Journal of Mammalogy, 95(6):1289–1298, 2014
Clymene dolphins (Stenella clymene) in the eastern tropical Atlantic:
distribution, group size, and pigmentation pattern
CAROLINE R. WEIR,* PHIL COLES, AMY FERGUSON, DUNCAN MAY, MICK BAINES, INÊS FIGUEIRDO, MAREN REICHELT,
LUIS GONCALVES, MARIJKE N. DE BOER, BARRIE ROSE, MATT EDWARDS, SUE TRAVERS, MIKE AMBLER, HUGO FÉLIX,
DAVE WALL, VALERIA A. A. AZHAKESAN, MIKE BETENBAUGH, LEA FENNELLY, SIGBJØRN HAALAND, GUUS HAK, TERJI
JUUL, ROB W. LESLIE, BRIAN MCNAMARA, NICHOLA RUSSELL, JACLYN A. SMITH, HEATHER M. TABISOLA,
ALEXANDRA TEIXEIRA, ELS VERMEULEN, JULIET VINES, AND ANDY WILLIAMS
Ketos Ecology, 4 Compton Road, Kingsbridge, Devon TQ7 2BP, United Kingdom (CRW)
Department of Zoology, School of Biological Sciences, University of Aberdeen, Tillydrone Avenue, Aberdeen, AB24 2TZ,
United Kingdom (CRW)
c/o Ketos Ecology, 4 Compton Road, Kingsbridge, Devon TQ7 2BP, United Kingdom (PC, AF, DM, MB, IF, MR, LG,
MNDB, BR, ME, ST, MA, HF, DW, VAAA, MB, LF, SH, GH, TJ, RWL, BM, NR, JAS, HMT, AT, EV, JV, AW)
* Correspondent: caroline.weir@ketosecology.co.uk
The Clymene dolphin (Stenella clymene) is endemic to warm Atlantic Ocean waters and is one of the least
known delphinids. We reviewed existing published data (primarily strandings, captures, and bycatch) and
unpublished sightings to examine the distribution, habitat, group size, seasonality, and pigmentation patterns of
Clymene dolphins within the eastern tropical Atlantic (ETA). Following photographic verification, 84 confirmed
and 8 probable at-sea sightings of ETA Clymene dolphins were analyzed. The documented records ranged from
~198N in central Mauritania to 14826 0 S in southern Angola, confirming 14 ETA range states. At-sea sightings
occurred in water depths of 437–5,000 m and at distances from shore of 21–937 km, corresponding with a
continental slope and oceanic habitat. Sightings within the wider ETA region had year-round occurrence. Group
size ranged from 3–1,000 animals, with 60.9% of groups comprising 50 animals. Photographic examination
revealed a complex and variable pigmentation pattern in ETA Clymene dolphins, which contrasts with the
simple tripartite pattern often described for this species. In particular, most ETA animals had a dark gray lateral
stripe extending diagonally along the flank from the beak to the genital area and a conspicuous dark gray eye–
flipper stripe of varying intensity and thickness. The at-sea sightings documented here significantly extend
current knowledge of the distribution, ecology, and appearance of the Clymene dolphin.
Key words:
Africa, conservation status, flank markings, Gulf of Guinea, habitat, seasonality, sightings, water depth
Ó 2014 American Society of Mammalogists
DOI: 10.1644/14-MAMM-A-115
The Clymene dolphin (Stenella clymene) was first described by
Gray (1846) from a single skull originating from an unknown
locality. The species was only validated in 1981 (Perrin et al.
1981), and until recently its occurrence was documented from
fewer than 200 verified records (Fertl et al. 2003). Clymene
dolphins are endemic to tropical and subtropical waters of the
Atlantic Ocean, including the Caribbean Sea and the Gulf of
Mexico (Perrin et al. 1981; Perrin and Mead 1994; Fertl et al.
2003; Jefferson 2009). Published records are strongly biased
toward the western Atlantic (Fertl et al. 2003), where surveys in
the Gulf of Mexico (Davis et al. 1998; Mullin and Fulling 2004;
Maze-Foley and Mullin 2006), off the Atlantic United States coast
(Mullin and Fulling 2003), and off the coast of Brazil (Moreno et
al. 2005) have revealed a regular oceanic presence of this species.
