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Aquatic Mammals 2024, 50(6), 479-494, DOI https://doi.org/10.1578/AM.50.6.2024.479
Aerial Photo-Identification of Sperm Whales
(Physeter macrocephalus)
Seán A. O’Callaghan,1 Fadia Al Abbar,2 Helena Costa,3 Rui Prieto,4
Martin Gammell,1 and Joanne O’Brien1
¹Marine and Freshwater Research Centre, Atlantic Technological University, Galway City, Ireland
E-mail: seanocallaghan212@gmail.com
2Wildlife Ecology and Conservation Group & Behavioral Ecology Group,
Wageningen University and Research, Wageningen, Netherlands
3Faculty of Biosciences and Aquaculture, Nord University, 7713 Steinkjer, Bodø, Norway
4Institute of Marine Sciences – OKEANOS, University of the Azores, Horta, Portugal
Abstract
Photo-identification is a staple tool used in
cetacean conservation studies since the 1970s
to monitor individuals on a regional and ocean
basin-wide scale to infer critical information
about habitat use, suitability, and shifts. This
technique has been extensively used on sperm
whales globally since it was developed in 1982,
initially using the tail fluke from deep diving
whales and the dorsal fin when appropriate.
From the mid 2010s onwards, the emergence of
domestically available unoccupied aerial sys-
tems (drones) has reshaped how whale research
can be conducted. Herein, we describe the suit-
ability of aerial images to determine the identity
of individual sperm whales (Physeter macro-
cephalus) using all available identifiable mark-
ings along their dorsal side to complement the
use of fluke notches and dorsal fin scars photo-
graphed from the surface of the sea from boat-
based platforms for photo-identification and to
maximize opportunities to identify and monitor
sperm whales. Drone data were gathered while
flying over sperm whales in Andenes, Norway;
Shetland, Scotland; Dursey Island, Ireland; and
Faial and São Miguel Islands, Azores, Portugal,
between 2017 and 2024, which enabled the entire
dorsal surface of sperm whales to be captured
and assessed. Aerial photographs and videos
were used to differentiate between 336 indi-
vidual sperm whales using physical character-
istics. We identified the main features of sperm
whales through aerial drone images, as well as
their prevalence in Atlantic high latitude forag-
ing grounds and lower latitude nursery grounds.
We discuss the advantages of using aerial drone
photographs to identify sperm whales in addition
to traditional boat-based photo-identification.
Key Words: sperm whale, photo-identification,
drone, Norway, Azores, life history
Introduction
Photo-identification has been a powerful population
monitoring tool for cetaceans since the 1970s when
it was first developed using cameras with black
and white film tape to photograph bottlenose dol-
phin (Tursiops truncatus) and killer whale (Orcinus
orca) dorsal fins (Würsig & Würsig, 1977; Bigg,
1982). The development of photo-identification rap-
idly evolved over time as the available technology
advanced and was applied to other cetacean species
(Balcomb et al., 1982; Würsig & Jefferson, 1990).
Humpback whales (Megaptera novaeangliae) were
identified by the ventral fluke coloration and scars/
marks, while southern right whales (Eubalaena aus-
tralis) were identified by callosity patterns on their
head (Katona et al., 1979; Jurasz & Palmer, 1981;
Payne et al., 1983; Würsig & Jefferson, 1990).
Photo-identification was applied to sperm
whales (Physeter macrocephalus) for the first
time in 1982 off Sri Lanka using black and white
and color film cameras (Whitehead & Gordon,
1986; Gordon, 1987). Permanent notches and
deformities along the fluke trailing edge as well as
any notches or wounds present on the dorsal fin or
along the body were used to differentiate between
individuals (Childerhouse et al., 1995; Dufault &
Whitehead, 1995). Over time, photo-identifica-
tion became the foundation of many sperm whale
research projects globally (Whitehead & Gordon,
1986; Gordon, 1987; Arnbom & Whitehead,
1989), benefiting from the increasing affordability
of digital SLR cameras and larger telephoto lenses
(Markowitz et al., 2003; Steiner et al., 2012;
Rødland & Bjørge, 2015; Kobayashi & Amano,
2019; van der Linde & Eriksson, 2019).
480 O’Callaghan et al.
Traditional photo-identification based on fluke
trailing edge shape has several limitations. Calves
do not normally display the fluke upon diving (and
when they do, there is often an indistinct trailing
edge; Gero et al., 2009; Frantzis et al., 2014; Sarano
et al., 2022). Whitehead (2001) noted that younger
sperm whales were less marked on their flukes, and
individuals with estimated lengths of < 10 m that
were < 15 y of age were less likely to deep dive or
raise their tail above the surface resulting in fewer
opportunities to gather fluke photo-identification
data on calf and juvenile sperm whales in contrast
to older, larger whales.
