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First evidence of bubble‐net feeding and the formation of ‘super‐groups’ by the east Australian population of humpback whales during their southward migration

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Abstract

The recovery of overexploited populations is likely to reveal behaviours that may have been present prior to harvest but are only now reappearing as the population size increases. The east Australian humpback whale (Megaptera novaeangliae) population (group V, stock E1) has recovered well from past exploitation and is now estimated to be close to the pre‐whaling population size. Humpback whales were thought to follow a ‘feast and famine’ model historically, feeding intensively in high‐latitude feeding grounds and then fasting while migrating and in calving grounds; however, there is growing evidence that animals may feed outside of known foraging grounds. This short article reports on the first photographically documented evidence of bubble‐net feeding by humpback whales in Australian coastal waters (n = 10 groups observed) and provides the first evidence of a second site in the southern hemisphere for the formation of ‘super‐groups’ (n = 6 super‐groups at discrete locations). The formation of super‐groups may be linked to changes in the type or density of prey available, either along the migratory route or in the feeding grounds of the previous summer. It is also possible that the increased population size following recovery make large group sizes while feeding more common. These findings strongly support evidence that feeding behaviour is not restricted to high‐latitude foraging grounds in the Southern Ocean, and that prey consumption prior to leaving the coastal waters of Australia may be a significant component of the migratory ecology of this population. Understanding how environmental variation influences the extent to which humpback whales depend on foraging opportunities along their migratory route, and where feeding occurs, will help to predict how future changes in the ocean will influence whale populations. This will also allow for more effective management measures to reduce the impact of threats during this important period of energy consumption.
RESEARCH ARTICLE
First evidence of bubble-net feeding and the formation of
super-groupsby the east Australian population of humpback
whales during their southward migration
Vanessa Pirotta
1
| Kylie Owen
2,3
| David Donnelly
4
| Madeleine J. Brasier
2
|
Robert Harcourt
1
1
Marine Predator Research Group,
Department of Biological Sciences, Macquarie
University, Sydney, New South Wales,
Australia
2
Institute for Marine and Antarctic Studies,
Ecology & Biodiversity Centre, University of
Tasmania, Tasmania, Australia
3
Department of Environmental Research and
Monitoring, Swedish Museum of Natural
History, Stockholm, Sweden
4
Killer Whales Australia, Box Hill South,
Victoria, Australia
Correspondence
Vanessa Pirotta, Marine Predator Research
Group, Department of Biological Sciences,
Macquarie University, Sydney, NSW 2109,
Australia.
Email: vanessa.pirotta@hdr.mq.edu.au
Funding information
Australian Research Council Linkage Grant,
Grant/Award Number: LP160100162
Abstract
1. The recovery of overexploited populations is likely to reveal behaviours that may
have been present prior to harvest but are only now reappearing as the
population size increases. The east Australian humpback whale (Megaptera
novaeangliae) population (group V, stock E1) has recovered well from past
exploitation and is now estimated to be close to the pre-whaling population size.
2. Humpback whales were thought to follow a feast and faminemodel historically,
feeding intensively in high-latitude feeding grounds and then fasting while
migrating and in calving grounds; however, there is growing evidence that animals
may feed outside of known foraging grounds.
3. This short article reports on the first photographically documented evidence of
bubble-net feeding by humpback whales in Australian coastal waters (n=10
groups observed) and provides the first evidence of a second site in the southern
hemisphere for the formation of super-groups(n=6 super-groups at discrete
locations).
4. The formation of super-groups may be linked to changes in the type or density of
prey available, either along the migratory route or in the feeding grounds of the
previous summer. It is also possible that the increased population size following
recovery make large group sizes while feeding more common. These findings
strongly support evidence that feeding behaviour is not restricted to high-latitude
foraging grounds in the Southern Ocean, and that prey consumption prior to
leaving the coastal waters of Australia may be a significant component of the
migratory ecology of this population.
5. Understanding how environmental variation influences the extent to which
humpback whales depend on foraging opportunities along their migratory route,
and where feeding occurs, will help to predict how future changes in the ocean
will influence whale populations. This will also allow for more effective
management measures to reduce the impact of threats during this important
period of energy consumption.
Robert Harcourt also contributed to field work for this paper.
Received: 11 November 2020 Revised: 2 March 2021 Accepted: 5 April 2021
DOI: 10.1002/aqc.3621
Aquatic Conserv: Mar Freshw Ecosyst. 2021;18. wileyonlinelibrary.com/journal/aqc © 2021 John Wiley & Sons, Ltd. 1
KEYWORDS
Australia, bubble-net feeding, foraging effort, humpback whale, migration, super-group
1|INTRODUCTION
Most rorqual whale species (Balaenopteridae) were severely
reduced as a result of industrial whaling, but many populations are
now recovering well with some approaching pre-whaling
abundance. The east Australian population of humpback whales
(Megaptera novaeangliae; group V, stock E1) was estimated to have
numbered around 30,000 animals prior to industrial whaling, but
was then reduced to a few hundred by the 1960s (Noad, Kniest &
Dunlop, 2019). Since whaling ceased, and protections were put in
place, the population had recovered to an estimated 24,545
(95% CI 21,63127,851) whales in 2015 (Noad, Kniest &
Dunlop, 2019). The recovery of populations to pre-exploitation
numbers allows behaviours not seen when populations were under
stress to re-emerge, and, given the heightened interest in wildlife
behaviour, possibly even be seen for the first time (Jackson
et al., 2020).
