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Detecting Dodgy Dolphins:
Assessing Physical Anomalies in Small
Cetaceans off La Gomera (Canary Islands, Spain)
Fabian Ritter1, Gratia Kautek
2 , Bettina Kelm
1, Axel Kelm
1
(1) M.E.E.R. e.V., Bundesallee 123, 12161 Berlin, Germany
(2) University of Vienna, Faculty of Life Sciences, Department of Cognitive Biology, Althanstraße 14,
1090 Vienna, Austria
Introduction
The prevalence of physical anomalies such as skin diseases in cetacean species has been of growing
concern worldwide (Wilson et al., 1997; Maldini et al., 2010; Burdett Hart et al., 2012; Gonzalvo et
al., 2015). Increasing anthropogenic impacts on marine cetaceans have led to some concern about
health status and overall fitness. As an example, immuno‐depression can be detected via cutaneous
anomalies such as skin diseases as a consequence of viral or bacterial infections (Van Bressem et al.,
2009; Burdett Hart et al., 2012). The waters off La Gomera are home to a great diversity of cetacean
species (Ritter, 2012) while the Canary Islands are a major tourist destination in Europe, suggesting
direct and indirect impacts on the marine fauna through coastal development, shipping, tourism, etc.
Several species resident to the archipelago are exposed to such anthropogenic impacts on a regular
basis. Observing their epidermal condition and appearance, e.g. via photo identification, provides
important insight into health status of the Canary Island cetacean fauna and can inform conservation
efforts and needs.
Methods
Photographic data was collected from platforms of opportunity during regular whale watching trips
off the coast of La Gomera from 1995 through 2014, using a variety of single lens cameras.
Photographs were rated according to quality (sharpness, exposure/brightness, proper representation
of anomalies). Only photographs of reasonable high quality were selected for analysis.
Anomalies were categorized as A) injuries, e.g. cuts, scars and wounds; and missing fractions or
whole body parts (see Figure 4); B) deformations, where the body shape showed a clear deviation
from the norm (see Figure 5), and C) suspected skin diseases, i.e. irregular appearance and/or
discolouration of parts of the skin (see Figure 3).
Injuries were classified as slight, moderate or severe considering the size of the anomaly and/or its
interference with surrounding tissue. Deformations were either apparently emaciated animals with
symptoms like ribs visible and a dent behind the blowhole; or animals showing humps or swellings of
some kind. Suspected skin diseases were divided into seven subcategories: a) tattoo lesions; b) dark‐
fringed spots; c) white‐fringed spots (see Burdett Hart et al., 2012); d) discolouration; e) pale spots
(described as ‚white dots‘ in Gonzalvo et al., 2015) and f) others: vesicular (van Bressem et al. 2009),
mottled lesions (Burdett Hart et al., 2012), and fin fringed spots (Wilson et al., 1997).
Results
967 Photos were analysed, representing a total of 186 individual small cetaceans representing five
species, all showing at least one anomaly. Apparent skin diseases were observed in various forms
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across all species in 69 individuals. 66 individuals comprising all species showed visible injuries from
moderate to high severity. As for deformations, symptoms of emaciation were detected in 28
bottlenose dolphins (Tursiops truncatus) and humps were found in two juvenile Atlantic spotted
dolphins (Stenella frontalis, see Table 1).
Photo ID All species ASD BD PW RTD CD
No. of ind. with anomalies 170 15 72 74 6 3
No. of photographs used 145 13 56 67 6 3
Injuries 66 8 17 37 3 1
Suspected skin disease 69 8 33 25 2 1
Emaciation 28 ‐‐ 28 ‐‐ ‐‐ ‐‐
Humps 2 2 ‐‐ ‐‐ ‐‐ ‐‐
Table 1: No. of photographs used for categorization of anomalies in small cetaceans off La Gomera. ASD = Atlantic spotted
dolphin; BD= bottlenose dolphin; PW= short‐finned pilot whale; RTD = rough‐toothed dolphin; CD= common dolphin
Tattoo lesions (see Figure 3a) were the most common skin anomalies (n=33), followed by dark
fringed spots (n=11). Slight and moderate injuries occurred more often than all other anomalies
except tattoo lesions (see Figures 1 & 2).