Without using the fluke for identification,
calves have been identified to date using the
dorsal fin and body where identifiable markings
were visible from a boat, but these characteristics
can vary considerably in usefulness depending on
the individual and their surfacing behavior (Gero
et al., 2009, 2015). Peduncle humps were also
used by Frantzis et al. (2014) to aid in calf iden-
tification. To ensure each sperm whale is identi-
fied, regardless of behavior, marks on other body
parts (e.g., head, body, flanks) can be used for
identification purposes, ideally by taking pictures
from both sides of the animal or from an elevated
position (Alessi et al., 2014; Frantzis et al., 2014;
Rødland & Bjørge, 2015; Oyarbide et al., 2023).
Additionally, identifiable features have been used
from an underwater perspective for sperm whales
in situations in which the photographer/videogra-
pher was in the water with the animal capturing
data from all visible sides of near surface whales
(Sarano et al., 2022).
Aerial photo-identification has also been used to
study large cetacean species since the 1980s with
manned aircraft such as fixed-wing planes to pho-
tograph North Atlantic right whales (Eubalaena
glacialis) and bowhead whales (Balaena mystice-
tus) capturing overhead photographs of surfacing
whales (Kraus et al., 1986; Rugh, 1990). The dis-
advantages of this aerial methodology include the
high cost of flight time and the noise created by
large aircraft that may affect animal behavior (Erbe
et al., 2018).
The rapid development of domestically avail-
able and more affordable unoccupied aerial sys-
tems (hereafter UASs or drones) has enabled
the advancement of research studies using aerial
data (Fiori et al., 2017; Johnston, 2019; Álvarez-
González et al., 2023). A variety of cetacean spe-
cies have been identified using aerial images taken
by drones, including bottlenose dolphins (Cheney
et al., 2022), Risso’s dolphins (Grampus griseus;
Hartman et al., 2020), Australian snubfin (Orcaella
heinsohni) and Australian humpback (Sousa sahu-
lensis) dolphins (Christie et al., 2021), pygmy
killer whales (Feresa attenuata; Currie et al.,
2021), belugas (Delphinapterus leucas; Ryan et al.,
2022), long-finned pilot whales (Globicephala
melas; Zwamborn et al., 2023), killer whales
(Durban et al., 2015), dwarf sperm whales (Kogia
sima; Baird et al., 2021), Antarctic minke whales
(Balaenoptera bonaerensis; Pallin et al., 2022),
North Atlantic right whales (Martins et al., 2020),
southern right whales (Christiansen et al., 2022),
gray whales (Eschrichtius robustus; Christiansen
et al., 2021), bowhead whales (Koski et al., 2015),
humpback whales (Napoli et al., 2024), fin whales
(Balaenoptera physalus; Degollada et al., 2023),
and blue whales (Balaenoptera musculus; Ramp
et al., 2021).
Drones have also been used to estimate the size
and mass of sperm whales to date (Dickson et al.,
2021; Glarou et al., 2022); however, to the best of
our knowledge, drone aerial images have not been
used for photo-identification of sperm whales.
Herein, we characterize the types of sperm whale
markings that can be recorded using a UAS, and we
assess the potential use of drones to recapture indi-
viduals between years, demonstrating how UAS
use can complement existing identification method-
ologies to enable additional opportunities to iden-
tify sperm whales at sea.
Methods
Study Areas
Dedicated fieldwork took place at Andenes,
Andøya, Norway, in 2020 and 2022-2024, primar-
ily within Bleik Canyon and Andfjord. Off the
Azores Islands (Portugal), fieldwork was under-
taken off Faial Island in 2017 (under Research
Permit Nos. 37/2016/DRA and 80/2017/DRA) and
around the coast of São Miguel from 2021 to 2024
(under Permit Nos. DRAM/LEMASM/2021/001,
DRAM/LEMASM/2022/005, DRAM/LEMASM/
2022/004, DRAM/LEMASM/2023/008, and
DRAM/LEMASM/2024/008). Opportunistic data
collection also took place at Shetland, Scotland,
and at Dursey Island, Ireland, in 2022 (Figure S1;
supplemental figures and video footage for this
article are available on the Aquatic Mammals
website).
Fieldwork was conducted using rigid inflatable
boats (RIBs) or small fiberglass vessels (< 12 m)
either during commercial whale-watching opera-
tions (with Whale2Sea in Norway) or dedicated
research trips (University of the Azores, University
of Tromsø in Norway; Picos de Aventura, Azores
Boat Adventures, and Terra Azul in the Azores).
Trips took place during good environmental condi-
tions—≤ 2 m swell and ≤ 3 Beaufort sea state with
some exceptions of 3 m swell at a Beaufort sea state
of 4. Precipitation occurred in some instances (rain
or snow) during some field days.