Many rorqual whale species are assumed to be capital breeders
that acquire energy resources when conditions are favourable, before
foregoing feeding and relying on energy reserves for reproduction
(Jönsson, 1997; Stephens et al., 2009). This assumption is based on
the empty stomachs of harvested northward-migrating whales and
few sightings of feeding behaviour on the migratory route and in
calving grounds. Traditionally, it was assumed that the east Australian
humpback whale population feeds predominantly over the Austral
summer in high-latitude feeding grounds within the Southern Ocean
(Chittleborough, 1965). However, increasingly, there is evidence of
this population feeding during the migration, especially during the
spring migration as they return to the Southern Ocean feeding
grounds (Stamation et al., 2007; Owen et al., 2015; Owen et al., 2017;
Andrews-Goff et al., 2018). This suggests that the feast and famine
migration model may not apply (Gales et al., 2009).
Humpback whales in the east Australian population have been
documented to feed along the migratory route as far back as old
whaling records (Lockyer, 1981). As the population has grown after
the cessation of whaling (Noad, Kniest & Dunlop, 2019; Pirotta
et al., 2020), accounts in the scientific literature of feeding behaviour
along the east coast of Australia have also increased (Paterson, 1987;
Gill, Evans & Wapstra, 1998; Stockin & Burgess, 2005; Stamation
et al., 2007; Owen et al., 2015; Owen et al., 2016). Some individual
whales have been shown to remain in productive feeding areas for up
to 10 days, taking advantage of the presence of krill (Owen
et al., 2015; Owen et al., 2016). Recent empirically based calculations
suggest that humpback whales may consume prey at such high rates
during migration that they could initiate a reversal in the depletion of
energy stores imposed by migration and could even rebuild a
component of their energy supplies before they reach their feeding
grounds (Owen et al., 2017). However, it is yet to be determined
whether this migratory feeding is opportunistic, in response to an
abundance of prey availability, or an essential aspect of their
migratory ecology and annual energy budget (Owen et al., 2017).
Humpback whales feed using a process called lunge feeding.
Humpbacks have a range of morphological adaptations, such as a
non-fused and outward rotating lower jaw, ventral pleating that
expands the volume of the buccal cavity, and baleen plates to filter
out prey items (Jurasz & Jurasz, 1979; Orton & Brodie, 1987;
Shadwick, Potvin & Goldbogen, 2019). Lunge feeding involves a
whale swimming at speed towards a patch of prey and engulfing large
volumes of prey-laden water. As lunge feeding results in high levels of
drag, it is an energetically expensive feeding behaviour (Goldbogen
et al., 2012). Therefore, it is only efficient when targeting dense
patches of prey.
Humpback whales have developed specialized behaviours that
increase the efficiency of lunge feeding by aggregating prey prior to
lunge feeding in the prey patch. For example, flick feeding and
lob-tailing involve the rapid movement of the flukes to create noise
and bubbles in the water column that entrap and stun prey (Jurasz &
Jurasz, 1979; Hain et al., 1982; Weinrich et al., 1992). Whales can also
blow bubbles from their blowhole to entrap prey. In the northern
hemisphere and in Antarctica humpback whales use bubble-net
feeding, where whales swim in a circle, at depth, expelling air
underwater in such a manner as to create a ring of bubbles around
their prey, after which they lunge towards the surface inside the ring
of bubbles (Ingebrigtsen, 1929; Jurasz & Jurasz, 1979; Wiley
et al., 2011). In some cases this behaviour also involves multiple
animals lunging into the same bubble net, in what appears to be
cooperative behaviour (Parks et al., 2014). Bubble-netting has been
well documented in the northern hemisphere in Alaska (Jurasz &
Jurasz, 1979) and Canada (Hain et al., 1982), as well as on the east
coast of the USA (Wiley et al., 2011). In the southern hemisphere, this
behaviour is also observed on the Antarctic Peninsula (Herr
et al., 2016). To date, the feeding behaviour of humpback whales off
east Australia has been described as skimming, surface lunge feeding,
or lunging at depth (Stamation et al., 2007; Owen et al., 2015; Owen
et al., 2016; Owen et al., 2017). In addition, the formation of bubble
curtains and clouds were observed off Eden, New South Wales, in
2011 (K. Owen 2020, unpublished data), and off Bermagui, New
South Wales in 2015, 2016, and 2017 (R. Harcourt 2021, unpublished
data). Bubble curtains and clouds are also used by humpback whales
to aggregate prey prior to lunge feeding (Friedlaender et al., 2009;
Hazen et al., 2009). However, to the best of our knowledge, bubble-
netting behaviour has never been observed off the east coast of
Australia.
In 2020, scientists, commercial whale-watching operators, and
recreational drone pilots captured feeding behaviours and mass
feeding aggregations along the coast of south-east Australia. In this
paper, we report on: (i) the first photographically documented
evidence of bubble-net feeding by humpback whales in Australian
2PIROTTA ET AL.
coastal waters; and (ii) evidence of a second southern hemisphere
super-grouplocation along a migratory route, previously only
documented in the waters of South Africa (Findlay et al., 2017).
2|OBSERVATIONS
Over the months of September and October 2020, a total of
10 observations of bubble-netting behaviour and six observations
of super-groups occurred over 43 days across two states (New
South Wales (NSW) and Tasmania (TAS); Figure 1; Table 1).
Observations of super-groups of humpback whales feeding began in
September 2020, between Narooma and Eden, NSW, Australia. This
is the same location where both Stamation et al. (2007) and Owen
et al. (2015; 2016; 2017) had previously documented feeding during
the southward migration of humpback whales. Anecdotal evidence
from the crew on whale-watching vessels suggests that the
numbers of whales seen off south-eastern Australia in 2020 began
increasing to surprising densities from 7 September 2020.