Figure 1: Occurrences of skin anomalies & injuries in small cetacean off La Gomera (1995‐2014)
Eight types of suspected skin lesions were identified. Tattoo lesions were documented most
frequently with 33 individuals from all five species (see Figure 2). 14 bottlenose dolphins and 12 pilot
whales (Globicephala macrorhynchus) were found to carry tattoo lesions as well as four Atlantic
spotted dolphins, one rough‐toothed dolphin (Steno bredanensis) and one common dolphin
(Delphinus delphis) (see Figure 1). Dark fringed spots occurred mainly in mild form on various parts of
taeoo lesions
dark fringed
spots
discolourafon
white fringed
spots
pale spots others slight injuries
moderate injuries
severe injuries
CD 1 0 0 0 0 0 1 0 0
RTD 1 0 1 0 0 0 2 0 1
PW 12 4 0 4 2 3 20 13 4
BD 14 5 6 3 3 2 4 8 5
ASD 5 2 1 0 0 0 0 7 1
0
5
10
15
20
25
30
35
No. of individuals sighted
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the back (n=11). Two pilot whales showed dark fringed spots on the fin. White fringed spots,
recorded four pilot whales and three bottlenose dolphins, were seen on different parts of the back
and often had a clustered appearance. Pale spots were seen on three bottlenose dolphins and two
pilot whales. Two dolphins had pale spots in moderate form whereas all others were mildly affected.
On eight individuals the skin showed discolouration of varying size. The discolouration of three
individuals was found in correlation to wounds and scratches. Six of the affected individuals were
bottlenose dolphins. One Atlantic spotted dolphins was a completely white animal (see Figure 3f).
One juvenile bottlenose dolphin showed large dark and pale irregular patches on one third of its left
flank (see Figure 3c). Other skin diseases sighted were fin fringed spots seen on two bottlenose
dolphins, as well as mottled white skin colouration (n=2) and vesicular lesion (n=1) seen on pilot
whales.
Figure 2: Physical anomalies found in small cetaceans off La Gomera 1995‐2014. Numbers indicate individuals. GREEN=
deformations. RED = injuries. BLUE = skin anomalies.
28 bottlenose dolphins showed appearance of emaciation. Eight of these were affected by other
anomalies, i.e. co‐occurrence with tattoo lesions, discolouration, pale spots, dark fringed spots or
slight injuries.
41 other animals also were affected by more than one anomaly, including six pilot whales and
bottlenose dolphins with three co‐occurring anomalies; one bottlenose dolphins with four and one
with six different anomalies.
Injuries were observed on all visible body parts and were documented in all species. The majority of
injuries were of moderate severity. Pilot whales were most affected by injuries (n=37). Severe
injuries were sighted on 11 individuals in 4 species (see Fig. 1), including amputations. Amputations
were mainly sighted as a loss of parts of the dorsal fin. One bottlenose dolphin showed a complete
taPoo lesions, 33
dark fringed spots,
11
discolouraRon, 8
white fringed
spots, 7
pale spots, 5
other skin diseases,
5
slight injuries, 27
moderate injuries,
28
severe injuries, 11
emaciaRon, 28
humps, 2
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loss of the fin (see Figure 4a). This individual was photographed five times over the whole
observation period.
Discussion
With this study, the occurrence and characteristics of physical anomalies in small cetaceans off of La
Gomera are reported for the first time. It is noteworthy that all photographs were taken from
platforms of opportunity during regular whale watching trips. It could be shown that individuals from
the five most common species showed different types of anomalies. The non‐systematic manner of
data collection, however, doesn’t allow assumptions about how large the fraction of affected animals
is in each population. Sample size was highly depended on various factors, e.g. which species was
seen first during a trip, the suitability of conditions to take photographs (e.g. light, sea state and
weather), the time of the year in relation to species seasonal abundance including annual variations
(see Ritter et al., 2011), the behaviour and swimming speed of the observed groups, the body parts
that could be seen, etc. In that sense, this study only represents a snapshot despite the study period
covering more that a decade, and the documented occurrence must be seen as a minimum
approximation to the true number of individuals.
