A sperm whale and orca encounter in the Bremer Canyon, south-west Australia

Written by Jennah Tucker

As a Marine Biologist onboard Naturaliste Charters, I have the opportunity to witness some incredible orca encounters, in the Bremer Sub-Basin area, in south-west Australia. On Tuesday 19th March 2024, the Naturaliste Charters team witnessed a pursuit and subsequent attack by a group of orcas (Orcinus orca) on a pod of sperm whales (Physeter macrocephalus). Sperm whales typically occur in offshore, deep-sea environments, therefore, the opportunity to witness and document such events is rare, with only a handful of accounts having been recorded globally (Pitman et al., 2001; Carwardine, 2020). In 10 years of operating in the Bremer Canyon area, Naturaliste Charters have witnessed multiple interactions between orcas and sperm whales. However, these accounts have largely been of harassment behaviours rather than attacks. Very few (once in 2016 and in 2021) were with as much intensity as what was witnessed here, and none have confirmed fatalities.

Here’s what we observed:

We spent the most part of the day observing individual orcas from three different groups from a distance as they embarked predominantly on long dives lasting up to approximately 8 minutes at a time, consistent with those of foraging behaviour. We were only capturing short glimpses of the orcas while they took a few short breaths at the surface before disappearing on another long dive, as they likely searched the area for prey. At around 1pm a large splash up ahead signalled to us a change in their behaviour. The orcas increased their swim speed and surged (moving and breaking the surface at speed) ahead of the boat, appearing to be in pursuit of something. The boat followed the orcas for approximately 6.2 nautical miles (11.5km) as they moved towards the continental shelf, from an initial depth of >800m, into only 80 metres of water. Being offshore orcas, this population is typically observed in water depths between 800-1000m (Salgado Kent et al., 2021). Approximately 30 orcas were spread out across more than 2 nautical miles during the chase, all headed in the same direction with an adult female at the lead, believed to be the matriarch of one of the orca groups, named Cookie.

Image by Jodie Lowe taken onboard Naturaliste Charters.

As the chase slowed, and the orcas began to regroup and dive, we expected to see a beaked whale surface, as these are often observed as prey targets for this population. Instead, the unmistakable arched back, and large, raised tail flukes of a sperm whale emerged, leaving those of us onboard completely astonished. There were five sperm whales, including one juvenile and four adults. The group of sperm whales were huddled in a tight group (of no particular shape) and appeared distressed, as suggested by behaviours such as frequent respiration, erratic changes in body orientation and raising their heads high out of the water, one with its mouth open. The orcas swam tight circles around the sperm whales who came into a circular formation with their heads facing inwards and their tails oriented outward, fluke swiping. Sperm whales have been observed to form defensive circular formations referred to as a ‘rosette’ (or ‘marguerite’; Nishiwaki, 1962), to protect calves or injured adults which are kept in the centre (Pitman et al., 2001; Gemmel et al., 2015; Carwardine, 2020).

Image by Machi Yoshida taken onboard Naturaliste Charters.

In addition to the ‘rosette’ formation, our crew observed a large dark bubble that rose to the surface amongst the huddle, which we initially thought was blood. Shortly after the dark bubble was observed, one of the orcas began tail slapping, and the other orcas moved off from the huddled sperm whales. The boat followed the orcas, in hope of finding more clues as to whether they had successfully predated on a sperm whale. The orcas remained in the area for some time but kept their distance from the sperm whales, who remained tightly grouped at the surface. We searched the area for scraps of animal tissue or a visible oil slick on the surface, which are generally present in the aftermath of a successful mammal predation, but these were not evident. We were however confused when the matriarch of one of the orca pods approached and circled our vessel with a small chunk of animal tissue in her mouth, which was thought to have been sperm whale tissue at the time. Eventually, the orcas continued along the shelf edge in shallower water. At least three known females from different orca groups surfaced with chunks of yellowish tissue in their mouths, which is not characteristic of mammal flesh. The sperm whales remained tightly grouped at the surface for approximately an hour after the orcas had moved off.