481
Sperm Whale Aerial Photo-Identification
Sperm whales were primarily located using a
directional hydrophone in Norway, and on some
occasions from a land lookout at the Andenes light-
house (~ 45 m above sea level) using 25 × 80 big-
eye binoculars. Once the sperm whale being acous-
tically tracked stopped clicking (indicating it likely
would resurface), the whale was located with the
naked eye. In the Azores, sperm whales were spot-
ted from land by vigias (land lookouts) using 15 ×
80 binoculars, and the vessel was directed towards
the animals while they remained at the surface. A
directional hydrophone was used to locate echolo-
cating sperm whales when no vigia was available.
Once at the surface, the sperm whale was
approached within 50 to 100 m, and the vessel
was positioned behind or to one side of the whale.
Photo-identification photos of sperm whales (e.g.,
body, dorsal fin, fluke) were taken using DSLR
and mirrorless cameras with telephoto zoom lens
when possible as part of existing long-term moni-
toring efforts in Norway and the Azores.
Aerial Photo-Identification Data Collection
Aerial photo-identification images were obtained
using one of several multi-rotor quadcopter models
(DJI Phantom Pro 3, DJI Phantom 4 Pro, Phantom
4 Pro V2.0, DJI Mavic Pro 2, and DJI Mavic Pro
3) that were operated using the DJI 4 Go app by a
trained drone pilot (authors SAOC, FAA, HC, and
RP). The drone was launched once the vessel was
in position by a sperm whale and was flown typi-
cally at 25 m; heights ranged between 5 and 40 m
(occasionally to 120 m) depending on the sighting
circumstances (e.g., number of whales together,
how widely spaced they were) while over sperm
whales at the surface.
From 2020 onwards, high-resolution video
footage (filmed in 4K/60fps) was taken during
the drone’s approach to sperm whales to ensure
some identifiable data were gathered if the whale
dived while it was approached. Data were then
primarily gathered in the zenithal position at 90°
(nadir view) directly above the animal. Both pho-
tographs and video footage were taken of each
sperm whale at the surface, with footage priori-
tized over photographs when individuals social-
ized or rolled onto their sides to ensure opportu-
nities to gather images for identification purposes
were maximized. Aerial footage also facilitated
more opportunities to capture the fluke when held
just below the surface during good environmen-
tal conditions (Beaufort sea state < 2; 1 m swell)
in which the fluke shape and trailing edge were
visible.
Footage was recorded when a sperm whale’s
diving sequence began at the start of a shallow dive
that it typically used to build momentum for a sec-
ondary deep dive. The body was most visible just
before the animal dived when it displayed the head,
body, tail stock, and tail fluke clearly. The wake cre-
ated by diving whales’ tails also provided a momen-
tary white color contrast that highlighted details of
the fluke’s trailing edge, especially when notches
were small in size (see supplemental video).
Image Quality Assessment
Photo-identification images were extracted either
as stills from video files or directly from JPEG
images collected by the drone when the target
sperm whale displayed its body in a clear field of
view (above and below water depending on envi-
ronmental conditions) and where identifiable phys-
ical features were clearly visible along the dorsal
surface or flanks of flown-over sperm whales.
Data were checked for image quality follow-
ing Arnbom (1987), where the focus, exposure,
orientation, and visibility of the sperm whale
determined the suitability of the aerial data col-
lected (Table 1). Flight data were reviewed for all
photographs and videos taken during each flight;
frames in which the sperm whale was most clearly
visible and identifiable were utilized to develop a
photo-identification catalogue using drone images
per field season at each location.
Table 1. Aerial photograph quality assessment criteria for sperm whale (Physeter macrocephalus) photo-identification data
collected using a drone; *Arnbom (1987).
Criteria Description
Focus Sharpness of the photo/video still*
Resolution Photo/video still quality overall related to the megapixels captured in shot
Glare Sun’s strength and effect in overexposing or backlighting the animal
Orientation Position of the sperm whale at the surface (e.g., dorsal, lateral, ventral sides)*
Wake Body parts obscured by the sperm whale’s wake or waves in poor weather
Fluke Fluke captured above the water upon diving; visible underwater
482 O’Callaghan et al.
Figure 1. Example of the body sections used to differentiate
between sperm whales (Physeter macrocephalus) for aerial
photo-identification purposes marked on a male sperm
whale off Andenes, Norway (Aerial still taken by Seán A.
O’Callaghan)
Characterization of Markings
To investigate the presence and prevalence of
physical features along a sperm whale’s dorsal
side, images were divided into five sections cor-
responding to the (1) head, (2) body, (3) tail stock,
(4) fluke, and (5) notch. Marks such as scarring,
indentations, lacerations, skin blotches/lesions, and
parasites were investigated along with the shape of
the tail stock, fluke, and fluke notch, as well as any
trailing edge markings (Figures 1 & 2; Table 2).