In contrast, the occurrence of the Clymene dolphin in the
eastern tropical Atlantic (ETA) is poorly documented (Jefferson 2009; Weir 2010). In their global review of the species,
Fertl et al. (2003) reported 2 capture records from the midAtlantic (Lütken 1889; Perrin et al. 1981) and 12 sighting,
stranding, and capture records from ETA waters. However, 2
of the ETA capture records reported in their appendix 3 (on 20
July 1957 and 27 October 1981, respectively—Cadenat and
Doutré 1958; Robineau et al. 1994) were erroneously
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FIG. 1.—Eastern tropical Atlantic countries (including Exclusive Economic Zones) and the location of all verified Clymene dolphin (Stenella
clymene) records. The southern border of the Gulf of Guinea extends from Cape Palmas in Liberia to Cap Lopez in Gabon (IHO 1953). Verified
range states are shown in dark gray. Countries: 1—Mauritania, 2—Senegal, 3—Cape Verde Islands, 4—The Gambia, 5—Guinea-Bissau, 6—
Guinea, 7—Sierra Leone, 8—Liberia, 9—Côte d’Ivoire, 10—Ghana, 11—Togo, 12—Benin, 13—Nigeria, 14—Cameroon, 15—Equatorial
Guinea (including Bioko and Annobón), 16—São Tomé and Prı́ncipe, 17—Gabon, 18—Republic of the Congo, 19—Democratic Republic of the
Congo, 20—Angola (including Cabinda), 21—Ascension Island, 22—Saint Helena.
duplicated as strandings in their appendix 2, resulting in only
10 ETA records. Since that review, a number of bycatch
records (Debrah et al. 2010) and a handful of at-sea sightings
(Weir 2006, 2011a, 2011b; de Boer 2010) have been published
for the ETA, but information remains scarce.
The International Union for Conservation of Nature (IUCN)
recently classified Clymene dolphins as a Data Deficient
species (Hammond et al. 2012). However, the paucity of
records in the ETA and documented mortality of the species in
Ghanaian fisheries (Debrah et al. 2010) led to the addition of
the ETA Clymene dolphin to the Conservation of Migratory
Species of Wild Animals Appendix II in 2008, as a migratory
species that needs, or would significantly benefit from,
international cooperation.
Given concern regarding the conservation status of ETA
Clymene dolphins (Van Waerebeek and Perrin 2007),
information on their distribution and ecology is urgently
required. This paper reviews previously published records and
presents a significant number of unpublished ETA sightings in
order to document ETA range states, provide information on
habitat, investigate seasonality, and assess behavior and group
size. Additionally, the pigmentation patterns of Clymene
dolphins photographed in the ETA were examined in order
to describe color pattern and to assess the potential for
confusion with other species during ETA sighting surveys.
MATERIALS
AND
METHODS
Study area.—The ETA is defined here according to the
eastern section of the tropical Atlantic biogeographic realm
characterized by Spalding et al. (2007). It comprises the west
coast of Africa from Mauritania south to Angola, including
oceanic islands (Fig. 1). For completeness, we include the midAtlantic island of Ascension. Consequently, there are 22
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WEIR ET AL.—CLYMENE DOLPHINS IN THE AFRICAN ATLANTIC
TABLE 1.—Criteria used to allocate sightings (n ¼ 104) to 5
verification categories. ‘‘Experienced observers’’ were defined as those
with considerable cetacean field experience that specifically included
previous encounters with Clymene dolphins (Stenella clymene; as
evidenced by photographs).
Category
1
2
3
4
5
Criteria
No. records
Photograph or video available, sufficient to confirm
identification. Accepted.
Animals viewed at very close proximity while
bow-riding by an experienced observer allowing
all key features to be noted, but photographs
were inconclusive or unavailable due to weather
(e.g., sun glare or torrential rain). Accepted.
Animals were positively identified in the field by
experienced observers and photographs were
provided that were suggestive, but inconclusive
(due to poor light or distance). Accepted as
probable record.
Photograph provided but animals could not be
unequivocally identified as Clymene dolphins
due to poor image quality (usually due to
distance of the animals). Observer uncertain or
lacked previous experience with the species, or
both. Rejected.
Photographs provided of ‘‘Clymene dolphins’’
proved to be misidentifications of other
delphinid species. Rejected.
80
4
8
8
4
potential Clymene dolphin ETA range states including 18
mainland countries and 4 island states and territories (Cape
Verde, São Tomé and Prı́ncipe, Ascension Island, and Saint
Helena). The offshore islands of Annobón and Bioko are
governed by, and considered with, Equatorial Guinea. Four
geographic regions were defined for analysis: 1) north-west
Africa (Mauritania to Liberia); 2) northern Gulf of Guinea
(Côte d’Ivoire to Equatorial Guinea); 3) southern Gulf of
Guinea to south-east Atlantic (Gabon to Angola); and 4)
international waters seaward of the Exclusive Economic Zones
(EEZ).
Literature review.—A literature review searched for
published Clymene dolphin records in scientific journals and
in available ‘‘gray’’ literature (e.g., International Whaling
Commission papers). Where records involved skeletal
remains, strandings, captures or bycatch, the species
verification was carried out by the authors of the studies in
question and specimen samples were usually stored in
museums (Supporting Information S1, DOI: 10.1644/
14-MAMM-A-115.S1). Where records included published
photographs, species identification was verified by the lead
author (CRW).