Super-group sizes ranged between 20 and 90 whales (n=6 groups)
(Table 1).
On 14 September 2020, a drone (flown under permitted state
rules, New South Wales Government, 2020) captured a super-group of
humpback whales feeding off Bournda (36.8314S, 149.9003E), NSW
(Figure 2). Drone footage shows tightly grouped humpback whales
feeding both at shallow depths and at the surface. The authors
independently counted from the same stills/video and estimated a
mean of 33 ± 5 animals, within five body lengths of each other, within
the single frame. This is higher than the definition of a super-group
(20 or more whales within five body-lengths of their nearest
neighbour; Findlay et al., 2017) and is a larger group than has
previously been documented feeding in this region (with a maximum
group size of 12; Owen et al., 2015). The typical group size of
migrating humpback whales in the east Australian population is two,
and this has remained consistent even as the population has grown
(Noad, Kniest & Dunlop, 2019). This footage was estimated (by the
drone pilot) to capture only a quarter of the total number of humpback
whales in the area at the time. In at least two independent cases,
evidence of bubble-netting behaviour can be seen (Figure 2; Table 1).
On the same day, further south off Eden, NSW (37.0667S,
149.9000E), bubble-net feeding was also observed by whale-watching
operators, with photographs clearly showing the circular formation of
the bubbles, with the two whales emerging at the surface, mouth
agape, in the middle of the bubble net (Figure 3). The following day,
drone footage and boat surveys by scientists recorded super-groups
and bubble-net feeding off Bermagui, NSW (36250S, 150040E).
Bubble-net feeding behaviour was also documented on 17 September
2020 between these locations, with at least two individuals observed
by whale-watching operators apparently feeding in a coordinated
manner. The prey species targeted during these events remains
unknown; however, observations from reliable observers suggest
that both schooling fishes and krill were targeted by the whales.
Other feeding behaviours more typical of this population, such as
surface lunge feeding, were also observed along the coast at this time.
In 2020, humpback whales were observed to feed over a wide
latitudinal range along the east coast of Australia. Feeding behaviour
was observed off Sydney, NSW, on 11 September 2020 (33.8980S,
151.2680E), 200 km further north of Eden. Feeding behaviour was
also observed further south off Victoria, including Phillip Island
(38.4899S, 145.2038E), Portland (38.3609S, 141.6041E), and
Wilsons Promontory (39.0849S, 146.4588E). Feeding has been
observed in this area over the last 3 years by whale-watching
FIGURE 1 Locations of humpback
whale (Megaptera novaeangliae) bubble-
netting behaviour (B) and super-group
(SG) occurrences in 2020 off New South
Wales (NSW) and Tasmania (TAS),
Australia. Humpback whales were also
observed feeding off Victoria (VIC);
however, no bubble-netting behaviour or
super-groups were documented
PIROTTA ET AL.3
TABLE 1 Summary of bubble-net feeding events by east Australian humpback whales (Megaptera novaeangliae) observed off south-eastern Australia during the 2020 southward migration
Date Location No. of whales Prey targeted Feeding behaviour/s Super-group Method of observation
14 Sep 2020 Bournda, NSW Approx. 4060 Unknown Bubble-net and surface lunge feeding Yes Drone, incidental sighting
14 Sep 2020 Eden, NSW Unknown Unknown Bubble-net and surface lunge feeding Unknown Whale-watching vessel,
incidental sighting
15 Sep 2020 Bermagui, NSW 60+Unknown Bubble-net and surface lunge feeding Yes Drone by scientists on a
dedicated research vessel
17 Sep 2020 The Pinnacles, NSW Unknown Unknown Bubble-net and surface lunge feeding Unknown Whale-watching vessel,
incidental sighting
22 Sep 2020 Narooma/Montague
Island, NSW
20+Unknown Bubble-net and surface lunge feeding Yes Scientists on a dedicated
research vessel
23 Sep 2020 Wallaga Lakes, NSW 60+Unknown Bubble-net and surface lunge feeding Yes Scientists on a dedicated
research vessel
24 Sep 2020 Cuttagee, NSW 90+Unknown Bubble-net and surface lung feeding Yes Scientists on a dedicated
research vessel
17 Oct 2020 South-East Tasmania 25+Unknown Bubble-net feeding No Drone and whale-watching
vessel, incidental sighting
19 Oct 2020 Fortescue Bay, TAS Approx. 50 (one bubble-netting) Krill Bubble-net feeding, echelon lunge feeding Yes Drone and whale-watching
vessel, incidental sighting
26 Oct 2020 Waterfall Bay, TAS Three within the bay, 20 in the
region, one bubble-netting
Krill Bubble-net feeding No Whale-watching vessel,
incidental sighting
Note: A super-group was defined as 20 or more whales within five body lengths of their nearest neighbour (Findlay et al., 2017).
4PIROTTA ET AL.
operators. Feeding was also observed off Tasmania approximately
1 month later, on 17, 18, and 26 October 2020. Further events of
bubble-netting behaviour and super-groups were once again
observed (Figure 3; Table 1). This demonstrates that over a 2-month
period, feeding behaviour by this population, including the
formation of super-groups, occurred over approximately 1,000 km of
coastline.