These physical features can be temporary or
permanent. Temporary features include lesions,
blotches, whale lice (Cyamus, Neocyamus), and sta-
tionary parasites (stalked species that are anchored
in one position such as Xenobalanus and Pennella
spp.; Hermosilla et al., 2015). These temporary
features can change within an encounter depend-
ing on a whale’s behavior (shedding skin while
Figure 2. Male, female, and calf sperm whale examples
with frequently recorded markings attributed to each sex
and age class (Illustration by Myriam El Assil)
animals are socializing and making body contact) or
between days (e.g., whale lice move slowly around
the epidermis layer). Skin lesions and blotches may
change between seasons depending on the whale’s
health status but may also be discarded as the whale
sheds its skin. Long lasting and apparently perma-
nent features include color patterns such as speck-
les, scars, white marks, and rake marks attributed
to individual variation in skin color (Hanninger
et al., 2023b). Rake marks may appear on sperm
whale bodies from social interactions with other
whales (e.g., on the head from aggressive intraspe-
cific fighting; Kato, 1984; Clarke & Paliza, 1988;
MacLeod, 1998; Eguiguren et al., 2023).
Smaller rake marks may develop on body
appendages where smaller dolphin species may be
able to bite (e.g., fluke edge or sides, dorsal and
pectoral fins) following interactions with other
species, such as killer whales, which is most likely
related to an attempted unsuccessful predation or
harassment event (Pitman et al., 2001; Weir et al.,
2010; Dunn & Claridge, 2013; Whitt et al., 2015;
Sucunza et al., 2022). Additional harassment from
483
Sperm Whale Aerial Photo-Identification
Table 2. Descriptions of physical features on sperm whale body sections visible in drone images that are useful for identification
purposes. Sources: *Arnbom & Whitehead, 1989; **Sarano et al., 2022.
Body section Category Longevity Description
Rake markings Variable Tooth scar markings appearing either white as scar damage or sliced
into the animal’s skin. Most prevalent on the left or right side of
adult male’s head, likely due to intraspecific conflict.
Speckles Apparently
permanent
A series of small white markings clustered together starting at the
anterior of the head moving posterior in various quantities.
Laceration Permanent A deep, straight cut on the animal, often into the blubber layer.
Likely caused by a vessel collision.
Head Indent Permanent A superficial to deep blunt area of damage to the sperm whale’s
head causing an impression to occur in its epidermis/blubber layer.
Shedding skin Temporary Skin patches that appear to be a lighter color to adjacent areas of
darker skin, often in sections indicating the skin layer is being shed.
Whale lice Temporary
Small white lice present on female and young sperm whales that change
position occasionally while moving on the sperm whale’s epidermis.
Lesion Temporary Whale pox or skin disease that causes localized skin discoloration.
Scarring Variable Damaged areas of skin appearing white where previous wounds
have healed.
Blotches Temporary Wide areas where the skin has changed color to grey or black.
White marks Permanent A linear or slightly curved white line along the animal, often parallel
to the dorsal fin along its flank or patches of white present around
the dorsal fin.
Body blotch Variable An often circular-shaped area around the dorsal fin where coloration
may vary from white, grey, or tinged with orange and yellow.
Body Dorsal indent Permanent A localized area anterior to the dorsal fin where an indentation has
been made into the animal.
Parasites Temporary Stalked parasites attached to the sperm whale, often along its flanks
and sometimes fluke. Whale lice may also occasionally occur.
Scarring Variable An area of bright white indicating tissue damage from a past
physical trauma that may originate from natural or anthropogenic
(e.g., entanglements, ship strikes) sources.
Calluses Permanent Greyish deformity on the dorsal fin related to female whales.*
Shed skin Temporary Lighter-colored skin patches indicating the skin was coming off.
Scarring Variable White area of tissue indicating an area where tissue healed from a
past physical trauma.
Tail stock Indent Permanent A divot into the tailstock.
Knuckle shape Likely temporary The roundness or pointiness of the knuckles on their trailing edge
which likely changes with age.
Triangular N/A Overall fluke shape appears triangular.
Fluke Curled N/A One or both of the tail fluke tips are curled inwards on itself.**
Damaged N/A Section of the fluke’s tip is missing.*
Raked Variable Prevalent rake marks from harassment or predation attempts by
smaller cetacean species—likely killer whales, pilot whales, false
killer whales, or Risso’s dolphins.
Line N/A Tail notch is straight when they meet at the centre.
V shaped N/A The tail notch does not touch on both sides; it sharply meets in the
middle.
Fluke notch U shaped N/A Horseshoe-shaped notch.