Unpublished sightings.—Experienced Marine Mammal
Observers were contacted directly by the lead author during
2012 to request information on Clymene dolphin sightings.
Open requests were posted on the Marine Mammal Observer
Association forum (www.mmo-association.org) on 27 January
and 27 November 2012. Opportunistic sightings were also
reported to the lead author during the course of investigations
into cetacean occurrence in the ETA region between 2004 and
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2011 (Weir 2011b). Initial examination checked that the
following minimum data were available: supporting
photograph or video, date, global positioning system
position, and group size. Sightings without this information
were omitted from the study.
Verification methods.—Fertl et al. (2003) emphasized the
difficulties in identifying Clymene dolphins to species level
and the importance of verification using photographs or video.
Key features used to identify Clymene dolphins from
photographs included tripartite color pattern comprising a
dark gray dorsal cape, mid-gray lateral field, and white ventral
surface; a rounded convex dip in the ventral margin of the
dorsal cape below the dorsal fin; gray eye–flipper stripe that
widens toward the flipper; pale stripe extending from the
blowhole to the apex of the melon; dark beak tip and lips; dark
dorso-mesial surface to the beak bordered by paler gray; and
distinctive ‘‘moustache’’ marking located one-third of the way
from the melon to the beak tip on the dorsal surface of the beak
(Perrin et al. 1981; Perrin and Mead 1994; Carwardine 1995;
Jefferson 1996; Reeves et al. 2002; Shirihai and Jarrett 2006;
Jefferson et al. 2008).
A single person (CRW) allocated sightings to 1 of 5
verification quality categories using the criteria outlined in
Table 1 and the key features described above. Categories 1 and
2 were accepted as Clymene dolphins. Category 3 sightings
were accepted as probable records. Category 4 and 5 sightings
were rejected. Additional information was requested for
Category 1–3 sightings including water depth and behavioral
notes (specifically including the presence or absence of bowriding and spinning behaviors).
Data analysis.—All records were mapped in ArcView 3.2
(Environmental Systems Research Institute, Inc. [ESRI] 1998)
Geographic Information System (GIS) using global positioning
system positions (sightings) or locality descriptions (stranding
and bycatch records). Each was assigned to a range state using
an EEZ shapefile (Flanders Marine Institute 2012). The depth
of most Clymene dolphin sightings (n ¼ 75) originated from
the vessel echosounder. For the remaining sightings (n ¼ 17)
water depth was calculated from the General Bathymetric
Chart of the Oceans Digital Atlas 2003 (General Bathymetric
Chart of the Oceans [GEBCO] 2003) contour data using GIS
(see Weir 2011a). The distance of each sighting from shore was
calculated using a custom-design script in GIS, and assigned to
neritic or pelagic habitat. Neritic was defined as the waters
extending from the coast to the shelf edge (, 200 m depth),
whereas pelagic referred to open waters seaward of the shelf
edge. Depth-related habitat is defined throughout this paper as
continental shelf/neritic (, 200 m depth); upper slope (200–
999 m); lower slope (1,000–2,000 m); and deep oceanic (.
2,000 m).
Aqua Modis monthly composites (4-km resolution) of sea
surface temperature (SST) data were downloaded from the
National Aeronautics and Space Administration Ocean Color
Web site (Ocean Color Web 2014) for every month and year
for which sightings were reported. A value was extracted for
each sighting (except one 1972 record that occurred prior to the
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TABLE 2.—Depths, distance from shore, sea surface temperature (SST), and group sizes of 92 Clymene dolphin (Stenella clymene) sightings in
4 regions: 1) northwestern Africa (Mauritania to Liberia); 2) northern Gulf of Guinea (Côte d’Ivoire to Equatorial Guinea); 3) southern Gulf of
Guinea to southeastern Atlantic (Gabon to Angola); and 4) international waters.
Water depth (m)
Distance (km)
SST (8C)
Group size
Region
n
X̄
SE
Median
X̄
SE
Median
X̄
SE
Median
X̄
SE
Median
1
2
3
4
All
17
36
35
4
92
2,429
2,521
1,666
4,560
2,267
154.0
158.0
92.9
38.2
101.0
2,261
2,368
1,721
4,555
2,123
116.8
88.2
116.5
908.2
139.9
6.1
11.6
6.2
23.4
18.0
113.4
66.8
118.8
928.4
108.3
21.4
27.7
27.9
27.9
26.6
0.67
0.23
0.12
0.37
0.31
20.4
27.1
27.9
28.0
27.7
62.8
47.1
108.2
39.0
72.9
10.1
7.0
29.0
18.4
11.8
50.0
40.0
50.0
35.0
47.5
availability of SST data) using a custom-designed script in
GIS. Statistical tests to analyse variation in water depth,
distance from shore, SST and group size between geographic
regions were carried out using Minitab 16 statistical software
(Minitab Inc. 2010).
