the different roles
played by adult female and male Killer Whales (see Pitman et al. 2001). Like in a pride of lions (Rudnai
1974) the adult females led the hunt.
Was the hunting technique a series of lunges at the much-bigger and
potentially dangerous prey, designed to minimize risk for the attacker? No Sperm Whale was observed killed during the
two incidents, as far as we could tell.
Yet we did see chunks being bitten off the quarry during the 18 March
attack and the immediate waters were stained with blood.
The role of the large male in hunting parties of
Killer Whales is unclear. The Heinrichs
video (2013) of a hunt by Killer Whales on Sperm Whales off southwestern Sri
Lanka shows an adult male Killer Whale in the thick of a melee, as attackers
appear to try to drown a juvenile Sperm Whale.
The male is seen actively participating in the attack, even though a
female is leading the pack and inflicting most of the injuries. Interestingly, none of the individuals recorded
from the attacks in north-west of the country match to the ones in the video
nor from the northern Indian Ocean Killer Whale catalogue (Northern Indian
Ocean Killer Whale Alliance (NIOKWA)).
None of the adult Killer Whale males we saw actually attacked Sperm
Whales; their role appeared to be to intimidate, frighten and corral breakaway
quarry. Other accounts of Killer Whale
attacks show adult males adopting aggressive, peripheral or passive roles
(Whitehead & Glass 1985; Arnbom et al. 1987;
Silber et al. 1990). Vidal & Pechter (1989) asserted that predation on large whales by
Killer Whales is successful when adult males are involved in the attack, and
that attacks on large whales involving only females and subadults are largely
unsuccessful. Estes et al. (2006),
mentioned that some specialization of roles have been noted in Killer
Whales. Adult females appear to be the
most active and effective individuals during an actual killing phase of an
attack on large whales. An adult male
participates in the successful attack on large whales only to finish off a
whale that has been critically wounded by the females and immature Killer
Whales; however, we did not see a pod of Killer Whales that lacked an adult
male, so we are unable to test these hypotheses. Budylenko (1981)
observed large male Killer Whales leading attacks; prey weakened by the males
were then ‘handed over’ to females and subadults for final despatch. Our observations do not support this
technique being used in Sri Lankan waters.
The females and subadults did a very effective job by themselves with no
adult male intervention. Cultural
differences among different communities of transient Killer Whales may account
for the utility of various hunting strategies in different geographical locations
(see Whitehead & Glass 1985).
The defensive marguerite formation appeared initially
to be dangerous for the Sperm Whales and a hopeless gambit, but is perhaps an
attempt by Sperm Whales to present to the predator bodies that they could
withstand being injured, yet survive, while shielding the vulnerable young at
the centre, with a lot of tail slapping.
Perhaps sufficient meat is bitten off during an attack to satiate the
Killer Whales, which then leave the young Sperm Whales alone. If this is true, it would be a clear and
striking demonstration of altruism among these sentient creatures. The marguerite formation also spreads risk
more or less evenly amongst the defenders.
During the 18 March attack, evidently the presentation of bodies failed
to satisfy the hunger of the large party of Killer Whales, hence the
abandonment of the passive technique and the reversion to the full-on
threatening forward-facing posture in a line, facing the same direction
(flotilla formation). It must be noted
that, despite the vulnerability of Sperm Whales as they keep their bodies
oriented inward while in marguerite formation, they are not entirely
defenceless; the tail stock can deliver a heavy blow. Pitman et al. (2001) asserted that the
marguerite formation is used when the Sperm Whale pod is small (10–15
individuals) whereas larger aggregations generally adopt the flotilla strategy
to thwart predator attack. We saw both
formations being used and the use of one or the other appeared to be determined
by the effectiveness of resisting the attackers.
Diving is also used as a defensive strategy by Sperm
Whales, and because they can dive at least 2km below the surface, it can be
hypothesised that it can be an effective defence against predators that are
unable to reach such depths (Rice 1989).
Berzin (1972) identified three separate fright
reactions of Sperm Whales — diving, aggregating at the surface and flight — but
did not identify the circumstances that gave rise to each. Our observations are similar to those of Pitman
et al. (2001), and show that a specific reaction is context-dependent. For example, small Sperm Whale pods will dive
if a vessel approaches, but large pods will remain at the surface until the
perceived threat is imminent. An attack
by predators, such as Killer Whales, will on the other hand, elicit a reaction
such as a marguerite formation or frontal confrontation (flotilla formation)
with jaws being open and shut threateningly (Ranil P.