Overlapping N/A Both sides of the notch meet, but one overlaps on top of another
either on the left or right sides.
Open N/A Notch does not join in the centre of the fluke and leans on one side
of the fluke’s trailing edge.
484 O’Callaghan et al.
short-finned pilot whales (Globicephala macro-
rhynchus), long-finned pilot whales, false killer
whales (Pseudorca crassidens), and Risso’s dol-
phins may also cause rake marks on sperm whale
bodies (Palacios & Mate, 1996; Weller et al.,
1996; Smultea et al., 2014; Fernández et al., 2022;
Hanninger et al., 2023b).
Permanent physical markings include indents,
lacerations, damaged flukes, and calluses. Indents
may have a natural cause but may also relate to blunt
trauma associated with ship strikes (Hanninger
et al., 2023a). Lacerations show a deep cut and
likely stem from ship strike injuries (Hanninger
et al., 2023a). Calluses on the dorsal fin are believed
to be from physical contact between females over
their lifetime (Arnbom & Whitehead, 1989).
Fluke shape, from an overhead perspective,
was used as identification criteria to differentiate
between sperm whales in addition to marks along
the fluke’s trailing edge, which is widely used in
the literature to identify individuals. Four catego-
ries were used: (1) triangular, (2) curled, (3) dam-
aged, and (4) raked (Figure S2). Fluke notch types
were an additional secondary identification fea-
ture when using the fluke shape and trailing edge
for identification purposes—for example, line,
V-shaped, overlapping, U-shaped, and open notches
(Figure S3). Head types and body marks for sperm
whales were differentiated from one another to
determine the number of sperm whales flown over
within and between seasons (Table 2; Figure 3).
Calf and juvenile sperm whales were distinguished
from one another using indents; whale lice; pres-
ence of shed skin; and permanent white markings
on heads, dorsal fins, and flukes (Figure 4).
Data Processing
The number of sperm whales identified in
Norway and the Azores were totaled within each
field season at each location. Whale age classes
were attributed to individuals by their physical
characteristics and in relation to the size of nearby
whales to gauge the group composition from
aerial data. Individuals were also differentiated
into adult, juvenile, and calf categories. To deter-
mine the suitability of using aerial photographs to
identify sperm whales, the whale recapture rate
between seasons in Norway and the Azores was
assessed by comparing catalogues created at both
locations to determine if marks used for identi-
fication purposes persisted between years. The
number of sperm whales with flukes captured
above water or as subsurface flukes was also
totaled in Norway and the Azores to gauge how
aerial images can help gather photo-identification
data on flukes. The prevalence of marks observed
with aerial images was compiled with tallies of
mark types per individual sperm whale on their
first sighting to evaluate how common they were
within the two study areas: (1) a high-latitude
foraging ground and (2) a lower-latitude nursery
ground.
Results
The number of individual identifications made in
Norway ranged from 21 (2020) to 60 (2024) and
totaled 160 individual sperm whales across four
field seasons. In the Azores, 11 sperm whales were
identified off Faial in 2017, while four to 67 were
identified in São Miguel between 2021 and 2024,
which tallied to 163 individual sperm whales in
four field seasons there but, when combined, 174
sperm whales were identified in the Azores overall.
Opportunistic data were collected from live sperm
whales that came into coves and bays in Scotland
and Ireland in 2022, representing two separate indi-
viduals. In total, 336 individual sperm whales were
documented during this study across all areas. Of
these, in the Azores, 75 adults, 25 juveniles, and 40
calves comprised the dataset. The male whales in
Norway, Scotland, and Ireland were deemed to be
subadult to adult in age class.
Aerial Fluke Photo-Identification
From aerial footage, fluke ups from 129 individu-
als in Norway and 46 in the Azores were recorded
above the water; these enabled the identification
of individual sperm whales from an overhead
dorsal perspective. More subsurface flukes were
recorded (when possible) in the Azores—94
individuals compared to 40 in Norway. The lone
male sperm whales in Scotland and Ireland did
not fluke up but were in relatively shallow water
when recorded.
Socializing females often remained at the sur-
face for prolonged periods of time (> 2 h), while
juveniles and calves either did not fluke up or
there were no distinguishing features present
on the fluke. Subsurface images of flukes that
were held flat just beneath the surface, in the
processes of diving, or if flicked above the sur-
face during biopsy sampling or satellite tagging
enabled identification confirmation because the
animals that were disturbed often did not fluke
up when diving after being sampled or tagged
(Figure 5). The white-water runoff from a fluke
that was lifted before a dive offered additional
contrast to the trailing edge and assisted with
identification.
Prevalent Aerial Identification Features
In
dentation marks on the head and white marks on
whale bodies were the most frequently recorded cat-
egories in both the Azores and in Norway (Table 3).