RESULTS
Summary of records.—Eight specific nonsighting records of
ETA Clymene dolphins were found during the literature review:
2 capture records, 2 strandings, 3 calvaria, and 1 skeleton of
unknown origin (probable bycatch—Supporting Information
S1). Additionally, 2 capture records (one involving 2 animals)
are documented from mid-Atlantic waters northwest of
Ascension (Supporting Information S1). These records span
the period from ~1846 to 1995. More recently, a cetacean
landing (bycatch and direct takes) monitoring program in Ghana
has photographically verified 52 Clymene dolphin specimens
between 1994 and 2010 (Supporting Information S1; Debrah et
al. 2010) and reported 13 cranial specimens in the University of
Ghana collection (Van Waerebeek et al. 2009).
A total of 104 (12 published and 92 unpublished) ETA
sightings were evaluated, of which 84 were accepted as
confirmed Clymene dolphins and 8 were accepted as probable
Clymene dolphins (Table 1). Ninety-two sightings were
therefore used for analysis (Supporting Information S2, DOI:
10.1644/14-MAMM-A-115.S1).
Four sightings were clear misidentifications and comprised
common dolphin (Delphinus sp.; n ¼ 2) and pantropical spotted
dolphin (Stenella attenuata; n ¼ 2). One published ‘‘probable’’
sighting (de Boer 2010) could not be photographically verified
because of distance of the animals and poor image quality, and
was not included further.
Range states.—At-sea sightings occurred between latitudes
of 18834 0 N (central Mauritania) to 14826 0 S (southern Angola
[Fig. 1]). When nonsighting records were also considered, the
northern range limit extended to ~198N.
Published nonsighting records confirmed 4 ETA range
states: Mauritania, Senegal, The Gambia, and Ghana (Supporting Information S1). The mid-Atlantic captures were
located in international waters outside of the Ascension Island
EEZ. Verified sightings occurred in 12 ETA range states:
Mauritania, Guinea-Bissau, Sierra Leone, Liberia, Côte
d’Ivoire, Ghana, Togo, Benin, Nigeria, Equatorial Guinea,
Gabon (including 1 sighting reallocated from the Republic of
the Congo—Weir 2006, 2011b), and Angola (Supporting
Information S2). Four sightings were located in international
waters outside of the EEZ. The combined sighting and
nonsighting records confirmed 14 Clymene dolphin ETA
range states.
Habitat.—The 89 sightings occurred in water depths ranging
from 437 to 5,000 m (X̄ ¼ 2,267 m, SE ¼ 101 m, median ¼ 2,123
m) and at distances from shore of 20.6 to 937.4 km (X̄ ¼ 139.9
km, SE ¼ 18.0 km, median ¼ 108.3 km). No sightings were
recorded in neritic habitat. Four records occurred in international
waters far from shore in deep water (Fig. 1; Table 2). SST values
for the sightings ranged from 19.68C to 31.18C (X̄ ¼ 26.68C, SE
¼ 0.318C, median ¼ 27.78C; Table 2).
There were statistically significant differences in water depth
(Kruskal–Wallis test: H2 ¼ 23.42, P , 0.0001) and distance
from shore (Kruskal–Wallis test: H2 ¼ 15.78, P , 0.0001) of
sightings between regions 1–3 (Table 2). Mann–Whitney tests
revealed significant differences in water depth between regions
1 and 3 (P ¼ 0.0001) and regions 2 and 3 (P , 0.0001), and in
distance from shore between regions 1 and 2 (P ¼ 0.0016) and
regions 2 and 3 (P ¼ 0.0005). Sightings in the northern Gulf of
Guinea (region 2) occurred closest to shore, whereas sightings
between Angola and Gabon (region 3) were in the shallowest
water (Fig. 2). There was a statistically significant difference in
SST between regions 1–3 (Kruskal–Wallis test: H2 ¼ 33.68, P
, 0.0001), and Mann–Whitney tests revealed that these
differences were highly significant between regions 1 and 2
(P , 0.0001), and regions 1 and 3 (P , 0.0001).
Temporal distribution.—Sightings occurred throughout the
year within the wider ETA (Fig. 3a). They were recorded in 10
months in the northern Gulf of Guinea and in the waters
between Gabon and Angola, and in 6 months (primarily July–
November) off northwestern Africa (Fig. 3a).
Group size and behavior.—Sightings comprised groups of
3–1,000 animals (X̄ ¼ 72.9 animals, SE ¼ 11.8 animals, median
¼ 47.5 animals, n ¼ 92). Most (60.9%) groups contained 50
animals (Fig. 3b). Comparing regions 1 to 3 only (due to low
sample size in region 4), there was no significant difference in
group size according to depth (categories: , 1,000 m; 1,000–
2,000 m; . 2,000 m; Kruskal–Wallis test: H2 ¼ 1.61, P ¼
0.447), distance from shore (categories: , 100 km; 100–150
km; . 150 km; Kruskal–Wallis test: H2 ¼ 3.06, P ¼ 0.216), or
geographic area (Kruskal–Wallis test: H2 ¼ 5.31, P ¼ 0.070).