Nanayakkara 2008, 2012, 2013, 2014, 2015). Flight is also possible, but we did not
observe diving as a defensive manoeuvre when under predator attack. We did, however, observe several individual
Sperm Whales, approximately 5–10 m below the surface. The inability of the vulnerable young to dive
deeper and faster than attacking Killer Whales may discourage defending Sperm
Whales from taking that approach.
We observed a pod of about 10–15 adult male Sperm
Whales rushing to the aid of a maternal pod during the March 18 incident. The question arises as to how the male group
was gathered and how the individuals were coordinated in responding to the
danger. Did the maternal pod signal
danger or did the males sense peril and respond accordingly? Caldwell et al.
(1966) and Arnbom et al. (1987) state that Sperm
Whales can sound long-distance alarm/summons calls when threatened. Of course, the gathering of superpods will shorten alarm response times considerably.
Mammal-hunting Killer Whales elsewhere occur mostly in
small-sized pods, whereas piscivorous and generalist feeders occur in
larger-sized pods of up to 30 individuals (Ford 2017; Dahlheim
& White 2010). Baird & Dill
(1996) suggested that the optimal group size for northern Pacific transient
mammal-hunting Killer Whales is three individuals and suggest that larger groups
would suffer the cost of increased probability of detection by prey and
therefore reduced hunting success, as the northern Pacific transients feed
mainly on seals. Other marine
mammal-eating Killer Whales have also been observed around the world in small
pods. Hoelzel
(1991) reported an average of two individuals for the Patagonian population,
while Beck et al. (2012) provided the figure of five for Killer Whales in
Scottish waters. Antarctic populations
of Killer Whales take the opposite tack.
The mammal-feeding Type A and Type B populations gather in large pods
—up to 38 individuals for the former and 24 for the latter (Pitman & Ensor
2003). These authors report a pod of 21 individuals of Type A Killer Whales
attacking an Antarctic Minke Whale Balaenoptera bonaerensis. Visser et al.
(2010) reported eight Killer Whales in New Zealand attacking a pod of false
Killer Whales Pseudorca crassidens. Transient Killer Whales that attack and kill
great whales generally operate in large pods, as the large group size would
probably be much more effective. As
such, the Sperm Whale hunters found in Sri Lankan waters operate in a similar
manner, in large pods of 10–20 individuals.
From our limited observations it appears that the
hunting packs of Killer Whales off Sri Lanka’s coast follow the pattern of
their Antarctic counterparts. But again,
the high numbers we observed may simply reflect a gathering that comes from the
temporary bounty and opportunity offered by the Sperm Whale superpods. Hunting packs of Killer Whales at other times
of year may be far smaller. Indeed,
Gemmell at al. (2015) did not report a massed attack when they observed the mesoplodont whale being killed. Another interesting observation is that while
mammal-hunting Killer Whales are generally silent in other localities, while
pursuing Sperm Whale superpods off northwestern Sri Lanka they were very vocal; our hydrophone
and recorder picked up loquacious chatter from the predators, even as they
attacked their huge prey. This sort of
vocalization has been recorded from Monterey Bay, California, where a pod of
Killer Whales has been recorded vocalizing frequently while hunting down a
female Grey Whale Eschrichtius robustus
(Goley & Straley
1994). Deecke
et al. 2005 stated that being silent may help in being stealthy and in locating
prey, and that active sound processing presumably becomes allowable, and might
be functionally important, once the Killer Whales have made contact with the
prey. As with the encounter of 18 March
2017, Deecke et al. (2005) also mentioned that the
sound produced by the hunting pack of Killer Whales might attract other distant
foraging Killer Whales to the site, to take advantage of the kill, if a kill
should happen. They went on to say that
the possibility is unlikely. Conversely,
from our April encounter, we did see a smaller pod suddenly appearing on the
scene and taking part in the attack. We
photographed the dorsal fins of the Killer Whales we observed and are in the
process of building up a catalogue, although it is likely that not all the
individuals were photographed (Appendix A).