Rake marks on the head were also more prevalent
485
Sperm Whale Aerial Photo-Identification
Figure 3. Frequent distinguishable head and body marking categories for female/juvenile sperm whales (top row) from
São Miguel, Azores, and male sperm whales (bottom row) from Andenes, Norway (Aerial stills taken by Seán A. O’Callaghan
at 25 m and cropped accordingly for demonstration purposes)
in Norway than the Azores where only one con-
firmed adult male was flown on the nursery grounds
(Table 3). A summary percentage of feature occur-
rence useful for aerial identification purposes in the
Azores and Norway are presented in Table 3. The
triangle-shaped fluke was the most common shape
in both the Azores and Norway followed by dam-
aged flukes being equally prevalent at both loca-
tions (Table 3). Flukes with rake marks were the
third most prevalent type but were only recorded in
Norway, while curled flukes were the rarest type,
also only noted in Norway (Table 3). The V-shaped
fluke notch was the most frequently recorded type
in the Azores and Norway followed by the line type
and then overlapping, respectively (Table 3).
Recaptures Between Years
Resightings were made for eight individual
whales in Norway during this study: one indi-
vidual was sighted 2 y apart (2020 to 2022) while
seven individuals were 3 y apart (2020 to 2023)
(Table 3). Scars and back blotch marks remained
486 O’Callaghan et al.
Figure 4. Sperm whale calf and juveniles displaying identifiable markings along their heads, bodies, and tail flukes
off São Miguel, Azores (Aerial stills taken by Seán A. O’Callaghan at different altitudes and cropped accordingly for
demonstration purposes)
the same for resighted sperm whales in addition
to the fluke’s trailing edge. Additional rake marks
were noticed on two sperm whales, while the
development of speckles and a new indent on the
skull crest of two other sperm whales were also
noted (Table 4). Resightings were also made for
four sperm whales at São Miguel in the Azores:
two were 1 y apart (2022 to 2023) and two were
2 y apart (2022 to 2024). These animals retained
their head/body scars, indentation(s), and white
markings along with some dorsal markings on
their flukes (Figure 6).
487
Sperm Whale Aerial Photo-Identification
Figure 5. Tail fluke trailing edges visible just beneath the surface before diving (1), while swimming just below the surface (2),
when diving without showing the tail fluke above water (3), and when a sperm whale reacted to being biopsy sampled (4). (Aerial
stills taken by Seán A. O’Callaghan at 25 m and cropped accordingly for demonstration purposes)
Table 3. Prevalent aerial identification categories for sperm whales in the Azores and Norway using permanent and variable markings
on the body and the fluke. *Fluke shales and notches tallied independent to one another and summed based on the available data.
Body section Category Azores % (n = 142) Norway % (n = 161)
Rake markings 1.4 4.34
Speckles 9.15 7.45
Head Laceration 2.11 6.83
Indent 19.0 29.81
Scarring 17.6 21.11
White marks 35.9 23.6
Dorsal indent 0.7 3.1
Body Scarring 7.74 1.24
Calluses 2.1 0.00
Scarring 1.4 1.24
Tail stock Indent 1.4 0.00
Knuckle shape 2.1 1.24
Azores % (n = 197)* Norway % (n = 288)*
Triangular 53.0 41.9
Curled 0.0 1.3
Fluke Damaged 5.1 3.4
Raked 0.0 3.1
Line 14.7 17.8
V shaped 20.4 23.7
Fluke notch U shaped 0.0 0.6
Overlapping 6.6 7.6
Open 0.5 0.6
488 O’Callaghan et al.
Table 4. Resighting rates for aerial photo-identified sperm
whales in Norway and the Azores, 2020-2024
Year Location
No. of
identifications
No. of
recaptures
2020 Andenes, Norway 21 0
2022 Andenes, Norway 32 1
2023 Andenes, Norway 55 7
2024 Andenes, Norway 60 0
2021 São Miguel, Azores 4 0
2022 São Miguel, Azores 67 0
2023 São Miguel, Azores 64 2
2024 São Miguel, Azores 32 2
Discussion
Boat-based photo-identification studies have
limitations where vessel proximity to animals,
the behavior of animals being grouped together or
widely spaced apart, in addition to boat maneu-
verability when close to animals, reduces the abil-
ity to identify whales farther away from the vessel
(Würsig & Jefferson, 1990). The use of a drone
allows for the surfacing animal to be approached
from greater distances as well as offers the abil-
ity to target multiple animals in a single flight in
comparison to a boat that may focus attention on
one sperm whale or groups that have a tight cohe-
sion that can affect the photographer’s ability to
capture identifiable shots. Additionally, drone use
enables the collection of a variety of data from a
multidisciplinary perspective when a drone is the
primary research tool for behavioural, photogram-
metry, blow sampling, and faecal sample collec-
tion projects (Costa et al., 2022; Glarou et al.,
2022; Álvarez-González et al., 2023). Using a
drone to gather data for individual identification
is especially useful in more intense research situa-
tions when the angle at which animals show iden-
tifiable features cannot be easily photographed
from a boat (e.g., during biopsy sampling and tag-
ging operations).