3|DISCUSSION
To our knowledge, this is the first time that bubble-net feeding has
been documented in the peer-reviewed literature for humpback
whales in the southern hemisphere outside of Antarctic waters, and,
importantly, this was observed across a widespread area off south-
east Australia. This is also the largest known group size of feeding
humpback whales ever recorded in Australian coastal waters. Prior to
this, the largest documented group size of feeding animals was
12 (Owen et al., 2015). This population is thought to feed
predominantly on Antarctic krill (Euphausia superba; Groß et al., 2020;
Harrison et al., 2020) in Antarctic waters (Franklin et al., 2012;
Constantine et al., 2014; Harrison et al., 2020). However, these
observations provide further evidence that extensive feeding occurs
prior to leaving the coastal waters of Australia.
These observations point to the plasticity of humpback whale
behaviour and their need to supplement their energy intake during
migration (Eisenmann et al., 2016; Owen et al., 2016; Andrews-Goff
FIGURE 2 Super-groups of east Australian humpback whales
(Megaptera novaeangliae) off the New South Wales coast, Australia.
Evidence of an estimated mean of 33 ± 5 animals (counted
independently by the authors) of humpback whales feeding below
and at the surface in two separate stills from the video (a and b). The
formation of a bubble column is visible at the lower left-hand corner
of (b). Images: Brett Dixon
FIGURE 3 Evidence of bubble-net feeding
by the east Australian population of humpback
whales (Megaptera novaeangliae) during the
southward migration from four different
locations off Australias south-east coast in 2020.
(a) An individual with expanded pleats feeding in
a bubble net in Eden, New South Wales (NSW),
Australia (photo: Cat Balou Cruises). (b) Two
individuals lunging in the same bubble net off
Eden (photo: Cat Balou Cruises). (c) Drone
footage of a bubble net visible at the bottom of
the image with a group of whales in the distance
off Bournda, NSW, Australia (photo: Brett Dixon).
(d) Bubble-net feeding documented at Haycock
Point (north of Eden), NSW (photo: Merimbula
Marina). (e) Evidence of bubble-net feeding from
drone footage, Tasmania, Australia (photo: Wild
Ocean Tasmania). (f) Humpback whale with
expanded throat pleats rising to the surface in a
bubble net off Tasmania, Australia (photo: Wild
Ocean Tasmania)
PIROTTA ET AL.5
et al., 2018). Supplemental feeding has also been observed in other
southern hemisphere populations, both off South Africa (Barendse
et al., 2010; Findlay et al., 2017) and South America (Alves
et al., 2009; Acevedo et al., 2013). Further evidence that foraging
behaviour in humpback whales continues while migrating south, after
leaving Eden, in the waters off eastern Tasmania exists from satellite
tracking data (Andrews-Goff et al., 2018). These observations also
align with evidence of feeding outside of Antarctic waters from stable
isotope analysis of baleen plates (Stephens et al., 2009; Eisenmann
et al., 2016).
Super-groups of humpback whales feeding in east Australian
coastal waters have never been documented before. It is possible that
an abundance of prey and other environmental conditions (e.g. water
temperature and nutrients) may have created high ocean productivity
suitable for such events; however, detailed information on how prey
availability varied in this year relative to others is unavailable.
Individuals may have been able to obtain sufficient energy from this
feeding that the time investment is worthwhile, despite the delay in
migration to the feeding grounds (Owen et al., 2017). Variability
in prey type and abundance, both in high-latitude feeding grounds
and along the migratory route, may influence interannual differences
in whale numbers and the evolution or spread of new feeding
behaviours in these stopover areas (Owen et al., 2017). For example,
while feeding off Eden, whales have been observed to form larger
group sizes and feed at a higher rate when targeting krill at the
surface than fish at depth (Owen et al., 2015; Owen et al., 2016). It is
also possible that changes in the availability of krill in the Southern
Ocean feeding grounds in the previous summer influence the extent
to which whales rely on opportunities to feed along the migratory
route, with fatty acid profiles of humpback whales in this population
recently linked to changes in the Southern Annular Mode (Groß
et al., 2020).
It is unknown whether the use of bubble-net feeding by the east
Australian population has evolved independently or through the
cultural transmission of feeding behaviours. The use of bubble
columns and clouds has been observed to be used by the east
Australian population over the last decade, and these features are also
regularly used by other populations (such as the Western North
Atlantic humpback population) that also bubble-net feed (Hain
et al., 1982; Friedlaender et al., 2009; Wiley et al., 2011). It is possible
that learning to close the net is the next step in the independent
development of this behaviour. However, as documented with other
humpback whale feeding behaviours, such as lobtailing (Allen
et al., 2013) and the production of song (Garland et al., 2017),
humpback whales are capable of cultural transmission. Although there
are seven geographically identified humpback whale breeding stocks
in the southern hemisphere, the extent to which these populations
mix remains unclear (Amaral et al., 2016). There is some genetic (Steel
et al., 2018) and satellite tag evidence (Riekkola et al., 2018) to
suggest that at least some individuals in the southern hemisphere may
move between different populations. This may expose the east
Australian population to novel feeding behaviours. Humpback whales
on the Antarctic Peninsula use bubble-net feeding behaviour similar
to that observed in this study to target krill (Herr et al., 2016). It is
therefore possible that bubble-net feeding has been introduced to
this population through the emigration of individuals from
neighbouring populations. The appearance of bubble-net feeding in
this population may therefore be further support for the movement of
individuals between populations in the southern hemisphere.