The behavior most commonly recorded during sightings (n ¼
76; 82.6%) was travel or porpoising. Aerial behavior was
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FIG. 2.—Relationship between water depth and distance from shore of Clymene dolphin (Stenella clymene) sightings (n ¼ 88) in 3 regions: 1)
northwestern Africa; 2) northern Gulf of Guinea; and 3) southern Gulf of Guinea to southeastern Atlantic.
logged for 54 (58.7%) sightings. Bow-riding (34.8%) and
spinning (32.6%) were each noted in around one-third of
sightings. Only 1 mixed-species assemblage was reported: 12
Clymene dolphins and 7 common dolphins identified within a
large group of 350 dolphins off Angola (Weir 2006).
Pigmentation pattern.—We observed several pigmentation
characteristics in ETA Clymene dolphins that had not been
emphasized in most previous descriptions of the species.
Dorsal cape. Previous studies had noted that the margin of
the dorsal cape dips ventrally beneath the dorsal fin (Perrin et
al. 1981; Perrin and Mead 1994; Carwardine 1995; Reeves et
al. 2002; Jefferson et al. 2008). However, in most ETA
Clymene dolphins the lowest point of the ventral margin was
located slightly further forward, below the base of the leading
edge of the dorsal fin (Fig. 4; Supporting Information S3, DOI:
10.1644/14-MAMM-A-115.S1).
Dark lateral stripe. The presence of a dark diagonal lateral
stripe was a prominent feature on most ETA Clymene
dolphins, but had not been noted in many previous studies
(e.g., Perrin et al. 1981; Perrin and Mead 1994; Carwardine
1995; Fertl et al. 2003). Jefferson et al. (2008, p. 238) noted
that there ‘‘may also be an indistinct dark band running
diagonally along the side, from the anus forward,’’ while
Shirihai and Jarrett (2006, p. 184) noted the presence of a
‘‘dark, ill-defined band . . . on mid body.’’ We found that a
distinct dark gray lateral stripe was conspicuous on many ETA
individuals, extending from the posterior edge of the beak and
curving upward through the eye toward the dorsal fin, reaching
its highest point above the flipper. The stripe angled diagonally
downward along the length of the animal toward the genital
area (Fig. 4; Supporting Information S3), and strongly
demarcated the lateral and dorsal fields from the white ventral
field in most ETA individuals. The demarcation was
particularly marked toward the rear of the ventral field, and
was more muted behind the flipper. The lateral stripe was
highly variable in intensity and extent. In individuals where the
eye–flipper and lateral stripes were pronounced, the stripes
converged behind the eye to produce a characteristic ‘‘masked’’
appearance (Supporting Information S3).
Mid-gray lateral field. The presence of a mid-gray lateral
field is a key component of the tripartite coloration pattern
often reported for this species. However, this feature varied in
extent and distinctiveness in ETA Clymene dolphins (Supporting Information S3). In some individuals the ventral
margin of the dorsal cape merged with the upper edge of the
lateral stripe so that no clear area of mid-gray lateral field was
present below the dorsal fin.
Eye–flipper stripe. Fertl et al. (2003) reported that
Clymene dolphins have an ‘‘indistinct’’ eye–flipper stripe.
However, most ETA animals had a conspicuous dark gray eye–
flipper stripe of varying intensity and thickness, usually
broadening toward the flipper (Fig. 4; Supporting Information
S3). Above the dark eye–flipper stripe was a narrow, welldefined white stripe extending from the back of the eye to the
trailing edge of the flipper. In some animals the area between
the merging eye–flipper and lateral stripes was relatively
‘‘clean’’ and the eye–flipper stripe terminated at the flipper (Fig.
4A). However, in others this area was a dusky gray color (often
causing the white eye–flipper stripe to stand out Fig. 4B), and
in some a dark gray streak extended backward above the flipper
into the ventral field (Fig. 4C).
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FIG. 3.—A) Temporal distribution and B) group size of Clymene dolphin (Stenella clymene) sightings (n ¼ 92) in 4 geographic regions: 1)
northwestern Africa (Mauritania to Liberia); 2) northern Gulf of Guinea (Côte d’Ivoire to Equatorial Guinea); 3) southern Gulf of Guinea to
southeastern Atlantic (Gabon to Angola); and 4) international waters.
Dorsal fin shape and color. Dorsal fin shape showed
considerable variation, ranging from small and triangular to
noticeably falcate or tall and erect (Supporting Information S3).
Some individuals had pale inner areas on the dorsal fin.