Unfortunately, the mystery animal tissue remains just that, a mystery! Given we only capture glimpses of the story as it unfolds on the surface, what happens below can only be speculated, meaning the day ended with a myriad of unanswered questions burning in everyone’s minds. However, after closer analysis of the photographs, video footage and behavioural observations recorded during the chaos of this interaction, while we were unable to confirm whether this was a successful predation event, it seems unlikely. What was momentarily thought to have been a bubble of blood at the surface, has since been confirmed as sperm whale faeces. Given their faeces appear reddish in colour, due to their diet consisting primarily of squid, it’s no surprise it was mistaken for blood as it dispersed through the water. Defecation in sperm whales has previously been observed in association with behaviours indicative of distress, however it is not known, whether for example, this is a stress response or an offensive technique to deter threats, such as predators.

Here’s what we know:

When startled or distressed, dwarf sperm whales (Kogia sima) and pygmy sperm whales (Kogia breviceps), which are much smaller (up to 2.7m and 3.8m, respectively; Carwardine, 2020) than sperm whales (up to 19.2m; Carwardine, 2020) and more vulnerable to predation, release a reddish-brown liquid from a sac in the lower intestine. This creates a murky cloud in the water which may mask the whale or deter predators (Scott & Cordaro, 1987; Carwardine, 2020).
While not yet recognised in the literature, there have been several accounts of sperm whales defecating when under perceived threat.

o In the Bremer Canyon area, this has been observed by Naturaliste Charters crew on multiple occasions where orcas have reportedly harassed sperm whales, stealing squid from them. In these accounts sperm whales have been observed both breaching and defecating during the interactions.

It is not unusual to observe sperm whales defecating at the surface before diving, given they shut down non-essential physiological systems, including excretory function, to be able to embark on long, deep dives (Kooyman et al., 1981). Therefore, it is unlikely that the muscular mechanisms required for defecation are used at depth (Whitehead, 1996).

o While we only witnessed the first faecal cloud in this instance, another vessel in the area reported observing multiple faecal clouds whilst the sperm whales were engaged in the interaction.

o A fluke up-dive was not observed immediately following the event and the sperm whales remained tightly grouped at the surface for approximately an hour.

Here’s what we don’t know:

Whether this attack by the orcas on the sperm whales was an attempted predation or perhaps harassment behaviour related to prey stealing or some other unknown driver.
While the rosette formation is a known defensive technique adopted by sperm whales, it is unknown whether this faecal release may have been a voluntary defence/offence strategy or an involuntary response.
The yellow-coloured tissue which was carried in the mouths of the orcas following this interaction remains a mystery. If we are able to gain a more complete understanding of what their diet consists of, it would help to answer a lot of our questions.

It is clear that we still have so much to learn about sperm whales, their unique behaviours and their interactions with orcas. We have begun reaching out to colleagues who specialise in sperm whale ecology and behaviour, and we look forward to chatting to many more, to share our observations and learn of theirs to gain more collective insight into their function during these fascinating encounters.

If you would like to share your observations with us, head to our contact page to get in touch, as we would love to hear from you!

References

Carwardine, M. (2020). Handbook of whales, dolphins, and porpoises of the world. Princeton University Press.

Gemmell, G., McInnes, J., Heinrichs, S., de Silva Wijeyeratne, G. (2015). Short Note: Killer Whale (Orcinus orca) Predation on Whales in Sri Lankan Waters. Aquatic Mammals, 41(3), 265-271, https://doi.org/10.1578/AM.41.3.2015.265

Kooyman, G.L., Castellini, M.A., Davis, R.W. (1981). Physiology of diving marine mammals. Annual Review of Physiology, 43, 343-356.

Nishiwaki, M. (1962). Aerial photographs show sperm whales’ interesting habits. Norsk Hvalfangst-Tidende, 51, 395-398.

Pitman, R.L., Ballance, L.T., Mesnick, S.I., Chivers, S.J. (2001). Killer Whale Predation on Sperm Whales: Observations and Implications, 17(3), 494-507.

Salgado Kent, C., Bouchet, P., Wellard, R., Parnum, I., Fouda, L., Erbe, C. (2021). Seasonal productivity drives aggregations of killer whales and other cetaceans over submarine canyons of the Bremer Sub-Basin, south-western Australia. Australian Mammalogy, 43, 168–178. https://doi.org/10.1071/AM19058

Scott, M. & Cordaro, J. (2006). Behavioral observations of the dwarf sperm whale, Kogia simus. Marine Mammal Science, 3, 353-354. https://doi.org/10.1111/j.1748-7692.1987.tb00322.x

Whitehead, H. (1996). Variation in the Feeding Success of Sperm Whales: Temporal Scale, Spatial Scale and Relationship to Migrations. The Journal of Animal Ecology, 65(4), 429-438.