The use of citizen science data has helped to document bubble-
net behaviour and the formation of super-groups during the
southward migration of the east Australian humpback whale. It also
enabled the detection of this behaviour over a broad area,
highlighting the significance of this behaviour at a population level
that would not have been possible through observations at a single
location. These opportunistic data, verified independently through
scientific assessment, highlight the role of citizen science in marine
mammal research (Pirotta et al., 2020), particularly where unexpected
behaviours may emerge as populations recover. This study also
demonstrates the value of citizen scientists and the scientific
community working collaboratively. These findings derive from both
land- and sea-based observations, which would not otherwise
have taken place in 2020 because of the COVID-19 global pandemic.
Working closely with scientists, citizen scientists provide an
opportunity to further disseminate the findings of this study.
The novel emergence of bubble-net behaviour and the formation
of super-groups observed in Australian coastal waters may have
conservation implications. First, observations of super-groups may
become more common off the east coast of Australia, as this
population of humpback whales continues to show adaptive
resilience. More whales may mean more opportunity to document
novel behaviours because of the higher number of individuals
transiting the Australian east coast. The possible cultural transmission
of behaviours may also indicate links and the potential presence of
individuals from other southern hemisphere populations, highlighting
the need for appropriate widespread population protections. As
environmental conditions change, the importance of annual feeding
during the southward migration may become more apparent. In this
region the East Australian Current (EAC) is strengthening, specifically
the EAC extension, which extends south along New South Wales into
Tasmanian waters (Ramos et al., 2018; Philips et al., 2020). As a result,
warmer waters occur further south, bringing a range shift of some
marine species, including some in their planktonic larval stages, which
may influence local productivity (Ramos et al., 2018). The enhanced
annual variability in local conditions has already been shown to impact
the foraging success of predators that feed on the same prey as these
whales, such as little penguins (Eudyptula minor) (Carroll et al., 2016),
suggesting that over time there may be large fluctuations in the
availability of prey, which may adversely affect whales if they become
reliant on this food source.
The continued growth of the east Australian humpback whale
population and the extension of southward migration feeding areas
supports the need for a reassessment of the conservation listing of
this population and the recognition of feeding locations federally.
Formal identification of feeding areas will help to ensure
additional protection of humpback whales in Australian waters from
6PIROTTA ET AL.
anthropogenic activities, such as tourism (e.g. whale watching),
commercial fisheries, and underwater seismic exploration. Further
research into the possible drivers of these occurrences will help to
better understand humpback whale ecology in Australian waters and
the importance of these feeding events to this population.
ACKNOWLEDGEMENTS
We would like to thank ecotourism companies Cat Balou Cruises, Eden,
Merimbula Marina, Merimbula and Wild Ocean Tasmania, Eaglehawk
Neck, Tasmania for contributing bubble net feeding images.
Observations in 2020 from the Narooma/Bermagui region occurred
during a project funded by an Australian Research Council Linkage
Grant to Ian Jonsen, R.H. and colleagues (LP160100162). We would
also like to thank Brett Dixon and Jason Iggleden (DroneSharkApp) for
contributing drone footage of humpback whale feeding.
CONFLICT OF INTEREST
All authors declare that they have no conflicts of interest associated
with this work. All drone footage was collected following state
regulations (New South Wales Government, 2020).
ORCID
Vanessa Pirotta https://orcid.org/0000-0003-0395-1859
Kylie Owen https://orcid.org/0000-0002-8986-482X
Madeleine J. Brasier https://orcid.org/0000-0003-2844-655X
Robert Harcourt https://orcid.org/0000-0003-4666-2934
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How to cite this article: Pirotta V, Owen K, Donnelly D,
Brasier MJ, Harcourt R. First evidence of bubble-net feeding
and the formation of super-groupsby the east Australian
population of humpback whales during their southward
migration. Aquatic Conserv: Mar Freshw Ecosyst. 2021;18.
https://doi.org/10.1002/aqc.3621
8PIROTTA ET AL.
... Specifically, wolves will equally space themselves in a circle around a lone prey to keep the prey immobilized [7], while orcas near Norway will cooperatively encircle herring into a tight ball near the surface in a strategy called "carousel feeding" [8]. Further, humpback whales near both Alaska [9] and Australia [10] have been documented to utilize "bubble-nets" which are produced by blowing bubbles during circular motion below a shoal of fish, giving rise to a cylindrical wall of bubbles that surround and contain the prey. ...
... These patterns show a remarkable degree of qualitative similarity across species [2][3][4][5][6]. For example, similar herding and containment (i.e., corralling) behavior has been observed during group hunting by wolves [7] and certain cetaceans [8][9][10] agents acting in different environment and task contexts exploit similar dynamical rules to achieve task success. ...
... Inspired by the similitude in the containment and encirclement strategies observed during human [11,12,17], as well as animal [7][8][9][10] and non-biological systems [13], the current study evaluated whether COC and circling behaviors can be understood more generally as invariant, emergent properties of human dyadic corralling behaviors. As opposed to limiting the behaviors of participants to hand movements on a tabletop display, participants were embodied in an immersive virtual reality environment in which they had to locomote across a large space to corral and contain the fleeing TA herd (see Fig 3). ...
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Social animals have the remarkable ability to organize into collectives to achieve goals unobtainable to individual members. Equally striking is the observation that despite differences in perceptual-motor capabilities, different animals often exhibit qualitatively similar collective states of organization and coordination. Such qualitative similarities can be seen in corralling behaviors involving the encirclement of prey that are observed, for example, during collaborative hunting amongst several apex predator species living in disparate environments. Similar encirclement behaviors are also displayed by human participants in a collaborative problem-solving task involving the herding and containment of evasive artificial agents. Inspired by the functional similarities in this behavior across humans and non-human systems, this paper investigated whether the containment strategies displayed by humans emerge as a function of the task's underlying dynamics, which shape patterns of goal-directed corralling more generally. This hypothesis was tested by comparing the strategies naïve human dyads adopt during the containment of a set of evasive artificial agents across two disparate task contexts. Despite the different movement types (manual manipulation or locomotion) required in the different task contexts, the behaviors that humans display can be predicted as emergent properties of the same underlying task-dynamic model.