DISCUSSION
Eastern tropical Atlantic range states and distribution.—In
their 2007 review, Van Waerebeek and Perrin verified 6 ETA
range states for the Clymene dolphin: Mauritania, Senegal,
Gambia, Ghana, Gabon (record reallocated from the Republic
of the Congo—Weir 2011b), and Angola. The sightings
reported here increase the documented range states to 14 (north
to south): Mauritania, Senegal, Gambia, Guinea-Bissau, Sierra
Leone, Liberia, Côte d’Ivoire, Ghana, Togo, Benin, Nigeria,
Equatorial Guinea, Gabon, and Angola. We were unable to
locate any records for Cape Verde (a sighting reported from
Cape Verde actually comprised pantropical spotted dolphin
[see Hazevoet et al. 2010]), Guinea, Cameroon, the Republic of
the Congo, the Democratic Republic of the Congo, or Saint
Helena, despite those being listed as range states by some
assessments (Culik 2011; Hammond et al. 2012). However,
given confirmed northern and southern limits in central
Mauritania and southern Angola, respectively, Clymene
dolphins are likely to occur in all intermediate range states.
Our records indicate that Clymene dolphins are widespread
in the ETA and that the scarcity of earlier records was likely
due to paucity of survey effort (as noted by Robineau et al.
1994) and confusion with other delphinids. Effort-related
analyses of this data set were not appropriate because of
variation in survey methods, observers and platforms, and
unknown potential impacts from anthropogenic sound (seismic
survey vessels were the platform for most sighting records).
However, those countries with the highest number of at-sea
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1295
FIG. 4.—Pigmentation pattern of eastern tropical Atlantic Clymene dolphins (Stenella clymene) based on photographs of live animals
(illustrations by Phil Coles): a) generalized overall appearance of flank pattern; a) and b) head where eye–flipper and lateral stripes are well defined
and converge at the eye to produce a distinct ,-shape; and c) head where eye–flipper and lateral stripes merge behind the eye and extend back into
the ventral field as a dark band.
sightings (i.e., Angola, Gabon, Côte d’Ivoire, and Mauritania)
were those where Marine Mammal Observers have been most
frequently utilized by industry in recent years.
Clymene dolphins occur as far south as 29859 0 S in the
southwestern Atlantic off Brazil (Moreno et al. 2005), but
14826 0 S is the southernmost ETA latitude currently documented. It seems unlikely that Clymene dolphins routinely occur
much farther south than Angola, because of the cold-water
Benguela Current influence off Namibia. However, their range
may potentially extend northward from the ETA into warm
temperate waters off Western Sahara, the Canary Islands, and
beyond. For example, sightings of another tropical delphinid,
Fraser’s dolphin (Lagenodelphis hosei), have recently been
recorded off Madeira and the Azores (~388N—Gomes-Pereira
et al. 2013).
Examination of the data showed that Clymene dolphins
occur year-round in the wider ETA and support a probable
year-round occurrence in both the northern Gulf of Guinea and
the waters from Gabon to Angola. The reported sightings
between Mauritania and Liberia were strongly seasonal (May
to November), most likely due to temporal variation in survey
effort in that region. Systematic year-round survey effort is
required throughout the ETA to assess seasonal movements.
Eastern tropical Atlantic habitat.—The Clymene dolphin is
usually considered to be an oceanic species occurring seaward
of the continental shelf (Perrin et al. 1981; Perrin and Mead
1994; Davis et al. 1998; Fertl et al. 2003). Sightings off Brazil
occurred over 1,050- to 4,500-m water depth (Moreno et al.
2005), whereas those in the Gulf of Mexico ranged from 612 to
1,979 m (X̄ ¼ 1,261 m—Davis et al. 1998) and from 688 to
3,065 m (X̄ ¼ 1,692 m—Maze-Foley and Mullin 2006). The 94
sightings analyzed by Fertl et al. (2003) had a depth range of
44–4,500 m (X̄ ¼ 1,870 m, median ¼ 1,675 m); however, the
sighting in 44 m was considered to be ‘‘atypical.’’ The depth
distribution of the sightings reported here was consistent with
those studies, confirming an occurrence in slope and deep
oceanic habitat in the ETA.
Slight differences in depth range and distance from shore
were apparent between the 3 geographic regions considered.
Because the distribution of cetacean survey effort was not
available, the significance of the observed trends cannot be
evaluated. However, it is likely that some differences do occur
due to the bathymetric variation between the geographic
regions. Although much of central and northern Angola and
Gabon has a shelf of around 60-km width, the shelf off Togo,
Benin, and Côte d’Ivoire in the northern Gulf of Guinea is
often less than 30 km wide. Seabed topography is usually
steeper in these areas of narrow shelf, so that water deepens
rapidly relatively close to shore. Consequently, although
occupying deep, oceanic habitat throughout the ETA, the
steepness of the seabed and the width of the shelf are likely to
be key influences on the exact water depths and distances from
shore that Clymene dolphins are recorded in each region.