Sperm whales did not appear to react to the
drone’s presence unless it was flown in very close
proximities (5 to 25 m) at which point their reac-
tion was to roll to one side, potentially trying to
visually look for the drone. The drone’s acoustic
output may be detected by sperm whales, but it
depends on the drone model and how it was flown
around the animals (Christiansen et al., 2016;
Laute et al., 2023). Dickson et al. (2021) noted no
noticeable reaction to the use of a DJI Inspire 1
Pro quadcopter when flown over sperm whales
between 25 and 30 m in altitude.
Our results demonstrate that several sperm
whale features can be seen in images obtained by
UASs and can reliably facilitate the identification
of individual animals. All population segments
(adult males and females, juveniles, and calves)
presented markings along their bodies that can be
used for photo-identification (Clarke & Paliza,
1988; Frantzis et al., 2014; Rødland & Bjørge,
2015; van der Linde & Eriksson, 2019). Aerial
photo-identification enables the collection of fluke
images from a dorsal perspective that allows for the
augmentation and merging of aerial images with
existing photo-identification catalogues to more
readily confirm the shape of fluke trailing edge(s)
that might be visible both ventrally (for boat-based
photo-identification) and dorsally (for aerial photo-
identification) but from different collection plat-
forms (Rødland & Bjørge, 2015; van der Linde &
Eriksson, 2019). Taking fluke images from an aerial
perspective helps account for a tilt that may affect
the visibility of a fluke’s trailing edge as a sperm
whale dives (Figure 7).
Young sperm whales often do not fluke up
when diving or their flukes may be unmarked.
Thus, the use of other body marks is required
to differentiate between different whales (Gero
et al., 2009; Frantzis et al., 2014). The use of
aerial images increases the chances of captur-
ing recognizable features and evaluating their
prevalence over time as an individual grows—
for example, white markings remained in sperm
whales resighted during this study, suggesting
some features may be more permanent than previ-
ously assumed. Physical marks on sperm whales
may originate from anthropogenic activities such
as entanglement in fishing gear and ship strikes
(Hanninger et al., 2023a); these interactions may
result in thin body scars from long-line hooks or
deep lacerations and indents (Ramp et al., 2021;
Hanninger et al., 2023a) as were noted on animals
in this study. These marks appear to become per-
manent and, thus, they represent an opportunity to
use them as identification criteria over prolonged
periods of time (up to at least 3 y in this study).
Whale lice, such as Neocyamus, that are present
on primarily female and young sperm whales are
white in colour, which contrasts with the skin of
surfacing sperm whales, making them more vis-
ible from an aerial perspective (Hermosilla et al.,
2015). In this study, their occurrence and slow
movements on the host’s body allowed for some
reidentifications within short timespans during
the same season for sperm whales in the Azores.
Additionally, skin marks that may be piebaldism,
where greyish-white patches or hypopigmented
skin patches may develop on sperm whale bodies,
489
Sperm Whale Aerial Photo-Identification
Figure 6. Recaptured sperm whales between years using aerial photo-identification categories with the body (Azores) and
tail fluke (Norway) between 2020 and 2024 (Aerial stills taken by Seán A. O’Callaghan at 25 m and cropped accordingly for
demonstration purposes)
490 O’Callaghan et al.
Figure 7. Tail fluke photos that were identifiable from both the aerial photographs and those taken from a boat for a female
(left) and male (right) (Photo credits: Top left photo provided by Francisco Garcia and top right photo provided by Marten
Bril, Whale2Sea; aerial stills taken by Seán A. O’Callaghan at 25 m and cropped accordingly for demonstration purposes)
particularly on the flanks adjacent to the dorsal fin
and the fluke, were useful long-term markings to
reidentify sperm whales (Hanninger et al., 2023b).
While shedding skin, lesions, blotches, and
parasites were recorded with some frequency in
our study, their adequacy for photo-identification
must be considered carefully, as well as how they
are related to the purpose of the study. Such tem-
porary marks (like shedding skin and parasites)
have been noted elsewhere but are often excluded
from long-term photo-identification catalogues
(Sarano et al., 2022). Sperm whales are thought
to shed their skin frequently in warmer (19° to
26°C) seawater temperatures and less frequently
in cooler temperatures (14° to 18°C) whereby skin
lesions or blotches may naturally be lost over time
to maintain the sperm whale’s health, which limits
their usefulness for reidentification purposes to
within-season periods (Pitman et al., 2019).