... Drone use by the general public has also become a popular method of observing and filming marine life. The advancements in drone technology, reductions in cost and Drones 2022, 6, 75 2 of 10 ready availability have resulted in many high-quality observations of marine animals; such observations potentially can contribute to science, even when scientists have not been in the field [13]. In some cases, high observer efforts have enabled the general public to document information (usually via social media) on the presence, habitat use and interactions of various species with humans. ...
... Direct observations of dwarf minke whales with calves and mother humpback whales with neonate calves (Figure 4) travelling north suggest that calving occurred south of Sydney's waters for both species. The platform's observations of humpback whales feeding off the coast of Sydney expand the distribution of feeding behaviours in NSW waters during the humpback whale's southern migration [13]. Humpback whales may be using NSW's waters to supplement feeding energy intakes in addition to Antarctic feeding grounds, taking advantage of possible prey distribution changes occurring in these southeastern Australian waters [13]. ...
... The platform's observations of humpback whales feeding off the coast of Sydney expand the distribution of feeding behaviours in NSW waters during the humpback whale's southern migration [13]. Humpback whales may be using NSW's waters to supplement feeding energy intakes in addition to Antarctic feeding grounds, taking advantage of possible prey distribution changes occurring in these southeastern Australian waters [13]. Additional observations of humpback whales feeding off Sydney were also made by other recreational drone users who shared their images via social media. ...
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Drones have become popular with the general public for viewing and filming marine life. One amateur enthusiast platform, DroneSharkApp, films marine life in the waters off Sydney, Australia year-round and posts their observations on social media. The drone observations include the behaviours of a variety of coastal marine wildlife species, including sharks, rays, fur seals, dolphins and fish, as well as migratory species such as migrating humpback whales. Given the extensive effort and multiple recordings of the presence, behaviour and interactions of various species with humans provided by DroneSharkApp, we explored its utility for providing biologically meaningful observations of marine wildlife. Using social media posts from the DroneSharkApp Instagram page, a total of 678 wildlife videos were assessed from 432 days of observation collected by a single observer. This included 94 feeding behaviours or events for fur seals (n = 58) and dolphins (n = 33), two feeding events for white sharks and one feeding event for a humpback whale. DroneSharkApp documented 101 interactions with sharks and humans (swimmers and surfers), demonstrating the frequent, mainly innocuous human–shark overlap off some of Australia’s busiest beaches. Finally, DroneSharkApp provided multiple observations of humpback and dwarf minke whales with calves travelling north, indicating calving occurring well south of traditional northern Queensland breeding waters. Collaboration between scientists and citizen scientists such as those involved with DroneSharkApp can greatly and quantitatively increase the biological understanding of marine wildlife data.
... The feeding aggregations documented in our study are among the largest ever reported for baleen whales in scientific literature. Similar in size are only the so called 'super-groups' of humpback whales at the South African and East Australian coasts 40,41 . Large groups (> 15 individuals) or group feeding events have not been described for fin whales anywhere else in the world. ...
... It was featured in the 2019 BBC nature documentary 'Seven Worlds, One Planet' , narrated by Sir David Attenborough, who notes the event as 'the largest congregation of great whales ever filmed' . It has been suggested that the recovery to pre-exploitation numbers allows the re-emergence of behaviours, that, due to extremely low population numbers, had no longer been performed or observed 41,46 . Lunge feeding, the dominant behaviour observed in feeding aggregations, is of particularly high energetic cost [47][48][49] . ...
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Full-text available
Fin whales (Balaenoptera physalus quoyi) of the Southern Hemisphere were brought to near extinction by twentieth century industrial whaling. For decades, they had all but disappeared from previously highly frequented feeding grounds in Antarctic waters. Our dedicated surveys now confirm their return to ancestral feeding grounds, gathering at the Antarctic Peninsula in large aggregations to feed. We report on the results of an abundance survey and present the first scientific documentation of large fin whale feeding aggregations at Elephant Island, Antarctica, including the first ever video documentation. We interpret high densities, re-establishment of historical behaviours and the return to ancestral feeding grounds as signs for a recovering population. Recovery of a large whale population has the potential to augment primary productivity at their feeding grounds through the effects of nutrient recycling, known as 'the whale pump'. The recovery of fin whales in that area could thus restore ecosystem functions crucial for atmospheric carbon regulation in the world's most important ocean region for the uptake of anthropogenic CO2.
... They are capital breeders, meaning they require enormous amounts of krill over the summer feeding periods to store lipid and protein reserves for later mobilisation to support the physiological costs associated with migration and reproduction (Stearns, 1989;Jönsson, 1997). There is growing evidence that Southern Hemisphere humpback whales (Megaptera novaeangliae) supplement their feeding throughout their southern migration, this is shown for the southwestern Pacific humpback whales, referred to as the E1 breeding stock (Paterson, 1987;Stamation et al., 2007;Gales et al., 2009;Pirotta et al., 2021). However, the potential environmental drivers behind this behaviour are largely unknown. ...