Many cetaceans carried slight injuries such as cuts on the leading or trailing edge of the dorsal fin as
well as other body parts. While ultimate causes are not known, the shape and location of many
injuries would suggest rakes from conspecifics or even shark bites, but some also can be related to
previous entanglements in fishing gear (see e.g. Figure 4d). A high number of individuals suffered
from moderate or severe injuries, some of which represented lesions typical for propeller strikes (see
Figure 4a‐c). Several species, including pilot whales have been reported affected by vessel collisions
in the Canaries (Ritter, 2010; Carrillo & Ritter, 2010). Pilot whales might be more prone to be hit by
propellers due to their often prolonged resting periods when animals stay close to the surface.
Skin diseases occurred in various types and most often in mild form according to the categorisation
by Gonzalvo et al. (2015). The occurrence of skin diseases can be an effect of anthropogenic stressors
such as pollution and eutrophication (Mouton and Botha, 2012; Harzen & Brunnick, 1997). Sources of
contaminants are shipping, runoff from urban areas and industrial activities as well as agriculture.
Infectious pathogens such as poxvirus (Geraci et al. 1979), herpes virus (Barr et al. 1989) or
lobomycosis (Migaki et al. 1971; Van Bressem et al. 2009) all lead to skin lesions such as those
observed during this study. Tattoo lesions and dark fringed spots have been related to poxvirus in
previous studies (Van Bressem & Van Waerebeck, 1996; Geraci et al., 1979; Van Bressem et al., 1999;
Van Bressem et al., 2006). Irregular dark pigmented skin lesions are correlated with morbillivirus
infection (Raga et al., 2008). Bacterial infections such as brucellosis occur in cetaceans worldwide and
can also be associated with cutaneous lesions (Miller et al., 1999; Foster et al., 2002). In the current
study evidence of viral or bacterial infection cannot be confirmed definitely, as this would have
required pathological studies. However, viral infection in the documented individuals can be
assumed, as lesion appearance shows similarity to those described in previous studies.
The fact that bottlenose dolphins were most affected by skin diseases as well as emaciation, together
with their more near‐shore distribution (Smit et al., 2010) can be seen as indicative. Garcia‐Alvarez et
al. (2014) found high levels of contaminants like persistent organic pollutants (POP) in Canary Island
bottlenose dolphin tissues. Emaciation, however, suggesting lower blubber thickness, can be caused
by diminishing food resources due to overfishing or ecosystem alteration. Emaciation often was co‐
occurring with skin lesions, again highlighting the prevalence of human impacts and the potential for
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cumulative and synergistic effects. An emaciated appearance can also be an effect of the
morphometrics of old individuals (Gómez‐Campos et al., 2011). However, the fact that several age
classes were observed showing the according symptoms, we are ruling out this explanation for most
individuals here. Future studies will need to focus on relating numbers of individuals with anomalies
to population size as well as on conclusively relating anomalies to the underlying causes.
Acknowledgements
This study was conducted with the support of the University of Vienna. M.E.E.R. e.V. is funded by the
Society for the Protection of Dolphins (Munich). Tina Sommer provided helpful comments on the
draft. Many thanks to our co‐operation partner OCEANO Gomera for willingly taking part in and
supporting scientific research. Special thanks go to the whale watching skippers who contributed to
this study. Finally, the work of M.E.E.R. e.V. would not be possible without the voluntary support of
its active membership.
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a) Tattoo lesion on a pilot whale calf
b) Mottled skin lesion on the fin of a pilot whale.
c) Juvenile bottlenose dolphin with severe skin disease (note the remora on the affected skin area)
d) Pale spots, discolouration and dark fringed spots on an
adult bottlenose dolphin
e) Open vesicular wound in an adult bottlenose dolphin f) all white Atlantic spotted dolphin
Figure 3: Different types of skin anomalies found in small cetaceans off La Gomera (Canary Islands)
© Maria Uhia
© Fatima Kutzschbach
Uhia
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a) Bottlenose dolphin with complete amputation of fin
b) Pilot whale showing deep cut in the fin
c) Atl. spotted dolphin showing (propeller) cuts on fin
d) Pilot whale with injury potentially stemming from previous
entanglement
Figure 4: Different types of injuries found in small cetaceans off La Gomera (Canary Islands)
a) emaciated bottlenose dolphin
b) emaciated bottlenose dolphin
c) Humps of unknown origin on a juvenile Atlantic
spotted dolphin
d) Hump on the genital region of a juvenile Atlantic spotted
dolphin
Figure 5: Different types of deformations found in small cetaceans off La Gomera (Canary Islands)