Likewise, verifying the presence of skin
lesions, blotches, and parasites represents a tool
that is mainly useful for reidentifying sperm
whales within a season rather than between sea-
sons depending on skin shedding rate and on
whale health as they can be visible from above
and provide a secondary identification charac-
teristic to help establish a known sperm whale’s
identity or verify that it previously was not
known. That said, Gaydos et al. (2023) used skin
lesions successfully to re-identify killer whales
from the Southern Resident population between
Canada and the United States, so these marks may
be a useful future tool for species such as sperm
whales given that such lesions may reflect health
status. Still, further long-term monitoring of such
marks on sperm whales is required to assess their
usefulness.
The advancement of technology to support
cetacean photo-identification projects has not
only been confirmed through the development
of new equipment to capture large volumes of
data from the sea’s surface (digital cameras) and
from the air (drones), but also from a data pro-
cessing perspective. Artificial intelligence (AI)
and machine learning has enabled the creation of
platforms such as Happy Whale and Flukebook to
receive, process, and match whales using identifi-
able features sourced from submissions made by
both the general public and researchers (Levenson
et al., 2015; Cheeseman et al., 2017; Patton et al.,
2023). This approach has been especially success-
ful in monitoring the movements and life histories
of humpback whales across entire populations
(Cheeseman et al., 2023) and may also prove
powerful in monitoring sperm whales when com-
bining all available photo-identification resources.
Overall, the incorporation of aerial drone images
for photo-identification purposes shows potential
to monitor sperm whale populations using the head,
body, and flukes from an overhead perspective.
Long-term monitoring of cetacean species through
the use of photo-identification forms the basis
from which population monitoring and movement
patterns of animals can be extracted. Utilizing
drones for the minimal to non-invasive gathering
of identifiable imagery while simultaneously sup-
porting other data collection methods will help to
assess the species and, in turn, inform protection
measures and policies for sperm whales. Aerial
photo-identification complements the traditional,
491
Sperm Whale Aerial Photo-Identification
boat-based photo-identification methods used on
sperm whales by obtaining flukes and dorsal fin
shots both above and below the water’s surface
along with the entire dorsal side of surfacing ani-
mals. This maximizes the possibility of identifying
individuals at various stages of their life cycles and
can yield additional opportunities for monitoring
some individuals across their life spans.
Note: The supplemental figures and video footage
for this article are available in the “Supplemental
Material” section of the Aquatic Mammals web-
site:
https://www.aquaticmammalsjournal.org/
supplemental-material.
Acknowledgments
This project would not be possible without a
huge amount of support from various people.
Massive thanks are due to Marten Bril from
Whale2Sea for taking me on and supporting this
work. Thanks to Zoë Morange, Dr. Tiu Similä,
and Ove Mikal Pédersen for help not only at
sea but also on land along with numerous cap-
tains and guides from Whale2Sea along with
Dr Jonathan Gordon for help in introducing
me up north. Additional thanks to Eve Jourdain
and Richard Karoliussen from Norwegian Orca
Survey and Dr Ian O’Connor from the Atlantic
Technological University for support with equip-
ment. Huge thanks to Pedro Miguel and Milton
Pedro from Picos de Aventura along with Rodrigo
Cabral and Natalia Pérez in particular, as well as
the company’s skippers and guides, for fieldwork
opportunities and assistance off São Miguel in
2022. Thanks to my southern season collaborator
Stéphanie Suciu from the MONICEPH Project at
the University of the Azores for the 2023 and
2024 field seasons off São Miguel for making
them both enjoyable and productive for both
our projects. Heartfelt thanks to Tomás Anselmo
from Azores Boat Adventures for the São Miguel
North Coast fieldwork in 2023. Nearly last but
not least, thanks to TERRA AZUL, specifically
to Miguel Cravinho, Stephanie Almeida, Filipe
Ferreira, Nuno “the Octopus” Pimentel, Nicole
Pereira, and Marylou Tropique, along with many
others, for the opportunity to undertake field-
work off the southern side of São Miguel in 2023
and 2024; to Rafael Martins, Anaïs Builly, and
Pablo Varona for Mr Liable in 2023; to Paulo
Luís Sousa from Azorean Seascape for the 2024
North Coast fieldwork; to Myriam El Assil
for producing the excellent illustration for this
study (
https://www.myriamelassil.com
); to Hugh
Harrop from Shetland Wildlife for making foot-
age
available from Shetland, Scotland; and
to Fintan Harrington for making the Dursey
Island, Ireland, sperm whale footage avail-
able to me. Funding for fieldwork was received
from the Marine Institute’s Networking Grant
in 2020 (NT/20/10) and 2022 (NET/22/43). The
Networking Initiative is funded by the Marine
Institute under the Marine Research Programme
with the support of the Irish Government.
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