... There are many possible reasons behind why whales may supplement their feeding, one being due to environmental conditions that favour higher productivity in feeding hotspots (e.g., Eden) in the Tasman Sea off eastern Australia (Stamation et al., 2007). Humpback "super-groups" from the same E1 breeding stock have been documented feeding off Southeast Australia (Pirotta et al., 2021). Super-group formation has been linked to phytoplankton blooms 1 month prior as well as reduced outward transport favouring an increase in humpback whale prey in coastal waters, as found in Southern Benguela (Dey et al., 2021). ...
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Full-text available
Baleen whales that undertake extensive long-distance migrations away from reliable food sources must depend on body reserves acquired prior to migration. Prey abundance fluctuates, which has been linked in some regions with climate cycles. However, where historically these cycles have been predictable, due to climate change they are occurring at higher frequencies and intensities. We tested if there were links between variability in whale feeding patterns and changes in climate cycles including the El Niño-Southern Oscillation (ENSO), Southern Annular Mode (SAM), and Indian Ocean Dipole (IOD). To reconstruct feeding patterns we used the values of bulk stable isotopes of nitrogen (δ ¹⁵ N) and carbon (δ ¹³ C) assimilated within the baleen plates of 18 humpback and 4 southern right whales between 1963 and 2019, then matched them with climate anomalies from the time in which the section of baleen grew. We show that variability in stable isotope values within baleen for both humpback and southern right whales is linked with shifts in climate cycles and may imply changes in feeding patterns due to resource availability. However, these relationships differed depending on the oceanic region in which the whales feed. In the western Pacific, Southern Ocean feeding humpback whales had elevated nitrogen and carbon stable isotope values during La Niña and positive SAM phases when lagged 4 years, potentially reflecting reduced feeding opportunities. On the other hand, in the Indian Ocean the opposite occurs, where lower nitrogen and carbon stable isotope values were found during positive SAM phases at 2–4-year lag periods for both Southern Ocean feeding humpback and southern right whales, which may indicate improved feeding opportunities. Identifying links between stable isotope values and changes in climate cycles may contribute to our understanding of how complex oscillation patterns in baleen are formed. As projections of future climate scenarios emphasise there will be greater variability in climate cycles and thus the primary food source of baleen whales, we can then use these links to investigate how long-term feeding patterns may change in the future.
... Therefore, the overall lipid loss may be greater than loss in morphometric body condition alone, which may explain the difference in body condition loss compared with the present study. Although humpback whales are thought to generally fast during migration and while on the breeding grounds, significant feeding opportunities have been recorded during the southern migration on the east coast of Australia (Stamation et al. 2007, Pirotta et al. 2021. Feeding behaviour during migration has been recorded in other humpback whale populations, including the east coast of America, South Africa, Brazil, Dominican Republic, Ecuador, Chile, and Mexico (Baraff et al. 1991, Gendron 1993, Swingle et al. 1993, Best et al. 1995, Danilewicz et al. 2009, De Sá Alves et al. 2009, Barendse et al. 2010, Findlay et al. 2017, Siciliano et al. 2019, García Cegarra et al. 2021. ...
Article
In order to exploit seasonally favourable habitats for feeding and breeding, humpback whales Megaptera novaeangliae undertake one of the longest migrations in the animal kingdom. Stored energy is crucial for a successful migration, but few studies have investigated the relationship between migration timing and body condition in baleen whales. Using unmanned aerial vehicles, we quantified the body condition of east Australian humpback whales. We collected data on 513 individuals (48 calves, 166 juveniles, 251 adults, and 48 lactating females) during their northbound and southbound migrations between June and October 2020. For adults and juveniles, we explored the loss of body condition between migration direction (north versus south) as well as the relationship of migration timing (day of year) and body condition. We found a significant loss in body condition between the northbound and southbound migrations for both adults (9.8%) and juveniles (18.3%). However, migration timing did not influence body condition for either reproductive class. Cow/calf pairs were analysed using relative calf length (percentage of maternal length) as a proxy for days postpartum. We found a positive curvilinear relationship between migration timing and calf body condition. However, lactating females showed no relationship between migration timing and body condition. Whilst body condition is important for capital breeding whales, the lack of a correlation found for adults and juveniles suggests that body condition is not the main driver of migration timing from feeding or breeding grounds. However, calf body condition may be a significant factor for the migration timing of cow/calf pairs.
... F lexible manipulation of bubbles in underwater environments is a crucial and fascinating survival skill of many creatures, such as respiration, 1,2 self-defense, 3,4 and predation. 5,6 Meanwhile, the dynamic manipulation of bubbles is also ubiquitous and critical to a wide range of applications in both scientific and industrial fields, such as gas evolution reactions, 7−9 heat transfer, 10−12 greenhouse gas collection, 13 fermentation, 14 and drug delivery. 14−16 However, limitations from buoyancy inhibition, hydrostatic pressure, gas dissolving, and easy deformability block the way of gas bubbles toward smart manipulation. ...
Article
Full-text available
Bubbles play a crucial role in multidisciplinary industrial applications, e.g., heat transfer and mass transfer. However, existing methods to manipulate bubbles still face many challenges, such as buoyancy inhibition, hydrostatic pressure, gas dissolving, easy deformability, and so on. To circumvent these constraints, here we develop a bioinspired anisotropic slippery cilia surface to achieve an elegant bubble transport by tuning its elastic modulus, which results from the different contacts of bubbles with cilia, i.e., soft cilia will be easily bent by the bubble motion, while hard cilia will pierce into the bubble, consequently leading to the asymmetric three-phase contact line and resistance force. Moreover, a real-time and arbitrarily directional bubble manipulation is also demonstrated by applying an external magnetic field, enabling the scalable operation of bubbles in a remote manner. Our work exhibits a strategy of regulating bubble behavior smartly, which will update a wide range of gas-related sciences or technologies including gas evolution reactions, heat transfer, microfluidics, and so on.