The distribution of Clymene dolphins appears to be restricted
to warm waters (Fertl et al. 2003; Moreno et al. 2005). SST
during sightings in the Gulf of Mexico ranged from 22.18C to
29.28C (X̄ ¼ 25.98C—Maze-Foley and Mullin 2006), whereas
off Brazil it ranged from 258C to 28.58C (Moreno et al. 2005).
We recorded a slightly wider SST range for the species in ETA
waters, varying from 19.68C to 31.18C. The coldest SSTs
recorded (19.5–20.68C) were for the 14 sightings off Mauritania.
The southernmost sighting recorded had a SST of 25.08C,
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Vol. 95, No. 6
FIG. 5.—Comparison in cape and lateral stripe patterns of: a) Clymene dolphin (Stenella clymene), and b) striped dolphin (Stenella
coeruleoalba) off Angola. Both species have a dark lateral stripe from eye to anus; however, the stripe of the striped dolphin runs almost
horizontally along the side whereas that of the Clymene dolphin slopes diagonally downward. The stripe is also finer and better defined around the
eye on the striped dolphin compared with the Clymene dolphin. The striped dolphin usually has a distinct shoulder blaze sweeping forward from
the cape (b, left-hand animal). However, in some individuals this is muted and indistinct (b, center animals) and may potentially cause confusion
with the dipped dorsal cape of the Clymene dolphin.
suggesting that the species’ range may extend some way
southward of that location in central Angola. Differences in the
SST of sightings between the 3 regions is likely the result of
oceanographic differences, with Mauritanian waters comprising
the Sahelian upwelling zone (Spalding et al. 2007) and having
lower water temperatures than the other regions.
Group size.—We recorded group sizes in the ETA of 3–
1,000 animals, but most groups comprised fewer than 50
animals. This correlates well with observations of group size
elsewhere, including Brazil (8–300 animals—Moreno et al.
2005) and the Gulf of Mexico (1–68 animals—Maze-Foley and
Mullin 2006). In 105 sightings analyzed by Fertl et al. (2003),
group size ranged from 1 (in a mixed-species school with
spinner dolphins [Stenella longirostris]) to 1,000 animals. The
mean (72.9 animals) and median (47.5 animals) group sizes
recorded in the ETA are remarkably similar to those reported
by Fertl et al. (2003) for the western Atlantic (76.1 and 47.0
animals respectively).
Pigmentation pattern.—Few publications have provided a
detailed description of the coloration pattern of the Clymene
dolphin, and previous descriptions have been based on animals
photographed or stranded in the western Atlantic, primarily within
the Gulf of Mexico (Perrin et al. 1981; Perrin and Mead 1994;
Jefferson 1996; Jefferson et al. 2008). We observed a complex
and highly variable pigmentation pattern in ETA Clymene
dolphins, which contrasts with the simple tripartite pattern often
described for this species. In other delphinid species such
intraspecific variation in coloration has been shown to relate to
factors including individual, age, sex, and geographic location
(Perrin 2009). The complexity was particularly evident in the
intensity and extent of, and intersection between, the lateral stripe,
lateral field, and the eye–flipper stripe. Even at distance, complex
lateral patterns, rather than defined tripartite coloration, were
apparent on leaping Clymene dolphins. Although the beak
moustache marking may be the species’ single most diagnostic
external feature (Fertl et al. 2003), we suggest that the combined
dipped dorsal cape, dark lateral stripe, and ‘‘clean’’ throat
appearance may be the best means of identifying this species at
distance in the ETA.
Confusion species.—Misidentifications of Clymene dolphins
occur by experienced cetacean biologists (see Fertl et al. 2003;
Hazevoet et al. 2010) and by experienced (as defined by
regulator standards—Joint Nature Conservation Committee
[JNCC] 2010) Marine Mammal Observers (this study). It is
likely that the number of misidentifications reported by Marine
Mammal Observers industry-wide is much higher than indicated
here, because this paper specifically targeted the most
experienced personnel. Both scientific and Marine Mammal
Observer surveys should routinely collect photographic or video
data to facilitate independent verification of species, and these
should be assessed prior to data use to ensure adequate standards
of data quality.
December 2014
WEIR ET AL.—CLYMENE DOLPHINS IN THE AFRICAN ATLANTIC
Previous studies have identified spinner and common
dolphins as potential confusion species (e.g., Perrin and Mead
1994; Reeves et al. 2002; Fertl et al. 2003; Jefferson et al.
2008). We also note superficial similarities in pigmentation
pattern with the striped dolphin (Stenella coeruleoalba) in ETA
waters (Fig. 5). Similarities in skull and body shape led
previous studies to note that Clymene dolphins appeared
intermediate between spinner and striped dolphins (Perrin et al.