While encounters with Killer Whales typically have
been considered rare and unpredictable off Sri Lanka, the area offshore from
the northwest to the northeast appears to support abundant Killer Whales
throughout the year (Ranil P. Nanayakkara
2009, 2010, 2011–2017.) and provides an opportunity to study the dynamics of
this little-known population.
Interestingly, before 2008, there was only one record of a Killer Whale
and that was an individual that landed ashore as bycatch (Ilangakoon
et al. 1992). Since then there have been
many sightings of Killer Whales off the south and southeastern
waters of the country (RN pers. comm. with whale watching operators). After the end of the 30-year war in Sri
Lanka, researchers have had access to the northwestern
and northeastern waters off Sri Lanka, resulting in
an increase in research activity.
Undoubtedly, Killer Whales have always been present, but researchers
have been absent, hence the contemporary rise in observations. Along with the considerable increase in
Killer Whale sightings there has been a related increase in observations of
their predation on large whales, such as the present paper and Gemmell et al.
(2015). Furthermore, anecdotal evidence
from the fisher community suggests that Killer Whales have been following Sperm
Whales superpods for many years in the waters off northwestern Sri Lanka.
Research in Sri Lanka into predator/prey relationships of Killer Whales
in the littoral waters off Sri Lanka is still in its infancy and warrants
additional study.
References
Arnbom, T., V. Papastavrou, L.S. Weilgart,
& H. Whitehead (1987). Sperm Whales
react to an attack by Killer Whales. Journal of Mammalogy 68(2):
450–453.
Baird, R.W. & L.M. Dill
(1996). Ecological and social
determinants of group size in transient Killer Whales. Behavioral
Ecology 7: 408–416.
Barrett-Lennard, L., C. Matkin, J. Durban, E. Saulitis
& D. Ellifrit (2011). Predation on gray whales
and prolonged feeding on submerged carcasses by transient Killer Whales at
Unimak Island, Alaska. Marine Ecology Progress Series 421: 229–241.
Beck, S., S. Kuningas,
R. Esteban & A.D. Foote (2012). The influence of ecology on sociality in the Killer
Whale (Orcinus orca). Behavioral Ecology 23: 246–253.
Berzin, A. (1972). The Sperm
Whale. Israeli Program for Scientific Translations, Jerusalem. (translated from
Russian), 394pp.
Budylenkgo, A. (1981). Distribution and some aspects of the biology of
Killer Whales in the South Atlantic. Report of the International Whaling
Commission 31: 523–525.
Caldwell, D.K., M.C. Caldwell
& D.W. Rice (1966). Behaviour of
the Sperm Whale, Physeter catodon L. Pages 677–717. In: Norris, K.S.
(ed.). Whales, Dolphins and Porpoises. University of California Press,
Berkeley, CA, USA.
Dahlheim, M.E. & J.E. Heyning
(1999). Killer Whale Orcinus
orca (Linneaus, 1758), pp.281–322 In: Ridgway,
S.H. & R. Harrison (eds.). Handbook of Marine Mammals, Vol. 6: The
second book of dolphins and the porpoises. Academic Press, 486pp.
Dahlheim, M.E & P.A. White (2010). Ecological aspects of transient Killer Whales (Orcinus orca) as predators in southeastern Alaska. Wildlife Biology 16: 308–322.
Ford, J.K.B. & G.M. Ellis
(1999). Transients: Mammal-hunting
Killer Whales of British Columbia, Washington, and southeastern
Alaska. University of British Columbia Press, 96pp.
Ford, J.K.B. (2017). Killer Whale Orcinus
orca. pp. 531–537 In: Würsig, B., J.G.M. Thewissen
& K. Kovacs (eds.). Encyclopedia of
Marine Mammals, 3rd Edition. Academic Press, Burlington, MA,
1190pp.
Forney, K.A. & P.R. Wade
(2006). Worldwide distribution and
abundance of Killer Whales, pp.145–162. In: Estes, J. (ed).
Whales, Whaling and Ecosystems. University of California Press,
Berkeley, California, USA, 418pp.
Gemmell, G.L., J.D. McInnes, S.J. Heinrichs & G. Wijeyeratne
(2015). Killer Whale (Orcinus
orca) Predation on Whales in Sri Lankan Waters. Aquatic Mammals 41:
265–271.
https://uk.whales.org/2015/04/01/an-armada-of-whales-wdc-in-sri-lanka/.
https://www.theguardian.com/environment/gallery/2017/mar/29/sex-death-sperm-whales-orcas-indian-ocean-in-pictures.