... The bubbles act as a boundary, confining and concentrating the prey before engulfment (Hain et al., 1982;Jurasz & Jurasz, 1979;Sharpe & Dill, 1997). This behavior has been recorded in Southeast Alaska, the Gulf of Maine, the Magellan Strait, and the Antarctic Peninsula (Acevedo et al., 2011;Hain et al., 1982;Jurasz & Jurasz, 1979;Mastick, 2016;Pirotta et al., 2021). Though there have been many recorded visual observations of bubble-net feeding from the surface, little is known about the coordination between participants involved in this foraging strategy. ...
Article
In many species, group foraging is a strategy used to increase the efficiency of individuals to find and exploit patchy prey. Humpback whales (Megaptera novaeangliae) are one of the few baleen whale species reported to use coordinated foraging strategies. One of these behaviors, bubble-net feeding, has been observed in several populations, though the behaviors of individuals within these groups are largely unknown. This study used multi-sensor kinematic tag data from 26 whales foraging in the Southern Gulf of Maine to analyze individual bubble-net feeding behaviors. Linear mixed effects models were used to test if there were differences in individual whales’ dive behaviors across group size. The results indicate that individuals performed consistent bubble-net feeding behaviors regardless of the size of their foraging group, except when using one specific foraging behavior, the upward spiral. Overall complexity of foraging dives, based on the three-dimensional movements of the dive, decreased with increasing group size when group members used upward spirals. This may indicate that in larger groups, participants in coordinated feeding events need to move less and expend less energy to corral prey. This study provides new insights into the effects of group size on individual behavior and group coordination in humpback whales.
... Locating and exploiting prey hotspots is essential to the foraging strategy of rorqual whales, but whale aggregations of the size and density noted here are not commonly reported. In the case of humpback whales, groups of the size and density discussed here have only been reported off South Africa seasonally and recently (Findlay et al., 2017), and have also only recently been observed during the southward migration off Australia (Pirotta et al., 2021). However, similarly large aggregations of rorqual whales were reported historically (e.g. ...
Article
Large groups of animals aggregate around resource hotspots, with group size often influenced by the heterogeneity of the environment. In most cases, the foraging success of individuals within groups is interdependent, scaling either constructively or destructively with group size. Here we used biologging tags, acoustic prey mapping, passive acoustic recording of social cues and remote sensing of surface currents to investigate an alternative scenario in which large, dense aggregations of southeast Atlantic humpback whales, Megaptera novaeangliae, and northeast Pacific blue whales, Balaenoptera musculus, were each associated with ephemeral krill aggregations large enough such that their availability to predators appeared to be influenced more by environmental features than by consumption, implying independence of group size and consumption rates. We found that the temporal scale and spatial extent of oceanographic drivers were consistent with the temporal scale and locations of predator aggregations, and additionally found that groups formed above bathymetric features known to promote zooplankton concentration. Additionally, we found calling behaviour counter-indicative of competition: blue whale foraging calls were anomalously high during observed aggregation time periods, suggesting signalling behaviour that could alert conspecifics to the location of high-quality resources. Modelled results suggest that the use of social information reduces the time required for individuals to discover and exploit high-quality resources, allowing for more efficient foraging without apparent costs to the caller. Thus, rorqual whales foraging in these environments appear to exhibit a social foraging strategy whereby a behaviour with negligible individual costs (signalling) provides information that enhances group foraging efficiency. The population density dependence of this social foraging strategy may help explain why some rorqual species were at first slow to recover from human exploitation, but have since increased more rapidly.
... whaling era 9 . Considering the global observational records, it was unprecedented until recently, when supergroups have also been reported in Australia 10 . This raises the question about the possible drivers of such events and the likelihood that they would become permanent. ...
Article
Full-text available
Seasonal feeding behaviour of humpback whales (Megaptera novaeangliae) has been observed in the coastal waters of the Southern Benguela where the species has been observed forming super-groups during the austral spring in recent years since 2011. Super-groups are unprecedented densely-packed aggregations of between 20 and 200 individuals in low-latitude waters and their occurrences indicate possible changes in feeding behaviour of the species. We accessed published data on super-groups occurrence in the study area in 2011, 2014 and 2015, and investigated oceanographic drivers that support prey availability in this region. We found that enhanced primary production is a necessary but not sufficient condition for super-groups to occur. Positive chlorophyll anomalies occurring one month prior to the super-group occurrences were identified, but only a concurrent significantly reduced water volume export from the region throughout October were conducive to the aggregations in the specific years. Hydrodynamic model results attributed the anomalous decreased volume export to the strength and orientation of the Goodhope Jet and associated eddy activity. The combination of random enhanced primary production typical of the region and emerging anomalous conditions of reduced water export in October since 2011 resulted in favourable food availability leading to the unique humpback whale aggregations. The novelty of this grouping behaviour is indicative of the lack of such oceanographic conditions in the past. Given the recency of the events, it is difficult to attribute this reduction in ocean transport to climatic regime shifts, and the origin should be likely investigated in the distant water mass interaction with the greater Agulhas system rather than in local intensifications of the upwelling conditions. A positive trend in the humpback whale population abundance points to the need to monitor the exposure of the species to the changing climate conditions.
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