1981; Jefferson et al. 2008; Jefferson 2009). Recent genetic
evidence indicates that the Clymene dolphin may have
originated through natural hybridization between spinner and
striped dolphins (Amaral et al. 2014). Our observations of
pigmentation patterns in the ETA (Fig. 5) may lend further
support to taxonomic similarities between these species.
Conservation status.—The status of the Clymene dolphin is
unknown throughout its range. Hammond et al. (2012) noted
that there are bycatch and directed takes in West Africa of
‘‘unknown, but likely escalating, scale.’’ We were able to locate
only 2 published capture records in the ETA (both from
Senegal) and a further 2 records from the mid-Atlantic, none of
which were recent (Supporting Information S1). Evidence for
bycatch in ETA fisheries currently originates solely from
Ghana (Supporting Information S1), where the proportion (of
the total cetacean bycatch) of Clymene dolphins landed in drift
gill-net and purse-seine fisheries has variously been calculated
as 34.5% (Ofori-Danson et al. 2003; Van Waerebeek et al.
2009) and 24.5% (Debrah et al. 2010). The occurrence of
bycatch in other range states is undocumented, but may be
significant. Additionally, Maigret (1981) and Weir and Pierce
(2013) underlined the lack of information on dolphin bycatch
in industrial tuna purse-seine fisheries in the Gulf of Guinea.
The ‘‘West African population’’ of Clymene dolphins was
recently added to the Conservation of Migratory Species of
Wild Animals Appendix II, due to the scarcity of ETA records
and evidence of high bycatch in Ghana (Van Waerebeek and
Perrin 2007). However, given the publication of 2 mid-Atlantic
capture records (Lütken 1889; Perrin et al. 1981), an
occurrence in offshore deepwater habitat (. 4,000 m—Fertl
et al. 2003; Moreno et al. 2005; this study), and an absence of
genetic or taxonomic studies to support regional differentiation,
it is currently unclear whether considering Clymene dolphins
as separate western and eastern Atlantic ‘‘populations’’ is the
optimal management approach.
In this paper we documented a widespread occurrence of
Clymene dolphins in the ETA, indicating that the previous
paucity of records reflected an absence of survey effort (and
identification difficulties) rather than a genuine rarity of the
species in the region. Nevertheless, verified records remain
relatively scarce in relation to other ETA cetacean species (e.g.,
comprising only 1.0% of 617 sightings of positively identified
delphinid species in Angola [Weir 2011b]). Robust information
on the spatiotemporal movements, abundance, population
structure, and mortality levels of Clymene dolphins is needed
before a full evaluation of conservation status can be made. As
noted by Van Waerebeek and Perrin (2007), the Clymene
dolphin appears to be a wide-ranging, mobile species for which
1297
coordinated transboundary conservation plans covering multiple range state Exclusive Economic Zones will be required for
effective management within the ETA.
ACKNOWLEDGMENTS
We thank the following companies (alphabetical) for their
permission to include previously unpublished data from their surveys
in this paper: BP Exploration (Angola) Ltd., Chevron (Nigeria and
Angola), China National Offshore Oil Company, Compagnie
Béninoise des Hydrocarbures, ConocoPhillips, ENI (Togo and
Angola), Kosmos Energy, Maersk Oil Angola, Ophir Energy,
Petrobras Oil and Gas BV—Benin, Petroleum Geo-Services (PGS)
Multi-Client (comprising BP Exploration (Angola) Ltd., Sonangol,
Statoil and Total (Angola)), Shell Benin Upstream Ltd., Shell
International Exploration and Production B.V., TGS NOPEC Angola,
Total (Côte d’Ivoire and Angola), and Tullow Oil (Ghana and
Mauritania Ltd.). R. Compton (RPS), N. Grosse (Geomotive), and A.
Hyam (GeoGuide) provided helpful assistance in gaining data
permissions. Thanks to the two reviewers whose comments improved
this manuscript.
SUPPORTING INFORMATION
SUPPORTING INFORMATION S1.—Published stranding, capture, and
skeletal records (by date) of the Clymene dolphin (Stenella clymene)
in the eastern tropical Atlantic.
Found at DOI: 10.1644/14-MAMM-A-115.S1 (40 MB DOC)
SUPPORTING INFORMATION S2.—Verified sighting records (n ¼ 92) of
the Clymene dolphin (Stenella clymene) in the eastern tropical
Atlantic. Presented by range state (north to south) and then by date.
Found at DOI: 10.1644/14-MAMM-A-115.S1 (40 MB DOC)
SUPPORTING INFORMATION S3.—Individual variation in the pigmentation patterns of eastern tropical Atlantic Clymene dolphins (Stenella
clymene).
Found at DOI: 10.1644/14-MAMM-A-115.S1 (40 MB DOC)
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Submitted 24 April 2014. Accepted 10 June 2014.
Associate Editor was Jeanette A. Thomas.