Heinrichs, S.J. (2013). https://www.youtube.com/watch?v=sRFp3kEBV-A.
Hoelzel, A.R. (1991). Killer Whale predation on marine mammals at Punta
Norte, Argentina: food sharing, provisioning and foraging strategy. Behavioral Ecology and Sociobiology
29: 197–204.
Ilangakoon, A.D., H.A.K. Subasinghe
& W.P. Mahendra (1992). On rare cetacean species off Sri Lanka including the
Killer Whale Orcinus orca (Linn.) (Delphinidae: Cetacea). Miscellaneous Note 3. Journal of
the Bombay Natural History Society 89: 363–365.
Ilangakoon, A.D., R. Jayewardene & L. Perera
(2011). First confirmed sightings of the
Killer Whale (Orcinus orca) in Sri
Lanka’s waters. Marine Biodiversity Records 3: 1–4. https://doi.org/10.1017/S1755267210000047
Jansen, A., X. Nguyen, V. Karpitsky & M. Mettenleiter
(1995). Central Command Neurons of the
Sympathetic Nervous System: Basis of the Fight-or-Flight Response. Science
Magazine 5236 (270).
Jefferson, T.A., P.J. Stacey &
R.W. Baird (1991). A review of
Killer Whale interactions with other marine mammals: Predation to co-existence.
Mammal Review 21(4): 151–180. .
Martenstyn, H. (2013). Out of the Blue, Guide to the Marine Mammals of
Sri Lanka, Southern India and the Maldives. Gunaratne
Offset (Pvt) Ltd., Sri Lanka, 256pp.
Northern Indian Ocean Killer Whale
Alliance (http://niokillerwhales.wixsite.com/niokwa/copy-of-id-catalogue-of-nio-killer).
downloaded on 3 April 2017.
Pitman, R.L., L.T. Ballance, S.I. Mesnick & S.J. Chivers
(2001). Killer whale predation on sperm
whales: observations and implications. Marine Mammal Science 17(3):
494–507. https://doi.org/10.1111/j.1748-7692.2001.tb01000.x
Pitman, R.L. & P. Ensor
(2003). Three forms of Killer Whales (Orcinus orca) in Antarctic waters. Journal
of Cetacean Research and Management 5: 131–139.
Reeves, R.R., J. Berger & P.J.
Clapham (2006). Killer Whales as predators of
large baleen whales and Sperm Whales pp. 174-187. In: Estes, J.A., D.P. DeMaster, D.F. Doak, T.M.
Williams, & R.L. Brownell, Jr. (Eds.), Whales, Whaling, and Ocean
Ecosystems. University of California Press, Berkeley, California, USA.
Rice, D.W. (1989). Sperm Whale Physeter
macrocephalus Linnaeus, 1758, pp. 177–233. In:
Ridgway, S.H. & R. Harrison, (eds). Handbook
of Marine Mammals. Volume 4. Academic Press, London, UK, 442pp.
Rudnai, J.A. (1974). The pattern of lion predation in Nairobi Park. East
African Wildlife Journal 12: 213–225.
Silber, G.K., M.W. Newcomer &
M.H. Perez-Cortes (1990). Killer
Whales (Orcinus orca) attack and kill a
Bryde’s whale (Balaenoptera
edeni). Canadian Journal of Zoology 68(7):
1603–1606. https://doi.org/10.1139/z90-238
Vidal, O. & G. Pechter (1989). Behavioral observations on
fin whale, Balaenoptera physalus,
in the presence of Killer Whale, Orcinus
orca. Fishery Bulletin, U.S. 87: 370–373.
Visser, I.N., J. Zaeschmar, J.
Halliday, A. Abraham, P. Ball, R. Bradley, S. Daly, T. Hatwell,
T. Johnson, W. Johnson, L. Kay, T. Maessen, V. McKay,
T. Peters, N. Turner, B. Umuroa & D.S. Pace
(2010). First record of predation on
false Killer Whales (Pseudorca crassidens) by Killer Whales (Orcinus
orca). Aquatic Mammals 36(2): 195–204. https://doi.org/10.1578/AM.36.2.2010.195
Whitehead, H. & C. Glass
(1985). Orcas (Killer Whales) attack
humpback whales. Journal of Mammalogy 66: 183–185.